PRODUCTION AND USE OF SHORT-LIVED RADIOISOTOPES FROM REACTORS

t g p ) INTERNATIONAL ATOMIC ENERGY AGENCY, VIENNA 1963 PRODUCTION AND USE OF SHORT-LIVED RADIOISOTOPES FROM REACTORS Since in many countries the new problems of producing, separating and applying short-lived radioisotopes are being faced for the first time, the IAEA convened an international Seminar on Practical Applications of Short-lived Radioisotopes produced in Small Research Reactors at its Vienna headquarters in November, 1962. More than 150 participants included reactor engineers and physicists, radiation chemists, industrial scientists, hydrologiste, physicians and agriculturists from 29 Member States. The present pro­ ceedings contain all the scientific papers submitted and the discussions which followed them.

PRODUCTION ET EMPLOI DES RADIOISOTOPES DE COURTE PÉRIODE OBTENUS DANS DES RÉACTEURS Beaucoup de pays ont à résoudre, pour la première fois, les nouveaux problèmes que posent la production, la séparation et l'application des radioisotopes de courte période. C'est pourquoi l'AIEA a organisé à son siège, à Vienne, en novembre 1962, des journées d'études sur les appli­ cations dee radioisotopes de courte période obtenus dans de petits réacteurs de recherche. Les partici­ pants, qui étaient plus de 150, comprenaient des spécialistes du génie et de la physique des réacteurs, des radiochimistes, des ingénieurs, des hydrologistes, des médecins et des agronomes, venant de 29 Etats Membres. Le présent ouvrage contient tous les mémoires scientifiques pré­ sentés et les discussions auxquelles ils ont donné lieu. ПОЛУЧЕНИЕ КОРОТКОЖИВУЩИХ РАДИОИЗОТОПОВ В РЕАКТОРАХ И ИХ ИСПОЛЬЗОВАНИЕ Ввиду того, что во многих странах новые проблемы получения, разде­ ления и применения короткоживущих радиоизотопов возникли впервые, Международное агентство по атом­ ной энергии созвало в Центральных учреждениях в Вене в ноябре 1962 го­ да международный семинар по практическому использованию ко­ роткоживущих радиоизотопов, полу­ чаемых в небольших исследователь­ ских реакторах. В семинаре приняли участие свыше 150 специалистов из 29 государств-членов, среди которых были инженеры и физики-специали­ сты по реакторам, радиохимики, ученые, работающие в промышлен­ ности, гидрологи, врачи и агрономы. Настоящие труды содержат все представленные научные доклады и дискуссии по этим докладам.

APLICACIÓN DE LOS RADIOISÓTOPOS DE PERÍODO CORTO PRODUCIDOS EN REACTORES Teniendo en cuenta que son muchos los países en que se plantean por primera vez los problemas de la preparación, separación y utilización de los radioisótopos de periodo corto, el OIEA reunió en su Sede de Viena en el mes de noviembre de 1962 un seminario internacional sobre las aplicaciones prácticas de los radio­ isótopos de periodo corto, producidos en pequeños reactores de investiga­ ción. Hubo más de 150 participantes, entre ellos ingenieros y físicos nucleares, químicos especializados en los efectos de las radiaciones, técnicos industriales, hidrólogos, médicos y agrónomos, procedentes de 29 Estados Miembros. En el presente volumen se reproducen todos los documentos científicos que se pre­ sentaron y se reseñan los debates a que dio lugar su examen. PRODUCTION AND USE OF SHORT-LIVED RADIOISOTOPES FROM REACTORS

VOL. II The following States are Members of die International Atomic Energy Agency:

AFGHANISTAN ITALY ALBANIA JAPAN ARGENTINA REPUBLIC OF KOREA AUSTRALIA LEBANON AUSTRIA LIBERIA BELGIUM LUXEMBOURG BRAZIL MALI BULGARIA MEXICO BURMA MONACO BYELORUSSIAN SOVIET SOCIALIST MOROCCO REPUBLIC NETHERLANDS CAMBODIA NEW ZEALAND CANADA NICARAGUA CEYLON NORWAY CHILE PAKISTAN CHINA PARAGUAY COLOMBIA PERU CONGO (LÉOPOLDVILLE) PHILIPPINES CUBA POLAND CZECHOSLOVAK SOCIALIST REPUBLIC PORTUGAL DENMARK ROMANIA DOMINICAN REPUBLIC SAUDI ARABIA ECUADOR SENEGAL EL SALVADOR SOUTH AFRICA ETHIOPIA SPAIN FINLAND SUDAN FRANCE SWEDEN FEDERAL REPUBLIC OF GERMANY SWITZERLAND GHANA THAILAND GREECE TUNISIA GUATEMALA TURKEY HAITI UKRAINIAN SOVIET SOCIALIST REPUBLIC HOLY SEE UNION OF SOVIET SOCIALIST REPUBLICS HONDURAS UNITED ARAB REPUBLIC HUNGARY UNITED KINGDOM OF GREAT BRITAIN AND ICELAND NORTHERN IRELAND INDIA UNITED STATES OF AMERICA INDONESIA URUGUAY IRAN VENEZUELA IRAQ VIET- NAM ISRAEL YUGOSLAVIA

The Agency's Statute was approved on 26 October 1956 at an international conference held at United Nations headquarters, New York, and the Agency came into being when the Statute entered into force on 29 July 1957. The first session of the General Conference was held in Vienna, Austria, the permanent seat of the Agency, in October, 1957.

The main objective of the Agency is "to accelerate and enlarge the contribution of atomic energy to peace, health and prosperity throughout the world".

Printed by the IAEA in Austria March 1963 PROCEEDINGS SERIES

PRODUCTION AND USE OF SHORT-LIVED RADIOISOTOPES FROM REACTORS

VOL. II

PROCEEDINGS OF THE SEMINAR ON THE PRACTICAL APPLICATIONS OF SHORT-LIVED RADIOISOTOPES PRODUCED IN SMALL RESEARCH REACTORS HELD BY THE INTERNATIONAL ATOMIC ENERGY AGENCY AT VIENNA, 5 -9 NOVEMBER 1962

INTERNATIONAL ATOMIC ENERGY AGENCY VIENNA 1963 PRODUCTION AND USE OF SHORT-LIVED RADIOISOTOPES . FROM REACTORS, IAEA, VIENNA, 1963 S T I/P U B /6 4 FOREWORD

There are many radioisotope applications in which it is important that the radiation should rapidly fall to an insignificant level once the initial intense activity has served its purpose. Such applications include diagnostic tests in medicine, where it is essential to reduce the radiation dose to the patient to a minimum, non-destructive testing methods which must be applied without contaminating the material or product concer.ned, and repeated routine tests which are possible only if the residual activity from the previous test is negligible. All these applications call for radionuclides whose half- lives are measured in hours or even minutes. Similarly, in the new but increasingly important technique of activation analysis, whereby the quantities of elements present in a material can be determined by irradiating the m aterial in a reactor and assaying the radionuclides produced, the latter are mainly short-lived and must be measured immediately. While the production of long-lived radionuclides can most economically be left to the large reactors at the main radioisotope centres, short-lived isotopes must be produced, or m aterials activation performed, in a reactor at or near the place of intended use or analysis; this, then, represents one of the most important uses for the large number of small reactors which have been installed in recent years, or will come into operation in the near future, in many parts of the world. Since in many countries the new problems of producing, separating and applying short-lived radioisotopes are being faced for the first time, the International Atomic Energy Agency believed it would be valuable to survey the state of the art by convening an international Seminar on Practical Applications of Short-lived Radioisotopes produced in Small Research Reactors at its Vienna headquarters in November, 1962. This Seminar provided an opportunity for the producers and users of short-lived radio­ isotopes from many countries to meet and discuss the pr.oblems presented by these new research tools. The more than 150 participants included reactor engineers and physicists, radiation chemists, industrial scientists, hydrologiste, physicians and agriculturalists from 29 Member States. The present proceedings contain all the scientific papers submitted and the discussions which followed them. The wide coverage of the Seminar in both the physical and the life sciences is indicative of the manifold uses of short-lived radioisotopes. Their potentialities are only just beginning to be realized, and the material in these proceedings represents little more than, an introduction to what promises to become a very big subject. It is hoped that it will be found a valuable introduction.

SIGVARD EKLUND M a rc h 1963 Director General EDITORIAL NOTE

The papers and discussions incorporated in the proceedings published by the International Atomic Energy Agency are edited by the Agency's edi­ torial staff to the extent considered necessary for the reader's assistance. The views expressed and the general style adopted remain, however, the responsibility of the na m e d authors or participants. For the sake of speed of publication the present Proceedings have been printed by composition typing and photo-offset lithography. Within the limi­ tations imposed by this method, every effort has been m a d e to maintain a high editorial standard; in particular, the units and symbols employed are to the fullest practicable extent those standardized or recommended by the competent international scientific bodies. The affiliations of authors are those given at the time of nomination. The use in these Proceedings of particular designations of countries or territories does not imply any judgment by the Agency as to the legal statue of such countries or territories, of their authorities and institutions or of the delimitation of their boundaries. The mention of specific companies or of their products or brand-names does not imply any endorsement or recommendation on the part of the Inter­ national Atomic Energy Agency. CONTENTS OF VOL. И

IV. ACTIVATION ANALYSIS R eactor-produced short-lived radioisotopes used in neutron activ atio n analysis ...... 3 V .P . G uinn Dosage de traces d'impuretés dans le béryllium par des méthodes non destructives __ . ____ -29 J. Petit et Ch. Engelmann Some techniques tor toe determination of isotopes of short half-life as applied to the activ atio n analysis o f beryllium ...... 39 C . A . B a ker Analyse par activ atio n e t d éterm ination des isotopes de courte période ...... 45 R. Loos Dosages d'éléments par leurs radioisotopes de périodes courtes dans l'analyse de l'alu m in iu m , du fer e t du zirconium des très hautes puretés ...... 53 Ph. Albert, M. Deyris, N. Deschamps et L. Fournet Analysis of tantalum and niobium by neutron activation of short-lived radionuclides ...... 73 Chong Kuk Kim Analyse de routine par radioactivation neutronique. Dosage non destructif du sodium, à concentrations moyennes, sur de petits échantillons dans des gels de silice-alumine e t dans des solutions ...... 79 D. Barthomeuf, P. Bussière et J. Laverlochère The use of short-lived radioactive isotopes in an activation analysis service programme ... 95 D. Gibbons and H. Simpson The use of the 10 kW Argonaut reactor at Petten for radioactivation, including the quantitative aspects of short-time irradiations ...... I l l H .A . D as Applications pratiques des radioéléments de courte période dans l'analyse par activation ... 127 B. Chinaglia, L. Ciuffolotti. G. B. Fasolo et R. Malvano Radioactivation analysis of strontium in rat-bone ash ...... 137 Y. Matsumura

V. APPLICATIONS IN MEDICINE

A pplications o f iodine-132 in studies of thyroxine turnover ...... 147 M . A n b a r Marquage au brome-82 de la serum-albumine humaine, de l’insuline et du fibrinogfene par voie électrochim iq ue ...... 161 U. Rosa, G. A. Scassellati et G. Pennisi Electrolyte concentrations of intra- and extracellular compartments in some internal diseases . . ; ...... 175 K. Itahara, K. Ito, T. Tominaga, T. Jimbo and T. Sato Short-lived radioisotopes and autoradiography of frozen m aterial ...... 187 R. Taugner and J. Iravani Les aiguilles d'yttrium-90 en endo-électron thérapie (bêtathérapie interstitielle)...... 201 B. Pierquîn, M. Mortreuil, H. Beyer, J. Dutreix, D. Chassagne, P. Galle et R. Jammes The technique and dosimetry oi pituitary implantation using sources of yttrium-90 ...... 213 Ai. H . Duggan, E. Jones, J.R. Mallard and G. F. Joplin Supplem entary Discussion ...... 223

VI. APPLICATIONS IN BIOLOGY

Applications of fluorine-18 in biological studies with special reference to bone and thyroid physiology ...... 227 M . A n b a r The use of copper-64 in the investigation of reaction mechanisms of enzymes, particularly as related to food processing ...... 247 J. C. Arthur, Jr. and T. A. McLemore Isotopic exchange of potassium in an illite under equilibrium conditions...... 261 М. E. Sumner and G. H. Bolt List of C hairm en and S ecretariat of the Sem inar ...... 263 List of Participants ...... 264 ACTIVATION ANALYSIS

REACTOR-PRODUCED SHORT-LIVED RADIOISOTOPES USED IN NEUTRON ACTIVATION ANALYSIS

V. P. GUINN GENERAL ATOMIC DIVISION, GENERAL DYNAMICS CORPORATION, SAN DIEGO, CALIF. . UNITED STATES OF AMERICA

Abstract:— Résumé — Аннотация — Resumen

REACTOR-PRODUCED SHORT-LIVED RADIOISOTOPES USED IN NEUTRON ACTIVATION ANALYSIS. Activation analysis, whether carried out with fast or slow neutrons, charged particles, or photons, is based upon the fundamental equation.

At = N Ф о [1 -exp (-0. 693 ] exp(-0. 693 td/t0>5).

The author discusses the role of its various parameters with special reference to reactor fluxes and cross-sections, and to short'lived induced activities. Even with activities having half-lives of a few minutes, post-irradiation radiochemical separations, with carriers, are sometimes necessary to eliminate serious interferences, and are feasible. Where possible, however, direct gamma-ray spectrometry is preferable. With the recent availability of versatile and reliable multi-channel pulse height analysers, and the concurrent development of a purely instrumental method of activation analysis, based on gamma-ray spectro­ metry, radioisotopes of very short half-lives have increased in importance and usefulness. In the author's laboratory a very large number of neutron-induced activities having half-lives in the range of seconds to minutes have been, and are being, utilized in instrumental neutron activation-analysis studies. In many cases these are now used quite routinely in this laboratory. A few of such regularly-used thermal neutron-induced activities include 11-s F20, 9.5-min Mg27, 2. 3-min Al28, 37-m inCl88, 8. 7 -m in Ca*9, 5. 8 -m in T ia , 3. 8 -min Vs , 10-min Co60m, b.l-m inC u66; 18-min Br80, 6. 6-m in Nb94m, l5*m in Mo*0*, 4. 4-m in Rh*04111 , 2.3-m inAg108, 54-min In116m , 9. 5-min Sn125, 3. 5-min Sbmm , 25-m ini128, 20-min Re18801 , and 30-min Pti". Examples of the utilization of many of these short-lived activities in analyses of commercial orscientific importance, and the corresponding sensitivities of detection at a thermal neutron flux of 1.8 x 1012 n /c m 2s , are given. Notwithstanding the well-known fact that very high fast neutron fluxes exist in typical research reactors, as well as high thermal neutron fluxes, very little effort has been made, to date, to utilize reactor fast neutrons for activation-analysis work. For example, in a 250 kW Triga reactor, in a core position where the thermal neutron flux is 4. 9 x Ю12 n /c m 2s, the neutron flux above 1.35 MeV is 2.3 X 1012n /c m 2s,'that above 3. 7 MeV is 4.1 x 1011, and that above 6.1 MeV is 6. 2 x 101®. Since most (n,p) and (n, a) reactions have thresholds in the 1-4 MeV region, it is evident that a research reactor provides a powerful means of analysing for many eleme'nts by means of fast neutron reactions. In fact, work in these laboratories has shown that sensitivities of detection for many elements, via (n.p) and (n,a) reactions, are from 100- to 1000-fold better using the fast neutron component of the 250 kW Triga flux than can be obtained with a typical small deuteron accelerator producing 14 MeV neutrons. Amongst the short-lived activities induced by fast neutron reactions (including (n, 2n) reactions also) that have been studied by the author in activation-analysis investi­ gations are 2.3-s C« (from 0»), 7.4-s N« (from 0«), 10-min N« (from N14), 7.4-s N» (from FW), 9.5-min Mg2? (from Al27.),2. 3-min Al28 (from S i28), 6. 6 -m in Al*» (from S i29), 9. 5-m in Mg27 (fr0m Si*»), 2. 3-m in Al2® (from psi), 2. 5-min pso (from P»i), 12-s P« (from S^), and 3. 8 -min V52 (from Cr52). The problem of suppressing thermal neutron activation of samples, so that the fast neutron-induced activities can be observed, is discussed, and results of the regular use of reactor fast neutrons for activation analysis, especially for the determination of oxygen in various matrices, are cited. In addition, the use of reactor high-intensity pulses, for neutron activation studies, is discussed. When the Triga is pulsed (by rapid ejection of the main control rod) a 10 - 20 ms duration power level of lx 109 to 2 x 109 W is achieved, providing an instantaneous total neutron flux of 3-6 x lO^6 n /c m 2s. For very short­ lived induced activities, one such pulse can generate more activity in a sample than can be achieved by

3 4 V. P. GUINN

irradiation all the way to saturation at the normal steady power level. For example, the pulse-induced activity level is 70 times that of the normal power saturation activity level for an induced activity with a half-life of 1 s, 14 times for a half-life of 5 s, 7 times for a half-life of 10 s, and 3. 5 times for a half-life of 20 s. For induced activities with half-lives greater than about one minute, steady irradiation at normal power levels is superior to a pulse. The Triga can be pulsed reproducibly about once every five minutes. Details of the pulse technique and examples of its use are presented.

EMPLOI, POUR L'ANALYSE PAR ACTIVATION NEUTRONIQtJE,. DE RADIOISOTOPES DE COURTE PÉRIODE PRODUITS DANS UN REACTEUR. L’analyse par activation, qu'elle soit faite à l’aide de neutrons rapides, de neutrons lents, de particules chargées ou de photons, repose sur l'équation fondamentale suivante:

At = N Ф о [1 -e x p (-0, 693 t¿ / t0

L'auteur examine le rôle des divers paramètres en tenant spécialement compte des flux et des sections efficaces, ainsi que des activités induites de courte durée. Même lorsqu'il s’agit de substances radioactives dont la période est de quelques minutes, il faut parfois procéder à des séparations radiochimiques après irradiation, à l'aide d'entraîneurs, pour éliminer les interférences graves. Ces séparations sont parfaitement réalisables, mais dans la mesure du possible, la spectrométrie gamma directe est préférable. Depuis qu'on a mis au point, d'une part, les analyseurs d'amplitude à plusieurs canaux dont le fonc­ tionnement est à la fois souple et sûr et, d'autre part une méthode d'analyse par activation purement instru­ mentale fondée sur la spectrométrie gamma, l'importance et l'utilité des radioisotopes de très courte période n'ont cessé de s'accroître. Dans son'laboratoire, l'auteur emploie depuis quelque temps, pour ses études sur l'analyse instrumentale par activation neutronique, de nombreux éléments dont l'activité est provoquée par des neutrons et dont la période varie de plusieurs secondes à quelques minutes. Dans beaucoup de cas, il s'en sert tout à fait régulièrement. Voici quelques-unes des substances activées par des neutrons thermiques, qui sont couramment utilisées: 20F (11 s); 27Mg (9,5 min), 28A1 (2,3 min), 38C1 (37 min), ^Ca (8, 7 m in), 5*Ti (5, 8 min), (3, 8 min), 60mCo (10 min), «Cu (5, 1 min), ^Br (18 min), MniNb (6, 6 min), i°*Mo (15 min), iwmRh (4,4 min), «8Ag (2, 3 min), uemin (54 min), i25Sn (9, 5 min), игтзь (3, 5 min), 1281 (25 min), werpRe (20 min) et *"Pt (30 min). L'auteur cite des exemples d'utilisation de bon nombre de ces éléments de courte période, pour des analyses commerciales ou scientifiques; il indique les sensibilités de détection correspondantes pour un flux de neutrons thermiques de 1,8 • 10** n/cm ^s. Quoiqu’on n'ignore nullement qu'il existe dans les réacteurs de recherche courants des flux très intenses de neutrons rapides, de même que des flux importants de neutrons thermiques, on n'a déployé jusqu'ici que fort peu d'efforts pour utiliser les neutrons rapides du réacteur pour des analyses par activation. Ainsi, dans un réacteur Triga de 250 kW, pour une position du cœur, telle que le flux de neutrons thermiques est de 4, 9 • 1012 n/cm 2- s, le flux neutronique est de 2, 3 • 1012 n /c m 2* s au-dessus de 1, 35 MeV, de 4,1* lO ^n /cm 2* s au-dessus de 3, 7 MeV, et de 6, 2 • 10M n/cm î-s au-dessus de 6,1 MeV. Vu que les seuils de la plupart des reactions (n, p) et (n, a) se situent dans la région de 1-4 MeV, il est évident qu'un réacteur de recherche cons­ titue un puissant outil permettant d'analyser de nombreux éléments au moyen de réactions où interviennent les neutrons rapides. En effet, les travaux effectués dans le laboratoire de l'auteur ont montré que, si l'on a recours aux réactions (n, p) et (n, a), les sensibilités de détection d'un grand nombre d'éléments sont de 100 à 1000 fois plus élevées avec le flux de neutrons rapides du réacteur Triga de 250 kW,qu’avec un petit accélé­ rateur ordinaire de deutérons produisant des neutrons de 14 MeV. Parmi les activités de courte période provo­ quées par les neutrons rapides (notamment par les réactions (n,2n)) que l'auteur a étudiées au cours de re­ cherches sur l'analyse par activation, il y a lieu de signaler les éléments suivants: 15C (source: 180) : 2, 3 s¡ *6N (source : 160) : 7,4 s : 13N (source: 14N) : 10 min; 16N (source: 19F ):7 ,4 s ; 2?Mg (source: 27A1) : 9, 5 m in: ША1 (source: 28Si) : 2, 3 m in: 29A1 (source: 29Si) : 6, 6 min; 27Mg (source: 30Si) : 9. 5 min; wAl (source: 31P) : 2,3 min; 30P (source: 3lP) : 2, 5 min; мр (source: ^S) : 12 s, et »V (source: a Cr) : 3, 8 min. L’auteur examine la possibilité d'éliminer l'activation des échantillons par les neutrons thermiques de manière à pouvoir Observer les activités provoquées par les neutrons rapides; il cite les résultats que donne l'emploi courant dans l'analyse par activation des neutrons rapides produits dans un réacteur, notamment pour la détermination de l'oxygène dans diverses matrices. Enfin, l'auteur étudie l'emploi des impulsions de flux de haute intensité dans les études par activation neutronique. Lorsque le réacteur Triga est puisé (par retrait brusque de la principale barre de contrôle), on obtient, pendant une durée de 10 à 20 ms, une puissance de 1 à 2 • 109 W, ce qui donne un flux de neutrons total instantané de 3 à 6 • 101® n/cm 2* s. Pour les activités provoquées de très courte durée, une seule impulsion RADIOISOTOPES USED IN NEUTRON ACTIVATION ANALYSIS 5 de ce genre peut produire plus d'activité dans un échantillon qu'on n'en pourrait obtenir à la puissance sta- tionnaire normale, en poursuivant l'irradiation jusqu'à la saturation. Ainsi, l'activité provoquée par impulsions est 70 fois plus élevée que celle qui est obtenue par irradiation à saturation à la puissance normale, lorsque la periode est de 1 s, 14 fois plus élevée pour une période de 5 s, 7 fois pour une période de 10 s et 3,5 fois pour une période de 20 s. Pour les activités provoquées dont la période dépasse une minute, l'irradiation con­ tinue aux niveaux de puissance normaux est supérieure â une impulsion. On peut soumettre.le réacteur Triga à des impulsions reproductibles à peu près toutes les cinfl minutes. L'auteur fournit des détails sur la technique des impulsions et donne des exemples de son application.

ИСПОЛЬЗОВАНИЕ ПРИ НЕЙТРОННОМ АКТИВАЦИОННОМ АНАЛИЗЕ КОРОТКОЖИВУЩИХ ИЗОТОПОВ, ПОЛУЧЕННЫХ В РЕАКТОРЕ. Независимо от использования быстрых или медленных нейтронов, заряженных частиц или протонов, активационный анализ всегда основан на уравнении [1-ехр (-0,693 ti/t0,sH exp (-0,693 td/toi5). Обсуждается роль различных параметров этого уравнения, в особенности ней­ тронных потоков в реакторе и поперечных сечений также в случае образования короткоживущих изо­ топов. Даже в случае изотопов с периодом полураспада несколько минут после облучения иногда не­ обходимо применять радиохимическое разделение с носителями для устранения серьезных помех, и такое разделение возможно. Однако там, где это возможно, предпочтительнее проводить непосредствен­ ный гамма-спектрометрический анализ. В связи с недавним появлением универсальных и надежных многоканальных импульсных амплитудных анализаторов и одновременно с развитием чисто инструменталь­ ного метода активационного анализа, основанного на гамма-спектрометрии, короткоживущие изотопы стали шире применяться. В лаборатории автора используется в исследованиях по инструментальному нейтронному активационному анализу большое число искуственных изотопов, образующихся при ней­ тронном облучении, с периодом полураспада от нескольких секунд до нескольких минут. В настоящее время во многих случаях анализ короткоживущих изотопов вошел в обычную практику лаборатории. Говоря лишь о некоторых постоянно используемых искусственных изотопах, образующихся под дейст­ вием тепловых нейтронов, следует назвать F20 с периодом полураспада 11 сек, Mg27 с периодом полу­ распада 9,5 мин, А1гвс периодом полураспада 2,3 мин, С1эв с периодом полураспада 37 мин, Са49 с периодом полураспада 8,7 мин, Ti51 с периодом полураспада 5,8 мин, V52 с периодом полураспада 3,8 мин, Совогос периодом полураспада 10 мин, Cuee с периодом полураспада 5,1 мин, Вгв0 с периодом полураспада 18 мин, Nbtí4,“c периодом полураспада 6,6 мин, Мо10А с периодом полураспада 15 мин, д^ю4шс периодом полураспада 4,4 мин, Agxoe с периодом полураспада 2,3 мин, Inlia с периодом полураспада 54 мин, Sn125 с периодом полураспада 9,5 мин, Sb122 с периодом полураспада 3,5 мин, I128 с периодом полураспада 25 мин, Re18S с периодом полураспада 20 мин и Pt199с периодом полу­ распада 30 мин. Приводятся примеры использования многих из этих короткоживущих исскуственных изотопов в анализах, представляющих коммерческий и научный интерес, и соответствующие данные по чувствительности их обнаружения в потоке тепловых нейтронов 1,8*1012н/сек•см2. Несмотря на хорошо известный факт, что в типичных исследовательских реакторах наряду с ин­ тенсивными потоками тепловых нейтронов имеются также интенсивные потоки быстрых нейтронов, до настоящего времени мало сделано по использованию быстрых нейтронов в реакторах для активационного анализа. Например, в реакторе Трига мощностью в 250 квт в активной зоне в том месте, где поток тепло­ вых нейтронов составляет 4,9*1012н/сек*смг, мощность потока нейтронов выше 1,35 Мэв составляет 2,3*1012н/сек’см2, мощность потока нейтронов-выше 3,7 Мэв составляет 4,1*10A1, амощность потока нейтронов выше 6,1 Мэв составляет 6 ,2»Ю10. Поскольку большинство реакций (п,р) и(п,а) имеет порог в области 1 - 4 Мэв, очевидно, что исследовательский реактор предоставляет мощное средс tro анализа многих элементов с использованием реакций, идущих на быстрых нейтронах» Опыт работы в этих лабораториях свидетельствует о том, что чувствительность обнаружения многих элементов, образующихся по реакциям ( nt р) и (п,а ) в 100 - 1 000 раз лучше при использовании компоненты быстрых нейтронов в потоке нейтронов в реакторе Трига мощностью в 250 квт, чем при использовании обычных небольших нейтронных ускорителей, являющихся источником нейтронов с энергией 14 Мэв* К числу короткоживущих искусственных изотопов, образующихся в результате реакций с быстрыми нейтронами (включая реакции (п, 2п), которые изучались автором при проведении исследований по активационному анализу, относятся С15,(из О18) с периодом полураспада 2,3 сек, И1в(иэ О1®) с периодом полураспада 7,4 сек, Nlü(M3 N1*) е периодом полураспада 10 мин, И 10(иэ F19) е пе­ риодом полураспада 7,4 сек, Mg27(H3 Al87) с периодом полураспада 9,5 мин, А128(иэ i28) с периодом полураспада 2,3 мин, А129 (иэ si2®) с периодом полураспада 6,6 мин, Mg27 (из Si30) 6 V. P. GUINN

о периодом полураспада 9,5 мин, А1гв(иэ Р31) с периодом полураспада 2,3 мин, Рэо(из Р31 ) с периодом полураспада 2,5 мин, Рэ*(из S34) с периодом полураспада 12 сек и Узг(иэ CrS8) с пе­ риодом полураспада 3,8 мин. Обсуждается проблема подавления активации за счет тепловых ней­ тронов для лучшего измерения активации, вызываемой быстрыми нейтронами* Приводятся результаты обычного применения быстрых нейтронов реакторов для активационного анализа, в особенности для определения кислорода в различных биологических образцах* В-третьих, обсуждается проблема использования ампульсных потоков реакторных нейтронов высокой интенсивности для исследований нейтронной активации* При работе реактора Трига в им­ пульсном режиме (при быстром выведении основного регулирующего стержня) достигается уровень мощности 1 - 2 млн квт продолжительностью 10 - 20 миллисек с постоянной общей величиной потока нейтронов 3-6*10 1вн/сек«смг • В случае образования изотопов с очень коротким периодом полурас­ пада один такой импульс может создать в образце большую активность, чем при облучении до состо­ яния насыщения при нормальном постоянном уровне мощности* Например, в случае активности с пери­ одом полураспада 1 сек* уровень активности, наведенной таким импульсом, в 70 раз выше уровня активности насыщения при нормальной мощности, в 14 раз больше для активности с периодом полу­ распада в 5 сек, в 7 раз больше для активности с периодом полураспада в 10 сек и в 3,5 раза больше для активности с периодом полураспада в 20 сек* Лля искусственных изотопов с периодами полураспада больше 1 мин постоянное облучение при нормальных уровнях мощности гораздо эффектив­ нее импульсного облучения* Реактор Трига может давать такие импульсы через кадые 5 минут. Пред­ ставлено подробное описание импульсных методов и примеры их использования*

EMPLEO, PARA EL ANALISIS POR ACTIVACION NEUTRÚNICA, DE RADIOISÓTOPOS DE PERÍODO CORTO PRODUCIDOS EN REACTORES. El análisis por activation, tanto si se efectúa con neutrones rápidos o lentos, partículas cargadas o fotones, se basa en la ecuación fundamental

At = N Ф a [1-exp (-0, 693 t./t0 5)] exp(-0, 693 tj/t0 5).

El autor examina el papel de los diversos parámetros, teniendo especialmente en cuenta los flujos en el reactor y las secciones eficaces, asi como las actividades inducidas de periodo corto. Incluso cuando se trabaja coi radioisótopos de un período de pocos minutos es a veces preciso efectuar separaciones radioquímicas con portadores después de la irradiación para eliminar interferencias graves. Estas separaciones son perfectamente realizables, pero en la medida de lo posible es preferible recurrir a la espectrometría gamma directa. Como hoy se dispone de analizadores de amplitud multicanales de funcionamiento seguro y adaptables a muchas condiciones de trabajo y se ha encontrado un método puramente instrumental de análisis por acti­ vación basado en la espectrometría gamma, los radioisótopos de períodos muy cortos van adquiriendo creciente importancia y utilidad. En el laboratorio del autor se emplean para análisis instrumentales por activación neutrónica muchos radioisótopos obtenidos por irradiación neutrónica, cuyos períodos son del orden de los se­ gundos o minutos. En muchos casos, se emplean para trabajos de rutina. Para mencionar sólo algunos de los radioisótopos activados por neutrones térmicos que se emplean regularmente, cabe citar el 2ор (Ц S), 27Mg (9,5 min), 28A1 (2, 3 min), aecl (37 min), <®Са (8, 7 min), 5*Ti (5, 8 min), S V (3, 8 min), «m eo (10 min), efCu (5,1 min), 80Br (18 min), ^m^jb (6, 6 min), loiMo (15 min), iwmRh (4, 4 min), loeAg (2, 3 m in), iwnain (54 min), 125Sn (9,5 min), ^2mSb (3, 5 min), u*i (25 min), “8™Re (20 min) y -i»Pt (30 min). El autor cita ejemplos del empleo de muchos de estos radioisótopos de período corto en análisis de importancia comercial o científica e indica las sensibilidades de detección correspondientes para un flujo de neutrones térmicos de 1,8 • 10i2 n /c m 2 s. Aunque es bien conocido el hecho de que en los reactores de investigación corrientes se producen flujos muy intensos de neutrones rápidos y de neutrones térmicos, hasta hoy se han desplegado muy pocos esfuerzos para emplear los neutrones rápidos del reactor en el análisis por activación. Por ejemplo, en un reactor Triga de 250 kW, en un punto del cuerpo en que el flujo de neutrones térmicos es 4 ,9 .10i2n/cm2s, el flujo de neu­ trones de energía superior a 1, 35 MeV es 2, 3 ' 1012 n/cm 2 s, siendo de 4 ,1 *10U para los de más de 3, 7 MeV y de 6,2* lOio para los de más de 6,1 MeV. Como los umbrales de casi todas las reacciones (n, p) y (n, a) son del orden de 1 а 4 MeV, es evidente que un reactor de investigación constituye un medio muy eficaz para analizar muchos elementos por sus reacciones con neutrones rápidos. En efecto, los trabajos realizados en los laboratorios del autor han demostrado que, si se utiliza la componente de neutrones rápidos del flujo del reactor Triga, de 250 kW, la sensibilidad de detección de muchos elementos por reacciones (n,p) y (n, a) es de 100 а 1000 veces superior que la obtenida con un pequeño acelerador de deuterones, que proporciona neutrones RADIOISOTOPES USED IN NEUTRON ACTIVATION ANALYSIS 7 de 14 MeV. Entrenlos radioisótopos de período corto inducidos por reacción con neutrones rápidos (incluyendo también reacciones (n, 2n) ) que el autor ha analizado por activación figuran el »C de 2,3 s (a partir de 180),

16N de 7 ,4 s (a partir de 1*0), “ N de 10 min (a partir de MN), i*N de 7, 4 s (a partir de 19F), 2*Mg de 9,5 min (a partir de 27Д1), « A l de 2, 3 min (a partir de “ Si), 29A1 de 6, 6 min (a partir de 29Si), 27M gde9,5m in (a partir de 30Si), 28Al de 2, 3 m in (a partir de 8lP), de 2, 5 min (a partir de sip), MP de 12 s (a partir de MS) y «V de 3, 8 min (a partir de ®Cr). El autor examina la posibilidad de evitar la activación de las muestras por los neutrones térmicos para poder observar los radioisótopos inducidos por los neutrones rápidos, e indica los resultados del empleo corriente de los neutrones rápidos del reactor para los análisis por activa­ ción, especialmente para la determinación de oxigeno en diversas matrices. Además, el autor examina el empleo de un reactor pulsante de alta intensidad en los estudios por acti­ vación neutrónica. Cuando se hace pulsar el reactor Triga (extrayendo rápidamente là principal barra de con­ trol), se alcanza durante 10 a 20 ms una potencia de 1 a 2 • 109 W, lo que produce un flujo neutrónico instantáneo total de 3 a 6 • 10*6 n/cmis. Cuando se trata de inducir radioisótopos de período muy corto, un solo impulso es capaz de generar en una muestra una concentración de radioisótopo mayor que la que se al* canza irradiando hasta saturación a la potencia estacionaria normal. Por ejemplo, para un radioisótopo de 1 s de período, la actividad inducida por un impulso es 70 veces mayor que la alcanzada por saturación tra­ bajando a potencia normal, siendo 14, 7 y 3,5 veces mayor para períodos de 5, 10 y 20 s, respectivamente. Cuando los períodos de los radioisótopos son superiores a 1 min la irradiación continua al nivel normal de po­ tencia da un rendimiento mayor que un impulso. El reactor Triga se puede hacer pulsar de manera reproducible aproximadamente una vez cada 5 min. El autor proporciona detalles sobre esta técnica por impulsos, así como ejem plos de. su aplicación.

1. ' INTRODUCTION

Of the numerous uses of a research reactor, one of the most practical and interesting is as a source of therm al and fast neutrons for work in the field of activation analysis. Activation analysis may be defined as a method of elemental analysis in which various elements in samples are made radio­ active by means of nuclear reactions and the various induced activities then identified and measured quantitatively. Activation analysis can be carried out by means of sample bombardment with various nuclear particles, e.g., neutrons, photons, or charged particles. Although photons and charged particles have a number of interesting and useful applications in the field of activation analysis, neutrons are by far the most widely useful particles. Attention in this paper is restricted to neutron activation analysis, utilizing fast and slow (thermal) neutrons generated in research reactors at fluxes in the range of 10П - 1013 n/cm2 s.

1. 1 Theory '

When a sample is exposed to a flux ф of neutrons, each isotope present in the sample undergoes nuclear reaction with the incident neutrons at a rate given by the equation: R ate of re a c tio n = Ni^cr, (1) in which N is the number of target nuclei of the atomic number and mass number in question in the sample, and cr is the cross-section for a particular type of interaction of such nuclei, per nucleus, with neutrons of the energy in question. The term N is equal to the product of the sample weight (g), tim es the fraction of the element in the sample, times the fractional abundance of the particular stable isotope in the element, tim es Avogadro’s number (6.02 X 1023), all divided by the chemical atomic weight of the element. 8 V. P. GUINN

With therm al neutrons (i. e ., neutrons in therm al equilibrium with the surroundings — 0.025 eV kinetic energy at 25°C), the only reaction possible in almost all cases is neutron capture. This type of reaction is referred to as a (n, 7 ) reaction, since one or more gamma-ray photons are emitted by the newly-formed nucleus promptly after neutron capture. In (n, 7 ) r e ­ actions the product nucleus is one of the same element, but with a mass number one unit higher than before capture. The product nucleus may be another stable isotope of the element, or it may be a radioisotope of that element. Only the latter case is of use in activation analysis. For example, ordinary magnesium consists of three stable isotopes, in fixed proportions: 78.8% Mg24, 10.1% Mg25, and 11.1% Mg2B[l]. Their therm al neutron capture cross-sections are 0.03, 0.27 and 0.03 b, respectively [1] (1 b= 10-24 cm2, the approximate physical cross-section of a typical nucleus). Neutron capture by Mg24 forms only stable Mg25, neutron capture by Mg25 forms only stable Mg26, but neutron capture by Mg26 forms radioactive Mg27, which decays by beta particle emission (and gamma-ray emission) with a half-life of 9.5 min.

1. 2 Fast neutron reactions

If fast neutrons (neutrons with energies > 1 MeV) are also incident upon the sample, reactions other than neutron capture may also occur. The most common fast neutron-induced reactions are (n, p), (n, a) and (n, 2n) reactio n s. With (n, p) reactions the incident fast neutron is captured, but a proton is then promptly ejected. The product isotope (stable or radioactive) has the same m ass number as the original nucleus, but an atomic number one unit lower — it is an isotope of a different element. In (n, a) reactions an alpha particle is expelled, so the product isotope has a mass number lower by three units than the original nucleus and an atomic number two units lower. It is also, then, an isotope of a different element. In (n, 2n) reactions, the product nucleus is an isotope of the original element, but with a mass number one unit lower. Fast neutron cross-sections not only differ from one isotope to another, but also depend considerably upon the neutron energy. Most (n, p), (n, a ) and (n, 2n) reactions are endoergic and hence exhibit energy thresholds, below which reaction is impossible.

1.3 Approach to saturation

If the product isotope in a given case is radioactive, some will be decaying even while the irradiation is going on. If irradiation is continued long enough, a steady state will be approached in which the rate of formation of the radioisotope equals its rate of decay. This situation is often termed "saturation activity'1. Further irradiation does not then increase the activity of that particular radioisotope in the sample, as long as the neutron flux remains the same. If, however, irradiation is discontinued before saturation is achieved, the induced activity of the particular radioisotope in question will be less than the saturation activity, and will be given by the equation

A 0 = N<^)ct [l-exp (-0.693 tj/t0_5)] dps, (2)

in which ti is the duration of the neutron exposure and t 0>5 is the half-life RADIOISOTOPES USED IN NEUTRON ACTIVATION ANALYSIS 9

(expressed in the same time units as tj) of the radioisotope in question. The parenthetical, or "saturation" term of Eq. (2) has numerical values ranging from zero at ti = 0, to unity as t¡ -» oo. At ti values of 1, 2, 3, 4.. .. tim es t05, the saturation term has values of 1/2, 3/4, 7/8, 15/16 .... Thus it is seldom worth-while to activate a sample for a period of time greater than a few half- lives of the radioisotope of major interest. Longer activations are, in fact, undesirable, as they result in generation of more longer-lived interfering activities. With short-lived activities, irradiation times are then quite short, resulting in a short overall analysis time.

1,4 Decay after irradiation

After conclusion of the irradiation, prior to counting, each induced activity then decays according to its particular half-life:

A t = A0 exp (-0.693 t d / t 0.5), (3) in which td is the decay time after conclusion of the irradiation. During counting of the activated sample, each activity continues to decay. If the counting period, tc, is very short compared with the half-life of the radio­ isotope in question, the number of counts, C, obtained from that isotope, divided by the counting time, is essentially the counting rate at the start of the counting period. For counting times of up to about one half-life of the isotope, half of the counting time should be added to td and the resulting counts, divided by the counting time, will then represent quite accurately (within 1%) the counting rate of that isotope at the midpoint of the counting period. For longer counting periods, a correction must be applied.

1. 5 Comparison technique

Rather than rely on literature values of isotopic abundances, atomic weights and cross-sections, or precise knowledge of the. neutron flux or irradiation time, a comparison method is used. A sample containing an accurately-known weight of the element of interest is irradiated at the same time as the unknown sample, under identical conditions, and is then counted identically. Then, by merely correcting the counting rate of one to the same decay time as the other, the two counting rates are in the same proportion as the weights of the element present in the two, one of which is known.

1,6 Interferences and separations

In most cases more than one radioactive species is generated, in de­ tectable amounts, by activation of the sample. If the one of interest is a gamma em itter, and interferences from other induced activities are not excessive, the analysis can be completed in a purely instrumental manner, by means of multichannel gamma-ray scintillation spectrometry. If the isotope of interest is a pure beta emitter (emitting no gamma rays, or essentially none), or if interferences are excessive, one must resort to post­ irradiation radiochemical separations with carriers and hold-back carriers. 10 V. P. GUINN

The chemical yield of the element is determined from the weight of carrier added and the weight finally recovered for counting. Radiochemical separations are virtually impossible with induced activities having half-lives of the order of seconds, difficult, but feasible, with those having half-lives of minutes, and relatively easy with those having half-lives of hours or longer. Such chemical separations, of course, add to the analysis time, so the purely instrumental method is generally preferred, if it is feasible.

1. 7 Optimum number of samples

If more than one element is of interest, standard samples of each element of interest are irradiated along with the unknown, and then counted in the same way as the sample. More than one sample can be irradiated at the same time, of course, providing that the half-life is not so short that decay prior to counting is excessive. Usually, with samples in which the activity of interest has a half-life of only a few minutes, or less, samples are activated and counted one at a time. In such cases, a pneumatic tube is used to get. the activated sample to the counter within a few seconds of the conclusion of the irradiation. With half-lives of the order of an hour, a number of samples (typically, 4-10) can be activated simultaneously, then counted successively. With longer half-lives, very large numbers of samples can be profitably activated simultaneously. In the TRIGA reactor, up to 40 samples can be activated simultaneously, at exactly the same flux, in the rotating specimen rack.

\ 2. ACTIVATION ANALYSIS INVOLVING SHORT-LIVED RADIOISOTOPES

With the recent availability of versatile and high-quality multichannel pulse height analysers [2, 3, 4], and the concurrent development of a purely instrumental method of activation analysis [5, 6, 7], based on gamma-ray spectrometry, radioisotopes of very short half-lives have increased in importance and usefulness.

2. 1 Sensitivities of detection

In the author’s work a large number of neutron-induced activities having half-lives in the range of seconds to minutes have been utilized in instru­ mental neutron activation analysis studies. In many cases these are used quite routinely. Of the total list of such activities which have been studied, the shorter lists shown in Tables I, II and UI include only those which have been studied in greater detail and which are used most frequently in the author’s laboratory. The sensitivities of detection shown in Tables I and II are based on a 1.8 X 1012n/cm2 s therm al neutron flux at the sample (a typical research reactor flux), and irradiation times of up to one hour. With the very short­ lived species, irradiation times much less than one hour are satisfactory, since the induced activity level reaches 98.4% of the saturation value in a period of time equal to six half-lives of the isotope produced. It is assumed that the induced activity is detected by gamma-ray spectrometry with a RADIOISOTOPES USED IN NEUTRON ACTIVATION ANALYSIS 11

TABLE I

THERMAL NEUTRON DETECTION SENSITIVITIES FOR 19 ELEMENTS (in 1-h irradiations at 1.8 X 1012n/cm 2 s therm al neutron flux) (Half-lives < 1 h)

Element Isotope formed Half-life Detectable (Mg)

Fluorine F 20 11 s 1,0

Magnesium Mg27 9.5 min 0.5

Aluminium Al28 2.3 min 0.01

Chlorine Cl3! 37 min o.i

Calcium Ca49 8. 7 min 5.0

Titanium T i51 5.8 min 0.05

Vanadium V52 3.8 min 0.001

Cobalt Co60® 10. 5 min 0.1

Copper Cu66 5.1 min 0.05

Bromine Br'° 18 min 0.005 •

Niobium NbMm 6.6 min 1.0

Molybdenum Мош 15 min 5.0

Silver Ag10" 2.3 min 0.05

Silver Ag110 24 s 0.0001 inu«m Indium 54 min 0.0001 Tin Sn125 9.5 min 0.5

Tellurium Те131 25 min 0.05

Iodine jl28 25 min 0.01 Hafnium Hfi7.»m 19 s 1.0

Platinum Pt*9 30 min 0.1

3 in X 3 in Nal(Tl) detector, and a 2-cm separation between sample and detector. The minimum quantity detectable is arbitrarily defined as that quantity which would produce an initial photopeak counting rate of 1000 cpm (for half-lives of less them 1 min), 100 cpm (for half-lives from 1 min to 1 h), and of 10 cpm (for half-lives greater than 1 h). These are the samé criteria employed by BUCHANAN [8], and utilize abundances and cross-sections listed in the GENERAL ELECTRIC COMPANY Chart of the Nuclides [1], decay schemes tabulated by STROMINGER, HOLLANDER, and SEABORG[9], and counting efficiencies and photopeak fractions given by HEATH [10]. The fast neutron sensitivities shown in Table III are based on the reactor- fission-spectrum integrated cross-sections given by ROY and HAWTON [11], 12 V. P. GUINN

TABLE П

THERMAL NEUTRON DETECTION SENSITIVITIES FOR 33 ELEMENTS (in 1-h irradiations at 1.8 X 1012 n/cm2 s therm al neutron flux) (Half-lives 1 h to 3 d)

Elem ent Isotope formed Half-life Detectable (P&

Sodium N a24 15 h 0.005

Potassium K 42 12.4 h 0.5

Manganese Mn56 2 .6 h 0.00005

N ickel N ¡6 5 2 .6 h 0.5 o>

Copper О с 12.8 h 0.001

Zinc Z n 69 m 14 h 0.1

Gallium Ga12 14 h 0.005

Germanium Ge” 82 m in 0.05

Arsenic As'6 27 h 0.005

Bromine B r'2 36 h 0.01

Strontium Sr8,m 2 .8 h 0.005

Zirconium Zr97 17 h 1.0

Molybdenum M o99 67 h 0.1

Ruthenium Ru106 4 .5 h 0.05

Cadmium Cd“5 54 h 0.5

Antimony Sb122 2 .8 d 0.01

Barium Ba139 85 m in 0.1

Lanthanum La140 40 h 0.005

Cerium Ce14S 32 h 0.1

Praeseodymium Pr142 19 h 0.05

Sam arium Sm 15s 47 h 0.005

Europium Е ц И г т 9 .3 h 0.0005

Gadolinium Gdls9 18 h 0.05

Dysprosium Dy165 2 .3 h 0.000005

Holmium Ho1'6 27 h 0.0001

Erbium Er171 7 .5 h 0.001

Lutetium Lu176 3 .7 h 0.00005 RADIOISOTOPES USED IN NEUTRON ACTIVATION ANALYSIS 13

TABI£ П (cont. )

Elem ent Isotope formed Half-life D etectable (Mg)

W 187 Tungsten 24 h 0. 005

Rhenium Re188 17 h 0.001

Iridium b l?4 19 h 0.001

Gold A u198 2. 7 d 0. 0005

Mercury H g1” 65 h 0.01

Uranium Np23» 2 .3 d 0.005

TABLE Ш

FAST NEUTRON (FISSION SPECTRUM) DETECTION SENSITIVITIES FOR 7 ELEMENTS (in 1-h irradiations at 1 X 1012n/cm2 s fission spectrum' flux) (Half-lives < 1 h)

Elem ent Reaction Half-life D etectable (Mg)

Nitrogen N14(n,2n)Nu 10.0 m in 13

Oxygen O16 (n, p) N 16 7 .4 s 5500

Fluorine FB ( n ,p ) 0 19 29 s 5.0

Fl9(n , a ) N16 7 .4 s 20.0

Silicon Si28(n,p) Al28 2 .3 m in 0.75

Si29(n,p) Al29 6 .6 m in 18

Phosphorus PM(n ,2 n )P M 2 .5 m in 86

P^Cn.ajAl28 2 .3 m in 2 .3

Sulphur S34(n .p )P 34 12.4 s 5400

Chromium Cr52(n,p)V 52 3 .8 m in 6 .0 and the flux obtained when operating the TRIGA reactor at 250-kW power. This corresponds to a fission neutron spectrum flux of 1012n/cm2 s in the pneumatic tube position. The other assumptions are the same as for Tables I and II.

2.2 Absolute and concentration sensitivities

It might be remarked that a typical sample size is one gram; hence the microgram values shown in the Tables correspond also to the lim its of 14 V. P. GUINN detection, expressed as parts per million (ppm) in a one-gram sample. Samples as large as 10 g are often employed, in which case the ppm limits are ten times better than those shown in the Tables. In the author’s labora­ tory samples are regularly activated in a pneumatic tube core position in a250-kW TRIGA Mark I reactor ata therm al neutron flux of 4.3 X1012n/cm2 s. For activation analyses involving longer-lived activities (half-lives of > lh), many samples can be activated simultaneously, at identical fluxes of 1.8 X 1012n/cm2 s, in the rotating "lazy susan" rack just outside the reactor core [8] . For studies in which higher fluxes are needed, a 1-MW TRIGA Mark F reactor is used. In this reactor eight sample tubes are available, in which the therm al neutron flux is 1.0 X 1013 n/cm2 s. Of the 19 elements listed in Table I (those forming therm al neutron capture isotopes with half-lives of less than 1 h), the median sensitivity is 0.05 fjg, or 0.05 ppm in a 1-g sample, or 5 parts per 109 in a 10-g sample. Of the additional 30 elements listed in Table II (half-lives of 1 h to 3 d), the median sensitivity is 0.005 дg, or 5 parts per 109 in a 1-g sample, 0.5 parts per 109 in a 10-g sample. Virtually all of these computed sensitivities have been realized in practice with various types of actual samples, where inter­ ference problems are minimal. Similar sensitivities (median, 0.1 Mg) are also obtained for 11 additional elements (Sc, Cr, Se, Rb, Cs, Nd, Tb, Tm, Yb, Ta, Th) which form activities with half-lives longer than 3 d.

2.3 Fast neutron reactions

Although the fission neutron spectrum sensitivities, by fast neutron reactions, listed in Table III are not as good as those obtained for most other elements with therm al neutrons, they are nevertheless quite useful. The median sensitivity of detection for the seven elements listed in Table III is about 15 Mg, and five of the elements are detectable to levels of 86 fig and lower. Only two are rather poor, О and S. Even these, however, correspond to sensitivities of 0.05% in a 10-g sample (and, in practice, the sensitivity attainable with oxygen is 5-10 tim es better than this arbitrarily-defined sensitivity). Many (n, p) and (n, a) reactions have thresholds in the range of 1-4 MeV, the Ole(n, p) N16 reaction being an outstanding exception (threshold, 9.6 MeV). Many (n, 2n) reactions have thresholds in the region of 10-12 MeV. Con­ siderable fast neutron activation analysis is carried on at the author’s labora­ tories and in many other laboratories \yith 14-MeV neutrons generated with small deuteron accelerators (Cockcroft-Walton or Van de Graaff), via the H3(d, n) He4 reaction. Although the 14-MeV cross-sections are generally much larger than the integrated-fission spectrum cross-sections (as a result of the fission spectrum shape,, peaking at about 1 MeV, and the reaction thresholds), the flux obtainable with a research reactor is typically about 10 000 tim es that obtainable with the small accelerators (1012 as against 10s). As shown in Table IV, this larger flux more them offsets the lower cross- sections, so that, for the seven elements listed, the reactor provides de­ tection sensitivities some 4 - 1100 tim es better (median, 90 times) than those attainable with the small accelerators. Problems due to therm al neutron activation of other elements in the sample, when employing reactor fluxes, require shielding of the sample during irradiation with cadmium and/or RADIOISOTOPES USED IN NEUTRON ACTIVATION ANALYSIS 15

TABLE IV

COMPARISON OF FAST NEUTRON DETECTION SENSITIVITIES WITH A 1012 REACTOR FISSION SPECTRUM FLUX AND A 108 14-MeV NEUTRON ACCELERATOR FLUX

Cross- sections Detection limits (mb) (Mg)

Reaction Threshold (MeV) FS 14 MeV FS 14 MeV

N14(n,2n)N13 10.9 0.03 6 13 650

o “ (n.P)N 16 9 .6 0.017 40 5500 23 000

F19(n, pJO19 4 .0 0 .5 130 5.0 190

F19(n, a)N 16 1. 5 5.7 50 20 23 000

Si28(n,p)Al28 3 .9 4 .0 250 0.75 120

Si29(n, p)A l29 3 .0 2 .7 100 18 4900

[^(п.гп)?30 11.8 0.01 11 86 780

[’“ (n.oOAl28 1.9 1.3 150 2 .3 200

S ^fn .p JP 34 4 .3 0.63 85 5400 400 000

Cr52(n,p)V S2 3 .4 0.8 80 6 .0 600

TABLE V

FLUXES OF VARIOUS ENERGY NEUTRONS IN THE TRIGA MARK I REACTOR AT 250-kW POWER

Neutron flux (n/cm* s)

Reactor location Thermal >10 keV > 1 .3 5 MeV > 3 .7 MeV > 6 .1 MeV

Rotary specimen rack 1.8 x 1012 1 .5 X 1012 1.8 X 1011 2. 5 X lO10 4 .0 X 109

Pneumatic tube position 4 .3 X 1012 3 .5 X 1012 7 .5 Х 1 0 Ц 1.2 X 1011 1.9 X 1010

Fuel-element ring D 4 .9 X 1012 9 .0 X 1012 2 :3 X1012 4 .1 X 1011 6.2 x 1010

boron. Considerable work is in progress in the author’s laboratory on developing effective and practical methods of utilizing reactor fast neutrons in activation analysis studies of a wide variety of types of samples. The method is already being used routinely for several elements, e. g ., N, O, Si, and S. The fluxes of high energy neutrons available in the 250-kW TRIGA Mark I reactor are shown in Table V. 16 V. P. GUINN

3. SPECIAL ADVANTAGES OF SHORT-LIVED ISOTOPES IN ACTIVATION ANALYSIS STUDIES

3. 1 Choice of short-lived or long-lived activity

In numerous instances one has the choice of determining a particular element, in various samples, by means of either a short-lived isotope of the element, or a longer-lived isotope of the element, induced by neutron activation. For example, copper may be determined by neutron activation analysis either by means of the 5.1-min Cu66- or the 12.8-h Cu64- induced activity. In cases where interfering activities are largely due to long-lived isotopes, there is an advantage in employing the 5.1-min Cu66 activity for the determination of the copper. In such cases one employs a short activation period(~5 min) to suppress the build-up of the longer-lived interfering activities, and then measures the gamma-ray spectrum of the sample very soon after the conclusion of the activation, before the Cu66 activity has decayed appreciably. Conversely, if the interfering activities are mostly short-lived isotopes, one is better off utilizing the 12.8-h Cu64 activity. In such cases one employs a longer activation period, to allow the Cu64 activity to approach saturation, and then allows the sample to decay for a few hours before determining its gamma-ray spectrum. Similar choices occur, for example, with cobalt (10-min Co60m or 5.2-yr Co60), bromine (18-min Br80or 36-h Br82), molybdenum (15-min Mo101 or 67-h Mo99), ruthenium (4.5-h Ru105 or 40-d Ru103), and platinum (30-min Pt199 or 3.2-d Au19^.

3. 2 Cases in which only a short-lived activity is available

In some cases, however, there is no choice. For example, activation of aluminium with therm al neutrons produces only one radioisotope: 2,3-min Al28. Here one is forced to work with a short-lived activity, and one relies on a short activation period (1-5 min), rapid delivery of the sample from the reactor to the scintillation counter (usually by means of a pneumatic tube), and rapid counting on a multichannel gamma-ray spectrometer. For maxi­ mum sensitivity the sample is usually counted for about one half-life of the short-lived isotope in question. Other examples of elements which produce (in significant amounts) only a short-lived gamma-emitting isotope, upon therm al neutron capture, are fluorine (11-s F20), magnesium (9.5-min Mg27), calcium (8.7-min Ca49), titanium (5.8-min Ti51), vanadium (3.8-min V54, and silver (24-s Ag110 and 2.3-m in Ag108).

3.3 Speed of analysis

Where short-lived activities are utilized in neutron activation analysis, there is an obvious saving of time. Activities with half-lives of seconds or minutes only require activation periods of seconds to minutes to approach their saturation activity levels. They must be counted very soon after com­ pletion of the activation, and they can only profitably be counted for a period of one or two half-lives. In a typical case a sample is activated for a period of time equal to one or two half-lives of the isotope of interest, allowed to decay for one, half of one half-life, and then counted for one or two half-lives. RADIOISOTOPES USED IN NEUTRON ACTIVATION ANALYSIS 17

Thus, the total time required for analysis, including activation, decay, and counting, is from 2.5 Ti to 4.5 T>, where Ti is the half-life of the isotope in question.

4. EXAMPLES OF THE USE OF SHORT-LIVED ACTIVITIES IN PRACTICAL NEUTRON ACTIVATION ANALYSIS

The following examples represent a small sampling of the numerous types of analyses performed in the General Atomic laboratories during the past year as part of the research and service activation analysis programmes. The examples chosen involve cases in which the half-life of the induced activity of major interest is less than one hour.

4.1 Vanadium in oil

Vanadium occurs, along with several other elements (e. g ., Cr, Ni) in crude oil in the form of metal porphyrins. Crude oils may range from 10 to evenlOOppmV. Since these compounds break down and deposit on the surface of cracking catalyst in refinery operations, causing a deleterious effect upon the selectivity of the catalyst, the feed stocks must be largely freed of vanadium and other metal contaminants prior to feeding to the cracking unit. The purification is usually accomplished by vacuum Hashing, since the metal porphyrins are significantly less volatile than the hydrocarbons present. Analyses of the distillate are needed that are sensitive down1 to levels of about 0.01 ppm V. A chemical procedure, following combustion of a large sample, is available, but is very tedious. In the author's laboratory de­ terminations of vanadium, down to levels as low as 0.001 ppm, are done rapidly, instrumentally, and routinely for many oil companies, utilizing the 3.8-min V52-induced activity (at 4 X 1012 therm al neutron flux) and gamma- ray spectrometry (1.43-MeV gamma ray).

4.2 Fluorine in fluorocarbon solutions

Dilute solutions of fluorocarbons in hydrocarbon oils have been analysed for fluorine, down to levels of about 1 ppm F, utilizing the 11-s F20-induced activity (at 4 X 10 12 therm al neutron flux) and gamma-ray spectrometry (1.63-MeV gamma ray). Such analyses are both rapid and non-destructive. The sensitivity for fluorine is about l/ug(0.1ppm in a 10-g sample) .Fluorine has also been determined at low levels in oil shale and other materials via th e F 19(n, p) O19 re a c tio n .

4. 3 Aluminium and calcium in greases

Some commercial automobile greases utilize aluminium soaps and/or calcium compounds as additives. The Al and Ca contents are readily de­ termined rapidly and routinely, even in very small samples, via the 2.3-min Al28 and 8.7-min Ca49-induced activities (4 X Í012 therm al neutron flux) and gamma-ray spectrometry (1.78-MeV and 3.1-MeV gamma rays, re­ 18 V. P. GUINN spectively). The sensitivity for A lis 0.01 fig, so aluminium can be determined down to levels of 0.017o even in samples as small as 0.1 mg. The Ca sensi­ tivity is 5 n g (0.01% in a 50-mg sample). Such analyses are of importance in studies of scientific crime detection with activation analysis techniques, in which the author's research group is engaged.

4.4 Aluminium and magnesium in cracking catalysts

Catalysts used for catalytic cracking in oil refineries usually consist of silica-alumina, silica-magnesia, or mixtures of these. Analysis of these for their A1 and Mg contents is, of course, quite straightforward by con­ ventional analytical methods, since these elements are present in percentage amounts and plenty of sample is available. However, this is a good example of a case in which activation analysis can provide a much faster analysis, the accurate determination of both elements being done instrumentally (2. 3-min Al28, 9.5-min Mg27) in a total analysis tim e of only about 10 min per sample. Magnesium-27 emits gamma rays of 0.84 and 1.02 MeV e n e rg y .

4. 5 Pesticides in food and crop samples

Due to the toxicity to man of many insecticides now used widely to protect crops from insect attack, or preserve foodstuffs from similar attack, toler­ ance levels have been set for many insecticides. These are usually in the rather low concentration range (typically, 0.1 - 50 ppm). Chemical analysis is quite feasible at these levels, but is very laborious. Chlorine-containing insecticides, however, are readily determined instrumentally by thermal neutron activation (2 X 1012 flux) of Cl in hydrocarbon extracts of the plant or food m aterial. The DDT contents of a number of foodstuffs have been determined in these laboratories by activation of organic chlorine in extracts. Levels as low as 0.01 ppm Cl are readily determined in an overall analysis time of about 20 min per sample. The induced activity utilized is 37-min Cl38 (1.59-and 2.15-MeV gamma rays). Nematocides in wide use are organic bromine compounds, such as 1, 2- dibromo 3-chloropropane. These are used to fumigate the soil, in which they effectively kill root-damaging nematodes. They gradually decompose in the soil, releasing bromide ion, which is picked up by the plants. Bromine is readily determined in plant and food samples [12] down to levels of about 1 ppm by instrumental activation analysis, utilizing either the 18-min Br8° activity (0.51-MeV /3+ annihilation and 0. 62-MeV gamma-rays) or the 36-h B r82 activity (0.55- and 0.77-MeV gamma-rays). The lim it of detection is in the ppm range because of interferences from several other induced activities (37-min Cl38, 2.6-h Mn56, 12.5-h K42, 15-h Na24). In the absence of such interferences, Br can be determined down to levels of 0.005 ppm (Br80) or 0.01 ppm (Br82) even in 1-g samples (at 2 X1012 therm al neutron flux). Again, total analysis time is only about 20 min per sample. The natural Br level in many plants is found to be of the order of 1 ppm. Wheat in storage is commonly fumigated with methyl bromide to kill insects which otherwise attack the wheat. Excessive doses, or repeated doses, can result in excessive Br contents in the wheat — by chemical reaction RADIOISOTOPES USED IN NEUTRON ACTIVATION ANALYSIS 19 of the CH3Br with chemical components in the wheat. Again, Br levels down to about 1 ppm are readily determined via the 18-min Br80 or 36-h Br82 activities. Methyl bromide-fumigated flour and. spice samples have also been analysed in this fashion.

4.6 Titanium, aluminium, and chlorine in plastics and synthetic rubber

"Ziegler" polymers, such as polyethylene and polypropylene, and certain types of synthetic rubber are made commercially with Ti-Al-Cl catalysts. Some of the catalyst inescapably remains in the final product, because it is chemical-bonded in the polymer molecules. Larger amounts, however, can remain in the polymer, physically trapped, if the washing of the product is not adequate. Excessive amounts of trapped catalyst are generally dele­ terious to the properties of the polymer. Thus, analyses for these elements, down to ppm levels, are often required. All three elements are determined instrumentally and routinely in a single therm al neutron activation at 2X1012 flux, down to levels of about 0.005 ppm (Ti), 0.001 ppm (Al), and 0.01 ppm (Cl) in a 10-g sample. The induced activities utilized are 5.8-min Ti51 (0.32-MeV gamma-ray), 2.3-min Al28, and 37-min Cl38.

4. 7 Silver in polymers

One particular organic polymer of interest is made commercially with a silver catalyst. The final polymer usually contains from 1 to 10 ppm Ag, depending upon the degree of purification. This polymer is readily dis­ tinguished from otherwise identical polymers, but prepared with other types of catalysts, by rapid instrumental therm al neutron activation analysis (4 X 101Z flux), utilizing the induced 2.3-min Agios activity (0.63-MeVgamma- ray). The sensitivity of detection for Ag is about 0.05 /ug (0.005 ppm in a 10-g sample).

4. 8 Hafnium in zirconium

Of interest in the nuclear reactor field, ppm levels of hafnium in zirconium have been determined in these laboratories via the 19-s Hf179m activity (at 4 X1012 therm al neutron flux)t In very short activations (30 s), the zirconium m atrix does not develop very much interfering 17-h Z r97 or 65-d Zr95 activity. The interference-free sensitivity for Hf is about 1 Mg (1 ppm in a 1-g sample).

4. 9 Oxygen in hydrocarbons, metals and other m atrices

In these laboratories oxygen has been determined in a great variety of m aterials, utilizing reactor fast neutrons and the O16 (n, p) N16 reaction. Levels as low as 50 ppm are generally determinable in 10-g samples. One complication is that the polyethylene vials used contain a significant amount of oxygen in the plastic. This causes a sizeable container blank correction, or requires rapid transfer of the sample, after irradiation, to a fresh con­ tainer. Since the N1B half-life is only 7.35 s, such transfer causes some loss in sensitivity. Another complication is that fluorine also forms N16, via the 20 V. P. GUINN

F 19 (n, a ) N16 reaction. It has a much lower fast neutron reaction threshold (1.5 MeV) than the O16 (n, p) N16 reaction (9.6 MeV) and hence is detected much more efficiently than oxygen — 275-fold more sensitivity. Thus, even small traces of F can result in erroneous О results, unless the contribution of fluorine to the N.16 activity is corrected for by separate measurement of F by the F 19 (n, p) 0 19 reaction. Nitrogen- 16 em its exceptionally high energy gamma-rays (6.13 MeV) in its decay, readily distinguished from other gamma- rays emitted by the sample. Oxygen-19 may be detected either by means of its 0.20- or 1.37-MeV gamma rays. Its half-life is 29 s. The fluorine interference is much less severe if a 14-MeV neutron source is used. In many cases, such as the alkali and other metals, and mineral and rock samples, therm al neutron activation of many matrix elements would make the sample too radioactive for proper counting. In such cases samples are activated in tubes that are wrapped with cadmium and boron-10. This suppresses the therm al neutron activation reactions by many orders of magni­ tude without interfering with the fast neutron reactions. Samples can be activated and counted, in the determination of oxygen, at the rate of one per minute. Low levels of oxygen have been determined even in such com­ plicated m atrices as steel, minerals, and caesium metal, as well as in simpler matrices, such as organic compounds, lithium metal and beryllium.

4.10 Nitrogen in organic compounds

In these laboratories nitrogen is routinely determined in various organic compounds and organic m ixtures via the N14(n, 2n)N13 reaction, employing reactor fast neutrons. Although the theoretical lim it of detection under these conditions is about 1 ppm N ina 10-g sample, the practical lim it of detection is about 100 ppm. This anomaly is due to the fact that organic m atrices also form N13 by means of the С13(р,п)№3 reaction, the fast protons resulting from collisions of fast neutrons with protons of the sample, the recoil protons then colliding with C13 nuclei present in the sample (C13 having am abundance of 1.11% in ordinary carbon). Thus, even a completely nitrogen-free sample shows an apparent nitrogen content of the order of 100- 500 ppm, the exact value depending on the С and H contents of the sample. This provides a sizeable blank correction and lim its the practical detection sensitivity for nitrogen to about 100 ppm. This recoil proton interference has been studied by the author, and also by GILMORE and HULL [13]. Nitrogen-13 is a positron em itter and has a half-life of 10 min.

5. ACTIVATION ANALYSIS WITH REACTOR PULSES

The TRIGA reactors used in these laboratories have a unique feature which has some interesting applications — they can be safely pulsed to ex­ trem ely high neutron fluxes of short duration. For example, the Mark I reactor can be pulsed to a power level of 109W, giving a peak total neutron flux of about 3X1016 n/cm2 s, with a half-width of about 15 ms. The Mark F reactor can be pulsed to 2 X109W, giving a peak flux of 6 X1016 n/cm ! s with a half-width of about 10 ms. These are of course higher fluxes than have yet been achieved by any reactor in steady operation. Pulsing can be done at intervals of about 5 min. RADIOISOTOPES USED IN NEUTRON ACTIVATION ANALYSIS 21

Such pulsing is achieved by rapid ejection of the main control rod from the reactor core, making the reactor supercritical. The flux and power level immediately increase at a great rate, reaching a peak within a matter of milliseconds. The excursion promptly quenches itself, with the control rod still out, and without any other external interference, because the hydrogen moderator in the hydrided U-Zr alloy fuel elements promptly rises to a high temperature (of the order of 500°C) as a result of rapid fission heating. At such tem peratures the hydrogen can only moderate neutrons to kinetic energies equivalent to a tem perature of 500°C. At such energies the U235 fission cross- section is much lower than at 0.025 eV (25°C) and the system becomes sub- critical. As the power level declines and fuel element tem peratures fall, the core steadies out, of its own accord, at a lower power level, of the order of several hundred kilowatts. The pulse is accompanied by a brilliant flash of Cerenkov radiation in the water surrounding the core. This behaviour of U-Zr-H fuel elements also provides the valuable feature of intrinsic sa fe ty . It is of interest to note that a single reactor pulse will induce more short-lived activity (half-lives < 30 s) than continuous irradiation to saturation at the normal reactor power level. For example, when the TRIGA Mark I reactor is given a 16 MW second pulse (peak power 109W, half-width 16 ms), the therm al and fast neutron fluxes rise to a level 3200 times their normal values for 250 kW steady-state operation. As shown in Table VI, the induced activity in such a pulse ranges from 35 tim es as much as for steady-state operation to saturation (for a half-life of 1 s) to 1.2 tim es as much (for a half-life of 30 s). This is true for both therm al neutron and fast neutron r e a c tio n s .

TABLE VI

RATIO OF ACTIVITY INDUCED BY A REACTOR PULSE (16 MW s) TO SATURATION ACTIVITY AT STEADY-STATE POWER (250 kW)

Radioisotope half-life Ratio pulse/steady (s)

1 35

2 18

3 12

4 8 .9

5 7.1

10 3 .5

20 1.8

30 1.2 22 V. P. GUINN

REFERENCES

[1 ] GENERAL ELECTRIC COMPANY, C hart of th e N uclides, (A pril 1956). [2] GUINN, V .P ., Advances in Activation Analysis, Proc. Atomic Ind. Forum., San Francisco (1960) 308. [3] GUINN, V .P ., "New Developments in instrumental Activation Analysis — Accelerators and Analyzers", Proc. Int. Conf. on Modem Trends in Activ. Anal., Texas A and M College (1961) 126. [4] GUINN, V .P ., Gamma Ray spectrometry Developments in activation analysis Studies, Proc. Instr. Soc. of Amer. 8 (1962) 283. [5] GUINN, V.P. and WAGNER, C .D ., "Instrumental Neutron Activation Analysis", Anal. Chem. 32 (1960) 317. 1.6 ] GUINN, V .P ., "Instrumental Neutron Activation for rapid, economical Analysis", Nucleonics 19 8 (1961) 81. [7] GUINN, V. P ., Neutron Activation Analysis, Int. Sci. and Tech., Prototype Issue (1961) 74. [ 8] BUCHANAN, J. D ., Activation Analysis with a TRIGA Reactor, Proc. Int. Conf. on modem Trends in Activ. Anal., Texas A and M College (1961) 72. [9 ] STROMINGER, D .. HOLLANDER, J.M . and SEABORG, G .T ., T able of Isotopes, Rev. Mod. Phys. 30 (1958) 585. [10] HEATH, R.L., Scintillation Spectrometry gamma-ray Spectrum Catalogue, IDO-16408 (USAEC). [11] ROY, I.C. and HAWTON, J. J., Table of estimated Cross-Sections for(n,p), (n,a) and (n,2n) Reactions in a fission neutron Spectrum, AECL-1181 (Atomic Energy of Canada, Ltd.). [12] GUINN, V.P. and POTTER. I.C ., "Determination of total bromine Residues in agricultural Crops by instrumental neutron Activation Analysis", J. Agri. and Food Chem. 1£ (1962) 232. [13] GILMORE, J. T. and HULL, D .E., "Nitrogen-13 in Hydrocaibons irradiated with fast Neutrons", Anal. Chem. 34 (1962) 187.

DISCUSSION

J, LALERE: I have some questions. First, in connection with the pneumatic tube, can you tell me (a) where the tube is located in relation to the core, (b) whether the fluxes outside the therm al range were calculated or measured, and (c) how long it takes for the sample to travel through the tube from the core to the counting position? On the subject of-pulsing, I should be interested to know whether you have actually used this method for activation analysis. If-so, did you irradiate a standard sample together with the sample to be analysed, and was the same counter used on both samples? V. P. GUINN: To answer your first question, there are some 80-90 fuel elements in the TRIGA core arranged in rings and the pneumatic tube ends in one of the vacant positions in the outermost or F ring — the rings are designated as A, B, C, D, E and F, starting from the centre. The various fast neutron fluxes you refer to are calculated ones and are based on fission-spectrum shapes. However, the general accuracy of our data has been checked by measurements with various threshold reactions at a number of reactor locations and the values, while they may not be accurate to within 10 or 20%, are certainly approximately correct. Our pneumatic tube is a relatively slow one. It takes almost exactly three seconds for the sample to get from the core to the counter end of the pneumatic tube. Another few seconds are required to remove the sample, in the polyvial, from the plastic rabbit. As for pulsed operation, we have not yet used this technique for our com mercial activation-analysis service but we shall be doing so shortly. RADIOISOTOPES USED IN NEUTRON ACTIVATION ANALYSIS 23

The method has, however, been successfully employed on a number of research sa m p le s. I might mention that the reactor can be pulsed reproducibly about once every 5-6 min. In one series of investigations with semi-conductor transient effects the reactor was pulsed 200 tim es consecutively, once every five minutes, and, visibly at least, the record was identical in each case. That, I think, also answers your final question. In this type of work it is not usual to activate a standard sample at the same time as the unknown sample. One tries to obtain reproducible conditions and then one can run a whole series of samples in separate pulses, a check being provided by the pulse intensity-duration record. Reproducibility is fairly good — around + 5%. A standard sample can be inserted at some point during this process but as a general rule the standard and the ordinary sample are not put in at the same time. This could of course be done but it would still be necessary to count the two in rapid succession or something of that sort. A. KOHN : Have you done any work on the determination of oxygen in metals, and, if so, what were the average oxygen contents in the samples you analysed and the accuracy of your measurements? V. P. GUINN: This is a field where activation analysis is of course very useful. We have analysed a large number of different metal samples for oxygen content, employing fission-spectrum fast neutrons in the TRIGA reactor and the Oie(n, p)N16 reaction. The samples are shielded from thermal neutrons by Cd and B10 carbide. The metals we have studied so far include Be, Li, Na, K, Cs, Fe, A1 and Zr. With chemical methods determinations of this sort would be rather difficult to carry out, particularly in the case of an element like caesium, which is spontaneously inflammable in air. The only substance that gives us any appreciable trouble in the reactor is rubidium. In spite of the fact that the capsule is provided with considerable cadmium and boron-10 shielding, there is still sufficient activation in the rubidium to make the determination of oxygen rather difficult, though it should be possible to suppress the therm al and low-energy-neutron activation of the rubidium considerably by using a sm all accelerator — and this we shall very shortly be in a position to do. With all the other substances the process is straightforward. As for, oxygen content, very few of the samples sent in to us for analysis have contained.less than 100 ppm; as we work withan accuracy of ± 10 ppm, we are pretty certain of this. Some of the people who send in samples imagine that the oxygen content is less than it is, owing to the difficulty of dealing with ihis problem by conventional analytical methods. We have probably had a few samples where the oxygen content was around 50 ppm but in the vast majority of cases the figure ranged between 100 and 1000 ppm. This applies not only to the alkaline m etals but also to other m etals such as iron and beryllium . Our current lim it of detection is about 20 ppm — for a 10-g sample — but this will soon be improved to about 1 ppm. We have done a good deal of work using standard samples with very accurately known oxygen contents and we find that accuracies of ± 2 - 3% of the true value can be achieved for oxygen contents between 500 and 1000 ppm. This rather surprised us — we expected something more like ± 5%. 24 V. P. GUINN

W. GEBAUHR: Have you compared your activation-analysis results with data obtained by other methods and, if so, what concentrations were involved? - . V. P. GUINN: In a number of specific cases we have satisfactorily cross­ checked our activation-analysis data with the results obtained from chemical and spectrophotometric analyses of the same samples. For example, we have checked with conventional methods down to 0.01 ppm Sb in water, 0.01 ppm Se in blood, and 0.1 ppm Br in food samples. Where it is possible to perform the activation analysis purely instrumentally, the method becomes essentially an absolute one which can then be used as a standard for other methods. W. GEBAUHR: One more question. Have you made any practical use of the pulsing technique? V. P. GUINN: No, not yet. Our work with pulsing has been of an experi­ mental nature so far. We have analysed quite a number of samples where very short-lived activities were involved. The results we have obtained with such isotopes as 7.35-s N16 and 12-s P 3 0 tally very well with the calculated sensitivities. However, as I have already pointed out, we are not yet using the pulsing technique commercially. The reason for this is primarily econo­ mic. So far we haven’t had to deal with a problem where it was necessary to pulse the reactor in order to obtain a higher degree of sensitivity. If a case should turn up where steady-state irradiation produces insufficiently accurate results, then we should obviously make use of the pulsing technique. Wher­ ever a choice is possible, however, steady-state irradiation is always prefer­ able because it takes less time. In the case of oxygen, for example, samples can be irradiated at the rate of one a minute whereas pulsing on a reproducible basis is possible only once every five minutes — and a certain amount of time has to be added for preparing the sample. It should certainly be possible to make use of the increased sensitivity obtainable with the larger pulses. At present we are looking for various’metastable isom ers with half-lives of 0.1 - 1.0 s. I am sure that some of these can be found although they are not referred to in the literature so far, and it should be possible to use them in activation analysis. L. STANG: In cases where there is no need for reproducibility, how often can the TRIGA reactor be pulsed? V, P. GUINN: I can’t give you an exact answer to that but my guess is every three or four minutes, though each succeeding pulse would not necessarily be as big as its predecessor. It’s a very interesting phenomenon, actually. The pulse is accompanied by a brilliant flash of light which lights up the entire building. If, as soon as the pulse is over, you re-insert the control rod so that the reactor is shut off, you can watch the core glow with Cerenkov radiation which dies off very rapidly. You can almost follow the half-lives of all the short-lived fission products merely by watching the ' fading intensity of the light. It dies down pretty rapidly and then it’s a matter of waiting for the fuel elements to cool down sufficiently to enable the reactor to be made critical and pulsed again. J. TOUSSET: Would you say that a 14-MeV accelerator would provide the same degree of sensitivity for oxygen determination as your reactor? V. P. GUINN: Yes, a sim ilar sensitivity — about 10 ppm — can be achieved with a small deuteron accelerator that generates 1010- 1011 14-MeV n/s and RADIOISOTOPES USED IN NEUTRON ACTIVATION ANALYSIS 25 provides usable fluxes of 108-109n/cm 2 s at sample locations, with samples of 1-10 g. Another important point is that fluorine interference, via the F!9(n, ff)Ni6 reaction, is some 250 times less serious with 14-MeV neutrons than with fission-spectrum neutrons — due to the fact that the threshold for the Oie(n, p)N16 reaction is very high (9.6 MeV) as compared with the thresh- hold for the (n, a )N16 reaction (1.5 MeV). At my former laboratory at the Shell Development Company we used a small accelerator of this kind regularly for determining oxygen in amounts down to approximately 10 ppm. P. BUSSIÊRE: As I understand it, you use your reactor solely for acti­ vation analysis. Since you have precise data on the load, you can be sure that the flux gradients throughout a column of samples are slight or known so that you need only insert one standard for 39 samples. Could you perhaps tell me how accurate your information on the flux for each sample is? In the particular case of aluminium and magnesium in cracking catalysts, could you perhaps indicate how accurate your determinations were? V. P. GUINN: Well, first of all, I should make it clear that the main TRIGA reactor that we use for this work, the Mark I 250-kW reactor, is not used exclusively for activation analysis at General Atomic.The activation analysis group uses it more than any other single group but accounts for no more than perhaps half its total time. It is operated sporadically, the only exceptions being eight-hour runs from time to time. This is due not to any intrinsic limitation in the reactor but simply to the fact that, thus far, there is not that much demand for reactor time. As I say, we use the reactor for other purposes besides activation analysis but during any one analysis the reactor is not tampered with. This means that a very high degree of control — within a fraction of 1% — is possible during any particular run. As for flux determinations, we nave checked me constancy ot the average flux in the 40 lazy susan tubes, at a given height, by activating 40 identical samples for 30 min with the rack rotating. Subsequent counting of these samples (Na24) indicated that they had all been exposed to an identical neutron flux, within the lim its of the counting statistics (about ± 0.5% in this case). Vertical and radial gradients have also been measured, and are small — a few percent per inch. You also asked about aluminium and magnesium in cracking catalysts. Well, here of course high levels are involved and most of the work I have done on this subject was carried out with an accelerator, which gives ample sensitivity. In this case these substances are major constituents of the cata­ lysts and not merely trace constituents. A reactor can also be used, which means a saving in time and smaller samples, etc. With these substances one is working well above the lim its of detection and accuracies of ± 2 - 3% of the correct values are obtainable. We have made checks with standard samples and have cross-checked with chemical analyses and the agreements were very good. J. HOSTE: On this question of fast neutrons and interference, I should like to make a brief comment in connection with some work we have been doing on the determination of traces of cobalt in nickel. If one irradiates at a cadmium ratio of 200, one obtains approximately equal peak heights from cobalt-58 and cobalt-60 when the content in the samples is about 1 ppm. It is possible, therefore, just by measuring the ratio of the cobalt-58 and 26 V.P. GUINN cobalt-60 peak heights, to make direct determinations of 0.1 ppm of cobalt in n ic k e l. С. C. THOMAS: Would Dr. Guinn care to give us his views on the analysis of phosphorus in the presence of very large quantities of sulphur? V. P. GUINN: In cases where the S/P ratio is very large, accurate phosphorus determinations based on P:S2 are not feasible since the latter isotope is formed not only by the P3i(n, y)P32 therm al-neutron but also by the S32(n, p)P32 fast-neutron reaction. All reactor therm al fluxes of any great magnitude also contain an appreciable fast-neutron component. Even when activations are carried out with and without cadmium shielding, it is stiH not possible to make accurate determinations if the S/P ratio is very large. There is also the problem of chlorine interference as a result of the C l 35(n, a)P32 fast-neutron reaction. Determination of induced P32 activity normally involves radiochemical separation and beta counting of the pure P32 activity, so that interferences from other activities emitted by isotopes with long half-lives, such as S35, are eliminated. In favourable cases, however, phosphorus can be determined, even in the presence of considerable amounts of sulphur and chlorine, by means of the P 31(n, 2n)P30 or the P31(n, or)Al28 fast-neutron reactions, or both. J. LALÈRE: I would have thought that the relative slowness of your pneumatic system — you mentioned an extraction time of about 3 s — would have offset the advantages to be gained from reactor pulsing, especially in the case of the very short half-lives you were using. V. P. GUINN: The enhancement of short-lived activity by means of pulsing remains the same — e. g ., 35-fold for an isotope with a half-life of one second — regardless of the decay time. However, you are right in the sense that the sensitivity can be further increased, for both pulsed and non­ pulsed operation with very short-lived induced activities, by reducing the sample transit time as much as pos sible .For the pulsing work we are planning to carry out — for half-lives of the order of tenths of a second — we intend to install a faster pneumatic tube with a transit time of half a second or less. J. LALÈRE: What is the total distance of the pneumatic tube? V. P. GUINN: I can’t remember exactly but it’s something like 60 or 70 ft. A. VUORINEN: Do you use the normal nylon rabbits for your fast- activation studies and does the period of three seconds you mention include the tim e taken to open the rabbit — or do you make measurements with the rabbit itself? V. P. GUINN: Our samples are placed in polyethylene vials and the polyvials are then put into larger and sturdier polyethylene rabbits. The 3 s referred merely to the transit time. A few more seconds are needed to remove the sample vial from the rabbit for counting. Since even the best polyethylene, polypropylene or polystyrene contain several hundred parts per million of oxygen, we find it necessary for measurements at very low oxygen concentrations to make a rapid transfer of the activated sample to a fresh polyvialbefore counting. In the case of certain samples — e.g. metallic caesium, which is spontaneously inflammable in air — transfer operations of this sort are not feasible. P. ALBERT: You have drawn attention to an important difference between the accelerator and the reactor, viz. the presence of therm al neutrbns in RADIOISOTOPES USED IN NEUTRON ACTIVATION ANALYSIS 27 the latter. Didn’t you find that the activity from the therm al neutrons inter­ fered with your measurements? You have already mentioned rubidium but didn’t you find in a general way that the activity from therm al neutrons simply swamped the detector? V. P. GUINN: Yes, the problem is not simply that in fast-activation work one is liable to come up against the activation of other components in the sample as a result of thermal neutrons, which may produce sim ilar gamma rays. The point is that the gross activity of the sample may be so high that it is impossible to count it or even for that m atter to handle it. Samples can be too hot. What we do when we are carrying out fast-neutron studies in the reactoristo use tubes lined with cadmium and boron - 1 0 ca rb id e . This reduces the therm al flux by many orders of magnitude. Unfortunately we have not yet evolved a method for cutting down the fluxes of the epithermal neutrons and resonance neutrons, which can also give rise to a sizeable amount of (n, 7 ) activation. We are attempting to develop multiple linings to suppress all these low-energy fluxes but we have quite a way to go yet. P. ALBERT: Yes, but when you use these thermal-neutron absorbers, isn’t there a risk of reactor shut-down? V. P. GUINN: The levels involved are not really high enough. Sometimes we use fixed tubes lined with cadmium and boron, in which case all one has to do is to build a little extra reactivity into the reactor to compensate for the absorption. When we find the proper combination of substances we intend to install a permanent pneumatic tube with a suitable lining. In the meantime, we are obliged to use rabbits lined with cadmium and boron. These naturally cause an abrupt change in the flux as soon as they are shot into the reactor. Suitable reproducibility is still possible, never­ theless, because, although the rabbit does change the flux every time it is inserted, the standard sample is sim ilarly affected. However, this is only a temporary expedient. F. NELSON: In connection with fast pneumatic-tube facilities, I should like to make a brief comment which I think might be of general interest. Some years ago Dr. E. C. Campbell of the Oak Ridge National Laboratory developed an apparatus which he called a "fast-fast pneumatic tube" and which might possibly be of interest to persons engaged in activation-analysis work*. This system made it possible to remove the sample from the rabbit immediately after transit so that counting could be started immediately after irradiation. The rabbit could be introduced into and removed from the reactor in much less time than is required with conventional pneumatic tubes, I believe. I do not recall how long it actually took but I should be glad to supply references to anyone interested in the apparatus. V. P. GUINN: This may have involved one of those rotating-disc devices for spinning round very small samples, which are activated at one point and counted at another. I know that techniques of this sort have been developed in the past for work on very short-lived activities with accelerators. For our purposes, however, where samples can easily weigh 1 - 1 0 g and be in the form of aqueous solutions, they have to be in a container which doesn’t get activated. In other words, there are certain mechanical limitations

* See, e .g ., CAMPBELL, E .C . and FETTWEIS, P .F ., Nuclear Instruments and Methods 14(1961)272. 28 V. P. GUINN which, to my mind, make it unlikely that the sample could be moved from the source to the detector in much less than, say, one-tenth of a second. P. ALBERT: What is the lifetime of the core when the reactor is running normally and when it is pulsed? V. P. GUINN: It’s difficult to give a precise answer to that. The reactor can operate at 1 MW and can be used 24 h a day, but for the normal operational situation, i. e ., 250 kW and not more than 8 h a day, the core lifetime is measured in years. In term s of nvt, there is no difference, as far as we know, between pulsed and normal operation for an equivalent period of time at the lower power levels. We have made m etallurgical examinations of a number of fuel elements that were pulsed as many as 3000 times and there was no evidence of any deterioration, hydrogen diffusion, etc. in excess of what one would expect normally. The approximate tem perature reached by these fuel elements, 500°C, is not very high for this type of m aterial. At the time the elements are actually fabricated, hydriding occurs at about 900°C when the hydrogen is diffused into the uranium /zirconium alloy. We feel confident they will be able to stand up to the heat levels of 8 X109 W which will be needed for the fluxes of 2 or 3X1011 n/cm2 s in the new version we will be using shortly. DOSAGE DE TRACES D’IMPURETÉS DANS LE BÉRYLLIUM PAR DES MÉTHODES NON DESTRUCTIVES

J. PETIT ET CH. ENGELMANN CENTRE D'ÉTUDES NUCLÉAIRES, SACLAY, FRANCE

Abstract — Résumé — Аннотация — Resumen

DETERMINING^TRACES OF IMPURITIES IN BERYLLIUM BY NON-DESTRUCTIVE METHODS. In view of the growing interest being taken in high-purity materials and the limitations to which conventional chemical analyses are subject, scientists have been making extensive use of neutron-activation techniques. In determining the various elements found in short-lived isotopes, it was found to be practicable, indeed necessary, to make the counts without carrying out chemical separation beforehand.- The method has proved extremely attractive because of its non-destructive character, an advantage which becomes more marked the shorter the irradiation period involved. Two main methods, which signify an extension of the gamma spectrography technique, are described ¿ Subtraction method: By using a magnetic-memory multichannel analyser and subtracting, one from another, two spectra of the same sample recorded at a suitable interval of time, it is possible to obtain the spectra of the short-lived nuclides alone. This method has been used particularly for determining the aluminium present in beryllium; the sensitivity was 0.01 ppm and a dozen analyses were made per hour. Coincidence method: The gamma-gamma coincidence spectrum was used to determine the copper content of beryllium in the presence of numerous other impurities, with a sensitivity of less than 0.01 ppm. By applying the gamma-spectrography method described above to the analysis of beryllium irradiated in EL-3 at Saclay, it has proved possible to determine traces of aluminium (А1Я,2.3 min), vanadium(V^^.e minX chlorine (Cl38, 37.5 m in ), manganese (Mn56, 2 .6 h ) , potassium (K**, 12.5 h ) , sodium (Na2*, 15 h) and copper (CuM, 12.8 h). Notwithstanding its relative simplicity, the utility of this method does not appear to be confined to very low concentrations. It can also be applied to materials other than beryllium.

DOSAGE DE TRACES D'IMPURETES DANS LE BERYLLIUM PAR DES MÉTHODES NON DESTRUCTIVES. L'étude des matériaux de haute pureté suscite un intérêt croissant; les limites de l'analyse chimique con­ ventionnelle ont amené différents chercheurs à utiliser l'activation aux neutrons de manière extensive. Pour doser les éléments qui forment un isotope de courte période, il est apparu utile, voire nécessaire, d'effectuer les comptages sans séparation chimique préalable; cette méthode s'est en outre avérée très intéres­ sante par son aspect non destructif, d'autant plus marqué que les périodes d'exposition sont courtes. Les auteurs décrivent principalement deux méthodes qui ont permis d*étendre le domaine d'application de la spectographiey. Méthode de soustraction: A l'aide d'un sélecteur multicanaux à mémoire magnétique, la soustraction dé deux spectres du même échantillon relevés à un intervalle de temps convenablement choisi fait apparaître le spectre des seules espèces de période courte. Nous avons appliqué cette méthode en particulier au dosage de l'aluminium dans le béryllium avec une sensibilité de 0,01 ppm en effectuant une douzaine d'analyses à l'h eu re. Méthode de coïncidence: Le spectre des coincidences y - y a permis de doser le cuivre dans le béryllium en présence de nombreuses autres impuretés avec une sensibilité inférieure à 0,0i ppm. En conclusion, l'application qui vient d'être décrite de la spectrographiey, après irradiation à la pile EL-3 de Saclay, a permis de doser dans le bérylliurti des traces d'aluminium (28A1 :2,3 m in), de vanadium (52V ï 3,8 m in), de chlore (SSCI ï 37,5 min) , de manganèse (“ Mn :2,6 h), de potassium («K : 12,5 h) , de sodium (Z4Na : 15 h ), de cuivre («¿Си: 12,8 h). La simplicité relative de cette méthode ne semble pas limiter son emploi aux concentrations très faibles; elle peut aussi s'appliquer à d'autres matériaux que le béryllium.

29 30 J. PETIT et Ch. ENGEL MANN

АНАЛИЗ СЛЕДОВ ПРИМЕСЕЙ В БЕРИЛЛИИ НЕДЕСТРУК1ИВНЫМИ МЕТОДАМИ. Растущий интерес к исследо- валив материалов высокой чистоты и ограниченные возможности обычного химического анализа побудили исследователей использовать активации нейтронами. Для проведения аналиэаэлементов* образующих короткожиеущий изотоп, представилось полезным* точнее, необходимым* произвести подсчет без предварительного химического отделения* этот метод оказался очень интересным» поскольку он не вызывал разрушения, и тем более примечательным* что периоды облучения являются короткими. Мы опишем главным образом два метода* которые позволили расширить область применения гамма* спектроскопии. Метод отделения*, с помощью многоканального селектора с магнитной записывающей лентой было произведено отделение двух спектров на одном и том же образце в течение соответствующим образом выбранного отрезка времени» которое дало спектр только одних короткоживущих элементов. Мы ис­ пользовали этот метод» в частности, при определении количества алюминия в бериллии с чувстви­ тельностью в 0*01 частей на миллион» произведя до двенадцати анализов в час. Спектр совпадений у-у позволил определить наличие меди в бериллии, несмотря ка присутствие многих других примесей с чуствительностью ниже 0,01 части на миллион. В заключение можно отметить» что только что описанное применение спектографии у после об­ лучения на реакторе El - 3 в Сакле позволило определить в бериллии наличие алюминия(А1ав - 2*3 минуты), ванадия (Vs2 - 3,8 минуты), хлора (С1эв - 37,5 минуты), марганца (Мп5® - 2,6 часа), калия (К42 - 12,5 часа), натрия (Na24 - 15 часов) и меди (Си®4 - 12,8 часа). Относительная простота этого метода, по-видимому, не ограничивает его применения только для очень слабых концентраций} он может также применяться и к другим материалам, а не только к одному бериллию.

DETERMINACIÓN CUANTITATIVA DE.VESTIGIOS DE IMPUREZAS EN EL BERILIO POR METODOS NO DESTRUCTIVOS. El estudio de los materiales de alta pureza despierta un interés cada vez mayor, y las limi­ taciones del análisis químico clásico indujeron a diversos investigadores a recurrir en medida creciente a la activación neutrónica. Para determinar cuantitativamente los isótopos de período corto, los autores estiman necesario y con­ veniente efectuar los recuentos sin proceder a una separación química previa; por otra parte, este método es muy interesante por su carácter no destructivo, tanto más acentuado cuando más breves son los períodos de irradiación. Los autores describen principalmente dos métodos que han permitido extender el campo de aplicaciones de la espectrografía gamma. Método de sustracción: Al emplear un selector multicanal de memoria magnética y restar dos espectros de la misma muestra trazados con un intervalo de tiempo adecuado, el espectro de los isótopos de período corto aparece aislado. Los autores han aplicado este método al análisis cuantitativo del aluminio en el berilio* alcanzando una sensibilidad de 0,01 ppm y han podido realizar una docena de análisis por hora. Método de coincidencia; El espectro de las coincidencias y-y ha permitido analizar cuantitativamente el cobre en el berilio en presencia de muchas otras impurezas, con una sensibilidad superio a 0,01 ppm. En conclusión, empleando la espectrografía y de la manera descrita después de irradiar las muestras en el reactor EL-3 de Saclay, se han podido determinar cuantitativamente en el berilio vestigios de aluminio (**A1 de 2,3 min), vanadio (52V, de 3,8 min), cloro (*Clf de 37,5 min), manganeso (5*Mn, de 2,6 h) .potasio («K,de 12,5 h),sodio (2*Na de 15 h) y cobre (MCu, de 12,8 h). La sencillez relativa del método sugiere que puede ser útil también para concentraciones no tan redu­ cidas; asimismo, pueden aplicarse sustancias distintas del berilio.

1. INTRODUCTION

Les matériaux de haute pureté suscitent un intérêt croissant et leur étude requiert la mise au point de méthodes analytiques très sensibles. L’ana­ lyse par activation a joué dans ce domaine un rôle privilégié, et, complétée par des séparations chimiques appropriées, a connu un développement im­ portant [l] . DOSAGE DE TRACES D’IMPURETÉS DANS LE BÉRYLLIUM 31

Cette méthode est évidemment limitée aux éléments formant des iso­ topes de période assez longue. Les progrès réalisés récemment dans l’in­ strumentation nucléaire ont permis un n o m b r e considérable de déterminations directes, notamment par spectrométrie y [2]. Elles ajoutent à la possibilité d’emploi de radioéléments à courte période l’avantage d’être rapides et non destructives. Mais les spectres obtenus sont généralement complexes. Pour les ana­ lyser, LEE [3] «t BATE f4j ont proposé une méthode de soustraction qui consiste à com penser Г activité d’im élénaerat \ doser par une source étalon du même élément; cette technique, très utile, est d’un emploi délicat si la période de l’élément considéré est courte. ANDERS [5] a relevé, pour des périodes très courtes, des spectres 'k intervalles de temps réguliers et analysé leur décroissance à l’aide d’une machine k calculer électronique. Nous nous proposons de décrire les méthodes de spectrométrie y u tili­ sées et les résultats obtenus dans l’analyse non destructive de béryllium de haute pureté.

2. MÉTHODES D’ANALYSE DES SPECTRES DE BÉRYLLIUM IRRADIE AUX NEUTRONS

Les principales impuretés rencontrées dans du béryllium de haute pu­ reté et dont l’analyse par activation aux neutrons est possible sans sépa­ ration chimique préliminaire sont, par ordre de période radioactive crois­ sante: Al, V, Cl, Mn, Cu, Na, K, W, Cr, Ta. Dans certains cas favorables, tous ces éléments peuvent être dosés en utilisant convenablement les décroissances différentes des isotopes obte­ nus par réaction (n, 7 ) Г6 ] . Mais le plus souvent la complexité du spectre due k la juxtaposition de plusieurs raies limite les possibilités de ce mode opératoire à certaines des impuretés mentionnées. Aussi avons-nous, afin d’étendre le domaine d’applications de la spectrom étrie y k des cas moins favorables, utilisé deux méthodes particulières décrites ci-dessous.

2.1. Méthode de soustraction.

Cette technique a dû être mise au point pour le dosage d’éléments à vie très courte, 28A1 et 52V, dans du béryllium électrolytique contenant des quantités importantes de chlore. Les caractéristiques nucléaires des émet­ te u r s y en présence sont reproduites au tableau I [7]. L’analyse de traces d’Al et de V est rendue impossible par la présence des pics de 3SC1 suivis du fond continu Compton. Aussi avons^nous m is à profit la propriété très intéressante des sélecteurs d’amplitude k mémoire magnétique de perm ettre la soustraction de deux spectres enregistrés à des instants différents. L’échantillon k analyser est irradié dans un canal pneumatique de la pile EL3 ci Saclay, pendant un temps variant de quelques secondes k quelques minutes suivant les teneurs en Al et Cl présentes,dans un flux de 6 - 1012 n /c m 2 - s environ, en même temps qu’un témoin contenant une quantité connue d’Al. Immédiatement après l’activation, on effectue un prem ier comptage; le spectromètre y e s t co m p o sé d ’un s é le c te u r d ’a m p litu d e t r a n s i s to r is é k 400 canaux du type SA-40 INTERTECHNIQUE, et d’une sonde k scintillations 32 J. PETIT et Ch. ENGELMANN

TABLEAU I

CARACTÉRISTIQUES NUCLÉAIRES DE 28A1, DE 52V E T DE 38C1

Radioélément Période Energie-y (min) (MeV)

28 Al 2,3 1,78

52 V 3,8 1,44

38C1 37,5 1,60 et 2,15

équipée d’un cristal Nal (Tl) de 5"X 3"; une minute environ s’écoule entre la sortie du réacteur et le début de la manipulation. Le stockage est effectué pendant une durée n’excédant pas 60 s. On obtient donc un spectre contenant à. la fois les pics de 38C1 et de 28A1, ce dernier pouvant être plus ou moins caché par les deux prem iers (fig. 1). Après un laps de temps variable, mais du même ordre de grandeur que la période de 28A1, on enregistre un second spectre dans la même série de mémoires, mais en soustraction jusqu’il compensation totale du pic à 2, 15 MeV de 38C1. La vitesse de décroissance de 28Al étant beaucoup plus grande que celle de 38Cl, le nombre d’impulsions d e '¿SA1 initialement enregistré est relativement peu diminué, de sorte que seule sa raie à 1, 78 MeV reste apparente; le dosage de cet élément est alors facile, par comparaison avec l’activité de l’étalon mesurée ultérieurement dans les mêmes conditions.

Figure 1

Be électrolytique, 1030 mg Irradiation: 30 s Comptage: 0,5 min Al: 5 ppm - Cl: 1000 ppm.* DOSAGE DE TRACES D’IMPURETÉS DANS LE BERYLLIUM 33

Théoriquement, il semblerait intéressant d’effectuer cette compensation du Cl quelques dizaines de minutes après l’enregistrement du prem ier spectre, 28Al ayant seul complètement décru. Mais, pratiquement, en raison de la dérive de position des pics due к l’équipement utilisé, la soustraction doit être effectuée aussi vite que possible. Des essais nous ont montré qu'en choisissant un intervalle de temps entre les deux opérations de l’ordre de 2 Ъ. 3 min (par exemple, 2, 3 min pour sim plifier les calculs ultérieurs), la soustraction s’effectue convenablement; le nombre de coups de 28A1 obtenu aprfes compensation représente la moitié de celui du prem ier enregistre­ m e n t. Les spectres des figures 1 et 2 illustrent l’intérêt considérable de cette méthode très simple. Alors que dans le cas de la figure 1, une estimation très approximative de la quantité d’Al présente est encore réalisable, la seconde figure montre l’impossibilité absolue d’un dosage direct sans com­ pensation. Le dosage du vanadium se fait exactement de la même façon.

38CI

ENERGIE CM'V)

Figure 2

Be électrolytique, 989 mg Irradiation: 10 s Comptage: 0,5 min Al: 1,6 ppm —Cl: 1200 ppm.

Cette méthode nous a permis d’effectuer jusqu’à 12 analyses par heure. La lim ite de sensibilité effective est de 1 ppm environ d’aluminium et de vanadium dans un matériau contenant 1000 ppm de chlore. Pour du béryllium refondu, où pratiquement tout le chlore est éliminé, la limite de sensibilité de cette technique de dosage dans les conditions expérimentales indiquées se situe vers 0, 01 ppm, si la teneur en manganèse n’excède pas quelques ppm; en effet, dans ce cas, l’élément gênant est 56Mn dont les pics sont à 1, 8 et 2, 12 MeV. Nous avons d’autre part établi que la reproductibilité et l’exactitude des résultats numériques sont meilleures par m esure de la hauteur des pics plutôt que de leur surface. En effet, la figure 2 montre que le pic 28Al résul­ tant de la soustraction de 38C1 du spectre initial est très petit par rapport 34 J. PETIT et Ch. ENGEL MANN

à ceux du chlore. Un déplacement très faible des deux pics de 38C1 entre les deux opérations peut fausser énormément la forme du pic, donc la me­ sure de sa surface, alors que la hauteur mesurable sur plusieurs canaux est en moyenne moins affectée; par conséquent, si l’on prend pour grandeur caractéristique de la teneur en Al, la hauteur du canal le plus chargé, l’in­ fluence de ce glissement est minimisée.

2.2. Méthode des coïncidences

En plus de la possibilité de soustraction déjà discutée ci-dessus, le sélecteur SA-40 permet d’effectuer des comptages en coïncidences que nous avons utilisés pour doser le cuivre à l’état de trace. L’isotope 63 donne en effet, par irradiation aux neutrons thermiques, le 64 Cu de 12, 8 h de période. Ce noyau étant un émetteur p*, nous avons mis à profit le fait que l’annihi­ lation de cette particule dans la m atière donne deux rayons y de 0,51 MeV chacun, émis avec une corrélation angulaire de 180°. Deux compteurs à scintillations, équipés de cristaux Nal(Tl) de 80 mm X 100 mm sont placés symétriquement de part et d’autre de la source, à une distance convenable de celle-ci. Le sélecteur n’enregistre une impulsion dans ses mémoires que si, dans un intervalle de temps inférieur au temps de résolution du dis­ positif électronique, une seconde impulsion provenant du compteur opposé est appliquée sur la voie de coïncidence. Or cette simultanéité existe pour les deux y résultant de l’annihilation /3+. On enregistre donc le pic pho­ toélectrique correspondant à un y de 0,51 MeV alors que les y d’énergie différente ne sont pas comptés, dans la mesure où ils n’entrent pas dans le sélecteur en même temps qu’une impulsion d’ouverture. Ce mode de fonc­ tionnement du sélecteur permet de réduire le mouvement propre jusqu’au 1 / 1 0 0 0 de sa valeur normale, abaissant, ainsi considérablement la limite inférieure des quantités de cuivre détectables dans un matériau extrême­ ment pur. Dans du béryllium de haute pureté, des teneurs en cuivre in­ férieures à 0,01 ppm peuvent être dosées sans difficulté en irradiant l’échan­ tillon pendent 30 min dans un flux de neutrons thermiques de 6 - 1012 n /c m 2 • s. Néanmoins, il convient de préciser que, si dans le matériau analysé, il existe d’autres émetteurs y très actifs, les coïncidences fortuites de ces derniers sont d’autant plus nombreuses que l’activité est plus grande et la limite inférieure de détection du cuivre s’en trouve relevée. Cette technique de dosage est particulièrement utile quand un élément à vie longue dans la m atrice, tel que le i82Ta dont la période est de 1 1 2 j, cache partiellement ou complètement le pic à 0,51 MeV de 64 Cu.L’échantillon est mis en sandwich entre deux écrans de plomb de 3 mm chacun, absorbant en outre une part très importante du rayonnement de basse énergie émis par i82Ta et éliminant ainsi une bonne proportion des coïncidences fortuites. La figure 3 montre le spectre d’un béryllium irradié, obtenu dans ces con­ ditions, en comptage normal. La figure 4 est relative au même échantillon, en utilisant le fonctionnement en coïncidence. Ce graphique montre que l’ac­ tivité du pic complexe du i«2Ta situé à environ 1,2 MeV est réduite à moins de 1/200 de sa valeur, permettant l'apparition du pic à 0,51 MeV de 64C u. Ce même spectre montre la présence d’un second pic à 200 kW environ pro­ venant des coïncidences fortuites très nombreuses, dans ce domaine d’éner­ gies où i82Ta émet plusieurs y [8] . DOSAGE DE TRACES D’IMPURETÉS DANS LE BERYLLIUM 35

ENERGIE (MeV)

Figwe 3

Échantillon d'alliage Be-Та, â O.Tfcde Ta.

Figue 4

Spectre do mfane échantillon qne celm de la figure 3 mais relevé en cdnddences (teneur en Cm 3 ppm).

3. RÉSULTATS

L'analyse non destructive du béryllium par les méthodes décrites a permis de doser effectivement les éléments Al, V, Cl, Mn, Cu, Na, K, W, Cr, Ta. Plus particulièrement, l'aluminium, le chlore, le manganèse et le cuivre ont fait l'objet de déterminations de routine en vue de contrôler l'élaboration de béryllium électrolytique [9], sa fusion et son raffinage par 36 J. PETIT et Ch. ENGELMANN

TABLEAU II

RÉSULTATS D'ANALYSE DE QUELQUES ÉCHANTILLONS DE BÉRYLLIUM DE HAUTE PURETE

Al Cl Mn Cu Nature du produit , (PPm ) (ppm) (ppm) (ppm)

Be électrolytique SR 5 450 23 5

Be électrolytique CEA 5 575 2.5 2

Be coulé 6 ' 6 0,7 4

Be de fusion de zone

Г T ête 0,07 < 0,5 0,02 8

L Queue 104 - 90 16 fusion de zone [10] -j. L’analyse est effectuée en deux étapes: dosage de l’alu­ minium par une irradiation de 1 miniute et dosage du chlore, du manganèse et du cuivre par une irradiation de 30 minutes; la prem ière dure environ 5 minutes, la seconde 15 minutes, soit au total 20 minutes par échantillon. Le tableau, II indique quelques résultats obtenus et donne une idée de la sensibilité effectivement atteinte dans quelques cas; dans l’ensemble, ces résultats sont assez voisins de ceux obtenus par MULLINS et coll.[ 11] et confirment certaines limites de sensibilité prévues par ces auteurs: nos essais ont montré^ en outre,qu’on pouvait abaisser la limite de détection de l'aluminium.

4. CONCLUSION

Les progrès de l’instrumentation nucléaire ont permis la mise au point de méthodes qui étendent les possibilités de la spectrom étrie y classique, en particulier vers les périodes courtes. En analyse par activation, ces méthodes se sont révelées simples, rapides et non destructives. Leur appli­ cation peut donc être envisagée à des matériaux autres que le béryllium et surtout d’une pureté beaucoup moins grande.

RÉFERENCES

[1] DESCHAMPS, N .. LEUILLOT, A. et ALBERT, P., Sur l'analyse systématique de aluminium après irradi­ ation aux neutrons, C.R. Acad. Sci. 254(1962) 682. FOURNET, L. et ALBERT, P ., Sur l'analyse systématique du zirconium après irradiation aux neutrons, C.R. Acad. Sci. 254(1962) 1076: [2] GUINN, V. P. and WAGNER, C .D ., Instrumental Neutron Activation Analysis, Anal. Chem. 32 (1960) 317. [3] LEE, W ., Direct estimation of y -ray abundances in radionuclide mixtures, Anal. Chem. 31(1959) 800. [4] BATE, L. C. and LEDDICOTTE, G. W ., Complement subtraction method of y-ray spectrometry for the quantitative analysis of complex mixtures of radionuclides, ORNL-2866, pp. 33-34. DOSAGE DE TRACES D’IMPURETÉS DANS LE BERYLLIUM 37

[5] ANDERS, O, U ., Use of very short lived isotopes in activation analysis. Anal. Chem. , 33 (1961) 1706. [6] ENGELMANN, C. et PETIT, J.F ., Irradiation de Be de diverses provenances en vue de l'analyse des impuretés par activation, Rapport CEA DM/983, (1961). Г7] SULLIVAN. W .H ., Trilinear Chart of Nuclides, USAEC (1957). [8] DZHELEPOV, B. S. and PEKER, L. К. , Decay schemes of radioactive nuclei, Pergamon Press (1961). [9] BOISDE, G ., BROC, М ., CHAUVIN, G. et CORIOU, H ., Production de Be de haute pureté par électro- raffinage en bain de sels fondus, Bull. inf. sci. tech. du CEA, 62 (1962) 29. [10] PETIT, J ., SCHAUB, B. et ENGELMANN, C ., Fusion de zone et analyse par activation, Bull. inf. sci. tech. du CEA 62(1962) 39. [11] MULLINS, W .T., EMERY, J.F., BATE, L.C. and LEDDICOTTE, G.W ., The determination of minor elements in ultrapure Be and its compounds by neutron radioactivation analysis, TID-7629 (1962) 245.

DISCUSSION

W. BOCK-WERTHMANN: In our laboratory we have obtained good results with a spectrum-subtraction method sim ilar to that described in your paper for determining aluminium in terphenyls and other m aterials. Details on the technique are given in a paper that was presented to last year's International Conference on Modern Trends in Activation Analysis at College Station, Texas*. We are now trying to develop a method, using more than two measurements, to differentiate between a number of nuclides with different half-lives. The only difficulty is that we obtain poor statis­ tics after subtraction. I should be interested to hear what experience you have had with counting statistics whenusingthe spectrum-subtractionmethod. C. ENGELMANN: To answer this question, we took samples contain­ ing the same amount of aluminium and subjected them to successive series of irradiations. The scattering of the results obtained from peak-height measurements proved to be less than 10 %. R. LOOS: When using your coincidence method for determining Cu64, you would surely have to correct for certain other factors. Any gamma em itter of sufficient energy would produce positrons that would in turn give rise to annihilation gammas. This means that Na24 would give you an anni­ hilation peak that would be liable to interfere with your Cu64 determination. C. ENGELMANN: The amounts of sodium present in the samples that are re-melted in our metallurgy department are so small that no correction is necessary. Speaking generally, however, the situation is as follows. When we are looking for copper with our coincidence method, using the two gamma rays produced by annihilation of the fi*, a high degree of sensitivity is possible because of the symmetry of the two gammas and the symmetri­ cal arrangement of the counters in relation to the source. The annihilation takes place within the source. In the case of the sodium, however, and particularly the 2. 76-MeV line of the Na24, the /3+ resulting from pair pro­ duction is produced in one of the counters. This does not have the same symmetrical-counter response as in the case of the 0. 51-MeV gammas and the 0. 51-MeV peaks are therefore only rarely affected. However, I cer­ tainly agree that this Na 24 effect cannot be ignored and corrections would certainly have to be made when there are very high levels of Na 24 a c tiv ity p re s e n t.

* BOCK-WERTHMANN, W. and SCHULZE, W., "Methodical Improvements of Activation Analysis", Modem Trends in Activation Analysis, Activation Analysis Research Laboratory, A & M College of Texas, College Station, Texas (1961) 145-148.

SOME TECHNIQUES FOR THE DETERMINATION OF ISOTOPES OF SHORT HALF-LIFE AS APPLIED TO THE ACTIVATION ANALYSIS OF BERYLLIUM

C. A. BAKER UNITED KINGDOM ATOMIC ENERGY AUTHORITY (RESEARCH GROUP), LONDON,ENGLAND

Abstract — Résumé — Аннотация —■ Resumen

SOME TECHNIQUES FOR THE DETERMINATION OF ISOTOPES OF SHORT HALF-LIFE AS APPLIED TO THE ACTIVATION ANALYSIS OF BERYLLIUM. It has b een necessary to analyse b ery lliu m m etal of high purity, prepared by distillation in a vacuum. The residual impurities are present at concentrations of a few parts per million and methods are described for determining some elements at this concentration level by radioactivation analysis. In the cases of the elements discussed, the only active isotopes formed by thermal neutron activation have a short half-life. Specific examples are given of such elements which can be de­ termined by direct gamma spectrometry of the irradiated beryllium. Two examples of rapid chemical sepa­ rations are also described where this is essential before the active isotope is counted, either because no gamma rays are emitted or because of a gross interference.

QUELQUES METHODES DE DETERMINATION DES RADIOISOTOPES DE COURTE PÉRIODE, APPLIQUÉES / A L'ANALYSE PAR ACTIVATION DU BERYLLIUM II a été nécessaire d’analyser du béryllium métal de grande pureté, préparé par distillation sous vide. Les impuretés résiduelles y subsistent à des concentrations de quelques parties par million. L'auteur expose des méthodes qui permettent, à ces taux de concentration, de déterminer certains éléments grâce à l’analyse par activation. Dans le cas des éléments étudiés, les seuls radioisotopes formés par activation des neutrons thermiques sont des radioisotopes à courte période. L'auteur donne des exemples précis de ces éléments, que l'on peut déterminer par spectrométrie gamma directe du béryllium irradié. Il donne en outre deux exemples de séparation chimique rapide, où il est indispensable de faire cette opération avant de procéder au comptage du radioisotope, soit parce qu'il n'y a aucune émission de rayons gamma,' soit parce qu'il y a des interférences.

НЕКОТОРЫЕ МЕТОДЫ ОПРЕДЕЛЕНИЯ КОРОТКОЖИВУЩИХ ИЗОТОПОВ, ПРИМЕНЯЕМЫХ ПРИ АКТИВАЦИОННОМ АНА­ ЛИЗЕ БЕРИЛЛИЯ. Необходимо било провести анализ металлического бериллия высокой чистоты, по­ дученного методом дистилляции в вакууме. Концентрация остаточных примесей составляла несколько частиц на миллион. Описывается методы определения некоторых элементов с таким уровнем концентра­ ции с помощью радиоактивационного анализа. В случае обсуждаемых элементов в результате проведения активации тепловыми нейтронами образуются только короткоживущие изотопы. Приводятся конкретные примеры таких элементов, которые могут определяться методами непосредственной гамма-спектрометрии облученного бериллия. Описываются также два примера быстрого химического разделения, которое необходимо до проведения измерения активного изотопа либо ввиду отсутствия испускания гамма-лучей, либо ввиду большого наложения посторонней активности.

TÉCNICAS EMPLEADAS EN EL ANALISIS POR ACTIVACION DEL BERILIO PARA DETERMINAR ISOTOPOS DE PERÍODO CORTO. En el laboratorio del autor, se presentó la necesidad de analizar berilio metálico de alta pureza obtenido por destilación al vacío. Las concentraciones de las impurezas residuales eran de algunas partes por millón, y la memoria describe métodos para analizar por radioactivación algunos elementos cuyas concentraciones son de este orden de magnitud. Los elementos de que trata la memoria sólo forman radio­ isótopos de período corto al ser activados por neutrones térmicos. El autor cita algunos de los elementos que puedan ser determinados directamente por espectrometría gamma del berilio irradiado; asimismo describe dos ejemplos de separación química rápida aplicada cuando ésta es esencial antes de proceder al recuento del isótopo activo, sea por no emitir éste radiaciones gamma o porque se producen serias interferencias. 39 40 C . A. BAKER

There is Some theoretical'evidence that the brittleness of beryllium is due to the traces of impurities in the metal as currently manufactured, and it is believed that the ultra-pure metal is intrinsically ductile. Considerable effort has been directed towards the preparation of high-purity beryllium, the initial aim being to reduce all the impurities below 10 ppm in order to provide m aterial for metallurgical investigation. One of the most promising processes is the fractional distillation of the metal in a high vacuum. This is being carried out at Harwell by Keen and Hooper. A charge of 400 g of beryllium is distilled from a beryllia cruc­ ible on to a tantalum condenser in a vacuum of 10-6 mmHg. The condensed m aterial is removed and broken down into small samples so that concentr­ ation gradients can be followed and any one portion may consist of only a few grams of metal on which several determinations of im purities are to be made. In order to achieve limits of detection of 10 ppm quantities of the o rd e r of lug of impurity must be estimated on a few hundreds of milligrams ' of sample. Such a project must be backed up by an analytical service which has methods available to determine the impurities with the necessary precision.. A variety of spectrographic and chemical techniques exist which have the necessary lim its of detection but for certain impurity elements radioactivation analysis is superior. In particular non-destructive techniques are very valuable since the sample remains available for other determinations. The basis of any analytical method is to measure some quantity which is characteristic of the m aterial being determined and which is in some way proportional to the amount present. In radioactivation analysis the measure­ ment can be made of the radioactivity induced by irradiation with thermalized neutrons. By choosing the irradiation time and the decay between the end of the irradiation and the commencement of counting, discrimination can be made against interferences, and in addition only the sample itself need be irradiated and we need not concern ourselves with reagent blanks intro­ duced during subsequent processing as these will not contribute to the measured ac tiv ity . In general, therm al neutrons penetrate deeply into m atter with undiminished intensity and have high cross-sections for nuclear reactions. They therefore provide,an ideal way of activating impurities which are distributed through­ out a sample.

ISOTOPES OF SHORT HALF-LIFE

In many cases the only active isotope formed by therm al neutron activ­ ation has a short half-life. Na, Mg, Al, Si and Mn can be cited as examples and in other cases it is advantageous to choose a short-lived isotope from several which are available. By doing so a saturation activity level can be achieved in a shorter irradiation time, and also the decay can be followed rapidly to confirm the radiochemical purity of the active product.

EXPERIMENTAL

The sample is irradiated together with one or more standards of known content for a period of time from half a minute to several hours, depending TECHNIQUES FOR DETERMINATION OF ISOTOPES OF SHORT HALF-LIFE 41

on the nuclide to be determined, and is then returned to the laboratory, usually by means of a pneumatic transfer system. The activity of the sample and the standards is then compared either directly or after suitable chemical separation of the required nuclide. Fortunately beryllium has little interaction with therm al neutrons. It is for this very reason that it is being considered as a canning m aterial for nuclear fuel elements. The cross-section for the (n, 7 ) reaction is very small and the product long-lived, and incidentally emits no y ray, and hence there is a negligible contribution to 'the radioactivity from the m atrix of beryllium. The small cross-section and low atomic weight of beryllium also mean that it does not shield the impurity elements from the neutron flux, but beryllium metal will alter the neutron energy spectrum by acting as a moderator and this could lead to error if the sample weight were large. Since there is no large background of gamma activity from the beryllium it is possible to determine certain impurity elements directly by assessing the characteristic gamma rays, using the technique of gamma spectrometry. It is essential to compare the sample with a standard of sim ilar size and shape in order to achieve the same counting geometry, and for this purpose dilute aqueous solutions of the standard of the same bulk as the sample have been used. The most rapid and elegant method based on this technique is exemplified by the determination of aluminium in beryllium . About 0. 5 g of sample is weighed and encapsulated in polythene and irradiated for 30 s. Included in the rabbit are dilute aqueous solutions of aluminium nitrate of known concentration and sim ilar volume to the sample. After recovery from the reactor the sample and standards are counted using a 3-in X 3-inNaI(Tl) crystal and a 10 0 -channel pulse-amplitude analyser adjusted to record the energy range from 1.6-2.0 MeV in the first 20 channels. One-minute counts are recorded over a period of at least 30 min and the decay curve plotted on logarithmic paper. The long-lived tail is due to Mn56, which also emits a у-ray near 1.8 MeV, and this can be subtracted graphically leaving only the component of half-life 2.3 min due to Al28. This activity is compared with the standards and a ratio of the aluminium content of sample and standard o b ta in ed . Other activities will have been produced during the irradiation, notably M n S 6 and C u 6 4 . These nuclides give rise to characteristic photopeaks in the gamma spectrum and the areas under these peaks can be assessed and the decay curves plotted and resolved in the same way.

CHEMICAL SEPARATION

Silicon is activated by therm al neutrons giving only one active isotope which has a half-life of 2 . 6 h which can be made the basis of a very sensitive method of determining silicon. However Si3i emits very few 7 -rays and it is necessary to count the energetic )3-rays. These will be indistinguishable from a very large number of jii-rays from isotopes of other elements and the active silicon must therefore be separated in a high degree of radio­ chemical purity from the irradiated beryllium. This is achieved by dissolving the sample in a mixture of nitric .and .hydrofluoric acids together with a known amount of'inactive silicon carrier. Concentrated sulphuric acid is then added 42 C. A. BAKER and the volatile silicon fluoride distilled in a stream of air in a polythene apparatus. The distillate is dissolved in water and the silicon recovered as silica by addition of an excess of aluminium nitrate and concentrated sulphuric acid. The silica is washed, ignited and mounted on a counting tray and the activity measured using an end-window GM tube. A standard, consist­ ing of a weighed quantity of pure silica, is irradiated at the same time as the sample and this is processed in the same way. After correction for chemical yield the relative activities give a m easure of the relative silicon content of the sample and standard. The sources are of course checked for correct half-life and also examined by gamma spectrometry to ensure the absence of other nuclides, particularly Mn&6, which has a sim ilar half-life. This type of chemical separation is ideal for radiochemical work because it is rapid and highly specific. The sensitivity of the method is 0.1 Mg Si, assuming an initial count-rate equal to the counter background, using a neutron flux of 1 0 12n /c m 2 s .

REMOVAL OF AN INTERFERENCE

Magnesium is activated by therm al neutrons to give Mg27, half-life 9. 5 min. A 7 -ray of 0.83 MeV is emitted during decay but it is not possible usually to observe this Y-ray directly because of the superposition of the 0.85-MeV y-ray from Mn6S. For example, if a sample containing equal weights of magnesium and manganese is irradiated for 10 min, then the ratio of counts in the energy region of 0. 83 MeV immediately after irradi­ ation will be approximately 1 to 300. It is therefore necessary to remove th e M n56 activity chemically before counting and this must be done rapidly before the magnesium has decayed appreciably. In order to save time after irradiation the sample is converted to beryllium nitrate using purified reagents before irradiation. The sample is then irradiated in company with a magnesium standard in dilute aqueous solution and a reagent blank made by evaporation of duplicate quantities of the acids used for the conversion to nitrate, for five minutes. The sample is then taken into solution in boiling dilute hydrochloric acid containing a known amount of inactive magnesium carrier and some manganese hold-back carrier. An excess of hot potassium permanganate solution is then added and after digestion for half a minute the manganese dioxide is filtered at the pump through a sintered glass filter. The filtrate passes directly into hot sodium hydroxide solution. The beryllium and the excess of permanganate remain in solution and the magnesium hydroxide can be centrifuged out and the supernate decanted. This precipitate is re­ dissolved in dilute hydrochloric acid containing some aluminium chloride and re-precipitated with sodium hydroxide. After washing the precipitate is again dissolved in acid and made up to a standard volume in a polystyrene container ready for counting. The Mg27 is counted, using a gamma spectro­ m eter adjusted to record counts in the region of 0. 83 MeV, and the decay curve is plotted. This chemical separation can be performed in eleven minutes, a little over one half-life of the required nuclide, and although it is not specific to magnesium it incorporates steps which provide adequate decontamination with respect to thfe im purities which are found in the present samples of TECHNIQUES FOR DETERMINATION OF ISOTOPES OF SHORT HALF-LIFE 43 beryllium and interfere with the counting of Mg27.. The sensitivity of the method is about 1 Mg-

CONCLUSION

This paper has presented examples of three general methods which can be applied to the determination of short-lived isotopes resulting from thermal neutron activation for the purpose of analysis. Many other techniques can be used for the purification of the required nuclide, for example solvent extraction and ion exchange chromatography, but the examples given will serve to show the value of the technique of activation analysis particularly for traces of impurities in beryllium.

DISCUSSION

W. GEBAUHR: You say that the condensed m aterial is broken down into small samples. I would have thought there was a danger of impurities entering the m aterial when this was done. I wonder if you could tell us how this breaking process is actually carried out? C. BAKER: The operation is carried out in a glove-box and pliers tipped with pure tantalum are used. Of course, the responsibility for providing representative samples lies not with the analyst but with the person who distills the beryllium. H. KEPPEL: What was your purpose in looking for silicon in your beryllium samples? There are surely other elements present in beryllium manufactured for use as reflector m aterial which are far more important than silicon. C. BAKER: The point is that we are trying to prepare beryllium of very high purity for metallurgical investigations, and for that reason it is important to reduce the levels of ail impurities as far as possible, quite irrespective of their neutron cross-sections. Our particular interest in silicon is that it seems to be introduced into the beryllium in the course of the distillation process from impurities present in the beryUia crucible. Furthermore, spectrographic and chemical methods of analysis do not produce consistent results. W. GEBAUHR: You mentioned that for magnesium determinations the beryllium is converted to beryllium nitrate. What quantities of magnesium are in the beryllium? And are you sure that all the magnesium is converted to the nitrate, i. e. that all the magnesium will still be present in the beryllium nitrate after the conversion process? C. BAKER: Magnesium is present in amounts of 10 ppm or less. I am not at all sure that all the magnesium is carried over into the beryllium nitrate but this could be checked by using the longer-lived magnesium isotope. P. ALBERT: I was most interested to hear, Dr. Baker, that you are faced with the same sort of problems as we are and are trying to solve them along sim ilar lines to ourselves. I fully agree that silicon has to be separated even in the case of relatively pure m aterials. We have been study­ ing a method very sim ilar to yours for achieving this. In this connection I should like to ask what yield you obtained for the chemical separation of your silicon. 44 C. A. BAKER

C. BAKER: We obtained yields of 60 - 70%. Where the remaining 30 - 40% is lost I don’t know, but this could, I suppose, be checked byusing a large quantity of active silicon tracer. I suspect that all the silicon is distilled but that not all of it is recovered by the addition of aluminium nitrate and sulphuric acid to the aqueous solution of the distillate. P. ALBERT: It is interesting that we both obtain the same radiochemical yield in spite of the fact that there is an appreciable difference between your experimental conditions and ours. As you will see in our paper*, our apparatus is made of copper and the silicon is separated in the form of SiFg Ba, so that I don’t see where the losses could occur. When you use your method, at what tem peratures do you distill the SiFg H2 and precipitate the S i0 2 ? C. BAKER: The distillation is carried out from a high-density poly­ thene vessel imm ersed in a bath of boiling saturated NaCl at 108°C. We recover the silica by adding saturated aluminium nitrate solution and con­ centrated H2S04 and then heating just to boiling point. P. ALBERT: Is your silicon absolutely pure? C. BAKER: Yes, it is remarkably pure. I followed the decay for six half-lives and there was no deviation from the published half-life. P. ALBERT: In that section of your paper where you describe your technique for determining magnesium, I was very impressed by the speed at which you were able to perform eight different operations. I might add that our method for determining magnesium is sim ilar to yours. It also involves a two-stage chemical procedure, with a chemical separation before irradiation and a radiochemical purification of the magnesium-27 after irradiation. I think that this method can be usefully applied to various types of analysis. This problem is discussed in our paper.

* ALBERT, Ph. , DEYRIS, M. , DESCHAMPS, N. et FOURNET, L .« S u r les dosages d ’élém ents par leurs radioisotopes de périodes courtes dans l'analyse de l’aluminium, du fer et du zirconium de très hautes puretés^ these Proceedings. ANALYSE PAR ACTIVATION ET DÉTERMINATION DES ISOTOPES DE COURTE PÉRIODE

R. LOOS DÉPARTEMENT DE PHYSIQUE, UNIVERSITÉ LOVANIUM, CONGO (LÉOPOLDVILLE)

Abstract — Résumé — Аннотация — Resumen

ACTIVATION ANALYSIS AND DETERMINATION OF SHORT-LIVED ISOTOPES. The Lovanium University, Leopoldville, is working in close collaboration with the TRICO Centre, which has a TRIGA (General Atomics) reactor of 50 kW maximum power. The reactor is located close to the Nuclear Physics Department where analysis of irradiated specimens is mostly carried out. This close proximity makes it possible to determine isotopes of a few minutes’ half-life, there being advantage in this case in using the pneumatic tube (flux: lO ^n/cntfs). For isotopes of longer life, irradiation is done in the rotary rack (flux: 3 X 1011 n/cm2 s), or the central thimble (flux: 2.5 x lO1^ n/cm2s at maximum point). Measurement of gamma-rayspectraisdone by means of a 400-channel analyser; working in 4 sub-groups of 100 enables rapid disintegration curves to be followed. In some cases (copper-64, etc. ) study of the coin­ cidence spectrum with a second detector may be useful. The method has enabled us to detect and to determine quantitatively the following isotopes in various irradiated specimens (diamonds, soil samples, insects): aluminium-28, magnesium-27, calcium-49, iodine-128, manganese-56, copper-64, potassium-42, sodium-24 and gold-198.

ANALYSE PAR ACTIVATION ET DETERMINATION DES ISOTOPES DE COURTE PERIODE. L’Université Lovanium de Léopoldville travaille en étroite collaboration avec le Centre TRICO, qui dispose d’un réacteur TRIGA (General Atomics) d’une puissance maximale de 50 kW. Le réacteur est à proximité du département de physique nucléaire où se font la plupart des analyses des échantillons irradiés. La courte distance permet la détermination d'isotopes ayant une période de quelques minutes; dans ce cas, l'emploi du tube pneumatique (flux 1012 n/cmz.s) est avantageux. Pour les isotopes à plus longue période, les irradiations se font dans la couronne rotative (flux 3*10U n/cm 2 • s) ou dans le tube central (2,5» 1012 n/cm2 * s au point de flux maximal). Les mesures de spectres de rayons gamma se font au moyen d'un analyseur à 400 canaux; l'opération en quatre sous-groupes de 100 permet de suivre des courbes de désintégration rapide. Dans certains cas,l'étude du spectre de coincidences avec un second détecteur peut être utile (cuivre-64, etc. ). La méthode nous a permis de déceler et de déterminer quantitativement les isotopes suivants dans divers échantillons irradiés (diamants, extraits de sol, insectes): aluminium-28, magnésium-27,calcium-49,iode-128, manganèse-56, cuivre-64, potassium-42, sodium-24 et or-198.

АКТИВАЦИОННЫЙ АНАЛИЗ И ОПРЕДЕЛЕНИЕ КОРОТКОЖИВУЩИХ ИЗОТОПОВ. Леопольдвильский университет Лованиум работает в тесном сотрудничестве с центром Трико, который располагает реактором Трига (Дженерал Атомикс) с максимальной мощностью в 50 квт. Реактор находится поблизости от департа­ мента ядерной физики, где производится большинство анализов облученных образцов. Короткое рассто­ яние позволяет проводить определение изотопов с периодом полураспада в несколько минут; в этом случае предпочтительнее пользоваться пневмопочтой (поток 1012)н/сек*см"2). Облучения более долго­ живущих изотопов производятся во вращающейся короне (поток 3*1011н/сек»смЭ) или э центральном канале (2*5 х 101гн/сек*смгпри максимальном значении). Измерения спектров гамма-лучей производятся с помощью 400-канального анализатора; при четы­ рех подгруппах по 100 представляется возможность наблюдать за кривыми быстрого распада. В от­ дельных случаях может оказаться полезным изучение спектра совпадений с помощью второго детектора (медь-64 и др.)- Применение этого метода позволило нам обнаружить и провести количественное определение сле­ дующих изотопов в различных облученных образцах (алмазы, пробы земли, насекомые): алюминий-28, магний-27, кальций-49, йод-128, марганец-56, медь-64, калий-42, натрий-24, золото-198.

45 46 R. LOOS (

ANALISIS POR ACTIVACION EN LA DETERMINACIÓN DE RADIOISÓTOPOS DE PERÍODO CORTO. La Universidad Lovanium de Leopoldville trabaja en estrecha colaboración con el Centró TRICO, que dispone de un reactor TRIG A (General Atomics) de una potencia máxima dé 50 kW. El reactor se encuentra cerca del departamento de Física Nuclear en el que se analizan casi todas las muestras irradiadas. Merced a la corta distancia entre dicho departamento y el Centro nuclear, es posible determinar isótopos cuyos períodos son de pocos minutos; en este caso, ofrece ventajas el empleo del tubo neumático (flujo 10tz n/cm ís), Cuando se trata de isótopos de período más largo, las irradiaciones se efectúan en la corona giratoria (flujo3-lOUn/cmSsj o en el tubo central (2,5-ЮИ n/cm2sen el punto de flujo máximo). Los espectros gamma se miden con un analizador de 400 canales; si se opera en cuatro subgrupos de 100, es posible seguir las curvas de desintegración rápida. En algunos casos (cobre-64, etc. ) puede ser útil estudiar el espectro de coincidencias con ayuda de un segundo detector. El método ha permitido al autor detectar y determinar cuantitativamente en diversas muestras irradiadas (diamantes, extractos de suelos, insectos) los radioisótopos siguientes; aluminio-28, magnesio-27, calcio-49, yodo-128, manganeso-56, cobre-64, potasio-42, sodio-24 y oro-198.

1. INTRODUCTION

Les petits réacteurs de recherche sont bien adaptés à la mise au point d'un programme d'analyse par activation. A l'Université Lovanium de Léopoldville nous disposons des installations du réacteur piscine TRIGA MK1 (General Atomics) du Centre TRICO. Le bâtiment qui abrite le réacteur est situé à très courte distance du Laboratoire de physique nucléaire de l'Université (R. Loos et F. Steffens),où se trouve l'appareillage nécessaire à l'analyse des échantillons activés. C'ette proximité facilite un transfert rapide des échantillons de sorte que des isotopes dont la période n'est que de quelques minutes (par exemple 28Al) peuvent être détectés. Plus tard, on étudiera l'utilité d'un rapprochement plus grand en vue de pouvoir détec­ ter des isotopes à période encore plus courte.

2. APPAREILLAGE POUR L'IRRADIATION

Au réacteur TRIGA, l'irradiation par les neutrons peut se faire de trois manières différentes: a) en utilisant la couronne rotative dans le réflecteur au graphite entourant le noyau; celle-ci contient 40 tubes pouvant recevoir des échantillons contenus dans des tubes en polythène. Le flux est 3 • 10П n/cm2 s à 50 kW. b) en utilisant le tube pneumatique où le flux est de 1012 n/cm2 s à 50 kW. On peut extraire l'échantillon très rapidement, mais il est contenu dans un tube en m atière plastique (le«rabbit>>) qui s'active fortement et qui est aussi contaminé extérieurement. L'échantillon scellé dans un petit sac en plastique est donc retiré du tube et, si possible, transféré dans un sac non irradié. L'opération prend environ une demi-minute. L'irradia­ tion peut se faire pendant 5 à 10minutes. L'emploi du tube pneumatique est avantageux pour les isotopes dont la période est de quelques mi­ n u te s. c) en'utilisant le tube central dans le noyau du réacteur où le flux maximum est 2, 5 • 1012 n/cm 2 s à 50 kW. L'échantillon scellé dans un petit sac en m atière plastique est descendu dans le tube central au moyen d'une ANALYSE PAR ACTIVATION ET DETERMINATION DES ISOTOPES 47

ficelle qui porte à son bout inférieur une petite masse de plomb pouvant toucher le fond de la cuve. La distance entre l'échantillon et le plomb est déterminée de telle façon que l'échantillon se trouve à l'endroit du flux maximum dans le tube central. Dans les références [1] et [2] on explique comment déterm iner cette position. Le flux en différents endroits du réacteur a été déterminé par activation de feuilles d'or dont l'activité est mesurée au moyen d'un scintillateur à rendement connu. Ce rendement a été mesuré au moyen de feuilles d'or ir­ radiées au réacteur au graphite BRI du CEN, Mol, Belgique.

3. APPAREILLAGE ET MÉTHODES DE MESURE

Pour l'analyse des échantillons nous avons jusqu'ici utilisé seulement la spectrométrie des rayons gamma. Antérieurement nous disposions d'analyseurs à un canal, mais depuis mai 1962 nous employons uns analyseur transistorisé à 400 canaux RIDL (Radiation Instrument Development Labora­ tories, Chicago, 111.). Les résultats sont enregistrés au moyen d'un im­ primeur. En vue de l'analyse des isotopes de courte période nous avons choisi un imprimeur rapide Hewlett-Packard (vitesse d'impression: 5 canaux par seconde, soit 100 canaux en 20 secondes). Les 400 canaux peuvent être groupés en quatre sous-groupes de 100 canaux. Ceci est avantageux pour les isotopes de courte période: quatre spectres successifs en 100 canaux peuvent être pris pratiquement sans perte de temps, après quoi on fait l'en­ registrement. L'échantillon est placé entre deux scintillateurs Nal(Tl), dont l'un est relié directement à l'analyseur multicanaux. L'autre est raccordé à un ana­ lyseur monocanal; dans certains cas son emploi est avantageux pour obtenir des spectres de coïncidence avec l'autre détecteur. Par exemple,dans le cas d'un émetteur de positrons, on règle l'analyseur monocanal sur l'énergie du rayon gamma d'annihilation (0,511 MeV) et on observe le spectre des coïncidences avec l'analyseur multicanaux. L'analyseur travaille généralement jour et nuit sans interruption; la stabilité est alors très grande, ce qui facilite l'interprétation des spectres. Pour analyser un échantillon inconnu nous l'activons généralement pen­ dant cinq minutes dans le tube pneumatique et nous prenons des séries de quatre spectres successifs en. 100 canaux de 30 secondes par spectre. Après 15 minutes on augmente la durée des comptages à deux minutes, puis à cinq minutes. On cesse au moment où l'activité est devenue trop basse. On réactive l'échantillon, de préférence dans le tube central, pendant une à deux heures. On prend des spectres à intervalles réguliers, au besoin avec des temps de comptage plus longs, ce qui peut prendre plusieurs jours. S'il y a intérêt, on active encore une fois pendant 8 à 12 heures dans le tube cen­ tral; alors des comptages peuvent parfois être faits pendant des semaines. L'emploi des différentes durées d'irradiation est avantageux; chacune donne une meilleure activité relative à certains isotopes par rapport à ceux de période plus longue. Les essais d'identification des isotopes de courte période fournissent très rapidement un grand nombre de spectres. Faute de moyens de calcul automatique il est impossible d'analyser ces résultats avec la rapidité avec 48 R. LOOS laquelle ils sont produits par l'analyseur multicanaux. N’ayant pas accès à une calculatrice à grand rendement, nous étudions actuellement la possibili­ té d'établir pour nos besoins un programme simple de calcul automatique; celui-ci devrait perm ettre de soustraire les. spectres d'éléments connus ou rapidement repérés (28 Al, 56Mn, 24Na, etc. ). Nous avons interprété nos ré­ sultats par les méthodes graphiques classiques (analyse des courbes de désintégration, des pics, etc. ).

4. RECHERCHES EN COURS

La plupart des problèmes d'analyse par activation sont conçus avec la collaboration d'autres départements de l'Université. Evidemment il s'agit généralement de déterminer des isotopes de longue période à côté d'isotopes de courte période; cependant ce sont souvent ces derniers qui suscitent des problèmes particuliers. Généralement on applique la méthode avec un but bien déterminé et les résultats devront être interprétés en tenant compte de ce but. Ainsi dans beaucoup d'échantillons on observe une forte contribution des spectres d'élé­ ments dont la présence ne présente pas d'importance pour le problème en­ visagé. Par contre, ces éléments tendent à masquer des spectres plus faib­ les d'autres éléments. Dans pratiquement tous les échantillons (diamants, extraits de sol, term ites) nous trouvons 28д 1 ) 56 м п et 24Na. Le spectre de l'aluminium (concentration souvent de l'ordre de plusieurs parties par million) disparaît rapidement, mais celui du manganèse perturbe pendant plusieurs heures, même pour des traces faibles, de l'ordre de 0 .0 1 ppm . Le sodium est fortement perturbateur aussi (concentrations de l'ordre de 1 ppm ). La détermination d'autres éléments de courte période devient alors difficile: la mesure de la période d'un pic devient plus difficile et la déter­ mination quantitative est sujette à une plus grande erreur. Néanmoins nous avons pu déceler et doser les isotopes de courte période suivants:'¿1 Mg, 49Ca, 128 1, MCu, 42k et 198Au. Souvent, comme dans le cas de l'or, il s'agit de traces très faibles. En collaboration avec le Département de biologie animale (A. Bouillon et G.Mathot) nous élaborons une méthode de dosage de calcium et de magné­ sium dans les term ites. Il serait relativement facile de doser le sodium, tandis que le dosage du potassium est beaucoup moins précis. La photo- métrie de flamme donne de meilleurs résultats. Par contre le dosage du calcium et du magnésium par activation présente un intérêt; la période est assez courte pour obtenir une réponse relativement rapide. On étudie actuel­ lement l'élaboration d'une méthode de routine. En même temps on a pu mettre en évidence des différences très marquées entre les membres de la population d'une term itière. Ainsi les ouvriers présentent une forte réten­ tion d'éléments empruntés au sol tandis que les larves donnent des spectres plus simples. Avec le Département de pédologie (G. Van Compernolle) nous étudions la mise au point du dosage de certains éléments dans des extraits du sol. Le département de pédologie dispose d'un fluorim ètre à rayons X. Avec cet appareil il est possible de faire des déterminations qualitatives avec ANALYSE PAR ACTIVATION ET DÉTERMINATION DES ISOTOPES 49 facilité-et exactitude; par contre la détermination quantitative est beaucoup plus difficile pour des échantillons de composition inconnue ou variable, la hauteur d'un pic étant influencée fortement par les autres éléments présents. L'analyse par activation présenterait l'avantage suivant: la hauteur nétte d'un pic ne dépend pas des autres radioisotopes présents bien que la précision obtenue soit diminuée. Les prem iers essais ont montré la possi­ bilité de déterminer certains éléments intéressants, notamment 64Cu et 1281, à côté d'autres isotopes intéressants de longue période. Avec la section de spectrographie (J. Charette) du Département de phy­ sique nous avons analysé des diamants. Ces diamants sont d'abord analysés par spectrographie infrarouge et on trouve certaines bandes d'absorption dont l'origine est inconnue. L'analyse par activation permet de déceler et de doser un certain nombre d'éléments dans ces diamants. On peut alors chercher une corrélation entre leurs concentrations respectives et l'inten­ sité des bandes d'absorption. Si une telle corrélation était trouvée et con­ firm ée par la suite^on aurait la possibilité d’interpréter les bandes considérées. Jusqu’ici nos analyses prolongées sur plusieurs diamants ont montré, en prem ier lieula présence des isotopes 28Al, 56Mn et 24Na, sans qu'on trouve une corrélation avec le spectre infrarouge. Occasionnellement on trouve des traces d'or et de cuivre. L'analyse des mêmes diamants se poursuit actuellement avec l'attention portée sur les isotopes de longue période. L'analyse des diamants présente une difficulté assez spéciale, due à leur prix élevé. Les diamants sont généralement mis à notre disposition pair les producteurs; certains échantillons ont une grande valeur. L'analyse par activation est considérée en général comme une méthode non-destruc­ tive. Dans le cas du diamant elle doit être considérée comme destructive: l'irradiation crée très rapidement des centres de couleur; la couleur ver­ dâtre diminue fortement la valeur de l'objet. Notons qu'après une irradia­ tion prolongée les diamants deviennent complètement noirs. On doit donc lim iter l'analyse à des échantillons de moindre valeur, parfois très impurs. La coloration par l'irradiation présente un intérêt pour la spectrographie et les échantillons irradiés peuvent donc encore être utiles. П y a aussi une autre difficulté qui est liée à la nature du problème. Д s'agirait en effet de trouver des impuretés dispersées de façon homogène et non en petits amas. L'analyse par activation ne permet pas de distinguer entre les deux types de distribution. L'analyse a d'ailleurs montré que les diamants qui avaient une texture irrégulière et qui probablement renfer­ maient des inclusions montraient aussi les concentrations d'impuretés les plus fortes.

5. ANALYSE PAR ACTIVATION ET AUTORADIOGRAPHIE

L'autoradiographie permet de déterminer la dispersion d'un isotope radioactif, même à l'échelle microscopique. Le problème est relativement simple dans le cas où un isotope radioactif a été incorporé dans l'échantillon. L'application de la méthode à des objets activés dans un ilux de neutrons cause plus de difficultés. En général on aura un mélange de plusieurs iso­ topes dont les énergies des rayons bêta sont différentes ainsi que les pé­ riodes. П est donc plus difficile de prouver qu'un point d'accumulation est 50 R. LOOS

celui d'un isotope bien déterminé. On peut interposer des feuilles filtrantes en macro- autor adiograpiue ou faire des expositions successives pour dif­ férencier les isotopes de périodes suffisamment différentes. Dans le cas où un isotope est fortement activé par rapport aux autres on peut aussi faire des déterminations valables en tenant compte du fait que d'autres isotopes pourraient être fortement concentrés en certains points. Au Département d'anatomie (J. Vincent) on a étudié la distribution du sodium dans l'os compact par autoradiographie de sections activées aux neutrons [3] . On attendait quelques heures avant de procéder à l'autoradio- graphie, pour permettre la désintégration des isotopes de chlore, etc. Après ce laps de temps le spectre des rayons gamma émis était identique à celui du sodium-24.

RÉFÉRENCES

[1] LOOS, R., Production et utilisation des isotopes sodium-24, potassium-42, cuivre-64 et molybdSne-99, These proceedings. [2] ROBLS, J. F ., Distribution du flux de neutrons dans l’ouverture centrale du réacteur TRIGA MK1 à Lépold- ville. Rapport du Centre TRICO 62/02, Léopoldville, (juillet 1962) 1-12. [33 VINCENT, J ., Distribution of Sodium in Compact Bone, as revealed by Autoradiography of Neutron- Activated Sections, Nature, 184 (1959) 1332.

DISCUSSION

V. P. GUINN: I should like to ask a question about the analysis of the diamonds. Would it perhaps.be possible to bleach out the colour centres by heating at moderate temperatures? I know that it is quite easy to do this — at a temperature of 200°C or so — in the case of glass. For example, at the Shell Development Company laboratories in California a closed-circuit tele­ vision camera is installed in the accelerator target room, and, because of radiation damage, the glass lens gradually darkens up. We generally place the lens in a drying oven overnight at about 200°C and the resultant bleach­ ing is sufficient to enable it to be re-used. With the diamonds, I am sure that 200°C would cause no harm but on the. other hand it might be too low a temperature. Perhaps at higher temperatures the colour could be bleached out without the diamond being adversely affected, R. LOOS: Of course, at higher temperatures the diamond would be liable to be converted to graphite. V. P. GUINN: That would take very high tem peratures indeed. C. TAYLOR: What happens, I think, if heat is applied, is that the green colour disappears but that the diamonds then take on a yellow colour which cannot be removed by further heating. N. GETOFF: Have you tried treating neutron-irradiated diamonds with ultraviolet or Co60 gamma rays? I believe that that is one way of re­ storing the original colour of neutron-irradiated solid compounds. R. LOOS: No, but that is something we may try out. H. KEPPEL: Did you make any attempt to determine trace elements such as molybdenum, vanadium and zinc in the presence of the standard elements found in soil? I am thinking of the connection between these ele­ ments and soil fertility. ANALYSE PAR ACTIVATION ET DETERMINATION DES ISOTOPES 51

R. LOOS: So far we have not made any attempt to determine the trace elements as such. Our investigations in connection with soils were carried out with the specific aim of comparing the activation-analysis data with results obtained by X-ray fluorescence spectrometry. V. P. GUINN: I think it might be of interest if I mentioned some work we have been doing on the identification of small soil samples for the pur­ pose of criminal investigation. The primary aim in this work was to detect trace-level constituents in soil samples so as to enable one sample to be identified with another. On one occasion —it was an actual murder case — we compared two tiny particles of soil, one taken from the vicinity of the suspect's house and the other from the murder weapon, and we were able to match trace levels of four elements (Sc, Co, Mn, Cr) very closely. These investigations were done instrumentally in the TRIGA reactor as non-destructive tests because of the need to produce the samples as evidence in court. E. SOMER (Chairman): Has this information been published? V. P. GUINN: No. These investigations are mentioned in the progress report of our Division of Isotopes, which was issued — but not publicly — about a month ago. The report also quotes the figures obtained in the case I have just referred to, although of course there is no explicit reference to the case itself because of the trial. E. SOMER: I think that it is important to publish data on this subject wherever possible. The more information is made public, the sooner acti­ vation analysis will stand a chance of becoming accepted as a means of supplying evidence in court. V. P. GUINN: That is a very important point. At the moment we are proceeding very cautiously and are attempting to build up a body of scientific evidence of our own on the subject. We feel confident that in time it will be possible to use information obtained with these techniques as legal evidence in co u rt.

DOSAGES D’ÉLÉMENTS PAR LEURS RADIOISOTOPES DE PÉRIODES COURTES DANS L ’ANALYSE DE L ’ALUMINIUM, DU FER ET DU ZIRCONIUM DE TRÈS HAUTES PURETÉS

PH. ALBERT, M. DEYRIS, N. DESCHAMPS ET L. FOURNET CENTRE D’ÉTUDES DE CHIMIE MÉTALLURGIQUE, VITRY, FRANCE

Abstract — Résumé — Аннотация — Resumen

USE OF SHORT-LIVED RADIOISOTOPES TO DETERMINE IMPURITIES IN ALUMINIUM, IRON AND ZIR­ CONIUM OF VERY HIGH PURITY. In the laboratory of Professor Chaudron at Vitry the authors are studying systematic radioactivation analysis of metals of very high purity, including aluminium, iron, zirconium and copper purified by the "zone melting” method and also industrial metals of high purity refined by double electrolysis (aluminium), electrolysis (copper), thermal dissociation of iodide (zirconium) and purification of the carbonyl compound (iron). For the purpose of these analyses the samples are irradiated with neutrons, deutons, protons andy-photons at 30 MeV in order to determine the amounts of oxygen, carbon and nitrogen present. The number of elements that can be analysed systematically after neutron irradiation is about 50, the half-lives of some elements being too short; this is true, for example, of V® (3.7 m in), С 1Э8 (37. 5 m in), 112в (25 min) , A128 (2.4 m in), Mg27 (9. 5 min) and Ti5* (5 .8 min) . There are other elements which cannot be separated and assayed with enough precision to permit system­ atic analysis; this is particularly true of Si2* with its half-life of 2.8 h, small capture cross-section and emission of fl’ radiation only. Nevertheless, it is necessary to know in what concentrations these elements are present in the metals because, in some cases, they constitute basic impurities of the industrial material to be purified; in other cases, a higher concentration may sometimes be expected in the purified metal than in the original. In this connection may be mentioned the content of vanadium in aluminium: the content in the "melted zone" metal is often higher than in the industrial metal, representing as much as 30% of all the impurities assayed. The paper describes the methods of determining the various impurities which the authors have studied. Particular attention is given to describing the assays of silicon, chlorine, bromine and iodine, done by the classical method of radiochemical separation after neutron irradiation. The silicon is distilled in SiFeHj. Chlorine, bromine and iodine are assayed on a single sample. The mixture of halogenides is treated with nitric acid to remove the iodine and bromine, and these two elements are carried across several absorbers by forced air-flow; the bromine is fixed in a solution of sodium sulphite and the iodine is absorbed in a soda solution. The chlorine, which is not removed by the nitric acid, is precipitated as silver chloride. In this way the con­ centration of chlorine in electrolytic iron and of iodine in "Van Arkel" zirconium was determined. The methods studied for assaying aluminium, vanadium, magnesium and titanium in aluminium, iron and zirconium are also described. In these assays, the traces of the element to be determined are separated, before irradiation, by a "non-isotopic entraining agent", and sometimes a quick radiochemical purification is carried out after irra­ diation. Vanadium, aluminium and magnesium can be assayed on a single sample in the case of iron and zirconium analyses. Separation had to be effected by means of a "non-isotopic entraining agent” before irradiation, either because chemical separation of impurities from iron and zirconium (for example) is tedious and difficult, or because the metal to be analysed has a very high activity during the first few minutes after irradiation (as in the case of aluminium) • It should be noted that it was possible, using gamma-spectrometry, to determine without separation vanadium and aluminium concentrations of 0.6 x 10“*and 2 x 10 ^respectively in pure iron or zirconium irradiated for 30 s in a flux ot 5 x 10** n/cm* s. Separation before irradiation is necessary if the greatest possible sensitivity is to be obtained, and also when metals of lesser purity are being dealt with.

53 54 Ph. ALBERT et al.

The paper shows the important contribution which assays with short-lived isotopes (2.4 min - 4 .6 h) are making to the authors' knowledge of the purity of their samples.

DOSAGES D'ÉLÉMENTS PAR LEURS RADIOISOTOPES DE PÉRIODES COURTES DANS L'ANALYSE DE V ALUMINIUM, DU FER ET DU ZIRCONIUM DE TRÈS HAUTES PURETÉS. Les auteurs étudient au laboratoire du Professeur Chaudron, â Vitry, l'analyse systématique par «radioactivation» des métaux de très haute pureté comme l'aluminium, le fer, le zirconium et le cuivre purifiés par la méthode de la «zone fondue», ainsi que des métaux industriels de haute pureté raffinés par double électrolyse pour l'aluminium, par electrolyse pour le cuivre, par le procédé de dissociation thermique de l'iodure pour le zirconium et par purification du composé carbonyle pour le fer. Pour ces analyses, les auteurs ont utilisé l'irradiation dans les neutrons, les deutons, les protons et les photons y de 30 MeV pour obtenir le dosage de l'oxygène, du carbone et de l'azote. L'analyse systématique après irradiation dans les neutrons est lim itée à une cinquantaine d'éléments. En effet, certains isotopes ont des périodes trop courtes comme le vanadium-52 (3,7 m in), le chlore-38 (37,5 min), l'iode-128 (25 min), l'aluminium-28 (2,4 min), le magnésium-27 (9,5 min) et le titane-51 (5 ,8 m in). Pour d'autres éléments il est impossible d'envisager leur séparation et leur dosage, avec une sensibilité suffisante, dans le cadre de l'analyse systématique; c'est notamment le cas du silicium-28, de période 2,8 h (faible section efficace de capture et émission d'un rayonnement ôpur). Cependant la connaissance de la concentration de ces éléments dans les métaux est nécessaire car, dans certains cas, ils constituent des impuretés de base du matériau industriel soumis au traitement de purification; dans d'autres cas, on peut parfois s'attendre, pour certains d'entre eux, à trouver une teneur plus élevée dans le métal purifié que dans le métal d'origine. Les auteurs signalent, par exemple, l'importance du dosage du vanadium dans l'aluminium. La teneur du métal de «zone fondue»est parfois plus élevée que celle du métal industriel et peut représenter jusqu'à 30% de la concentration totale en impuretés dosées. Les auteurs décrivent les méthodes étudiées pour ces dosages dans les différents cas qu'ils ont rencontrés. Cet exposé concerne notamment la description du dosage du silicium, du chlore, du brome' et de l'iode, effectué selon la méthode classique pat séparation radiochimique après l'irradiation dans les neutrons. Le silicium est distillé en SiF$H2. Le chlore, le brome et l'iode sont dosés sur une seule prise d'essai; on déplace l'iode et le brome en traitant le mélange des halogénures par l'acide nitrique et les deux éléments sontentraïhés par une circulation forcée d'air à travers plusieurs absorbeurs; le brome est fixé dans une solution de sulfite de sodium et l'iode est absorbé dans une solution de soude. Le chlore qui n'est pas déplacé de la solution nitrique est précipité en chlorure d* argent. Les auteurs ont ainsi dosé le chlore dans le fer électrolytique et l'iode dans le zirconium «Van Arkel». D'autre part, les auteurs décrivent aussi les méthodes qu'ils ont étudiées pour doser l'aluminium, le vanadium, le magnésium et le titane dans l'aluminium, le fer et le zirconium. Dans ces dosages, les traces de l'élément recherché sont séparées, avant l'irradiation, sur un «entraîneur non isotopique»; dans certains cas une purification radiochimique rapide est effectuée après l’irradiation. Il est possible de doser sur une seule prise d'essai le vanadium, l’aluminium et le magnésium (cas de l'analyse du fer et du zirconium). Les auteurs ont été contraints d'effectuer une séparation sur «entraîneur non isotopique» avant l'irra­ diation, soit à cause de la durée et de la difficulté des séparations chimiques des impuretés du fer et du zirco­ nium, par exemple, soit à cause de la très forte radioactivité du métal analysé pendant les minutes qui suivent l'irradiation (cas de l’aluminium). Il est à remarquer qu'ils ont pu, en spectrométrie y, doser sans séparation des concentrations de 0, 6 • 10“6 de vanadium et de 2* 10" 6 d'aluminium dans le ter ou le zirconium purs irradiés 30 s dans un flux de 5 • 1012 n /c m 2- s. Les séparations préalables à l'irradiation sont nécessaires pour obtenir de plus grandes sensibilités et aussi dans le cas des métaux de moins grande pureté. Dans leur mémoire, les auteurs montrent la contribution importante que les dosages par les radioisotopes de courtes périodes (2,4 min à 4, 6 h) apportent à la connaissance du degré de pureté des échantillons.

ДОЗИРОВКА ЭЛЕМЕНТОВ С ПОМОЩЬЮ КОРОТКОЖИВУЩИХ РАДИОИЗОТОПОВ ПРИ АНАЛИЗЕ АЛХМИНИЯ, ЖЕЛЕЗА И ЦИРКОНИЯ ОЧЕНЬ ВЫСОКОЙ ЧИСТОТЫ. В лаборатории профессора Шодрока и Витри мы ознакомились с систематическим анализом путем "радиоактивации" таких металлов очень высокой чистоты, как Алю­ миний, железо, цирконий и медь, очищенных при помощи метода ''зонной плавки", а также металлов DOSAGES D'ÉLÉMENTS PAR LEURS RADIOISOTOPES 55

промышленного назначения высокой чистоты. К последним относятся очищенный двойным электролизом алюминий, очищенная электролизом медь, полученный методом термической диссоциации иодида цирконий и выделенное в чистом виде из карбонилового соединения железо. Для проведения этих анализов мы использовали облучение нейтронами, дейтронами, протонами и у~Фо- тонами энергией 30 Мэв в целях дозировки кислорода, углерода и азота. Систематический анализ после облучения нейтронами ограничен пятьюдесятью элементами. Действи­ тельно, некоторые изотопы являются слишком короткоживущими, например ванадий-52 (3,7 мин), хлорке (37,5 мин), Йод-128 (25 мин), алюминиЙ-28 (2,4 мин), магний-27 (9,5 мин), титан-51 (5,8 мин). В отношении других элементов не представляется возможным с достаточной чувствительностью и в рамках систематического анализа предусмотреть их выделение и дозиметрию. Именно так обстоит дело в случае с кремнем-28 при его периоде в 2,8 часа (слабое эффективное сечение захвата и только @-иэлучение). Однако знание концентрации этих элементов в наших металлах необходимо, так как в определен­ ных случаях они представляют собой основные примеси в металле промышленного назначения, который направлен для очищения. В иных случаях можно столкнуться с более высоким содержанием примесей отдельных из этих элементов в очищенном металле, нежели в исходном. Мы отметим, например, значе­ ние дозировки ванадия в алюминии. Содержание металла в области "расплавленной зоны" бывает порой более высоким, чем в металле промышленного назначения, и может достигать до 30% обшей концентра­ ции дозированных примесей. Мы опишем методы, исследованные для проведения количественных анализов в различных случаях, с которыми мы столкнулись. Наше изложение коснется в основном описания анализа кремния, хлора, брома и йода, проведенного по обычному методу радиохимического выделения после облучения ней­ тронами. Кремний был подвергнут дистилляции в Si FeH2. Хлор, бром и йод были дозированы на одну пробу для анализа. При обработке смеси галоидных солей азотной кислотой йод и бром замещаются, и оба элемента пропускаются с помощью сильной воздушной струи через несколько поглотителей: бром фиксируется в растворе сульфита натрия, а йод поглащается в растворе натрия. Хлор, который не вытесняется из азотнокислого раствора, выпадает в составе хлористого серебра. Таким путем нами была проведена дозиметрия хлора в электролитном железе и йода - в цирконии "Van Arkel". С другой стороны, мы опишем также методы, которые мы изучили для проведения количественных анализов на присутствие алюминия, ванадия, магния и титана в алюминии, железе и цирконии. Ь этих анализах следы изыскиваемого элемента выделились до облучения "на неизотопном носи­ теле"; в некоторых случаях быстрое радиохимическое очищение производилось после облучения. Пред­ ставляется возможным дозировать ванадий, алюминий и магний на одну пробу для анализа (случай с анализом железа и циркония). Мы были вынуждены провести отделение на 'неизвестном носителе" до облучения либо по причине длительности и трудности отделения химическим путем примесей железа и циркония (например), либо ввиду очень сильной радиоактивности исследуемого металла в течение нескольких минут после облу­ чения (в случае с алюминием). Следует отметить, что нам удалось при ^-спектрометрии провести дозирование без выделения концентраций в 0,6*10“® ванадия и в 2*10~е алюминия в чистом железе иди чистом цирконии, об­ лученных в течение 30 сек в потоке 5*101 а н/сма,сек. Предварительные выделения при облучении необходимы для получения самых больших чувствитель­ ностей, а также в случае с металлами значительно меньшей чистоты. В нашем докладе мы раскроем важный вклад, который вносится количественным анализом с по­ мощью короткоживущих радиоизотопов (от 2,4 мин до 4,6 час) в определение степени чистоты наших образцов.

DETERMINACIÓN CUANTITATIVA DE RADIOISÓTOPOS DE PERIODO CORTO EN LOS ANALISIS DE ALUMINIO, HIERRO Y CIRCONIO DE ALTA PUREZA. En el laboratorio del Profesor Chaudron, en Vitry, los autores analizan sistemáticamente por "radiactivación” metales de grado de pureza muy elevado como el aluminio, hierro, circonio y cobre purificados por el método de la "zona fundida", así como metales industriales muy puros refinados por electrólisis doble en el caso del aluminio, electrólisis simple en el del cobre, disociación térmica del yoduro en el del circonio, y purificación del compuesto carbonilo en el del hierro. Han realizado estos análisis irradiando las muestras con neutrones, deuterones, protones y fotones y de 30 MeV a fin de determinar cuantitativamente el oxígeno, el carbono y el nitrógeno. 56 Ph. ALBERT et al.

El análisis sistemático después de la irradiación neutrónica se limita a unos 50 elementos. En efecto, algunos isótopos tienen períodos demasiado breves, como el vanadio-52 (3,7 m in), el cloro-38 (37,5 m in), el yodo-128 (25 m in), el aluminio-28 (2,4 m in), el magnesio-27 (9,5 min) y el titanio-51 (5,8 min). Otros elementos no se pueden separar y valorar con sensibilidad suficiente para un análisis sistemático; éste es principalmente el caso del silicio-28 de 2,8 h de período (sección eficaz de captura muy baja y emisión de radiaciones 0” puras) * Sin embargo, es preciso conocer la concentración de estos elementos en los metales citados porque, en ciertos casos, constituyen impurezas de base de los materiales industriales sometidos al tratamiento de purificación; en otros casos suele encontrarse un contenido más elevado en el metal purificado que en el metal de origen. Com ejemplo, los autores señalan la importancia de la determinación cuantitativa del vanadio en el aluminio. El contenido del metal de "zona fundida" es a veces más elevado que el del metal industrial y puede representar hasta el 307o de la concentración total de las impurezas que se determinan. Los autores describen los métodos estudiados para estos análisis en los diversos casos con que se han encontrado. La memoria se refiere principalmente a la determinación cuantitativa del silicio, del cloro, del bromo y del yodo, efectuada por el método clásico de separación radioquímica después de la irradiación neutrónica. El silicio se destila en forma de SiFçH2. El cloro, el bromo y el yodo se determinan en una misma muestra; el yodo y el bromo se desplazan tratando la mezcla de los halogenuros con ácido nítrico y arrastrando ambos elementos mediante aire en circulación forzada a través de varios absorbedores; el bromo se fija con una solución de sulfito de sodio, en tanto que el yodo se absorbe en una solución de sosa. El cloro, que no queda desplazado de la solución nítrica, se precipita en forma de cloruro de plata. De esta manera los autores han valorado el cloro en el hierro electrolítico y el yodo en el circonio "Van Arkel”. Describen también los métodos estudiados para determinar el aluminio, vanadio, magnesio y titanio en aluminio, hierro y circonio. En estas determinaciones, se separan los vestigios del elemento que se busca; antes de la irradiación con un portador no isotópico, y en ciertos casos, después de la irradiación se efectúa una purificación radio­ química rápida. El vanadio, aluminio y magnesio se pueden analizar en una misma muestra (caso de los análisis del hierro y del circonio). Por diversos motivos los autores se han visto obligados a efectuar una sepa­ ración con portador no isotópico antes de la irradiación, porque la separación química de las impurezas del hierro y del circonio (por ejemplo) es larga y difícil, o porque el metal que se analiza presenta una radiacti­ vidad muy elevada en los minutos que siguen a la irradiación (caso del aluminio). Los autores hacen notar que sin separación previa han logrado determinar por espectrometría y concentra­ ciones de 0,6«10“6de vanadio y 2« 10“6 de aluminio en el hierro o el circonio puros irradiados durante 30 s con un flujo de 5 • 101* n/cm^s. Las separaciones antes de la irradiación son necesarias para alcanzar sensibilidades mayores y también en el caso de los metales de menor pureza. En la memoria se pone de relieve la importante contribución que aportan las determinaciones cuanti­ tativas con ayuda de radioisótopos de período corto (2,4 min a 4,6 h) al conocimiento del grado de pureza de las muestras.

INTRODUCTION

Nous étudions au Laboratoire du Professeur Chaudron à Vitry, l'analyse systématique après radioactivation par les neutrons thermiques des métaux de très haute pureté comme l’aluminium, le fer, le zirconium et le cuivre purifiés par la méthode de la «zone fondue». L’analyse systématique par radioactivation est employée aussi pour sélectionner les métaux industriels de haute pureté soumis à la purification par «zone fondue»; ce sont l’alu­ minium raffiné par double électrolyse, le zirconium préparé par la méthode de dissociation thermique de l’iodure (Van Arkel), le fer obtenu par décom­ position du composé carbonyle et le cuivre électrolytique. Les dosages de l’oxygène, du carbone, de l’azote et du fluor sont effectués par irradiations par des protons, des deutons et des photons y de 30 MeV [1]. Mais un certain nombre d’éléments ne peuvent être dosés au cours de l’analyse systématique par radioactivation dans les neutrons. Les radio- DOSAGES D'ÉLÉMENTS PAR LEURS RADIOISOTOPES 57 isotopes d’éléments tels que le vanadium-52 (3,7 min),le chlore-38 (37,5 min), l'iode-128 (25 min), l1 aluminium-28 (2,4 min), le magnésium-27 (9,5 min) et le titane-51 (5,8 min), ont des périodes trop courtes. Pour d’autres éléments, il est impossible d’envisager leur séparation et leur dosage, avec une sensibilité suffisante, au cours de l’analyse systé­ matique. C’est le cas notamment du silicium-31 (2,64 h) qui a une faible section efficace de capture et émet un rayonnement |3~ accompagné seule­ ment de 0,07% de photons y. Nous classons également dans ce groupe le soufre et le phosphore dont les radioisotopes ont de longues périodes (87 j e t 15 j). Cependant, la connaissance de la concentration de ces éléments dans nos métaux est nécessaire car ils constituent des impuretés de base des métaux industriels soumis au traitement de purification. Dans certains cas, on peut même s’attendre à trouver une teneur plus élevée dans le métal puri­ fié que dans le métal industriel; ceci est, par exemple, le cas du vanadium dans l’aluminium [7]. Nous distinguerons, d’une part, les dosages par radioactivation sans séparation chimique ou avec traitement de séparation radiochimique après l’irradiation et, d’autre part, les dosages par radioactivation d’un élément séparé avant l’irradiation sur un «entraîneur non isotopique».

I. DOSAGES PAR RADIOACTIVATION AVANT LA SEPARATION RADIOCHIMIQUE ET DOSAGES SANS SÉPARATION CHIMIQUE

MEINKE a particulièrement étudié d’une façon systématique les possibi­ lités de l’analyse par radioactivation produisant des radioisotopes de pé­ riodes courtes [2]. Nous donnerons ici la description des méthodes que nous avons utilisées pour doser le chlore, le brome et l’iode dans l’aluminium, dans le fer et le zirconium ainsi que l’aluminium et le vanadium dans le fer et le zirconium. Nous décrirons également la méthode que nous avons mise au point pour le dosage très difficile du silicium dans l’aluminium.

1. Dosages du chlore, du brome et de l’iode

La transposition de la méthode classique de séparation convient parfai­ tement à l’analyse radiochimique [3]. Ainsi, dans le cas du zirconium, le métal est dissous dans l’acide fluorhydrique en présence de 10 à 25 mg des entraîneurs chlore, brome, iode. On chasse les halogènes par l’action de 15 cm3 d’acide nitrique en chauffant pour distiller; une circulation d’air à travers l’appareil entraîne les vapeurs de brome et d’iode et on capte suc­ cessivement, le chlore (entraîné partiellement) dans l’acide nitrique,le brome dans le sulfite de sodium (100 g/l) et l’iode dans la soude 2N. On précipite l’iodure et le bromure d’argent dans les solutions de sulfite de sodium et de soude. Le chlore se trouve, en partie, dans la solution d’attaque et en partie dans le prem ier flacon absorbeur à l’acide nitrique; on le précipite sous forme de chlorure d’argent dans les deux solutions. Cette méthode de séparation permet le dosage simultané de très petites quantités de chlore de brome et d’iode. La sensibilité, dans nos conditions d’irradiation (flux de 5 • 1012 n/cm2- s pendant 30 min) estde l’ordre de 0,01 58 Ph. ALBERT et al.

à 0,2 ppm (pour 1 g de zirconium), la mesure de la radioactivité étant effec­ tuée environ une heure après l’irradiation. A cette sensibilité on ne trouve pas de chlore, brome, iode dans l’aluminium. Le fer électrolytique (électro- lyse en solution chlorhydrique de chlorure de fer II) contient de 300 à 900 ppm de chlore. L'élim ination de cet élément ne peut être obtenue par simple recuit dans l’hydrogène même à haute tem pérature (1300°C) mais une fusion de quelques^minutes abaisse la teneur en chlore à moins de 1 ppm. Le fer de «zone fondue» contient moins de 0,01 ppm de chlore. Dans le zirconium «Kroll» (réduction du chlorure de zirconium par le magnésium) refondu au four à arc on ne trouve pas d’halogène à cette sensibilité. Mais par contre on rem arquera que nous avons dosé de 0,5 à 1 ppm d’iode dans les épingles de zirconium «Van Arkel» (dissociation de l’iodure de zirconium) [4].

2. Dosages de l’aluminium et du vanadium sans séparation chimique

a) L’aluminium-28 émet un rayonnement y de 1,78 MeV. Ceci permet la mesure de cet élément en présence d’autres radioisotopes dont l’énergie des photons y est inférieure comme c’est le cas pour le fer pur, le zir­ conium et son impureté principale, le hafnium dont la section efficace de capture des neutrons est importante. Par cette méthode directe et très rapide on a pu doser des teneurs d’aluminium dans le zirconium allant de 0,6 à 39 ppm (irradiations de 10 à 20 s); voir les tableaux. L’emploi d’un spectromètre y à sélecteur à mé­ moires multiples permet de soustraire la radioactivité des isotopes de longues périodes après la décroissance de celle de l’aluminium-28 (2,4 min) ce qui augmente la précision et la sensibilité du dosage. Dans divers échantillons de fer électrolytique et de fer de «zone fondue» nous avons dosé des concentrations d’aluminium comprises entre 17 et 65 ppm.

b) Le vanadium-52 émet un rayonnement y de 1,43 MeV et son dosage direct est également possible dans le zirconium et dans le fer purs. La sen­ sibilité de détection du vanadium est environ 20 fois plus grande que pour l ’a lu m in iu m (oy= 20 ctai). La différence d’énergie des rayons y de 52V et de 28A1 permet leur dosage simultané sans séparation chimique des deux isotopes et cela, dans un grand domaine de concentrations relatives différentes. Les figures 1 et 2 montrent l’importance relative des pics photoélectriques de 52V et de 28A1 pour des concentrations relatives en aluminium et en vanadium Cai/Cv com prises entre 60 et 16. On rem arquera qu’il est difficile d’envisager, sans sépa­ ration chimique des deux isotopes, le dosage du vanadium en présence d’aluminium si le rapport Cai/Cv est supérieur à 60.

c) Limite de sensibilité des dosages non destructifs. La première cause qui limite la sensibilité des dosages est la présence d’impuretés créant une radioactivité trop importante. Ainsi le chlore-38 (T¿ = 37,5 min) dans le fer électrolytique gêne le dosage de teneurs en aluminium de l’ordre de quelques ppm. Enfin l’analyse non destructive de certains éléments à grande section efficace de capture, comme le cuivre, est pratiquement impossible. Cet OAE DÉÉEt PR ER RADIOISOTOPES LEURS PAR D'ÉLÉMENtS DOSAGES

OJ

L H7Г

Figure 1 Figure 2 Spectre du rayonnement y émis par un précipité de 36 Mg d'aluminium-28 Spectre du rayonnement y émis par un précipité de 16 jjg d’aluminium-28 et 0,6 (jg de vanadium-52, 2 min après l'irradiation. et 1 jig de vanadium-52, 1 min après l'irradiation. Rapport des concentrations CA1/C y = 60. сл со 60 Ph. ALBERT et al.

élément a, en effet, un isotope dont la période est 5 min, le cuivre- 66, qui émet des photons y assez énergiques (1,04 MeV). Par contre, l’avantage principal de ces méthodes non destructives est la rapidité de l’analyse. En outre, on évite toute pollution par les réactifs ou le m atériel employé dans les séparations chimiques (voir le tableau I). Dans les cas favorables tels que l’analyse du fer pur et du zirconium pur, les sensibilités de détection sont respectivement de l’ordre de 0,05 ppm (soit 5 • 10‘8) d’aluminium et de 0,01 ppm (soit 10-8) de vanadium.

TABLEAU I

SÉPARATION CHIMIQUE DU VANADIUM ET DE L’ALUMINIUM, ET PURIFICATION DU VANADIUM

A. Séparation chimique du vanadium et de l’aluminium avant l’irradiation

1. Dissolution Al +HC1 6N (+eHg).

2. Cristallisation de A1C13, 6 H20.

3. Concentration du filtrat.

4. Seconde cristallisation de A1C13,6 H20 dans un faible volume de solution.

5. Précipitation de Fe(OH)3«entraîneur du vanadium» par coprécipitation.

6. Dissolution et reprécipitation en milieu NOjH - NOjNH, du (Fe(OH)3 + tV) pour éliminer le chlore.

7. Irradiation de Fe(OH)3 +eV.

B. Purification radiochimique du vanadium-52 après radioactivation

1. Dissolution et addition des entraîneurs vanadium et aluminium et du traceur vanadlum-48.

2. Elimination de Al par la 8-hydroxyquinoléine.

3. Extraction du cupferronate de vanadium dans le chloroforme.

4. Analyse du spectre y enregistré au spectrographe à 100 canaux.

3. Dosage du silicium dans l’aluminium

Le seul isotope du silicium produit par irradiation dans un flux de neu­ trons thermiques, le silicium-31, a une période courte (T¿ = 2,64 h). Il émet un rayonnement |3- ainsi qu’un rayonnement y (seulement 0,07%) dont l’énergie est de 1,26 MeV. La section efficace de capture des neutrons est très petite : a = 0,0033 b (soit 0,11 X 0,03 b). Aussi le dosage de très petites quantités de silicium est-il difficile et il exige la séparation chimique com­ plète des autres radioisotopes créés par l’irradiation de l’échantillon. DOSAGES D’ ÉLÉMENTS PAR LEURS RADIOISOTOPES 61

Nous avions déjà étudié ce dosage en 1952, mais la sensibilité était lim itée à environ 3 ppm en raison de la faible valeur des flux de neutrons utilisés et de l’imperfection du compteur de rayonnement |3" employé [5]. La méthode de dosage que nous proposons est, encore aujourd’hui, fon­ dée sur la séparation du silicium par distillation de SÍF6 H2. L’échantillon d’aluminium (0,4 à 1 g) est irradié pendant 30 min dans un canal pneumatique de la pile EL3 à Saclay (flux : 5 • 1012 n/cm 2 • s) ou pen­ dant une nuit dans la pile EL2 (16 h dans un flux de 2,5 • 1012 n/cm2-s). Après un décapage soigné, l’échantillon laminé est dissous dans un mélange des acides chlorhydrique, nitrique et sulfurique (10 cm3 de chaque acide) en présence de silicium entraîneur (6 mg de silicium). Après insolubilisation aux fumées blanches on dilue la solution sulfurique et on ajoute 1 cm3 de gélatine à 1% pour faciliter la filtration de la silice [3]. Après une deuxième précipitation de silice entraîneur on a isolé 98% du silicium (lre précipita­ tion 92%, 2e précipitation 6%, 3e précipitation 2%). Cette silice précipitée est impure et retient par adsorption ou co­ précipitation des radioisotopes de périodes longues et même d’après cer­ tains essais, du manganèse-56 dont la période est la même que celle du silicium (2,6 h). Nous avons fait quelques essais pour identifier les radioisotopes qui sont entraînés par la précipitation de la silice lors de l’analyse de nos échan­ tillons d’aluminium de haute pureté. Les figures 3 et 4 montrent d’une part les courbes de décroissance de la radioactivité des isotopes entraînés sur la silice insolubilisée et, d’autre part, les spectres de leur rayonnement 7 .

56 0 MeV

0 250 500 750 1000 MeV •SPECTRE DU RAYONNEMENT y EMIS

c E X a. E x 6 *x o 3h o

10 ' 20 40 60 80 100 (h) DÉCROISSANCE OU RAYONNEMENT EMIS

Figure 3

Spectre du rayonnement y et courbe de décroissance de la radioactivité du premier précipité de Si Oj. Analyse d'un aluminium raffiné industriel. .. 62 Ph. ALBERT et al.

Figure 4

Spectre du rayonnement y et courbe de décroissance de la radioactivité B” du second précipité de SiOa • Analyse d*un aluminium raffiné industriel (même échantillon que dans l’exemple de la figure 3).

On peut identifier aisément les périodes et les pics photoélectriques des radioisotopes de l‘antimoine-122 (Tj= 2,8 jetEy= 0,560MeV) et du cuivre-64 (T^ = 12,8 h et Ey = 0,510 MeV). Dans les exemples présentés on ne décela pas la présence du radioisotope du manganèse-56 (T$ = 2,6 h et Er = 0,840 MeV) mais la teneur de cet élément était très faible dans l’aluminium étudié. En décroissance fT on peut déceler, sur le premier précipité de silice, une période de 2,6 h qui peut être attribuée au 3isi ou à des traces de 56Mn. Il apparaît clairement, d’après les courbes de décroissance, qu’il est im­ possible de mettre en évidence une faible radioactivité de silicium-31 dans les précipités de silice. De plus, une très faible quantité de manganèse pourra masquer complètement la présence du silicium car l’activité spéci­ fique du manganèse est 4000 fois plus grande que celle du silicium (crMn = 13,3 b e t osi = 0,003*3 b). Il est donc nécessaire de purifier le précipité de silice pour isoler le 31Si radiochimiquement pur afin d'obtenir une grande sélectivité et une grande sensibilité du dosage du silicium. SHORT [ 6j purifie la silice par plusieurs cycles de redissolution- insolubilisation et il élimine par des précipitations séparées des radio- isotopes du manganèse et du tungstène entraînés par la première insolubi­ lisation de la silice. DOSAGES D’ ÉLÉMENTS PAR LEURS RADIOISOTOPES 63

Dans notre méthode, on purifie le silicium par distillation de SiFgH 2 et précipitation de SiFgBa en milieu acide chlorhydrique-alcool. La silice pré­ cipitée est placée dans un «réacteur» en cuivre, puis on introduit 2 cm3 d’acide fluorhydrique et 3 cm 3 d’eau et on chauffe. Le distillât de SiFgÜ2 e st recueilli dans une solution acide (50 cm3) de chlorure de baryum à 10%. On ajoute, après distillation complète de SiFgH^ 100 cm3 d’acide chlorhydrique 12N et 150 cm 3 d’alcool. SiF 6 Ba est insoluble mais F2Ba est soluble. Une Seconde précipitation de SiFgBa entraîneur est effectuée pour vérifier la qualité de la prem ière séparation. Le rendement total de la séparation chimique du silicium est en moyenne de l’ordre de 60%. La dispersion maximum des résultats des dosages est de ± 17%. Le poids des précipités de SiFgBa est de l’ordre de 120 mg (26 mg/cm2). La mesure de la radioactivité du silicium-31 est faite dans un ensemble de comptage à faible mouvement propre 0,77 cpm), dont les compteurs Geiger à circulation de gaz (hélium-isobutane) ont une «fenêtre» de 0,9 mg/cm2. La radioactivité est enregistrée automatiquement pendant la décroissance du silicium-31 (2,64 h). Cet enregistrement continu de la radioactivité permet une mesure très précise. Même quand le radiosilicium-31 est accom­ pagné d’une certaine radioactivité d’isotopes de périodes longues on peut déceler avec une grande sensibilité une très faible quantité de silicium. La courbe de la figure 5 montre la décroissance de la radioactivité d’un préci­ pité de SiFgBa contenant 4 microgrammes de silicium irradié (échantillon à 12 ppm ). La sensibilité du dosage du silicium pour une irradiation de 30 min à 5 • 1012 n/cm2> s est de l’ordre de 0,1 ppm (échantillon de 1 g) à 0,2 ppm (échantillon de 0,5 g). L’activité du silicium est de l’ordre de 50 à 100 cpm/ IJg e t le comptage /3 permet de mesurer avec précision 10 cpm comme le montre la courbe de la figure 5. En irradiant plus longtemps la sensibilité du dosage pourra atteindre 0,05 ppm. Les teneurs en silicium dosées dans nos échantillons d’aluminium raffi­ nés par double electrolyse se situent entre 3 et 7 ppm. Dans l’aluminium de «zone fondue» nous avons trouvé une teneur de silicium comprise entre 0,7 et 0,3 ppm.

II. DOSAGES PAR RADIOACTIVATION APRÈS SÉPARATION CHIMIQUE SUR ENTRAÎNEUR NON ISOTOPIQUE

Dans un grand nombre de cas, le dosage d’un élément par un radio- isotope de courte période a été réalisé en effectuant une séparation radio- chimique très rapide après l’irradiation [ 2]. Cependant, pour l’analyse du zirconium, la durée des séparations chi­ miques de la plupart des impuretés est trop longue pour perm ettre un do­ sage sensible par les isotopes de périodes courtes. Pour l’analyse du cuivre ou- de l’aluminium, la très grande radioactivité induite dans le métal irradié impose l’emploi de protections très importantes qui, en les compliquant, rendent les séparations radiochimiques bien trop longues et très coûteuses. C’est pourquoi nous effectuons alors, avant l’irradiation, la séparation de l’élément à doser sur «entraîneur non isotopique» de celui-ci. Pour les élé­ ments dont nous décrirons le dosage, cet entraîneur est le fer. Nous donne- 64 Ph. ALBERT et al.

TEMPS

Figure 5

Courbe de décroissance de la radioactivité du silicium-31 (T | = 2,64 h) d'un précipité de SiF6Ba. Echantillon d'aluminium industriel raffiné par double électrolyse (7 ppm ). 0,57 g étalon = 32 cpm /pg. rons ici la description des méthodes que nous avons utilisées pour doser l’aluminium et le vanadium dans le fer, le zirconium et le cuivre. Nous dé­ crirons également la méthode que nous avons mise au point pour le dosage très difficile du vanadium dans l’aluminium. Enfin nous indiquerons aussi les séparations chimiques que nous étudions pour doser le titane et le magné­ siu m .

1. Dosage du vanadium dans l’aluminium

Nous rappellerons, en prem ier lieu, que nous avons déjà décrit le dosage du vanadium dans l’aluminium 17]. Il nécessite, à la fois, une séparation préalable à l’irradiation des traces de vanadium sur un «entraîneur non iso­ topique» et une purification radiochimique du 52V après l’irradiation. Le tableau I résume l’ensemble des séparations chimiques effectuées pour isoler le vanadium. Après dissolution de l’échantillon d’aluminium, la plus grande partie de cet élément est éliminée par la cristallisation, à froid, de AICI3. 6 H 2O en solution chlorhydrique saturée. Le vanadium, en traces, est coprécipité sur un hydroxyde de fer entraîneur qui retient également l’aluminium restant en solution (de l’ordre du milligramme). Après l’irradiation de cet «hydroxyde de fer» la mesure directe de l’ac­ tivité du vanadium n’est pas possible car les quantités d’aluminium présentes sont bien trop grandes et nous avons déjà indiqué que le dosage de 52V n’est possible que pour Cai/Cv^ 60. Donc nous dissolvons l’hydroxyde de fer dans l’acide chlorhydrique en oxydant le vanadium à sa valence supérieure par l’eau oxygénée après avoir ajouté dans la solution des entraîneurs de vana­ dium et d’aluminium. Ce dernier est précipité par la 8 -hydroxyquinoléine DOSAGES D’ ÉLÉMENTS PAR LEURS RADIOISOTOPES 65 en milieu ammoniacal. Le pH de la solution est ajusté à environ 1,5-2 et le cupferronate de vanadium est extrait par le chloroforme. La phase extraite est analysée au spectromètre y et le dosage du 5 2 y se fait par la mesure de l'intensité du pic photoélectrique de 1,43 MeV. Le rendement de l'extraction du cupferronate de vanadium est assez bon généralement mais il peut varier entre 48% et 85%. Pour calculer aisément ce rendement d'extraction, on a ajouté dans la solution de 1 ' entraîneur de vanadium une quantité convenable de 48v (T^ = 16 j) dont les énergies des photons y (0,98 et 1,31 MeV) sont inférieures à celles du 52V (1,43 MeV) et qui donc ne risque pas, en petite quantité, de masquer le 5 2 y , Le dosage du vanadium dans les échantillons d'aluminium de «zone fondue» a montré que cet élément se concentre en tête des barreaux dans la partie du lingot qui est purifiée en ce qui concerne 1 ' ensemble des im ­ puretés 117 J. Il est donc important de doser le vanadium dans les aluminiums raffinés industriels qui sont soumis à la purification par «zone fondue»pour sélectionner les plus purs. Nous avons trouvé dans nos échantillons d'alu­ minium de «zone fondue» des teneurs de 0,15 à 0,6 ppm de vanadium.

2. Dosages de 1' aluminium, du vanadium et du magnésium dans le zirconium, le fer et le cuivre, de hautes puretés

Dans 1' analyse non destructive du zirconium et du fer il est impossible de doser le magnésium dont la section efficace de capture est très faible (gms = 0,03X0,11 = 0,0033 b). Les dosages de 1' aluminium et du vanadium dans le fer électrolytique deviennent très difficiles pour des teneurs de l'ordre de quelques ppm, la radioactivité de 1 ' impureté chlore (pics photoélectri­ ques de 2,15 MeV et 1,64 MeV) masquant celles des radioisotopes 28A1 (1,78 MeV) et 52y (1,43 MeV). Mais, dans le fer et le zirconium purs, la sensibilité du dosage non destructif est de l'ordre de 0,05.10'6 pour 1' alu­ minium. La sensibilité du dosage du vanadium dépendra, comme nous 1'avons vu, de la teneur en aluminium; mais dans les cas favorables elle atteint aisém en t 0, 0 1 -10 -6. Le dosage non destructif de radioisotopes de très courtes périodes tels que 28Д1 et 52y n' est pas possible dans le cuivre. En effet, même pour des irradiations d'une durée de 10 s la radioactivité de 66Cu (7 de 1,04 MeV) sature le détecteur à scintillation (o*6Cu = 2,2X0,31 = 0,66 b). Nous avons donc étudié les possibilités de dosage de 1' aluminium, du vanadium et du magnésium dans le zirconium, le fer et le cuivre, en sépa­ rant chimiquement avant irradiation les traces d'im puretés sur un entraî­ neur non isotopique de celles-ci. Dans le tableau II nous décrivons les différentes étapes des séparations chimiques effectuées avant 1 ' irradiation que nous proposons pour le dosage de 1 ' aluminium, du vanadium et du magnésium dans les métaux. Nous travaillons sur deux parties aliquotes de la solution de l'échan­ tillon. A la seconde nous ajoutons une quantité connue N de l 1 élément à doser. Soit X la teneur réelle de l'im pureté dans l'échantillon, A la valeur trouvée sur la première partie aliquote, B la valeur trouvée sur la seconde partie aliquote, le rendement R des séparations chimiques est donné par la relation: r, B - A 66 Ph. ALBERT et al.

TABLEAU II

SEPARATION CHIMIQUE AVANT IRRADIATION DE L’ALUMINIUM, DU VANADIUM ET DU MAGNÉSIUM

1. Dissolution de l'échantillon.

2. Séparation du métal analysé.

3. Addition de 1'«entraîneur non isotopique»constitué de 5 mg de fer.

4. Précipitation par NH4OH pur de Fe(OH)3 + tAl +eVcoprécipités.

5. Lavage très soigné au N03 NU, pour éliminer le chlore.

6. Addition de l'«entrafneur non isotopique»constitué de 5 mg de fer.

7. Précipitation en milieu NOs NH,. - NH4OH à pH 10-11 de l'oxinate de fer + eMg. coprécipité.

et la teneur réelle X par la relation:

Tous les traitem ents chimiques étant effectués sur les deux parties aliquotes en même temps avec les mêmes réactifs on élimine ainsi les cau­ s e s d 1 erreurs pouvant provenir de la pureté des réactifs (voir «limite de sensibilité»). Des «essais à blanc» permettent de faire la correction due aux pollu­ tions par les réactifs et montrent la nécessité d'élim iner, préalablement de ceux-ci les éléments gênants. Nous avons appliqué cette méthode à analyse du zirconium, du fer et du cuivre 19 J. Le zirconium est attaqué au chlore anhydre et le chlorure est dissous en solution chlorhydrique 4N (4, 8 J. On précipite le mandélate de zirconium en solution C1H 4N contenant environ 10 mg de métal par ml par une solu­ tion saturée d'acide mandélique (1 ml d'acide pour 10 mg de zirconium) à 95°C en laissant cristalliser le sel pendant 30 min. Après refroidissement, le précipité est filtré et lavé avec une solution C1H 1,5 M et 0,1 M en acide mandélique. L'excès d* acide mandélique dans le filtrat est éliminé par trois extractions successives par des fractions de 40 ml d'éther éthylique. Le fer est dissous dans l'acide nitrique et éliminé par extraction de son chlorure par 1' éther. Le cuivre est dissous dans 1' acide nitrique et éliminé par électrolyse. Les précipités d'aluminium et de vanadium sont irradiés 10 à 20 s dans un canal pneumatique à EL3 (Saclay) et le magnésium pendant 1 à 3 min. L' analyse des spectres 7 est effectuée dans un spectromètre à 400 ca­ naux utilisé en groupant les canaux en 4 centaines. Trois mesures sont faites à 1 min d'intervalle aussitôt après l'irradiation, puis l'étalon est enre­ gistré dans le quatrième groupe de canaux. Après 15 à 20 min on décompte DOSAGES D’ ÉLÉMENTS PAR LEURS RADIOISOTOPES 67 des premières mesures l'activité résiduelle de l'échantillon qui est due aux isotopes de longues périodes. On n' observe plus, après 30 min de décroiss- sance, de radioactivité de courtes périodes (quelques minutes à 10 m inutes) dans nos échantillons. Les rendements des séparations chimiques sur entraîneur fer non isoto­ pique sont de l'ordre de 100% pour l'alum inium et le vanadium et de 85% pour le magnésium. Nous avons étudié aussi les possibilités de dosage du titane. Le dosage de cet élément est peu sensible. Sa faible section efficace de capture (a = 0,14 X0,053 =0,0074 b) et son rayonnement y de moyenne énergie (0,32 MeV) nécessitent une séparation chimique des autres éléments. Mais sa courte période de 5,8 min oblige à trouver une méthode de séparation très rapide. C' est pourquoi dans 1' analyse du zirconium, nous avons été amenés a effec­ tuer sa séparation avant 1' irradiation. Après séparation du zirconium, les impuretés sont complexées par 1 ' éthylénediamine-tétracétate de sodium (EDTA) 0,02 M; le pH est ajusté entre 8 et 9 et on effectue deux extractions par 1'oxine à 1% dans le chloroforme [10]. Le solvant est évaporé et l'oxine détruite puis le titane est coprécipité par la soude sur 5 mg de fer «en­ traîneur non isotopique». Le tableau III réunit les résultats de quelques dosages d'aluminium et de vanadium effectués sur nos échantillons de zirconium, de fer et de cuivre.

TABLEAU Ш

ANALYSES PAR RADIOACTIVATION DE L’ALUMINIUM, DU ZIRCONIUM, DU FER ET DU CUIVRE PAR LES RADIOISOTOPES DE PÉRIODES COURTES Eléments dosés (en ppm)

Métal analysé Aluminium Vanadium Magnésium Silicium Chlore Iode

Aluminium raffiné par ... 0.35 à 0,40 ... 3 à 7 < 0 ,0 1 < 0.01 double électrolyse

Aluminium de ... 0 ,6 à 0,15 ... .$ 0,3 à 0,7 < 0,01 < 0,01 «zone fondue»

Fer électrolytique 42 à 65 1,7 à 3,5 ... — 600 à 900 < 0,01

Zirconium «K roll» 39 0,6 ¿ 1 0 ... < 0,01 < 0,01 refondu à l'arc

Zirconium 5 « 0,5 ...... < 0,01 0,5 à 1 «Van Arkel»

Cuivre OF НС 15 .$0.2 — ......

On peut estim er les sensibilités de nos dosages à 10-6 pour 1' aluminium, 5 - 10 ‘ 8 pour le vanadium et environ 1 0 - 10-6 pour le magnésium. Dans le zirconium Kroll déhafnié refondu au four à arc électrique nous avons décelé une teneur en titane de l'ordre de 40 ppm (40- 10-6). 68 Ph. ALBERT et al.

3. Limite de sensibilité des dosages par radioactivation après séparation ch im iq ue

Les séparations chimiques des impuretés avant l'irradiation rendent possible l'analyse de métaux ayant une grande section efficace de capture des neutrons. Cependant l'em ploi de ces méthodes fait perdre les principaux avan­ tages de l'analyse par radioactivation directe. En effet, il est très difficile de séparer, sur un entraîneur non isotopique, les traces d'un élément à doser sans aucune pollution par les impuretés des réactifs et sans pertes par adsorption ou entraînement au cours de la séparation du métal analysé. Ainsi nous avons constaté dans l'analyse du vanadium dans l'aluminium qu'il est très difficile d'obtenir des réactifs assez purs pour avoir une pol­ lution en vanadium inférieure à 0,1 ppm (ÎO-7). Or la sensibilité absolue de la méthode d'irradiation, en tenant compte du temps nécessaire à la purification radiochimique après l'irradiation, est de l'ordre de 0 ,0 1 à 0,02 p p m (1 à 2 • 1 0 ’8) de v an a d iu m . De même le dosage du magnésium est fortement gêné par les pollutions en manganèse (à cause de la présence du même pic photoélectrique y à 0,84 MeV) et en chlore (dont les énergies y sont plus grandes et dont la période est trop voisine) de 1' oxinate de magnésium. En effet, sans ces pollutions la sensibilité du dosage du magnésium pourrait atteindre l'ordre de grandeur de la partie par million ( 10 -6) si on augmentait la durée de l'irradiation et celle de la mesure de la radioactivité*. C est pourquoi nous avons recherché l'origine des pollutions de manganèse. L'oxine (réactif pur) contient environ 0,45 • 10*6 de manganèse, ce qui introduit 0,0045 mg de manganèse dans la solution. L'acide chlorhydrique et les autres acides introduisent du chlore et du manganèse. On retrouve ainsi, sur l 1 oxinate de fer «entraîneur» des traces de magnésium à doser, de l'ordre de 0,03 à 0,07 p g de manganèse quels que soient les soins appor­ tés à la purification des réactifs. Les traitements de purification radiochimique après 1'irradiation, avec «entraîneur» de l'élém ent à doser et «entraîneur en retour» des impuretés gênantes, permettent d'accroître la durée des irradiations. Celle-ci peut apporter un gain de sensibilité notable malgré la perte de temps qui résulte des séparations chimiques. Ce gain de sensibilité sera d'autant plus im ­ portant que les périodes seront plus longues (10 à 20 min par exemple). Toutefois; il peut être très intéressant de faire une séparation demandant 10 min pour isoler radiochimiquement pur un isotope dont la période est de 3,7 min ou de 5,8 min comme le montre 1' exemple du dosage du vana­ d iu m d an s 1 ' aluminium. Dans le dosage du magnésium nous remarquerons que la précipitation de l 1 hydroxyde de fer (voir le tableau II) est la principale cause de pertes par adsorption de cet élément à l'échelle des traces (10 à 100 ¡Jg). En effet, des essais «en traceur» fait avec 27Mg montrent que sans entraîneur ce radioisotope s 'adsorbe très facilement et en grande quantité sur l'hydroxyde

# Nous recherchons actuellement une méthode d'extraction du magnésium qui permettrait de gagner beaucoup de temps et d'accroître la sensibilité. DOSAGES D’ ÉLÉMENTS PAR LEURS RADIOISOTOPES 69 de fer si 1' ammoniaque utilisée est carbonatée par absorption du C0 2 a t­ mosphérique. En prenant grand soin d'employer une ammoniaque très pure nous avons obtenu pour la séparation du magnésium, avant l'irradiation des rendements de 1' ordre de 85%. Mais, en ajoutant une quantité importante de sels ammoniacaux tels que CINH4 ou NOÿNH4 (à 1' échelle de 200 mg pour 100 ml de solution) avant la précipitation de Fe(OH )3 par 1' ammoniaque, on réduit considérablement l 1 adsorption du magnésium qui n'excède alors jamais 5%. Par contre, en présence du magnésium comme entraîneur, 1' adsorp­ tion du radioisotope sur Mn0 2 par exemple, est relativement peu importante si on lave bien le précipité.

CONCLUSION

Nous avons donné quelques exemples de dosages, par les radioisotopes de périodes courtes, d'éléments dont la détection par les méthodes chimiques classiques est aussi très difficile et dont la sensibilité est parfois insuffisante.

TABLEAU IV

ANALYSES DE ZIRCONIUM ET DE FER

Dosage de l 'aluminium (en'ppm)

Zirconium

Zirconium de «zone fondue» 0,63 à 1,97

Zirconium «Kroll»

Eponge 28,3

Eponge fondue au four & arc 19 i 26

Eponge fondue au four î électrons:

fusion rapide 7 à 10

fusion lente 2 à 4

Zirconium « V a n A rk el» 5

fondu au four à électrons 0.6

Fer

Fer électrolytique 42 a 65

Fer de « zone fondue» 4.5

Fer obtenu par «dissociation du chlorure» 1,7 i 16 (très hétérogène)

\ 70 Ph. ALBERT et al.

Dans le cas de l'analyse de certains éléments comme l'aluminium, le zir­ conium et le cuivre, on devra effectuer, avant l 'irradiation, la séparation de l'im pureté à doser sur un entraîneur non isotopique. Selon les teneurs et les sections efficaces de capture des neutrons des impuretés à doser, on pourra se contenter de séparations chimiques avant l'irradiation et d'une irradiation très courte oü on sera obligé d'effectuer encore après l'irra ­ diation une seconde purification selon, cette fois,- les méthodes radiochi- miques classiques, pour éliminer les radioisotopes gênants provenant des pollutions apportées par la séparation avant l'irradiation. Nous avons pu ainsi préciser le titre de métaux de hautes puretés (voir les tableaux III et IV). Ainsi dans l'analyse du zirconium «Kroll» par exemple, nous dosons par les radioisotopes de courtes périodes 80 ppm d'im puretés métalliques qui s'ajoutent aux 230 à 250 ppm trouvées par analyse systématique de ce mé­ tal. Dans l'aluminium de «zone fondue», on dose autant d'im puretés par les radioisotopes de courte période que dans toute l'analyse systématique. Ainsi la somme de 48 impuretés dosées peut ne pas dépasser 0,8 ppm(8'10-7) et par courtes périodes, on dose de 0,6 à 0,8 ppm (Actuellement le carbone et le vanadium). On notera que pour une analyse faite sur des éléments ayant été irradiés dans un flux de 10i2n/cni-s, la somme des limites de détection des éléments non décelés atteint 2,5 ppm pour environ 40 éléments.

RÉFÉRENCES

[1] ALBERT , Ph., Nouvelles propriétés physiques et chimiques des métaux de très haute pureté, Colloque international, Centre national de la recherche scientifique, Paris (1962) 11. ALBERT, Ph,,.Ultra High Purity Metals, American Society for Metals, Metals Park Ohio, USA, Reinhold Publishing Co. (1962) 68-83. ALBERT, Ph., Radioisotopes in the Physical Sciences and Industry II, IAEA, Vienna (1962) 243. ALBERT, Ph., Modern Trends in Activation Analysis, College Station, IAEA, USA-EC.A.M. College of Texas (1962) 78-83. [2] MEINKE, W.W., Radioisotopes in the Physical Sciences and Industry П, IAEA, Vienna (1962) 277, MEINKE, W .W ., Modern Trends in Activation Analysis, IAEA, USA-ЕС, A.M. College of Texas (1962)36. [3] CHARLOT, G ., Les méthodes de la chim ie analytique, 4e é d ., Masson et Cie, Paris (1961). [4] FOURNET, L ., Thèse 3e cycle, Paris (1962). [5] ALBERT, P h., MONTARIOL, F ., REICH, R. et CHAUDRON, G ., 2* Radioisotopes Conférence Oxford, Butterworths London (1954) 75. [6] SHORT, H.G., Analyst 83(1958) 624. [7] DEYRIS, M. et ALBERT, P h ., Revue de m étallurgie LIX, I<1962) 14. [8] FOURNET, L. et ALBERT, Ph. ,C .R . Ac. Sc. 254(1962) 1076. [9] FOURNET, L., DESCHAMPS, N. et ALBERT, Ph., C.R. Ac. Sc. 254(1962) 1640. [10] MORRISON, G. H. and FREISER, H ., Solvent Extraction in an aly tical Chem istry, J. WILEY and Sons, New York (1957).

DISCUSSION

W. GEBAUHR: I cannot see that it is really a good idea to apply acti­ vation analysis after chemical separation. The advantage of activation analy­ sis lies mainly in the absence of blank values. In cases where it is possible to perform normal chemical separations without obtaining blank values, what is the point in using activation analysis to estimate the element that has been DOSAGES D’ ÉLÉMENTS PAR LEURS RADIOISOTOPES 71 separated? This can be done by other methods which are cheaper and less time-consuming. P. ALBERT: As I explained in the paper, we fully appreciate that some of the advantages of activation analysis are forfeited when pre­ separations are performed before irradiation. The reason that we continue to use the method nevertheless, e.g. for determining vanadium, titanium and magnesium, is that it provides us with a higher degree of sensitivity than can be obtained with any other analytical method available at our laboratory. It is important to realize, I think, that a pre-separation of this sort does not really isolate the element you are trying to estimate. The object is merely to separate it by means of a non-isotopic carrier from the bulk and elements possessing too high a neutron capture cross-section, making due allowance for the half-lives of the radioisotopes which have to be dis­ tinguished. Conventional analytical methods are not necessarily easier and are certainly no more reliable than radioactivation, even when partial pre­ separation has to be resorted to. L. G. ERWALL: Have you considered the possibility of using spectrum stripping as a means of increasing the sensitivity for vanadium in the presence of aluminium? P. ALBERT: You must remember that we need sensitivities of the order of 0. 01 ppm to be able to establish with certainty overall purities of the order of 1 ppm or even less. Mr. Engelmann and Mr. Petit found that, in general, their subtraction method was better than the spectrum-stripping technique, but obviously this latter method would be the only possible one if one had to deal with two radioisotopes with half-lives as sim ilar as those of V52 (3. 7 min) and Al28 (2. 3 min). Spectrum stripping could, we think, be used for separating V52 and Al28 in cases where the A1:V ratio was well over 60. Nevertheless, that would not be sufficient for our analyses of vanadium in aluminium samples. T he F e(O H )3 carrier we use sometimes retains over one milligram of alu­ minium, so that it will always be necessary, I think, to carry out a radio­ chemical purification after irradiation. V. P. GUINN: Spectrum stripping is certainly an extremely useful technique in the sort of case you describe, Dr. Albert, i. e., where there is a small amount of V62in the presence of a large amount of Al28. It is important to realize, however, that, even under ideal conditions of identical spectrometer gain, there will always be a limitation in the form of counting statistics. The high counting rate of the Al28 in the vicinity of the V52 photo­ peak inevitably raises the lim it of detection of the V52 above what it would normally be in the absence of the Al28. Radiochemical separation, carried out rapidly, can of course remove this limitation, decreasing the limit of detection of the Vs2 to a lower value. In practice, gain shifts at high count­ ing rates can make it impossible to use the spectrum-stripping method. This is a very serious problem. Some improvements have been developed recently. There is an electronic circuit, for example, which is now available commercially in the United States at a reasonable cost; this is able to stabi­ lize the gain very rapidly, in a m atter of microseconds, even at very high counting rates. I don't know what the limitations of the apparatus are but I have tried it out and it does hold the gain Constant even at extremely high counting rates.

ANALYSIS OF TANTALUM AND NIOBIUM BY NEUTRON ACTIVATION OF SHORT-LIVED RADIONUCLIDES

CHONG KUK KIM DEPARTMENT OF CHEMISTRY, ATOMIC ENERGY RESEARCH INSTITUTE, SEOUL, KOREA

Abstract — Résumé — Аннотация — Resumen

ANALYSIS OF TANTALUM AND NIOBIUM BY NEUTRON ACTIVATION OF SHORT-LIVED RADIO­ NUCLIDES. The tantalum and niobium content of ore has been determined by thermal neutron activation analysis of 6. 6-min NbMm and 16.5-min Тагит. The measurements were made using a 10-min irradiation in a flux of 1012 n cm"2 s-1, a 7-min radiochemical separation and gamma spectrometry.

ANALYSE DU TANTALE ET DU NIOBIUM PAR ACTIVATION NEUTRONIQUE DE RADIOÉLÉMENTS A COURTE PÉRIODE. On a déterminé la teneur en tantale et en niobium de minerais en utilisant la méthode d'analyse par activation neutronique (neutrons thermiques) de **m Nb (période: 6,6 min) et de и* m Ta (période: 16,5 min). Après irradiation pendant 10 min dans un flux de 1012 n cm"! s-i on a procédé à une séparation radiochimique pendant 7 min et on a effectué les mesures par spectrométrie gamma.

АНАЛИЗ ТАНТАЛА И НИОБИЯ МЕТОДОМ НЕЙТРОННОЙ АКТИВАЦИИ КОРОТКОЖИВУШИХ ИЗОТОПОВ. Содержав»# тантала и ниобия в рудах определено в результате проведения активационного анализа с помощью тепловых нейтронов Nb94 с периодом полураспада 6,6 мин и Та162с периодом полураспада 16,5 щга. Измерения проводились путем облучения в течение десяти минут в потоке 1012 н см”2 сек ^радио­ химического разделения в течение семи минут и затем с помощью гамма-спектрометрии.

ANÁLISIS DEL TÁNTALO Y DEL NIOBIO POR ACTIVACION NEUTRÓNICA DE RADIONÚCLIDOS DE PERÍODO CORTO. Se describe ei análisis del tántalo y del niobio por activación neutrónica de radionúclidos de período corto. Se ha determinado la concentración de tántalo y niobio en el mineral mediante el análisis por activación neutrónica del MmNb (de 6,6 min) y del ^m Ta (de 16,5 min), Las mediciones se efectuaron por espectrometría gamma después de una irradiación de 10 min con un flujo de lOi^n cm-2 s-i y una sepa­ ración radioquímica de 7 min.

1. INTRODUCTION

Metals such as beryllium, magnesium and aluminium, which are currently used for cladding uranium fuel elements in nuclear reactors, have low thermal-neutron absorption cross-sections and good corrosion resistance but are not strong at high temperature. While niobium does not have as low a cross-section as the above-mentioned metals, it far surpasses them with respect to strength at high temperature. With higher-energy neutrons, the absorption cross-section of metals decreases considerably aiid the dis­ advantage of niobium decreases. Inasmuch as the trend in power reactors is toward higher operating tem peratures to obtain better efficiencies, niobium is likely to see service in future reactors [1]. Geological formations, characteristic of potential sources of niobium, are widespread in Korea [2] . These ores also contain tantalum. In order to assess the country's reserves, a rapid, accurate and sensitive method for analysis of ores was required.

73 74 CHONG KUK KIM

Among the many methods currently used for analysis of niobium and tantalum, the colorimetric method appears to be most sensitive [3]. However, the application of this method requires effective methods of separating the earth acids from iron, tungsten, molybdenum and other elements which would interfere in the colorim etric determinations and such a separation is difficult and time-consuming. Moreover, corrections for "reagentblanks" become quite appreciable at low concentrations. Neutron activation analyses of short-lived Nb94m and Ta182m were therefore attempted.

2. EXPERIMENTAL TECHNIQUE

2.1. General

Ore to be analysed was first ground to a fine powder with a clean agate m ortar and pestle. Weighed, powdered samples were seeded in pharmaceutical- type gelatine capsules and irradiated for 10 min. in nylon "rabbits" in the pneumatic tube system of the TRIGA MARK II nuclear reactor of the Atomic Energy Research Institute in Korea [4]. This system perm its irradiation at a therm al neutron flux of about 1.2X1012n cm ‘2s_1(at full power of 100kW) and delivery to a hood in a hot laboratory within 2 s after the end of irradi­ ation . Samples were then treated chemically and analysed, using a scintilr lation counter with a 2-in X 2-in Nal (Tl) crystal, coupled to a RCL 256- channeí puise height analyser. Gold, flux-monitoring foils weighing between 0.1 and 0.2 mg were taped inside the cap of the nylon "rabbit".

2.2. Radiochemical separation

During the irradiation, Nb95 tracer and carrier solution containing 3 mg of niobium and 12 mg of tantalum (prepared by dissolution of metals in concentrated hydrofluoric acid followed by the addition of concentrated sul­ phuric acid and diluting) were evaporated to dryness in a platinum crucible and 4-5 g of potassium pyrosulphate added. The irradiated sample was trans­ ferred from the gelatine capsule to the crucible, and the mixture fused for one minute. The outside of the crucible was then cooled by dipping into a beaker of water and the melt made to solidify in a thin, readily-dissolved coating by manipulation of the crucible. The melt was dissolved by adding 10 ml of 0.33-M tartaric acid and 10 ml of saturated oxalic acid, and heated gently to accelerate dissolution. The resulting clear solution was then transferred to a boiling mixture of 10 ml saturated ammonium acetate, 10 ml of 0.1-M EDTA, 10 ml of 0.33-M tartaric acid, 20 ml of saturated ammonium chloride and 50 ml of distilled water [5]. To the solution, 10 ml of 10% tannic acid was added and 2 M am­ monium hydroxide added drop by drop until the solution became turbid and finally tantalum tannate started to precipitate. At this point the pH of the solution was kept between 3.5 and 4.0. The solution was then cooled in a crushed-ice bath for one minute while agitating. The precipitate was filtered ANALYSIS OF TANTALUM AND NIOBIUM BY NEUTRON ACTIVATION 75 through a'W hatman No. 42 filter paper on a glass filter and mounted on a counting card for measurement with the gamma-ray spectrom eter. The pH of the filtrate was then raised to 5 by adding a few more drops of 2-M ammonium hydroxide to precipitate niobium tannate. Care was taken not to raise the pH to more than 5.5 since tannic acid would be precipitated even in very weak alkali solution. The second precipitate was mounted on a counting card and used for m easurem ent of Nb94111. The entire procedure was completed in about 7 min with an average recovery of 60% for tantalum and 40% for niobium. Fusion with Na20 2 in a nickel crucible and KHF2 in a platinum crucible can be employed depending on the types of samples. The chemical recovery of niobium was determined from the area under the 0.75-MeV Nb^s photopeak. Tantalum in the sample was weighed as Ta^Os after the complete ignition. The weight corresponding to the activity from the calibration curve was subtracted when the samples contained a fairly large amount of tantalum compared with the amount of tantalum carrier added prior to the separation.

2.3. Activity determination

Spectra obtained from the niobium and tantalum fractions are shown in Figg. 1 and 2. The characteristic X-rays at 16.6 and 57.8 keV for niobium [6] and tantalum respectively were measured. The half-life of the niobium characteristic X-ray peak was found to be 6.6 min. The peak corresponding to the 67-keV gamma-ray from 111-dTa182 formed during the 10-min irradi­ ation was subtracted from the Ta182m plus Ta182 peak.

Hg. a

Gamma-ray spectra of 6.6-min Nb94m fraction separated from an ore, taken at 6 .6-min Intervals. 76 CHONG KUK KIM

CHANNEL No.

Fig. 2

Gamma-ray spectra of 16.5-min Ta^®^m subtracted from long-lived Ta1®^. 16.5-min T allin. 2-inx 2-in Nal crystal; source distance 1.0 cm.

2.4. Results and discussion

Results obtained from the activation analysis of the Korean ore and the waste are summarized in Table I. In the Table, the ores I, II, and III are from the same powdered, well-mixed sample but different amounts are taken to check reproducibility. The data shows that the deviation is less than one per cent. The waste is also powdered, mixed and different amounts taken (denoted as waste I, II and III). NLSS F ATLM N NOIM Y ETO ACTIVATION NEUTRON BY NIOBIUM AND TANTALUM OFANALYSIS

TABLE I

ACTIVATION ANALYSIS FOR NIOBIUM AND TANTALUM ORE AND ITS WASTE FROM THE TAN ROCK MINE, KANGWON DO, KOREA

S am ple A m ount Yield of Nb Nb found Level o f N bjO s Yield of Ta T a found Level of irrad iated radiochemical in sam ple radiochemical T a 2O s in separation separation sam ple (g) № (g) № ~ (%) (g) (%)

Concentrated

O re I 0.0109 30 4.45 X 10-’ 4 1 .1 60 1 .8 0 X 1 0 '4 1 6 .4

II 0.0098 40 3.96x10'» 40.5 58 1.62X 10~* 1 6 .5

III 0.0050 32 1.31x10-» 41.0 65 8.2 X 10"5 1 6 .4

average:40.9 average:16.4

Waste I 0.00585 40 6 .4 8 X 1 0 ' 4 1 6 .2 62 7 . 1 7 X 1 0 '5 1 2 .3

II 0 .01460 46 2 .3 2 X 10-» 1 6 .0 60 1.81X lO'4' 1 2 .4

Ш 0 .0 1 2 3 23 2 ,0 3 x 10"» 1 6 .5 70 1.5 2 X 10"4 1 2 .3

average: 16.2 a v erag e: 1 2 .3

- j 78 CHONG KUK KIM

Calibration curves using a known amount of Nb and Та metal powder (Johnson and Matthey) were taken under severed conditions of measurement of the Nb94m and Ta182m X -rays. The amount of Nb94"1 and Ta182m was deter­ mined from the area under the 16.6-keV'and 57.8-keV photopeak. The curves show straight lines and these are then used to evaluate the niobium and tantalum contents in the ore and waste by interpolation. Background and interfering Compton radiations from other activities remaining in the sample were eliminated by extrapolation of the base line from both sides of the photopeak. A total photopeak area of 100 cpm was considered to be the prac­ tised low lim it of detection. With a neutron flux of about 10i2n cm-2 s-i the method enables the tantalum and niobium content of these ores to be measured with a practical lower lim it of about 3X 10'7 g and IX 10-6 g, respectively. The chemical separation of earth acids from other elements and tantalum from niobium has been studied elsewhere [7-12]. Tantalum precipitation as tannate was adopted to separate niobium from it by adjusting the pH up to 4.0. The pH was the main determining factor of this separation. The chemical recovery of tantalum at pH 4.0, using Ta182 tracer, is about 90%. In this work, however, the recovery was only about 60% since a rapid separation was required for the short-lived nuclide and it was hard to adjust exactly to pH 4 for the separation. The advantage of this type of analysis for niobium and tantalum is that one sample irradiation gives analysis of two elements simultaneously in less than 20 çiin and correction for reagent blank is unnecessary, since only the niobium and tantalum which were originally irradiated with the sample will be activated and m easured in the analysis.

REFERENCES

[1] GONSER, B.W. and SHERWOOD, E .M ., Technology of Niobium, John Wiley and Sons, In c ., New York (1958) 35. p ] YUN, T.S., "Occurrence of Uranium and Thorium in South Korea". 1st UN Int. Conf. PUAE6 (1956) 176. [3] SANDELL, E. B., "Colorimetric Determination of Traces of Metals”, Interscience Pub. (1959) 682. [4] KAISER, D.G. and MHNKE, W .W ., "Activation Analysis of trace Cobalt in Tissue using 10.5 minute Co60m" Talanta 3(1960) 255. [5] BELEKAR. G.K. and ATHAVALE, V .T., Separation of Niobium from Tantalum, Titanium, Tin and Antimony by means of 8-Hydroxyquinoline, Analyst 82(1957)630. [6] MADDOCK, R.S. and MEINKE, W.W., US Atomic Energy Commission Report AECU-4438 (1959) 63. [7] STEINBERG, F.P., "The Radiochemistry of Niobium and Tantalum", Nuclear Science Series Report NAS-NS -3039 (1961) Д -53. [8] POSKANZER, A.M. and FOREMAN, B.M., Jr., "A Summary of T.T, A. Extraction Coefficients", Inorg. Nuclear Chem. 1£ (1961) 323. £9] HILLEBRAND, W.F. and LUNDELL, G .E.F., Applied inorg. Analysis, John Wiley and Sons (1955) 588. [10] BANDI, W .R .. BUYOK, E .C ., LEWIS, L.L. and MELNICK, L, M ., "Anion Exchange o f Z r. T i, Nb, Ta, W and Mo", Anal. Chem. 33 (1961) 1275. [11] CUNNINGHAM, T.R., "Determination of Columbium and Tantalum in stainless Steel", Ind. Eng. Chem., Anal. Ed. 10_ (1938) 233. [12] ISHIMORI, T. and WATANABE, K., "Inorg. ext. Studies on the System of TBP-Nitric Acid", Bulletin of the Chem, Soc. of Japan 33 10 (1960). ANALYSE DE ROUTINE PAR RADIOACTIVATION NEUTRONIQUE. DOSAGE NON DESTRUCTIF DU SODIUM, A CONCENTRATIONS MOYENNES, SUR DE PETITS ÉCHANTILLONS DANS DES GELS DE SILICE-ALUMINE ET DANS DES SOLUTIONS

D. BARTHOMEUF et P. BUSSIÈRE INSTITUT DE RECHERCHES SUR LA CATALYSE , VILLEURBANNE ET J. LAVERLOCHÈRE CENTRE D'ETUDES NUCLEAIRES, GRENOBLE, FRANCE

Abstract — Résumé — Аннотация — Resumen

ROUTINE NEUTRON RADIOACTIVATION ANALYSIS. NON-DESTRUCTIVE ASSAY OF SODIUM, AT MEDIUM CONCENTRATIONS, IN SMALL SAMPLES OF SILICA - ALUMINA GELS AND IN SOLUTIONS. A potential development of activation analysis is its application in the range of medium concentrations, when the usual chemical or physico-chemical methods are too complicated, onerous, or of poor precision. It is then of importance to find working conditions which give optimum precision and versatility of activation analysis at the lowest possible cost. The authors give the results of neutron activation assay of sodium in silica-alumina gels, in the range of 0,1 to 3ft by weight. Several tens of samples are analysed at a time. A technique for preparing samples for irradiation is described-The sodium content is obtained by 0-counting with a Geiger-Müller tube. Calibration is effected by incorporating a few standards consisting of known quantities of sodium car­ bonate among the unknown samples,enclosed in an irradiation tube. The activity per milligram ot sodium can thus be plotted against the place of each sample in the tube. This method was developed on the basis of a study which is also described of neutron flux along a file of several dozen irradiated samples. The different sources of error in activation analysis áre discussed in detail. In determinations of die type described, a precision better than 3% cannot be expected. Enhancement of the stability of the detection devices should, however, permit an accuracy of 2ft to be achieved.

ANALYSE DE ROUTINE PAR RADIOACTIVATION NEUTRONIQUE. DOSAGE NON DESTRUCTIF DU SO­ DIUM, A CONCENTRATIONS MOYENNES, SUR DE PETITS ÉCHANTILLONS DANS DES GELS DE SIU C E- ALUMINE ET DANS DES SOLUTIONS. L’analyse par activation peut trouver une voie de développem ent dans le domaine des concentrations moyennes lorsque les méthodés chimiques ou physico-chimiques s'avèrent trop compliquées, onéreuses, ou peu précises. Il est alors important de rechercher les conditions de travail qui améliorent la précision, la commodité, et le prix de revient de l'analyse par activation. C*est dans ce sens que le présent travail a été conduit. Les auteurs présentent les résultats de dosage par activation neutronique de sodium fixé par des gels de silice alumine, oû il se trouve aux concentrations de 0,1 à 3ft en poids. L'analyse est pratiquêé sur des séries de plusieurs dizaines d'échantillons. On présente en particulier une technique de préparation des échan­ tillons pour l'irradiation. La teneur en sodium est déterminée par cümptage 0 au compteur de Geiger-Miller. L’étalonnage est réalisé en incorporant, parmi les échantillons inconnus renfermés dans un tube d’irra­ diation, quelques témoins constitués de quantités connues de carbonate de sodium. On peut ainsi dresser la courbe de l'activité par milligramme de sodium en fonction de la position de chaque échantillon dans le tube. Cette méthode s'appuie sur une étude( également présentée ici, de la répartition du flux de neutrons d'un réacteur dans un empilement de quelques dizaines d'échantillons contenus dans un tube d'irradiation. On discute de façon plus complète les facteurs d'erreurs en analyse par activation. Dans les dosages tels que ceux de l'application particulière présentée, on ne peut pas s'attendre à une précision meilleure que 3%. L'amélioration des conditions de stabilité des appareillages de détection doit permettre d'obtenir une précision de 2ft.

79 80 D. BARTHOMEUF et al.

ОБЫЧНЫЙ НЕЙТРОННЫЙ РАДИОАКТИВАШОННЫЙ АНАЛИЗ. НЕДЕСТРУКТИВНОЕ ИСПЫТАНИЕ НАТРИЯ СРЕДНЕЙ КОНЦЕНТРАЦИИ НА НЕБОЛЬШИХ ОБРАЗЦАХ В СИЛИКОГЛИНОЗЕМНЫХ ГЕЛЯХ И В РАСТВОРАХ. Активационный анализ может найти свое дальнейшее применение в области средних концентраций, когда химические и физико- химические методы окажутся слишком сложными, дорогостоящими или малоценными. Тогда важно будет изыскать рабочие условия, которые повысят точность,создадут больше удобств и снизят себестоимость активационного анализа. Именно в этом направлении была проведена настоящая работа. Авторы излагают полученные при помощи силикоглиноземных гелей результаты нейтронного актива­ ционного анализа натрия, который находился в них при концентрациях от 0,1% до 3% в весовом выра­ жении. Анализ был проведен на серии в несколько десятков образцов. В частности, излагается ме­ тод подготовки образцов для облучения. Содержание натрия определено путем 0-счета на счетчике Гейгера-Мюллера. Калибровка производилась путем помещения среди неизвестных образцов, заключенных в канал для облучения, нескольких контрольных образцов при определенных количествах карбоната натрия. Это дает возможность вывести кривую активности, выраженную через миллиграммы натрия в функции положения каждого образца в канале. Этот метод применялся при изложенном здесь же исследовании распределения потока нейтронов реактора во время загрузки реактора несколькими десятками образцов, содержащихся в канале для облучения. Более полно освещаются факторы возникновения ошибок при активационном анализе. В работе под­ черкивается,что при проведении подобных испытания нельзя ожидать точность foiьшей,чем Э^.Улучпение условий стабильной роботы аппаратуры по обнаружению должно позволить получать точность s пределах 2¿«

ANÁLISIS DE RUTINA POR RADIOACTIV ACION NEUTRÔNICA, DETERMINACIÓN NO DESTRUCTIVA DE CONCENTRACIONES MEDIAS DE SODIO EN MUESTRAS PEQUEÑAS DE GELES DE SÍLICE-ALÚMINA Y EN SOLUCIONES. Es de suponer que el análisis por activación encuentre crecientes aplicaciones en el intervalo de las concentraciones medias, en los casos en que los métodos químicos o fisicoquímicos resulten demasiado complicados, onerosos o poco precisos. Así, pues, es importante buscar condiciones de trabajo que permitan mejorar la precisión, la comodidad y el costo de los análisis por activación. Este fue el objectivo del presente trabajo. Los autores presentan resultados de la determinación cuantitativa por activación neutrónica del sodio fijado por geles de sílice-alúmina, donde se encuentra en concentraciones de 0,1% a 3°}o en peso. El análisis se efectúa en series de varias decenas de muestras. En particular, presentan una técnica de preparación de las muestras para la irradiación. El contenido en sodio se determina por recuento 6 con un tubo Geiger-Müller. La calibración se efectúa intercalando entre las muestras desconocidas contenidas en un tubo de irra­ diación, algunas muestras testigo constituidas por cantidades conocidas de carbonato sódico. De esta manera, se puede trazar la curva de la actividad por miligramo de sodio en función de la posición de cada muestra en el tubo. El método se basa en un estudio, descrito en la memoria, de la distribución del flujo neutrónico de un reactor en un apilamiento de varias descenas de muestras contenidas en un tubo de irradiación. Los autores discuten más extensamente las fuentes de error en el análisis por activación. En las deter­ minaciones cuantitativas como la que se describe en la memoria no cabe esperar una precisión superior al 3%, pero aumentando la estabilidad de los aparatos de detección, se ha de alcanzar une précision del 2°]o.

1. INTRODUCTION

L'analyse par activation, après les nombreux travaux qu*elle a suscités Г1], occupe surtout une place de choix parmi les méthodes d*analyse de traces. Toutefois, elle ne réussit pas toujours à s’affranchir de toute manipulation chimique. Cependant cette méthode peut aussi perm ettre de faire des dosages à des teneurs plus ordinaires (en pour mille, en pour cent, etc.) et a déjà été appliquée dans ce sens [2]. Dans ce domaine, la précision, la facilité d’irradiation et le prix de revient prennent beaucoup plus d’importance qu’en microanalyse. Les grands àvantages que peut offrir cette technique l’emporteraient facilement sur les inconvénients si ces derniers pouvaient être minimisés ANALYSE DE ROUTINE PAR RADIOACTIVATION NEUTRONIQUE 81

à peu de frais. A l’occasion du problème précis que nous nous posons, nous avons cherché des solutions générales concernant les techniques de pré­ paration des échantillons pour l’irradiation et le comptage, et nous les pré­ sentons ici, en même temps que l’étude de la répartition d’un flux de neu­ trons dans une colonne d’échantillons. Nos analyses portent sur du sodium absorbé par des gels de silice- alumine au cours d’une étude de certaines propriétés catalytiques de ces solides, décrite ailleurs [3]. Les concentrations sont comprises entre 0,1 et 3% en poids. L’analyse par activation prend alors un caractère apparent de grande simplicité, car après la décroissance de 28A1 et de 31Si aucune activité parasite décelable ne vient perturber celle de 24Na. Celui-si se prête particulièrement bien à une détermination, puisque les rayonnements/8 suffi­ samment énergiques (1,38 MeV) ne nécessitent que de très faibles correc­ tions d’autoabsorption, et qu’en définitive un simple compteur de Geiger- Müller suffit à ce travail. Les mêmes dosages par les méthodes chimiques sont très longs à cause de la mise en solution. Cette dernière est encore nécessaire en photométrie de flamme, et de plus, en photométrie ordinaire, il faut éliminer le silicium qui donne une interférence. L’analyse par acti- ,vation devient alors compétitive de ces procédés, à condition qu’elle puisse être réalisée sur de petits échantillons, et que le coût, la durée du travail et la précision soient intéressants. On trouve sans doute d’autres situations de ce genre en analyse.

2. PRÉPARATION DES ECHANTILLONS POUR L’IRRADIATION ET LE COMPTAGE

Pour arriver à effectuer un dosage en série, il faut placer le plus grand nombre possible d’échantillons dans un tube standard d’irradiation du CEA, offrant un espace libre intérieur ayant un diamètre de 23 mm et une hauteur de 65 mm. Cette dernière est encore réduite à cause de la présence d’un lest dans le cas d’une irradiation en pile piscine. Les porte-échantillons doivent présenter une bonne tenue à l’irradiation à cause de l’action des neutrons et du rayonnement y. Ils ne doivent pas s’activer eux-mêmes ni leurs impuretés à un taux trop élevé. REIFFEL et STONE [4] ont utilisé de petites capsules en graphite «nucléaire», placées dans des tubes analogues mais un peu plus longs, puis­ qu’ils y introduisaient jusqu’à 20 capsules ayant une hauteur de 5 mm cha­ cune. Le produit à activer gisait dans le fond de la capsule, sous une forme qui se prêtait directement au comptage de l’activité |3 après l’enlèvement du couvercle vissé. WINCHESTER [5] confectionne des échantillons prêts pour le comptage y à partir de feuille ou de lame mince de polythène. Nous avons également utilisé la feuille de polythène mais n’avons pas envisagé l’irradiation d’échantillons prêts pour le comptage. Souvent, en effet, le lot doit accomplir un voyage au cours duquel la reproductibilité de la géométrie risquerait d’être fortement perturbée. Nous nous sommes en outre libérés des problèmes de repérage. Tous les échantillons à irradier sont en effet réunis sur un même support de la façon qui sera décrite ci- dessous. On part de bandes de polythène ayant une épaisseur de 0,1 mm et une largeur de 20 mm, débarrassées préalablement des poussières par 82 D. BARTHOMEUF et al.

un lavage à l’eau savonneuse et par un rinçage abondant à l’eau ordinaire suivi d’un rinçage à l’eau distillée, et séchées. Un pliage en accordéon permet de faire entrer l’ensemble dans un tube standard d’irradiation, tout en assurant l’empilement satisfaisant des sachets dont il est constitué. Le cas échéant, une masselotte en plomb complète le volume disponible et tasse la colonne.

2.1. Poudres

Pour chaque poudre, nous avons choisi d’irradier une quantité suffisante permettant de confectionner, par la suite, un seul échantillon de mesure d’activité, soit environ 20 mg. Sur la bande de polythène, on préforme les emplacements nécessaires à l’aide d’une petite presse manuelle équipée d’un fer à souder usuel, dont les éléments essentiels sont représentés sur la figure 1. On amène d’abord de proche en proche la bande sur la matrice

V///A DURALUMIN

Щ VERRE

0 \ cm

Figure 1

Appareillage pour la confection des sachets soudés.

du montage décrit à la figure la, et l’on appuie quelques instants la panne chauffante pour obtenir un renflement permanent capable de contenir le produit. La bande étant ainsi préparée, la presse est modifiée (voir fig. 1 b). La matrice est remplacée par une plaque de verre percée d’un trou au dia­ m ètre de la forme précédente, une nouvelle panne creuse et constituant seulement une couronne chauffante est montée sur le fer à souder. On amène alors chaque renflement de la bande dans le trou de la plaque de verre et on le remplit de poudre. On pose dessus un carré en polythène et on applique pendant quelques instants la panne chauffante. On réalise ainsi un sachet soudé renfermant le produit. Il est bon d’interposer entre le carré de poly­ thène et la couronne chauffante un petit morceau de papier fin. On procède de la même manière pour toute la bande. Un tube d’irradiation standard du CEA peut contenir un accordéon de 40 échantillons de cette espèce. ANALYSE DE ROUTINE PAR RADIOACTIVATION NEUTRONIQUE 83

Après l’irradiation, cet accordéon est extrait facilement du tube et ex­ pédié à son propriétaire. Ce dernier peut confectionner les échantillons de comptage suivant la méthode appropriée, à condition d’employer pour chacun d’eux le contenu total d’un sachet (voir paragraphe 3.2.). Dans notre cas, la poudre est tassée dans la cavité circulairejayant un diamètre de 16 mm-et une profondeur de 0, 5 mm^d’un porteur en duralumin, puis on recouvre de scotch.

2.2. S o lu tio n s

Nous déposons à l’aide d’une micropipette, en évaporant en même temps sous léger courant d’air froid, une quantité connue de chaque solution (dans n o tre c a s 10 ± 0,05 mm3), sur un disque de papier filtre le plus pur possible. Parm i trois qualités, savoir le papier Whatman n°l pour chromatographie, le filtre Millipore et le filtre sans cendre Durieux, nous avons retenu le dernier, le premier et le second renfermant davantage d’impuretés suscep­ tibles d’être activées; ils contiennent respectivement quatre et deux fois plus de sodium que le troisième (essais réalisés par radioactivation et par spectrométrie y). Chaque disque est mis en sachet suivant la technique pré­ cédente, mais l’opération est plus simple car il n’est pas nécessaire de préform er la bande. Les échantillons obtenus finalement étant très minces, on peut en m ettre 70 dans un tube d’irradiation standard CEA. Pour le comptage il suffit, après avoir enlevé le disque de son sachet, de le placer sur un porteur convenable, en le fixant au besoin avec une petite goutte de colle collodion (une colle à l’eau provoque une diffusion néfaste à la reproductibilité de la géométrie).

2.3. Tenue à l’irradiation

En aucune manière la manipulation avec les matériaux mis en oeuvre, pour des irradiations d’une heure à ÎO*2 n^/cm 2 • s n’a été gênée. Lors d’autres essais, des irradiations d’une semaine à 1011 nj/cm 2 - s n’ont pas altéré gravement le papier Durieux, qui peut encore être transvasé avec précaution de son sachet dans le porteur de comptage, à condition de ne pas le faire avec des pinces.

3. ÉTUDE DE LA VARIATION DE FLUX DE NEUTRONS DANS UNE COLONNE D’ÉCHANTILLONS

3. 1. Variation en hauteur

Calcul

On sait que la fraction d’un flux de particules absorbée par réaction nucléaire dans un échantillon mince contenant N noyaux cibles est égale à crN, o étant la section efficace totale pour la réaction considérée. Dès que le produit crN devient appréciable, on peut observer une perturbation du flux au voisinage de l’échantillon. Cette perturbation est amplifiée lorsqu’on augmente le nombre d’échantillons voisins. 84 D. BARTHOMEUF et al.

On calcule aisément, à partir des données publiées dans la littérature [6], les valeurs de ctN pour les divers noyaux constituant les échantillons. Dans notre cas, on en déduit, en %, par sachet: - enveloppe de polythene (70 mg): 0, 3 surtout dû àl’hydrogfene, - gel de silice-alumine (20 mg): 0,01 surtout dû àl’hydrogène, - COsNa2 (20mg): 0,012 dû au sodium, - disque de papier filtre (5 mg de cellulose): moins de 0,002, - nitrate de cobalt (1 mg de cobalt): 0,04, - aluminium du tube d’irradiation, sur une hauteur de 1 mm (soit 20 mg Al): 0, 01. On voit que l’effet maximum est dû au sachet de polythène, et, plus pré­ cisément, à l’hydrogène qu’il contient. Et l’on peut déjà prévoir que dans un empilement de quelques dizaines de sachets, le flux utilisable diminuera progressivement depuis chacune des extrémités jusqu’aux échantillons situés au milieu de la colonne, pour lesquels la perturbation risque d’atteindre quelques pour cent. D’ailleurs un calcul plus précis doit introduire d’autres considérations que la réaction nucléaire, en particulier le libre parcours moyen de transport et la longueur de diffusion des projectiles dans lemüieu contenant l’échantillon (dans notre cas, les neutrons thermiques et l’eau). Encore faut-il que ces valeurs ne soient pas trop différentes pour l'échan­ tillon, ou que celui-ci soit très mince. W.D. ALLEN[7] récapitule les études publiées par ses prédécesseurs sur la perturbation du flux au voisinage d’un disque très mince d’absorbant. SOLA [8] puis MARTINEZ [9] ont poursuivi l’étude de ce sujet. Ainsi les valeurs que l’on obtiendrait pour la dépression du flux au voisinage d’un de nos disques de polythène, exprimées en %, sont les suivantes: a) selon BOTHE [10] et TITLE [11], vérifiés aussi par KLEMA et RICHTIE [12] : 0,5, b) selon SKYRME [13], vérifié aussi par THOMPSON [14] : 0,6, c) selon HUGHES [15] , CHRISTY [16] et TITLE [11] : 0,3, d) selon MEISTER [22] : 0,1. Ne compter avec l’absorption se justifie dans les cas limites, en parti­ culier 123] si les rapports de modération sont égaux pour l’élément absor­ bant et pour le modérateur de la pile (dans notre cas, respectivement les substances hydrogénées et l’eau, ils sont assez voisins). Ces calculs nous conduisent seulement à une estimation de l’effet global attendu pour un nombre assez important d’échantillons: ici quelques pour cent, avons-nous dit. Si l’on obtient, comme c’est le cas, une valeur assez élevée pour introduire une erreur appréciable en analyse par activation, il est nécessaire de reconsidérer la situation, car en dehors de géométries très particulières et pratiquement irréalisables, il est fort peu commode de passer de la perturbation provoquée par un échantillon en son voisinage, à celle qui peut exister en tout point d’un volume contenant plusieurs échan­ tillons. On peut alors essayer de traiter le problème uniquement à partir de l’absorption des neutrons dans l’ensemble du montage, en supposant que le flux dans lequel est placé le tube d’irradiation est isotrope. Le cas habituel d’un tube d’irradiation plein d’échantillons est repré­ senté sur la figure 2 (coupe du cylindre de rayon r et de hauteur 2h par un plan axial). La symétrie du système nous permet de considérer seulement ANALYSE DE ROUTINE PAR RADIOACTIVATION NEUTRONIQUE 85

A i ТГ ' ¡ l

P!

°¥

— i— B

Figure 2

Géométrie d’une colonne d'échantillons. les valeurs du flux le long de l’axe. En un point P de celui-ci arrive uni­ quement la fraction e"^ (si 1 = MP) des neutrons dirigés suivant MP. Le flux est alors proportionnel à +—1Г 2 J e-*11 de. 1Г "T Les bornes tiennent compte de la symétrie par rapport à AB. Le facteur de transmission se calcule en considérant d’une part la valeur de ц = ZoiViVi étant le nombre par cm3 de nucléides de l’espèce i ayant une section efficace de uipour la réaction avec les neutrons), d’autre part les discontinuités en C et D, qui conduisent à 1 = r/cos в pour M situé entre C et D, et à 1= y/cos (jr/ 2 - 0 )pour M situé entre B et C ou D et A (y = AP). En particulier, pour le flux en A il n’y a pas d’absorption entre 0 et + n¡2, et y = 2h. Pour le flux en B, il suffit de prendre le double de l’inté­ grale calculée entre 0 et +ît/2 avec y = h. Toutes ces intégrales se cal­ culent, au mieux, graphiquement. Il est intéressant de confronter un tel calcul avec les résultats expéri­ mentaux de HUGHES et LEVIN [17], obtenus pour des cylindres de cobalt caractérisés par r = 3,75 mm et h = 15 mm. Le calcul précédent, appliqué à ces cylindres donne Фо/Фа = 0,27. Les activités Aq et Ад des petits disques de cuivre de 1 mm de diamètre, placés en ces points pour servir de détec­ teurs, devraient être dans le même rapport, car leur taille influe très peu. Hughes et Levin ont mesuré Aq /A a = 0,32. L’accord est sans doute satis­ faisant, car on n’est pas très sûr de l’isotropie du flux de neutrons utilisé. La situation est un peu plus délicate dans notre cas. Les dimensions du tube d’irradiation sont environ le double de celles des cylindres de cobalt de Hughes et Levin, la diffusion dans le polythène est plus forte que dans le cobalt, et d’ailleurs voisine de celle qui existe dans le modérateur d’une pile. Elle provoque la diminution du nombre de neutrons parvenant en P à partir de M suivant MP, mais elle donne lieu à l’apparition en P des neu­ trons d’autres'provenances. En tous cas, si l’on ne considère que l’absorp­ 86 D. BARTHOMEUF et al. tion, pour une colonne de 60 sachets de polythène contenant des disques de papier sur lesquels on a déposé des quantités égales (environ 1 mg) de cobalt à partir d’une solution de nitrate, le calcul précédent indique A o /A a - 0,995. Le calcul d’erreur présenté plus loin montre que chaque mesure est enta­ chée d’une erreur d’environ 2%. Même avec un nombre de points important, on ne peut pas s’attendre à déceler la dépression de flux O si le flux ex­ térieur est isotrope et constant dans la zone d’irradiation. Les expériences réalisées, que nous allons décrire maintenant, le con­ firm ent mais indiquent surtout que la condition d’isotropie et de constance du flux est rarem ent réalisée.

Mesures La figure 3 montre en effet l’activité /3, ainsi que l’activité y d es deux pics totaux du 60Co, de 60 disques, irradiés en empilement (voir para­ graphe 2.2.), durant une heure au flux d’environ 1012 n/cm2 • s dans la pile piscine MÉLUSINE du Centre d’études nucléaires de Grenoble, le trentième disque étant situé dans le plan médian neutronique du cœur. On n’observe pas de dépression de flux, comme on s’y attendait.

5000 ■

0 0.0 o o 4500 -

4000-

P0SITI0N DANS LE TUBE

Figure 3

Activité de soixante échantillons disposés en colonne et irradiés au même flux.

Cependant le tube contenant cette charge était l’un des quatre tubes irradiés en même temps dans la pile suivant le schéma de la figure 4. Il s’agissait du tube n°4. Les trois autres contenaient des échantillons pour le dosage du sodium dans des gels de silice-alumine, l’absorption des neu­ trons par chacun d’eux étant très comparable à celle provoquée par un échan­ tillon de cobalt. Les étalons de carbonate de sodium répartis dans ces tubes ont montré des activités que nous reproduisons sur la même figure, où la précision globale est traduite par les traits verticaux. Les deux tubés les plus éloignés du cœur ont été affectés d’une dépression de flux en leur sommet, celui qui se trouvait dans le plan frontal du tube contenant les échantillons de cobalt semble, comme ce dernier, ne pas manifester de dépression de flux. ANALYSE DE ROUTINE PAR RADIOACTIVATION NEUTRONIQUE 87

Figure 4

Activation d'un groupe de tubes.

Dans une expérience précédente, où des précautions avaient été pour­ tant prises en vue d’obtenir un flux constant, nous avons trouvé cependant, pour l’activité de 60 échantillons de cobalt, la répartition de la figure 5, aussi bien en comptage j3 qu’en comptage des pics totaux de spectres y. On observe d’ailleurs, pour cette dernière expérience, une variation d’allure périodique du flux de neutrons, telle que suivant la région on peut avoir d’un échantillon à l’autre .une différence relative d’aussi bien 2% que 0,2%.

3.2. Variation en largeur

Le flux de particules varie très rapidement lorsqu’on s’éloigne de la source, et il en résulte deux types d’erreurs possibles. La première est due à la précision de l’empilement des échantillons. Le dispositif expérimental que nous avons décrit permet d’empiler les sachets de façon que leurs centres soient alignés sur l’axe de la colonne à 0,5 mm près. Ce décalage introduit, lors des irradiations dans MÈLUSINE, une variation relative du flux de neutrons d’environ 0,5%. La seconde se produit si l’on veut confectionner plusieurs échantillons pour le comptage avec le contenu d’un seul sachet. La figure 6 illustre un tel effet: deux échantillons de comptage sont réalisés pour chaque sachet de carbonate de sodium. L’erreur qui en résulte pour la mesure de l’activité 88 D. BARTHOMEUF et al.

Figure 5

Activité de soixante échantillons indiquant la variation du flux de neutrons dans l'espace utilisé pour l'irradiation.

Figure 6

Effet de la variation du flux de neutrons le long du diamètre d'un échantillon sur un double prélèvement. par mg de sodium atteint 5% si on se fie à l’activité d’une seule des deux p r is e s .

4. DOSAGE DU SODIUM DANS LES GELS DE SILICE-ALUMINE

Les diverses modalités d’irradiation et de comptage, ainsi que leurs bases, ont été décrites de manière détaillée dans les deux sections précé­ dentes. Il reste seulement à préciser que les étalons de carbonate de so­ dium sont intercalés régulièrement dans la file des échantillons à doser, à raison de un étalon pour quatre échantillons inconnus. Ensuite a lieul’irra­ ANALYSE DE ROUTINE PAR RADIOACTIVATION NEUTRONIQUE 89 diation au flux convenable, soit 1010 pour les disques de papier filtre impré­ gnés de 10 mm3 de solution contenant de 3 • 10"4 à 10-3 mg de sodium, et 109 n/cm2, s dans le cas des poudres contenant de 0,25 à 5% en poids de sodium. Dès le retour au laboratoire, chaque sachet est ouvert et son con­ tenu placé dans la coupelle de comptage. Dans le cas des poudres, la quantité versée et tassée dans la coupelle de comptage, comprise entre 19 et 21 mg, est en même temps pesée avec une précision de ± 0,05 mg, puis la coupelle est recouverte de scotch. Les principales réactions nucléaires dues aux neutrons thermiques se produisant au cours de l’irradiation sont les suivantes : 27Al (n, -y)28Al (période: 2,3 min), 3oSi (n, 7 )31Si (période: 2,6 h), % a(n, y)24Na(période: 15 h).

De plus les neutrons rapides donnent lieu à la réaction parasite 27A 1 (n, a)24Na sur l’aluminium. Mais la section efficace de cette réaction est faible, elle ne devrait être prise en considération que pour m esurer des teneurs en sodium inférieures à 0,01% [ 18J. Notre dosage est basé sur la troisième des réactions (n, y) ci-dessus. L ’a c tiv ité en 28A 1 introduite par la prem ière est rapidement réduite à une valeur négligeable. Par contre il faut attendre 24 heures pour que l’activité due au31Si ne gêne pas. Ce temps a été déterminé par de nombreuses courbes de décroissance. Après cette période de refroidissement, on compte toutes les coupelles. Celles des étalons permettent d’établir la courbe de variation du taux de comptage par mg de sodium le long de l’accordéon irradié. On en déduit la quantité de sodium pour chaque inconnu.

4.1. Précision de la méthode

Précision sur le taux de comptage d ’un échantillon inconnu a) Sur la pesée d’un échantillon de poudre: 0, 2%. Sur le pipettage de 10 mm3 de solution et dépôt sur les disques de papier filtre: 0, 5%. b) E rreur statistique de comptage inférieure ou égale à 1%: en faisant deux comptages de chacun au moins 10 000 coups, à des temps différents et en tenant compte ensuite de la période connue de décroissance. c) Chaque taux de comptage donne lieu à un certain nombre de corrections. - L’efficacité du tube de Geiger-Müller est testée fréquemment à l’aide d’un étalon d’uranium. La précision de la correction éventuelle est liée à l’erreur statistique de comptage et peut introduire une erreur de 0, 5%. - Déduction du mouvement propre. - Correction de temps mort. Pour que l’erreur introduite par cette correction soit négligeable, on ne dépasse pas le taux de comptage de 10 000 c/m in avec un tube de temps mort 200jus. - Correction d’autoabsorption, due à la différence des poids des échan­ tillons (poudres ou disques de papier) pour une même surface occupée. Elle est faible, de l'ordre de 0,5%, et établie avec une précision très suffisante à partir du parcours des /3 dans les échantillons, lui-même pris égal au parcours dans 1' aluminium donné par la loi de Feather et considéré comme égal à sept fois le parcours-m oitié [19]. 90 D. BARTHOMEUF et al.

- Décroissance radioactive du sodium-24, suivant la période ae 15, 0 ± 0, 05 heures [20, 21]. D’où découlent deux corrections: La durée des comptages intervient d’abord, puisque 6 minutes entraûient une décroissance de 0, 5%. La correction pour des temps de comptages diffé­ rents se fait avec une précision suffisante. Il faut ensuite comparer tous les taux de comptages à une même origine des temps. L’imprécision sur la période conduit à une erreur, proportionnelle au temps de dé­ croissance, qui atteint 0, 25% pour une période. L’ensemble des corrections discutées dans ce paragraphe c) introduit une erreur inférieure ou égale à 1%. d) Déduction du taux de comptage correspondant à la même quantité de poudre «sans sodium» ou au disque de papier non imprégné. Cette correction est inférieure à 10% des taux de comptage les plus faibles, donc faite avec une précision suffisante. Elle correspond seulement au sodium présent à l’état d’impureté dans le gel de silice-alumine, les solutions, ou le p a p ie r .

Précision sur le taux de comptage par milligramme de eodium

Chaque étalon est traité comme il vient d’être dit. Mais le fait d’utiliser pour les étalons la courbe moyenne tracée à l’aide d’une dizaine de points ramène l’erreur globale à environ 1%.

Erreur totale sur la détermination des teneurs inconnues

L’ensemble des sources d’erreurs discuté aux paragraphes relatifs à là précision sur le comptage d’un échantillon inconnu, conduit à une précision d’environ 2% sur le taux de comptage d’un échantillon inconnu. Puisqu’on utilise ensuite le taux de comptage par mg de sodium, connu à 1% près, la concentration est connue à 3% près. Dans le cas de taux de comptage faibles qui ne peuvent être poursuivis très longtemps, l’erreur statistique entraîne une augmentation de cette erreur, qui peut atteindre 5%. Nous avons confronté nos résultats avec ceux de l’analyse chimique pra­ tiquée en même temps sur quelques échantillons de poudre. Ils concordent bien, dans la limite des précisions respectives des deux méthodes, comme le montrent les valeurs des concentrations, exprimées en % en poids, figu­ rant dans tableau I. Il est bon de noter que la précision de l’analyse par voie

TABLEAU I

RÉSULTATS COMPARÉS DE L’ANALYSE CHIMIQUE ET DE L’ANALYSE PAR RADIOACTIVATION DU SODIUM DANS LES GELS DE SILICE-ALUMINE

ECHANTILLON III Ш IV 1 2 3

Na par activation 1,56 1,65 4 ,3 4 .8 1,61 1,89 2,78

Na par voie chimique 1.77 1.47 4 ,4 4 .8 1.95 1.98 2.90 ANALYSE DE ROUTINE PAR RADIOACTIVATION NEUTRONIQUE 91 chimique est de 2 à 5% suivant les cas. Une série de m esures d’activités de poudres imprégnées de 24 Na nous a donné une reproductibilité, en l’ab­ sence de problèmes de flux neutroniques, comprise entre 1 et 2%.

4. 2. Coût de la méthode

Temps nécessaire

Mise en sachets, expédition, réception, confection des échantillons de comptage, comptages, calculs nécessitent une heure de travail par échan­ tillon de poudre, et quarante minutes pour un échantillon réalisé à partir d’une solution. Ces temps sont tout-à-fait compétitifs de ceux des autres m é th o d e s .

Frais d'irradiation

Le coût d’une irradiation et des frais d’expédition (de Lyon à Grenoble et retour) ne dépasse pas 2 F par échantillon. Dans le cas de flux faible comme celui que nous utilisons pour nos teneurs qui sont relativement impor­ tantes, il s’agit même seulement de 1 F par échantillon.

Prix de l'appareillage De l’ordre de 8000 F.

5. CONCLUSION

Nous avons décrit en détail une technique permettant d’irradier des quan­ tités suffisantes d’échantillons destinés à l’analyse par radioactivation de r o u tin e .

Le dosage du sodium, à des concentrations comprises entre 0,25 et 5% en poids dans les gels de silice-alumine, est ainsi effectué de façon systé­ matique sans aucune opération chimique, à l’aide d’un compteur de Geiger- Müller ordinaire. La précision atteint la valeur 3%, la durée et les frais de l’opération par échantillon sont compétitives de celles des autres mé­ thodes. On prélève 20 mg seulement pour les solides et 10 mm3 seulement pour les solutions.

D’une façon très générale, la répartition d’un flux de neutrons dans une colonne d’échantillons, dont nous avons présenté une étude, nécessite à la fois la présence d’un assez grand nombre d’étalons de l’élément à doser (souvent jusqu’à un étalon par échantillon inconnu comme le pratique WINCHESTER 15] pour des dosages analogues) et l’établissement de la courbe de variation de l’activité spécifique le long de la colonne. Nous présentons une critique de la précision. Valable d’une façon plus générale, elle montre qu’il est actuellement difficile de demander à l’analyse par radioactivation une précision meilleure que 3%. 92 D. BARTHOMEUF et al.

REMERCIEMENTS

Nous remercions M. P.Turlier pour ses dosages photométriques de cobalt à l’occasion des expériences sur la répartition des flux de neutrons, et M. A. Laurent pour son assistance technique tout au long de cette étude.

RÉFÉRENCES

[1]KOCH, R.C., Activation Analysis Handbook, Academic Press, New York (1960). GIBBONS, D. , LOVERIDGE, B.A. and MILLETT, R.J. , Radioactivation Analysis, a bibliography,Rapport AERE I/R 2208 (1957). GIBBONS, D ., MAPPER, D ., MILLETT, R.J. et SIMPSON. H., ibid., 1er supplément (1960). BOCK-WERTHMANN, W. und SCHULZE, W. , Aktivierungsanalyse, Rapport AED-C-14-1. [2]HOSTE,J., BOUTEN, F. and ADAMS, F ., Minor constituent analysis with neutron activation,Nucleonics 19, 3(1961) 118. [3] BARTHOMEUF, D ., Contribution à l*étude des propriétés acides des gels mixtes silice-alumine, Thèse 3ème Cycle, Lyon (1962). [4]REIFFEL, L. and STONE, C. A ., Neutron activation analysis of tissue: measurements of sodium, potassium and phosphorus in muscle, J. Lab. Clin. Med. 49 (1957) 286. L5] WINCHESTER, J. W ., Determination of potassium in silicate minerals and rocks by neutron activation analysis, Anal. Chem. 33 (1961) 1007. SCHROEDER, G .L. and WINCHESTER, J. W ., D eterm ination of sodium in silicate minerals and rocks by neutron activation analysis, Anal. Chem. 34 (1962) 96. [6]KOC«, R.C., loc. cit. [11 SULLIVAN, W .H ., Trilinear Chart of Nuclides, Government Printing Office, Washington (1957). [7] ALLEN, W .D., Neutron Detection, George Newnes, Londres (1960). [8] SOLA, A ., Flux perturbation by detector foils, Nucleonics 18,3 (1960) 78. [9] MARTINEZ, J.S ., Neutron self-shielding in one-dimensional absorbers. Rapport UCRL-6526 (1961). [10]BOTHE, W ., Zur Methodik der Neutronsonden, Z. Phys. 120 (1943) 437. [11]TITLE, C.W ., Slow neutron detection by foils. Nucleonics 9, 1 (1951) 60. [12] KLEMA, E. D ., R1CHTIE, R .H ., Therm al neutron flux m easurements in graphite using gold and indium foils, Phys. Rev. 87 (1952) 167. [13]SKYRME, T. H .R., Reduction in neutron density caused by an absorbing disk, Rapport AERE MS 91 et91a (1961). [14] THOMPSON, M.E., Rapport AERE RP/R 1549 (1954) et J. Nucl. Engng 2 (1955) 286. [15]HUGHES, D .J., Pile neutron research, Addison-Wesley Publishing Company, Cambridge (1953). [16]CHRISTY, R.F., Rapport MDDC-1175 (1947). [17] HUGHES, D.J. and LEVIN, J., Flux-depression and self-protection in the production of radio-cobalt, Nucleonics 11, 7 (1953) 8. [18]ROCHLIN, R .S., Fission-neutron cross sections for threshold reactions, Nucleonics 17, 1 (1959) 54. [19]GLENDENIN, L.E., Nucleonics 2, 1 (1948) 12. _ [20] STROMINGER, D ., HOLLANDER, J. M. et SEABORG, G. T . , Table of Isotopes, Rev. Mod. Phys. 30 (1958) 610. [21] JOZEFOWICZ, E .T ., Half-life of sodium-24, Nukleonika 6 (1961) 379. [22] MEISTER, H ., Storung der Neutrondichte in der Umgebung einer absorbierenden Sonde, Z. Naturf. 11a (1956) 356. [23] RANDALL, J. D. et WALKER, J. V ., The elimination of flux perturbation associated with neutron detecting foils, Nucl. Sc. Engng 11 (1961) 69.

DISCUSSION

H. KEPPEL: If you don’t have your own neutron source and you are dependent on an outside reactor, how do you guarantee the accuracy of your re s u lts ? ANALYSE DE ROUTINE PAR RADIOACTIVATION NEUTRONIQUE 93

P. BUSSÍERE (on behalf of D. Barthomeuf, et al. ): What happens is the following. We irradiate up to 40 samples, each containing 20 mg of powder. Of these, 30 are unknown samples and 10 are standards spaced out at identical intervals. In this way a curve can be plotted providing a direct indication of the activity per milligram of the element being analysed. Once the activity of the unknown samples has been determined, reference is made to this curve to ascertain, at each position on the column, the counting rate per m illigram of the element being analysed. V. P. GUINN (Chairman): I have a certain amount of experience with the analysis of silica alumina as a cracking catalyst and I think it is im ­ portant to realize that the situation that has just been described — the acti­ vation analysis of silica-alum ina gels for sodium — is a fairly exceptional one. With this particular type of sample there is no substance that has a half-life comparable to the Na24 as well as high-energy beta particles. This makes it possible to work with a Geiger counter on a very economical and routine basis. Oxygen determinations present a sim ilar situation because only №® will provide the extremely high-energy gamma rays or beta part­ icles required. Here again a relatively simple counting system is possible. However, if one needed to analyse this same type of sample for a wide variety of elements (V, Na, Ni, Cr, etc. ) — and in the case of silica-alumina catalysts this would certainly be of interest in the petroleum industry — the problem would be much more complex. Multi-channel gamma-ray spectro­ metry and even radiochemical separations would then be needed to analyse some of the substances at the levels at which they occur. At the Shell Development Company laboratories, where I used to work, a great deal of activation analysis of this kind, with cracking catalysts, was carried out by my group.

THE USE OF SHORT-LIVED RADIOACTIVE ISOTOPES IN AN ACTIVATION ANALYSIS SERVICE PROGRAMME

D. GIBBONS AND H. SIMPSON WANTAGE RESEARCH LABORATORY, WANTAGE, ENGLAND

Abstract — Résumé — Аннотация — Resumen

THE USE OF SHORT-LIVED RADIOACTIVE ISOTOPES IN AN ACTIVATION ANALYSIS SERVICE PRO­ GRAMME. Short-lived radioisotopes, especially those with a half-life of one hour or less, offer several ad­ vantages when used in activation analysis. These include more favourable sensitivities and selectivities (in some cases); shorter total processing times, giving the results more rapidly and often more cheaply; and, in non-destructive analyses, the possibility of re-activation for repeat determinations. The disadvantages associated with such short half-lives are gradually being overcome. Rapid radio­ chemical separation techniques have been developed so that processing can be completed without excessive radioactive decay. The availability of improved gamma-ray spectrometers coupled with modern data handling techniques has extended the range of non-destructive analyses, thus reducing the need for radiochemical purifi­ cations. The uses of short-lived radioisotopes in activation analyses are illustrated by reference to actual analytical problems encountered in the operation of an activation analysis service programme. Thus, in the determination of rubidium in caesium salts, the use of 1.0-min Rb86mconsiderably reduces the build-up of matrix activity with little loss in sensitivity. In the determination of calcium ip tissue, 8.8-min Ca4® gives quicker results since the irradiation time is much reduced and the decay curve can be followed for a reasonable number of hálf-lives in less than an hour. The determination of selenium can be accomplished non-destructively in some biological materials with enhanced sensitivity using 17.5-s Se77111. In complex materials, where a chemi­ cal separation is necessary, 18.6-min Se®1 still gives a more favourable sensitivity than Se75. In the determi­ nation of cobalt in the presence of nickel, long irradiations to produce Co60 produce interfering amounts of Co® by the (n,p) reaction on nickel. Short irradiations, followed by measurement of 10.5-min Co6cm, reduce this interference considerably and also give an improved sensitivity. Several types of automatic units for use in counting short-lived radioisotopes are described, including photographic recording techniques, an automation sample changer and various programming units.

EMPLOI DES RADIOISOTOPES A COURTE PÉRIODE DANS UN SERVICE D'ANALYSES PAR ACTIVATION. Les radioisotopes à courte période, notamment ceux dont la période est égale ou inférieure â une heure, pré­ sentent divers avantages lorsqu'ils sont utilisés pour l'analyse par activation. Parmi ces avantages on peut citer les suivants: sensibilité et sélectivité (dans certains cas) plus favorables; temps de traitement total plus court, d*où résultats plus rapides et souvent â meilleur compte; enfin, pour les analyses non destructives, possibilité de réactivation pour de nouvelles mesures. On surmonte progressivement les difficultés inhérentes à des périodes aussi comtes. On a mis au point des méthodes de séparation radiochimique rapide telles que le traitement peut être effectué sans qu'il se produise une désintégration radioactive excessive. L'emploi de spectromètres gamma perfectionnés et de méthodes modernes de traitement des données a élargi le champ des analyses non destructives, réduisant ainsi la nécessité de procéder à des purifications radiochimiques. Les auteurs illustrent les applications des radioisotopes à courte période aux analyses par activation en décrivant les problèmes d'analyse qu'ils ont eu effectivement à résoudre dans leur service d'analyse par acti­ vation. C'est ainsi que si l'on veut déterminer la quantité de rubidium présente dans des sels de césium, l'emploi de ^^R b, dont la période est de 1,0 min, réduit considérablement l'accumulation de l'activité matricielle pour une perte de sensibilité faible. Pour déterminer le calcium présent dans le tissu, c'est le49Ca, dont la période est de 8,8 min, qui donne les résultats le plus rapidement étant donné que la durée de l'irradiation est très réduite et qu'en moins d'une heure on peut suivre la courbe de désintégration pour un nombre appré­ ciable de périodes. La détermination du sélénium dans certaines matières biologiques peut être réalisée par analyse non destructive avec une sensibilité accrue, à l'aide de ™mSe, dont la période est de 17,5 s. Dans 95 96 D. GIBBONS and H. SIMPSON le cas de matières où une séparation chimique est nécessaire, *iSe, dont la période est de 18,6 min, donne une sensibilité meilleure encore que76Se. Dans la détermination du cobalt en présence du nickel, des irra­ diations prolongées jusqu'à ce que l'on obtienne du eoco produisent des quantités interférentes deHCo, dues â la réaction (n,p) sur le nickel. Cependant de brèves irradiations, suivies de la mesure de'œmCo, dont la période est de 10,5 min, réduisent sensiblement cette interférence et améliorent la sensibilité. Les auteurs décrivent plusieurs types d'appareils automatiques pouvant être utilisés pour le comptage des radioisotopes à courte période ainsi que des méthodes d’enregistrement photographique, un changeur d'échan» tillons automatique et divers ensembles de programmation.

ИСПОЛЬЗОВАНИЕ КОРОТКОЖИВУПИХ РАДИОАКТИВНЫХ ИЗОТОПОВ В ПРОГРАММЕ АКТИВАЦИОННОГО АНАЛИЗА. Короткоживущие радиоизотопы, особенно с периодом полураспада, равным одному часу или менее, об­ ладают некоторыми преимуществами при использовании в активационном анализе. К числу этих пре­ имуществ относятся: более высокая чувствительность и избирательность (в некоторых случаях)¡мень­ шая продолжительность обработки, что приводит к экономии времени и средств; возможность повторной активации для проведения вторичного определения в случае недеструктивного метода анализа. Постепенно устраняются недостатки, связанные с коротким периодом полураспада. Разработаны методы быстрого радиохимического разделения, в результате обработка может быть завершена без существенного радиоактивного распада. Наличие совершенных гамма-спектрометров вместе с методами обработки современных данных расширило число недеструктивных аналитических методов, тем самым уменьшилась необходимость проведения радиохимической очистки. « Использование короткоживущих изотопов в активационном анализе иллюстрируется ссылкой на насущные проблемы анализа, разрешение которых предусмотрено в осуществлении программы актива­ ционного анализа. Так, при определении рубидия в солях цезия применение Rbseu с десятиминутным периодом полураспада значительно уменьшает рост обшей активности при небольшой потере чувстви­ тельности. При определении кальция в тканях применение Са*ь с периодом полураспада в,в минуты значительно сокращает продолжительность анализа, поскольку значительно сокращается время облучения и в течение менее получаса можно проследить за кривой распада, охватив при этом достаточное число периодов полураспада. Можно провести определение селена в некоторых биологических материалах без разрушения при увеличении чувствительности за счет использования Se7™ с периодом полураспада 17,5сек. В случае сложных материалов, для которых необходимо химическое разделение, использова­ ние Se®* дает более высокую чувствительность, чем Se79. При определении кобальта в солях никеля длительное облучение для получения Сово приводит к образованию мешающих количеств Со5в в резуль­ тате реакции (п,р). Кратковременное облучение с последующим измерением Совом с периодом полу­ распада 10,5 мин приводит к значительному уменьшению этого фона, а также улучшает чувствитель­ ность. Описываются некоторые типы автоматических приборов, используемых при измерении активности короткоживущих изотопов, включая методы фоторегистрации, автоматическая смена образцов и раз­ личные программирующие устройства.

EMPLEO DE RADIOISOTOPOS DE PERIODO CORTO EN LOS SERVICIOS DE ANALISIS POR ACTIVACION. Los radioisótopos de período corto (igual o inferior a 1 h) ofrecen diversas ventajas en lo que atañe al análisis por activación. Entre otras, un aumento de la sensibilidad y de la selectividad (en algunos casos); un tiempo total de tratamiento más corto que proporciona resultados más rápidos y con frecuencia más económicos y, en el análisis no destructivo, la posibilidad de reactivar la muestra para repetir las determinaciones. Los inconvenientes inherentes a los períodos tan cortos se van superando paulatinamente. Ya no es esencial tener acceso directo a un reactor puesto que existen laboratorios generadores de neutrones. Además, se han desarrollado técnicas de separación radioquímica rápida que permiten acabar el tratamiento antes de que la desintegración esté demasiado avanzada. Con los espectrómetros perfeccionados y las técnicas modernas de manipulación de datos se ha ampliado el campo de aplicación de los análisis no destructivos, disminuyendo así la necesidad de purificaciones radioquímicas. La memoria describe el empleo de radioisótopos de período corto en análisis por activación citando problemas analíticos reales que se presentan en los servicios de análisis por activación. Por ejemplo,empleando rubidio-86m de 1,0 min al determinar el rubidio en sales de cesio se reduce considerablemente el incremento de actividad de la matriz, en tanto que la sensibilidad disminuye poco. Al determinar el calcio en tejidos, el calcio-49 SHORT-LIVED RADIOACTIVE ISOTOPES IN ACTIVATION ANALYSIS 97 de 8,8 min permite obtener los resultados más rápidamente, pues el tiempo de irradiación se reduce aprecia- blemente y en menos de una hora se pueden observar las curvas de desintegración correspondientes a un número razonable de períodos de semi-desintegración. El empleo de selenio-77m de 17,5 s permite determinar con mayor sensibilidad este elemento en algunas sustancias biológicas aplicando procedimientos no destructivos. En materiales complejos, donde es necesaria una separación química, el selenio-81 de 18;6 min da una sensi­ bilidad todavía mayor que la del selenio-75. En la determinación del cobalto en sales de níquel, las irradia­ ciones largas paraobtenercobalto-60se producen por la reacción (n,p) con el níquel cantidades de cobalto-58 que perturban las determinaciones. Las irradiaciones cortas seguidas de la medición del cobalto-60m de 10,5min reducen considerablemente estas interferencias y mejoran también la sensibilidad. Se describen varios tipos de aparatos automáticos adecuados para el recuento de radioisótopos de período corto; técnicas de registro fotográfico,cambiamuestrasautomáticos y diversos equipos de programación.

1. INTRODUCTION

The principles and applications of activation analysis have been described extensively [1,2], but will be reviewed briefly here. When a m ass M of an element is irradiated with a flux 0 of nuclear particles per cm2 per second, the radioactivity R induced is

R = 0. 6O 25(M /A )0o-f { l - e '° - 693t/T}{e'0-693T/T} (1) disintegrations/s w h e re : A is the gram atomic weight of the element a is the cross-section in barns for the nuclear activation reaction f is the fractional abundance of the target isotope t is the half-life of the induced radioactivity t is the irradiation time in the same units as т. T is the decay time between irradiation and measurement, in the same units as т. This provides a sensitive measure of minor constituents of a sample [3, 4, 5] if the induced radioactivity due to one component can be distinguished or separated from all other radioactivities present. Simple mixtures can often be resolved by decay-curve analysis while, in more complex samples, gamma-ray spectrometry may be used to measure one gamma-ray emitting isotope in the presence of others if the relative energies and intensities are suitable. If the gamma-ray spectrum is too complex, it may be difficult to measure a particular gamma-ray, especially if higher-energy radiation is present. Such interferences may often be eliminated by use of more complex apparatus [6, 7, 8] or by simple chemical separations in the presence of an inactive carrier [9, 10]. For really complex samples, or where maximum sensitivity is required, extensive radiochemical purification with added carrier may be necessary [11, 12] but, after such purification, a simple counting system (such as a GM counter) usually suffices for the m easure­ ment of radioactivity.

2. ADVANTAGES OF SHORT-LIVED RADIOISOTOPES

Short-lived radioisotopes, especially those with a half-life of one hour or less, offer several advantages when used in activation analysis. 98 D. GIBBONS and H. SIMPSON

TABLE I

DETERMINATION OF CERTAIN ELEMENTS BY MEANS OF SHORT-LIVED AND LONG-LIVED RADIOISOTOPES

Element Active Half- "о-Г Time Detectable** Radiation determined isotope life (b) irradiated* (g) measured

Si31 2.6 h 3.4X 10"3 1 d 2 X 10-7 6 Silicon A l28 2.3 min 3.7 X 10'3 10 min 2 XIO-7 в(у) p32 14.2d 5.7 X 10"2 Id. 3 X 10’4 в Sulphur s37 5.0 min 2. 0 X 10"5. 30 min 6 X 10'5 8

Ca45 153 d 1.3 x io -2 1 d 2 X 10-4 в Calcium C a49 8 .8 min 2.1 X 10-3 1 h 10"6 а

Sc46 84 d 2.2 X 10 1 d 3 XlO*8 В. Г Scandium Sc46" 1 20 s 1.0 X 10 2 min 4 X10"“ Г Co60 5.2 yr 3.6 x io 1 d 4 X 10“ 7 Cobalt в. Г Co“m 10.5 min 1.6X10 1 h io-9 У Zn69m 13.9 h 1.9 X 10-2 1 d 10"7 в, у Zinc Zn69 59 min 1.9 X 1 0 '1 1 h 2 X 10"8 в Se75 120 d 2.3 X 10-1 1 d З Х Ю '6 у Selenium Se771" 17 s 6.3 X 1 0 '1 2 min 10-8 У

Br82 35.9 h 1.8 1 d 10-8 В. Г Bromine Br80 17.6 min 4.3 1 h 10"9 в

Rb86 18.6 d 5.4 X 10'1 1 d 2 XlO -7 в Rubidium Rbs6m 1.0 min 3.6 X 10‘2 5 min 4 X 1 0 '7 У

Sr89 51 d 4 .2 X 10"3 1 d 5 X 10‘ 5 в Strontium Sr87m 2.9 h 1.3X 10"1 1 h io-7 У

Ru103 40 d 4 .5 X 1 0 '1 1 d 5 XlO-6 S, у Ruthenium Ru105 4 .5 h 1.3X 10"1 l h 2 X 10"7 8

Ag110m 253 d 1.6 1 d 10"6 Г (В) Silver

Notes: This Table was compiled using the data of BAUMGARTNER [19], but for the thermal and fast neutron fluxes found in BEPO. The radioisotopes listed have been selected to show the various advantages of using short-lived radioisotopes. In each case, the most favourable long-lived and the most favourable short-lived radioisotopes are given.

* The irradiation time for the longer-lived radioisotopes is limited to 1 d. Even this may be longer than the normal operating period of a small research reactor. The irradiation time for the shorter-lived radio­ isotopes is limited to 1 h or the approximate saturation time, whichever is the shorter. ** The detection sensitivity is calculated on the basis of the most favourable counting method (beta particles orgamma-rays as appropriate), with a requirement of 100 cpm for beta particles and 180 cpm (high energy) and 250 cpm (low energy) for gamma-ray spectrometry. These levels are taken to give comparable values for the expression (counting rate)2/background. SHORT-LIVED RADIOACTIVE ISOTOPES IN ACTIVATION ANALYSIS 99

TABLE I (cont'd)

Elem ent Active H alf- " o -f" Tim e Detectable** Radiation determ ined isotope life (b) irradiated * (g) measured a < 00 2 min io-“ В Silver 24 s 5 .3 In m m 50 d 2.4X 10"2 1 d 10”T 8 Indium In116 m 54 min 1 .5 X 10"2 l h >: 6 X 1 0 '11 В

SnE1 27 h 4 .6 X 1 0 '2 1 d 5 X lO -1 В Tin Sn125 9 .5 min 1.2 X 10-2 1 h 3 X 10-’ 8(7)

T e “ 7 9 .4 h 1 .5 X 10м 1 d io-7 в Tellurium Т е 81 25 min 7 .7 X lO -2 1 h 6 X 1 0 -8 в. 7

Ba131 12 d 9. 5 X 10-3 1 d Poor У Barium Bans 85 min 3 .6 X W 1 1 h 4 x 1 0 -* в, У

Hf181 45 d 3 .5 1 d 2 X 1 0 -7 Г (в) Hafnium Hf175m 19 s 2 .0 X 10 2 min io-9 У

Tl204 3 .6 yr 2.4 1 d 5 x 10-6 в Thallium

Np23' 2 .3 d 3 .0 1 d 3 X 1 0 '1 в. у Uranium и 235 23.5 min 3.0 1 h 5 X 1 0 -’ в. У

2. 1. Improved sensitivities (see Table I)

For a given element, bombarded in a given flux of nuclear particles, equation (1) sim plifies to:

R « C T f { l- e '° - 693t/T} (2)

providing that R is measured within a small fraction of a half-life after the end of irradiation. Thus, the induced radioactivity (and, therefore, the de­ tection sensitivity) is dependent, mainly, on the product (a • f ). As can be seen in Table I, some elements have greater values of (cr. f) for those iso­ topes which lead to short-lived radioactivities.

Secondly, R is dependent on the saturation factor {1 - e-0'693 t/T } which approaches the maximum value of unity when t is greater than about 5T.Thus, in a given amount of available time, it will be possible for the saturation factor to approach closer to unity for short-lived radioisotopes than for longer-lived ones. This is particularly important in the use of sm all re­ search reactors as sources of activating particles, where it may not be con­ venient to operate for more than a few hours at a time. 100 D. GIBBONS and H. SIMPSON

2. 2. Increased speed of analysis

From Eq. (2), it can be seen that activation for one half-life gives a saturation factor of 0. 5. Thus, unless the maximum sensitivity is really required, there is little point in irradiating for more than one half-life. Con­ sequently, the irradiation time required is directly proportional to the half- life . Where radiochemical purifications are necessary and possible, they must obviously be streamlined to a large extent, so that processing times are reduced. Where long half-lives are used, there is a natural tendency to use less hectic and often unnecessarily elaborate separation scheme,s. Finally, one of the main checks on radiochemical purity, the measure­ ment of the half-life of the separated radioactivity, can be made in a rela­ tively short time. It is usually necessary to follow the decay of the radio­ activity for at least five half-lives. This can take an inconveniently long time with medium half-life radioisotopes and is virtually impossible with the really long-lived ones. Naturally, any reduction in the total time spent on an analysis brings down the cost involved. Thus, the use of short-lived radioisotopes, where possible, can make activation analysis more competitive with conventional methods of analysis.

2.3. Improved selectivity

Selectivity in activation analysis can be improved in several ways through the use of short-lived radioisotopes. As mentioned above, half-lives can be measured more conveniently as a check on purity. In some cases, the shorter half-life may be resolved more easily from other radioactivities present. In others, the shorter half- life may be used simply to provide a second half-life measurement as an additional check. The availability of short-lived radioisotopes, in providing a greater range of usable isotopes, enables the nuclear characteristics to be selected to make the analysis more favourable. Thus, it may be possible to select an isotope emitting much more energetic beta particles than an interfering radioactivity; or one emitting gamma-rays where the longer-lived radio­ isotope emitted only beta particles; or one where the gamma-rays are of a more conveniently measurable energy.

2. 4. Increased precision

The availability of two different half-lives, as mentioned above, means that the sample may be analysed in term s of the shorter-lived activity and then, after this has decayed away, the analysis may be repeated on the longer-lived component without re-irradiation. More important, however, in non-destructive analyses, a very short-lived impurity can often be re­ activated several tim es for repeat determinations without a significant in­ crease in the general matrix activity. Thus, a single sample can be sub­ jected to several repeat analyses, to increase precision, without introducing SHORT-LIVED RADIOACTIVE ISOTOPES IN ACTIVATION ANALYSIS 101 additional variations in the form of sample inhomogeneity. Also, where low activities are involved, even at saturation, the total number of counts re­ corded can be built up to a statistically good level by such repeat irradiations.

2, 5. Reduction of activity levels

The fact that the use of short-lived radioisotopes enables irradiation tim es to be shortened means that where m atrix activity tends to be long- lived, the build-up of induced matrix activity can be reduced. Thus, handling problems, waste disposal and non-destructive measurements are all simpli­ fied.

2. 6. Double tracer techniques

One important advantage of the use of short-lived radioisotopes is that double tracer techniques can be used. In radiochemical activation analysis, the separation is made in the pre­ sence of added inactive carrier, with the result that the chemical yield of the process can be measured. However, this means that a reasonable weight (say 10-20 mg) of carrier must be used if this yield is to be measured simply (e.g.,by weighing). Separation techniques such as ion exchange, solvent ex­ traction or evolution methods can be very rapid and simple if low ( ng) quantities of carrier are used. This situation is resolved readily by using a short-lived radioisotope for the activation analysis and then adding a longer-lived one as carrier. After the purification, the short-lived com­ ponent, resolved through decay or energy measurements, is used as a meas­ ure of the element and then, after suitable decay, the longer-lived carrier is used to measure the chemical yield.

3. DISADVANTAGES OF SHORT-LIVED RADIOISOTOPES

Most of the disadvantages associated with the use of short-lived radio­ isotopes naturally hinge on the fact that the radioactivity decays very rapidly.

3.1. Geographic problems

When short-lived radioisotopes are used in activation analysis the in­ duced radioactivity must be m easured within minutes, if not seconds, of the end of the irradiation. This implies close access to the reactor — a situation which is more easily realized now that small, low-cost, research reactors are becoming more generally available.

3.2. Processing problems

The radiochemical purification of very short-lived radioactivities is, quite obviously, a problem and, for very short half-lives, is virtually im­ possible. Fortunately, many very rapid radiochemical separations, pioneered by MEINKE and others [13, 14], are now available. Although it is not always 102 D. GIBBONS and H. SIMPSON possible to obtain a complete radiochemical purification, it is relatively easy to eliminate the bulk of the interfering activities by a simple separation to enable the analysis to be completed by gamma-ray spectrometry. In this instance, the use of more complex electronic equipment [ 7] or of modern data handling techniques [15, 16, 17], to subtract out unwanted radioactivities from the gamma-ray spectrum, enables the need for radiochemical separa­ tions to be minimized.

3.3. Counting problems

The use of very short-lived radioisotopes introduces counting problems into both gamma-ray spectrometry and simple GM counting. These problems arise from the fact that, if the period of each measurement is to be kept to a reasonably small fraction of a half-life then, in order to record a statisti­ cally good number of events, the instantaneous counting rate may need to be too high for the recording equipment, particularly for some of the "slow" gamma-ray spectrometers which are in use. Ideally, equipment with a very short dead-time is required for this type of measurement, but one solution is to use the multi-channel analyser solely to examine the purity of the gamma-ray spectrum in a single measurement, and then to follow the decay of the desired gamma-ray activity with a single channel analyser set at the appropriate energy. Where half-lives are to be determined or resolved, the counting, rate must be recorded at known intervals and, if this process is to be timed ac­ curately, it is desirable that the equipment be controlled automatically with a rapid data read-out. Since activation analysis is usually made on a com­ parative basis, it is often required to measure sample and standard in rapid succession so that, once again, a certain degree of automation is to be pre­ f e r re d .

4. AUTOMATIC EQUIPMENT

. A range of automatic equipment, for use in activation analysis, has been developed, both independently and in conjunction with Automatics Group (AERE) Harwell.

4.1. Printing scalers

The half-life of a radioisotope is probably the one nuclear characteristic measured most frequently. Naturally, this requires a series of sequential measurem ents which is easily made using an automatic printing scaler. The scaler type 1009* has a two-decade neon lamp display and can pro­ vide an output signal every 100 pulses. This output is fed into the left-hand three digits of an IVO five-digit printing register with a split printer. At the end of the counting period, determined by a timing unit type 1003, the re­ sidual information stored on the neon lamps is read out as follows. A pulse generator supplies pulses to a mechanical register in parallel with the scaler.

* This, and subsequent similar numbers refer to standard AERE electronic units. SHORT-LIVED RADIOACTIVE ISOTOPES IN ACTIVATION ANALYSIS 103

When the scaler count has been made up to 100, the "100-out" signal is not fed to the IVO unit but is arranged to trip a relay causing the subsequent scaler pulses to be diverted to the right-hand two digits of the IVO, which is now in parallel with the mechanical register. Finally, when the register peaches 100, the IVO unit prints this latter total, which corresponds with the original residual counts on the neon lamps, together with the "hundreds" total originally stored. This combined number then gives the total counts recorded. The equipment then re-sets automatically and starts a new count, either immediately or on receipt of an external command signal. This unit has a read-out time of 20 s, which is fast enough for most purposes but, for use with half-lives below one minute, it has been super­ seded by a unit [18] which is arranged to inspect the counts stored on four decades of neon lamps and to print the total on an ADDO-X printing/adding machine. This unit requires some modifications to the scaler, but has a read-out time of less than two seconds. For really high speed work, a photographic read-out unit is also avail­ able. An automatic oscilloscope camera, controlled by a sequence unit which provides fully automatic working of the scaler, is arranged to photograph five decades of neon lamps operated by a bank of three scalers. At the end of a counting period, the photograph is taken, the film wound on automatic­ ally, all units re-set and the next counting period started.

4. 2. Automatic sample changer

While the printing scaler is very useful for the determination of the half-life of a single radioactive sample, it is of little use for comparing the half-lives of two samples (e.g., an unknown and a standard) irradiated at the same time. An automatic sample changer was therefore developed to be as versatile as possible to allow the automatic determination of decay curves and beta particle energy distributions. The unit, optimistically named as an "Automatic Nuclide Comparator" provides for the counting and timing of up to six samples, at any one of five selected distances from the detector, in conjunction with up to 40 absorbers, in any one of twelve fully automatic cycles. The results are printed out se­ quentially on paper tape and include counts recorded, counting time, total time, sample number, shelf height and absorber thickness.

4. 3. Automatic gamma-ray spectrometry

The 100-channel pulse height analyser type 1363 has been modified ex­ tensively for automatic, repetitive operation, digital read-out in octal notation and analogue read-out on a strip-chart recorder. A dead-time com­ pensating unit is also included. With automatic working, the analyser and a timing scaler are allowed to count under the control of the dead-time compensating unit for a pre-set live-time. At the end of this period, both the analyser and scaler are stopped and contents of the memory are printed out in octal notation in about 3 min (slow) or 1. 5 min (fast). The slow print-out is preferred, in general, as it has a more convenient format and can be arranged to include elapsed time 104 D. GIBBONS and H. SIMPSON and channel identification. At the end of the print-out, all units are re-set and counting is re-started automatically for the same live-time as before. A plot of the gamma-ray spectrum can also be obtained, in the slow read-out mode, through a unit which decimalizes the octal information and provides an analogue signal to a strip-chart recorder which then plots a histogram of the spectrum. The two units can work independently, or in synchronisation, so that the histogram can be used for peak identification and the digital information used in any calculation of peak areas. An automatic photographic read-out unit has also been developed for use where time is particularly valuable. This is basically the same as the photo­ graphic scaler recording/control unit, but is arranged to photograph the cathode ray tube binary display and to provide fully automatic working in conjunction with the dead-time compensating unit. A sample changer has also been added recently to the 1363 system. This sample changer is a modified version of the Activated Foil Comparator type 1718, and provides for the sequential counting of up to 40 low activity sam ples.

4. 4. Delay units

While continuous repetitive counting periods are essential when dealing with very short half-lives, with somewhat longer half-lives they can result in inconveniently long counting periods or a surfeit of data points. Delay units have therefore been designedfor use with all the automatic systems described above, in which the automatic cycle is interrupted at the end of each counting period until a pre-set delay period, measured from the beginning of the counting period, has elapsed. Thus, it is possible to obtain say, 5-min counts every hour, or perhaps 10-s counts every minute. These units are also useful, when used with the automatic gamma-ray spectrometer, even when a delay is not really required. By setting the delay to be slightly longer than the real time for the most active count (usually the first one in a decay study), each subsequent count will begin at a known point in time, thus enabling the decay curve to be plotted more accurately.

5. APPLICATIONS OF SHORT-LIVED RADIOISOTOPES IN ACTIVATION ANALYSIS

The following analyses, described to illustrate the advantages outlined in Section 2 of this paper, were all made using the BEPO reactor at a flux of 1012 n/cm z s.

5.1. Determination of rubidium

The rubidium content of caesium sulphate was required as a check on the determination by flame photometry. Rubidium is usually determined, in activation analysis, via the 18. 7-d Rb86 because of the favourable abundance and activation cross-section of Rb85 . However, as can be seen from Table II (calculated from the data of BAUMGARTNER [19] ), in the presence of caesium, inconveniently high SHORT-LIVED RADIOACTIVE ISOTOPES IN ACTIVATION ANALYSIS 105

TABLE II

CAESIUM INTERFERENCE IN RUBIDIUM DETERMINATIONS

Rubidium Half- Irradiation Relative isotope - life tim e * caesium activity**

Rb86 18.7 d 5 d 20/1

Rb88 1 8 .0 min 2 h 0 .5 /1

Rb86m 1 .0 min 1 min 0.004/1

* Irradiation time chosen for comparable rubidium gamma-ray activities, allowing for differing abundances and detection efficiencies. ## Total caesium activity relative to rubidium gamma-ray activity, allow­ ing for differing abundances and detection efficiencies on a gram-for-gram basis.

caesium radioactivities are produced. Use of the 18-min Rb88 isotope re­ duces the caesium activity somewhat, but use of the 1. 0-min RbB6m isotope gives by far the best discrimination against the build-up of m atrix activity and with little loss in detection sensitivity for rubidium. In order to eliminate the effects of neutron self-shielding, the caesium sulphate samples were irradiated in solution and standards were prepared by the addition of extra rubidium (approximately equal to the amount ex­ pected to be present) to duplicate samples. The activated samples were then measured using a single-channel gamma-ray spectrometer set up to count the 0. 56-MeV photopeak. The decay of both sample and standard was fol­ lowed, and the 1. 0-min Rb86m activity resolved from the longer-lived inter­ fe re n c e . The rubidium content was shown to be 0. 6% ± 0. 05, compared to 0. 7 - 1. 0% by flame photometry.

5. 2. Determination of calcium

The use of 8. 8-min Ca49 instead of 153-d Ca4b for the determination of calcium offers several advantages. Despite the low isotopic abundance of Ca48 , the practical sensitivity is more favourable since it is possible to activate to saturation in a reasonable time (about one hour). The 3. 1-MeV gamma-ray of Ca4a is easier to detect than the weak beta particles of Ca46, and is of higher energy than many possible interfering activities. Also, once again, the decay of the radioactivity can be followed through several half- lives in less than an hour. This isotope was therefore used for the determination of relatively large concentrations of calcium in very small samples of tissue. The samples were irradiated, together with a dilute calcium solution standard, for about 10 min. The samples were dissolved by wet oxidation, in the presence of inactive calcium carrier, and the Ca49 activity was separated from the bulk of interfering activity by a single precipitation of calcium oxalate. The decay 106 D. GIBBONS and H. SIMPSON

of the 3. 1-MeV photopeak was followed, using the 100-channel gamma-ray spectrometer, and the Ca49 activity was resolved from longer-lived inter­ fe re n c e s . Comparison with the calcium standard gave a calcium content of 150 ppm.

5. 3. Determination of selenium

Selenium can be determined through a range of radioisotopes of which the three most important are perhaps 120-d Se75, 18-min Se81 and 17. 5-s Se77m. While Se75 provides ample time for extensive radiochemical separations, and emits easily-detectable gamma-rays, it offers the least favourable detection sensitivity. Se81 offers improved sensitivity but, being a pure beta particle em itter, cannot be used for non-destructive analysis. On the other hand, Se77m provides even better sensitivity together with an easily-meafeured gamma-ray. The latter isotope was chosen for the determination of selenium in small samples of arsenic selenide where, although high sensitivity was not essential, the method had to be non-destructive and give the minimum of matrix activation as the samples were required for further experiments after a n a ly sis. Samples and standards (consisting of known mixtures of arsenic and selenium) were irradiated individually for one second, in the presence of gold foil flux monitors, and were transferred rapidly to a single-channel gamma-ray spectrometer, where the decay of the 0. 16-MeV photopeak was followed using the photographic recording scalers. The gold foils were then m easured later and used to correct for slight flux variations between the irradiation of sample and standard. The selenium results were checked by several repeat analyses. These values were in good agreement, but showed that the arsenic selenide samples, from the one specimen, were quite inhomogeneous (Table III). The very short-lived Se77m activity could not be used for the determ i­ nation of selenium in dried milk samples, as several other easily-activated elements producing short-lived activities were also present. The 18-min Se81 isotope was used, therefore, in conjunction with a rapid radiochemical

TABLE III

DETERMINATION OF J3ELENIUM IN ARSENIC SELENIDE

Selenium found Sample No. (Average) As/ Se (mg)

1 15.5 0.26

2 8.18 0.55

3 1.81 0.14 SHORT-LIVED RADIOACTIVE ISOTOPES IN ACTIVATION ANALYSIS 107 separation, developed by BOWEN et al. [20]. The purified selenium activity was measured with a GM counter and checked for purity by decay analysis. This method gave good sensitivity, good selectivity and was reasonably rapid (Table IV).

TABLE IV

DETERMINATION OF SELENIUM IN DRIED MILK

Se content Dried milk sample (ppm)

1 0.10, 0.10

2 0.34, 0.29

3 0.27, 0.24

5. 4. Determination of cobalt

WESTERMARK and FINEMAN [21] have reviewed many of the advantages of Co60m over Co60 in the determination of traces of cobalt by activation analysis. In the presence of nickel, however, such a comparison becomes more complex. When the sample is irradiated over a long period of time (four weeks) to produce detectable levels of Co60 radioactivity, Co58 is also produced, by the reaction Ni58 (n, p) Co58, in amounts corresponding to 400^c Co58/gNi, compared to 87me Собо /g Co. This interference can be reduced to less than 1/uc by irradiation to saturation (one hour) and measurem ent of Co60m and, at the same time, the sensitivity for cobalt is improved. Such a procedure, however, introduces a new interference due to the reaction Ni60 (n, p) Co60m. The cross-section for this reaction is not known, but must be less than the total for the reaction Ni60 (n, p)Co60, which is about 2 mb. This corresponds to ~10мс C o 60m j g Ni on a 1-h irradiation. Providing that the Ni/Со ratio is not excessive, this interference is no problem. The cobalt content of ammonium phosphate, containing small quantities of nickel, was determined as 0. 12 ppm, using the method of W estermark and Fineman. ,A separate determination of the nickel content indicated that the maximum total interference from nickel was less than 1%.

6. CONCLUSIONS

Short-lived radioisotopes can be used to great advantage in activation analysis. The gains, especially in term s of speed and sensitivity, outweigh the few limitations which can, in general, be overcome. 108 D. GIBBONS and H. SIMPSON

ACKNOWLEDGEMENTS

The authors wish to thank D. Lawson for assistance with the ex­ perim ental work and the construction of various automatic units; also G. H. Moss, R. L. Elliott, J. C.H. Geisow, I. Hawthorne and R. J. Jacobs for the design and construction of the printing scaler, the automatic sample changer, and the automatic control and digital read-out units for the gamma-ray spectrometer.

. REFERENCES

[1] JENKINS, E.N. and SMALES, A.A. "Radioactivation Analysis", Quarterly Reviews 10 (1956) 83. [2] MAPPER, D.,"Neutron Activation Analysis as an analytical Tool", Chimia 14(1960) 241. [3] GIBBONS, D ., LOVERIDGE, B.A. and MILLETT, R .J ., Radioactivation Analysis, AERE Report I/R 2208 (1957). [4] GIBBONS, D ., MAPPER, D ., MILLETT, R.J. and SIMPSON, H ., Radioactivation Analysis, AERE Report I/R 2208 1st Suppl. (1960). £5] BOCK-WERTHMANN, W. and SCHULZE, W ., Aktivierungsanalyse, Gmelin Institute Report AED-C-14-1 (1961). [6] PEIRSON, D .H ., "Radiochemical Analysis by gamma-ray Spectrometry", Atomics 7 (1956) 316. [7] PUTMAN, J .L. «nd TAYLOR, W .H., "Subtraction of gamma-ray Spectra", Int.J. Appl.Rad.Isot. 1(1957) 315. [8] ALBERT, R.D., "Anti-coincidence gamma-ray scintillation Spectrometer”, Rev.Sci.Instr.24(1953) 1096. [9] GIBBONS, D ., "The determination of Gold in biological Materials by neutron Activation Analysis”, Int.J. Appl. Rad. Isot. 4(1958) 45. £10] MORRISON, G.H. and COSGROVE, J.F., "Activation Analysis of trace Impurities in Germanium using scintillation Spectrometry", Anal.Chem. 28 (1956) 320. [11] GIBBONS, D ., Determination of Cadmium in super pure Zinc, Proc.Int. Symp. Microchem., Birmingham 1958 (1959) 332. £12] ALBERT, P . , "System atic Analyses of zone m elted A lum inium and Iron',’ Pure and A pplied C hem . 1 (1960) 111. £13] МЕШКЕ, W.W. ."Techniques for fast Radiochemistry 7 Proc.Int. Conf.Modem Trends in Activation Ana­ lysis, College Station, Texas, 1961 (1962) 36. £14] KUSAKA, Y. and MEINKE, W .W., Rapid radiochemical Separations, National Acad. Sci. NAS-NS-3104 (1961). £15] KUYKENDALL, W .E., WAINERDI, R.E. et al. . "An Investigation of automated Activation Analysis',’ Proc. Conf. Radioisotopes in the Physical Sciences and Industry, Copenhagen 1960, IAEA, Vienna 2(1962) 233. £16] FITE, L .E., GIBBONS, D. and WAINERDI, R .E., Computer coupled automatic Activation Analysis, USAEC Report TEES-2671-1 (1961). [17] SALMON, L ., Analysis of gamma-ray scintillation Spectra by the Method of Least Squares, AERE Report R 3640 (1961). £18] LIGHTOWLERS, E ., Private com m unication. £19] BAUMGARTNER, F . , T abelle zurNeutronenaktivierung, Kerntechnik 3(1961) 356. £20] BOWEN, H .J.M . and CAWSE, P .E ., Private com m unication. £21] WESTERMARK, T. and FINEMAN, I ., A rapid Method for the Determination of Cobalt in Reactor Steel by Activation Analysis, Proc. 2nd UN Int. Conf. PUAE 28 (1959) 506.

DISCUSSION

V. P. GUINN (Chairman): I would like to make one general comment on the use of short-lived isotopes. Anyone who is engaged in activation- analysis work will obviously choose the type of isotope that best suits his SHORT-LIVED RADIOACTIVE ISOTOPES IN ACTIVATION ANALYSIS 109 needs; he won’t care what the half-life is. For one type of sample a short­ lived isotope might be best, whereas for another a very long-lived isotope of the same element might be more appropriate. Until the advent of the modern multi-channel analyser, however, I think that mariy of the short­ lived isotopes were relatively neglected. The conventional chemical methods one had to use took a great deal of time and there was a tendency to keep to long-lived isotopes. With the gamma-ray spectrometry techniques now avail­ able, however, short-lived isotopes are much more convenient than they used to be.

THE USE OF THE 10-kW ARGONAUT REACTOR AT PETTEN FOR RADIOACTIVATION, INCLUDING THE QUANTITATIVE ASPECTS OF SHORT-TIME IRRADIATIONS

H. A . DAS REACTOR CENTRUM NEDERLAND, PETTEN, NETHERLANDS

Abstract — Résumé — Аннотация — Resumen

THE USE OF THE 10-kW ARGONAUT REACTOR AT PETTEN FOR RADIOACTIVATION, INCLUDING THE QUANTITATIVE ASPECTS OF SHORT-TIME IRRADIATIONS. Some problems and possibilities in per­ forming activation analysis with a small reactor using short irradiation times are described. A brief survey is given of the reactor and its application for chemical purposes. Three problems occurring when working with a small reactor and the solution we have found for them are discussed: (a) the calibration of short-lived radioisotopes using direct y-spectrometry; (b) the evaluation of the inevitable errors adherent in activation analysis using short irradiation times; and (c) the analytical use of (n.a) reactions by measurement during irradiation. Some results are mentioned.

EXPERIENCES DE RADIOACTIVATION MENÉES A PETTEN AU MOTEN DU RÉACTEUR ARGONAUTE DE 10 kW Y COMPRIS LES ASPECTS QUANTITATIFS CONCERNANT LES IRRADIATIONS DE COURTE DURÉE. L'auteur expose les possibilités qui s'offrent pour l'analyse par activation au moyen d'irradiations de courte durée dans un réacteur de faible puissance et il se penche sur certains des problèmes qu’elle pose. Il décrit brièvement le réacteur et ses applications à des expériences de chimie. Il explique comment il a résolu trois problèmes particuliers à un réacteur de faible puissance comme celui de Petten : a) étalonnage des radioisotopes à courte période par spectroscopie directé; b) évaluation des erreurs inévitables qui se pro­ duisent dans les analyses par activation avec des irradiations de courte durée et c) emploi aux fins d'analyse des réactions (n,a) grâce à des mesures pratiquées durant l'irradiation. Enfin, il donne quelques résultats numériques.

ИСПОЛЬЗОВАНИЕ РЕАКТОРА "АРГОНАВТ" МОЩНОСТЬЮ 10 квт В ПЕТТЕНЕ ДЛЯ РАЛИОАКТИВАЦИИ. При про­ ведении активационного анализа в небольшом реакторе с кратковременным периодом облучения воз­ никают некоторые проблемы и возможности. Лается краткое описание реактора и его использования для химических целей. Рассматриваются следующие три проблемы, возникающие во время работы небольших реакторов, подобных данному, и приводятся найденные решения: а) калибровка короткоживущих изотопов при помощи прямой ^-спектрометрии; б) оценка неизбеж­ ных ошибок, связанных с активационным анализом при кратковременном облучении; в) аналитическое использование (п ,а ) реакций посредством измерения во время облучения; приводятся некоторые итоги проделанной работы.

EMPLEO DEL REACTOR ARGONAUT DE 10 kW DE PETTEN PARA ANÁLISIS POR RADI ACTIVACIÓN, INCLUYENDO LOS ASPECTOS CUANTITATIVOS CONCERNIENTES A LAS IRRADIACIONES DE CORTA DURACIÓN. La memoria expone algunos de los problemas y de las posibilidades que ofrece el análisis por activación con un reactor pequeño empleando tiempos de irradiación cortos, Describe brevement el reactor y sus aplicaciones con fines químicos. Examina tres problemas que se plantean al trabajar con un reactor del mencionado tipo y la manera en que se han resuelto: a) calibración de radioisótopos de período corto por espectroscopia y directa; b) evaluación de los errores que inevitablemente se cometen en el análisis por activación cuando se emplean tiempos de irradiación cortos; y c) fltilización de reacciones (n, a ) con fines analíticos efectuando mediciones durante la irradiación. La memoria cita algunos resultados obtenidos.

111 112 H .A. DAS

1. INTRODUCTION

1.1. Equipment

At Petten two reactors are available for the production of short-lived radioisotopes. Both installations have a facility for rapid sample-changing during operation. Irradiations for the production of radioisotopes are carried out in the 20-MW HFR materials-testing reactor. The small Argonaut-type reactor, usually referred to as LFR, is mainly used for research purposes. Thus, as far as the chemists are concerned, it serves as an instrument for testing quantitative methods based on short irradiation times in the fields of isotope preparation, flux measurements and activation analysis. Two types of irradiation facilities are available for this work: five vertical channels in the centre of the annular core and fifteen horizontal tubes in the thermal column. The reactor is operated discontinuously, re­ maining on the desired power level during about five to ten hours a day.When working at 10 kW, the maximum therm al flux is 2.9 X 1010 n cm '2 s_1 in the horizontal facility and 1.3 X 10H n c m * 2 s_1 in the vertical channels. The central vertical channel and a group of three adjacent tubes in the hori­ zontal facility are used. The other vertical irradiation positions serve for the study of threshold reactions in a known flux pattern. In front of one channel in the therm al column we have constructed a modified concrete shield having a central hole serving as an inlet for either a pneumatic rabbit sys­ tem or a device for instantaneous measurements of (n, a) reactions.

1.2. Quantitative aspects

In the work with the LFR, use is made of four quantitative techniques: (a) Quantitative detection of instantaneously-occurring alpha activities. (b) The rapid calibration of the produced short-lived radioisotopes. (c) The absolute measurement of the fluxes around and in samples, and of flux patterns in the facilities. (d) The comparison of standards and samples in activation analysis. In these investigations we have made quite extensive use of quantitative nuclear spectrometry.

2. AN APPARATUS FOR THE QUANTITATIVE RECORDING OF (n, a) REACTIONS

2.1. First experiments

The analytical applications of (n, a) reactions using neutron sources are well known [1] .A serious drawback to this technique is the low value of the r a tio

specific count-rate/background.

We first performed measurements on boron using .a flux of about 500 n cm-2 s_1 from a 3-c Po-Ве source. Samples of boric acid were placed USE OF 10-kW ARGONAUT REACTOR AT PETTEN 113 at a distance of 1 mm from the zinc-sulphide screen of an alpha-probe which was connected to a one-channel spectrometer. The maximum value of the afore-mentioned ratio proved to be seven, with the specific count-rate ex­ pressed as counts per milligram of boron. Next, we performed experiments with reactor neutrons. It was found to be possible to construct calibration curves by bringing the alpha-probe in a horizontal channel at power levels up to 1 W. However, with this set­ up the ratio between specific effect and background was only two and a half.

2.2. The apparatus

To overcome this, set-ups were constructed having two types of light guide, one for high - and one for low - power levels. The high-power level set-up consists'of a well-polished lucite rod (330 cm long, 35 mm diam.) which is covered with magnesium oxide and mylar wrapping. The rod is protected by a pertinax tube and supported inside by rings of the same ma­ terial. The outer end of this assembly protrudes about 50 cm out of the reactor. It is connected optically with the photomultiplier. The other end is equipped with a zinc-sulphide screen. The protecting tube is closed by a light-tight stopper in which samples can be placed on small aluminium discs at a distance to the screen of 1 mm. The chief difficulty in construct­ ing this apparatus is to obtain a sufficiently long lucite rod and to make the reflector-layer light-tight. Commercially available lucite rods (110 cm) are welded together with a saturated solution of lucite in chloroform. The magnesium oxide is applied in the form of a specially-prepared lacquer. Up to 100 W the set-up for measurements at low-power levels is used. Here the light pipe is only 110 cm in length and is covered by an aluminium jacket. The reflector is made of aluminium foil. This apparatus is satis­ factory for most applications. At 100 W, the count-rate for boron is about 6 X 106 с m in-l mg-i with a ratio specific count-rate/background of 1090; the area of the aluminium discs used here is 3 cm2. The mentioned ratio increases roughly proportionally to the square root of the power level.

3. CALIBRATION OF A NUMBER OF RADIOISOTOPES BY QUANTITA­ TIVE GAMMA-RAY SPECTROMETRY

3.1. Principles

Gamma-ray spectrometry is a useful technique for the calibration of a number of radioisotopes. In the course of our work a method for absolute gamma-ray spectrometry was developed. The most important applications to the short-lived radionuclides resulting from neutron activations are found in the calibration of F*8 , Na24 , Cl38 and Cu64 . The technique can be re­ garded as a modified coincidence counting method, using a w ell-crystal detector instead of two separate counters [2], [3], [4]. The method is justi­ fied only if no appreciable angular correlation exists. The influence of the latter can however be eliminated by special experimental conditions or by applying a correction to the results obtained. The simplest case is pre­ sented by a decay scheme of one negatron, followed by a gamma-cascade 1 H.A. DAS 114

TABLE 1

POSSIBLE COMBINATIONS OF TWO COINCIDENT GAMMA-RAYS IN SCINTILLATION COUNTING

N = T + a - e ^ - £Ci) ( l - £yj - £ C j) N = T + S1 Sj / S 12 . USE OF 10-kW ARGONAUT REACTOR AT PETTEN 115

(cf. Table I). We can express the intensities of the two primary photopeaks (Si and S2 ) as a function of the overall detection efficiencies for both gammas, either as a primary photon (ey) or after Compton-scattering (ec) and of the true number of disintegrations (N)

51 = s. (1 ■ S • ec >N (1) » 1 2 2

52 = e7i (1 - eTi - )N (2)

The intensity of the sum peak is equal to

S12 = c7i N. (3)

It is readily seen (Table I) that, if T is the total content of the entire gamma- ray spectrum, after appropriate corrections for background

N = T + Si S2/S12 (4)

In the case of pair production the formation of pair peaks by S2(S2 and S2 ) gives rise to corresponding sumpeaks (Sj.2 and S"2 ) but does not alter the latter formula (cf.* Table II). Similarly two other expressions exist which can be used as a check on the method

N = T + Sx S 2 / S i 2 (5) and

N = T + S! S2/S"12 (6)

Measurements on Na24 gave a discrepancy of 0.6% between the formulae (4) and (5), The form er can be used not only for the calibration of Na24 but also for the calibration of the long-lived radioisotopes Sc46 and C660 (cf. Table III).

3.2. Influence of angular correlations i It is not difficult to show that the formulae are correct only if the detect­ ing crystal has an inversion point in which the source can be mounted. Other­ wise Si2 will be too small and consequently Si and S2 somewhat too great, resulting in a positive systematical error. In principle the only possible form of the detector is a cylinder pierced along its axis by a cylindrical tunnel, with the source mounted in its centre. A large spectroscopic crystal containing a deep and narrow well will nevertheless give sufficiently accurate results. In the most unfavourable event of two gammas having a strong angu­ lar correlation of 180° , the positive error for a point source at the bottom is of the order of 2% if a 2^-in X 2^-in crystal with a well of 1 1/4 in X 3/8in is used. In all other cases the error is negligible. This can be checked by observing the influence of the position of the source in the well on the result of the calibration. For Na24, Sc46 and Co6° the variations proved to be ran­ dom, not exceeding the standard deviation of the measurement. 1 H.A. DAS 116

TABLE II

TWO COINCIDENT G A M M A RAYS, ONE SHOWING PAIR FORMATION

C ounted as Counted as Counted as Counted as

original C om pton a photon at a photon at Not counted

photon (E-0.51) MeV (E-l. 02) MeV /I

Counted as «y £v N C ( 1 “ € “ ec " €p " ep ) ^ '1 ' 2 Ъ 4 N /i *2 г pi y 2 o riginal first sum peak second sum peak third sum peak first photopeak

photon ( S i,) (S'l2) ( S a )

Counted as £ € N £C S N ec £p N £c ■ £y ‘ £c ■ £p • £p ) N C om pton I 2 4 4 N 1 2 cx Px 1 1 2 2 Vl V 2

(i-iy -£c ) (1-^, - t - £ p ) N Not (1' V S )e>iN V £PlN '1 1 r 2 2 F1 Г2 second photopeak p air peak pair peak counted not counted at all (Si) at (E-0.51) MeV at (E -l. 02) MeV

Si 4

N = T+(1-e, -c )(l-« -cc -£„ -£-) N = T+SiS,/Su =T+S1Si/S'u = T+S1Si/S^ rl I *2 2*1** USE OF 10-kW ARGONAUT REACTOR AT PETTEN 117

TABLE III

SOME GAMMA-RAY CASCADE-EMITTING RADIONUCLIDES PRODUCED IN REACTORS

Nuclide H alf-life First gamma Second gamma (MeV) (MeV)

Ne4 23 40 s 0.439 1.65 46 Sc 8 4 .2 d 0.885 1.12 48 Cr 23.5 h 0.116 0.31 „ 60 Co 5 .2 yr 1.17 1.33 155 Sm 23.5 min 0.105 0.246

3.3. Calibration of positron-emitters

Calibration of positron-emitting nuclides can be performed based on the quantitative annihilation of the positrons. Small sources surrounded by an aluminium foil are placed on the well bottom. Here we obtain

N = . T + S2 / 4 S 12 (7) where S denotes the 0. 51-MeV photopeak. The possible applications to short­ lived radionuclides are numerous (cf. Table V). Most of them are not easily made in a reactor. The most interesting cases are F18 and Cu64 .

3.4. Coincidences of a positron and a gamma-ray

The method can be applied to triple coincidences and coincidences of a positron and a gamma (cf. Table VI). As none of the short-lived radio­ nuclides involved can be conveniently made in a reactor, we will not dis­ cuss the evaluation of the three possible formulae in these cases. It can be derived that the quantitative annihilation of the emitted positrons is not necessary here.

3.5. The calibration of Cl3® and EulS6 .

Some radionuclides with a branched decay scheme can be calibrated. Examples are Cl38 and Eu156 . The decay scheme of the latter shows two negatrons. One is followed by a cascade of a 0.199-MeV and a 0.089-MeV gamma-ray (-yj and y2 ), the other by a lone gamma-ray of 0.089 MeV. The latter is not coincident with the cascade gamma-ray of equal energy. Let 118 H .A. DAS

TABLE IV

POSSIBLE COMBINATIONS BETWEEN THE ANNIHILATION GAMMA-RAYS

Counted as Counted as Not counted * original Compton I \ photon

Counted as £y N £T ec N y i - t y - € C) N

original 1. 02 MeV 0.51 MeV

photon sum peak photopeak

Counted as ecZN Compton V c N ec ^ " ~ €c^ ^

^ 1 - er ' ec>N ( l - e r - ec )2 N Not 0.51 MeV not counted counted photopeak at all

N = T + ( 1 - 6y - ec )2 N = T + S2/ 4 S U .

TABLE V

POSITRON -EMITTING RADIONUCLIDES

Nuclide Half-life Nuclide Half-life

V 8 112 m in S c4* 0.65 s

NeVT W 18 s T i‘ 5 3.05 h

Na 23 s v47 33 min

M g23 12 s MnS° 0.28 s

A l25 7 .5 s Mni , 51 45 min „ S8 A l26m 7 s Cu 9 min ** 64 S i2 7 5 s Cu 12.8 h j 122 s31 2 .6 h 3 .5 min

C a39 1 .0 s Eu 18 min

S c41 0.87 s ......

* 97% 6+ - emission. * * 19% 0 + - emission. USE OF 10-kW ARGONAUT REACTOR AT PETTEN 119

TABLE VI

COINCIDENCES OF A POSITRON AND A GAMMA

Nuclide Half-life Gamma Positron (MeV) emission (%)

o14 72 s 2. 31 99.6

Na22 2.6 yr 1.28 89.5

P 28 0 .28 s 1.78 100.0

к 38 7.7 min 2.16 100.0

Sc 4 .0 h 1.16 93.0

Mn», 5 2 21 min 1.43 34.0

the partition over these two possibilities be as a : (l-а). Then the formulae for the three resulting photopeaks run

Si = (1 - e - ec >N (8) “ Sx У* 2 . a e - eCi)N + (1 - а)еуг N (9) S2 = Уг (1;S x

ev N (10) S 12 = “ Eït • 2

The number of disintegrations not registered is equal to

N - T = e(l - e - ec )(1 - € - ec )N + / j L 1 72 2

(1 - e )(l - S - ec ) N (11) ¡2 2

The insertion of the expressions for the three photopeaks in the latter equa­ tion results in the original calibration formula

N = T + S xS2/S 12 (4)

The decay-scheme of Cl38 differs from that of Eu158, showing a direct decay to the ground state with a relative intensity of 53%. The result of the cali­ bration is thus 0.47N (cf. Tables Vila and Vllb).

3.6. Advantages of the method <»

The method described has the advantage of being applicable to very weak sources. An activity greater than 10"3 цс can be measured. Specific 120 H. A. DAS

TABLE Vila

THE POSSIBLE COMBINATIONS OF THE GAMMA RAYS IN THE CASE OF Cl38

C l38 ( T = 37 m in) i

53% V \ \ . 31%

\ \ í e í 4 "*.

- 3.75 MeV

2.16 MeV

0 In38 Ar 9 S Decay-scheme of Cl

Partition over direct 6 - decay and gamma-ray emission as f : (1-f) = 0.53 : 0. 47. Partition over cascade and single 2.16-MeV gamma ray as a : ( 1 - a ) = 0.66 : 0.34.

activities of Cc^^sources can therefore be determined from samples' of this nuclide of 0. 3 me or more, and subsequently measuring the resulting Co6° activity. The standard deviation diminishes from approximately 7 to 2\io, as the strength of the source increases. The upper limit of sample activity is roughly 1цс. The results can be checked by calculating the ratios of the different quantities involved for a number of measurements. No sys­ tem atical error could be detected by comparison with other calibration m e th o d s .

3.7. Extension to other radionuclides

It is possible to calculate the detection efficiencies from the calibration results obtained. If this is done for a number of samples identical in form and measured with the same crystal in the same geometry, a correlation results between ey and the gam m a-ray energy in the form of log Су = a- Э lo g E . This can be useí for the calibration of radionuclides with simple decay schemes, showing only one negatron and one gamma, like Al28 and V52. The direct calculations of the Compton efficiencies are completed, using the values obtained from the spectra of the afore-mentioned radioisotopes. TABLE Vllb S O 1-W ROAT ECO A PTE 121 PETTEN AT REACTOR ARGONAUT 10-kW OFUSE COMBINATIONS IN THE CASE OF Cl38

Counted as Counted as Counted as Counted as n \ * original photon at photon at Not counted Com pton photon (E -0 .5 1 ) MeV (E-1.02) MeV i \

Counted as f a e e N f a e e N o rig in al /i Рг f “ V p , H ¡1 2 ' “ V 1 " V V W N photon (Siî) (S'n) (S'ñ)

Counted as f a e ev N f a e . € N f a e e N faeCia - er -epi- v eC2)N C om pton 1 *2 ci P2 f “ 4 ep . N c i г

Not f a d - e ^ - e ^ N f f“ ( l - 4 -ec )e N+ fa(l-e^ -ec )e N + f a ( 1 - e - e ) e N+ Га(1-еу1-ес Н1-еуг-ер1- ^ - е с)Н + 4 1 K2 M 1 P1 '1 1 2 counted f(l -a ) ty N f(l-a )eD N f(l‘-a)€p N f (1 - a ) e. N 1 f(l-« )(!-«y ‘ «p ’ «p ’ ec> N K2 *1 2 h *1 2 2 (Sj) (S'2 ) (s"2 ) not counted at all 122 H .A . DAS

For such a simple decay scheme the following formulae apply

T=(er +ec)N (12)

S = erN. (13)

From measurements on samples with unknown activity we can therefore c a lc u la te

T/S-l = ec/ey. (14)

This makes it possible to construct a curve for ec from the e c u r v e . The partition of the registered disintegrations over the different com­ binations follows from the calculated efficiencies. This enables comparison of crystals to be made (cf. Table VIII).

table v in

PARTITION OF THE DISINTEGRATIONS OVER THE DIFFERENT POSSIBILITIES FOR A SMALL Na24 SOURCE (M easured on the well'bottom of a 2j-in X 2^-in(l 1/4-in X 3/8-in) Harshaw well crystal)

4. ABSOLUTE FLUX MEASUREMENTS IN SHORT IRRADIATIONS

4.1. Survey

In the course of our work it was felt to be desirable to measure fluxes of therm al and fast neutrons, and of tritium . The latter are important in tritium activations by means of the reaction Li6 (n,a) H3. USE OF 10-kW ARGONAUT REACTOR AT PETTEN 123

4.2. Thermal fluxes

Relative measurements of the thermal flux can be carried out by sub­ mitting manganese and gold foils to a short irradiation. An absolute deter­ mination is possible either by a direct calibration of Na24 and Sc46 or by em ploying C 0 6 O formed out of C o 6°m . The above-mentioned relation between ey and the gamma-ray energy can be used on V52 ,

4. 3. Fast fluxes

Applications of quantitative gamma-ray spectrometry in the mapping out of fast fluxes are found in the direct calibration of Na24, formed out of Mg24 and Al27, and the indirect calibration of V52 from the (n, p) reaction with Cr52 . For irradiations longer than one hour at fluxes of 109 n cm-2 s*1 or higher, the titanium-scandium reaction can also be employed.

4.4. Tritium fluxe s

The preparation of Mg2» and the determination of oxygen by means of Fis are the most important applications of tritium activations. The deter­ mination of tritium fluxes in a homogeneous mixture of, for instance, LiF and MgF2., can be carried out with thin discs of lucite, which contains 32.0% of oxygen.

5. ERRORS INHERENT IN QUANTITATIVE ACTIVATION ANALYSIS WITHOUT CHEMICAL SEPARATION

5.1. General

The possible applications of quantitative activation analysis depend to a great extent on the accuracy which can be obtained. It is important to know therefore what constitutes the total statistical error, which in our work is between 3 and 10%, and to what extent results from different days can be compared to each other without applying a correction. If such comparison is permitted, a calibration curve for a particular irradiation facility can be constructed.

5.2. Errors in the measurements

The standard deviations of the measurements are calculated by obser­ ving the ratio of two photopeaks which are described by the same type of formula. Consequently these photopeaks vary in the same manner with the co u n tin g geometry. The variation in this ratio of peak areas is the com­ bination of the error in the determinations of the areas and that due to irre- producible differences in counting geometry. For our measurements, the former ranges from 3. 1 to 4. 5%; the latter can thus be calculatedjn general, the variation of the area of the photopeaks with geometry is m easured by an absolute calibration of point sources in different positions on the axis 124 H. A. DAS of the detecting crystal. The results show that the main statistical error arises from small variations in-counting geometry. This agrees well with the fluctuations in the total error and with the fact that there is only a slight increase in the standard deviation with greatly decreasing concentrations.

5.3. Errors due to irradiation

The standard deviation due to the average flux difference between two samples may be calculated by comparing the fluctuations in the results of absolute measurements to those in the determination of the photopeaks. It is found not to be in excess of 2% in the case of liquids and 4% in the case of solids, using sample-weights up to 100 mg. Differences between experiments performed on different days were assessed by irradiating solutions containing hafnium and sodium. The slopes of the calibration lines obtained on different days were compared to each other and to an averaged curve, based upon all the measurements. The outcome of these comparisons was a standard deviation of 3 to 4%.

REFERENCES

[1] WANKE, H. and MONSE, E.U., Z. Naturforsch. 10a (1955) 667. [2] ROSE, M .E., "The Analysis of angular Correlation and angular distribution Data", Phys. Rev. 91 (1953) 610. [3] CROUTHAMEL, C.E.(Ed.), Applied gamma-ray spectrometry, Pergamon Press (1960) 443. [4] BRINKMAN, G.A., Standardization of radioisotopes, Thesis, Amsterdam (1961).

DISCUSSION

D. GIBBONS: I should like to ask a question in connection with errors of measurement. What method did you use for the evaluation of peak areas? H. DAS: We investigated four different methods: (1) Plotting the gamma spectrum and subtracting the continuous part of the spectrum, the resultant peak area then being determined by simply counting the number of square millim eters; (2) Estimating the peak area by means of a Gaussian formula,

CHW^

where H is the peak height, is the width of the peak at half-height and С is a constant (1. 025); (3) Using a fixed (average) width at half-height and thfen taking,only the height of the photopeak. This method is only useful, however, in the case of routine analyses; (4) Summation of the total content of the gamma-ray spectrum in the peak interval and subsequent subtraction of the continuous part of the spec­ tru m . The last method proved to be the best, yielding standard deviations as low as 2. 5% (average value 3%). USE OF 10-kW ARGONAUT REACTOR AT PETTEN 125

I should like to make one further rem ark. Our greatest difficulty with this calibration method arose in connection with the evaluation of the proper value of T, the total number of counts. What we did was to extrapolate down to zero energy over the region where the interference of background and the noise of the photomultiplier was not negligible. By extrapolating in this way, one arrives at an uncertainty factor of about 1% in the final result. A. VUORINEN: I should like to ask whether when making absolute measure­ ments of therm al fluxes you prefer the gamma-gamma coincidence method or the beta-gamma coincidence technique now used by many scientists. H. DAS: We use both techniques and we constantly compare the results obtained.

APPLICATIONS PRATIQUES DES RADIOÉLÉMENTS DE COURTE PÉRIODE DANS L ’ANALYSE PAR ACTIVATION

B. CHIN AGUA, L. CIUFFOLOTTI, G. B. FASOLO ET R. MALVANO CENTRE DE RECHERCHES NUCLÉAIRES SORIN, SALUGGIA, ITALIE

Abstract — Résumé — Аннотация — Resumen

PRACTICAL APPLICATIONS OF SHORT-LIVED RADIONUCLIDES IN ACTIVATION ANALYSIS. Activation analysis by means of short-lived radionuclides has found some remarkable applications in the SORIN Research Centre at Saluggia. The paper describes the special techniques of irradiation, chemical separation and measurement required to obtain adequate accuracy and good sensitivity. It has proved possible to apply the method to analysis of elements with a half-life down to 10 s, with a consequent enormous gain in time. The method has been of benefit in several different spheres, as in solving metallurgical and technical problems (e. g. study of impurities in special-purpose materials) and in geochemistry and biology.

APPLICATIONS PRATIQUES DES RADIOÉLÉMENTS DE COURTE PÉRIODE DANS L'ANALYSE PAR ACTI­ VATION. L'analyse par activation au moyen de radioéléments de courte période a trouvé de remarquables applications au Centré de recherches SORIN, à Saluggia. On décrit dans le mémoire les techniques particulières d'irradiation, de séparation chimique et de mesure qui sont indispensables pour obtenir une précision satisfaisante ainsi qu'une bonne sensibilité. On a pu ainsi étendre la méthode â l'analyse dféléments dont la période peut atteindre dix secondes, réalisant de cette façon un remarquable gain de temps. Plusieurs branches ont tiré profit de cette méthode, soit dans la résolution de problèmes métallurgiques et technologiques (par exemple étude des impuretés dans des matériaux d'emploi spécial), soit en géochimie et en biologie.

ПРАКТИЧЕСКОЕ ПРИМЕНЕНИЕ КОРОТКОЖИВУЩИХ РАДИОИЗОТОПОВ ПРИ АКТИВАЦИОННОМ АНАЛИЗЕ. Активационный анализ с помощью короткоживущих радиоизотопов нашел замечательное применение в Соринском иссле­ довательском центре в Садуцце. Дается описание особых методов облучения, химического выделения и измерения, которые не­ обходимы для получения удовлетворительно/} точности и хоропгой чувствительности. Представляется также возможным распространить применение метода на количественный анализ элементов, период которых может достигать 10 сек, добиваясь таким образом замечательного вы­ игрыша во времени. Многие отрасли хозяйства уже воспользовались этим методом либо при решении металлургических и технологических проблем (например, при исследовании примесей в металлах специального назна­ чения), либо в геохимии и биологии.

APLICACIONES PRÁCTICAS DE LOS RADIONÚCLIDOS DE PERIODO CORTO EN EL ANAUSIS POR ACTI­ VACIÓN. El análisis por activación empleando radionúclidos de período corto ha encontrado aplicaciones notables en el Centro de Investigaciones SORIN de Saluggia. En la memoria se describen técnicas especiales de irradiación, de separación química y de medición, indispensables para alcanzar una precisión y sensibilidad satisfactorias. Se han podido analizar elementos de un período de hasta 10 s, logrando así un considerable ahorro de tiem po. El método ha beneficiado a muchos campos de aplicación, sea para resolver problemas de metalurgia y technología (por ejemplo en el estudio de las impurezas presentes en materiales destinados a usos especiales), sea en geoquímica o en biología.

127 128 В. С HINA GLIA et al.

1. INTRODUCTION

L’analyse par activation s’est remarquablement développée grâce au grand nombre de réacteurs de recherche existant aujourd'hui. Elle contribue utilement au progrès de plusieurs branches de la science et de l’industrie. Presque 80% des éléments peuvent être analysés avec succès par cette méthode; ces éléments présentent presque tous beaucoup d’intérêt au point de vue pratique. Toutefois, 15% de ces éléments donnent naissance à des radioéléments de période inférieure à 10 min et leur emploi exige des dispo­ sitifs rapides d’irradiation et d’extraction des échantillons ainsi que des tech­ niques de mesure particulières. Dans certains cas, des caractéristiques nucléaires favorables font pré­ férer un radioisotope de courte période 'à un autre de période beaucoup plus longue. Ainsi 22% des éléments qui peuvent être activés en pile ont une pé­ riode inférieure à 10 min; de ce fait, des irradiations très brèves sont suffi­ santes pour atteindre des activités spécifiques élevées. De cette façon, on réduit soit les activités interférantes, soit l’éventuelle contribution de ré­ actions secondaires, etonpeut surtout effectuer des analyses nondestruc- tives, en réalisant ainsi un gain de temps remarquable. L’emploi de radio­ éléments à courte période ajoute aux avantages propres de la méthode d’ana­ lyse tels que la sensibilité, la"précision et la souplesse, la rapidité d’exé­ cution qui permet de réduire le coût de l’analyse proprement dite[l, 2, 3] .

2. TECHNIQUES EXPERIMENTALES

La pile piscine du Centre de recherches de Saluggia possède un flux de neutrons therm iques de 4 • 1013 n /cm2 • s dans le cœ ur et de 2 • 10i2.n/cm2 • s dans le dispositif pneumatique d’irradiation, à 2 MW (niveau de puissance actuel). Ce dispositif pneumatique perm et des temps d’irradiation dont le minimum est de deux secondes, tandis que le temps de transfert est d’une seconde; ce dispositif est utilisé pour les analyses de radioéléments de très courte période. Dans ce cas, l’échantillon et l’étalon de comparaison sont irradiés k part avec un moniteur pour corriger les variations éventuelles d e flu x . Les étalons sont constitués de solutions à l’état liquide ou évaporées sur papier « Whatman» n° 3 ou encore d’alliages d’aluminium préparés à cet effet. Les m esures de radioactivité sont effectuées par spectrométrie y ou 3, soit après avoir procédé à un traitement radiochimique, soit par une analyse non destructive. Comme détecteurs y et j3 on utilise communé­ ment un scintibloc de haute résolution muni d’un cristal Nal (Tl) 3" X 3" et un scintillateur plastique l" X 1" respectivement. Les impulsions délivrées par ces détecteurs sont envoyées à un sélecteur à 200 canaux pour l’analyse en énergie des spectres obtenus. Si les radioéléments étudiés possèdent une période très courte, on peut obtenir en même temps l’information concernant l’énergie ainsi que l’infor­ mation relative k l’évolution dans le temps, en utilisant le dispositif décrit dans un de nos rapports précédents [1] , qui donne la courbe de décroissance par un grand nombre de points; chaque point de la courbe représente l’acti- APPLICATIONS PRATIQUES DES RADIOÉLÉMENTS DE COURTE PÉRIODE 129 vité correspondant à. l’intervalle d’énergie sélectionné par un sélecteur à u n c a n a l. De cette façon il est possible d’éliminer des composants éventuels qui interfèrent avec le radioélément étudié. Par exemple on a pu m ettre en évidence l’activité du 20F et du 28A1 dans un échantillon de cryolite. La spec­ trom étrie Э est employée avec succès au lieu du simple comptage avec un compteur GM lorsqu’il est nécessaire d’éliminer du spectre /3 une activité interférante qui n’a pu être éliminée par voie chimique, à cause de diffi­ cultés propres à la séparation, ou en raison du fait que l’élément cherché possède une période trop courte. Par exemple, la mesure du chlore par la spectrométrie y est souvent sérieusement gênée par la présence de 56Mn même pour des irradiations de 5 à 10 min, de telle sorte que l’emploi du scintillateur plastique a paru préférable, sans entraîner, de perte de sen­ sibilité. En, effet le 38C1(T^= 38 min) décroît en émettant, pour 53%, des rayons j3 dont le maximum d’énergie est de 4,8 MeV, valeur bien supérieure à celle du 56Mn (Eg max = 2,8 MeV). Donc, si on considère le spectre /3 à partir de 3 MeV, ce qui représente presque 25% du spectre total, on élimine aisément toute activité gênante.

3. APPLICATIONS DES RADIOELEMENTS DONT LA PERIODE EST INFÉRIEURE A DIX MINUTES

Le босо métastable a été employé avec succès dans de nombreuses ana­ lyses par spectrométrie y non destructive: Le rayonnement de 59 keV est détecté par un cristal mince de Csl, pour réduire les interférences dues aux rayonnements de plus haute énergie. Voici quelques exemples: a) Dosage du cobalt dans des feuilles d’aluminium (alliage 1%) employées comme sondes de flux neutronique: dans ce but, il né serait pas possible d’utiliser le cobalt de longue période ni, évidemment, des procédés d’ana­ lyse destructive. La reproductibilité de ces mesures est de ± 2%environ, et le temps nécessaire pour l'analyse de dix sondes est de 40 min environ. b) Détermination de traces de cobalt dans le fer pur (préparé par décom­ position du fer-carbonyle) et dans l’acier inoxydable 304L. Les échan­ tillons sont dissous dans HCl en présence d’entraîneur de Со, la plus grande partie du fer est extraite par l 'éther, et le Со est précipité par le nitrose a-naphtol j3. Le comptage est effectué sur la source solide et le rendement chimique est établi par pesée. La pureté radiochimique est satisfaisante, les rendements sont >95%. c) Distribution des traces de cobalt dans des tissus biologiques pour la re­ cherche de différentes concentrations entre des tissus cancéreux et les tissus normaux adjacents. Les échantillons, incinérés avant l’irradiation, sont dissous dans HCl dilué en présence d’entraîneur de Co. Après une extraction préalable par éther et acétylacétone, le résidu de fer dans la phase aqueuse est complexé par KF et le cobalt extrait par méthyliso-

butylcétone sous forme de complexe sulfocyanique ci pH 5 - r 7.Le comptage est effectué directement sur la phase organique, d’après laquelle on établit ensuite le rendement chimique par spectrophotométrie d’absorption à 625 m/и. La purification radiochimique est suffisante pour la spectro- 130 B. CHINAGLIA et al.

m é tr ie y. Le rendement est de 75-80% et le temps nécessaire pour la séparation est de 20 min environ. d) Détermination du vanadium et de l’aluminium dans des échantillons de caoutchouc synthétique oîi ces éléments représentent des résidus de cata­ lyseurs. Cette analyse a été effectuée par spectrométrie y directe des rayons de 1,44 et 1,78 MeV respectivement. e) Dosage du vanadium dans des petits échantillons de pétroles et d’asphaltes (où la concentration de V varie de 0,02 à 200 ppm), important pour l’étude de l’origine du gisement [4]. f) Le hafnium (T¿ = 19 s) a été détérminé dans des échantillons de zirconium et d’oxyde de zirconium suivant la méthode décrite ci-dessus. L’analyse par activation est très utile dans ce cas, car l’analyse du hafnium par voie chimique ou chimico-physique est très laborieuse. g) Enfin l’analyse du soufre peut être non destructive si on utilise le 37S dont la période est de 5 min; la sensibilité réalisable dans nos conditions est de 10*4 g. Cette valeur n’est pas si mauvaise qu’elle paraît: en effet les quantités des échantillons à analyser peuvent être considérables sans que les résultats de la mesure soient affectés d’une façon sensible par l’atténuation des rayons y du 37S qui ont une énergie de 3,1 MeV. Les ré­ sultats de ces analyses sont rassemblés dans le tableau I.

TABLE i

RÉSULTATS D'ANALYSES FONDÉES SUR L ’EMPLOI DE RADIOÉLÉMENTS DONT LA PÉRIODE EST INFÉRIEURE A DIX MINUTES

Echantillon Élément cherché Concentrations mesurées (ppm)

Fer pur Со 1,5

Acier 304L Со 140

Tissus biologiques Со 0,3 i- 60

Caoutchouc synthétique Al 200 i- 300

V 100 4-140

Pétroles V 0,02 -r 200

Zr et Zr02 Hf 200 -r 400

Polyphéniles Al 0,9 200

4. APPLICATIONS DE RADIOÉLÉMENTS DONT LA PÉRIODE EST SUPÉRIEURE A DIX MINUTES

Les radioéléments dont la période est supérieure à 10 min ont été em­ ployés pour l’analyse des traces dans plusieurs échantillons, suivant des procédés classiques. Nous avons rassemblé dans le tableau II les résultats obtenus dans l’étude de quelques problèmes. APPLICATIONS PRATIQUES DES RADIOÉLÉMENTS DE COURTE PÉRIODE 131

TABLEAU П

RÉSULTATS D’ANALYSES FONDEES SUR L’EMPLOI DE RADIOÉLÉMENTS DONT LA PÉRIODE EST SUPÉRIEURE A DIX MINUTES

Concentrations mesurées Echantillon Élément cherché (ppm)

Mn 0.7 t 2

Cu 0,01+ 16

Ga < 0,01+ 2,5 Aluminium « Z . F » La 0.03+ 0.15

Dy 0,01+ 0,15

W 0,08+ 1,5

Na 0,5 t 3

Cl 3 +30

Mn 0.02+ 0,4

Polyphényles Cu 0,02+ 0.2

Ni <0,1

Mo 0,05

Au 0,001

Mn 0,01 + 1

Cu 0.5 + 12

Pétroles et Asphaltes Ni < 0,01 +100

Mo 0,01 +• 8

Au < 1-10-5+MO'-*

Mn 5-10-4+ 0,1 Urine As 0,01 + 0,05

RÉFÉRENCES

[1] CHINAGL1A, B ., CIUFFOLOTTI, L ., F ASOLO, G. B. and MALVANO, R. .Use of short-lived radionuclides in activation analysis» Energía Nucleare 9 (1962) 503. [2] BROWNLEE, J. L ., USAEC Report TID-6311 (1960). [3] MEINKE, W .W ., "Activation analysis utilizing fast radiochemical separations and particle neutron gene­ rators", Radioisotopes in the Physical Sciences and Industry II, IAEA, Vienna (1962) 277. [4 ] CIUFFOLOTTI, L . , COLOMBO, U . , MALVANO, R. and SIRONI, G ., Trace-M etal Analysis in oils and Asphalts by Neutron-Activation Techniques (Communication présentée au «International Meeting on Organic Processes in G eochem istry», Milan (septembre 1962)). 132 В. С HINA GLIA et al.

DISCUSSION

P. ALBERT: I imagine that the Whatman paper you used for supporting the samples contained sodium, phosphorus, and perhaps even manganese? L. CIUFFOLOTTI (on behalf of B. Chinaglia et al. ): Yes, but we de­ termined the sodium content beforehand. The concentrations were not very high for our purposes. P. ALBERT: We have examined a number of different types of filter and chromatographic paper from this point of view and it is very difficult to find papers with the degree of purity necessary for activation-analysis work. We have established, however, that the chromatographic papers are not the purest ones. Some of the filter papers are purer. V.P. GUINN (Chairman): We have examined quite a few different types of filter and other papers in some research we have been doing on various types of writing paper, for purposes of criminal investigation. So far we have found no.paper that does not contain sizeable amounts of sodium; it is generally present at very appreciable levels, e.g. in the 10-100 ppm range, and well within the detection range for reactor fluxes. There is always a sodium residue, however much you try to clean the papers up by acid- extraction and other techniques. Manganese usually shows up as well, and also a small amount of chlorine. W. BOCK-WERTHMANN: In our laboratory we have been making a systematic check of the impurity content of papers that can be used for paper-chromatography in conjunction with activation analysis. The im­ purity that gives rise to most activity after an irradiation period of a few hours is sodium. After examining some 200 papers, including some pro­ duced abroad, we discovered that the lowest sodium content was to be found in some of the chromatographic papers produced by the firm of Schleicher and Schüll, Dassel, Federal Republic of Germany; these are apparently washed in acid by the factory. We shall be publishing details on these in­ vestigations in the near future. A. WARD: Under (c) in Section III of their paper, the authors mention cobalt in connection with carcinogenic and healthy tissues. I wonder if Mr. Ciuffolotti could tell us a little more about the type of tissues or organs involved and the results of experiments. L. CIUFFOLOTTI: We have only just started these investigations and no definitive results are available yet. We have only examined 10 cases and we really need 50 to provide us with enough information to judge whether there is a systematic difference between the cobalt concentration in can­ cerous and normal tissue. At present we are examining stomach tissue. A. WARD: It might interest you to know that we plan to carry out sim i­ lar investigations on stomach cancer in our new centre in Scotland. G. PETEOU: As the paper we have just heard is the last one which deals with the technical applications of radioactivation, I wonder if 1 might be allowed to make a few general rem arks on the subject at this point. All the papers we have heard so far have been concerned with actiyation- analysis techniques that are based on the use of reactors. I should like to draw attention to an activation-analysis technique which can be applied in geophysical investigations, e.g. in the oil industry, and which relies simply APPLICATIONS PRATIQUES DES RADIOÉLÉMENTS DE COURTE PÉRIODE 133 on a Po-Be source. In Romania this method has been used for determining the water or petroleum content of the layers of earth through which drill­ holes have been sunk in cases where the water in the deposits is rich in NaCl (the concentration has to exceed 100 g/1). The technique consists in ir­ radiating the layers for about 10 h and then measuring the induced radioactivity. In the absence of Na24 one gets the characteristic decay curve of gamma- active radioelements with shorter half-lives than Na24, e.g. Ca, Mg, Mn, Cl, Si, Al. Simultaneously, with this technique, we carried out a chemical analysis of the contents of the petroleum layers using Na naphthenate tagged with Na24. Experimental laboratory models were used to study the effects of the irradiations and also to investigate the behaviour of the Na naphthenate in the medium under investigation. Good results were obtained. V. P. GUINN: As you say, we have confined our attention so far to relatively high-flux sources from reactors. Of course, one can also work with accelerator fluxes of the order of 10s or 109 and also', as you mention, with isotopic sources with fluxes of 104 or 10s . Useful applications are possible at all levels, but the number of elements that can be detected grad­ ually decreases until one arrives at the 0. 1 or 0. 01% level, when only a limited number of determinationá are possible. With regard to the specific problem of oil-well logging, not only isotopic sources but also sealed sources can be used. I believe Dr. Erwall had a question which also bears on this? L. G. ERWALL: Yes. As you know, it is common practice in oil-well logging to use small accelerators to study the spectrum of the prompt gam­ mas emitted by the (n, y) reaction. I believe that extensive work is going on at the Armour Research Foundation with a view to studying the possibilities of using prompt gammas as an aid to routine activation analysis in industry too. I wonder, Mr. Chairman, could you say a few words on the general utility of capture gammas for this purpose? V. P. GUINN: I should be glad to make a few comments on this although I must warn you that my information is only second-hand. Certainly, the use of the prompt gamma rays emitted by samples follow­ ing the capture of therm al neutrons or the inelastic scattering of fast neu­ trons does constitute a form of nuclear analysis. Whether you want to in­ clude these techniques under the heading of activation analysis, of course depends on how you define the latter term . Very short-lived species, name­ ly the transient nuclear excited states and their transitions, are involved in this type of work, and gamma-ray spectrometry has to be performed during activation (irradiation) instead of afterwards. The product need not neces­ sarily be a radioactive species after its prompt decay to the ground state. Small isotopic neutron sources and tiny accelerator neutron sources have been developed for carrying out in situ analyses of this sort in oil wells. The method is also being considered for use in making automatic analyses of the surface of the moon. In the case of the oil companies, the technique usually involves the lowering of a very small sealed-type accelerator into the well, where it generates 14-MeV neutrons. These undergo inelastic scattering in the surrounding formations; the gamma rays that are given off and the inelastic scattering then provide a pretty fair indication of the major elements present in the formation under investigation. 134 B. CHINAGLIA et al.

The method raises many difficult instrumentation problems. Since even H, С and О emit prompt gamma rays efficiently, it is possible to detect really only the main constituents of samples — not the trace con­ stituents. Another important point is that the gamma rays emitted with this method frequently go up to very high energies, which gives rise to spectro­ metry problems. The spectra obtained look like very poor gamma-ray spectra, judged by ordinary criteria. Work can be carried out on this basis, nevertheless. Carbon can be picked up, for example, as well as oxygen and hydrogen, which is normally not too easy with straightforward activation a n a ly sis. The same thing applies to the prompt capture-gammas when the neutrons are allowed to slow down in the medium and are then captured emitting gam­ ma rays characteristic of the isotopes that capture them. As far as I am aware, the Armour Research Foundation group is not tackling this problem particularly from the standpoint of activation analysis. They seem to be engaged on making a very careful survey of prompt-gamma spectra. A catalogue has already been issued by the Soviet group working on this subject; it is now the standard work in fact. There is a whole region, however — I think it is in the low-energy gamma-ray region — that is still not adequately mapped out, and this is what the Armour group is trying to do. W. W. MEINKE: My information is more or less the same. The Armour Research Foundation group is, I think, compiling a catalogue of prompt-gamma spectra — similar in format to the Heath catalogue for radioisotope gamma-ray spectra. They are using the Armour reactor, which is a typical research reactor, and does not provide the highest flux available in the country by any means. In general, I think that prompt-gamma analysis is a very promising field of investigation. Very few groups are working on the problem at the present time. I should like to add one or two general rem arks on the subject of acti­ vation analysis. During the past few years progress in this field has mainly involved improvements in physics and electronics "black boxes" for the analyst, be he physicist, engineer or chemist. In cases where the analyst is not a chemist and is allergic to chemistry, he will tend to confine his attention to these black boxes, thus concentrating on the non-destructive, gamma-spectrometric type of activation analysis. The point I want to make is that the development of chemical black boxes for physicists and engineers offers equally challenging possibilities. There is no reason why automation should not be applied to some of the straightforward radiochemical separations currently employed in activation analysis. The sample could go directly into the chemical black box, from there into a measurement black box, and the data could then be fed into a computer. If this were done, I am sure there would be far less reluctance than there is at the present time to give the chemical aspect of activation analysis its proper due, even in work on short-lived isotopes. V. P. GUINN: I believe that there is in fact one such black box already available. One of the California laboratories has now produced a complete system for carbon-14 dating. The device takes care of the combustion, the purification and the counting, so that it is an electronics and a chemical APPLICATIONS PRATIQUES DES RADIOÉLÉMENTS DE COURTE PÉRIODE 135 black box combined. It is in fact a completely automatic system for age determination. W. W. MEINKE: That is an excellent example and it serves to show that if the demand is great enough — as it is with carbon-14 dating—these black boxes can be developed.

RADIOACTIVATION ANALYSIS OF STRONTIUM IN RAT-BONE ASH

Y. MATSUMURA TOKYO WOMEN'S MEDICAL COLLEGE, TOKYO, JAPAN

Abstract — Résumé — Аннотация — Resumen

RADIOACTIVATION ANALYSIS OF STRONTIUM IN RAT-BONE ASH. The concentration of strontium normally present in most biological materials is so low as to be beyond the reach ot conventional chemical analytical methods. Since 1958 the Japanese Research Reactor 1 (JRR-1) has been available for use in general scientitic studies, which has made possible neutron activation analysis ot biological trace elements in Japan. The author has investigated the application of neutron activation analysis to quantitation of stable stron­ tium in rat-bone ash, taking advantage of the production of short-lived radioisotopes. Strontium has four stable nuclides. Activation by thermal neutrons will produce several kinds ol radioactive nuclides. These might also be produced trom rubidium and yttrium, which are hardly present in living materials. The strontium content of rat-bone ash, from animals which had been fed for three weeks with high fat, high protein, and control diets, was determined. The gamma-ray spectrogram of a radiochemically-purified specimen, which had been irradiated for two hours in the reactor, showed three distinct peaks at 0.150, 0.369 and 0.513 MeV. Most of the activities were due to the production of Srwrn, To a lesser extent, Sresmand Sr85 were also produced. From the area of main peak, the content of strontium in rat-bone ash was calculated. It is found to be within the range of 100-180 Mg/g.

ANALYSE PAR RADIOACTIVATION DU STRONTIUM CONTENU DANS LA CENDRE D'OS DE RAT. Dans la plupart des matières biologiques le strontium est normalement présent à une concentration si faible qu’il ne peut être décelé par les méthodes classiques d'analyse chimique. Depuis 1958, on peut utiliser le premier réacteur de recherche du Japon (JRR-1) pour des travaux scientifiques de caractère général, et il a ainsi été possible de procéder à l'analyse, par activation neutronique, des oligoéléments présents dans les tissus biologiques. L'auteur étudie comment, en tirant parti de la production de radioisotopes à courte période, on peut se servir de l'activation neutronique pour déterminer la quantité de strontium stable contenu dans la cendre d'os de rat. Le strontium a quatre isotopes stables. L'activation par un flux de neutrons thermiques produit plusieurs sortes de radioéléments. Ceux-ci pourraient aussi être obtenus à partir du rubidium et de l'yttrium qui n'existent qu'en quantités négligeables dans la matière vivante. L'auteur a déterminé la teneur en strontium de cendres d'os de trois groupes de rats à qui on avait admi­ nistré pendant trois semaines, au premier une nourriture riche en lipides, au deuxième un régime riche en protides et au troisième un régime témoin normal. Le spectrogramme gamma d'un échantillon purifié par des méthodes radiochimiques, qui avait été irradié pendant deux heures dans le réacteur, présentait trois pics distincts à 0,150, 0,369 et 0,513 MeV. Les activités étaient dues principalement à la production de87mSr. Il y a eu aussi production, en moins grande quantité, de85mSr et deessr. D'après la surface de la crête principale, on a calculé la teneur en strontium de la cendre d'os de rat. On constate qu'elle est de l'ordre de 100-180 |ig/g.

РАДИОАКТИВАЦИОННЫЙ АНАЛИЗ СТРОНЦИЯ В ЗОЛЕ КОСТЕЙ КРЫС. Концентрация стронция, присутствую­ щего в корме в большинстве биологических материалов, настолько мала, что недоступна обнаружению обычными химическими аналитическими способами. С 1958 года, когда Японский исследовательский реактор l(jRR-l) стали использовать и для проведения общих научных исследований, оказалось воз­ можным применение нейтронного активационного анализа биологических микроэлементов в Японии. Автор изучал применение нейтронного активационного анализа для количественного определения стабильного стронция в золе костей крыс, использовав возможность получения короткоживущих радио­ изотопов. Стронций имеет четыре стабильных изотопа. Активация с помощью потока тепловых ней­ тронов приводит к образованию различных радиоактивных изотопов. Оки могут образовываться из рубидия и иттрия, не содержащихся в живых тканях. 137 ■ с 138 Y. MATSUMURA

Определялось содержание стронция в зо.е костей крыс, получавших контролируемую диэту, бо­ гатую жиром и белком. При гамма-спектрографии радиохимически чистых образцов, облучавшихся в течение двух часов в реакторе, обнаружены три отчетливых пика при 0,150, 0,369 и 0,513 Мэв. Наибольшая величина активности была связана с образованием стронция-87т. В меньшем количестве были получены строн- ций-85т и стронций-85. Содержание стронция в золе костей крыс вычислялось из площади главного пика. Оно равнялось 100 - 180 мкг/г.

DETERMINACIÓN DEL ESTRONCIO EN CENIZAS DE HUESOS DE RATA POR RADIACTIVACION. En la mayoríade las sustancias biológicas, la concentración normal de estroncio es tan baja que escapa a la detec­ ción por los métodos clásicos de análisis químico. Desde que en 1958 se autorizara el empleo del Reactor de Investigación I del Japón (JRR-1) para estudios científicos de carácter general, se han podido analizar por activación neutrónica vestigios de elementos de interés biológico. Aprovechando la formación de radioisótopos de período corto, el autor investigó la aplicación del aná­ lisis por activación neutrónica a la determinación cuantitativa del estroncio estable en cenizas de huesos de rata. El estroncio posee cuatro núclidos estables. Su activación con un flujo de neutrones térmicos origina varios núclidos radiactivos. Estos se pueden formar asimismo a partir del rubidio y del itrio, muy escasos en las sustancias vivas. El autor determinó la concentración de estroncio en cenizas de huesos de ratas sometidas durante tres semanas a una dieta rica en grasas o rica en proteínas y de animales testigo alimentados con una dieta normal. Los espectrogramas gamma de las muestras purificadas radioquímicamente irradiadas durante dos horas en el reactor, presentan tres máximos bien definidos en 0,150, 0,369 y 0,513 MeV. La mayor parte de la acti­ vidad detectada se debe al CT|nSr. En menor proporción, se forman también esmsryWSr. El contenido en estroncio de las cenizas de los huesos de rata se calculó en función del área del máximo principal. El autor encontró que las concentraciones oscilan entre 100 yl80|ig/g.

1. INTRODUCTION

The concentration of strontium normally present in most biological mat­ erial is so low that it is beyond conventional analytical methods. Conse­ quently the values reported are too divergent to be of much use. Radio­ activation analysis has proved to be one of the most reliable and convenient methods for the investigation of trace elements in living matter [l, 2, 3j. SOWDEN and STITCH 14], investigating trace elements in human tissue, reported on the application of neutron activation analysis for the determ i­ nation of strontium in bone. Because of its long half-life, the danger from strontium-90 has in­ creased with the repetition of atomic bomb experiments. Once absorbed in mammals, strontium deposits mainly in bone tissues and strontium -90 ir­ radiates bone marrow, the important haematopoietic organ. The measurement of strontium in the body would be assessed more fully by determination of the content of stable strontium in various tissues than by simple tracer experiments, using radioactive isotopes of strontium. For such research the Japan Research Reactor 1 (JRR-1) was used for neutron activation analysis of strontium to ascertain its turnover in rat bone under various nutritional conditions.

2. EXPERIMENTAL

2.1 Animals

Albino rats, between two and three months of age and weighing 200 to 300 g, were maintained in iron metabolic cages and fed with Oriental Chow RADIOACTIVATION ANALYSIS OF STRONTIUM IN RAT-BONE ASH 139

MF for at least three weeks. Distilled water was given freely throughout the whole period. The experimental diet Was given for six weeks. After decapitation, the femurs were removed carefully from the soft tissues, soaked overnight in 1 M KOH and rinsed thoroughly with distilled water. The femurs obtained from one group of five rats were placed in a silica crucible, dried for 1 h at 100°C, and then ashed for 7 h in an electric muffle furnace at 500°C.

2.2. Strontium standard In an agate m ortar 323. 6 mg of strontium nitrate (Sr(N03)2 • 41^0) — corresponding to 100 mg of strontium — was diluted with 1 kg of calcium carbonate*. The latter was found to contain about 70 Mg/g strontium and the strontium standard was therefore assumed to be 170 ng/g.

2. 3 Neutron flux The maximum output of JRR-1 is 50 kW; it was driven routinely at40kW. The available neutron flux for the rabbit was 1011 n/cm2 s.

2.4 Activation of samples and standards About 2 g of the standard sample, each consisting of weighed mixtures of strontium nitrate and calcium carbonate (containing'70, 120 or 170 jug strontium) and six samples of bone ash, each wrapped in polyethylene sheets, were introduced into small polyethylene containers (rabbits) to be irradiated for 2h in the air-driven tubes of JRR-1.

2. 5 Radiochemical purification After irradiation for 2 h the activity at the surface of the rabbits was 1500 m r/h. This decreased to 700 m r/h within 10 min. The specimens werë f . left aside for 30 min before handling to allow the intense radioactivity from the isotopes of short half-life to decay. All chemical manipulations were carried.out from behind a lead shield, 10 cm thick. Discarded radioactive solution was also stored in polyethylene bottles which were placed behind a lead shield during the analytical pro­ c e d u re s . The irradiated samples were weighed into numbered 50-ml glass-stop- pered centrifuge tubes. Approximately 6. 0 ml distilled water and 2. 0 ml strontium carrier (containing 128 mg strontium in the form of strontium nitrate) were added to each of them; 10 ml fuming nitric acid were then care­ fully added to dissolve the samples. Strontium nitrate was precipitated by the further addition of 10 ml fuming nitric acid. The tubes were cooled in an ice bath for 10 min and centrifuged (1000 g) for 10 min. The supernatant was discarded. The precipitate was dissolved in 2 ml distilled water, re-precipitated by the addition of 10 ml fuming nitric acid and the supernatant discarded a s b e fo re .

* Purchased from the Junsei Chemical Works. 140 Y. MATSUMURA

The insoluble nitrate was re-dissolved in 2 ml distilled water and trans­ ferred into a 15-ml centrifuge tube, washing twice with 2 ml distilled water. The combined solution was made alkaline by means of ammonia water and precipitated with the addition of ammonium carbonate. The carbonate pre­ cipitate was dissolved in a minimum quantity of water and strontium was re-precipitated twice as nitrate, discarding the supernatant at each pro­ cedure. Nitrate precipitate was re-dissolved in distilled water and scav­ enged, using barium chromate and iron hydroxide [5]. Finally, purified strontium was transferred into a polyethylene tube as nitric-acid solution and radioactivity was measured with a well-type scintillation counter (Fig. 1). The chemical yield of the strontium carrier was assayed gravimetri- cally in the form of strontium carbonate.

Bone ash plus strontium carrier

Dissolve in HNOj Add fuming nitric acid C entrifuge

I 1 Discard supernatant Dissolve ppt in distilled water Add fuming nitric acid C entrifuge

,------1------, Discard supernatant Dissolve ppt in H 2 о Make alkaline Add carbonate

Discard supernatant Dissolve ppt

Nitrate precipitation repeated I------1 Discard supernatant Dissolve ppt Barium carrier added Chromate precipitation

I------1 Discard ppt Supernatant Carbonate precipitation

Discard supernatant Dissolve ppt Iron carrier added Hydroxide precipitation

Discard ppt Supernatant I Carbonate precipitation

Fig. 1

Scheme of radiochemical purification RADIOACTIVATION ANALYSIS OF STRONTIUM IN RAT-BONE ASH 141

A gamma-ray spectrum was drawn using an automatic 256-channel pulse height analyser.

3. RESULTS

The gamma-ray spectrum of the radiochemically-purified specimen is shown in Fig. 2. A sample of Hg203 was used to calibrate the gamma-ray energy, assuming that the main peak of Hg2°3 was 0. 279. MeV [6].

BONE ASH

0.389

Fig. 2

Gamma-ray spectrogram obtained by 256-channel pulse height analyser

The strontium standard sample showed three distinct peaks. Most of the activity was due to the production of Sr87*11', the peak of which is at 0. 389 MeV. To a lesser extent, Sr85 and Sr8&m were also observed. The purity of the calcium carbonate used to dilute strontium was not (Sufficient to obtain accurate results. It was inferred to contain rather a high quantity of strontium. From the results shown in Table I, it is assumed that the calcium carbonate is contaminated with strontium at the level of about 70 ppm. The commercial calcium carbonate was purified through nitrate recrystallization and carbonate precipitation. Thus the strontium content of calcium carbonate was reduced to about 8 ppm. This figure is applied to obtain the quantity of strontium in bone ash (Table II).

4. DISCUSSION

Strontium has four stable nuclides. Activation by therm al neutrons pro­ duces several kinds of radioactive nuclides which are summarized in 142 Y. MATSUMURA

TABLE I

RADIOACTIVATION ANALYSIS OF CALCIUM CARBONATE USED AS STRONTIUM DILUENT

Calcium carbonate Strontium nitrate Weight of irradiated Recovery of Activity Sr added (as Sr) sample Sr CO, concentration te) (g) te) 6°) (cpm /g) (ppm)

Group I

Brand

A 100 0 1. 9854 71.2 4 505 59

A 100 0.05 2. 0429 59.2 7 989 105

A 100 0.1 2. 0666 69.1 11 560 151

Group П

A 100 0 1. 9546 64.0 7 340 39

В 100 0 1. 9312 61.5 3 015 16

С 100 0 1. 9279 62.7 6 580 35

D 100 0 1. 9609 55.0 1 560 8.2

D 100 0.05 1. 9994 56.0 11 530 61

D 100 0.05 1. 9608 60.5 10 570 57

TABLE П

ACTIVITY OF STRONTIUM INDUCED IN RAT-BONE ASH AND STANDARD STRONTIUM AFTER TWO HOURS’ IRRADIATION

Weight of irradiated Recovery of Activity Sr Sample sample SrCOj concentration № (cpm /g) (ppm) Standard Strontium 1.9318 59.8 2 320 60

" 1.9318 68.4 5 680 110

” 2.0898 78 .2 8 660 160

Rat-bone ash 1. 6762 65.5 9 048 167

Rat*bone ash 1.2853 59.4 9 520 177

Standard strontium 1. 9609 55.0 1 560 8.2

■ 1. 9994 56. 0 11 530 58

" 1.9608 60.5 10 570 58

Rabbit-bone ash 1.9878 65.5 15 420 81

Rabbit-bone ash 2. 0172 62.0 18 450 93 RADIOACTIVATION ANALYSIS OF STRONTIUM IN RAT-BONE ASH 143

TABLE Ш

THERMAL NEUTRON ACTIVATION OF STRONTIUM

Stable nuclides S rM S rK S r " S r "

Natural abundance 0.56 9.86 9.02 82.56

Thermal neutron 1 1.3 0.005 cross-section (b)

Activated nuclides S jism S r85 S r,7m Sr*>

H alf-life 70 min 65 d 170 min 54 d

Radiation and its IT 0.007 energy (MeV) y 0.223 у 0.513 y 0.389 8 1.48 К 0.150

Table III. These nuclides might be produced from rubidium and yttrium, which are contained in only small amounts in living m aterial. Irradiation for 2 h produced chiefly Sr87m and S r 8 5 m . Other radioactivity deriving from elements other than strontium in bone ash were completely removed by the radiochemical purification procedure. This was clearly demonstrated from the gamma-ray spectrum and also from the half-life.

5. SUMMARY

(a) The application of neutron activation analysis to the measurement of stable strontium in bone ash is discussed. The Japan Research Reactor 1 was utilized successfully as a source of neutron flux of 1011 n/cm 2s. (b) Radiochemical purification recovered strontium in the range of 60 to 70%. Calcium or other co-existing elements were completely removed by the procedure. (c) Two hours irradiation produced mainly S r8 7 m . (d) The strontium content of rat-bone ash from rats fed for three weeks or more on Oriental Chow MF, was found to be within the range of 160 to 200 ppm .

REFERENCES

[1] SFENCER, R. P ., MITCHELL, T. G. and KING, R ., M edical Application of neutron Activation Analysis”, Int. J. of Appl. Rad. and Isot. 3 (1958) 104. [2] LENIHAN, J. M . A ., "Radioactivation Analysis in Biochemistry and Medicine", Radioactivation Analysis, froc. Symp. IAEA/ICSU, Vienna (1959), Butterworths, London (1960) 81. [3] BROOKSBANK, W. A ., LEDDICOTTE, G. W. and MAHLMAN, H. A ., "Analysis for trace Im purities by neutron Activation", J. Fhys. Chem. 57 (1953) 815. [4] SOWDEN, E. M. and STITCH, S. R ., "Trace Elements in hum an Tissues: 2. Estim ation of the C oncen­ trations of stable Strontium and Barium in human Tissues", Biochem. J. 62(1957) 104. [5] i BRYANT, F . J . , CHAMBERLAIN, A .C ., MORGAN, A. and SPICER, G. S . , Radiostrontium Fallout in biological Materials in Britain, AERE HP/R (1956) 2056, 2526. [6] KINSMAN, S., Radiological Health Handbook. U.S. Department of Health, Education and Welfare, Bureau of State Services, Cincinnati, Ohio. 144 Y. MATSUMURA

DISCUSSION

H. KEPPEL: Did you also determine the strontium content of the food and was any discrimination factor observed between strontium uptake and bone-ash concentration? Y. MATSUMURA: We are currently planning experiments to study the discrimination factor between strontium and calcium uptake. The results will be published. H. KEPPEL: As the strontium content in bone ash is dependent on the calcium in the diet, the strontium is usually calculated per gram of calcium. Did you estáñate this value? Y. MATSUMURA: Our experimental hypothesis was that there is dis­ crimination between calcium and strontium in animal organisms. H. KEPPEL: Have you compared your results with flame-spectro- photometry data? Y. MATSUMURA: No, not yet. A. WARD; If your work on strontium uptake is related to the question of strontium -90 uptake in human beings from fall-out, I do not see how ex­ periments can be devised to find out whether any pathological effects occur as the result of such extremely small quantities of ingested material. Y. MATSUMURA: Well, the point is that although the quantities of strontium in bone are small, ingested strontium would remain in animal organisms for a long time if the turnover rate of the element were low. To obtain the turnover rate, the quantity of stable strontium in the body has to be determined. V. P. GUINN (Chairman): Thank you, Dr. Matsumura. Before we close, I should like to make one comment which might be of general interest to participants. It concerns a meeting that was held last month in Gatlinburg, Tennessee, on the application of computer techniques to radiochemistry and activation analysis. It turned out to be a very good meeting and quite a lot of new m aterial emerged. The proceedings will be appearing in a few months' time and information can be obtained by writing to Dr. D. G. O' Kelly at the Oak Ridge National Laboratory. I believe that the proceedings are due to come out in the monograph series of the National Research Council. APPLICATIONS IN MEDICINE

APPLICATIONS OF IODINE-132 IN STUDIES OF THYROXINE TURNOVER

M . ANBAR WEIZMANN INSTITUTE OF SCIENCE AND IAEC SOREQ RESEARCH ESTABLISHMENT, REHOVOT, ISRAEL

Abstract — Résumé — Аннотация — Resumen

APPLICATIONS OF IODINE-132 IN STUDIES OF THYROXINE TURNOVER. Iodine-132 has been applied in our laboratories to two different problems in thyroid physiology. Determination of radiation damage to the thyroid at relatively low doses of internal radiation: It has been found that the rate of production of protein-hound iodine (PBI) by the thyroid significantly increases 24 h after the thyroid has absorbed doses of internal radiation in the range 50-1 OU rad. These findings were made possible by using I13i as the source of internal radiation and Ia * as an indicator of the rate of production of PBI. Next, U32 was used as a source of internal radiation as well as a tracer for PB I production, because it was possible to determine the effects oí radiation without interference of the radiological dose. These experiments, which have been carried out on rats, are presently being extended to human patients to determine the possible radiation damage of tracer doses of I131. During this investigation, special techniques were developed to cope with the specific requirements of using I*32 in thyroid studies. A quantitative determination of the rate of thyroxine deiodination in humans: In the course of an extensive investigation of factors which affect the rate of deiodination of thyroxine in mice and rats it became of interest to determine this process in humans. The change in conceritration of labelled thyroxine with time reflects the composite disappearance of thyroxine, including clearance via liver and re-absorption from intestines. In any procedure chosen, the inorganic iodide liberated from the labelled thyroxine has to be assayed. Con­ sequently the fate of iodide in the system determines the method of investigation. In humans the relative rates of deiodination and iodide clearance are about 1: 70 and thus a steady-state concentration of iodide in serum is attained. The stationary concentration ot labelled iodide, originating from the degraded labelled thyroxine, is dependent on two parameters — the rate of deiodination of thyroxine and the rate of iodide clearance. If the steady-state concentration of iodide-131 in blood could be determined as well as the rate of iodide clearance, then the rate of deiodination could be evaluated. Iodide-132 was therefore used as a tracer to determine both the steady- state concentration of I^i originating from labelled thyroxine and to evaluate the rate of iodide clearance both by kidneys and by the thyroid gland. The experimental procedure was as follows: Thyroxine labelled with I131 was injected into patients 48 h prior to an injection of iodide* 132. The activities of I«i and U32 in blood and urine, as well as the I13* uptake in the thyroid gland, were measured for 8 - 10 h following the iodide-132 administration. The steady-state concentration of iodide-131 in serum was determined from the ratio of activities of I131/1 132 in urine and the total I132 activity in serum. The rates of iodide clearance were determined by the aid of iodide-132 by the conventional methods. From these determinations it was possible to calculate the rate of deiodination of thyro­ xine in humans.

EMPLOI DE L'IODE-132 DANS DES ÉTUDES SUR LE RENOUVELLEMENT DE LA THYROXINE. L’iode-132 a été utilisé dans les laboratoires de recherche de la CEAI pour l'étude de deux problèmes se rapportant à la physiologie de la thyroïde. Détermination des radiolésions de la thyroïde causées par des doses relativement faibles de rayonnement interne: On a constaté que le taux de production, par la thyroïde, d'iode lié aux protéines augmente sensible­ ment 24 heures après l'absorption par la thyroïde d'une dose de rayonnement interne de l'ordre de 50 à 100 rad. Ces conclusions ont été établies en utilisant l’iode-131 comme source de rayonnement interne et l'iode-132 comme indicateur du taux de production de l'iode lié aux protéines. On a ensuite utilisé l'iode-132 à la fois c o m m e source de rayonnement interne et com m e indicateur de la production d'iode lié aux protéines, car il était possible de déterminer les effets des rayonnements sans qu'il y ait interférence de la dose radiologique. Ces expériences, pratiquées sur le rat, sont maintenant étendues à l'homme afin de déterminer les radiolésions

147 148 M. ANBAR que pourraient provoquer des doses d’iode-131 employé comme indicateur. Au cours de ces recherches, on a mis au point des techniques spéciales qui permettent de satisfaire aux exigences particulières de l'utilisation de l'iode-132 dans les études sur la thyroïde. Détermination quantitative du taux d^appauvrissement de la thyroxine en iode chez l'homme: Après avoir procédé à une étude approfondie des facteurs qui influent sur le taux d’appauvrissement de la thyroxine en iode chez la souris et le rat, on a cherché à déterminer ce processus chez l'homme. Le changement de concentration de la thyroxine marquée, en fonction du temps, traduit la disparition de la thyroxine par diverses voies, notamment son élimination par le foie et sa réabsorption à travers la paroi intestinale. Quelle que soit la méthode choisie, il faut mesurer la quantité d'iode inorganique libérée par la thyroxine marquée. Laméthode de détermination dépend donc du sort de l'iode dans l'organisme. Chez l’homme, le rapport entre le taux d'appauvrissement en iode et celui de l’élimination d’iode est d’environ 1/70, et on obtient ainsi une con­ centration d’iode dans le sérum en régime stationnaire. La concentration en régime stationnaire de l'iode marqué provenant de la dégradation de la thyroxine marquée, est liée à deux paramètres — le taux d’appauvrissement de la thyroxine en iode et le taux d'élimi­ nation de l'iode. Si l’on peut déterminer à la fois la concentration en régime stationnaire de l’iode-131 dans le sang et le taux d'élimination de l’iode, il devient possible d’évaluer le taux d'appauvrissement en iode. L'iode-132 a donc été utilisé comme indicateur pour déterminer la concentration en régime stationnaire de l’iode-131 provenant de la thyroxine marquée et pour évaluer le taux d’élimination de l'iode par les reins et par la glande thyroide. L'expérience s'est déroulée dans les conditions suivantes: On a injecté aux malades de la thyroxine marquée à l’iode-131, 48 heures avant de leur faire une injection d'iode-132. On a mesuré l’activité de i'iode»131et de l’iode-132 dans le sang et dans l'urine ainsi que le taux de fixation de l'iode-132 par la glande thyroïde, 8 à 10 heures après l’injection de l’iode-132. La concentration en régime stationnaire de l'iode-131 dans le sérum a été déterminée d'après le rapport entre les activités de l'iode-131 et de l’iode-132 dans l’urine et l’activité totale de l’iode-132 dans le sérum. Les taux d'élimination de l'iode ont été déterminés à l’aide de l’iode-132 par les méthodes classiques. C’est à partir des résultats obtenus que l’on a pu.calculer le taux d'appauvrissement de la thyroxine en iode chez l'homme.

ПРИМЕНЕНИЕ ЙОДА-132 В ИССЛЕДОВАНИИ ПРЕВРАЩЕНИЙ ТИРОКСИНА. Йод-132-применяется в наших ла­ бораториях для изучения двух различных проблем физиологии щитовидной железы. Определялось радиа­ ционное повреждения щитовидной железы при сравнительно низких дозах внутреннего ¿¿лучения. Об­ наружено, что скорость образования щитовидной желёзой йода, связанного с белком (PBI), значи­ тельно возрастает чере'э 24 часа пооде поглощения железой дозы внутреннего облучения порядка 50 - 100 рад. Эти данные были получены в результате использования J 131 в качестве источника внутреннего облучения и J132 в качестве показателя скорости образования PBI. Далее, J132 при­ менялся в качестве источника внутреннего облучения,, а также изотопного индикатора образования PBI, потому что можно было определить влияние излучения без помех, создаваемых радиологической дозой. Эти исследования, выполнявшиеся до сих пор на крысах, в настоящее время провёдены у боль­ ных с целью определения возможного радиационного повреждения, причиняемого индикаторными доза- m h J131> в ходе этих исследований были выработаны специальные методики, удовлетворяющие конкрет­ ным требованиям применения J132 при изучении функции щитовидной железы. Количественно определялись скорости дейодирования тироксина у человека. В ходе широких ис­ следований факторов, влияющих на скорость дейодирования тироксина у мышей и крыс, возник интерес к вопросу определения этого процесса у человека. Изменения, в зависимости от времени концентрации меченого тироксина, отражают сложный процесс исчезновения тироксина, включая удаление его пе­ ченью и вторичное всасывание из кишечника. При любой избранной методике необходимо определить количество неорганического йодида, высвобождаемого из меченого тироксина. Соответственно, судьба йодида в системе определяет метод исследования. У человека соотношение между соответствующими скоростями дейодирования и очищения йодида составляет приблизительно 1:70 и, таким образом, в сыворотке сохраняется постоянная концентрация йодида. Неизменность концентраций меченого йодида, образующегося из разложившегося меченого тироксина, зависит от двух параметров - скорости дей­ одирования тироксина и скорости очищения йодида. Если бы можно было определить постоянную кон­ центрацию J132 в крови, а также скорость очищения йодида, то можно было бы оценить и скорость дейодирования. В связи с этим J 132 применялся как изотопный индикатор для определения как по­ стоянной концентрации J 131, образующегося из разложившегося меченого тироксина, так и для оценки скорости удаления йода через почки и щитовидную железу. I132 IN STUDIES OF THYROXINE TURNOVER 149

Порядок проведения опыта был следующий: Тироксин, меченный J 131, вводился больным за 48 часов до инъекции J 132. Величины активности J 13i и J132 в крови и моче, равно как поглощение J132 в щитовидной железе, измерялись в течение И - Ю часов после введения J132. Постоянная концентрация J 132 в сыворотке определялась из со­ отношения активности J 131/J 132 в моче и общей активности J 132 в сыворотке. Скорости удаления Йодида определялись обычными методами с помощью J 132. Из этих определений можно было рассчитать скорость дейодирования тироксина у человека.

APLICACIONES DEL YODO-132 EN ESTUDIOS SOBRE RENOVACIÓN DE LA TIROXINA. El yodo-132 se ha utilizado en los laboratorios de la Comisión israeli de energía atómica para estudiar dos problemas de fisiología de la tiroides. Determinación de las radiolesiones de la tiroides causadas por dosis relativamente bajas de irradiación interna: Se ha encontrado que el índice de producción tiroidea de yodo ligado a la proteína (PBI) aumenta considerablemente 24 horas después de haber absorbido la glándula una dosis de irradiación interna del orden de 50 a 100 rad. Este resultado se alcanzó empleando 131Icomo fuente de radiaciones internas y 132I como indicador de la producción de PBI. En otros experimentos se empleó 1321 a la vez como fuente de irradiación interna y como indicador de la producción de PBI porque fue posible determinar los efectos de las radiaciones sin que interfiriera la dosis radiológica. Estos experimentos llevados a cabo con ratas, se están extendiendo actualmente al hombre con miras a determinar las radiolesiones que podrían provocar las dosis de 131I empleado como indicador. En estas investigaciones se perfeccionaron técnicas especiales que permiten satisfacer las exigencias particulares del empleo de 1S2I en el estudio de la tiroides. Determinación cuantitativa de la velocidad de desyodación de la tiroxina en el hombre: Después de haber procedido a un estudio detallado de los factores que afectan a la velocidad de desyodación de la tiroxina en ratones y ratas, se procuró determinar este proceso en el hombre. La manera en que la concentración de tiroxina marcada cambia con el tiempo refleja la desaparición de tiroxina, que se debe a muchas causas como la depuración plasmática en el hígado y la reabsorción a través de la pared intestinal. Sea cual fuere el pro­ cedimiento escogido, es preciso determinar cuantitativamente el yodo inorgánico liberado por la tiroxina mar­ cada. Así, pues, el método de investigación depende del destino del yoduro en el organismo. En los seres humanos, las velocidades relativas de desyodación y de depuración plasmática del yoduro están en la relación de 1 : 70, por lo que se alcanza una concentración estacionaria del yoduro en el suero. Esta concentración de yoduro marcado procedente de la degradación de la tiroxina marcada, depende de dos parámetros: la velocidad de desyodación de la tiroxina y la velocidad de depuración plasmática del yoduro. Si fuera posible determinar la concentración estacionaria del yoduro-131 en la sangre y la velocidad de depuración plasmática del yoduro se podría calcular la velocidad de desyodación. Por tanto, se empleó yoduro-132 como indicador para determinar la concentración estacionaria del Ull procedente de tiroxina mar­ cada y para evaluar la velocidad de depuración plasmática del yoduro tanto por los riñones como por la tiroides. El método experimental fue el siguiente: Se inyectó al paciente tiroxina marcada con Mil y, 48 horas después, yoduro-132. Durante ocho a diez horas después de la administración de yoduro-132, se midieron las actividades de 13*1 y 132I en la sangre y en la orina4 así como la captación tiroidea de 132I. La concentración estacionaria del yoduro-131 en el suero se determinó a partir de la razón entre las actividades del Ш1 y del 13ZI en la orina y de la actividad total del *32I en el suero. Las velocidades de depuración plasmática del yoduro se determinaron por los métodos clásicos utilizando como indicador *32I. A partir de los resultados obtenidos, se calculó la velocidad de desyodación de la tiroxina en el hombre.

A. DETERMINATION OF RADIATION DAMAGE TO THE THYROID* The level of protein-bound fodine (PBI) in the serum of rats was found to undergo significant changes within 24 h after their thyroids were ir­ radiated internally by iodine-131 at total doses above 150 000 rad [8]. In subsequent studies, it was found that labelled thyroglobulin is released from the thyroid upon internal irradiation with doses above 250 000 rad [9] and also at 130 000 rad [8]. No effect was, however, observed after the admi­ nistration of 100 цс I131, which deliver to the thyroid a dose of about 15 000

* By Anbar, M. and Inbar, M. 150 M. ANBAR rad [9, 10]. A slight increase in the РВР3* was observed in rats at total- body irradiation, of 450 rad 48 h after irradiation [11]; this effect was, how­ ever, interpreted as being due to an enhanced turnover. In clinical investigations, it was established that thyroglobulin is re­ leased into circulation as a result of therapeutic doses of internal irradiation [12] of the order of 10 000 rad. In a recent clinical study it was suggested that some thyroglobulin is released at much lower doses (about 1000 rad) and that the extent of thyroglobulin is not necessarily proportional to the dose of radiation [13]. Iodine-131 is being used in clinical studies on a routine basis as a tracer for the rate of formation of PBI. The PBI131 formed in the thyroid is released into the circulation a short time after the administration of iodide-131 and it approaches a constant level within 24 h [14] ; the half-time disappearance of the labelled PBI from circulation is of the order of 8 d [15]. The doses applied in these examinations, 25-50 цс, yield a total radiation dose of 35-70 rad to the thyroid [2], 21% of which is delivered within 48 h following administration. If this dose of local irradiation induced small changes in the rate of PBI formation, or in its composition 24 h after the administration of the radioactive tracer, these would hardly be demonstrable when the PBP31 in the serum is examined. The PBI131 found in the circulation after 24 h will overshadow sm all changes in the rate of PBI131 output, or in its composition. Iodine-132 may be applied to determine the rate of PBI formation and its composition at any given time after the administration of I131. The results thus obtained are representative of the state of PBI production without inter­ ference of the labelled PBI previously formed. Iodine-132 was applied in the present study as follows : Rats (five rats per group) were injected intraperitoneally with "carrier- free" iodide-131 or iodide-132 as necessary. One hour after injection of the iodide blood samples were drawn from the tail. The serum was separ­ ated and the PBI was precipitated by trichloroacetic acid. The iodide was then precipitated by silver nitrate and both PBI and I’ were radio-assayed consecutively in a well-type scintillation counter.The butanol non- extractable fraction in the PBI was determined by the conventional method, first re­ moving the iodide by an anion exchange resin. The PBI was first counted; it was thereafter subjected to consecutive extractions with water-saturated n-butanol, and counted again. When necessary the measured activity was corrected for decay of I132. When the experiment was performed on rats containing 1131, care was taken to adjust the energy discrim inator of the counting system so as to cut off any I131 activity. The doses absorbed from I131 and 1132 which had accumulated in the thyroid, were calculated, using the for­ mulae of FELLER et al. [8]. External irradiations were carried out with a Sr9o-Y90 source plated on a silver foil (8X8 mm); the foil was attached to the necks of the rats by an adhesive tape for a predetermined time. The source was calibrated by low geometry beta counting and the absorbed dose- rate at 5-mm depth was calculated to be 40 rad/min. The experimental results presented in Table I show the PBI level in rats one hour after the administration of iodide-132 at different time inter­ vals after absorption of different doses of radiation. In the first three groups of experiments Ii32wa.s used both as an internal source of radiation and as I132 IN STUDIES OF THYROXINE TURNOVER 151

TABLE I

PROTEIN-BOUND IODINE IN SERUM OF RATS AFTER INTERNAL AND EXTERNAL LOCAL IRRADIATION OF THYROID GLANDS (PBI132 determined 1 h after intraperitoneal injection)

Time after РВ1Ш/РВ1“ + 1“ Source of Dose Dose Accumulated first 1 h after radiation dose irradiation administration of I й* (ЦС) (rad) (rad) (h) (X 100)

1. Int. I1® 200 200 1 3.5 2. " ” . 450 8 000 8000 24 23 3. ” " 350 6 000 14000 48 19 4. " " 240 4 000 18000 72 18 5. " " 180 3 000 21000 96 19

6. In t.I“ * 20 20 1 4 .2 rj П « 60 1000 1000 24 14 8. " 40 700 1700 48 18.2

9. Ext. Sr90-Y90 1600 1600 1 4 .2 10. Int.I“2 60 1000 2 600 24 14.5 11. " " 40 700 3 300 48 19.2

12. I n t . I » 20 20 1 2.6 ( 0.5*) 13. Ext. Si80-Y80 120 120 24 5.7 ( 2 .8 * ) 14. " 200 200 24 4.8 ( 4.0*) 15. " 400 400 24 7.1 (34.0*) 16. " 1600 1600 24 14.5 (59,0*) 17. Int. I « 40 700 2300 48 15.0

18. Int. U® 20 20 1 4 .8 19. " 1Ш 0 .5 50 50 24 7 .5 (3 8 * * ) S S О 1.5 150 150 24 8 .5 (4 0 * * ) 21. " " 5 .0 500 500 24 9 .0 (43*S=)

* Percentage of butanol non-extractable activity in the PBI#. ** РВ1Ш/РВ1Ш+1Ш 24 h after 1ш administration. an indicator of the extent of production of labelled PBI within one hour after injection. The fourth group summarizes the effect of external irradiation, whereas in the fifth group, the thyroids were internally irradiated with I*3* at a much lower dose-rate than that of the external irradiations. It may be seen that previously-intact animals form in one hour about. 3-5% PBI [1, 6, 9, 12, 18] in the range of 20-2000 rad, irrespective of the immediate dose absorbed [1, 6, 9, 12, 18]. When examined 24 h after the initial irradiation, a sharp rise in the labelled PBI production-rate is observed [2, 7, 10].When the same rats were examined at 48, 72 and 96 h after irradiation, and the accumulated dose increased up to 21 000 rad [5], there was no further in­ crease in the rate of PBI production. Almost analogous behaviour is observed at lower accumulated doses up to 3000 rad [7, 8, 10, 11, 16,17]. At much lower doses (less than 1000 rad), the increase in the rate of 152 M. ANBAR

PBI production depends on the administered dose; a similar effect is obtained whether the dose is given externally at a high dose-rate (40 rad/min) or internally (less than 5 rad/h) [13-16, 19-21]. The extent of PBI131 production in 24 h, which was examined simultaneously with the PBII32 produced within one hour, also showed a slight increase with the absorbed dose [19-21]; this increase, however, is much less conspicuous, because a major part of the PBI131 present in the blood at 24 h has been formed during the first hours after administration, that is, before any radiologically-induced changes have occurred. The lowest dose of radiation which was still found to affect the rate of labelled PBI production is less than 50 rad [19] (50 rad is the accumulated dose over 24 h, but it should be remembered that the effects of radiation manifest themselves only a few hours after irradiation). This is of the order of magnitude of doses delivered to patients when determining the rate of formation of PBI. In one series of experiments (group 4)thebutanolnon-extractablefraction of the PBI has been determined, and it was found to increase rapidly with the increase of the absorbed dose [12-16]. This has previously been observed, but at doses one hundred times higher [10,12]. W hen th e P B I 1 3 2 determinations were carried out, 2 or 4 h after the adm inistration of iodide-132, the difference between irradiated and non­ irradiated rats became much sm aller. It seems that the irradiated gland releases some abnormal PBI at a faster rate than the release of normal PBI from the non-irradiated gland, but the equilibrium level of PBI in blood of irradiated and non-irradiated animals has a sim ilar value.

B. A QUANTITATIVE DETERMINATION OF THE RATE OF THYROXINE DEIODINATION IN HUMANS*

The turnover of thyroxine in humans has been the subject of a number of investigations [15] during which the РВП31 level in blood was followed for over ten days. In the course of an extensive investigation of factors which affect the rate of deiodination of thyroxine in mice [16] and rats [17] it be­ came of interest to determine the rate of this process in humans. The change in concentration of labelled thyroxine with time reflects the composite disappearance of thyroxine, inoluding clearance via liver and reabsorption from the intestines [18]. In any procedure chosen to assess the process of deiodination, the inorganic iodide liberated from the labelled thyroxine has to be determined. Consequently, the fate of iodide in the system determines the method of investigation. In rats, for instance, thyroidectomy and nephrectomy were performed to avoid substantial losses of iodide, which would prohibit any quantitative interpretation [17,19] .In humans the relative rates of deiodination and iodide clearance are about 1:70; .thus a steady- state concentration of iodide in serum is attained. The stationary concentration of labelled iodide originating from the degraded labelled thyroxine is dependent on two param eters — the rate of deiodination of thyroxine and the rate of iodide clearance. The rate of

* By Anbar, M ., Guttman, S ., Rodan. G. and Stein. J. A. I132 IN STUDIES OF THYROXINE TURNOVER 153 deiodination can thus be evaluated from measurements of the steady-state concentration of iodide originating from the labelled thyroxine and the rate of iodide clearance. The steady-state concentration of labelled iodide originating from thyroxine is of the order of 1 - 2% of the total labelled iodine content in the serum; hence, it is impossible to determine its value directly with suffi­ cient accuracy. On the other hand, iodide is selectively excreted by the kidneys and under non-pathological conditions of the kidney no protein-bound iodine is excreted in urine. If iodide-132 is administered into serum and is allowed to mix with the iodide-131 which originates from the deiodination of thyroxine-I131, both isotopes will be excreted in the urine at a rate propor­ tional to their concentration in serum. From the relative amounts of iodide-132 and iodide-131 in urine, and the concentrations of PBI131 and of 1132 in serum , the concentration of I131 in serum and the ratio of I131/PBI13i may be determined with satisfactory accuracy. The method is advantageous in that it yields directly the rate' of deiodination of thyroxine and the examin­ ation takes only 6-8 h.

EXPERIMENTAL

P ro c e d u re

Fifty m icrocuries of 1-thyroxine labelled with I13i (Abbott Laboratories Cat. No. 6706) were injected intravenously into patients 48 h prior to an injection of iodide-132. The 48 h period allows thorough equilibration of the thyroxine as well as removal of any iodi-de or iodo-organic im purities. On the day of examination, the patients were injected with a dose of 250 цс of P 32 (integral radiation dose to thyroid — 3 rad [2]; integral whole body dose — 50 m r [1]). Urine voided was then collected for 3-4 h, and its volume (U) and its iodide-132 concentration (n) (in term s of percentage of the injected dose) were determined. Four hours after injection (which provides ample time for equilibration of iodide-132 with the iodide pool in the organ­ ism [14], the 1132 uptake in the thyroid was determined by comparing the 11Э2 activity in the thyroid to that of a phantom containing the injected dose of D32, after the energy discrim inator was set to cut off any Im radiation. Simultaneously with the uptake measurement, a blood sample was taken into a heparinized test tube. After separation of serum by centrifugation, proteins were precipitated by trichloroacetic acid (TCA) containing carrier iodide (0.2 M). The precipitate was then washed with TCA and all the supernatants were collected. Iodide was then precipitated from the supernatant fluid by silveri nitrate and centrifuged. The PBI and iodide fractions were counted in a well-type Nal scintillation counter, with a single channel analyser, which enable complete discrimination againt 1131 radiation and counting of the 1132 activity witfy 7% efficiency (at a background of 20 cpm). The iodide in the urine samples was also assayed as silver iodide after adding sodium iodide carrier. Each measurement was compared with a standard sample containing 4 .10-4 of the injected dose; thus no corrections for radioactive decay were re q u ire d . 154 M. ANBAR

Urine was again collected for 2-3 h after which the thyroid uptake was measured and another blood sample taken. This procedure was repeated after another 2-h interval. After the P32 activity was determined, thesamples of iodide in urine and PBI in blood were allowed to stand for 48 h to permit complete decay of the I132 activity. The P-31 activity was then determ ined under optimal measuring conditions and compared with a standard sample containing 4 .10"4 of the injected dose of labelled thyroxine-1131. From the activities of iodide-132 (n) and iodide-131 (m) in urine, and those of PBIisi (a) and iodide-132 (c) in blood, it was possible to calculate the rate of deiodination of the labelled thyroxine.

RESULTS AND DISCUSSION

Derivation of formulae

Definitions: kd = rate of deiodination kc = rate of iodide clearance by the kidneys kT = rate of iodide clearance by the thyroid a = concentration of thyroxine 1131 in blood b = concentration of iodide-131 in blood с = concentration of iodide-132 in blood m = concentration of iodide-131 in urine n = concentration of iodide-132 in urine

As concentrations appear only as ratios, their units may be chosen arbitrarily. We have defined them as percentage of the injected dose per m illiliter of blood or urine.

Ц) К urine I' < kj, * thyroid

dl*"/dt = kda - (kc + kT)b

At equilibrium b/a = k(j/(kc + kT); kd = b/a X (kc + kT). A fter equilibration of I132 with I131

m/n = b/c b = m. c/n If с is determined at two tim es, ti and t.2, an d t 2 - t j = A t

-fk +k_)At c„ = ci e 1 с T'

In c : / c 2 = (kj. + kjOAt kc + kT = 1/t 2.3 log Cj/c2 kd = (m /n X c/a) 2.3 log Cj/c2 X 1/At

It is also possible to derive values of kc and kt from the experimental d a ta . I132 IN STUDIES OF THYROXINE TURNOVER 155

TABLE lia

DETERMINATION OF THE RATE OF DEIODINATION OF THYROXINE BY THE DOUBLE TRACER TECHNIQUE Part 1 - Experimental data

Designation of patient

AВ С

First interval ( min) (Att) 220 222 207 Vol. of urine (ОД (ml) 316 714 116 4a I. D. I132 per ml urine (i^) X102 7.0 3 .4 13.2 "la I. D. I132 excreted in urine 22.1 24.3 15.4 °lo I.D. I132 in the thyroid (TL) 9 .9 11.0 11.8 % I. D. I132 per ml urine ( mp X103 4 .2 9 .4 2.8 "¡а I. D. iodide-132 per ml serum (ct) X103 2. 65 2.8 2.8 ° h I. D. PBI13i per ml serum (a^ X102 1.22 3.0 2.5

Second interval ( min) ( At2) 195 165 182 Vol. of urine (ОД(т1) 968 334 76 ° k I. D. I132 per ml urine (пг) X102 1.69 2.6 8 .3 "¡o I. D. I132 excreted in urine 16.4 8.7 6.3 % I. D. I^ 2 in the thyroid ( T¿) 11.2 11.4 11.7 % l.D . I13* per ml urine ( m¿) x 103 1.6 8 .0 2 .0 % I. D. iodide-132 per ml serum (c ¿ X103 1.98 2.25 2. 52 la I. D. PBI131 per m l serum (a2) x 102 1.20 3 .0 2.3

Third interval (min)(Atj) 120 120 118 Vol. of urine (U3)(ml) 354 426 51 ”¡ 0 1. D. I132 per ml urine (nj) X102 1.89 1.31 7.72 "¡o I.D. I132 excreted in urine 6.7 5.6 3.94 % I. D. I*32 in the thyroid (T3) 12.2 13.6 10.9 "¡a I. D. I132 per ml urine (mj) 2 .6 4 .6 20.8 % 1. D. iodide-132 per m l serum (Cj) X103 1.66 1.9 2. 35 lo I. D. PBI131 per ml serum (aj) X102 1.18 3.2 2 .3

Defining also

U = volume of urine excreted in At T = percentage of injected dose taken up by the thyroid during At V = volume of distribution of iodide

U2n 2 = kcV i i ^ + c.^A t Т з-Tj = kTV iiCi+CjJAt

kc = 2U2n2/VjCj + c2)At kT = 2(T2-T 1)/(c1 + c2)At

V = 2(100-U1n 1-Uan2-T1-T2)/(c1 + c2)1 in g e n e r a l 156 M. ANBAR

V = 2(100-T ,-E U sn,)/(c,_1 + ck) ■ kd = (m /n X c/a) (U2n2 + T2 - T1)/(100-U1n1-U2n2-T1T2)At.

The first method is most sensitive to errors in the determination of Cj and Cj; the ratio (m/n X с/a) may be averaged from determinations made at different tim es. The second*extended method involves less errors of measurem ent since the concentration of iodide-132 in urine is more-than ten tim es that in blood, and the urine volume can be determined with ac­ c u ra c y .

In this method of double labelling, the short half-life of iodine-132 is a great disadvantage. We have therefore recently switched over to use iodine-125 as the second tracer isotope.

TABLE lib

DETERMINATION OF THE RATE OF DEIODINATION OF THYROXINE BY THE DOUBLE TRACER TECHNIQUE Part 2 - Calculation of specific rate constants

Designation of patient

A В С

2 .3 log cj/ cj ( ^ ) 0.290 0. 216 0.106

m2/n 2 X c2/a 2 = (qj) x 10* 1.64 2 .3 2. 66

• q2/A tj = kj x 105 (m in 'l) 2.44 3.02 1.54

2 .3 log c2/ c 3 (P3) 0.175 0.170 0. 074

m j/n jX C j/a j (qj) XlO* 1.66 2. 08 2.75

ps xq3/At3 = kjXIO5(m ln-i) 2.42 2.95 1.72

и 2П2+ T j-T i ; (Uj) 17.7 10.7 6.3

Uinj+ U2nj+ : (Vj) 49.7 4 4 .4 33.8

Uj /(100-V j) ¡ (Wj) 0.352 0.192 0.101

kj = w2-q2/AtjXl05(min-i) 2.96 2.68 1.48

7.7 7 .8 3.94 U3n3+Tr T2i(u¡P U ^ + U jnjt U3n3+T3;(v3) 57.4 52.2 37.0

U j/(100-v3) ¡(Wj) 0.180 0.166 0. 062 1.43 kd = Ws' 10s ( m i r r 1) 2 .5 2.83 k. average X 10s (m in -1) 2.58 2. 87 1.54 d t | (days) 18.6 16.7 31.2 I132 IN STUDIES OF THYROXINE TURNOVER 157

Clinical examinations

Although only a limited number of patients have been examined by this method as yet, the results show that it can be applied as a routine procedure and may provide important clinical information. Table П gives data on rates of thyroxine deiodination for three patients examined. The clinical results, which will be published elsewhere, show that the rate of deiodination is considerably increased in hyperthyroid states and diminished in old age, in hypothyroid states and under the effect of propyl­ thiouracil. It is suggested that the rate of deiodination may serve as a better indicator of the clinical state of a patient than the rate of iodine uptake or of thyroxine production.

REFERENCES

[1] COOK, G .B ., EAKINS, J. and VEALL, N ., Int. J. Appl. Rad. Isotopes 1 (1956) 85. [2] HALMAN, К. E and POCHIN, E.E. , Brit. J. Radiol. 31 (1958) 581. [3] GOOLDEN, A .E .G . and MALLARD, J. R ., Brit. J. Radiol. 31 (1958) 589. [4] BORNER, W. , Klin. Wschr. 39 (1961) 990. [5] CÁVAL1ERI, R. R. and KING, E. K. , J. Nucl. M edicine 2 (1961) 119. [6] ROBSON, J. , AERE M 749 (1960). [7] BORNER, W. , HAMANN, W. and MOLL, E. , N ucl. M edizin 2 (1962) 277. [8] FELLER, D.D. , CHAIKOFF, I.L. , TAUROG, A. and JONES, H.B. , Endocrinology 45 (1949) 464. [9] TONG, W., TAUROG, A. and CHAIKOFF, I.L. , J. biol. Chem. 195 (1952) 407. [10] TAUROG, A ., EVANS, E.S. , POTTER. G. D. and CHAIKOFF, I. L. , Endocrinology 67 (1960) 609. [11] VITTORIO, P.V. and ALLEN, M.J. , Radiation Research 13 (1960) 256. [12] ROBBINS, J . , PETERMANN, M. L. and RALL, J .E .. J. biol. C hem . 208 (1954) 387. [13] OWENS. C .A ., McCONAHEY, W. M. , CHILDS, D .S. and McKENZIE, B .F ., J. C lin. Endocrinol. Metab. 20 (1960) 187. [14] QUIMBY, E .H ., REITELBERG, S. and SILVER, S ., Radioactive Isotopes in Clinical Practice, Ch. 22 Lea and Febiger, Philadelphia (1958). [15] STERLING, K. and CHODOS, R.B., J. Clin. Invest. 35 (1956) 806. [16] ANBAR, M. and INBAR, М., Bull. Res. Counc. Israel 11a (1962) 51. Am. J. Physiol, (in press). [17] STEIN, J .A ., ANBAR, M ., GUTTMANN, S. and ERNST, N ., Nature 192 (1961) 1303. [18] INGBAR, H. and FREINKEL, N ., Recent Progress in hormone Research 16 (1960) 353. [19] ANBAR, М ., STEIN, J.A. , RODAN, G. , GUTTMANN, S. and HOCHMANN, A. , Bull. Res; Counc. Israel 11a (1962) 50.

DISCUSSION

B. MALAMOS: I should like to mention that in our thyroid clinic, where over 200 uptake tests a month are performed, we are making increasing u s e of 1132 for the diagnosis of thyroid diseases because there is no doubt that the irradiation dose is thereby very much diminished. In those cases, however, where we have to make plasma measurements (48-h PBI) and perform scanning, it is difficult to make use of B32, so that in such cases we still have to rely on I13i. I should like to make one remark on the subject of the treatment of thyro­ toxicosis patients. When Ii3i treatment is administered to such patients, it is important to know as soon as possible whether or not euthyroidism has been established. Two attempts have been made to use 1132 for this purpose: 158 M. ANBAR

in one case large amounts of 1132 were used and uptake tests performed; in the other, tracer doses of 1132 were administered and measurements were made of inorganic 1132 urine excretion. We have now tried adm inistering 80-100 цс of 1132 three, six and nine weeks after the 1131 treatm ent, making uptake measurements and using a 256-channel analyser for the isotope dis­ crimination. The results are encouraging but not absolutely reliable because of overlapping. Details on this work are given in a paper presented a month ago at the Journées Médicales du Proche et Moyen Orient at Teheran. K. SCHEER (Chairman): Thank you, Dr. Malamos, for your obser­ vations. You have touched on one of the main problems connected with the thyroid-function test, viz. whether it is possible to make a proper examin­ ation of thyroid function with a short-lived isotope such as I132.In many cases only the initial phase of the thyroid function can be m easured in this way, and that is often insufficient for a diagnosis. In my own country, where a relative iodine deficiency exists, we cannot dispense with determinations of the radioactive PBI in the serum, so that the initial tests can only be considered as screening tests. As for examining thyroid function very soon after a therapeutic dose of 1131, there are of course other isotopes of iodine that are even more use­ ful for this purpose, for example 1125, which has a much longer half-life but very different radiation characteristics. Because of its very low gamma energy this isotope can easily be measured in the presence of much larger am ounts of 1131. K.H. EPHRAIM: I am rather interested in this technique of measuring the uptake of 1125 in the thyroid in the presence of much larger amounts of 1131. I should like to ask M r. Scheer what dose of 1125 is used and how much 1131 is present when this method is applied. Is gamma spectrometry used? If so, what does one do to avoid disturbances as a result of Compton scatter from the 1131 affecting the P 25 photopeak? K. SCHEER: For a full investigation of the thyroid function, we use a mixture with 1 цс of 1131 for the uptake m easurem ents and 15 цс of 1131 f o r scans and blood-sample measurements. Because of the difference in con­ centration, there is very little interference with the 1125 photopeak on the part of 1131 Compton scatter. When m easuring 1125 in the presence of larger amounts of 1131, a very thin crystal has to be used. This results in a decrease in counting efficiency for the 1131. Since the K-radiation of 1125 is only 27 kV, an efficiency of 100% can be obtained, even.with a crystal as thin as 2 mm. In the case of the 360-kV gamma of 1131, the crystal would only have an efficiency of around 5-10% . K.H. EPHRAIM:The difference in efficiency you mention would certainly apply in the case of the 1131 photopeak. It would not apply, however, to Il3i Compton scatter of low energy. K. SCHEER: Yes, but in a thin crystal the absorption and hence the efficiency is very low. K.H. EPHRAIM: I agree. But that would not apply to the body of a patient What you are comparing is the efficiency for the 1131 photopeak, i.e. 360 kV, and the 27 kV of the 1125. What you should be comparing, I think, is the effi­ ciency for the P25 photopeak and the efficiency for the Compton scatter in the same region of Ii3i. I132 IN STUDIES OF THYROXINE TURNOVER 159

K. SCHEER: I don’t think it is possible to obtain a good external m easure­ ment of incorporated 1125. We work only'with small samples of blood or excreta measured outside the body.

MARQUAGE AU BROME-82 DE LA SERUM-ALBUMINE HUMAINE,DE L ’INSULINE ET DU FIBRINOGÈNE PAR VOIE É LE C TROC HIMIQUE

U. ROSA, G. A. SCASSELLATI ET G. PENNISI CENTRE DE RECHERCHES NUCLÉAIRES SORIN, SALUGGIA, ITALIE

Abstract — Résumé — Аннотация — Resumen

BROMINE-82 LABELLING OF HUMAN SERUM ALBUMIN, INSULIN AND FIBRINOGEN BY ELECTRO­ CHEMICAL MEANS. The authors describe results obtained with a method using bromine-82 to label human serum albumin, fibrinogen and insulin, three organic substances of special importance in diagnostics and bio­ logical research. The method involves electrolytic bromination in an aqueous solution; this is performed in an electrolysis cell, whose anodic zone containing the substance to be labelled is partitioned from the cathodic zone by a dialysis membrane. For each of the three substances mentioned, the degree of bromination produced by a direct current (200, 200, 300 x 10"6 was studied as a function of anode potential in 10'3 and 10’4 M solutions of NH4Br, the amount of bromine-labelled substance formed being checked by radioelectrophoresis for various anodic potential values differing from each other by 50 mV. By immuno-electrophoresis it was ascertained that dénaturation of albumin and fibrinogen only starts at anodic potential values for which the degree of labelling is already very high as compared with that yielded by chemical methods of labelling. • The method here described has the advantage of rapid execution and is well suited to remote handling in a shielded zone.

MARQUAGE AU BROME- 82 DE LA SÉRUM-ALBUMINE HUMAINE, DE L’INSULINE ET DU FIBRINOGÈNE PAR VOIE ELECTROCHIMIQUE. Les auteurs exposent les résultats obtenus par une méthode de marquage au brome- 82 de trois substances organiques particulièrement intéressantes pour l’usage diagnostique et pour la recherche biologique: albumine de sérum humain, fibrinogène et insuline. La méthode comporte une bromuration électrolytique en solution aqueuse qu’on exécute dans une cellule d’électrolyse dont la zone anodique contient la substance à marquer et est cloisonnée par rapport à la zone cathodique par une membrane à dialyse. Pour chacune des trois substances susmentionnées, on a étudié le rendement de bromuration à courant constant (100, 200, 300* 10~6A) en fonction du potentiel anodique, en solution 10-â et 10'4 M de NH4Br, en contrôlant par radioélectrophorèse la quantité de produit marqué au brome formé, pour différentes valeurs du potentiel anodique décalées de 50 mV. Pour l’albumine et le fibrinogène, les auteurs ont vérifié par immuno-électrophorèse que la dénaturation de ces protéines ne commence qu'à partir des valeurs du potentiel anodique pour lesquelles le rendement du marquage est déjà très élevé par rapport aux méthodes de marquage par voie chimique. Cette méthode présente l’avantage d'une grande rapidité d’exécution et s'adapte bien à une manipulation à distance, en enceinte blindée.

ЭЛЕКТРОХИМИЧЕСКОЕ МЕЧЕНИЕ ИЗОТОПОМ БРОМА-82 АЛЬБУМИНА ЧЕЛОВЕЧЕСКОЙ СЫВОРОТКИ, ФИБРИНОГЕНА И ИНСУЛИНА. Излагаются результаты, полученные с помощью метода мечения изотопом брома-62 трех органических веществ, представлявших особый интерес для диагностического применения и биологи­ ческих исследований: человеческого сывороточного альбумина, фиброногена и инсулина. Метод включает в себя электролитическое бронирование в водном растворе в электролитической ванне, анодная зона которой содержит вещество для мечения и отделена от катодной зоны Аналити­ ческой перегородкой. Для каждого из вышеуказанных веществ было проведено исследование коэффи­ циента бромирования в растворе К Н4Вг при 10"* и 10“4М при постоянном токе (100, 200, 300»10"®А), в зависимости от анодного потенциала; количество изготовленного меченного бромом вещества кон­ тролировалось радиоэлектрофорезом при различных значениях анодного потенциала, вплоть до 50 мв. В отношении альбумина и фибриногена с помощью иммуно-электрофореза было установлено, что денатурация этих протеинов начинается лишь при таких значениях анодного потенциала, при которых

161 162 U. ROSA, G. A. SCASSELLATI et G. PENNISI

выход образовавшихся меченных продуктов ухе очень высок по сравнению с химическим методом ме- чения. Преимуществами этого метода являются его быстрота и возможность управления на расстоянии процессом, происходящим в экранированном корпусе.

MARCACIÓN DE SUEROALBUMINA HUMANA, DE INSULINA Y DE FIBRINÓGENO CON BROMO-82 POR VÍA ELECTROQUÍMICA. La m em oria expone los resultados obtenidos por un método de marcación con bromos 82 de tres sustancias orgánicas de particular interés en el diagnóstico y en las investigaciones biológicas: sueroalbúmina humana, fibrinógeno e insulina. El método consiste en una bromuración electrolítica en solución acuosa, que se efectúa en una celda cuya zona anódica contiene la sustancia a marcar y está separada de la zona catódica por une membrana diali- zadora. En cada uno de los tres casos, se ha estudiado el rendimiento de la bromuración con corriente de inten­ sidad constante (100, 200, 300 • 10~6 en función del potencial anódico, en soluciones 10“s y 10~4 molares de NH4Br, controlando por radioelectroforesis la cantidad de producto marcado con bromo que se forma para diversos valores del potencial anódico a intervalos de 50 mV. En el caso de la albúmina y del fibrinógeno, se ha comprobado por inmuno-electroforesis que la des­ naturalización de estas proteínas comienza solamente a partir de valores de potencial anódico para los que el rendimiento de la marcación es ya muy elevado en relación con los métodos de marcación por vía química. Este procedimiento presenta la ventaja de ser muy rápido y de poder llevarse a cabo por mando a distancia en un recinto blindado.

1. INTRODUCTION ' '

L’évolution des applications, dans le domaine de la médecine et de la biologie, des protéines marquées, surtout de celles qui sont marquées à l’iode-131, a suggéré, par analogie, la mise au point de méthodes de bro­ muration qui permettent d’employer concurremment, en plus des protéines marquées à l’iode-131, les mêmes produits marqués au brome-82. Comme dans le cas de l’ioduration, c’est surtout par l’intermédiaire de la molécule de tyrosine que le brome est introduit dans la molécule de sérum-albumine, de l’insuline et du fibrinogène car la tyrosine [l]fait partie des groupes que l’on trouve généralement dans les protéines (4,7% dans la. sérum-albumine, 5,5% dans le fibrinogène et 13% dans l’insuline [2]). Si l’ioduration de la sérum-albumine n’est pas contrôlée soigneusement, il se peut que les réactions secondaires d’oxydation modifient la structure de la protéine, par exemple, par oxydation de la cystine avec rupture des ponts S-S. Dans ce cas, en plus des modifications des caractéristiques bio­ logiques, la sérum-albumine montre une mobilité électrophorétique et des réactions immunitaires différentes [3J. Dans le cas de la bromuration, il se peut que les réactions secondaires d’oxydation jouent un rôle plus important; par exemple, la cystine est oxydée en acide cystéinique bien plus rapidement par le brome que par l’iode [4]. Cela peut expliquer la difficulté que nous avons éprouvée à brom urer la sérum-albumine par le système Вг'-ВгОз suivant une méthode analogue à celle qu’on adopte avec succès pour l’ioduration [5]; dans ces conditions nous avons obtenu avec un très faible rendement (0,001 mg Br/mg SA), une sérum-albumine bromée qui est dénaturée, considérablement déjà, par l’essai à l’acide trichloroacétique (АТС). On parvient à de meilleurs résultats en faisant réagir, par stratification sans agitation, une solution aqueuse de sérum-albumine avec une solution chloroformique de brome. Dans ces conditions on obtient une albumine bro­ mée non dénaturée par l’essai à l’acide trichloroacétique; par contre, le MARQUAGE AU BROME-82 DE LA SERUM-ALBUMINE 163 rendement de bromuration est très variable (maximum: 8 * 10' 2 mgBr/mgSA) et la méthode ne saurait être conseillée pour la préparation courante à cause des difficultés évidentes d’opération. Il apparaît donc que l’on ne peut éviter ou réduire la dénaturation de la protéine qu’en employant une concentration très réduite de brome (à l’état de B r2). En préparant le brome par l’électrolyse d’une solution de NH 4B r, an peut contrôler la vitesse de formation du Br 2 en choisissant une valeur con­ venable du courant d’électrolyse. Dans ce cas, la protéine à bromer est ajoutée à la solution de NH4Br dans la zone anodique de la cellule d’électro­ lyse; une membrane à dyaliser sépare la zone anodique de la zone catho­ dique pour éviter la diffusion de la protéine vers la cathode.

2. PARTIE EXPÉRIMENTALE

Pour chaque valeur de l’intensité du courant, la quantité totale de brome qui réagit avec la protéine est évidemment une fonction de la durée del*élec­ trolyse fixée, une fois pour toutes, à trois heures. Une méthode de bromu­ ration de plus longue durée n’aurait pas d’intérêt vu la courte période du b ro m e -8 2 . Pour ce qui concerne le choix d’une valeur appropriée du pH de la solu­ tion de'protéine, on a réalisé la bromuration du fibrinogène et de la sérum- albumine à pH=6,5 - 6 , 8 , valeur de l’ordre du pH du plasma. Dans le cas de l’insuline on a choisi une valeur de pH= 2,5; dans ces conditions, l’insu­ line est stable en solution et garde son activité biologique [ 6].

COUiOMÈTRE

POTENTIOMETRE ENREGISTREUR

Figure 1

Cellule d'électrolyse et circuit de mesure 1. Electrode en feuille de platine 2. Electrode en fil de platine 3. Membrane â dyalyse cathodique 4. Tube de remplissage de la zone 164 U. ROSA, G. A. SCASSELLATI et G. PENNISI

Nous décrirons d’abord l’appareillage employé et les méthodes de con­ trôle des protéines bromées que l’on obtient par électrolyse.

2 . 1 . Appareillage et circuit de mesure et de contrôle (fig. 1)

La cellule d’électrolyse est formée d’un récipient en verre Pyrex ayant une capacité de 15 - 20 ml et renfermant une anode annulaire en feuille de platine (diamètre:20 mm, hauteur: 20 mm, surface totale utile: 12,7 cm2). La cathode est formée d’un fil de platine placé à l’intérieur d’un tube en verre Pyrex (diamètre: 10 mm) dont le fond est fermé par une membrane à dyalise (diamètre moyen des pores: 48 A, épaisseur: 25 ц). L’alimentation de la cellule d’électrolyse est assurée par un coulomètre (modèle Metrohm E211) dont la précision de réglage du courant est de 0,1%, Une électrode au calomel est plongée dans le compartiment anodique; le potentiel qui s’éta­ blit entre l’anode et l’électrode de référence est mesuré à l’aide d’un poten­ tiomètre de précision (modèle Metrohm E353) branché sur un enregistreur.

2.2. Technique de bromuration

Dans le compartiment anodique de la cellule d’électrolyse on introduit une quantité fixe de la protéine à brom er ( 1 0 0 mg de sérum-albumine ou de fibrinogène, 5 mg d’insuline)* dissoute dans 10 ml d’une solution de NH 4Br marquée au brome-82 à une concentration comprise entre ÎO -4 et 10'2 M; 0,5 ml de la même solution de NI^Br sont introduits dans le compar­ timent cathodique. Deux échantillons de 10 Л sont prélevés de la solution contenue dans le compartiment anodique toutes les 60 minutes; l’un pour déterminer, par radioélectrophorèse sur papier, la quantité de brome fixée par la protéine, l’autre pour contrôler l’activité totale de la solution. L’électrolyse est arrêtée après trois heures et la solution est éluée sur une colonne de résine anionique Dowex (lx- 8 , 50- 100 mesh, diamètre de la colonne: 10 mm, hau­ teur: 100 mm) pour séparer la protéine des bromures. On vérifie d’abord l’absence des bromures dans la protéine par radioélectrophorèse sur papier, ensuite on fait un prem ier contrôle de dénaturation à l’aide d’une précipi­ tation avec l’ATC. Si on ne décèle pas la présence de produits dénaturés, on fait des contrôles successifs par électrophorèse et immunoélectrophorèse sur gélose.

2.3. Méthodes de contrôle a) Essai par précipitation à l’acide trichloroacétique

Une portion de la protéine marquée au brome-82 est additionnée d’ATC à 5% (2 ml); à partir de l’activité du surnageant, on peut calculer la fraction non précipitable, constituée par les produits de dénaturation de la protéine.

* Sérum-albumine humaine livrée par Г lSl(Istituto Sieroterapico Italiano) en solution à 5% et â faible concentration saline (NaCl 0,3%) . Fibrinogène ISI lyophilisé, correspondant à la fraction I du plasma humain selon Cohn et ayant la composition suivante; fibrinogène 61% bêta-globulines 16% gamma-globulines 9%, alpha-globulines 9^ a l­ bumines 6%. Insuline cristallisée BDH (23 u. i. /mg d'insuline). MARQUAGE AU BROME- 82 DE LA SERUM- ALBUMINE 165

b) Radioélectrophorèse sur papier

L’électrophorèse sur papier est adoptée non seulement pour vérifier l’absence de bromures libres dans le produit, mais aussi pour m esurer la quantité de protéines bromées qui s’est formée au cours de l’électrolyse. On analyse des échantillons de 10 X sur papier Whatmann n°l en em­ ployant un tampon Véronal-acétate de sodium à pH= 8 , 5 (Véronal sodique: 4,4 g, acétate de sodium: 4,7 g, acide acétique: 0, 1 M et 30 ml, H¿0 jusqu’à 1000 ml). On applique aux électrodes une tension constante de 200 V pendant 90 minutes; le gradient de potentiel est de l’ordre de 7-8 V/cm et le courant est de 2-3 mA. On obtient l’électrophorégramme de la bande de papier à l’aide d’un dispositif automatique d’enregistrement de la radioactivité. Les quantités d’albumine bromée et d’ion bromure sont mesurées directement sur le radioélectrophorégramme par intégration des aires des pics corres­ pond ants.

c) Electrophorèse et immunoélectrophorèse sur gélose

On emploie la technique de GRABAR et WILLIAMS [7] avec une solution- tampon Véronal dont le pH= 8 , 2 et dont la force ionique ц = 0,02 (Véronal sodique: 4,12 g, HCl: 0,1 M et 59,7 ml, H 2O ju s q u ’à 1000 m l). En appliquant aux électrodes 250-280 V, on m esure aux bords de la plaque de gélose une différence de potentiel de 75 V (4,5-5 V/cm); avec un courant de 30-35 mA, la durée de l’électrophorèse est de cinq heures. Lors­ que l’électrophorèse est terminée, les plaques sont immergées pour deux heures dans un bain de tampon-phosphate (pH= 6,9 et ц = 0,1); on effectue ensuite la précipitation spécifique contre un immunsérum équin anti-sérum humain normal, fourni par Serpasteur. Le réactif colorant employé est le Noir amide (Noir amide: 1 g, acide acétique: 1 M et 450 ml, acétate de so- dium:'0,l M et 450 ml, glycérol: 100 ml). Quelques essais de contrôle ont été aussi effectués à l’aide de l’appareil LKB pour micro-immunoélectrophorèse (modèle 6800A), suivant la tech­ nique proposée par SCHEIDEGGER [8 ], qui présente l’avantage d’une réduc­ tion remarquable de la durée d’opération.

2.4. Résultats

a) Bromuration de la sérum-albumine

Par une série d’expériences selon la méthode de bromuration précitée, on a constaté que pour obtenir un rendement acceptable en sérum-albumine bromée (voir tableau I),.on doit électrolyser 100 mg de sérum-albumine pen­ dant trois heures avec un courant de 300 piA. Avec une intensité croissante .du courant, on réussit à lier à la protéine des quantités croissantes de brome, mais si on atteint une valeur de courant comprise entre 1,8 et 2 mA,on provoque une dénaturation de la protéine qye l’on peut déceler déjà par le test à l’ATC. La limite raisonnable qu’il vaut mieux ne pas dépasser est d’environ 1,5 mA pendant trois heures (tableau II). Dans ces conditions, la sérum-albumine bromée ne montre pas de dénaturation à l’essai par 166 U. ROSA, G. A. SCASSELLÁTI et G. PENNISI

TABLEAU I

BROMURATION DE 100 mg DE SÉRUM-ALBUMINE EN SOLUTION DE NH4BR 1- IQ'2 M, AVEC UN COURANT DE 300 цА

Br lié à Degré de Rendement Potential t Br déchargé la protéine saturation de bromuration anodique (m g Br/mg SA) (h) (m g Br/m g SA) de tyrosine Cft) (mV) 6°)

1 0,89 ‘ 10"2 0,01- 10‘ 2 0,25 0,01 820

2 1,79 ' 10-2 0,05 • 10'2 1,28 0,04 820

3 2,68 • 10-2 О © со h-* о 2,46 0,05 820

Figure 2

Contrôle par électrophorèse et immunoélectrophorèssur gélose de la sérum-albumine humaine bromée. 1. Analyse électrophorétique d*une albumine bromée à 1,5 mA pendant trois heures (en bas) vis-à-vis de la même albumine inactive. 2. Analyse électrophorétique du sérum humain normal. 3. Analyse immunoélectrophorétiqued'une albumine bromée à 1,5 mA pendant trois heures (en haut)vis-à-vis de la même albumine inactive. 4. Analyse électrophorétiqued*une albumine bromée à 1,5 mA pendant deux heures (en haut) vis-à-vis de la même albumine inactive. 5. Analyse immunoélectrophorétique d'une albumine bromée à 1,5 mA pendant trois heures (en haut) vis-à-vis du sérum humain normal. 6. Analyse immunoélectrophorétique d*une albumine bromée à 1,5 mA pendant deuxheures (en haut) vis-à-vis du sérum humain normal.

électrophorèse et immunoélectrophorèse sur gélose (fig. 2). En maintenant le courant à une intensité de 1,5 mA pendant trois heures, la quantité de brome déchargée à l’anode est de 2,6 • 10-2 mg Br/m g SA. C’est probable­ MARQUAGE AU BROME-82 DE LA SERUM-ALBUMINE 167 ment la valeur optimale; si elle est dépassée, la protéine est dénaturée par l ’oxydation. On retrouve cette limite lorsqu’on fait les mêmes essais de bromuration avec des quantités différentes de protéines. Ainsi, avec une solution de20mg de sérum-albumine dans 10 ml de NH4Br 1 • 10-'2 M et une intensité de courant de 300 цА pendant trois heures, donc avec une quantité de brome déchargée à l’anode de 2,6 • 10-2 mg Br/mg SA, on obtient des résultats tout à fait sem­ blables à ceux qui sont indiqués au tableau II (voir tableau III). En admettant que la réaction de bromuration ait lieu seulement sur les groupes de la tyrosine, on pourra introduire dans la molécule de la sérum- albumine au maximum une quantité de brome correspondante à la trans­ formation complète de la tyrosine en 3,5-dibromotyrosine.

TABLEAU II

BROMURATION DE lOOmg DE SERUM-ALBUMINE EN SOLUTION DE NH4BR l -Ю - 2 M, AVEC UN COURANT DE 1,5 mA

t Br déchargé B rlié à Degré de Rendement Potentiel 1a protéine saturation de bromuration anodique (h) (mg Br/mg SA) (m g Br/m g SA) de tyrosine 6°) (mV) C?»)

1 4.47 • 10'2 0,20 • ÎO’2 5.26 4,57 840

2 8,95 • 1 0 '2 0,60- 10-2 15,57 6.67 843

3 13,42 • 10'2 1,70 • 10-2 43.70 24,44 843

TABLEAU Ш

BROMURATION DE 20 mg DE SERUM-ALBUMINE EN SOLUTION DE NH 4BR Ы 0 - 2 M, AVEC UN COURANT DE 300 цА

Br lié à Degré de Rendement Potentiel t Br déchargé la protéine , saturation de bromuration anodique (m g Br/mg SA) (h) (m g Br/m g SA) de tyrosine (%) (mV) 6 ‘)

1 4,48 ’ 10'2 0,20 • 10"2 5,03 4,37 823

2 8.95- ÎO'2 0.58 • 10’2 14,88 8,60 823

3 13,43 • 10-2 1,62- 10-2 41,78 23,0 823 168 U. ROSA, G. A. SCASSELLATI et G. PENNISI

Il en suit que l’addition de 1,7 • 10-2 mg Br/mg SA correspond à 40% de la capacité de saturation de la tyrosine (4,7% dans la sérum-albumine) con­ tenue dans 1 mg de sérum-albumine. En admettant pour la préparation un bromure d’ammonium irradié ayant une activité spécifique de 1-2 mc/mgBr, la sérum-albumine bromée qu’on obtient dans les conditions précitées aura une activité spécifique de 170-340 цс/mg environ. Il est vraisemblable que des réactions d’oxydation aient lieu tout de même pendant Г électrolyse, même si la quantité de brome totale déchargée ne dépasse pas la valeur optimale déjà indiquée; on ne saurait d’ailleurs autrement expliquer un ren­ dement si réduit de la bromuration, vu que seulement 12% environ du brome déchargé à l’anode entre dans la molécule de la protéine. Ces réactions d’oxydation n’intéressent peut-être que les groupes ter­ minaux, comme par exemple les groupes S-H, sans provoquer la dénatu­ ration de la protéine, avec un effet comparable au traitement de préoxyda­ tion adoptée par MacFARLANE[9]pour la préparation de la sérum-albumine iodée. La-concentration de la solution de NH4Br qui, dans les expériences dé­ crites, est d’environ 10-2 M, a tout de même un effet sur la bromuration, qui pourtant est réalisé à courant constant. Le rendement de la solution de NH4Br (tableau IV); pour des concentrations de NH4Br plus faibles que 10-2 M une partie du courant est peut-être utilisée pour la décomposition de NaCl provenant de la solution d’origine de sérum-albumine, ce qui serait prouvé par la valeur élevée du potentiel anodique dans ces conditions de concentra­ tio n .

TABLEAU IV

BROMURATION DE 100 mg DE SERUM-ALBUMINE A CONCEN­ TRATIONS VARIABLES DE NHy3R, AVEC UN COURANT DE 300 цА

Br lié à Degré de Rendement Potentiel t Concentrations la protéine . saturation de bromuration anodique de N H ^r (h) (m g Br/m g SA) de tyrosine (“7») (mV) (M) m

3 5- 10-3 9,6 ' 1<Г4 2 ,4 0,035 1000

3 1- i o - 3 1,5 • 1(T4 0,3 0,016 1000

3 5-10-4 0,8 • 10'4 0.2 0,009 1125

b) Bromuration de l’insuline

Pour la mise au point de la méthode de bromuration, on a employé une faible quantité d’insuline ( 5 mg), dissoute dans 10 ml d’une solution 10~2 M de NH^Br dont le-pH a été amené à la valeur 2,5 par HC1 10-1 M. MARQUAGE AU BROME- 82 DE LA SERUM- ALBUMINE 169

Déjà pour des faibles valeurs du courant d’électrolyse on a remarqué la formation de l’insuline bromée. A 500 цА la quantité de brome fixé sur l’insuline est de 4,7 • 10-2 mg Br/m g insuline; dans ces conditions, la quan­ tité totale de brome déchargée est de 4,47 mg, soit 0,89 mg Br/mg insuline (tableau V).

TABLEAU V

BROMURATION DE 5 mg D’INSULINE EN SOLUTION DE NH4BR 1 • 1 0-2 m, AVEC UN COURANT DE 500 цА

Br lié à Degré de Rendement Potentiel t Br déchargé la protéine saturation de bromuration anodique (mg Br/mg ins. ) (h) (mg Br/mg ins.) de tyrosine Cft) (mV) (%)

1 0,30 1,60- 1 0 '2 14 5,3 827

2 0,60 3,20- IO '2 28 5,4 829

3 0,90 4,7 0 - 10"2 41 5,0 829

f- 7 'a 9

■m 8 I io

Figure 3

Contrôle par électrophorèse sur gélose de l’insuline et du fibrinogène (fraction I du plasma). 7 et 8. Analyse électrophorétique d’insulinenormale(en bas) et de la même insuline bromée àôOOpApendant trois heures vis-à-vis d'une sérum-albumine normale. 9 et 10. Analyseélectrophorétiquede la fraction I du plasma et de la meme fraction 1 bromée à 1,5mA pendant trois heures vis-à-vis d’une sérum-albumine normale.

En admettant pour la préparation un bromure d’ammonium irradié ayant une activité spécifique de 1-2 mc/mg Br, l’insuline bromée que l’on obtient dans les conditions décrites ci-dessus aura une activité spécifique de 100-200 fic/mg environ. Une telle activité spécifique est plus que suffisante pour pouvoir employer l’insuline bromée dans les recherches biologiques; surtout si on considère une décomposition possible par radiolyse du produit actif, il convient de ne pas dépasser cette valeur d’activité spécifique. 170 U. ROSA, G. A. SCASSELLATI et G. PENNISI

L’insuline bromée ainsi obtenue a été contrôlée à l’ATC; étant donné la faible quantité d’insuline, on ajoute un entraîneur de sérum-albumine avant la précipitation. Dans le cas de l’insuline, cet essai de dénaturation est par­ ticulièrement important puisqu’on sait [ 1 0 ] que la perte de l’activité biolo­ gique de l’hormone entraîne la formation de produits de dégradation que l’on retrouve dans le surnageant après précipitation à l’ATC. Aucune différence de mobilité électrophorétique par rapport à l’insuline non marquée n’a été mise en évidence par électrophorèse sur gélose (fig. 3). c) Bromuration du fibrinogène

Les essais de bromuration du fibrinogène ont été réalisés en utilisant 10 0 mg de la fraction 1 du plasma, lyophilisée et dissoute dans 10 m l de so ­ lution 10-2 m de NILtBr. Avec une intensité du courant de 1,5 mA pendant trois heures et un pH de la solution de 6 ,6 - 6 ,8 environ, la quantité de brome

TABLEAU VI

BROMURATION DE 100 mg DE FIBRINOGENE (FRACTION I) EN SOLUTION DE NH4BR 1 • 10-2 M, AVEC UN COURANT DE 1,5mA

Br lié à Degré de Rendement Potentiel t Br déchargé la protéine saturation de bromuration anodique (h) (mg Br/mg fr.I) (mg Br/mg fr.I) de tyrosine (%) (mV) №) Б 1 4,47 • 10'2 O O 1,56 1,72 840

2 8,95 • 10'2 0,16- 1 (Г2 3,30 1,92 843

3 13,42. К Г2 0,20 * 10-2 4,15 0,85 845

déchargée à l’anode est de 13,42 mg, soit 1,34 • 10-1 mg Br/m g fraction I. On introduit ainsi 2 • 10-3 mg Br/m g fraction I (tableau VI). Bien que très faible, cette quantité de brome est une valeur limite à ne pas dépasser pour éviter le risque de dénaturation de la fraction I et en particulier du fibrinogène; si une quantité plus importante de brome est dé­ chargée à l’anode, Le produit bromé est dénaturé dans la plupart des cas. Dans le cas de la bromuration de la fraction I du plasma, le brome peut entrer non seulement dans la molécule du fibrinogène, mais aussi dans les autres protéines (albumine, globulines) contenant le groupe de la tyrosine. Cela est déjà mis en évidence lors du contrôle par électrophorèse sur papier. L’interprétation des résultats de ces essais de bromuration sur la frac­ tion I est compliquée par l’altération du fibrinogène en solution, indépen­ damment du traitem ent de bromuration; c’est pourquoi on doit lyophiliser sans délai le produit bromé et réduire la durée des essais de contrôle autant MARQUAGE AU BROME- 82 DE LA SERUM- ALBUMINE 171 que possible. Dans ces cas, en raison de sa rapidité d’exécution, la tech­ nique de micro-immunoélectrophorèse de Scheidegger donne de meilleurs résultats que la technique de Grabar et Williams, adoptée pour le contrôle de la sérum-albumine bromée. Aucune différence de mobilité électrophorétique par rapport à la frac­ tion I non bromée n’a été mise eïi évidence par l’électrophorèse sur gélose (fig .3 ).

3. CONCLUSIONS.

Les résultats exposés sont, en réalité, des résultats prélim inaires; il serait, en effet, très intéressant de pousser plus loin l’étude des phéno­ mènes secondaires qui ont lieu pendant l’électrolyse et ne pas se borner à des essais de contrôle chimico-physiques. Des contrôles biologiques sont d ’a ille u r s p ré v u s . On peut tout de même affirm er dès maintenant que la technique de bro­ muration par voie électrochimique est capable de fournir des protéines bro- mées sans provoquer une dénaturation importante, si l’on se fonde sur les résultats des contrôles par électrophorèse et immunoélectrophorèse sur g é lo se . La valeur d’activité spécifique qu’on peut atteindre est suffisante pour la plupart des applications dans le domaine de la médecine et de la biologie. Un avantage remarquable de cette technique réside dans le fait qu’elle peut être adaptée aux exigences de la manipulation à distance derrière un écran de protection et qu’elle réduit, en même temps, le risque d’une con­ tamination par le brome gazeux.

RÉFÉRENCES

[1] GILMAN, H ., Chimica Organica Superiore, Edizioni Scientifiche Einaudi (1956) 1256. [2] FIESER, L. et FIESER. M ., Advanced Organic Chemistry, Reinhold Publ. Corp. N.Y. (1961) 1025. [3] HUGHES, W. L. etSTRAESSLE, R., Iodination of Human Serum Albumins, J. Amer. Chem. Soc. 72 (1950) 452. [4] YAMAZAKI, K ., Potentiometric Determination of Cystine and Cysteine, J. Biochem. (Japan) 12 (1930) 207. [5] VEALL, N .. PEARSON, J.D . e t HANLEY, T ., The Preparation of ‘“ la n d 132I Labelled Human Serum Albumin for Clinical Traces Studies, Brit-, J. Radiol. 28(1955) 633. [6] PIPER, D ., ALLEN, J. e t MURLIN, F . , Physical and C hem ical Behaviour of Insulin, J. Biol. Chem . 58 (1924) 321. [7] GRABAR, P. et WILLIAMS, C .A ., Immunoelectrophoretic Analysis of Mixtures of Antigenic Substances, Biochem. biophys. Acta 17 (1955) 67-74. [8] SCHEIDEGGER, J . J . , A New Technique of Im m uno-electrophoresis in Agar Gel. Intern. Arch. Allergy appl. Immunol. 7(1955) 103. [9] MacFARLANE, A .S., Labelling of Plasma Proteins with Radioactive Iodine, Nature 181 (1958) 53. [10] TOMIZAWA, H. H. , NUTLEY, M .L ., NARAHARA, H .T . e t WILLIAMS. R. H ., Inactivation of Insulin by Rat-Liver Extracts, J. Biol. Chem. 214 (1955) 285.

DISCUSSION

P. TEMPUS: Have you actually used Br82-labelled compounds in animal experiments? As bromine is not a normal element in physiological liquids, 172 U. ROSA, G. A. SCASSELLATI et G. PENNISI

it would be interesting to know whether or not such compounds behave like non-labelled ones. U. ROSA: Our paper merely presents a labelling technique and no biological results are as yet available. I should perhaps point out that I am a chemist and that this work has been carried out in conjunction with doctors from the University of Pisa, where experiments are currently in progress to obtain data on the biological behaviour of the compounds. Our doctors have already compared the behaviour of brominated and iodinated albumin for cardiac-output measurements with the double-labelling technique and I believe that the results were entirely satisfactory. I think it is important to point out that the amount of bromine reaching the proteins does not necessarily correspond to a three-hour electrolysis quantity. A suitable specific activity is obtained after one hour. B. MALAMOS: In double-tracing medical experiments do you think that tagging with Br82has any advantage over the use of two iodine-isotope la b e ls ? U. ROSA: Of course, the short half-life of Br 82 is a drawback. On the other hand, it has an energy-emission level which makes it very attractive from the point of view of external analyses, and the specific activity is high enough to enable brominated proteins to be used one week after they have been prepared. I should add that the reason we decided to try out bromine labelling in the first place was that I1^ is so very expensive. K. SCHEER (Chairman): At the moment we pay $10 for one millicurie of I125 but we have been told that it might become possible for the price to be reduced to $5. The supplier is Oak Ridge. L. STANG: On the other hand, it is extremely easy to make I125 in a small research reactor. K. SCHEER: Another important economic consideration is that a single chemical preparation is sufficient for a fairly prolonged experimental period because of the 60-d half-life. To return to the question of bromine, however, I think that considerable interest,attaches to double-tracer techniques with this substance. It has already been pointed out that the gamma rays of bromine can be measured outside the body, which is very difficult in the case of the low-energy gamma rays produced by Iiz&. I have heard that very good results have been ob­ tained in double-tracer digestion experiments on neutral and acid fats labelled w ith I 131 and with bromine. It seems reasonable, therefore, to expect satis­ factory results with the double labelling of albumins and other proteins with iodine and bromine. P. TEMPUS: In connection with the storing of I125-labelled compounds, I should like to ask Mr. Scheer how he stores his m aterial — in solid or in liquid form? K. SCHEER: I was referring to I125-hippuran, which we store in a rather dilute solution. As a m atter of fact, we don’t worry about a free- iodine content of 5%, or even 7 or 8 %. It is obvious, however, that if the amount of free iodine has to be kept down to a minimum, the compound has to be prepared fresh. Even if the compound were stored in the form of a - salt, decomposition by radiation would be unavoidable. P. TEMPUS: We are currently preparing I131-labelled polyvinyl pyrol- idone and we have found that when this substance is stored in a refrigerator MARQUAGE AU BROME-82 DE LA SERUM-ALBUMINE 173 for periods of one or two weeks the free-iodine content remains at less than 1%. I have no experience with your substance but I think that the same results could be obtained with serum albumin. Dry freezing seems to suppress radiation damage in such m aterials. K. SCHEER: This is probably a question of the migration and diffusion of free radicals. The diffusion rate would be lower with a dry substance and at low temperatures. Under laboratory conditions, however, i.e. in a deep­ freeze, decomposition is unavoidable.’ I think a period of two to three weeks would be the maximum period for storing an iodinated compound. W. PAUL: I think it is generally accepted that the iodinated albumin, which is in current use is denatured, i. e. not identical with circulating albu­ min. Surely brominated proteins must be sim ilarly denatured? U. ROSA: Although we obtained very good results with our chemical and physical tests, obviously such controls are never as valuable as actual biological tests. At best, we expect the same degree of dénaturation with the bromine as one gets with iodine. M. ANBAR: My own experience in quite a different field suggests that, in view of the phenomenon of radiation-induced debromination, it would be extremely unwise for you to try to prepare for future use large batches of brominated proteins labelled with high specific activities. Of course, under physiological conditions debromination is less marked than de-iodination but as a result of radiation damage the situation is liable to be reversed. For this reason alone, therefore, I don’t think that bromine is a feasible substitute for I125except in special cases, e.g. circulation studies, where external measurements are required. U, ROSA: I would agree that it is not advisable to prepare a large stock of this substance. Our own method has been to make small batches rather than to prepare one large batch to be broken up subsequently. The doctors working on these experiments have not noticed any debromination of the molecules, nor was this phenomenon observed after five days in a paper-radioelectrophoresis check. We don’t know what would happen after two weeks but this is not so very important in view of the short half-life of the bromine. M. ANBAR: Our experience in the field of radiation chemistry with iodinated and brominated aromatic compounds in aqueous solution indicates that the best way to preserve halogenated compounds of high specific acti­ vity is to keep them in as dilute a solution as possible and then to add some preservative, e. g. glycerol or glycol. The resultant competition for the free radicals formed in solution maintains the compounds longer in their original form. U. ROSA: Our method for storing the brominated albumin was simply to keep it at a tem peraturè of around 5°C. H. KEPPEL: Do you think there would be anything to be gained by applying serum albumin labelled with inactive iodine and then exchanging the iodine for radioactive bromine? U. ROSA: The advantage of iodinating, say, albumin electrochemically is that this makes it possible to work with a 1 0 -* molar iodine solution, i.e. at a concentration 10 times lower than with the Pearson method. With bro­ mine the situation is different. The concentrations of bromine required are 174 U. ROSA, G. A. SCASSELLATI et G. PENNISI hundreds of times higher, so that there would be little point in an exchange of this sort. Furthermore, the risk of dénaturation is doubled, since there is already a certain dénaturation with the iodination. ELECTROLYTE CONCENTRATIONS OF INTRA- AND EXTRACELLULAR COMPARTMENTS IN SOME INTERNAL DISEASES

K. ITAHARA, K. ITO, T. TOMINAGA, T. JIMBO AND T. SATO TOHOKU UNIVERSITY, SENDAI, JAPAN

Abstract — Résumé — Аннотация — Resumen

ELECTROLYTE CONCENTRATIONS OF INTRA- AND EXTRACELLULAR COMPARTMENTS IN SOME INTERNAL DISEASES. It was reported by the authors, at the Third Japanese Conference on Radioisotopes, held in 1959, that they had measured the total body water ( D p space), extracellular fluid volume (mannitol space) and total exchangeable sodium and potassium in oedematous and hypertensive patients. In the present paper, they report their studies of the sodium and potassium concentrations in extra- and intracellular fluids, using Na*4 and K1®, in patients with essential hypertension, primary aldosteronism and periodic paralysis. The Nae (expressed as mEq/kg body weight) in ten hypertensive patients was 45.2 (normal 39.5) on an average, and the average value of Ke in 14 of these cases was 32.5 (normal 42.7). The ratio of intracellular concentration К/Na was 1.8 (normal 2.9) and the ratio of intra- and extracellular potassium concentrations was 26.6 (normal 28.4) on an average. It was therefore considered that in these, patients potassium was excreted from the urine by an increase in K- clearance and its content was thus decreased in the total body. In two cases Of primary aldosteronism, one case with paralytic attacks had an increased value (37.2) of this potassium concentration ratio and the other case without paralytic attack had a normal value (29.5). In another two patients with non-familial periodic paralysis, this concentration ratio of extra- and intra­ cellular potassium was 42.8 and 48.7 respectively, during the induced attack, while potassium excretion in the urine was not increased. It was demonstrated that transmineralization had developed from extra- into intracellular fluids. When a complete or incomplete paralysis was induced by glucose and insulin in five out of eight patients with a paralytic history, this concentration ratio was over 38.0 during each attack. It was also disclosed that an increase in this value was correlated with the severity of the paralysis. The pathogenesis of paralysis therefore seems to be due to the difference in intra- and extracellular potassium concentrations, in addition to an increase in the resting potential of muscles. Table I gives the electrolytic compositions of these diseases.

CONCENTRATION DES ELECTROLYTES DANS LES COMPARTIMENTS INTRA- HT EXTRACELLULA 1RES, DANS CERTAINES MALADIES INTERNES. Les auteurs ont signalé, lors de la troisièm e Conférence japonaise sur les radioisotopes, tenue en 1959. qu'ils avaient procédé à des mesures de la masse totale de l'eau de l'orga­ nisme (espace-eau lourde), du volume des liquides extracellulaires (espace-mannitol) et des quantités totales de sodium et de potassium échangeables chez les malades atteints d'œdème et d’hypertension. Ils étudient maintenant, à l'aide de24Na et de 4гк, les concentrations de sodium et de potassium dans les liquides extra- et intracellulaires chez des malades atteints d'hypertension, d*aldostéronisme primaire et de paralysie périodique. Chez dix malades atteints d’hypertension, la valeur moyenne de la concentration du sodium échangeable (Nae), exprimée en mEq/kg de poids du corps, était de 45,2 (valeur normale: 39,5) et chez 14 autres malades, là valeur moyenne de la concentration du potassium échangeable (Ke) était de 32,5 (valeur normale: 42,7). Le rapport des concentrations intracellulaires К/Na était de 1,8 (valeur normale: 2,9) et le rapport des con­ centrations du potassium intracellulaire et du potassium extracellulaire de 26,6 (valeur normale: 28,4), On estime donc que, chez ces malades, du potassium est éliminé dans l'urine par suite d'une augmentation de la «clearance » de K, et qué ia teneur en potassium de l'organisme entier diminue. Etudiant deux cas d'aldostéronisme primaire, on a constaté que dans le premier cas, accompagné d'atta­ ques de paralysie, le rapport des concentrations du potassium avait augmenté (37,2) tandis que dans le second, qui n'était pas compliqué d'atteintes de paralysie, sa valeur était restée normale (29,5). Chez deux autres malades atteints de paralysie périodique non héréditaire, le rapport des concentrations du potassium intracellulaire et du potassium extracellulaire était de 42,8 et 48,7, respectivement, pendant

175 176 K. ITAHARA, et al» l'attaque qui avait été provoquée, tandis que l'élimination de potassium par l'urine n'augmentait pas. Il a été démontré qu’un transfert de minéraux s'était produit entre les liquides extracellulaire et intracellulaire. En provoquant un© paralysie complète ou incomplète par le glucose et l'insuline chez des malades ayant déjà subi des attaques de paralysie, on a constaté dans cinq cas sur huit que le rapport des concentrations dépassait 38,0 pendant chacune des attaques. On a aussi constaté que l’augmentation de cette valeur était liée à la gravité de la paralysie. La pathogenèse de la paralysie semble donc due non seulement à une augmentation du potentiel de repos des muscles mais aussi à la différence entre les concentrations intra- et extracellulaires du potassium. Tableau I indique les différentes compositions électrolytiques enregistrées dans ces maladies.

ВНУТРИКЛЕТОЧНАЯ И ВНЕКЛЕТОЧНАЯ КОНЦЕНТРАЦИЯ ЭЛЕКТРОЛИТОВ ПРИ НЕКОТОРЫХ ВНУТРЕННИХ ЗАБОЛЕ­ ВАНИЯХ. В 1959 году на третьей Всеяпонской конференции по радиоизотопам нами было сделано со­ общение об измерении общего количества воды в организме (с помощью Da0 ) , объема внеклеточной жидкости (о помощью маннита), общего обмениваемого натрия и калия у больных с отеками и ги­ пертонической болезнью. В данной работе авторы сообщают результаты исследований концентрации натрия и калия во внеклеточной и внутриклеточной жидкости с использованием радиоактивного натрия Na24 и радиоактивного калия К42 у больных с эссенциальной гипертонией, первичным альдостерониз- мом и периодическим параличом. Содержание внеклеточного Nae (в миллиэквивалентах на 1 к г веса тела) у десяти пациентов, больных гипертонией, составляло в среднем 45,2 (в норме 3 9 ,5 ), и средняя величина внеклеточного калия (К е ) при 14 определениях составила 3 2,5 (в корме 4 2 ,7 ). Соотношение внутриклеточных кон- ценграций K/Na равнялось 1 ,8 (в норме 2 ,9 ) , а внутри- и внеклеточной концентрации калия соста­ вило в среднем 26,6 (в норме 2 8 ,4 ). Поэтому считалось, что у этих пациентов калий выделялся с мочой вследствие увеличения клиренса калия и содержание его в организме уменьшалось. Из двух больных с первичным альдостерониэмом у одного с приступами паралича коэффициент концентрации калия был повышен (37,2), а у другого, без приступа, был нормален (29,5). У двух других пациентов с ненаследственным периодическим параличом этот коэффициент кон- цек' рации вне- и внутриклеточного калия составлял соответственно 42,8 и 48,7 во время провоциро­ вав юго приступа, хотя выделение калия с мочой не увеличивалось. Было показано,что трансмшнералж- эация происходила извне во внутриклеточную жидкость. Когда полный или неполный паралич был вызван введением глюкозы и инсулина у пяти из восьми больных параличом, это отношение концентраций со­ ставляло во время каждого приступа свыше 3 8 ,0 . Было обнаружено также, что рост этой величины соответствовал тяжести паралича. Поэтому патагонеэ паралича, по-видимому, обусловлен разницей внутри- и внеклеточных концентраций калия в дополнение к росту потенциала покоя мышц. В таблице, помещенной в работе, приводится состав электролитов при этих заболеваниях.

CONCENTRACIONES DE ELECTROLITOS EN COMP ARTIMIEN TOS INTRA Y EXTRACELUL ARES EN ALGUNAS ENFERMEDADES INTERNAS. En la tercera Conferencia sobre Radioisótopos que se celebró en 1959 en el Japón, los autores presentaron una memoria sobre la medición de la masa total de agua del organismo (espacio E^O), del volumen de los fluidos extracelulares (espacio rhanitol), y de las cantidades totales de sodio y potasio inter­ cambiables en enfermos edematosos e hipertensos. La memoria actual describe el estudio de las concentraciones de sodio y potasio en los fluidos extra e intracelulares empleando 24Na y 42 К en sujetos que padecen hipertensión, aldosteronismo primario y parálisis periódica. En 10 hipertensos, el valor medio de la concentración de sodio intercambiable ( Nae) - expresada en mEq/kg de peso corporal - era de 45,2 (valor normal: 39,5), en tanto que en 14 otros enfermos, el valor medio de la concentración de potasio intercambiable (Ke) ascendía a 32,5 (valor normal: 42,7). La razón de las con­ centraciones intracelulares К/Na era de 1,8 (valor normal: 2,9).y la razón de las concentraciones intra y extra- celulares de potasio ascendía a 26,6 (valor normal: 28,4). Por consiguiente, se estima que en estos pacientes el potasio se excreta con la orina como consecuencia de un incremento de la depuración plasmática, y que el contenido de potasio disminuye en el organismo entero. De dos casos de aldosteronismo primario uno, con ataques de parálisis, presentaba un valor incrementado (37.2) de esta razón de las concentraciones de potasio, y el otro caso que no sufría ataques de parálisis, dio un valor normal (29,5). En otros dos enfermos con parálisis periódica no hereditaria, la razón de concentración del potasio extra e intracelular era, respectivamente, de 42,8 y 48,7 durante el ataque inducido, mientras que la excreción del CONCENTRATIONS OF INTRA- & EXTRACELLULAR COMPARTMENTS 177 potasio por la orina no había aumentado. Se demostró que la transmineralización se había extendjdo de los fluidos extrácelulares a los intracelulares. Al inducir con glucosa e insulina una parálisis completa o incompleta en ocho pacientes con antecedentes de parálisis, se encontró en cinco de ellos una razón de concentración superior a 38,0 durante cada ataque. También se observó que el incremento de este valor guarda una relación con el grado de parálisis. Por lo tanto, la patogénesis de la parálisis parece ser debida no solamente a un in­ cremento del potencial muscular en reposo sino también a la diferencia entre las concentraciones intra y extra- celulares del potasio. En el cuadro I se indican las composiciones electrolíticas observadas en estas enfermedades.

1. PRODUCTION AND DISTRIBUTION OF SHORT-LIVED RADIOISOTOPES PRODUCED BY JR R - 1. *

The first biological experiment in Japan using Na24 produced by a small cyclotron in Tokyo was carried out in 1938 by Prof. Nishina, a pioneer of radioisotopes in Japan. The research reactor usually operated for the production of short-lived radioisotopes is the Japan Research Reactor No. 1 (JRR-1). It is one of the five operating reactors in Japan and belongs to the Japan Atomic Energy Research Institute (JAERI) at Tokai village'. This reactor is of the boiling- water type and has a maximum power of 50 kW and a maximum therm al neutron flux of 1.2X 10i2n/cm 2 s. It reached its critical point in August 1958 and its operation has continued satisfactorily for nearly 4000 h. During its period of operation, it was used to irradiate about six thousand samples for purposes of activation analysis, production of radioisotopes, fuel research, and so on, and a further 20% were irradiated on requests from outside the Institute. Short-lived radioisotopes (half-life up to three days) distributed outside the Institute by the end of March 1962 were as follows: Na24, 216 me; K42, 158 m e; Cu64, 18 m e; A s76, 2 m e; B r 82, 5 .7 m e; Au198, 149 m e; Y90, 2.3 m e; T e 13lm, 0.5 m e; La*40, 14 m e; and Cd*15, 2 m e. These were delivered to universities (about 60%), hospitals and institutes, where they were used for hydrological research, such as estimation of the flow rates in rivers (Na24), clinical experiments (Na24, K42, Br82, C u 6 4 ) , and tracer experiments in agricultural and scientific research (Cu64, As?6, e tc . ). The development of methods for the production of radioisotopes of un­ usual specifications is also being studied. Sodium-24 was prepared from a magnesium oxide target by using the Mg24^ , p) Na24 reaction without the addition of sodium carrier; its specific activity was estimated to be 6X 102 m c/g Na. C arrier-free As77 was obtained from the reaction Ge76 (n, y) Ge77 As77 by the use of germanium oxide or germanium metal as a target. F18 was produced in the JRR-1 reactor by bombarding 0-16 nuclides with H3 which was obtained by the reaction Li6 (n,a) H3 and the specific activity of the F 18 produced was 500 m c/g of F. High specific activity Cu64 was also produced by using the Szilard-Chalmer's effect on copper phthalocyanate or copper oxinate. Copper-64 products thus obtained had a high specific activity two

* Section 1 contributed by N. Shibata, JAERI. 178 K. ITAHARA, et al. hundred times that of Cu 64 which was produced by the ordinary (n, y) r e ­ a c tio n . Seven kinds of processed radioisotopes and 23 kinds of irradiated units are now for saie.

2. CLINICAL USE OF Na24 and K42

2.1. M aterials and methods

The authors used the processed Na24 and the irradiated unit of K42 fo r measurem ent of the total exchangeable sodium and potassium in patients with certain internal diseases, such as hypertension, aldosteronism, peri­ odic paralysis, cardiac- renal- and cachexic-oedema. Calculation of the total exchangeable sodium (Nae) and potassium (Ke) followed the general rule in isotope dilution studies

лт„ ______N a24 injected - Na24 ex c rete d to 24 h e S erum Na24 S erum Na23 (in m eq/1) [1-3]

K 42 administered - K42 excreted to 40-48 h K e in m eq U rin e K42 Urine K?9 (in meq/1) [4]

Na24 with specific activity of 1 m c/g as sterilized saline solution was in­ jected intravenously, 10 0 цс to each subject, and the samples were obtained 24 h after the injection. About 150-200 цс of irradiated K 2 CO 3 with 0.3 m c/g of K 42 s p e c ific activity was administered orally to each subject and the samples were ob­ tained 40-48 h after administration by our method. The specific activity of K 42 irradiated by a small research reactor was too low and therefore not satisfactory for intravenous injection in biological subjects. Radiosodium and radiopotassium were given at intervals of a week under nutritional stable conditions to in-patients without changeable therapy for electrolytes. Antipyrine space and mannitol space were measured for the total body water (TBW) and extracellular fluid (ECF) respectively, and the electrolyte and its extra- and intracellular concentrations were calculated as follows:

Extracellular sodium in meq = serum sodium concentration (meq(l)) X extracellular fluid (1)

Extracellular potassium in meq = serum potassium concentration ( meq/1) X extracellular fluid (1) Intracellular sodium in meq = Nae meq - extracellular sodium

Intracellular potassium in meq = Ke meq - extracellular potassium

Intracellular electrolyte concentration in m eq/l intracellular electrolyte (meq) TBW - E C F CONCENTRATIONS OF INTRA- & EXTRACELLULAR COMPARTMENTS 179

2.2. Total exchangeable sodium (Nae) and potassium (K^) in hypertensive p a tie n ts .

The Nae and Ke in normal adults, essential hypertension, primary aldosteronism, and cachexia or under-nutrition in the male or female are shown in Fig. 1. On an average the normal value of Na,, for both male and

Kt nEq/ltg Nat SO 30 20 ¿0 60 NORMAL male (121 - - (7) fera Ш ______(.)

ESSENTIAL HYPERTENSION mate (11) (36) fern. (7) (15)

PRIM. ALDOSTERONISM male

fern.

CACHEXIA UNDER-NUTRITION) (7) (8)

Fig -1 Total exchangeable sodium (Nae) and potassium (Ke) J : after operation of adrenal gland adenoma. ( ) : number of cases.

female was 39.5 meq/kg body weight and that of Ke was 42.7 meq/kg body weight, which are sim ilar to the values reported by CORSA [4], ARONS [6] o r ED ELM A N [2]. The Nae in 10 patients with essential hypertension was 45.2 meq/kg on an average, and'the average value of К«, in 14 cases was 32.5 meq/kg. It was shown by us that the Nae values of hypertensive patients are notably higher than the mean value in normal adults and that there was a dose corre­ lation with the systolic and diastolic blood pressure levels (Figs. 2 and 3) and there is also fair correlation with abnormal findings in eyegrounds and electrocardiographic changes. Furtherm ore, in this experiment a tendency towards lower potassium content was established in these patients. The mean ratio Nae/K ewas 1.39 (0.89 in the normal adult) in patients with essential hypertension. Four patients with prim ary aldosteronism, who usually complained of high blood pressure, often with attacks of paralysis, caused by hypersecretion of aldosterone from the adrenal adenoma, showed high values of Nae/kg body weight and rem arkably low values of Ke/kg body weight in all eases. The Nae/K e ratio ranges of 1.78 - 2.68 were higher than those in essential hyper­ tension. However, after the surgical removed of the adrenal adenoma, the 180 K. ITAHARA, et al.

mEq/kg

Fig. 2

Correlation between diastolic blood pressure and Nae in hypertensive patients ■ ft unary aldosteronism A Renal hypertension О Male «Female

mEq/kg

Fig. 3

Correlation between diastolic blood pressure and Ke in hypertensive patients

x Cushing syndrome Renal hypertension ^ } frimary aldosteronism О Male • Female values of Nae and Ke returned to the normal range in all cases. In patients with cachexia or under-nutrition the value of Nae/kg body weight was very variable, but that of Ke was conspicuously low, both in term s of body space and relative to body weight. CONCENTRATIONS OF INTRA- & EXTRACELLULAR COMPARTMENTS 181

2.3. Electrolyte concentrations of extra- and intracellular fluids in hyper­ tensive patients (Table I, Fig. 4)

Intracellular concentrations of sodium (Nafc and potassium (K)¡ were calculated by the formulae described above. The concentration of sodium was high in hypertension, and even higher in prim ary aldosteronism, than in the normal subjects, whereas the potassium concentration of intracellular fluid was low in hypertension, and even lower in prim ary aldosteronism, than in the normal subjects. Furtherm ore, in the case of hypertension the intracellular concentra­ tion ratio (K)i/(Na)i was 1.8, being lower than the normal ratio 2.9, and the ratio of intra- to extracellular potassium concentration (K)i/(K)0 was 26.6

TABIZ I

ELECTROLYTE CONCENTRATIONS IN HYPERTENSION

Normal Ess. hypertension Prim, aldosteronism

(14) (4)

Serum K mçq/1 4 .4 3 .9 2 .2 ~ 2 .9

Kg m eq/kg 4 2 .7 3 2 .5 j 2 4 . 1 ~ 2 9 . 4 j

[К] ¡ meq/1 125.1 103.8 j 63.5 ~ 88.1j

[K ]0 meq/1 4 .4 3 .9 2 .2 ~ 2 . 9 |

[K]¡/[K]0 28.4 26.6 28.9 ~ 3 8 .0

(10) (3)

Serum Na meq/1 142.0 142.0 139 ~ 145

Nae m eq/kg 39.5 4 5 .2 f 51. 6 ~ 6 4 .7 |

[Na]¡ meq/1 4 3 .2 5 8 .5 f 57.3 ~ 94. б |

[N a]0 142.0 142.0 139 ~ 145

[Na] 0/[Na]¡ 3.3 1.2 1 .5 ~ 2 ,7

Nae /K e 0.89 1 .3 9 | 1.78 ~ 2.68^

( ) : number of cases.

J. : sign of relative high or low. [ ]j,: intracellular concentration. [ ] : extracellular concentration. 182 К . IT АН ARA, et al.

m E q /f

HYPERTENSION ALDOSTERONISM

Fig. 4

Intracellular potassium concentration in hypertensive patients ■ Cushing syndrome p After op. OMàle • Female

(normal 28.4) on average. It is suggested therefore that in hypertension the increase in sodium exceeds the decrease in potassium, the former being plus 35% and the latter minus 17%. This tendency was also shown inprimary aldosteronism, but in this case the decrease in intracellular potassium concentration was associated with a corresponding decrease in serum p o ta s s iu m .

2.4. Electrolyte concentration of extra- and intracellular fluids in periodic p a ra ly s is (F ig. 5)

At first, two patients with non-familial periodic paralysis were studied as to sodium and potassium concentrations during the period without paralytic attacks. In these cases Nae indicated the subnormal value of 32.3 - 33.4 meq/kg and the intracellular concentration of sodium in low values of 7.9 and 14.3 respectively for the two patients. The Kg/kg body weight and intracellular potassium concentration were at normal levels. In eight non- familial patients with or without hyperthyroidism the value o f K e /k g body weight, intracellular and serum potassium concentrations were in the normal range during the period without paralytic attacks. When a complete or incomplete paralysis was induced by glucose added to insulin, in four cases with a paralytic history the ratio of intra- to extracellular potassium concentration rose to over 38.0 during each attack. It was also CONCENTRATIONS OF INTRA- & EXTRACELLULAR COMPARTMENTS 183

BEFORE ATTACK DURING ATTACK AFTER ADMIN. OF KCt

Fig. 5

Concentration ratio of intra- to extracellular potassium in periodic paralysis О Paralytic attack (+) • Paralytic attack (-) Д Normal A Primary aldosteronism

disclosed that the increase in this ratio correlated with the severity of the paralysis. In all cases the potassium excretion in urine was not increased, while the serum potassium levels were decreased, more or less, and the sodium excretion in urine was increased during induced attack. Therefore, the pathogenesis of this paralysis seems to be due to the difference between intra- and extracellular potassium concentrations, in addition to an increase in the resting membrane potential or the muscles [10, 11] and to the change of ion transport between extra- and intracellular spaces.

,3. SUMMARY OF CLIN ICAL A SPECT

It was recently reported that aldosterone, a chief mineral corticoid secreted physiologic ally by the adrenal cortex, was excreted in large quanti­ ties in the urine of the patients with primary aldosteronism [12] and malignant hypertension [13] . CONN, et al. [14] discussed the relationship of aldosterone secretion to paralytic attacks. Our experiments using radio­ isotopes were planned at the levels of intra- and extracellular concentrations of these electrolytes in clinical patients and the following characteristic findings on electrolyte composition were obtained for each disease: 1. In hypertensive patients there is a tendency not only to retain sodium but to lose potassium in total exchangeable electrolytes and in intra­ cellular concentration. 184 К . ITAHARA, et al.

2. In prim ary aldosteronism the most remarkable tendency is to a low serum potassium level and an increase of potassium excretion in the urine [15]. 3. In periodic paralysis the ratio of intra- to extracellular potassium concentration is raised to over 38 during the induced attacks. The role of the mineralcorticoid in these diseases has been discussed by TO RIKA I [16] and by IT AHARA [10].

REFERENCES

[1] MOORE, F. D ., "An Introduction to the clinical and investigative Use of isotope dilution Methods”, Radioisotopes in Medicine (1953), USAEC (1955) 452. [2] EDELMAN, I. S. et al. "Body Sodium and Potassium. IV. The norm al total exchangeable Sodium ; its Measurement and Magnitude”, Metabolism 3 (1954) 530. [3] MANERY, J. F ., Methods in medical Research. IV. Radioisotope Method for determining Volume of extracellular Fluid in the Animal Body, Year Book Publ., Chicago (1951) 53. [4] CORSA, L., Jr.. et a l., "The Measurement of exchangeable Potassium in Man by isotope Dilution", J. Clin. Invest. 29 (1950) 1280. [5] ITAHARA, K. et al., "On the Measurement of total exchangeable Potassium", Nisshin Igaku (Jap. J. Med. Progr. ) 4T_ (1960) 750. [6] ARONS, W. L. et a l., "The simultaneous Measurement of exchangeable Sodium and Potassium utilizing ion exchange Chromatography", J. Clin. Invest. 33 (1954) 1001. [7] ITAHARA, K. et al. , "Studies on total body Water (VIHth Report)", Abstracts Papers of 56th annual Meeting, J. Jap. Soc. Int. Med. (1959) 86. [8] TOMINAGA, T... "Total exchangeable Sodium in human Hypertension", J. Jap. Soc. Int. Med. 50 (1961) 560. [9] ITAHARA, K ., "Edema in Cachexia", Jap.J. Nephrology 4 (1962) 65. [10] ITAHARA, K ., "Periodic Paralysis", Clinical Neurology 1^ (1961) 450. [11] GROB, D ., "Potassium Movement in Patients with familial periodic Paralysis", Am. J. Med. 23 (1957) 356. [12] COIN, J. W., "Primary Aldosteronism, a new clinical Syndrome", J. Lab. and Clin. Med. 45(1955)356. [13] ÍTAHARA, K. et a l., Studies on body Water and electrolyte Metabolism. Clinical Use of heavy Water, Radiosodium and Radiopotassium. Proc. 3rd Conf. on Radioisotopes, Tokyo (1959) 805. [14] CONN, J. W. et a l., "Intermittent Aldosteronism in periodic Paralysis", Lancet(i)(1957) 802. [15] SHIOJI, R ., "The Responses of urinary Aldosterone, electrolyte Excretions and serum Levels of Electrolytes to potassium Load in hypertensive Subjects", Jap.J. Nephrology 3 (1961) 543. [16] TORIKAI, T ., "Aldosterone and Hypertension", Folia Endocr. Jap. (in press).

DISCUSSION » C. MALAMOS: If I understand correctly, you used dilution analysis with your patients. I should like to comment that in our experience we have found the whole-body counting technique to be better for long-term studies.- At the time we performed our experiments, we used N a 2 2 but for our clinical investigations we have now started using Na24, which has since become available. For short-term studies, of course, the dilution technique is preferable. I might add that in addition to the groups of diseases mentioned by you - where our data are very sim ilar to yours — we have also obtained very interesting results with Addison's disease. CONCENTRATIONS OF INTRA- & EXTRACELLULAR COMPARTMENTS 185

К. ITAHARA: Thank you for your interesting comment. As there is only one whole-body counter available in Japan, we have unfortunately not been able to carry out any experiments of the sort you mention.

SHORT-LIVED RADIOISOTOPES AND AUTORADIOGRAPHY OF FROZEN MATERIAL

R. TAUGNER AND J. IRAVANI UNIVERSITY OF HEIDELBERG, FEDERAL REPUBLIC OF GERMANY

Abstract — Résumé — Аннотация — Resumen

SHORT-LIVED RADIOISOTOPES AND AUTORADIOGRAPHY OF FROZEN MATERIAL. Autoradiography on frozen material was originally applied to the localization of soluble isotopes (and their compounds) in tissues. Three methods are available: freeze cutting, freeze drying and freeze substitution. Each of these methods is subject to specific hazards: melting whilst cutting and the possibility of dehydration during processing and exposure (freeze cutting); dislocation and elution of the tracer during infiltration with the embedding medium and processing of slices ( freeze drying) and also as a result of the necessary gradual déhydration and fixation (freeze substitution). Apart from the state of solubility of the tracer, for radioisotopes with short half- life, rapid processing is of paramount importance. Here autoradiography after freeze cutting was until recently the only method available and is therefore described in detail. In conclusion it is shown that the disadvantages listed above can be largely avoided by means of what may be called "freeze* grinding". Here the frozen tissue is first ground coarsely, then finely in liquid nitrogen and stored at -190eC. In this way very hard materials, e.g. bone- containing tissues, and also tissues with large water-containing.compartments, can be radiographed quickly with a minimum of artefacts due to dislocation, and with satisfactory resolution.

RADIOISOTOPES DE COURTE PÉRIODE ET AUTORADIOGRAPHIE DES MATIÈRES CONGELÉES. L’auto- radiographie des matières congelées a été tout d'abord utilisée pour localiser les isotopes solubles (et leurs composés) dans les tissus. Il existe à cet égard trois méthodes différentes: découpage, séchage et substitution, le tout sous congélation. Chacune de ces méthodes présente des risques déterminés: fusion pendant le découpage et déshydration éventuelle pendant le traitement et l’exposition (première méthode); dislocation et élution du radioindicateur pendant l'infiltration dans le milieu récepteur et pendant le traitement des tranches(deuxième méthode), ou encore à la suite de la déshydratation graduelle et de la fixation nécessaires (troisième méthode). Abstraction faite de l'état de solubilité de l'indicateur dans le cas de radioisotopes de courte période, il importe au plus haut point que le traitement soit rapide. A cet égard, l'autoradiographie après découpage était récemment encore la seule méthode employée; les auteurs la décrivent donc en détail. Pour conclure, ils démontrent qu'on peut éviter dans une large mesure les divers inconvénients énumérés plus haut en recourant à la pratique dite de «broyage sous congélation». Dans cette méthode, le tissu congelé est d'abord broyé d’une façon assez grossière, ensuite plus finement dans de l'azote liquide pour être enfin emmagasiné à une température de -190°c. La méthode permet donc de procéder— moyennant un minimum d'artefacts dus à la dislocation, et avec une résolution satisfaisante — à une radiographie rapide de matières très dures, telles que les tissus osseux, et de tissus contenant de fortes concentrations d'eau.

КОРОТКОЖИВУШИЕ РАДИОИЗОТОПЫ И РАДИОАВТОГРАФИЯ ЗАМОРОЖЕННЫХ МАТЕРИАЛОВ. Авторадиография замороженных материалов первоначально применялась для локализации растворявшихся изотопов (и их соединений) в тканях. Существуют три метода: резание в замороженном состоянии, осушение в за­ мороженном состоянии и замещение в замороженном состоянии. Каждый их этих методов имеет свои специфические недостатки: плавление при резке и возможность дегидратации во время обработки и облучения (резание в замороженном состоянии); дислокация и вымывание индикатора во время инфиль­ трации с вметающей средой и обработки образцов (осушение в замороженном состоянии), а также вследствие необходимой постепенной дегидратации и фиксации (замещение в замороженном состоянии). Помимо полноты растворения радиоактивного изотопа, для короткоживущих радиоизотопов очень важной является быстрота обработки. В этом случае авторадиография после резания в замороженном состоянии вплоть до последнего времени была едиственным доступным методом и в связи с этим она подробно описана. В заключение показано, что упомянутые выше недостатки могут быть в значитель­ ной степени уменьшены применением метода, который может быть назван "размалывание в замороженном состоянии". При этом методе замороженная ткань сначала размалывается грубо, а затем мелко в жид-

187 188 R. TAUGNER and J. IRAVANI

кои азоте и хранится при температуре -190°С. Таким способом очень твердые материалы, например, ткани, содержащие кости, а также ткани с большим содержанием воды, могут быть прорадиографи- рованы очень быстро, с удовлетворительным разрешением и с минимальными ошибками за счет дис­ локации .

RADIOISÓTOPOS DE PERIODO CORTO EN LA AUTORRADIOGRAFÍA DE MATERIALES CONGELADOS. En un principio, la aütoriadiografla de materiales congelados se aplicó a la localización de radioisótopos solubles (y de sus compuestos) en tejidos. Existen tres métodos: corte por congelación, secado por congelación y susti­ tución por congelación. Cada uno de ellos presenta inconvenientes específicos: la fusión que se produce al cortar y el riesgo de deshidratación durante la preparación y exposición del corte (corte por congelación): la dislocación y elución del indicador durante la infiltración con el medio de inclusión y la manipulación de los cortes (secado por congelación) y también como consecuencia de la deshidratación gradual y de la fijación necesarias (congelación por sustitución). Cuando se trabaja con radioisótopos de período corto, es de primordial importancia operar rápidamente, pues con ello se evita asimismo una disolución excesiva del indicador. Hasta hace poco tiempo, la autorradio- grafia consecutiva al corte por congelación, que se describirá en detalle, constituía el único método aplicable en la práctica. En la última parte de la memoria, los autores demuestran que es posible evitar los inconvenientes citados procediendo a lo que podría llamarse "trituración por congelación”. Con arreglo a esa técnica, el tejido con­ gelado se muele primero hasta un grano grueso, después hasta otro más fino en nitrógeno líquido, y se conserva a - 190°C. De esta manera, se pueden radiografiar rápidamente materiales muy duros, como tejidos que con­ tienen hueso, y tejidos con grandes cavidades acuosas, logrando que los errares debidos a la dislocación sean mínimos, pero conservando un poder de resolución satisfactorio.

PA R T I

Autoradiography is used in the field of biology to determine the dis­ tribution of radioisotopes in animal and plant tissues. In order to assure the proper juxtaposition of film and tissue, the method requires careful preparation of the biological m aterial to be investigated—usually in the form of thin histological sections. These sections can be prepared either by the traditional method of histological fixation and embedding, or from frozen tissue. The present paper is restricted to the autoradiography of frozen animal tissue, which is characterized by the two special properties described be­ low :

1. When properly handled, the autoradiography of frozen tissue is a rela­ tively short procedure up to the exposure of the tissue sections on the film. Thus it is suitable if short-lived radioisotopes are to be used. The possible methods of preparing frozen tissue for autoradiography (to be dealt with in greater detail later on) are the following:

1.1 freeze-drying, which is the oldest method [2J ; 1.2 freeze-substitution as described by SIMPSON [6]; 1.3 freeze-cutting [7] ; and— a new method — 1.4 freeze-grinding. The time required by each of these methods — up to the point when the tissue section is ready to be juxtaposed to the film — is different:

1.1 Depending upon the size of the tissue specimen and the drying temper­ ature, freeze-drying as such can be accomplished within about 5 h, although SHORT-LIVED RADIOISOTOPES AND AUTORADIOGRAPHY 189 at this speed the reliability is somewhat decreased (vide infra). The subse­ quent embedding of the dried material in paraffin or carbowax and the prepa­ ration of the histological sections require another few hours. It is clear that the use of radioisotopes having half-lives within this range is almost impracticable. Thus, as far as the time of histological processing is con­ cerned, freeze-drying offers only very few advantages over the traditional methods of histological fixation with protein coagulating agents.

1.2 The same is true, to an even greater extent, of freeze-substitution, where dehydration of the frozen tissue is effected through the exchange of tissue water and alcohol at -20 to -40°C. Again depending upon the size of the specimen, this method takes from two to three days. Here again, the processed tissue must be embedded in paraffin and histological sections prepared. Thus freeze-substitution cannot be used with isotopes whose half- life lies within the one to two days' range.

1.3 Once the frozen tissue has been mounted on the microtome, freeze- cutting can be carried out without further preparation. It can be accom­ plished in a cool chamber ULLBERG [9] such as is used for frozen sections of whole animals, or in so-called cryostats. There are smaller-size cryostats, such as the Dittes-Duspiva type used in our laboratory, for cutting individual organs, and larger-size ones fitted with a heavy sliding microtome for whole mice and rats. The freeze-cutting method takes from 10- 20 min from the freezing of the tissue to the exposure of the sections on the film. This is probably the maximum speed of processing which has been obtained so far.

1.4 Freeze-grinding can be accomplished either in a cool chamber or in a cryostat. In order to avoid artefacts, which we shall discuss later on, the procedure is carried out in liquid nitrogen. The length of time needed to prepare m aterial for exposure on film is from half an hour to one hour.

2. The second property characterizing the autoradiography of frozen tissue is the possibility of conserving soluble radioisotopes and labelled compounds in their natural in vivo distribution. It bears on work with radioisotopes of short or long half-lives. As regards short-lived radioisotopes, the prob­ lem of artefact-free radiographic representation is particularly important for K42 and Na24, which occur in animal tissue almost exclusively in an ionic, highly diffusible state. From the standpoint of reliability, the various methods present numerous problems. Each method has its own advantages and disadvantages, so that selection of the appropriate method must depend upon the experi­ mental conditions.

2.1 Freeze-drying can be carried out within the indicated time of 5 h only at relatively high drying temperatures around -30°C. This temperature exceeds the eutectic point of СаС1г, for example, which means that the possibility of diffusion inside small liquid volumes cannot be entirely dis­ counted. As an embedding medium for lipid-soluble activity, the water- soluble carbowaxes can be used and for water-soluble activity the lipid- 190 R. TAUGNER and J. IRAVANI soluble paraffin; even so, when the dehydrated tissue is infiltrated by the embedding m aterial at 50-70°C, a change in the distribution of activity can­ not be excluded. Both before and during exposure, the freeze-dried tissue section may take up water because of its hygroscopic property despite the protective embedding m aterial. Another source of error can occur in the localization of radioisotopes in larger, fluid- filled structures of the tissue (vid e in f r a ). The advantages of the freeze-drying method are the ease in slicing the embedded tissue and — as compared with other methods for handling frozen tissue —the relatively good preservation of histological structures. Contact between section and film — and thus the resolution—can be satisfactory with the ''contact" method, which is the only reliable procedure in this case.

2.2 The freeze-substitution method can hardly be carried out within one to two days if temperatures are kept at a desirably low minimum. There are decisive disadvantages concerning the localization of radioisotopes — for example, the localization of lipid-soluble m aterial is definitely falsified by the alcohol. In the case of water-soluble compounds as well, there is the possibility of dislocation and elution, since tissue ice is first dissolved by alcohol. Further disadvantages of the freeze-substitution method are the hygroscopic property of the tissue and the ordinarily very poor preser­ vation of the tissue structures. Contact and resolution will be sim ilar to that in the case of freeze-drying.

2.3 In addition to the shortness of the procedure involved, autoradiography with frozen sections offers the advantage that infiltration by the embedding medium can be omitted. Contact is excellent if the individuad sections are stretched over the film by means of a rapidly evaporating substance, e. g. n-hexane ("mounting” method). The disadvantage of this method, namely that the available' stretching substances are lipid solvents, is relevant only in the case of lipid-soluble radioisotopes — but here, of course,the disadvan­ tage is of decisive importance. We adopted the procedure of checking this source of error by means of parallel control radiograms, in which exposure Was made either by means of the ’’contact" method or by thawing the section briefly for stretching on the nuclear plate. Although all of these methods entail a certain element of risk, careful controls usually make it possible to avoid errors. The autoradiography of frozen sections is open to two typical sources of e r r o r ; (a) The tissue can be sliced with ease only at temperatures from -5 up to -20°C. This means that liquid phases are unavoidable. In addition, the pressure of the knife (depressing melting point) and the heat created as a result of the energy dissipated in the cutting process, should melt the ice temporarily. According to THÜRNBURG and MENGERS [8] , however, this micro-melting, zone is thin and can be disregarded for all practical purposes. In any case, it is a necessary prerequisite for cutting. (b) If the tissue contains fairly large liquid-filled structures, such as blood vessels or glandular ducts, bits of ice may be lost through shattering during SHORT-LIVED RADIOISOTOPES AND AUTORADIOGRAPHY 191 the slicing operation. Moreover, in the cool chamber atmosphere of the cryostat or, later, during the exposure, sublimation of the ice occurs. Conse­ quently— as a result of "fragmentation" —the radioisotopes dissolved in the contents of the ducts may appear to be heterogeneously distributed ir> the autoradiographic image. They may even be found clinging to the walls of the ducts [3] . The subsequent drying of frozen sections has been incor­ porated into a "dry" mounting autoradiographic technique by Fitzgerald. The sources of error are presumably about the same, but the unmodified handling of the frozen sections, with the unintended drying during the ex­ posure, is sim pler. The drying process, incidentally, can be avoided if the sections are obtained and exposed under liquid petrolatum.

2.4 The disadvantages inherent in the autoradiography of freeze-cut sections (thawing, drying and fragmentation) can be avoided, as far as possible, by the freeze-grinding method. This method, as described by PELLERIN [5] , gives adequate resolution only in the macroscopic range. We have used the following procedure: The frozen tissue is turned down and the surface is ground smooth in liquid nitrogen. While still in liquid nitrogen the tissue is applied to the film and stored for exposure. Satisfactory resolution is ob­ tained, if great care is taken to prepare an even and smooth surface and a radioisotope with a low energy of /3-radiation (preferably tritium) is used. The method is complicated and has the following drawbacks: A single organ yields only a very limited number of radiogram s — sometimes only one. The histological identification of the activity-containing areas on the cutting surface after exposure is quite difficult. The relative thickness of the tissue specimen exposed requires the use of tracers with a low energy of 0-radiation. As far as we can see, none of the short-lived radioisotopes discussed in this Seminar meets this requirement. None the less, for other waterr-soluble isotopes the freeze-grinding method will probably play an important role as a control for other radiographic methods. All methods for the radiographic representation of diffusible compounds in frozen tissue demand proper freezing. Freezing must be in vivo and as quick and deep as possible. The problems involved in the freezing technique have been described in detail elsewhere [4) .

PA R T II

The following examples of our work on freeze-cutting autoradiography relate only to kidney function. Two points should be mentioned: firstly, our aim will be the discussion of the reliability of the method; in this context the half-life of the radioisotopes employed is unimportant. Secondly, the application of autoradiography of soluble radioisotopes in the kidney is especially difficult since, owing to the m icrostructure of the kidney and its function, vastly different concentrations are found close together. In some experiments we were interested in the concentrations of radio­ isotopes in succesive regions of the tubules, the chief interest being the comparison between epithelium and lumen fluid. In our experience, the concentration of radioisotopes inside the tubular cell can, in principle, be 192 R. TAUGNERandJ. IRAVANI satisfactorily determined by freeze-cutting autoradiography. However, as mentioned in Part I, the localization of the activity in the large fluid-filled lumina is significantly distorted. If high concentrations of radioisotopes exist in.the lumen, accurate results of intracellular determinations may­ be prevented by certain artefacts arising from this source. Best results for intracellular activity are therefore obtained if radioisotope concentra­ tions in the lumen are relatively low. Concentrations in the lumen can be indirectly estimated by autoradiography of plasma and urine. In the kidney cortex acid-soluble phosphorus is present as about 86% organic phosphate, found mainly in the cells, and 14% as orthophosphate. After injection of P 3 2 - orthophosphate, the radiophosphate is distributed in this proportion over the kidney cortex. Thus the activity of the lumen fluid plays a minor part. For this reason the following results ought to be reliable: 5 min after intravenous injection of P 3 2 - orthophosphate P 3 2 is found in the cells of the proximal tubule excluding the pars recta. This is shown in Fig. la for the cat. If glomerular filtration is reduced by ligature of the ureter, small portions only of the proximal tubule produce blackening (Fig. lb). This means that P32 - orthophosphate reaches the cells of the proxi­ mal convolution mainly after previous filtration and that the outer (basal) membrane of these cells is much less permeable to it. Figure 2a shows schematically the diminishing activity towards the end of the proximal tubule when the ureter is obstructed. It is a histological reconstruction of the first quarter of the proximal convolution based on an alternating series of slices e a c h 6 ц thick. The blackening corresponds to those slices in the series which were used for autoradiography. Figures 2b and 2c, even further simplified, show blackening obtained after clamping the ureter and during free flow. The entire proximal tubule including pars recta is shown. Accord­ ing to these results, P32 - orthophosphate enters the intr'acellular phosphate pool on its way being reabsorbed. Thus phosphate reabsorption can be localized in the proximal tubule excluding the pars recta. Similar but optimal conditions are found during the intracellular storage and binding of labelled foreign m aterials. For example, after mercurial diuretics a concentration gradient between lumen and cells of the order of about 1: 800 is built up. Here the activity in plasma, interstitial fluid and tubular urine can be entirely disregarded. Figure 3 shows the distribution of mercury-203-mersalyl and -chlormerodrin 2 h after intramuscular in­ jection. In the rat there is a juxtamedullary accumulation of mersalyl (Fig. 3a) whereas chlormerodrin is scattered throughout the cortex (Fig. 3b). Microscopic examination reveals that m ersalyl is stored in the cells of the distal third of the proximal tubule and chlormerodrin in those of the middle third. As a first approximation this would mean that these regions are the loci of action of these m ercurial diuretics. Of course one is not always in the happy position to find high intracellu­ lar concentrations of radioisotopes. 1131-diodrast and Ii3i-hippuran are se­ creted by the cells of the proximal tubule. In this process they are said to be first stored intracellularly and then to reach the lumen by diffusion. To verify the latter assumption a comparative determination of the lumen and cell concentration would be desirable. Figure 4 shows that the concentration of I131 is high within the region of the proximal tubule. Sometimes, however, the lumen is clear or small dark spots may be seen surrounded by dark HR-IE RDOSTPS N ATRDORPY 193 AUTORADIOGRAPHY AND RADIOISOTOPESSHORT-LIVED

1 mm ..

Fig. la Fig. lb

Autoradiograph of proximal tubule of kidney (cat) As la, but with glomerular filtration reduced by ligature of the urethra 194 R. TAUGNER and J. IRAVANI

Fig. 2a

Diagram of first quarter of the proximal convolution showing diminishing activity towards end of tubule when urethra is obstructed.

Fig. 2b

Simplified diagram of the proximal convolution showing blackening obtained after clamping the urethra. SHORT-LIVED RADIOISOTOPES AND AUTORADIOGRAPHY 195

l / V

Fig. 2c

As 2b, but with free flow. rings. As stated in Part I, this may be due in part to the shattering of small pieces of ice during the operation of slicing. Moreover in the atmosphere of the cool chamber sublimation of the ice occurs with consequent fragmen­ tation or deposition of radioisotopes on the wall of the tubules. Additional evidence for these conclusions is provided by the use of labelled compounds which have a much higher concentration in the lumen than in the cell. The intended comparative determination of the lumen and cell concentration of J131-diodrast and 1131-hippuran could therefore not be carried out.

Inulin, often used for the estimation of the intercellular volume, does not enter the body cells but is restricted to the extracellular compartment. It is filtered by the glomerulus of the kidney and is neither reabsorbed nor secreted by the tubule cells and therefore used to determine the glomerular filtration rate. As a result of autoradiography after chemical fixation of kidney tissue intracellular storage had been assumed. This finding seemed to point to tubular transport of inulin and thus to cast doubt on fundamental kidney physiology. Freeze-cutting radiography shows that inulin is definitely not stored in the tubular cell (Fig. 5). Actually this radiograph is obtained by clamping the ureter. Inulin reaches the capsular space behind the glomerular filter and from here the adjacent lumina. Thus it was shown that clamping of the ureter does not lead to the so called "stop flow" but only to a "slow flow". Here the coarse granular blackening again points to artificial fragmentation of the frozen filtrate. Since the concentration of inulin cannot be determined, the inverse relationship existing between it and the volume of tubular urine can unfortunately not be used for the deter­ mination of the amount of water reabsorbed along the tubules.

For an estimation of the permeability of the tubules, besides clamping the ureter, use can be made of the intratubular micro-injection of radio­ isotopes at the kidney surface. In this way the lumen of one nephron only will contain the activity. Blackening in the area surrounding the duct will point to local permeability. We have performed such experiments with radio­ sulphate (Fig. 6) and radiosodium. The blackening can be seen in three areas in this figure. Depending on fluid movement in the particular area, dilution Fig* 3

Autoradiograph of proximal tubule of kidney (rat), showing distribution of Hg20s -mersalyl (Fig. 3a) and Hg2® -chlormerodrin (Fig. 3b) 2 h after intramuscular injection. t W "

■ ■ >. 197 AUTORADIOGRAPHY AND RADIOISOTOPES SHORT-LIVED r

i ü H

Autoradiograph of kidney, after clamping the urethra, showing distribution of inulin.

Autoradiograph of kidney In region of proximal tubuit distribution of IIS1 -hippuran. 198 R. TAUGNER and J. IRAVANI

Fig. 6

Autoradiograph of kidney in the region of a nephron, after intratubular micro-injection of Na^S04. of the extratubular isotopes will be different. Hence qualitative answers . only are obtained.

REFERENCES

[1] BLANK, H. , Me CARTHY, PH. L. and De LAMATER, E. D ., Stain Technol. 26 (1951) 193. [2] GROSS, J. and LEBLOND, C. P ., M cG ill M ed.J. 15 (1946) 399. [3] KINTER, W. B., LEAPE, L. L. and COHEN, J.J., Amer. I. PhysioL 199 (1960) 931. [4] MARYMAN, H. T ., Science 124 (1956) 515. [5] PELLERIN, P., Comp. rend. Acad. sc., Paris 244 (1957) 1555. [6] SIMPSON, W. L., Anat. Rec. 80 (1941) 173. [7] TAUGNER, R ., .HOLE, H ., G RIGOLE IT, G. and WAGENMANN, U ., Naunyn Schmiedeberg's Arch. exp. Path. Pharmak. 234 (1958) 330. TAUGNER, R. and WAGENMANN, U .. Naunyn Schmiedeberg's Arch. exp. Path, ftiarmak. 234 (1958)336. TAUGNER, R.. IRAVANI, J . , TAUGNER, G.. vonEGIDY. H. and BRAUN, A ., Naunyn Schm iedeberg's Arch. exp. Path. Pharmak. 241 (1961) 393. [8] THÜRNBURG. W. and MENGERS, P. E ., J. HistQchem. and Cytochem . 5 (1957) 47. [9] ULLBERG, S ., Proc. 2nd UN Int. Conf. PUAE 24 1 (1958) 248. SHORT-LIVED RADIOISOTOPES AND AUTORADIOGRAPHY 199

DISCUSSION

W. A. DE VOOGD VAN DER STRAATEN: I should be interested to know how you apply the tissue to the emulsion with your freeze-grinding technique. R. TAUGNER: If it is possible to obtain a plain surface, the object can be applièd directly to the film. Otherwise, special techniques are needed to provide good contact and resolution.

LES AIGUILLES D’YTTRIUM^O EN ENDO-ÉLECTRON-THÉRAPIE ( BÊ T AT HE R AP IE INTERSTITIELLE)

B. PIERQUIN, M. M O R TREUIL, H. BEYER, J. DUTREIX, D. CHASSAGNE, P. GALLE ET R. JAMMES CENTRE D'ETUDES NUCLÉAIRES, SACLAY, FRANCE

Abstract — Résumé — Аннотация — Resumen

YTTRIUM-90 NEEDLES IN INTERSTITIAL BETA-RAY THERAPY. The Technical Unit for Interstitial Irradiation Therapy by Radioisotopes, of the Gustave Roussy Institute is at present studying, in collaboration with the Saclay Nuclear Centre, some therapeutic applications of interstitial beta-therapy using yttrium-90. Equipment: The needles consist of a stainless-steel tube, 1-mm diam ., 0.1-mm wall thickness and 30 or 40 mm in length, closed at one end by a sharp point and at the other by a projecting head for attaching a pull-out wire. The yttrium oxide cylinders or seeds (5 mm x 0.6 mm) are irradiated for one week at a flux of 2.7 x 1012 n/cir? s and are loaded three or five in each needle. Dosimetry: These yttrium-90 needles are supplied by the Saclay Centre with a standard activity of 1 -1 .5 me/cm (radioactive length). The activity is monitored both by а 4-тг counter and by a film densitometer. The reference dose is calculated by standard method at 2 mm from the tube wall assuming, with a certain approximation, a dose-rate of 10 rad/min for an activity of 1 me/cm. Therapeutic applications: Yttrium-90 needle radiobiology is still an almost unexplored field. The rapid fall-off in the dose beyond 3 mm from the needle wall causes difficulty in obtaining uniform distribution of irradiation in the treated tissues. In principle, the positioning of needles at 5 - 6 mm distance one from another is a possibility, but requires an implanting device capable of extremely delicate control, as an error of lor2m m may cause too many hot or cold points. For that reason the authors decided to use the needles, at a first stage, in benign vascular tumours, with no biological attempt to obtain uniform irradiation of the tissue, the aim being confined to creating sclerotic areas in bands centred around the needles and separated by areas of tissue having received little or no irradiation. In this way it was-hoped to obtain an adequate sclerogenous effect in a certain number of tuberous angio­ mas while at the same time giving the patients the advantage of a very weak integral dose. The lack of diffusion in healthy tissues is of particular advantage in the case of angiomas situated close to radiosensitive tissues (eyeball, breast) or to the genital glands. The results obtained in the first cases treated appear to be satisfactory. As a second stage, the authors intend to use these needles in malignant cutaneous tumours, again where situated close to healthy radiosensitive tissues (e.g. cancer of the eyelid).

LES AIGUILLESD*YTTRIUM-90 EN ENDO-ÉLECTRON-THÉRAPIE (BÊTATHÉRAPIE INTERSTITIELLE). En collaboration avec le Centre nucléaire de Saclay, l'Unité technique de Curiethérapie interstitielle par radioisotopes de l'Institut Gustave Roussy étudie actuellement quelques applications thérapeutiques de bêta- thérapie interstitielle par yttrium-90. Matériel: Les aiguilles sont constituées par un tube en acier inoxydable de 1 mm de diamètre et de 0,1 mm d'épaisseur de paroi. Longues de 30 ou de 40 mm, elles sont fermées à l'une des extrémités par une pointe aiguë et à l'autre par une tête débordante permettant de fixer un fil de rappel. Les cylindres ou grains d'oxyde d'yttrium (5 mm x 0,6 mm) sont irradiés pendant une semaine au flux de 2,7 . 10i2n/cn&set empilés par trois ou cinq dans chacune des aiguilles. Dosimètrie: Ces aiguilles d'yttrium-90 sont livrées par le Centre de Saclay avec une activité standard de 1 à 1,5 m e/cm (longueur radioactive). L'activité est contrôlée à la fois par compteur 4 тг et sur film en densimétrie. La dose de référence est calculée de façon standard à 2 mm de la paroi du tube, en admettant, avec une certaine approximation, un débit de dose de 10 rad/miri pour une activité de 1 m e/cm.

201 202 B. PIERQUIN et al.

Applications thérapeutiques: La radiobiologie des aiguilles d’yttrium- 90 est encore mal explorée. En effet, la chute rapide de la dose au-delà de 3 mm de la paroi de l'aiguille rend difficile une distribution homogène de l'irradiation dans les tissus traités. On peut, en principe, envisager de disposer chaque aiguille 5 ou 6 mm l'une de l'autre, mais cela implique un dispositif d'implantation d'un contrôle très délicat, une erreur de 1 ou 2 mm pouvant entraîner des points chauds ou des points froids excessifs. C'est pourquoi les auteurs ont envisagé, dans un premier temps, l'utilisation des aiguilles dans des tumeurs angiomateuses bénignes, en ne recherchant pas biologiquement une irradiation homogène du tissu, mais en cherchant seulement à créer des zones de sclérose en manchons concentriques aux aiguilles, séparés par des zones de tissus peu ou pas irradiés. Us espèrent ainsi obtenir un effet sclérogène suffisant dans un certain nombre d'angiomes tubéreux, tout en donnant aux malades les avantages d'une dose intégrale très faible. L'absence de diffusion dans les tissus sains est particulièrement intéressante pour les angiomes proches de tissus radiosensibles (globe oculaire, glande mammaire) ou proches des glandes génitales. Les résultats actuels sur les premiers cas traités paraissent sátisfaisants. Dans un deuxième temps, ils comptent utiliser ces aiguilles dans des tumeurs malignes cutanées, proches également des tissus sains radiosensibles (cancer de la paupière, par exemple).

ИГЛЫ ИЗ ИТТРИЯ-90 ДЛЯ ЭНДОЭЛЕКТРОННОЙ ТЕРАПИИ ВНУТРИТКАНЕВОЙ БЕТА-ТЕРАГ^И. В наотоящеее время в сотрудничестве с ядеркым центром Сакле технический отдел внутритканевой радиотерапии института Густава Русси изучает некоторые виды терапевтического применения внутритканевой бета­ терапии с помощью иттрия-90. Исходный материал. Игла состоит из неокисляющейся стальной трубки диаметром 1 мм, длиной 30 - 40 мм при толщине стенок 0,1 мм. Один ее конец закрыт остроконечным швом, а другой - вы» ступающей головкой, позволяющей фиксировать нить для извлечения иглы. Цилиндры или зерна окиси иттрия (5 мм х 0,6 мм) подвергаются облучению в течение недели потоком в 2,7‘Ю Ж* н/см^'сек и затем помещаются по три или пять штук в каждую из игл. Дозиметрия. Полученные из центра Сакле иттриевые иглы имеют стандартную активность от 1 до 1,5 мк/см (радиационная длина). Активность одновременно контролируется счетчиком 4тг и на пленке денситометра. Отсчетная доза определяется стандартным образом с учетом толщины стенок трубки 2 мм и до­ пуском, при известном приближении расхода дозы в 10 рад/мин при активности в 1 мк/см.

Терапевтическое применение. Радиобиологическое действие игл из иттрия-90 еще слабо иссле­ довано. Действие иглы быстро уменьшается на расстоянии свыше 3 мм от иглы, что затрудняет гомо­ генное облучение тканей. Можно в принципе предусмотреть расположение каждой иглы на расстоянии в Ь или 6 мм одна от другой, однако, это требует наличия устройства для вживления при соблюдении тщательного контроля. При ошибке в 1 или 2 мм могут возникнуть значительные колебания дозы облучения. Вот почему авторы предусмотрели пока использовать иглы только для лечения доброкачествен­ ных ангиом, ве стремяоь при этом к гомогенному в биологическом отнопении облучению ткани, а ста­ раясь лишь создать зоны склероза, концентрически располагающиеся возле игл, отделенные зонами елабо иди оовоем не облученных тканей. Давая больным преимущественно очень слабые кумулятивные дозы, авторы надеются подучить та­ ким путем склерогенный эффект, достаточный для излечения некоторых ангиом. Отсутствие диффузии в здоровых тканях имеет значение для ангиом, находящихся поблизости от радиочувотвительных тканей (глазное яблоко, молочная железа) либо вблизи половых желез. Предварительные результаты представляются авторам удовлетворительными. В дальнейшем предполагается использовать иттриевые иглы для лечения злокачественных опухолей кожи, расположенных вблизи от здоровых радиочувствительных тканей (например, при раке века).

AGUJAS DE ITRIO-90 EN LA ENDO-ELECTRÓNTERAPIA (BETATERAPIA INTERSTICIAL). La "Unité Technique de Curiethérapie Interstitielle par radioisotopes'* del Instituto Gustave Roussy, estudia actualmente, en colaboración con el Centro Nuclear de Saclay, algunas aplicaciones terapéuticas de la betaterapia inters­ ticial con itrio* 90. Material: Las agujas consisten en tubos de acero inoxidable de 1 mm de diámetro y 0,1 de espesor de pared. Tienen de 30 a 4p mm de largo y una de sus extremidades está rematada por una punta aguda, mientras que la otra está cerrada por una cabeza con reborde que permite fijar un hilo para extraer la aguja. AIGUILLES D*YTTRIUM-90 EN ENDO-ELECTRON-THERAPIE 203

Los cilindros o granos de âxido de itrio (S X 0,6 mm) se irradian durante una semana con un flujo de 2.7 • 1012n/cirfs y se introducen en las agujas a razón de tres o cinco en cada aguja. Dosimetría: El Centro de Saclay suministra las agujas de itrio- 90 con una actividad normalizada de 1 a 1,5 m c/cm (longitud radiactiva). La actividad se controla simultáneamente por recuento 4 ir por densi- metría mediante película. La dosis de referencia se calcula siempre de la misma manera, a 2 mm de la pared del tubo, suponiendo que la intensidad de dosis es del orden de 10 rad/min para una actividad de 1 mc/cm. Aplicaciones terapéuticas: La actividad radiobiológica de las agujas de itrio- 90 no está bien estudiada aún. La dosis disminuye rápidamente a partir de 3 mm de la pared de la aguja, lo que dificulta la irradiación homogénea de los tejidos tratados. En principio, las agujas se podrían colocar a 5 6 6 mm una de otra, pero esto requiere un dispositivo de implantación muy difícil de manejar; un error de 1 ó 2 mm podría producir excesivos puntos calientes o fríos. Por tal motivo, en una primera etapa, los autores utilizaron las agujas en tumores angiomatosos benignos sin tratar de irradiar homogéneamente el tejido, sino solamente de crear zonas de esclerosis, concéntricas a las agujas, separadas por zonas de tejido poco o nada irradiadas. De esta manera, esperan lograr en algunos angiomas tuberosos un efecto esclerógeno suficiente con la ventaja de que los enfermos reciben una dosis integral muy reducida. La ausencia de difusión en los tejidos sanos tiene particular interés para los angiomas situados cerca de tejidos radiosensibles (globo ocular, glándula mamaria) o próximos a las gónadas. Al parecer, los resultados obtenidos en los primeros casos tratados son satisfactorios. En una segunda etapa, los autores esperan poder utilizar estas agujas en tumores cutáneos malignos situados también en la vecindad de tejidos sanos radiosensibles (por ejemplo, cáncer de los párpados).

L’endo-électron-thérapie en m atériel solide n’a été que peu utilisée sur le plan clinique. La répartition du rayonnement en bêtathérapie n’intéresse qu’un volume tissulaire très réduit autour de la source, ce qui entraîne une distribution très inhomogène de la dose. Néanmoins, son utilisation présente un intérêt particulier par rapport à l’endo-photon-thérapie: celui de supprimer toute dose parasite distante de la source radioactive. Il en résulte une protection intégrale des tissus sains environnants, une protection intégrale in toto du malade et de l’opérateur. Il nous a donc paru intéressant de commencer l’étude de cette technique d’irradiation, particulièrement dans le cas d’angiomes chez le jeune enfant.

1. DESCRIPTION DU MATERIEL

Etudié et réalisé par le Service des radioéléments du Centre nucléaire de Saclay, le m atériel actuel se compose d’aiguilles de longueur radioactive de 25 mm ou de 15 mm (fig. 1, 2, 3, 4). Rappelons tout d’abord les caractéristiques de l’yttrium-90. Sa période est de 2, 7 j. Son émission gamma est pratiquement inexistante. L’émission bêta consiste en une infime proportion (0, 02%) dont l’énergie est de 0,52 MeV, et en une deuxième partie (99,9%) dont l’énergie est de 2, 26 MeV. Il s'agit donc d’un rayonnement bêta dont l’énergie est relativem ent très élevée. L’irradiation préalable des grains d’oxyde d'yttrium est effectuée à Saclay dans un flux de neutrons de 2, 7 . 1012 n/cm 2, s, pendant une semaine. Ceci perm et d’obtenir un m atériel dont la radioactivité est de l’ordre de 1, 5 m c/cm au moment de la livraison à l’Institut Gustave Roussy. 204 B. PIERQUIN et al.

Figuré 1

Aiguilles d’yttrium-90 de 25 et 15 mm de longueur radioactive.

Í

• î j i —gi

Figure 2

Introduction des grains d’yttrium- 90 dans l’aiguille d’acier inoxydable. LONGUEUR TOTALE 41,5 IULE D TRU-0 N NOEETO-HRPE 205 ENDO-ELECTRON-THERAPIE EN YTTRIUM-90 D’ AIGUILLES 3 36 2.5

n

GRAIN D'OXYDE D’YTTRIUM 0 6 /1 0 , l = 5mm

Figure 3

Schfeme des aiguilles d'yttrium-90. 206 B. PIERQUIN et al.

Figure 4

Dose délivrée par une source ponctuelle 0. en un point situé à une distance x. D (x) - 2035 j¡ e1 ' ^ rad/mc. h (i/ = 6,2).

Description d’une aiguille de 25 mm de longueur radioactive

Cette aiguille se compose d’un tube d’acier inoxydable dont le diamètre hors tout est de 1 mm, avec une paroi de 0, 1 mm. Une extrémité de ce tube d’acier est fermée par une pointe d’acier de 3 mm de longueur dont la base est munie d’un petit cylindre d’acier de 3 mm de longueur, servant de bouchon et introduit de force dans la lumière du tube. L’autre extrémité du tube est fermée par une tête en acier munie d’un bouchon identique à celui de la pointe. La tête proprement dite est en forme de cube de 2 mm de diamètre, perforé d’un trou de 1 mm permettant de passer un fil de suture. Dans la lumière de ce tube d’acier, on introduit successivement cinq cylindres ou grains d’oxyde d’yttrium, de 5 mm de longueur chacun, et dont le diamètre est de 0, 6 mm. Cette introduction nécessite des manipulations délicates, les grains devant être introduits après activation, ces petits cy­ lindres étant assez fragiles. Néanmoins, le jeu de 0, 2 mm dans la lumière du tube (ouverture intérieure 0; 8 mm) permet de les faire glisser sans diffi­ culté, une fois introduits dans la lumière de l’aiguille. On adjoint, du côté de la tête de l’aiguille un cylindre d’oxyde d’yttrium supplémentaire mais inactif afin de laisser un espace non radioactif entre la tête de l’épingle et la zone radioactive de l’aiguille. Cet espace est de 9 m m a u to ta l. Pour une longueur radioactive de 25 mm, la longueur hors tout de ces aiguilles longues est de 41, 5 mm. AIGUILLES D*YTTRIUM-90 EN ENDO-ELECTRON-THERA PIE 207

Pour les aiguiHes de 15 mm de longueur radioactive, le m atériel de support reste identique pour la fermeture à chaque extrémité. La longueur hors tout de ces aiguilles courtes est de 31, 5 mm (voir fig. 1). Des vérifications ont été effectuées au CEN de Saclay dans différents milieux pour déterminer l’existence de fuites éventuelles. Celles-ci sont pratiquement inexistantes, la fermeture de ces aiguilles s’avérant de bonne étanchéité.

2. DOSIMETRIE

Nous avons étudié la dosimétrie de ces aiguilles d’yttrium -90 à la fois sur des données théoriques de calcul et sur des données pratiques en étudiant sur des films radiographiques la répartition du rayonnement autour de l ’a ig u ille .

2. 1. Calcul théorique de la répartition de la dose autqur d'une aiguille d'yttri­ u m - 90.

Ce calcul a été établi en partant de la formule suivante, établie pour calculer la dose à une distance x d’une source ponctuelle d’yttrium -90:

D (x) = 2035 -j exp (1 - vx) rad/m c • h

Le milieu étudié est le plexiglas, dont le facteur v = 6, 2. Cette formule n’est applicable qu’à une distance x égale ou supérieure à 0, 161 mm.

Figure 5

Dose reçue par le point P situé à une distance variable dans le plan équatorial d'une ligne radioactive 208 B. PIERQUIN et al.

Si l’on calcule la dose pour des distances croissantes à partir de 2 mm jusqu’à 10 mm, on obtient une courbe droite semi-logarithmique qui aboutit à une valeur quasi nulle au delà de 1 cm (fig. 5). A partir de ce calcul fondamental autour d’une source ponctuelle, on peut calculer la dose autour d’une ligne radioactive en considérant cette ligne comme un ensemble de points radioactifs et en intégrant la dose calculée en un point P à partir de ces différents points. Pratiquement, on établit ce calcul en situant le point P sur une perpendi­ culaire abaissée à l1 extrémité d'une ligne radioactive dont la longueur ne dépasse pas 10 mm. On sait, en effet, qu1 au delà de 10 mm la dose est pra­ tiquement négligeable. On aboutit finalement à une courbe de décroissance en fonction de la distance qui se présente sous forme de droite semi-logarithmique (fig. 6).

CONTACT 1m m 2 mm 3 mm

Figure 6

Autoradiographies des aiguilles d’yttrium-90 avec des épaisseurs successives de plexiglas.

2. 2. Calcul expérimental par densimétrie sur film radiographique

Cette méthode a un double intérêt: a) vérifier la concordance des valeurs obtenues avec celles du calcul th é o riq u e ; b) pouvoir apprécier expérimentalement la dose à des distances beaucoup plus proches de l’aiguille. Nous avons utilisé des films Kodak de type M, émulsionnés sur une seule face. Les mesures ont été faites de millimètre en millimètre, en ajoutant successivement des lames en matière plastique de 1 mm d'épaisseur. On prend soin de recouvrir le film d’un papier noir afin d’éviter les phéno­ mènes parasites de photoluminescence et d’effet Cerenkov. La durée d’application pour des épaisseurs de 1 à 4 mm de plexiglas et des activités de 0, 5 à 1, 5 m c/cm a varié entre 1 et 4 min. Le développement est effectué en 3 min dans un révélateur à 20° , suivi de 5 min dans le fixateur. La lecture en densimétrie s’est effectuée avec un voile de fond de 0, 15. Les valeurs obtenues ont été comparées à des films mesurés dans des con­ ditions identiques à partir d’une source de strontium-90 étalonnée. On aboutit finalement à une courbe donnant lieu à une décroissance semi- logarithmique en ligne droite dont la pente est presque parallèle à celle de la courbe obtenue par calcul théorique (fig. 6). On voit donc que la décroissance de la dose de millimètre en millimètre se fait selon un rapport ^ j. AIGUILLES D*YTTRIUM-90 EN ENDO-ELECTRON-THERAPIE 209

C’est sur ces données théoriques et expérimentales du calcul de la ré­ partition de la dose autour d’une aiguille d’yttrium -90 (0, 1 mm de paroi d’acier) que nous avons fixé une dose de référence standard pour nos appli­ cations cliniques. Cette dose a été calculée à 2 mm de la paroi de l’aiguille; sa valeur est de 10 rad/min pour une activité linéaire de 1 mc/cm. - Chaque livraison d’aiguilles d’yttrium-90 est enfin contrôlée dans son activité globale par une mesure effectuée dans une chambre 4jr à partir d’un étalonnage préalable. (Cette mesure est faite à partir du rayonnement de fre in a g e ).

3. APPLICATIONS CLINIQUES

3. 1. Données biologiques a) Données biologiques dans le volume cible

La dose de référence dans notre étude clinique et biologique a donc été calculée à 2 mm de la paroi de chaque aiguille. Il existe donc autour de chaque aiguille un manchon tissulaire dont le diamètre total (aiguille com­ prise) est de 5 mm, et qui reçoit une dose s’élevant très rapidement en se rapprochant de la paroi de l’aiguille, et atteignant d’autant plus rapidement des valeurs nécrogènes que la dose de référence à 2 mm est plus élevée. Par contre, au delà de cette distance de 2 mm, la dose décroît très rapidement pour atteindre des valeurs biologiquement nulles à partir de 4 à 5 mm, quelle que soit la valeur de la dose de référence. Nous avons donc expérimenté les effets biologiques de cette endo- élec­ tron-thérapie en cherchant délibérément à réaliser des manchons d’irradi­ ation à dose très élevée de 5 mm de diamètre environ, séparés les uns des autres par des zones peu ou non irradiées. IL s’agissaitdonc d'une irradiation très hétérogène où il ne pouvait pas être question, comme en endo-photon- thérapie, d’une dose minima de référence intéressant l’ensemble du Volume- cib le. 1 Néanmoins, nous avons cherché à réduire au minimum l’importance relative de la fraction du volume-cible sous-dosée, en effectuant des implan­ tations avec un écart de 6 à 8 mm entre chaque aiguille, ce qui ne laisse finalement qu’un espace sous-dosé de 1 à 3 mm. Cet espacement réduit suppose une implantation très rigoureusement parallèle entre les différentes lignes radioactives si l’on veut éviter de larges zones sur- ou sous-dosées, avec les risques de nécrosé ou de non-stérilisation qu’elles comportent. b) Données biologiques à distance du volume-cible

Les avantages radio-biologiques de l’endo-électron-thérapie sont alors évidents: l’absence de toute irradiation parasite évite toute radio-lésion dans les tissus sains environnants ou à distance. Ceci-est particulièrement im­ portant lorsqu’il s’agit d’irradier des lésions à proximité de tissus sains dont il importe de respecter la fonction: on peut citer le globe oculaire, la glande mammaire, les ovaires, les épiphyses fertiles chez l’enfant. Ce 210 B. PIERQUIN et al. respect des tissus sains prend une importance dominante lorsqu’il s’agit de traiter des lésions bénignes où le pronostic vital n’est pas en jeu.

3.2. Données cliniques

Partant de ces données biologiques, nous avons cherché, sur le plan clinique, à évaluer les résultats que nous pourrons obtenir au niveau d’an­ giomes. Cette expérimentation nous paraissait justifiée: a) parce qu’il s’agissait de tumeurs bénignes où les risques de sous- dosage ne comportent pas d’inconvénients vitaux; b) parce qu’il slagissait de tumeurs vasculaires où une destruction partielle du tissu vasculaire était susceptible d’agir sur l’ensemble de la masseangio- mateuse et de la scléroser complètement; c) enfin et surtout parce que l’endo-électron-thérapie par yttrium-90 assure des conditions de protection très satisfaisantes comparativement à celles de l’endo-photon-thérapie par radium, particulièrement lorsqu’il s’agit d’un enfant en bas âge. L’intérêt de cette protection n’est d’ailleurs pas négligeable pour l’opérateur luir même qui peut effectuer des applications minutieuses sans risque d’irradiation in toto.

3.3. Technique d’implantation

La technique n’a rien de très particulier dans ses principes généraux. Elle répond à celle qui est habituellement appliquée pour toute implantation d’aiguilles; elle doit par conséquent répondre à un parallélisme aussi rigou­ reux que possible. A l’aide d’une pince à bords plats et non crantée, sous anesthésie géné­ rale, après un repérage soigneux des points d’implantation prévus pour chaque aiguille et en tenant compte d’un écartement de 6 à 8 mm entre chaque point, nous implantons successivement les aiguilles en un ou deux plans, selon l’épaisseur de l’angiome. On s’efforce de сощ-vrir toute l’éten­ due de la formation angiomateuse en cherchant cependant à ne pas déborder les lim ites de la tumeur afin d’éviter toute irradiation parasite des tissus sains. П ne s’agit donc pas d’encadrer la lésion par des sources radioactives, mais de la pénétrer en s’arrêtant aux limites de l’angiome. Un contrôle par cliché radiographique peut être effectué à la demande en fin d’application. Les mensurations à partir des points d’implantation permettent, par ailleurs, d’établir un schéma de l'implantation. Les doses appliquées ont été, sur la dose de référence .definie à 2 mm de la paroi de chaque aiguille, de 1000 à 1500 rad par application. En fonction de l’activité du m atériel au moment de l’application, la durée de l'irradiation a varié entre 1 et 6 h.

3.4. Résultats immédiats

Nous avons, dans l’état actuel de notre expérimentation (septembre 1962), traité, depuis février 1962, une douzaine de malades pour des angi­ omes cutanés dont les dimensions n’excédaient pas 2, 5 cm pour le petit dia­ mètre. П s’agissait des localisations suivantes: AIGUILLES D’YTTRIUM-90 EN ENDO-ELECTRON-THERAPIE 211

zone sus- ou sous-orbitaire: 3 cas tro n c 3 cas fe sse 2 ca s, vulve 3 cas c u isse 1 c a s.

Les résultats cliniques immédiats sont les suivants: bonne tolérance dans les jours qui suivent, sans réaction cutanée apparente, régression de l’angiome dans les semaines qui suivent (8 à 12 semaines) dans des propor­ tions apparemment comparables à celles qui sont obtenues par traitement au radium, avec une dose minimum identique (1000 à 1500 r). Notre ex­ périence est cependant encore trop réduite (la première application remonte au mois de février 1962) pour que nous puissions en tirer des conclusions définitives. Des précisions plus détaillées seront apportées en novembre 1962 lors­ que nous aurons pu reviser les dossiers de ces douze malades dans le cou­ rant du mois d’octobre.

DISCUSSION

K. SCHEER: I agree with Dr. Pierquin that with ^-em itter implants these insufficiently irradiated areas are unavoidable, but in the case of cavernous haemangioma I do not think it matters, as the centres of sclerosis will suppress these areas. On the other hand I believe that in these areas the dose due to bremsstrahlung would have to be taken into account. Have you done any calculations or measurements of the dose due to brem sstrah­ lung in these insufficiently irradiated areas, or in more distant areas such as the eyeball in the case of implantation in the cheek, or the testicles or ovaries in the case of implantation two or three centimeters away? What is the dose due to brem sstrahlung at these distances? B. PIERQUIN: I have not done this myself, but these doses at a dis­ tance have been estimated by Madame J. Dutreix using a Plexiglas assembly —I do not have the exact figure in my mind but I believe the dose calculated at 2 cm was 7 to 8%, in other words very weak. I ami not a physicist, but I think the bremsstrahlung dose for yttrium is also very weak, in fact less than 2 or 3% with the geometry that we have, but I cannot give exact figures because I did not do such calculations myself. A. WARD: Before asking my question I would just like to say that I am inclined to agree with your rem arks about the dose due to brem sstrah­ lung. Now, could you explain in greater detail how you measured the dose with the film? B. PIERQUIN: I would hesitate to answer this from the physical stand­ point, as I am à doctor, not a physicist. From the purely clinical point of view I can say that we base our method on the standard reference dose of 10 rad/m in for a linear activity of 1 m c/cm 2 mm from the wall of the needle. Since we are told the actual activity by Saclay, we can determine the usual clinical doses of 1000 to 1500 rad by means of a simple rule of three. When 212 B. PIERQUIN et al.

we receive needles we naturally check their activity against a reference standard (using a 4w-counter), but this is a routine task and raises no special difficulties, either for yttrium or for any other substance. It can be seen from this that the application tim es are of the order of one or two hours in the case of an activity of 1 mc/cm; if, however, we receive or use the mat­ erial after a delay of two or three days and find that the activity has de­ creased to a value of, say, 0. 5 m c/cm (owing to its short half-life), we have to lengthen these tim es accordingly — but the maximum time of appli­ cation does not usually exceed five or six hours. No account is taken of decay during the actual application periods, because for a period of a few hours the percentage decay is very small. THE TECHNIQUE AND DOSIMETRY OF PITUITARY IMPLANTATION USING SOURCES OF Y®°

MARY H. DUGGAN, ELIZABETH JONES A N D J.R . MALLARD DEPARTMENT OF PHYSICS, HAMMERSMITH HOSPITAL, AND G.F. JOPLIN DEPARTMENT OF MEDICINE, POSTGRADUATE MEDICAL SCHOOL, LONDON, ENGLAND

Abstract — Résumé — Аннотация — Resumen

THE TECHNIQUE AND DOSIMETRY OF PITUITARY IMPLANTATION USING SOURCES OF Y *. Pituitary ablation by needle implantation of Y90is finding increasing use in the treatment of breast and prostatic cancer, as well as diabetic retinopathy, Cushing’s disease, acromegaly, and perhaps exophthalmos in Graves' disease. Yttrium-90 is the most suitable radioisotope when complete ablation of the gland is sought. This is because only 6-particles are emitted, the maximum range (7mm) of which is comparable with the dimensions of the gland. The implantation of rods of standard activity into the gland, irrespective of its size, does not permit a standard dose level to be delivered to the gland and the method of implantation is to select the size and activity of the source to fit the dimensions of the gland in question. Thus consistency in procedure may be attempted from one implant to another. The shape of the gland and the mode of access to it is such that complete destruction may conveniently be obtained by implanting two.sources. Each source is a rod of sintered Y20^, (2-mm diam ., and of length cut to suit the individual gland length). The rod activity is also selected to suit the gland dimensions: typically, it is from 2 to 3 me. Radiation dose has been experimentally related to geometry and activity. Mix D wax is used as the tissue- equivalent absorber, film as the detector and a calibrated Sr90 source (which decays into Y90) as the standard. One outcome of this work is that the pituitary gland requires a radiation dose of between 100 000 and 200 000 rad for'necrosis and ablation.

TECHNIQUE ET DOSIMETRIE DE L’IMPLANTATION DE SOURCES D'YTTRIUM-90 DANS L'HYPOPHYSE. L'ablation de l’hypophyse par implantation d'aiguilles à l’yttrium-90 est de plus en plus utilisée dans le traite­ ment du cancer du sein et de la prostate, comme dans celui de la rétinite diabétique, de la maladie de Cushing, de racromégalie, et peut-être de l’exophthalmie associée à la maladie de Graves. Lorsqu'on recherche l'ablation totale de la glande, l’yttrium- 90 est le radioisotope qui donne les meilleurs résultats car il n’émet que des particules bêta, dont le parcours maximum (7 mm) équivaut aux dimensions de la glande. Si l’on implante des aiguilles d'activité standard dans la glande sans tenir compte de ses dimensions, on ne peut pas administrer à la glande une dose standard; il convient donc d'adapter les dimensions et l’activité de la source aux dimensions de la glande. On peut ainsi s'efforcer de rationaliser la méthode d’une implantation à l ’autre. Etant donné la forme de la glande et son mode d'accès, il est possible d’obtenir une destruction totale par implantation de deux sources. Chacune de ces sources est constituée par une aiguille de Y2 0 3 fritté, d*un diamètre de 1 mm et d'une longueur adaptée aux dimensions de la glande. L'activité de l’aiguille est égale­ ment déterminée en fonction des dimensions de la glande: elle est en général de 2 à 3 me. La dose de rayonnement a été calculée expérimentalement d’après la géométrie et l’activité. On a utilisé de la cire «M ix D » comme absorbant équivalent au tissu, un film comme détecteur et une source au strontium-90 étalonnée— dont l'yttrium- 90 est un descendant—comme étalon. L’une des conclusions auxquelles les présents travaux ont abouti est que la nécrose et l’ablation de l'hypo­ physe exigent une dose de rayonnement comprise entre 100 000 à 200 000 rad.

ДОЗИМЕТРИЯ ИМПЛАНТИРОВАННЫХ В ГИПОФИЗ ИГЛ ИТТРИЯ-90. Удаления гипофиза путем имплантации иттриевой иглы находит все возрастающее применение при лечении рака грудной и предстательной

213 214 M. H. DUGGAN et al.

желез,так же как ■ при лечении диабетической ретинопатии, болезни Кушинга, акромегалии и, возможно, экзофтальма при базедовой болезни. ИттриЙ-90 является наиболее подходящим изотопом, когда требуется полное удаление железы, так кейс он испускает только бета-частицы, максимальный радиус действия которых (7 мм) соизмерим о размерами желез. Имплантация в железу стержней стандартной активности, независимо от их ве­ личины, недопустима из-за стандартного уровня дозы, вводимой в железы, тогда как целью метода имплантации является возможность выбора величины и активности источника соответственно размерам рассматриваемой железы. Таким образом качество методики может совершенствоваться от одного им­ плантата к другому. Форма железы и доступ к ней таковы, что полное разрушение железы может быть достигнуто пу­ тем имплантации двух источников, каждый из которых предотавляет собой стержень из спекшегося *а°а (диаметром 1 мм при длине, соответствующей индивидуальному размеру железы). Актшвнооть отержня подбирается в соответствии с размерами железы: как правило, она составляет 2 - 3 милли­ кюри.

DOSIMETRÍA DE LA IMPLANTACIÓN DE FUENTES DE эоу EN LA HIPÓFISIS. En el tratamiento del cáncer mamario y de la próstata,de las retinopatías diabéticas, de la enfermedad de Cushing, de la acromegalia y, ocasionalmente, délas exoftalmia en la enfermedad de Graves, se recurre cada vez más a la ablación de la hipófisis por implantación de agujas de soy. Este radioisótopo es el más adecuado cuando se procura lograr la ablación completa, porque sólo emite partículas 6 cuyo alcance máximo (7 mm) es comparable con las dimensiones de la glándula. Si se implantan en la glándula varillas de actividad normalizada, Independientemente de su tamaño, no se le puede admi­ nistrar una dosis standard, de modo que el método de implantación consiste en elegir un tamaño y una actividad de la fuente adaptados a las dimensiones de la glándula en cuestión. De esta manera, se procura que el proce­ dimiento sea uniforme en todas las implantaciones. La forma de la glándula y el acceso a ella son tales que la mejor manera de lograr su destrucción completa es implantar dos fuentes, consistentes en varillas de Y20 3 sintetizado (de 1 mm de diámetro y de longitud adap­ tada a las dimensiones de la glándula). La actividad de la varilla se elige también convenientemente; en los casos característicos está comprendida entre 2 y 3 me. Los autores han encontrado experimentalmente la relación entre la dosis de irradiación por una parte y la geometría y la actividad por otra. Como absorbedor equivalente al tejido, utilizaron cera Mix D; como detector, una película y como patrón, una fuente calibrada de *>Sr( que se desintegra formando 90Y). La memoria examina la validez de este procedimiento. Este trabajo permitió comprobar que la necrosis y la ablación de la hipófisis requieren dosis que oscitan entre 100 000 y 200 000 rad.

1. INTRODUCTION

The destruction of the pituitary gland by implantation of sources of radio­ active yttrium-90 has been used extensively in the treatment of breast cancer [1, 2]. Recently, it has shown promise in arresting blindness resulting from diabetes. The rationale behind this treatm ent is as follows : the pituitary gland exercises a controlling influence over other hormone-secreting glands in the body; if it is destroyed, the function of these other glands and hence the progress of hormone-dependent diseases may be controlled. The selection of the Э-em itter, Y90, has primarily resulted from the necessity to localize the radiation as much as possible within the small volume of the gland so as not to over-irradiate vital nervous tissues in its vicinity, e.g. the optic nerves. The emphasis of this paper is on the contribution of radiation dosimetry to the procedure, the technique and results being described only in outline. We consider radiation dosimetry to be essential both for the planning of implants and for the evaluation of the adequacy of the implants. The latter may suggest modifications required in order to improve the technique. TECHNIQUE AND DOSIMETRY OF PITUITARY IMPLANTATION 215

2. EVALUATION OF DOSIMETRY DATA

The method now in use is a modification of that described by MALLARD e t a l .[3 ]. Our sources are of compressed yttrium oxide, formed into rods 1-mm diam. and varying between 2 and 8 mm in length, according to the size of the gland to be implanted. Y90 is produced by neutron activation at the Atomic Energy Research Establishm ent, Harwell. (A neutron flux of 1.2 X 1012 n/cm 2 s produces an activity of 2 me in a 6-mm rod in three days.) The half-life of Y90 is 64 h and it emits /3 particles having a maximum energy of 2.2 MeV. The following data is required for all rod lengths in use : (i) a calibration factor relating dose delivered to activity. This enables rods of the correct activity to be ordered; (ii) a calibration factor relating dose delivered to deflection on a meas­ uring instrument. The strength of the rods may then be checked before implant. (The /3 window of a re-entrant ionization chamber is used (NBL Type 1383) the deflection being in ццА on a DC am plifier (Avo Type 1388A); (iii) depth dose curves; and (iv) isodose surfaces. For convenience, the depth doses are normalized with respect to the dose delivered at 1 mm from the surface of the rod on the minor axis. Figure 1 shows depth dose_ curves for 2-mm and 8-mm rods.

Fig-1

Depth dose curves for 2-mm and 8-mm rods

Figure 2 shows isodose lines around a 6-mm rod and the isodose sur­ faces are obtained by rotating the diagram about the major axis of the seed. The calibration factors for each length are collected in Table I. 216 M. H. DUGGAN et al.

5 mm i------1

Isodose lines around an Y90 rod. Figures indicate percentage of dose delivered at 1-mm broadside.

TABLE 1

CALIBRATION FACTORS FOR Y90 RODS

Total at 1- mm broadside ( rad) Rod length (mm ) per me activity per ¡¡¡¡A deflection

2 983 000 2150

3 794 000 1740

4 647 000 1600

5 529 000 1260

6 494 000 1210

7 437 000 1130

8 361 000 1020

The standard error of these figures is about ± 5%.

These data have been established experimentally using a wax (known as Mix D*) as a radiation absorber, a photographic film as detector, and a S r 9 0 standard plaque as a means of calibration (see Fig. 3).

* Composed of: paraffin wax, 60.8%; polyethylene, 30.47»; magnesium oxide, 6.4%and titanium oxide, 2.4%, with a density of 0.99 g/стз. TECHNIQUE AND DOSIMETRY OF PITUITARY IMPLANTATION 217

MIX D MIX D ABSORBER - - - OF KNOWN THICKNESS MIX 0 "ROD

Fig- 3

Diagram showing the arrangements of rod, absorber and film in dosimetry evaluation.

Mix D is considered to be tissue-equivalent [4] so that the absorption of (3-rays in it may be regarded as the same as that for tissue. It may be machined into plates from \ mm in thickness upwards. The dose delivered is obtained in term s of the density of blackening of the film which is measured with a densitometer using a pin-hole light source. This is interpreted by comparison with blackening produced by a Sr90 plaque, the dose-rate from which has been independently established by more conventional techniques using an ionization chamber.

3. PRE-IMPLANT PLANNING

To plan an implantation, it is necessary first to ascertain the dimensions of the bone declivity (fossa) containing the gland. A lateral skull radiograph gives the length and the depth of this fossa. The width is obtained from an antero-posterior radiograph. Using these dimensions, together with the dosimetry data described in section 2, it is possible to specify the length, activity and position of the rods required to deliver a selected dose to the gland. The pituitary tissue requires an extremely high dose for its destruction [5j: between 100 000 and 200 000 rad. This must be achieved without over-dosing the covering tissue over the top of the gland (diaphragma) and the entry holes bored through the fossa walls to allow entry of the rods. If these receive a dose appreciably in excess of 300 000 rad total, then complications may ensue. Figure 4 shows the pre-implant plan for a fossa of average dimensions. A rod 6 mm in length and 2.7 me in activity is placed centrally in each half of the gland. The peak dose to the diaphragma, entry hole and also to the sidewalls is 300 000 rad.

3 mm \ ( ' Л v Vnm - о о i=^=i3 mm

* ..9 mm.. *► p*---- H mm.... *

LATERAL VIEW ANTERO-POSTERIOR VIEW

Fig. 4

Diagram showing the planned positions for rods in a fossa of average dimensions. 218 M. H. DUGGAN et al.

4. IMPLANTATION TECHNIQUE

Implantation is carried out by passing a hollow needle into the pituitary gland, guided by a radiologist viewing continually with image intensification in both lateral and antero-posterior projections. A hole is drilled through the nasal, ethmoid and sphenoid bones; the implant needle is then passed into the gland and the rods placed in position by a combination of extrusion of the rod and withdrawal of the needle.

5. ASSESSMENT OF ADEQUACY OF IMPLANT

5.1. By pituitary function testing

Destruction of the pituitary gland is best tested clinically by measuring the change produced in the function of the thyroid gland whose activity is controlled by the pituitary gland. Details of this and other methods are not included in this paper.

5.2. By post-implant dosimetry

The fraction of the gland volume believed to receive more than the aver­ age necrotic dose of 150 000 rad is calculated. (The necrotic dose is the dose required to destroy the pituitary cells.) Until the patient comes to post­ mortem the true shape of the gland is not known, and in these calculations one has to assume that the gland conforms to the most probable situation, that is, it is a close fit within the bony fossa. The dimensions of the latter and the positions of the Y 9 0 rods can be derived from post-implant radio­ g ra p h s . The fraction of the fossa volume receiving more than 150 000 rad is :

V /V, 150 000 ' fossa

Accurate estimation of these two volumes is lengthy. It has been under­ taken both by calculation and by the use of three-dimensional model re­ constructions. In the calculation, the fossa is considered to be built up from sections, each sufficiently thin to be regarded as having uniform area, and for it to be reasonable to use a single derived isodose line for any one section. The fraction of the fossa receiving more than 150 000 rad is then the sum of all the planar areas enclosed by 150 000 rad outlines divided by the sum of all the sectional areas. Three-dimensional reconstructions are made using magnified copies of the post-implant radiographs to orientate appropriately magnified rods representing the Y90 sources. Wax isodose surfaces are fitted round the rods which are melted together where the isodose surfaces overlap. The shape of the fossa is superimposed on the combined wax isodose surfaces by means of a wire frame shaped from the radiographs, which slices through the wax isodose surface where necessary, that is, in regions where the isodose surfaces extend beyond the periphery. TECHNIQUE AND DOSIMETRY OF PITUITARY IMPLANTATION 219

LATERAL VIEW ANTERO-POSTERIOR LATERAL VIEW SHOWING VIEW SHOWING LEFT ROD RIGHT ROO

, 6 m m , ------1 5 0 OOO-RAO CONTOUR

( d w V = T/ 6 |l.d.w.| LEFT 6 Ц 1 298 m m 3 RIGHT 8* 6 5 133 J

Fig. 5

Diagram illustrating an example of post-implant dosimetry (patient M.G. )

The results have shown that when the limit of accuracy required is only ± 10%, the following very simple method of calculation is satisfactory. The volume of the fossa is approximated to the area in the lateral view multiplied by the width of the fossa. In the case of patient M .G ., shown in Fig. 5, this is

60 mm2 X 15 mm = 900 mm3

V150000 is approximated to the sum of two ellipsoidal volumes, one asso­ ciated with the left-hand rod and the other with the right-hand rod. Consider­ ing the left-hand rod, the appropriate diameters are 7| mm, 6 mm and 7 mm. Thus the volume is

Vi50000 = » /6 <7-5) (6) <7) = 165 mm 3‘ S im ila rly , Visooooiright) = тт/6 (8.5) (6) (5) = 133 m m 3 .

Hence, the fraction of the fossa receiving more than 150 000 rad is

Чбоооо/Vfossa = 2 9 8 /9 0 0 = 33%.

The more accurate calculation led to a value of 40%. The discrepancy between the two results is thus 7%. The more rapid method of calculation gives a value which is sufficiently accurate to be useful in describing the adequacy of an implant.

6. COMPLICATIONS

The main complication is CSF rhinorrhoea.This is a leakage of cerebro­ spinal fluid which appears to be due to both entry holes and diaphragma re­ ceiving a dose considerably in excess of 300 000 rad. Treatment is by the insertion of a tapered stainless-steel screw to seal the needle hole. 220 M. H. DUGGAN et al.

7. CLINICAL RESULTS

7.1 Breast cancer

Approximately 50% of patients show some objective improvement, but a really worth-while response and prolongation of life are only found in 25% of c a s e s .

7.2 Diabetic retinopathy

Twenty patients have been implanted and followed up for 12 months or more. The majority is considered to have shown a significant improvement in retinopathy based on a study of serial photographs of the retina.

8. OTHER APPLICATIONS OF PITUITARY IMPLANTATION

This paper has been concerned with implantation when complete de­ struction of the pituitary gland is sought. In the treatment of Cushing’s dis­ ease, acromegaly and exophthalmos in Graves’ disease, partial destruction is sought, the object being to diminish pituitary function or to destroy a pi­ tuitary tumour. In these cases promising results are being obtained using metallic grains of Au198, either alone or together with rods of Y90[6].

ACKNOWLEDGEMENTS

We are indebted to our colleagues Professors Russell Fraser and R.E. Steiner, andDrs.J.W . Laws, R. Morgan and R. Morrison, for allow­ ing us to publish results from a joint study.

REFERENCES

[1] FRASER, R. , JOPLIN, G .F ., LAWS, J. W ., Morrison, R. and STEINER, R .E ., "N eedle Im plantation of Yttrium Seeds for Pituitary Ablation in Cases of secondary Carcinoma", Lancet 1^ (1959) 382. [2] FRASER, R. and JOPLIN, G. F ., "Therapeutic pituitary Ablation", Modern Trends in Endocrinology(1962) 691 [3j MALLARD, J .R ., McKINNELL, A. and FRANCOIS, P .E ., "Seeds of pure b e ta -ra y Em itter (Y ttrium -90) for radiation Hypophysectomy", Nature 178 (1956) 1240. [4] JONES, D.E.A. and RAINE, H.C. , "Solid phantom Material", Brit. J. Radiol. 22 (1949) 549. [5] RASMUSSEN, T. B ., HARPER, P. V. and KENNEDY, T ., "The Use of S-ray Sources for Destruction of the Hypophysis", Surgical Forum 4 (1952) 681. [6] JOPLIN, G .F., FRASER, R ., STEINER, R.E., LAWS.J.W. andJONES, D .E.A ., "Partial Pituitary Ablation by Needle Implantation of Gold-198 Seeds for Acromegaly and Cushing's Disease", Lancet 11 (1961) 1277.

DISCUSSION

L. G. STANG: Could one of the authors explain to those of us who do not have a medical background the significance of the difference between the two techniques described in this paper and the paper by B. Pierquin et al. — in one case the needle was left in and in the other case it was removed. Is the reason for this a medical one or is it connected with the activity that can be introduced? TECHNIQUE AND DOSIMETRY OF PITUITARY IMPLANTATION 221

M. DUGGAN: I'm not quite sure whether Dr. Pierquin actually mentioned the doses to which the angiomas are to be raised? L. G. STANG: I believe he said 1000 rad — which is certainly much lower than in your case. M. DUGGAN: Yes, very much lower, because we find that we cannot be sure of getting ablation under 100 000 rad. B. PIERQUIN: I should like to point out that radiobiologically there is a great difference between hypophyseal radiotherapy and the irradiation ■of angiomas. We radiotherapists are normally concerned with destroying a certain cellular type, or certain tissular elements,whilst avoiding damage to the neighbouring structure. In the case of the hypophysis, however, we are concerned with the total destruction of a gland which is particularly resistant to radioactivity, there being no question of conserving any part of the gland; the aim here, then, is to give the maximum possible dose, and the figures therefore appear by comparison with ours quite fantastic, being of the order of 100 000 to 150 000 rad, as I know from work carried out at the Gustave Roussy Institute — work sim ilar to that done by Miss Duggan. It is clear, however, that this hypophyseal destruction is a special ca se . When we give doses of the order of 1000 - 1500 rad in the case of an­ giomas, the intention is m erely to inhibit some particular vascular cell development without affecting the essential nature of the irradiated tissue. A. WARD: What is Mix D, referred to in section 2 of your paper? M. DUGGAN: D. E. A. Jones, of Mount Vernon Hospital near London, made up a number of mixes — А, В, С and D— whilst investigating tissue- equivalent m aterials. Mix D is described in reference [4] of our paper. Briefly, it consists of 60.8% paraffin wax (by weight), 30.4% polyethylene, 6.4% magnesium oxide and 2.4% titanium oxide. This constitutes tissue- equivalent m aterial. C. TAYLOR: What is the accuracy of calibration required for these grains? Is it preferable for any error to be on the high side or on the low sid e ? M. DUGGAN: We are able to tolerate variations from the specified activity of the order of ± 10%. We prefer the rads to err on the high side rather than the low, because usually the implant plan can be modified to accommodate a greater activity: if the seeds are placed a little lower, the peak dose to the diaphragm still does not exceed 300 000 rad, because the half-value layer of~Y90 /З-rays in tissue is as small as 1 mm. The floor of the fossa, as a resalt, receives a higher dose than originally planned, but this can tolerate a very high dose. A. WARD: What errors are actually encountered in positioning these yttrium implants? Are they comparable with the half-thickness for dosage? M.DUGGAN: In general the accuracy of implantation is good, but some­ times the seeds tend to follow the needle as it is withdrawn, and sometimes they seem to flop down. The errors involved are occasionally comparable to the half-value layer for Y90 )3 particles in tissue. B. PIERQUIN: 1 would like to say a few words on this subject. At the Gustave Roussy Institute we have developed a technique to avoid difficulties caused by implantation errors: we use grains having an activity somewhat 222 M. H. DUGGAN et al.

less than yours, but they are implanted at a greater number of points. We implant these grains, of about 2 mm radially around the centre of the hypo­ physeal cavity so that a more uniform dose distribution is ensured. Although the two-grain method is theoretically very good, a high degree of accuracy is required in the positioning of the grains with respect to each other and with respect to the walls in order to avoid giving too high a dose to the walls, especially in view of the fact that with your technique it is necessary to use grains of very high activity. M. DUGGAN: We have had experience of the technique you describe, inserting a number of seeds into the gland by means of a side-ejector needle. This technique, however, was abandoned several years ago in favour of the sim pler and more refined two-seed implant. We estimate that the required accuracy of placement (to less than 1 mm) can be obtained by viewing the whole process through an image intensifier, and this would appear to be- borne out by the results we obtain (about 80% of all our patients are ablated). K. SCHEER: I understand that the most serious complication with this pituitary implantation technique using ^-em itters is rhinorrhoea. What is the incidence of this complication? In how many cases is there spontaneous recuperation, and in how many cases are you forced to adopt surgical m e a s u r e s ? M. DUGGAN: We have to date implanted about 200 patients and I think the incidence of CSF rhinorrhoea is of the order of 20%. Often it will clear itself up, otherwise a screw has to be inserted. I think so far only two cases have had to be closed surgically. SUPPLEMENTARY DISCUSSION

Medical applications of other short-lived radioisotopes — technetium -99™

K. SCHEER (Chairman): I think it might be useful to spend a few minutes discussing an isotope, viz. technetium-99m, whose physical characteristics make it particularly attractive for medical purposes. There are no beta particles liable to deliver an undesirable body dose. The gamma energy of 140 keV is very convenient from the standpoint of shielding and collimation, and there is not too much self-absorption in the body. I wonder if I could ask Mr. Stang from Brookhaven to comment. L. STANG: Г had hoped that someone, preferably an M .D., would present a paper forecasting what particular isotope characteristics will be required in the near future. In this connection, I certainly think that technetium - ЭЭ171, the six-hour technetium, is of interest. It is available from Brookhaven but our production method can be copied by those who prefer to make the isotope themselves — details can be found in the paper I presented at the present Seminar, in the section devoted to Mo". One of the advantages of Tc99m is that it can be made available in gene­ rator form, i.e.. it can be milked by the user from 65-h Mo" in the same way as I132 can be milked from T e i 3 2 . In other words, it has all the many advantages of a short-lived isotope and at the same time it can be extracted in the user's own laboratory. Another useful feature is that Tc99m has medium-soft gamma rays of slightly over 100 keV so that it can irradiate a larger volume than is possible with beta particles but it will not irradiate the whole body. Moreover, because of this medium-soft gamma radiation good collimation of scanning equipment is relatively easy and inexpensive. I believe that Tc99m can be used for tagging plasma and that it is there­ fore useful for cardiac-output and cardiac-circulation studies. I have also been told that the thiocyanate complex of T c 9 9 m can be made and used for liver scanning, and that Tc99m can be used directly for thyroid-scanning and determining cerebral circulation times. K. SCHEER: I would just like to add that I had in fact intended to present a paper on technetium at the present Seminar but work was held up because of the difficulty of obtaining the isotope. It was only here that I learned that technetium has been available from Brookhaven for almost a year now.

223

APPLICATIONS IN BIOLOGY

APPLICATIONS OF FLUORINE -18 IN BIOLOGICAL STUDIES WITH SPECIAL REFERENCE TO BONE AND THYROID PHYSIOLOGY

M . AN BAR THE WEIZMANN INSTITUTE OF SCIENCE AND IAEC SOREQ RESEARCH ESTABLISHMENT, REHOVOT, ISRAEL

Abstract — Résumé — Аннотация — Resumen

APDLICATIONS OF FLUORINE-18 IN BIOLOGICAL STUDIES WITH SPECIAL REFERENCE TO BONE AND THYROID PHYSIOLOGY. At the authprs laboratories fluorine-18 was applied during the last three years to a great variety of problems in biology and medicine. Methods were developed to prepare fluorine by each o f theOl¿(p,n), О*6 (H d, n) and Fw (n,2n) reactions. Radiofluorine-labelled compounds were prepared by isotopic exchange, by synthesis, by recoil labelling and by retention of fluorine in fluoro-organic compounds under­ going the (n, 2n) reaction. Special low- level counting techniques were developed to cope with the low activities of tracer amounts of organic fluoro-compounds. Fluoride-18 ions were applied to studies in bone physiology. It was found that F“ follows calcium in many aspects ot its physiological behaviour; the accumulation ol F in bone was found to increase under the influence o f vitamin D and of testosterone, whereas cortizone and estrogens diminished the extent o f fluoride accretion. The pattern of distribution of fluorine in the organism was modified when administered in the form of a cationic complex. Fluorine-18 labelled YF’1"1’ or ZF"1"3 were found to follow the pattern o f distribution o f the parent cations. Fluoroborate ions were shown to accumulate in the thyroid gland to an extent comparable to that o f iodide ions. Fluoroborate ions do not undergo any organic binding in the thyroid, and their uptake is a specific, indication of the function of the "trapping stage” in the gland. Fluorine-18 labelled fluoroborate has been applied to a variety o f problems in throid physiology. It has been shown that TSH diminishes the uptake o f BF4 in the first few hours after administration and enhances it after 24 h. The inhibitory action of iron, copper, zinc, cadmium, fluotide, thiocyanate and other ions on the iodine uptake was simulated by BF¿ ; thus the trapping stage was shown to be involved. In an analogous series of experiments sulphydryl- containing compounds, as well as azide ions, were found to enhance the trapping o f fluoroborate, although they diminish the overall iodine uptake. Next, it was demonstrated that the trapping stage is much less radiosensitive than the stages of thyroxine formation and release. A quite different application of Flb-labelled fluoroborate ions was in the localization of brain tumours, by directional coincidence scanning owing to the limited permeability of these ions via the intact blood- brain barrier. Fluorine-18 labelled fluoraromatic chelating agents were prepared and applied to problems in bone physiology. Fluorine-18 labelled aromatic vital dyes were used in investigating problems of permeability through biological membranes. Fluorine-18 labelled fluorine containing antimetabolites including 5-fluorouracyl and fluoro-orotic acid, have been prepared and applied to physiological problems, including cancer research.

' EMPLOI DU FLUOR-18 DANS DES ÉTUDES BIOLOGIQUES, NOTAMMENT SUR LA PHYSIOLOGIE DES OS ET DE LA THYROÏDE. Dans les laboratoires de la CEAI, le fluor-18 a été utilisé au cours des trois dernières années pour résoudre de nombreux problèmes de biologie et de médecine. Des méthodes ont été mises au point pour préparer le fluor par chacune des réactions l80 (p ,n ), l 60 (H 3, n)et 18F(n,2n). Des composés marqués au radiofluor ont été préparés par échange isotopique, synthèse, marquage par recul et rétention du fluor dans des composés fluorés organiques soumis à la réaction (n, 2n). Des techniques spéciales de comptage ont été mises au point pour mesurer les faibles activités de doses traceuses de composés fluorés organiques. Les ions 18F" ont été utilisés pour des études sur la physiologie des os. On a constaté que l'ion F’ est semblable au calcium en de nombreux aspects de son comportement physiologique; on a observé que la fixation F par l'os augmente sous l'influence de la vitamine D et de la testostérone tandis que la cortisone et les oestro­ gènes réduisent le taux de fixation. Le mode de distribution du fluor dans l'organisme se modifie lorsqu’ il est administré sous la torme d'un complexe cationique. On a constaté que la distribution de YF++ ou ZFt3 marqués au fluor-18 est la même que pour les cations générateurs.

227 228 M. ANBAR

ün a montré que l'accumulation des ions fluoboratesdansla glande thyroïde est comparable à celle des ions d’ iode. Les ions fluoboratesnesont soumis à aucune liaison organique dans la thyroïde, et leur fixation constitue une indication spécifique de la phase de « capture» qui a lieu dans la glande. Le fluoborate marqué au fluor-18 a été utilisé pour résoudre divers problèmes relatifs Ь la physiologie de la thyroïde. On a montré que ia thyréostimuline (TSH) diminue la fixation de BF4 au cours des premières heures qui suivent son ad­ ministration et l'augmente après 24 heures. L'action inhibitrice des ions fer, cuivre, zinc, cadmium, fluorure, thiocyanate, etc. sur la fixation de l'iode a été simulée au moyen de BF4 , ce qui a mis en évidence le rôle du phénomène de capture. Au cours d'une série analogue d'expériences, on a constaté que les ions azides, comme les composés sulfhydryles, stimulent la capture du fluoborate tout en réduisant la fixation totale d'iode. Il a ensuite été démontré que la phase de capture est beaucoup moins radiosensible que les phases de formation et de libération de la thyroxine. Une application très différente des ions fluoborates marquée au fluor-18 est la localisation de tumeurs du cerveau, par exploration directionnelle par coïncidence, grâce à la perméabilité lim itée de la paroi intacte des vaisseaux sanguins du cerveau à ces ions. On a préparé des agents de chélation à base de composés aromatiques marqués au fluor-18 et on les a utilisés pour des études de physiologie des os. On s’est servi de colorants vitaux aromatiques marqués au fluor-18 pour étudier des problèmes de perméabilité des membranes biologiques. Des antimétabolites contenant du fluor marqué au fluor-18 notamment 5-fluo-urocyle et de l'acide-fluo-orotique, ont été préparés et utilisés pour résoudre des problèmes de physiologie, notamment dans la recherche sur le cancer.

ИСПОЛЬЗОВАНИЕ ФТОРА-18 В БИОЛОГИЧЕСКИХ ИССЛЕДОВАНИЯХ С УДЕЛЕНИЕМ ОСОБОГО ВНИМАНИЯ ВОПРОСАМ ФИЗИОЛОГИИ КОСТЕЙ И ФИЗИОЛОГИИ ПИТОВИДНОЙ ЖЕЛЕЗЫ. В течение последних трех лет фтор-18 при­ меняется в нашей лаборатории для различных биологических и медицинских исследований. Разработаны методы получения фтора в результате реакций с 0 1в (p,n), 0 1в (Н3 ,п), и F 18 (п,2 п ) . Соединения, меченные радиоактивным фтором, были подучены методом изотопного обмена синтеза, мечения отдачей и удерживанием фтора во фтороорганических соединениях в результате реакции (п,2 п). Разработана специальная техника счета низкого уровня активности для работы с малыми активностями индикатор­ ных количеств органических фтористых соединений. Ионы фтора-18 были использованы при изучении физиологии костей. Было обнаружено, что физио­ логическое поведение F“ во многом аналогично поведению кальция; оказалось, что накопление Р~ в костях увеличивается под влиянием витамина D и теостерона, в то время как кортизон и эстрогены уменьшают степень накопления фтора. При введении фтора в виде катионного комплекса характер его распределения в организме изменялся. Было установлено, что меченные F10YF++ или ZF+3 подчиняются правилам распределения исходных катионов. Было показано, что ионы фтороборатов накапливаются в щитовидной железе в количестве, срав- нимом о накоплением ионов иода. Ионы фтороборатов не вступают в какие-либо органичеокие связи в щитовидной железе, и их поглощение является специфическим показателем функции "стадии захвата” для железы. Фторобораты, меченные Р1в применяются д.;я решения различных проблем физиологии щито­ видной железы. Показано, что TSH уменьшает поглощение BF; в первые несколько часов после введения и увеличивает через 24 часа. BFJ оказывал такое же тормозящее действие на процесс поглощения йода, как и железо, медь, цинк, кадмий, фтористые соединения, тиоцианат и другие ионы, что указы­ вает на нарушение' фазы захвата. При проведении аналогичной серии опытов было обнаружено, что соединения, содержащие сульфгидрильные группы, равно как и ионы азида, увеличивают захват второ- боратов, хотя и уменьшают общее поглощение йода. Далее, было показано, что в фазе захвата чувст­ вительность к облучению значительно меньше, чем в стадиях образования и выделения тироксина. Фторобораты, меченные F18, широко применялись для определения локализации мозговых опухолей о помощью направленного сканнирухвцего устройства на совпадениях, ввиду ограниченной проницаемости Для этих ионов неповрежденного гематоэнцефадического барьера. Быод получены и применялись в исследованиях физиологии костей фтороароматические комплексо- образупцие реагенты, меченные Р1в. Ароматические прижизненные красители, меченные Р1в,пряменялюь ори изучении вопросов проницаемости биологических мембран. Для физиологических исследований, включающих изучение рака, получены и применяются антиметаболиты, меченные Рхв, в том числе пяти- Фтористый урацил и фтористооротическая кислота.

APLICACIONES DEL FLUOR-18 EN ESTUDIOS BIOLOGICOS, CON ESPECIAL REFERENCIA A LA FISIOLO­ GIA DEL ESQUELETO Y DE LA TIROIDES. En los últimos tres años el fluór-18 se ha venido aplicando en los laboratorios del autor a una gran variedad de problemas biológicos y médicos. Se han desarrollado métodos APPLICATIONS OF F18 IN BIOLOGICAL STUDIES 229 para preparar flúor por las reacciones l ! 0 (p ,n ), 160 ( àH,n) y 18F(n,2n). Se prepararon compuestos marcados con radioflúor por intercambio isotópico, síntesis, marcación por retroceso y retención de flúor en compuestos ñuoroorgánicos que experimentan la reacción (n,2n). Se han perfeccionado técnicas especiales de recuento de baja intensidad para poder registrar las actividades de vestigios de compuestos orgánicos del flúor. Los iones fluoruro-18 se han utilizado én estudios de fisiología de los huesos. Se encontró que el F~ tiene un comportamiento fisiológico paralelo al del calcio en muchos aspectos; se comprobó que la acumulación de F" en los huesos aumenta bajo la influencia de la vitamina D y de la testosterona, mientras que la cortisona y los estrógenos disminuyen la acumulación de fluoruro. El esquema de distribución del flúor en el organismo se modificó al administrar este elemento en forma de complejo catiónico. Se encontró que el esquema de distribución del YF't1‘ o del ZF + marcados conl8F sigue a la de los cationes de características comparativas. Se demostró que los iones fluoroborato se acumulan en la tiroides en una cantidad comparable a'la de los iones yoduro. Los iones fluoroborato no se fijan a la materia orgánica de la tiroides, y su fijación cons­ tituye un índice específico de la "función de captación" de la glándula. El fluoroborato marcado con 1KF se ha utilizado en el estudio de diversos problemas de fisiología tiroidea. Se ha demostrado que la hormona esti­ muladora de la tiroides reduce la captación de BF¿ durante las primeras horas que siguen a la administración y la incrementa después de 24 hours. El BF^ estimula la acción inhibidora que ejercen sobre la captación de yodo los iones hierro, cobre, cinc, cadmio, fluoruro, tiocianiato y otros, demostrando que en ella interviene la función de captación. En una serie análoga de experimentos, se encontró que los compuestos sulfhidrílicos y las azidas incrementan la captación de fluoroborato, aunque disminuyen la captación total de yodo. Seguida­ mente, se demostró que la función de captación es menos radiosensible que las funciones de formación y liberación de tiroxina. Otra aplicación muy distinta de los iones fluoroborato marcados con18F fue la localiza­ ción de tumores cerebrales por exploración direccional de coincidencias en la que se aprovecha la baja perme­ abilidad para estos iones de la barrera sangre- cerebro intacta. Se prepararon agentes de quelación fluoroaromáticos marcados con 18F y se aplicaron a problemas de fisiología de tejido óseo. Para estudiar la permeabilidad a través de membranas biológicas, se emplearon colorantes aromáticos vitales marcados con18F. Se han preparado antimeiabolitos que contienen flúor, marcados co n 1BF, entre otros, él 5-flu'orouracílo y. el ácido fluoroorótico y se han aplicado al estudio de problemas fisiológicos e investigaciones sobre el cáncer.

A. THE PRODUCTION AND USE OF FLUORINE-18-LABELLED ORGANIC COMPOUNDS*

Introduction

Fluoro-organic compounds have gained interest in recent years in pharmacology and biological research [1J. To mention only a few examples, fluorosteroids, e.g. fluorohydrocortisone, dexamethasone, fluoximesterone and triamcinolone, show in many cases greater pharmaceutical potency than their hydrogen analogues [2]. Fluorine-substituted antimetabolites, starting with fluoroacetic acid and ending with fluoropyrimidine analogues — 5-fluoro- uracil and 5-fluororotic acid — are of interest in biochemistry, physiology [1], toxicology [3], as well as in cancer therapy [4]. Fluoro-organic compounds labelled with F18 as radio-tracer would faci­ litate extensive studies in these different disciplines. Unlike C14 or tritium, fluorine-18 emits positrons of moderate energy (0.65 MeV) which may be easily detected by their annihilation radiation in conventional gamma-» counting equipment. Fluorine-18 may also be useful in chemical or biological systems to trace the behaviour of a variety of organic compounds, as long as the process under study does not discriminate between the fluoro-derivatives and its

# By M. Anbar and P. Neta. 230 M . ANBAR hydrogen analogue 15]. Owing to the strength of the C-F bond (energy of dis­ sociation, 100 kcal/mole) there is little chance for its cleavage in biological systems, as well as in many chemical reactions (except for nucleophilic' substitution of aliphatic fluorine). Consequently, labelling with fluorine-18 as a tracer involves fewer pitfalls than those encountered with radioactive iodine or bromine.

The production of F i8 and its synthetic incorporation into organic compounds

The main drawback to F18 as a tracer is its relatively short half-life (112 min); although this does not prohibit its application in many biological or medical problems [6-10], it does limit the possible preparative methods of labelled tracer compounds. Any method of introducing radiofluorine into an organic tracer compound should not take more them 2-3 h including all stages of purification and purity analysis. It would also be impractical to employ Fi8 as a tracer if the time of transportation from the site of production to the laboratory wherè it is to be ueed exceeds 3-4 h. C arrier-free Fie may be produced in a nuclear reactor by irradiation of oxygen-containing lithium salts [11] by the Li6(n, He*)H3, Oi6(H3, n)Fie reactions. Alternatively, the Oi8(p, n)Fi8 reaction may be applied [12] if a proton accelerator of 3-10 MeV'is available. Fluorine-18 may also be pro­ duced by the Fi9(n, 2n)Fi8 reaction, the threshold energy being 10.4 MeV; the neutrons may be produced by a neutron generator or in a nuclear reactor utilizing fast fission neutrons. In most cases it is not possible to attain isotopic exchange between fluoride ions and an organically-bound fluorine; thus synthetic methods have to be applied. C arrier-free fluorine is available in the form of fluoride ions and these must be used in any synthetic method as the starting m aterial. Fluorine may be introduced into a predeterrriined position in a molecule by a variety of methods [13] : the substitution of another halogen by the aid of a metal fluoride, e.g. SbF3, by the addition of HF to a double bond 114], or by the decomposition of a phenyl diazonium fluoroborate. In the last case fluorine may be easily introduced into the fluorinating reagent by chemical exchange [15]. It should, however, be remembered that the majority of synthetic methods of producing fluoro-organic compounds require the use of fluorine in a great excess and the yields are always calculated on the basis of the organic mother compounds 113]. In all cases cited the yield of the fluorine which becomes organically bound is very small; in many cases it is less than 1%. Moreover, the time of synthesis, from the step when fluo­ ride is introduced to the moment of separation of the final purified product, may amount, even under optimal conditions, to one or two half-lives of F 18. Thus a maximum yield of 1% of the initial activity in the labelled product is a fair estimate. Nevertheless, it is possible to use synthetic methods for preparative purposes. C arrier-free fluorine-18 may be produced in a reactor on a routine basis at activities of 10-100 me per batch. The final product will then have an activity of 0.1-1 me in, say 100 mg of the final p r o d u c t. APPLICATIONS OF F18 Ш BIOLOGICAL STUDIES 231

The production of labelled compounds by fluorine atoms produced in situ

A different approach to the production of labelled fluoro-organic com­ pounds is the in situ incorporation of F18 produced in the organic compound. This may be achieved by irradiation of organic m aterial containing both lithium and oxygen, e. g. lithium salts of oxygen containing acids in a flux of therm al neutrons. It had been found that fluorine-18 atoms produced by this reaction substitute hydrogen on carbon [16]. The molar-labelling yield of this substitution process is proportional to the number of hydrogens avail­ able for substitution. Aliphatic hydrogens are substituted to a greater extent than aromatic : on the average, 0.7% of the total F18 activity produced is organically-bound per aliphatic hydrogen, as compared with 0.5%per aro­ matic hydrogen. Fluoride ions, the only inorganic form of fluorine in the system, are quantitatively removed by passing a solution of the irradi­ ated m aterial through chromatographic alumina columns. If, for instance, lithium propionate C^H^COOLi is irradiated in a flux of slow neutrons, 3.5% of the F18 activity will be found as alpha and beta fluoropropionic acids; on irradiation of lithium benzoate, CgH^COOLi, only 2.5% of the total activity is incorporated into the aromatic nucleus. With molecules containing a larger number of hydrogens, this labelling method may produce carrier-freefluoro- derivatives carrying a substantial proportion of the F 18 atoms distributed at random at the various sites available for substitution. Lauril alcohol, for example, can be labelled with an overall labelling yield of up to 20%. If the molecule to be labelled does not carry lithium or oxygen atoms, the labelling may be carried out by dissolving a hydrogen-free lithium salt, e.g. LiCNO or lithium oxalate, in the compound to be labelled [16]. The labelled flu oro-compound may be isolated from the reaction mixture at any required specific activity by adding the stable compound as carrier, together with the undesired isom ers as hold-back carriers, followed by appropriate methods of fractionation, e.g. distillation, column or gas chromatography. This method cannot be used when the difference between the physical properties of the isom ers produced is small. When the method is applicable, the pure labelled product may be separated within one hour of the end of reactor irradiation, i.e. about one half-life faster than by most synthetic methods.

The production of F18-labelled fluoro-compounds by the F 19(n, 2n) reaction

The synthetic production of labelled specific fluoro-derivatives of complex molecules, like steroids, would result in a final labelling yield of 0.3% [17] or less; on the other hand, it is impractical to attempt to separate a desired derivative.from a compound containing about 30 hydrogen atoms which have more or less equal chances of undergoing substitution by the lithium-oxygén labelling technique. The only method which may eventually offer a solution to this problem is the formation of F*8 in the fluoro-organic compound by the Fi9(n, 2n) reaction. Fluorine bound to carbon does not neces­ sarily sever the chemical bond when transm uted from F19 to F18, and is retained at a relatively high yield at the very position of its parent atom [18]. The percentage of retention in solid fluoro-compounds is about 10% of the 232 M. ANBAR total activity produced. However, this method has one major drawback-the flux of fast neutrons (E>10.4 MeV) in a nuclear reactor is rather low, and the total activity produced per mole of Fi9 is only one-thousandth of the total activity produced per mole of Li6 . A fast neutron generator (< 14.5 MeV) with a flux of 10Ю n / c m ? s would produce Fi8 at a yield comparable to that obtainable in a nuclear reactor with a flux of 5.1013 nvt. Comparing the synthetic and the (n, 2n) methods for the production of a fluorosteroid, one may obtain 20 цс (100 juc/g) by the synthetic method [ 17], as compared with 1 цс (specific activity — 2 pc/g) by irradiation for one hour in a reactor at a flux of 5-1013 nvt .It is obvious that the (n, 2n) labelling method is com­ petitive only when the synthetic method requires more than a few hours for its accomplishment, or when only low specific activities are required.

Low-level counting of fluorine-18

Extensive biological studies with fluorine-18-labelled pharmaceuticals require low-level counting techniques. Using two 2-in X 2-in sodium iodide scintillation crystals, 6 mm apart, in a coincidence arrangement with two single-channel analysers, the authors were able to obtain a counting efficiency of 5% with a background of 1.2 cpm. The sensitivity could be increased to 10% with an increase in background to 10 cpm.Under the form er conditions activities of the order of 0.1 mpc may be counted with 10% accuracy within 10 min; samples of ten-fold activity under the latter conditions may be counted with 3% accuracy within 5 min. In distribution studies on sm all animals using labelled fluoro-organic compounds, total activities of only 0.1 цс wese injected at specific activities up to 5 m c/g, i.e. doses of theorder of 20-50 ц g could be administered, and 0.1% of the injected dose could be radio-assayed with 10% accuracy. These levels compare favourably with studies applying C14 as a radio-tracer and using commercially-available labelled compounds (range of specific acti­ vities 10-100 цс/g) with conventional low-level equipment.

B. THE APPLICATION OF Fi8-LABELLED FLUORIDE AND CATIONIC FLUORO-COMPLEXES IN STUDIES OF BONE PHYSIOLOGY*

The distribution of fluoride ions at physiological levels in mammalian tissues has been the subject of several extensive investigations employing fluorine-18 as a tracer [19-22]. . It was of interest to investigate whether fluoride metabolism is dependent on hormones in analogy to that of calcium, i. e. whether Fi8 may be used as a tracer for physiological changes in hone which have previously been established by following the behaviour of calcium ions. This study was also extended to ¡determine the behaviour of cationic fluoro-complexes in bone tis s u e .

# By M. Anbar, N. Ernst and G. Rodan. APPLICATIONS OF F18 IN BIOLOGICAL STUDIES 233

The preparation of labelled fluoride ions

Fluorine-18 was prepared by irradiation of Li^ 0 3 utilizingthe Ыб(п,а)Щ 0 16(H3, n)F18 reactions. Three gram s of Li2C03 of normal isotopic compo­ sition were sealed in a silica tube and irradiated for 1 h at a flux of 5 X 1012n/cm2 s. After irradiation, the tube was crushed in a stainless-steel beaker and the carbonate was dissolved in a slight excess of 6 N HCl.One mM of concentrated H3P04 was added, followed by 20 mg CaC03. The solution was then neutralized. The calcium phosphate which co-precipitated the fluo­ ride was filtered off, washed and then dissolved in a 6 H HCl. This solution was then diluted with isotonic NaCl solution and neutralized. About 3 me of carrier-free fluoride-18, radiochemicallÿ pure to one part in 105, were obtained by this procedure. The dose injected per rate was 5 цс F 18- A negli­ gible amount, less than one ц Ш of calcium and phosphate ions, accompanies each d o se .

The turnover and distribution of fluoride tracer in hormone-treated rats

Rats were treated for short periods, 3-7 d, by injections of steroid hormones, as well as with ethylene diamine telracetate (EDTA) as a de­ calcifying agent. It was found that these treatm ents affect the physiological patterns of the fluoride tracer in analogy to their effect on calcium meta­ bolism [23-25]. Rats of local strain under normal and special dietary and pharmacolo­ gical conditions were examined. The uptake of F18 4 h following intraperi- toneal injection was determined in the following tissues: tibia diaphysis, tibia epiphysis, broken tibia diaphysis, skull, incisor tooth, blood and kidney. In order to get comparable results, values were calculated in term s of

% Injected dose % Injected dose ______g wet tissue mg Ca in same tissue after due correction for animal weight and excretion. The rate of excretion was determined by a total-body counting before sacrifice as compared with a phantom containing the injected dose under the same geometric conditions. Some of the results are summarized in Table I. After the administration of cortisone at a dose of 2.5 mg/d for 4 d, a decrease of 47% in fluorine uptake by the epiphysis and callus was observed. The rate of excretion was diminished and the amount of fluoride excreted in urine within 4 h was only 72% of that of the controls. These results are in accord with the known catabolic effects of cortisone as well as with its effect on electrolyte balance. Oestrogen injected for 6 d at a dose of 5000 i.u. /d was found todecrease the fluoride uptake. Epiphysis, diaphysis, callus and skull gave 67, 86, 72 and 81% respectively of the normal values. The known antiosteroporotic action of oestrogen may be due either to an enhanced bone formation (osteo­ genesis) or to a decrease in the rate of resorption (osteoclasis), both of which occur simultaneously in normal bone metabolism. The results with 234 M . ANBAR

TABLE I

THE EFFECT OF HORMONE TREATMENT ON THE TURNOVER AND DISTRIBUTION OF TRACER FLUORIDE IONS (4 h after i.p. -injection)

Testo­ Controls Oestrogen Cortisone sterone EDTA

Percent inj dose/g blood 0.026 0.058 0.036 0. 031 0. 022

" " epiphysis 7 .6 5 .2 4 .1 10. 0 8 .4

" " diaphysis 3 .6 ' 3.1 2.4 4 .6 3.4

" " skull 3.7 3 .0 2.8 4 .4 3.2

dose excreted in urine 26.0 23.0 36.0 30.0 34.0

" dose per gram Ca in epiphysis 0.080 0.053 0.041 0 . 102 0.107

" dose per gram Ca in diaphysis 0.026 0.022 0.017 0.032 0.026

dose per gram Ca in skull 0.030 0.017 0. 017 0. 029 0. 029

Sp. act. epiphysis/diaphysis 2.11 1. 68 1.71 2.17 2.47

Sp. act. per gram Ca epiphysis/diaphysis 3.08 2.41 2.41 3.19 4.11 fluoride-tracer ions suggest that the oestrogen action is due to a decrease in resorption rather than to an increase in the rate of formation [26]. Testosterone propionate was injected subcutaneously (12.5 mg pro­ longed action) 6 d before fluorine-uptake experiments. The uptake of fluoride in all bone tissues examined was increase; the most conspicuous increases were observed in epiphysis (+30%) and in callus (+69%)? The results are in agreement with the proved anabolic action of androgens.

In order to obtain more information on the mechanism of fluoride uptake it was examined in the presence of an acute dose of EDTA; 40, 28 and 4 h prior to sacrifice doses of 30 mg sodium EDTA in 1 ml were injected intra- peritoneally. A slight decrease in fluoride uptake was observed in diaphysis, skull and callus. On the other hand, an increase of 29% in the percent- injected-dose accumulated per gram calcium was obtained in the epiphysis. According to the prevailing concepts of bone calcification, the fluoride uptake takes place by an ion exchange process with hydroxide or perhaps carbonate ions, which occurs in the hydration shell of the bone crystal. The rate of this process is dependent on the surface area of the bone crystals. This explains the increased uptake during a décalcification process. In the case of oestrogen action the opposite phenomenon takes place : the surface area is diminished when the resorption is inhibited.

It may be concluded that fluoride ions at tracer concentrations are indi­ cators of metabolic activity of bone rather than of bone growth. Further details of this study, as well as the implications of these findings for dif­ ferential diagnosis of bone pathology will be discussed elsewhere [27]. APPLICATIONS OF F18 IN BIOLOGICAL STUDIES 235

The effect of Zr+4, Sc*-3 and Y+3 on the fluoride-tracer turnover in rats

It has been suggested that the distribution pattern of fluoride in the organism is determined by the formation of complexes with calcium and magnesium. It was considered of interest to investigate the behaviour of inorganic cationic fluoro-complexes of high stability, e.g. the complexes of zirconium, scandium and yttrium. Although cationic complexes of fluoride may undergo fast isotopic exchange with fluoride, the pattern of distribution and excretion of radiofluoride in vivo was found to be altered in the presence of these cations. The results of this study have been published elsewhere [7]. H e re w e shall present only the salient findings (Table II). It may be seen from Table II that the distribution of fluorine activity is affected by minute amounts (0.1 mg) of zirconium ions. An enhanced clear­ ance of fluorine activity from the circulation was observed, demonstrated both by decreased specific activity in tissues and increased relative acti­ vities in the liver and kidney. Although the absolute accumulation of radio-

TABLE II

THE DISTRIBUTION OF FLUORIDE-18 IN THE PRESENCE OF COMPLEXING IONS IN VARIOUS TISSUES OF RATS, TWO HOURS AFTER INJECTION (RELATIVE SPECIFIC ACTIVITY - TISSUE/SERUM)

Compound NaFM NaF«+ Zr(S04), NaFU+SCj(S04)j N aF»+ Y(NOj), injected

Dose per (at 0.1 0.1 + 1 .0 0.1 + 1 .0 0.1 +1 0 .0 (iM) Tissue

Serum 1.0 1.0 1.0 1.0

Liver 1.3 2.46 1.65 1.81

Spleen 0.5 1.80 0.86 0.94

Kidney 3.35 7.15 2.17 0.91

Lung 1.25 2.14 2.04 0.58

Muscle 0.5 0.82 0.35 0.15

Brain 0.23 0.61 0.17 0.07

Diaphysis 50.6 65.6 14.9 4.96

Epiphysis 106 146 36.2 10.9

Incisors 44 77.2 17.6 4.1

Skull 45.5 80.5 20.8 8.05

Cartilage 31.0 78 20.9 7.55 236 M. ANBAR fluorine in bone is sm aller than found in the absence of zirconium, its con­ centration related to serum is increased; this effect becomes more pronounced w ith tim e. These results can be explained by considering the chemical and physio­ logical behaviour of zirconium. Zirconium forms an extremely stable complex with fluoride ions. (The dissociation constant of ZrF +3 is about 10-iOat 25X^ [28], as compared to CaF+ with a dissociation constant of about 3 X 10_1 [29]. As: the zirconium was administered at a ten-fold excess compared to fluoride, a ll th e F 18 áctivity was in the ZrF+з form. The behaviour of fluorine activity in the presence'of zirconium suggests that practically all the fluorine is bound to zirconium and shares its metabolic fate. The great affinity of zir­ conium to the osteoid m atrix has been pointed out and utilized to displace other heavy metals[ 30]. It has been shown [ 31 ] that only 36% of adm inistered zirconium is deposited in bone, as compared with 53% for fluoride ions, and the biological half-life of the form er in the total body of man is only one half that of fluoride [32]. These findings are in accordance with the present experimental results on the effect of zirconium on fluoride distribution and c le a ra n c e . Scandium also forms a stable fluoro-complex, ScF+2, with a dissociation c o n sta n t 10-6 [ 3 5 ]. The solubility of its acid phosphates is higher than those of zirconium; thus it may compete effectively for fluorine under physio­ logical conditions. The rate of fluorine excretion is enhanced in the presence of scandium and the extent of accumulation in bone tissue is markedly reduced, both relatively and absolutely. These results are in accordance with the fact that only 2 0 % of the scandium in circulation is deposited in b o n e [34]. Little quantitative data have been obtained on the stability of fluoro- yttrium complexes, but the effect of yttrium ions on fluorine distribution in vivo suggests the existence of a rather stable complex. Stable amino acid complexes of yttrium [35] may also contribute to the capability of yttrium to bind fluorine under physiological conditions. The high affinity of yttrium to bone [36] and the decrease in the relative concentration of fluorine in bone with increasing doses of yttrium [37] add to the parallelism between the observed distribution of fluorine activity and the pattern of yttrium distri­ bution. It may be concluded that the pattern of distribution of fluorine activity may be altered in the presence of cations which form stable fluoro-complexes. Alterations in fluorine activity distribution in different regions of bone formation may provide significant information for differential diagnosis.

C. THE APPLICATION OF F 18-LABELLED FLUOROBORATE IONS TO PROBLEMS IN THYROID PHYSIOLOGY*

The effect of fluoroborate ions (BF 4) on the iodine uptake in the thyroid gland of rats was found to be sim ilar to that of perchlorate (CIO4 ) [38] . C10| ions were shown to accumulate in the thyroid to a higher extent than

By M. Anbar, S. Guttmann, M. Inbar and Z. Lewitus APPLICATIONS OF F18 IN BIOLOGICAL STUDIES 237 in other tissues [39] .The thyroid/serum concentration gradients of СЮ 4 attained at doses of 5-20 mg KCIO4 were comparable to the gradients found for Г at the same doses; however, these values were much lower than those for tracer doses of I*. It was of interest to determine whether the analogy between iodide and BF¿ and СЮ 4 ions may be further extended, by following the distribution of BF4 in various tissues, particularly in the thyroid gland. A s BF4 ions labelled with F1® are available at much higher specific activities than ОТ6 O i, it became possible to investigate their behaviour at microgram doses and to compare it with that of tracer doses of I- ions, cumulate specifically in the thyroid gland, showing a behaviour sim ilar to iodide ions. Perchlorate and iodide ions were found to interfere with fluoro- borate uptake. The effect of the thyroid stimulating hormone (TSH) in the various phases of thyroid function, including the trapping of iodide ions, has been established [40, 41]. In view of the fact that perchlorate and fluoroborate behave sim i­ larly to iodide in relation to the thyroid, it was also of interest to investigate the effect of TSH on their accumulation. From the results published elsewhere [10] it is evident that there was a significant increase in the accumulation of the fluoroborate 24 h following the TSH injections. The increase in the concentration ratios of perchlorate and fluoroborate under the stimulation of TSH implies that the regulatory mechanism of the thyroid-trapping function as mediated by TSH is not speci­ fic for iodide alone. The accumulation of fluoroborate ions in the thyroid gland and its similar behaviour to iodide in TSH-treated animals, encouraged the authors to apply fluoroborate ions to a variety of problems in thyroid physiology currently under investigation in this laboratory. The general notion in the interpretation of our experimental results was that wherever there is a parallelism between the behaviour of fluoro­ borate and iodide, it indicates an involvement of the trapping stage, whereas, if no such analogy is observed, it means that the change in iodine turnover is due to another phase in thyroid physiology. The cases discussed below may be considered as examples of potential applications of labelled fluoro­ borate ions in thyroid physiology.

Experimental

Labelled fluoroborate ions have been prepared by isotopic exchange with fluoride-18 ions, as has been described elsewhere [8 , 15]. The specific acti­ vity of KBF J8' applied in the present study ranged between 10-100 /jc/m g. KBFJ in neutral saline solution was injected intraperitoneally to albino mice (iocal strain, average weight 20 g), or to albino rats (local strain, 3 months old, average weight 160 g). The uptake of KBFJ8 in thyroids of mice was determined by measuring the total activity of the thyroid, which was excised together with a section of the trachea. As the radiochemical purity of the KBFf has been tested [8], and the F ‘ activity did not exceed 0.5%, little error was involved in counting the thyroid in the presence of the cartilage of the trachea. In any case, another section of the trachea was occasionally counted to determine the background due to the cartilage. This did not exceed 15% of 238 M. ANBAR the total activity of the thyroid. The uptake of thyroids of rats was determined as described elsewhere [9]. The specific activity of thyroids was calculated from the total activity, assuming the average weight of 4 mg for mice and 10 mg for the thyroids of rats. These specific'activities (cpm/g tissue) were related to the specific activity of the serum. The number of experimental animals was 10 mice and 5 rats per group; the same number of animals was used in the control experiments. All de­ terminations were carried out one hour after intraperitoneal injection of the labelled potassium fluo'roborate.

Results and discussion

1. It has been found that mice kept on oxine or riboflavine diets show an increased uptake of iodine in their thyroids. This enhanced'uptake is probably due to a stimulation of the pituitary gland, because a substantial drop in iodine uptake beiow the normal level was observed for a few days after termination of the diet. It was of interest to find out whether the enhanced accumulation of iodine is accompanied by a parallel increase in the BF¿ u p ta k e . Mice placed on oxine diet (dissolved in drinking water) have shown after 10 d (ingestion of 17 mg oxine) a 43 ± 12% increase in their iodine uptake as compared with controls. In the analogous fluoroborate experiment, the same mice were found to accumulate BF^to a greater extent by 39±10% as compared with their controls. In a sim ilar examination, mice on riboflavine diet (also dissolved in drinking water) have shown after 20 d (ingestion of 1 0 mg riboflavine) am increase in iodine uptake of 63 ± 13% as compared to an increased fluoro­ borate uptake of 41 ± 7%. The increased fluoroborate uptake corroborates the conclusion that oxine and riboflavine diets affect the thyroid through a stimulation of the pituitary gland.

2. In a study on the effect of various anions on the behaviour of the thyroid, it has been found that fluoride, azide and thiocyanate ions inhibit the uptake of iodine within one hour of injection. This effect may be due to an inter­ ference with the iodide trapping or with some subsequent stage of thyroxine synthesis. In order to decide between these two possibilities, a series of experiments was carried out with KBFJ8. Labelled fluoroborate ions (0.05 mg KBF4 per mouse) were injected into mice 2 h after an injection of 0.5mgNaF. T he BF4 uptake found was only 45 ± 3% of that of the control group, compared with a sim ilar effect on the iodine uptake (40 ± 7% of the controls). Ana­ logously, a dose of 0.14 mg NaCNS per mouse decreases fluoroborate uptake to 50 ± 12% of the normal level, compared to an inhibition of iodine uptake of 60 ± 11%. These results may be compared with a 20 ± 5% decrease ob­ served in fluoroborate uptake upon administration of 0.28 mg Nal, and a 35 ± 5% decrease after a dose of 0.24 mg KC104. It is evident that both fluo­ ride and thiocyanate ions affect the trapping stage.

3. Azide ions which were found to diminish iodine uptake by 2 2 ± 3%, one hour after injection of 0.08 mg NaN3, showed ah increase of 42 ± 7% influoro- APPLICATIONS OF F18 IN BIOLOGICAL STUDIES 239 borate uptake under the same conditions. This result may imply that azide ions inhibit organic binding in the gland and simultaneously stimulate the trapping stage. This kind of effect is not unique, as sulphydryl-containing compounds were found to exhibit a sim ilar effect[42]. The fluoroborate uptake was found to increase by 40 ± 6% one h ou r a fte r the injection of 2 mg cysteamine hydrochloride per mouse. This result may be compared with a sim ilar effect of propylthiouracil on iodide uptake, re­ ported by WOLLMAN and REED [42].

4. It has been observed by HALMI 141] that the iodine accumulation in the thyroid is diminished in the first few hours after the administration of exo­ genous thyrotropic hormone (TSH). This drop was attributed to a decrtease in iodide uptake. To check on this assumption, we have examined fluoroborate uptake in mice 2 h after the injection of 1 USP unit of thyroid-stim ulating hormone. A drop of 30 ± 7% in fluoroborate uptake was observed. The fluoro­ borate uptake was determined in another group of mice; 24 h after the admi­ nistration of the same dose of TSH, a slight increase ( 10 ± 4%) w as o b se rv e d . These findings corroborate the hypothesis of Halmi on the biphasic effect of TSH .

5. The rate of appearance of protein-bound iodine in the serum of rats was found to rise substantially 24 h after local irradiation of their thyroids. This was accompanied by a drop in the extent of iodine accumulation in the gland. It was of interest to determine whether this diminished uptake is solely due to an enhanced release of thyroxine and thyroglobulin from the gland, or whether the trapping stage too, has been radiologically impaired. An experiment was carried out on rats which received a local dose of1600rad 24 h prior to the uptake determinations. Whereas the iodine uptake was lower by 45 ± 8% in the irradiated animals one hour after injection, the fluoroborate uptake was equal within ± 3% in the irradiated and control groups. This result means that the high radiosensitivity of the thyroid is not shared by all its physiological functions and that the trapping stage is relatively non-sensitive to radiation. It may be concluded that labelled fluoroborate ions may be applied as an efficient tool in the investigation of a variety of problems in thyroid physiology.

D. THE APPLICATION OF FLUORINE-18-LABELLED COMPOUNDS FOR , THE LOCALIZATION OF BRAIN TUMOURS *

The central nervous system has been shown to be partially impermeable towards certain substances which are evenly distributed by the blood and lymph systems in other tissues. This selectivity has been attributed to a "blood-brain barrier" which selectively rejects certain large anions and molecules. The "blood-brain barrier" has been found to be impaired in various pathological states [43].

* By M. Anbar, H. M. Askenasy, N. Ernst, S. Guttmann and Y. Laor. 240 M. ANBAR

As roentgenological contrast examinations do not always provide un­ ambiguous information on brain tumours, attempts were made to utilize disturbances in the "blood-brain barrier" for their detection and locali­ zation [43]; gamma-emitting tracers were employed enabling localization of irregularities in the distribution of the tracer, which might be attributable to lesions. Several isotopes have been applied as tracers for the localization of space-occupying intra-cranial lesions. These include gamma emitters, e.g. iodine-131, (sodium iodide [47]), labelled serum albumin [45, 46] ■ RISA, labelled iodo fluoroescein [43, 47], mercury-203 (labelled neohydrin [47]) and the positron-em itters arsenic-74 (as sodium arsenate [49] ) and copper-64 (labelled copper versenate [ 50]). It is evident that the annihilation radiation of positron em itters offers a better spatial resolution of the affected regions than the gamma em itters. Since As74 is not a pure positron em itter (53% positrons simultaneously with 0.596-MeV gamma ray) a high degree of collimation and consequently high tracer doses are required to insure good directional resolution. A single brain examination involves a dose of about 2.5 me, resulting in a total-body radiation dose of over 5 rad. Cu^4 emits only 19% positrons with a radiation dose of over 3 rad to the liver, which is the critical organ for the turnover of copper versenate [50J. In order to cut down the radiation dose, it was necessary to find a positron-emitting tracer which would not penetrate the "blood-brain barrier" and would be superior as As74 o r Cu^4 in its n u c le a r p ro p e rtie s . F lu o rin e - 18 was considered for the purpose. As fluorine-18 is a pure positron emitter with a short half-life (110 min), a single examination using 300 ц с w ould expose the patient to a total-body radiation dose of only about 10 m r. Thus, the exposure risk involved in such an examination would be negligible. The requirem ents for fluorine-labelled compounds to be applied to the localization of a brain tumour would be : 1. It should be excluded by the "blood-brain barrier" from healthy parts of the central nervous system. 2. It should not accumulate in any critical organs. 3. Its biological half-life should be long compared with the physical half- life of fluorine-18. The simplest chemical form of fluorine would be fluoride ions, but these do not fulfil requirem ent 2 , as fluorine ions accumulate in bone tissues. Inorganic fluoro-complexes which do not undergo rapid isotopic exchange with fluoride ions and do not accumulate in any specific organ, fulfil all three requirements. Fluoroborate ions were chosen for brain tumour localization because they are relatively large anions and their chemical, as well as physiological behaviour has been previously investigated by us [9]. The accumulation of fluoroborate in the thyroid gland may be overcome by applying doses of low specific activity.

Comparative studies

In order to compare the efficiency of the various potential tracers for brain tumour localization these tracers were examined in a comparative APPLICATIONS OF F18 IN BIOLOGICAL STUDIES 241 study on rats. The parameters investigated were the blood/brain and muscle/brain specific-activity ratios. It was assumed that the permeability of brain lesions is of the same order as that of muscular tissue [43]. The accretion in bone tissues was checked together with the rate and route of excretion. Scanning the brain in vivo is not applicable in the presence of relatively high concentrations of tracer in the skull.

TABLE III

EXAMINATIONS OF SPACE-OCCUPYING INTRACRANIAL LESIONS BY THE AID OF FLUOROBORATE ION LABELLED WITH F 18

KBFj® examination

Clinical findings Positive Negative

X. Meningioma 5

2. Glioma S 1

3. Vascular malformation 2 2

4. Tumour of third ventricle 1 1

5. Métastasés of bronchus carcinoma 1

6. Acusticus tumour 1

7. Exophthalumus 1

8. Encephalitis 1

9. Tumour of the pituitary 1 3

10. Eosinophilic granuloma 1

11. No pathological findings 9

12. Uncertain cases 1

The high blood/bram relative specific activity ratios (Table III) attained with fluoroborate were of the same order as those obtained with sodium arsenate and copper ver senate. Fluoroborate, in contrast to the other tracers examined, shows fast clearance from the organism, proceeding mainly via the kidneys. Fluoro- fluorescein- F18, which has a higher molecular weight, shows very limited permeability into the muscles, and should detect changes in the brain vas­ cularization, rather than alterations in tissue permeability.

Clinical examinations

The detailed clinical findings are being published elsewhere [8 ]. As this paper is concerned with the different applications of F18, the same results will be presented here in brief for the benefit of those who are mainly interested in the application of short-lived isotopes. 242 M. ANBAR

TABLE IV

COMPARISON OF VARIOUS TRACERS FOR THEIR PENETRABILITY INTO BRAIN TISSUES OF RATS

Time after Sodium Copper Relative specific FM-labelled Fu-labeU ed injection arsenate versenate fluoro- activ ity potassium (min) As7® C u « fluorescein fluoroborate

Blood 30 22 37 29 55 Brain 120 14 12 11 44

Muscle 30 5.7 4 .2 1.5 3 .6 Brain 120 4 .0 8 .3 1 .2 6 .4

Cranial bone 30 0.25 0.14 0.08 0.35 Blood 120 0.27 0.8 0.63 0. 26

Blood at 30 min 2.2 2 .2 2.9 6 .2 Blood at 120 min

Inj. dose in intestines 0o) 120 36 32 18 2.6

Doses of 200-300 цс of KBFJ8 at a specific activity of 10 ¡лс/m g w e re orally administered. Two hours after administration skulls of the patients were scanned at eight different symmetrical points lying in two planes. The activity was measured using two scintillation detectors connected to a coin­ cidence analyser. Further information was gaine'd from the individual chan­ nels, counting the annihilation photons independently. The distribution of activity in the skulls of normal individuals was found to be symmetrical at the points tested. Deviations from symmetry in patients were attributed to local pathological changes. From the coincidence measure­ ments, together with the information from the individual channels, it was possible to relate a deviation from homogeneous distribution of activity to a particular anatomical section of the brain. It can be seen from the clinical examinations presented in Table IV that in cases of meningiomas or gliomas, as well as in the presence of other brain tumours, the fluoroborate tracer method gave satisfactory indications. In 16 out of 18 positive results the localization of the lesions was confirmed within 5 cm; in two cases — one meningioma and the other a lesion which caused exophthalmus —only the lateralization of the affected hemisphere was indicated by other clinical methods. A good correlation was found between negative findings by the fluoro­ borate method and the corresponding pathological findings. In all cases posi­ tive tracer results were clinically confirmed; only in one case the fluoro­ borate method gave a false negative result when it failed to detect a glioma. If the automatic scanning technique developed by SWEET and BROWNELL [50] were adapted for fluoroborate, the radiation dose to the patient would still be thirty times smaller than that delivered by arsenate. Moreover, the APPLICATIONS OF F18 IN BIOLOGICAL STUDIES 243 fluoroborate examinations, because of the short half-life of F18, may be repeated after a few hours if it is necessary to confirm the diagnosis.

REFERENC ES

[1]SAUNDERS, B.G ., Advances in fluorine Chemistry, Butterworths, London, 2(1961) 183. [2] NES, W. R., The steroid Hormones in medicinal Chemistry, A. Burger ed., Interscience, New York(1960). [3]PATTISON, F.L. М ., Toxic aliphatic fluorine Compounds, Elsevier, Amsterdam (1959), [4]CLARK, R.L., Cancer Chemotherapy, Ch.C. Thomas, Springfield (1961). [5] ANBAR, М ., GUTTMANN, S ., ERNST, N. and RAMA TI, Z . , A com parative Study on the Perm eability of various Ions into the central nervous System of Rats, Israel AEC Report IA (1961) 668. [6] DURBIN-WALLACE, P. W ., J. D ent. Res. 33 (1954) 785. [7] ANBAR, M. and ERNST, N ., Int. J. Appl. Rad. Isotopes 13 (1962) 47. [8] ASKENASY, H .M ., ANBAR, М .. LA OR, Y ., KOSARY, I .Z . and GUTTMANN, S ., A m er. J. Roent. Nucl. Med. (1962) (in press). [9] ANBAR, М ., GUTTMANN, S. and LEWITUS, Z .. Endocrinology 66 (1960) 888. [10] LEWITUS, Z ., GUTTMANN, S. and ANBAR. М .. Endocrinology 70 (1962) 295. [11] BERNSTEIN, R.B. and KATZ, J. J., Nucleonics 11 10(1953) p. 46. [12] CARLSON, C .H ., SINGER, L ., SERVICE. D .H . and ARMSTRONG, W .D ., Int. J. Appl. Rad. Isotopes 4 (1959) 210. [13] HUDLICKY, M ., Chemie der organischen Fluorverbindungen, Deutsch.Verlag der Wissenschaften, Berlin (1960). [14] LOVELACE* A .M ., RAUSCH, D .A . and POSTELNEK, W ., A liphatic fluorine C om pounds, Reinhold, New York (1958),. [15]ANBAR, M. and GUTTMANN, S.. J. Phys. Chem. 64 (1960) 1896. [16] ANBAR, M. and NETA, P., J. Amer. Chem. Soc. 84 (1962). [17] BERNSTEIN, S. et al., J. Amer. Chem. Soc. 81 (1959) 1689. [18] ANBAR, M. and NETA, P., J. Chem. Phys. (in press). [19] WALLACE, P. W ., Metabolism of F18 in normal and fluorosed Rats.UCRL (1953) 2196. [20] DURBIN-WALLACE, P. W. , J. D ental Res. 33 (1954) 785. [21] CARLSON. C .W ., ARMSTRONG, W.D. and SINGER, L ., Amer. J. Physiol. 199 (1960) 187. [22] CARLSON. C. H .. ARMSTRONG, W.D. and SINGER, L ., Proc. Soc. Exp. Biol, and Med. 104 (1960) 235. [23] GRAU, F . , Acta Physiol. Scand. 48 suppl. 167 (1960) 1. [24] ALRO, A .G ., GRONROUS, N .. Acta Endocrinol. £ [(1 9 6 1 ) 63. [25] HARRISON, H.C. , HARRISON, H.E. and PARK. E. A ., Proc. Soc. Biol. Med. 96 (1957) 768. [26] BUDY, A.M ., Ann. N. Y. Acad. Sci. 64 (1956) 428. [27] ANBAR. М .. RODAN, G. and STEIN, J.A. (to be published). [28] CONNICK, R.E. and McVEY, W .H.. J. Amer. Chem. Soc. 71 (1943) 3182. [29] CONNICK, R. E. and TSAO, M .S., J. Amer. Chem. Soc. 76 (1954) 5311. [30] DURBIN, P. W .. H ealth Phys. 2 (1960) 225. [31] HAMILTON, J.G. . Metabolic Properties of Pu and allied Materials.UCRL 98 (1948). [32] ICRP Committee II on "Permissible Dose for Internal Radiation", Table 12, Health Phys. 3 (1960) 154. [33] BJERRUM J. et al., "Stability Constants", Part II, The Chem. Soc. Spec. Publ. 7 (1958). [34] HAMILTON, J.G ., The metabolic Properties of various Materials, UCRL 1561 (1951). [35] ROSOFF, B ., Ann. N. Y. Acad. Sci. 88 (1960) 479. [36] RAYNER, B ., TU T T, M. and VAUGHM, J . , Brit. J. Exp. Pathol. 34 (1953) 138. [37] DAUDLEY, H.C. and GREENBERG, J., J. Lab. and Clin. Med. « (1956) 891. [38] ANBAR. М ., GUTTMANN. S. and LEWITUS, Z . . Nature 183 ( 1959) 1917. [39] ANBAR, М., GUTTMANN, S. and LEWITUS, Z ., J. Appl. Rad. Isotopes 7 (1959) 87. [40] HALMI, N. S ., Vitamins and Hormones 19 (1960) 133. [41] HALMI, N .S ., GRANNER. D .K ., DOUGHMAN, D. J . , PETERS, B .H . and MULLER,G., Endocrinology 67. (1960) 70. [42] WOLLMAN, S.H . and REED, F .E ., Amer. J. Physiol. 202 (1962) 182. [43] MOORE, G .E., Diagnosis and Localization of brain Tumours, Charles C. Thomas, Springfield (1953). 244 M. ANBAR

[44] ASKENASY, H. М., KOSARY, I. Z. , LEWITUS, Z. and BRAHAM, J. Acta Neurochirurgica 9 (1961) 538. [45] PLANIOL, Th. .«Diagnostic des lésions intracraniennes par la gamma-encephalographie à l'aide de la serumalbumine humaine marquée à l'iodeisi>i Medical Radioisotope Scanning, Proc. IAEA/WHO Seminar, IAEA, Vienna (1959) 189. [46] PLANIOL, T h., Diagnostic des lesions intracraniennes par-les radioisotopes, Masson et Cie, Paris (1959). [47] TOTUS, E .C . and OKI TA, G. T . , Cancer Res. 21 (1961) 201. [48] BLAU, M. and BENDER, M. A ., "Clinical Evaluation of Hg2o3 Neohydrin and Ц31 A'lbumin in brain Tumour Localization", 7th Ann. Mtg Soc. Nucl. Medicine (1960). [49] SWEET, W.A. and BROWNELL, G .L ., J. Amer. Med. Assoc. 157 (1955) 1183. [50] SWEET, W. W ., MEALEY, J . , BROWNELL, G .L. and ARONOW, S ., "Coincidence Scanning with Positron emitting Arsenic or Copper in the Diagnosis of focal intracranial Disease", Medical Radioisotope Scanning, Proc. IAEA/WHO Seminar, IAEA, Vienna (1959) 163.

DISCUSSION

W. PAUL: I understand that Brownell (Boston) has both a positron scan­ ning system and an adjacent reactor. Do you know whether he is attempting to use fluoroborate? M. ANBAR: No, I’m afraid not. Of course different considerations arise in different cases. For brain scanning the fluoroborate technique has certain advantages as compared with the A s^o r the Hg204 techniques, since the fluoroborate has better nuclear properties, being a pure positron emitter, and the patient receives a much lower radiation dose in an examination with fluoroborate. On the other hand, the short half-life of F18 constitutes a dis­ advantage, so that any hospital planning jto carry out brain tumour locali­ zation should take these various factors into account in deciding which iso­ tope to use. K.H. EPHRAIM: I have a question regarding the technique of brain scanning dealt with in this paper. In section D the author states that "It is evident that the annihilation radiation of positron em itters offers a better spatial resolution of the affected regions than the gamma em itter". Further in the same section it is stated that "In 16 out of 18 positive results the localization of the lesions was confirmed within 5 cm". This does not appear to be a particularly good spatial resolution, so I should like to ask whether you used any collimating system and, if so, what system did you use? M. ANBAR: The purpose of our study was primarily to determine whether BFJ8 can be used for brain tumour localization. We used improved laboratory equipment in this preliminary study but the scanning équipment was not collimated. The results obtained are thus quite gratifying. Obviously, much better spatial resolution could be achieved with appropriate positron scanning equipment. C.C. THOMAS: I should like to mention that, since April 1962, except during July and August, Dr. Blau and Dr. Bender of Roswell Park Memorial Cancer Institute, Buffalo, New York, have been receiving two shipments of fluorine a week from the W estern New York Nuclear Research Institute. M. ANBAR: I am interested to hear this. I presume they are comparing F 18 with Hg204, which they have been using for the last two years. H. KEPPEL: I am interested in the use of F-ions for studying the meta­ bolism of calcium in bones. I understand that F-ions have a solution effect on the bone structure m aterial. Do your results throw any light on this? APPLICATIONS OF F18 IN BIOLOGICAL STUDIES 245

M. ANBAR: Well, you have to distinguish here between the pharm a­ cological effects of fluoride ions at high concentrations and the behaviour of tracer concentrations of fluoride ions. We added only a very small amount of carrier in our separating procedure, so there is no question of the pharma­ cological action of fluorine as a decalcifying agent. The fluoride ions just got into the bone lattice and replaced hydroxide ions in the apatite structure. We also did some experiments, which I think are not mentioned in the paper, using large amounts of fluoride carrier; then the whole picture changed, and we just got the classical pharmacological fluoride effects. A. WARD: In the United Kingdom there are conflicting opinions with regard to the introduction of fluoride into the public water supply to reduce tooth decay. Nobody seems to know exactly how fluoride works in this respect, so I would like to ask whether your group has performed any research on this subject using F18. M. ANBAR: I am sure F18 is the most appropriate tool for such investi­ gations, which have in fact been carried out in the United States in the early 1950’s. Our own group is not doing any active research along these lines.

THE USE OF COPPER-64 IN THE INVESTIGATION OF REACTION MECHANISMS OF ENZYMES, PARTICULARLY AS RELATED TO FOOD PROCESSING

J.C. ARTHURJR. AND T . A. McLEMORE SOUTHERN REGIONAL RESEARCH LABORATORY, NEW ORLEANS, LOUISIANA, UNITED STATES OF AMERICA

Abstract — Résumé — Аннотация — Resumen

THE USE OF COPPER- 64 IN THE INVESTIGATION OF REACTION MECHANISMS OF ENZYMES. PARTI­ CULARLY AS RELATED TO FOOD PROCESSING. The oxidative enzym es of plant tissues are often dorm ant or only slightly active during the resting state, becoming active on the injury of the tissue or on separation from the tissue. During food processing this results in an acceleration of the oxidation of the natural substrates and polymerization of the products, which discolour the tissue. Copper oxidases are the principal enzymes involved in catalysing these reactions. The activation of the enzyme also leads to its reaction inactivation. One of the causes of die phenomenon of reaction inactivation is the decrease in the effective concentration of the enzyme, probably by the removal or binding of its metal prosthetic group copper. By using copper- 64, in vitro, it was shown that, in a resting solution, cupric ion can complex and/or exchange with the copper of the enzyme and that, in oxidizing solu­ tions, an additional amount of cupric ion can be complexed. Cu-o-quinone- type complexes have higher for­ mation constants than Cu-p-quinone- type complexes. The amount of cupric ion complexed was decreased, if the ion was added io an oxidizing solution after the initiation of polymerization of the o-quinone type re­ action products. The kinetics of the exchange and complexing processes for cupric ions with enzyme and reaction products are discussed mathematically.

EMPLOI DE CUIVRE-64 DANS L'ETUDE DES MECANISMES DE REACTION DES ENZYMES, NOTAMMENT EN CE QUI CONCERNE LA PREPARATION DES DENRÉES ALIMENTAIRES. Les enzym es oxydants des tissus végétaux sont souvent inactifs ou très peu actifs à l'état de repos et ne deviennent actifs qu'en cas de lésion du tissu ou lorsqu'ils sont séparés de celui-ci. Lors de la préparation des denrées alimentaires, ce phénomène a pour effet d'accélérer l’oxydation des substrats naturels et de polymériser les produits, ce qui donne lieu à une décoloration du tissu. Les oxydases de cuivre sont les principaux enzymes qui interviennent comme cataly­ seurs dans ces réactions. L’activation de l'enzyme entraîne en outre une inhibition de la réaction qu'il subit. Une des causes de ce phénomène est la diminution de la concentration effective de l’enzyme, qui résulte vraisemblablement de l'élimination ou de la liaison du cuivre de son groupe prothétique. Il a été démontré, en utilisant du cuivre-64 in vitro, que dans une solution en repos l'ion cuivre peut former un complexe ou faire l'objet d’un échange avec le cuivre de l'enzyme et que, dans les solutions oxydantes, une quantité supplémentaire d’ions cuivre peut rentrer dans le complexe. Les complexes du type Cu-o-quinone ont des constantes de formation plus élevées que les complexes du type Cu-p-quinone. On a observé que la quantité d’ions cuivre rentrant dans le complexe diminuait lorsque les ions étaient ajoutés à une solution oxydante après le commencement de la polymérisation des produits de réaction du type o-quinone. Les auteurs examinent, du point de vue mathématique, la cinétique des phénomènes des échanges et de la formation de complexes entre les ions de cuivre et les produits des enzymes ou les produits de réaction.

ПРИМЕНЕНИЕ МЕДИ-64 ДЛЯ ИССЛЕДОВАНИЯ МЕХАНИЗМОВ ФЕРМЕНТАТИВНЫХ РЕАКЦИЙ, СВЯЗАННЫХ С ОБРАБОТ­ КОЙ ПИЛИ. Окислительные ферменты растительных тканей часто не активны или лишь слабо активны в стадии покоя, становясь активными при повреждении тканей или при отделении от нее. при обработ­ ке пищи это приводит к ускорению окисления естественных субстратов и полимеризации продуктов, что меняет цвет ткани. Катализаторами этих реакций в основном являются медные оксидаэн. Активация фермента ведет к его реакции инактивации. Одной иэ причин феномена реакции ин­ активации является снижение эффективной концентрации ферментов, возможно, за счет удаления или

247 248 J .C . ARTHUR Jr. and T . A. McLEMORE

связывания его металлосодержащей простетической группы медью. С помощью меди-64 in v it r o , было показано, что в покоящемся растворе ион двухвалентной меди может образовывать комплексы или об- ыениваться с медь» фермента, и что в окисляющихся раст.ворах добавочные количества иона двух­ валентной меди могут образовывать комплексы. Комплексы медно-орто-хинонового типа имеют более высокую константу образования, чем комплексы медно-паро-хинонового типа. Количество комплексе- образующего иона двухвалентной меди уменьшалось, если ион добавлялся к окисляющемуся раствору после начала полимеризации продуктов реакции орто-хинонового типа. Обсуждается с математической точки зрения кинетики процессов обмена и комплексообразования для ионов двухвалентной меди с ферментом и продукты реакции.

EMPLEO DE COBRE- 64 EN EL ESTUDIO DE LOS MECANISMOS DE REACCIONES ENZIMA TICAS DE INTERÉS PARA LA ELABORACION DE ALIMENTOS. Las enzimas oxidantes de los tejidos vegetales se encuentran a menudo latentes o sólo presentan una leve actividad durante el estado de reboso, activándose al sufrir el tejido una lesión o al separarlas de él. En la elaboración de alimentos, este efecto acelera la oxidación de los substratos naturales y provoca polimerizaciones que alteran el color de los tejidos. Las principales enzimas que catalizan estas reacciones son las cuproxidasas. La inactivación de la reacción se debe, entre otras causas, a una disminución de la concentración efectiva de la enzima, probablemente por eliminación o por fijación del cobre de su grupo prostético. Con ayuda de cobre 64 in vitro se demostró que en una solución en reposo, el ion cúprico puede complejarse o intercambiarse con el cobre de la enzima, o ambas cosas, y que las soluciones oxidantes pueden formar un complejo con una cantidad adicional de ion cúprico. Las constantes de formación de los complejos del tipo Cu-o-quinona son más elevadas que las de los complejos del tipo Cu-p-quinona. Al afladir el ion a una solución oxidante después de iniciada la polimerización de los productos de reacción del tipo o-quinona disminuyó la cantidad de ion cúprico complejado. La memoria examina matemáticamente la cinética del intercambio y de los procesos en virtud de los cuales se forman los complejos del ion cúprico con la enzima, así como con los productos de reacción.

The control of enzymatic browning and discolouration of fruits and vege­ tables during food processing is an important factor in retaining the natural colour and flavour of the products. The browning generally results irom oxid­ ation of naturally- occurring substrates catalysed by naturálly-occurring copper oxidases and from subsequent polymerization of the products of oxid­ ation. The browning reactions are associated with a terminal oxidation, and in freshly harvested fruits and vegetables the reactions do not usually occur. In the respiration cycle of most fruits and vegetables ascorbic acid may reduce the o-quinone-type products formed, delaying the browning reaction. When the plant cellular tissue is injured through aging or processing, the substrate, copper oxidase, and oxygen are brought together, following which the browning reaction occurs [2]. The copper oxidases discussed in this report are limited to polyphenol oxidase isolated from the sweet potato (Ipomoea batatas), tyrosinase isolated from the common mushroom (Psalliota compestris), and ascorbic acid oxidase isolated from the summer crookneck squash (Cucurbita pepo condensa). It has been demonstrated that these oxidases are complex copper compounds with a copper content of about 0.2%. Assuming two atoms of copper per reacting unit of the enzyme, an empirical molecular weight of about 64 000 can be calculated. Generally, the activity of purified enzyme is proportional to copper content; dialysis against aqueous solutions of hydrogen cyanide removes the copper and enzymatic activity disappears; subsequent addition of cupric ion restores the activity, and this copper is not removed by dialysis against water; and dialysis against water saturated with carbon monoxide does not decrease the copper content but does inhibit the enzymatic activity [13]. USE OF Cu64 IN INVESTIGATION OF REACTION MECHANISMS 249

A significant experiment, indicating the essential role of copper in the mechanism of copper oxidase catalysis, was as follows: The gas space of a manometric vessel was filled with carbon monoxide, and the main compart­ ment contained a solution of copper oxidase. One of the two side tubes of the vessel held catechol, the other cyanide. On the addition of catechol to the oxidase solution, carbon monoxide was taken up, one molecule for every two atoms of copper. On the addition of cyanide to this solution, the uptake of carbon monoxide ceased and previously-bound carbon monoxide was released. It was concluded that the oxidase reacts by valency change cuprous cupric, with carbon monoxide inhibiting action by combining with monovalent copper and with cyanide inhibiting action by splitting off copper from the protein of the oxidase [8, 13] . The proposed equation for the oxid­ atio n w as:

protein (Cu++)2 + catechol = protein (Cu+)2 + <э- quinone + 2H-1"

The phenomenon of reaction inactivation may be due to complexing of the copper of the oxidase with the oxidation products or to splitting off the copper from the protein of the oxidase by complexing it with the oxidation products. The use of the short-lived radioisotope copper-64 offers another method for evaluating the role of copper in the browning reactions of fruits and vegetables. By using copper-64 in the presence of large quantities of enzyme, the exchange of copper ion with the copper of the enzyme under different resting and oxidizing conditions can be determined. By using copper-64 in the presence of catalytic quantities of enzyme, the complexing of copper ion by the oxidation products from different substrates can be evaluated and yield some additional understanding of the mechanisms of oxidation of different substrates. In this report we will review the results of these types of experiments.

THE ROLE OF CQPPER

Does the enzymatic action of copper oxidase depend on a dissociable bond between the reacting unit of the enzyme and copper during the oxidizing condition? Is this1 bond non-dissociable during the resting condition? Does partial inactivation of the copper oxidase by dénaturation or by reaction inactivation change the nature of the copper bond to the reacting unit of the enzyme? Does copper form complexes with the oxidation products? Radio­ active copper-64 has been used to study these reactions and to indicate the nature of the bonds formed. Assuming a dissociable bond between copper and the reacting unit of the enzyme, it follows:

Cu2 -protein + 2 Cu64++ - kl ^CuS4-protein + 2 Cu++ k 2 w here e = total concentration of enzyme 250 J .C . ARTHUR Jr. and T . A. McLEMORE

с = total concentration of cupric ions

= concentration of tagged enzyme

у = c o n c e n tra tio n of C u 64++

dv = kj(e - x) (y) - k2(c - y) (x)

Since the forward and reverse reactions are the same, kj = k2 = к

Ну th e n — = k(ey- cx) (1 ) where xt and yt are concentration of tagged enzyme and concentration of Cu64++ at infinite time t: x + y = xt +yt (correcting for decay) then y = xt + yt -x (2)

In this case at infinite time t the distribution of Cu64++ will be as follow s :

xt/yt = e/c • (3>

Combining equations (2) and (3) and substituting in equation (1), it fol­ low s:

d x /d t = к (e + c) (xt - x) .

Integrating

X t x ~ к (e + c) j'dt - In (1 - x/x() = к (e + c) t . (4) о 1 b Therefore, if the total concentrations of the reacting unit of the enzyme and of cupric ions remain constant, the rate of appearance of radioactive copper in the enzyme, which initially contained only stable copper, will be first order with respect to radioactivity. Assuming a nonr dissociable bond between copper and the reacting unit of the enzyme, it follows that kj = 0. However, it would be possible for the protein to bind some additional copper at chemically-active sites. Reaction inactivation of the enzyme is probably due to complexing of the copper by the oxidation products of the substrates as follows:

Cu2rprotein + products ------=> Cu2-products + protein,

o r C u2 - p r o te in + p r o d u c ts ------^ Cu2 (p ro d u c ts )-p ro te in . USE OF Cu64 IN INVESTIGATION OF REACTION MECHANISMS 251

In either case the copper would probably form a bond between copper and the products having a low dissociation constant. Therefore, the rate of appearance of radioactive copper in the enzyme (when a dissociable bond occurs) will be first order only until reaction inactivation has been initiated.

SEPARATION OF COPPER IONS AND OXIDASE

The use of copper-64 in determining the role of copper in oxidases re­ quires a rapid and quantitative separation of ionic copper from the oxidase, substrate and products. The dose of ionizing radiation from the copper-64 müst be kept at a minimum to prevent radiation inactivation of the oxidase, indicating the use of a low specific activity copper sulphate. The relatively short half-life of copper-64 also requires that experiments be designed for completion in a short time. In a typical experiment, Cu64S04 solution was added to a resting or oxidizing solution of oxidase and substrate. After a predetermined time, the copper ion was removed from the solution. The total amount of copper associated with the oxidase or oxidized substrate was determined analytically; the amount of copper-64 associated with the oxidase or oxidized substrate was radio-assayed. A relatively constant ratio of total copper to protein of the oxidase was noted. The method used for the separation of the copper ions from the oxidase was based prim arily on the hypothesis that the quantity of a cation bound to a definite amount of cation exchanger at equilibrium was proportional to the concentration of free ions in the solution. The use of cation exchangers for the quantitative determination of formation constants of metal complexes and chelates and for the preparation of biochemicals has .been reported [10, 11, 12] . The cation exchanger could be used as a resin in a column through which the solution was passed or as a m aterial which could be added to and then quantitatively removed from the solution.

N ON- DISSOC IAB LE COPPER BONDS

The non-dissociable bond of copper in resting ascorbic acid oxidase and in reaction-inactivated ascorbic acid oxidase was demonstrated by lack of exchange between ionic copper-64 and copper of the oxidase. Key ex­ periments of JOSELOW and DAWSON [6, 7] are summarized in Table I. A five-fold increase in purification of the oxidase, as shown by relative activity did not alter the exchange. Also, the protein of the oxidase apparently did not react with the ionic copperr 64 to form complexes under the experimental conditions used. The nature of the bonds of copper in resting ascorbic acid oxidase in the presence of substrate are shown in Table II [6, 7] . Under an atmosphere of nitrogen a small amount, 2-6%, of the copper of the oxidase exchanged with ionic copperr64. Comparing this exchange with the exchange occurring under an atmosphere of oxygen, the presence of non-dissociable bonds of copper is indicated. The exchange observed may be due to some dénaturation of the oxidase under the atmosphere of nitrogen as shown by its decrease in relative activity during the experiment. 252 J .C . ARTHUR Jr. and T .A . McLEMORE

ta b l e I

NON-DISSOCIABLE COPPER BOND OF RESTING ASCORBIC ACID OXIDASE»), b)

Relative Oxidase Cu content Cu64 Tim e of Cu activity added contact exchanged

(mg) (Mg) 0 ® (h) (%)

1.0 2.7 5.2 5.2 16 0

2.1 1.6 3 .6 3 .6 1 0

5 .3 2.6 6 .4 6 .4 1 0

a) Adapted from JOSELOW, M. and DAWSON, C .R ., I. Biol. Chem . 191 (1951) 1-10, 11-20.

^ Cu64 added in 0.1 M acetate buffer, pH 5.6. Ionic copper removed on passage of the solution through column containing ion exchange resin in the Na+ form.

TABLE II

DISSOCIABLE COPPER BOND OF OXIDIZING ASCORBIC ACID OXIDASEabb>

Relative activ ity Oxidase Cu content C u 64 Ascorbic acid Atmosphere Cu Before After added added exchanged (mg) (Mg) (Mg) (mg) (%)

1 .0 0.03 2.7 5 .2 5.2 50 0 2 34

1 .0 0.7 2.7 5 .2 5.2 50 n 2 6

2 .1 0 .0 4 1 .6 3.6 3 .6 100 Oj 30

2 .1 1 .4 1.6 3 .6 3.6 100 Nj 2

5 .3 0 .3 2.6 6.4 6.4 100 0 2 27

5 .3 3 .5 2 .6 6 .4 6 .4 100 N2 3

a) Adapted from JOSELOW, M. and DAWSON, C .R ., J. Biol. Chem . 191 (1951) 1-10, 11-20.

Ascorbic acid in 0.1 M acetate buffer, pH 5.6 was used. The components of the reaction mixture did not significantly interact with the Cu64. Ionic copper removed on passage of the solution through column containing ion exchange resin in the Na+ form. USE OF Cu64 IN INVESTIGATION OF REACTION MECHANISMS 253

The presence of non-dissociable bonds of copper and oxidase in resting polyphenol oxidase in the absence of substrate is not clearly demonstrated, as shown in Table III [3] . There is an exchange in resting oxidase propor­ tional to the ratio of ionic copper added to copper of the oxidase.

t a b l e ш

DISSOCIABLE AND NON-DISSOCIABLE COPPER BONDS OF POLYPHENOL OXIDASE a) ■b)

Cu44 Added Initial Ot Cu** complexed and/or (Mg) uptake exchanged |il/m in (Mg)

38 C) 19

38 d) 29 31

38 6) 4 19

38 ^ 15 20

76 C) • • 31

76 d) 29 60

a) ARTHUR, J .C ., Jr. and McLEMORE, T. A ., J. Agr. Food Chem . 7 (1959) 714-6.

b) Copper in enzyme, 36 Mg.

c) No substrate.

^ Catechol present in substrate concentration (20 mg/3 ml).

Hydroquinone present in substrate concentration (3 mg/3 ml).

^ Hydroquinone, plus trace of catechol, present in substrate concentration.

Similarly, in the case of resting tyrosinase in the absence of substrate, as shown in Table IV, the copper of the oxidase exchanged slowly with,the ionic copper [4, 5] . Apparently, tyrosinase having a high cresolase activity exchanged its copper more rapidly with ionic copper than tyrosinase having a high catecholase activity.

DISSOCIABLE COPPER BONDS

The dissociable bond of copper in oxidizing polyphenol oxidase was demonstrated by the first order incorporation of copper-64 in the oxidase, 254 J.C . ARTHUR Jr. and T .A . McLEMORE

TABLE IV

COPPER BOND OF TYROSINASE*)-ь>

Substrate Tyrosinase Cu content Reaction Cu tim e exchanged (mg) (m g) (Mg) (min) 6 ° )

4-tert. -butyl catechol (1.0) 2 . 2 C) 3.7 50 28

4-tert. -butyl catechol (1.0) 3.1 d> 3.7 50 6

4,5-dimethyl catechol (1.0) 2.3 C) 4 .5 50 30

4-tert. -butyl phenol (1.0)+ 1 2 .2 C) 3.7 240-260 1 4-tert. -butyl catechol (0.01)J

4-tert.-butyl phenol (1.0) + "1 2 .4 d) 2 .2 240-260 0 4-tert. -butyl catechol (0.01)J

3,4-dimethyl phenol (1.0) 2 .4 C) 3.6 250 15

3,4-dimethyl phenol (1.0) 3.1 d> 3.7 250 5

L-tyrosyl-L-alanine (2.0) 2.2 C) 3.7 100 33

none 2 . 2 C) 3.7 40 4

none 2.2 C) 3.7 840 10

none 2.4 d) 2.2 40 10

none 2 .4 d) 2 .2 270 14

a) Adapted from DRESSLER, H. and DAWSON, C. R ., Biochim. Biophys. Acta 45 (1960) 508-14, 515-24.

Substrate in 0.1 M acetate buffer, pH 5.7, Cu®4 added was the same as the copper content of the enzyme. Ionic copper removed on passage of the solution through column containing ion exchange resin in the Nat form. c) High catecholase activity. d) High cresolase activity.

as calculated by equation (4) and shown in Fig. 1 [3]. As reaction-inactivation was initiated, the rate of incorporation in the oxidase deviated from first order. The presence of dissociable bonds of copper in both resting and oxidizing polyphenol oxidase is also shown in Table III [3] . The amount of USE OF CU64 IN INVESTIGATION OF REACTION MECHANISMS 255

TIME (min)

Fig. 1

Relationship between copper complexed and/or exchanged by oxidizing polyphenol oxidase* A. Copper complexed and/or exchanged. B. Oxidation of catechol substrate at pH 6.7, 25eC.

copper ion complexed and/or exchanged was greater with oxidizing polyphenol oxidase on a substrate of catechol than with resting oxidase or oxidizing oxidase on a substrate of hydroquinone. The amount of copper ion complexed and/or exchanged by the oxidase was proportional to the ratio of ionic copper added to the copper of the oxidase, indicating the presence of a dissociable bond of copper in both resting and oxidizing oxidases. Similarly, the rate of incorporation of copper-64 in resting tyrosinase was initially first order, with a greater rate for a high cresolase preparation than for a high catecholase preparation, as calculated from data published by DRESSLER and,DAWSON [4] . This indicated the presence of a dissociable bond of copper in resting tyrosinase. The presence of a dissociable bond of copper in oxidizing tyrosinase on several satisfactory substrates is shown in Table IV [5] . Preparations having high catecholase activity incorporated a greater amount of copper г 64 ■ in the oxidase than preparations having high cresolase activity. The amount of copperr64 incorporated in the oxidase was also dependent on the type of substrate used. As the concentration of 4rtert. rbutyl catechol was inr creased from about 0.01 to 4 mg, the amount of copperr64 incorporated in the oxidase increased to a maximum. Similarly, using a substrate of 4, 5r dimethyl catechol, a greater amount of copper-64 was incorporated in the oxidase at a substrate concentration of 2 mg as compared with that at 1.0 mg [5] .

* ARTHUR, J .C ., Jr. and McLEMORE, T .A ., J. Agr. Food Chem . 7 (1959) 714-6. 256 J .C . ARTHUR Jr. and T . A. McLEMORE

The presence of a dissociable bond of copper in oxidizing ascorbic acid oxidase is shown in Table II [6, 7] . As the relative activity of the oxidase was increased, the amount of copper exchanged decreased slightly, perhaps not significantly. There was a high degree of reaction inactivation of the oxidizing enzyme, as compared with the resting enzyme.

COMPLEXING OF COPPER IONS

The enzymatic browning reaction is associated with reaction inactivation of the oxidase. This phenomenon probably results from the complexing of the copper of the oxidase. By using catalytic quantities of oxidase, the for­ mation of copper complexes with the oxidation products of substrates can be determined. The complexing of ionic copper with oxidation products of several satisfactory substrates for tyrosinase is shown in Table V [1] . In the case of catechol substrate the largest amount of copper was complexed. For the o-dihydric phenols of chlorogenic, caffeic and protocatechuic acids, the addition of other groups to the aromatic ring affected the apparent activi­ ty of the oxidase and the amount of copper complexed. In the case of hydro- quinone, a p-dihydric phenol, the amount of copper complexed was very

t a b l e v

COMPLEXING OF Cu++ BY TYROSINASE OXIDIZED SUBSTRATES^' b>

Cu ++ complexed (Mg) Initial О; (m g /3 m l) uptake pH 6.7 (p i/ min) pH 5.6 .. pH 6.7 pH 7.8

Hydroquinone (3) + trace catechol (0.4) 12 0.04 0.19 0.50

C atechol (20) 10 0.77 1.01 0.90

Chlorogenic acid (3) 8 0.22 0.08 0.38

Caffeic acid (3) 6 0.40 0.23 0.23 Protocatechuic acid (3) 0.2 0.00 --- 0.00 Hydroquinone (3) 0 0.06 0.00 0.00

a) ARTHUR, J .C ., Jr. and McLEMORE, T .A ., J. Am. Chem . Soc. 78 (1956) 4153-5.

Tyrosinase, 20 Mg; CuM++ added at zero time, 3.8 fig ; cation exchanger, phosphorylated cellulose, added at 60 min ; phosphate buffer 0.05 M; 25’C. USE OF Cu64 IN INVESTIGATION OF REACTION MECHANISMS 257 low. Hydroqulnone containing a trace of catechol was a very active substrate; the amount of copper complexed was less than in the case of catechol but was significant. Using catalytic quantities of tyrosinase the effect of dénaturation of the diluted oxidase by aging and the time of addition of ionic copper on the amount of copper complexed are shown in Table VI [1] . The decrease in oxygen uptake in the first minute is a m easure of the dénaturation of the oxidase. The amount of copper complexed decreased with dénaturation of

TABLE VI

PARTIAL DENATURATION OF TYROSINASE AND POLYMERIZATION OF OXIDATION PRODUCTS AND COMPLEXING OF Cu++ a) ,b)

Initial Ог Cu++ complexed Age of uptake (Mg) diluted enzyme ОД/m in )

pH 5.6 pH 6.7 pH 5.6 pH 6.7

CuM++ added at 0 .0 h

Fresh 23 34 1.88 2.45

24 h 10 10 0.77 1. 01

CuM ++ added at 0 .5 h

Fresh 17 18 1. 03 0.23

a) ARTHUR, J .C ., Jr. and McLEMORE, T .A ., J. Am. Chem . Soc. 78 (1956) 4153-5.

Tyrosinase,20 (Jg ¡ catechol, 20 mg/3 ml ; phosphate buffer 0.05 M ; 25° С ; Cu61 ++ added, 3.8 (Jg ; cation exchanger, phosphorylated cellulose, added at 60 min. the oxidase. When ionic copper was added after 0.5 h of oxidation, the amount of copper complexed was less than when the copper was added at zero time. However, with the addition of ionic copper at zero time (about a one hundred-fold excess of ionic copper over the copper of the oxidase) the apparent activity of the oxidase was greater than when the ionic copper was added at 0.5 h. This difference in activity could account for the dif­ ference in copper complexed.

MECHANISM OF OXIDATION

Resting ascorbic acid oxidase has a non- dissociable bond of copper and protein, and the oxidizing oxidase, a dissociable bond. Resting tyrosinase and polyphenol oxidase have both non-dissociable and dissociable bonds of 258 J .C . ARTHUR Jr. and T .A . McLEMORE copper and protein. These oxidases, in an oxidizing condition, showed a large increase in dissociable bonds. Resting tyrosinase having highcresor lase activity exhibited a greater number of dissociable bonds than resting tyrosinase having high catecholase activity. The most stable copper complex formed with tyrosinase was o - quinone. ¿-Quinones of chlorogenic and caffeic acids also formed copper complexes; however, the formation constants were apparently less than for o-quinone. Protocatechuic acid and hydroquinone were poor substrates for tyrosinase. Although hydroquinone containing a trace of catechol was a good sub­ strate for tyrosinase, the copper complex formed was less stable than the copper-o_-quinone, complex and was also more dependent on pH. The mechanism of the oxidation of hydroquinone, using catechol as a mediator, has been proposed as (1) the catalysed oxidation of catechol; (2) the chemical reaction of o-quinone and hydroquinone to yield catechol and hydroxy- hydroquinone; and then (3) catalysed oxidation of the form er to o-quinone and of the latter to hydroxy-o-quinone [9] . If this mechanism of oxidation of hydroquinone is accepted, it would appear that the presence of the hydroxyl group of hydroxy-<>- quinone was a determining factor in the for­ mation constants of its copper complexes. Another possibility is that hydro­ quinone was oxidized to p-quinone. Then the differences in copper, not ex­ tracted from the solution by the cation-exchange m aterials, would indicate a higher formation constant for copper-o-quinone than for copper-p-quinone. The relatively constant ratio of copper to reacting unit of the oxidase in resting, oxidizing and inactivated conditions would indicate that reaction inactivation resulted from the formation of a complex of oxidized substrate+ copper + protein of the oxidase. This would decrease the number of dis­ sociable bonds of copper and the activity of the oxidase. This mechanism of enzymatic inhibition would be sim ilar to that occurring on contacting copper oxidase with carbon monoxide.

CONCLUSIONS

1. The enzymatic action of copper oxidase depended on a dissociable bond between the reacting unit of the enzyme and copper during the oxidizing condition. 2. The bonds between copper and the reacting units of tyrosinase and polyphenol oxidase during the resting condition were dissociable, but to a lesser degree than in the oxidizing condition. The bond between copper and the reacting unit of ascorbic acid oxidase during the resting condition was non-dissociable. 3. Reaction inactivation of the copper oxidase resulted from the com- plexing of oxidized substrate + copper + protein, decreasing the number of dissociable bonds of copper and protein.

R EFERENCES

[1] ARTHUR, J.C ., Jr. and McLEMORE, T.A ., J. Am. Chem. Soc. 78 (1956) 4153-5. [2] ARTHUR. J.C ., Jr. and McLEMORE, T.A ., J. Agr. Food Chem. 4 (1956) 553-5. [3] ARTHUR, J.C ., Jr. and McLEMORE, T. A .. J. Agr. Food Chem. 7 (1959) 714-6. [4] DRESSLER, H. and DAWSON, C.R., Biochlm. Biophys. Acta 45 (1960) 508-14. USE OF Cu64 IN INVESTIGATION OF REACTION MECHANISMS 259

[5] DRESSLER, H. and DAWSON, C .R ., Biochim . Blophys. A cta 45 (1960) 515-24. [6] JOSELOW, M. and DAWSON, C.R., J. Biol. Chem. 191(1951) 1-10. [7] JOSELOW, M. and DAWSON, C. R., J. Biol. Chem. 191 (1951) 11-20. [B] MASON, H .S., Nature 177 (1956) 79-81. [9] NELSON, J. M. and DAWSON,'C.R. , Advances in Enzymol. 4 (1944) 99. 110] SCHUBERT, J., J. Phys. Colloid Chem. 52 (1948) 340-50. [11] SCHUBERT, J. and RICHTER, J. W ., J. Am. Chem. Soc. 70 (1948) 4259-60. [12] SCHUBERT, J. and RICHTER, J. W ., J. Phys. Colloid Chem. 52 (1948) 350-7. [13] WARBURG, O ., "Heavy metal prosthetic Groups and enzyme Action", Oxford Univ. Press(1949) London.

DISCUSSION

M. ANBAR: Did the addition of strong chelating agents affect the rate of breakdown of your organic copper compounds? From your results, one would expect the chelating agent to have an effect only under oxidizing condi­ tio n s. J.C. ARTHUR: The copper oxidases were not contacted with strong chelating agents during oxidizing conditions. After termination of the oxidiz­ ing conditions, the resting oxidase solutions were contacted with chelating agents, such as ion-exchange celluloses and resins, to separate the ionic copper from the copper enzymes. A constant ratio of total copper to protein was obtained. H. KEPPEL: I am interested in how you isolated the enzymes and how you identified the oxidation products. J.C. ARTHUR: The oxidation was stopped by lowering the pH once the ascorbic acid oxidase, to take that example, was in an oxidizing condition; it had been determined that below the optimum pH of the oxidation, with a pH value of 2 or 3, there was no combination of copper with the oxidation products. Then, when ascorbic acid oxidase - or tyrosinase - was isolated, when we were using relatively large quantities, a spectrophotometric analysis was made of these products to determine total copper. By determining total protein content we could see that the ratio of protein to copper content stayed relatively constant.

ISOTOPIC EXCHANGE OF POTASSIUM W AN ILLITE UNDER EQUILIBRIUM CONDITIONS*

M.E. SUMNER AN D G. H. BOLT LANDBOWHEGESCHOOL, WAGENINGEN, NETHERLANDS

Abstract — Résumé — Аннотация — Resumen

ISOTOPIC EXCHANGE OF POTASSIUM IN AN ILLITE UNDER EQUILIBRIUM CONDITIONS. The kinetics of potassium exchange in an illite was studied, using K42. In contrast to existing chemical extraction procedures, K42 exchange allows the investigation of the exchange to be made under equilibrium conditions. Up to the present time few attempts have been made in this direction, because of the relatively low specific activity of the available K« isotope (about 10 mc/gK). In combination with the fact that the equilibrium concentration of К in the soil'solution is usually less than about 10'4 molar, this implies that the observed count-rate at the outset of the experiment is of the order of 1000 cpm/ml solution, and thus about 10 cpm/ml after three days of equilibration. If the rate of exchange is to be studied over longer periods, the use of low-background counting equipment becomes imperative. Experiments were carried out with a number ot samples from the same illite, varying in percentage K-saturation and pre- treatment. The results indicate that after a very fast initial exchange (presumably К ions present in surface positions) the subsequent exchange is very slow, and in a number of cases non-detectable within a period of about eight days.

ÉCHANGE ISOTOPIQUE DU POTASSIUM DANS L'ILLITE DANS DES CONDITIONS D'EQUILIBRE. Les auteurs ont étudié à l’aide de la cinétique de l’échange du potassium dans l’illite. Contrairement aux procédés d’extraction chimique existants, l’emploi de permet d'étudier l’échange dans des conditions d’équi­ libre. Jusqu'à présent, il y a eu très peu de tentatives en ce sens du fait de l’activité spécifique relativement faible de l’isotope disponible (environ 10 mc/g de K). Etant donné que la concentration d’équilibre de K dans la solution de sol est généralement d'une molarité inférieure à environ 10*4 , le taux de comptage observé au début de l'expérience est de l’ordre de 1 000 cpm/ml de solution et n’est plus que de 10 cpm/ml après trois jours d’équilibrage. Si l'on désire étudier le taux d’échange pendant des périodes prolongées, il est indispensable d'utiliser des appareils de comptage à faible bruit de fond. Les expériences ont porté sur plusieurs échantillons de la même illite, dont le pourcentage de saturation en K et le degré de pré-traitement variaient. Les résultats indiquent qu’après un échange initial très rapide (vraisemblablement des ions K se trouvant à la surface), l'échange est ensuite extrêmement lent; dans plusieurs cas, aucun échange n’a pu être détecté avant l’expiration d'une huitaine de jours.

ИЗОТОПНЫЙ ОБМЕН КАЛИЯ В ИЛЛИТЕ В УСЛОВИЯХ РАВНОВЕСИЯ. Изучалась кинетика обмена калия в идлите о помощью К48. В противоположность существующим химическим экстракционным методам, обмен К42 дает возможность изучать обмен в условиях равновесия. До настоящего времени делалось немного попыток в этом направлении ввиду сравнительно низкой удельвой активности имеющегося изотопа К4г (около 10 милликюри на 1 г калия). Поскольку равновесная концентрация калия в почвенном растворе ооотавдяет меньше, чем 10~4 М, представляется, что наблюдаемая расчетная величина в начале опыта ооотавляет цифру порядка 1 ООО отсчетов в минуту на 1 мл раствора и, таким образом, около 10 от- очетов в минуту через три дня после установления равновесия. Если величина обмена изучается в течение более длительного периода, возникает необходимость в использовании счетного оборудования для низкого фона. Опыты проводились с рядом образцов из того же иллита с разным процентным содержанием калия в стадии насыщения и при различной предварительной обработке. Результаты свидетельствуют о том, что пооле очень быстрого обмена в начале процесса (вероятно, с ионами калия присутствующими ка поверхности), последующий обмен протекает очень медленно, и в ряде случаев его невозможно об- недужить даже через 6 дней.

* This article is published in Soil Science (Dec. 1962).

261 262 M .E. SUMNER and G .H . BOLT

INTERCAMBIO ISOTÓPICO DEL POTASIO EN UNA ILITA EN CONDICIONES DE EQUILIBRIO. Los autores han estudiado la cinética de intercambio del potasio en una ilita utilizando42 K. Contrariamente a las técnicas de extracción química existentes, el empleo de42 К permite investigar el intercambio en condiciones de equilibrio. Hasta el presente, se han hecho pocos intentos en esta dirección debido a la actividad especifica relativamente baja del isótopo42 К de que se disponía (unos 10 mc/g de K). Si se tiene en cuenta además el hecho de que la concentración de equilibrio del К en el suelo en solución suele ser inferior а 10"4 molar, se comprenderá que el índice de recuento al comienzo del experimento sea del orden de 1000 cuentas/min .cm3 de solución, decreciendo por lo tanto a unas 10 cuentas/min • cm3 a los tres días de mantener la sustancia en equilibrio con la solución. Si se ha de estudiar la velocidad de intercambio durante períodos largos, es im­ prescindible utilizar equipo de recuento de baja actividad de fondo. Se realizaron experimentos con varias muestras de una misma ilita, variando los porcentajes de saturación del К y los tratamientos previos. Los resultados indican que después de un intercambio inicial muy rápido (probablemente de iones К superficiales), las velocidades de intercambio se reducen considerablemente y en varios casos dejan de ser détectables al cabo de unos ocho días.

DISCUSSION

H. KEPPEL: Do you know whether the authors did an X-ray analysis of the m ineral before and after the exchange? It is known that the illite will change its lattice through chemical and physical treatment. H. BROESHART (on behalf of M.E. Sumner and G.H. Bolt): I know that an analysis of the clay was made and it was found to contain 80% illite, 5% kaolinite, 10% quartz and 5% of an expanding illite mineral. As far as I know no checks were made after the experiments. H. KEPPEL: The potassium atoms within the lattice of the illite are very strongly bonded and the time for equilibrium with other cations is very long — even in the presence of calcium ions, which enlarge the lattice. Have the authors investigated the exchange with respect to time? H. BROESHART: The authors are currently engaged in such an investi­ gation, but using potassium enriched in K40, for you need an isotope with yery long half-life for this type of study. K. FRÜHAUF: I just wanted to comment on the high value for the am­ monium exchange. This is due partly to the fact that molecular ammonia is adsorbed on the lateral faces of the crystals, and partly to the adsorption of ammonium ions. SEMINAR ON PRODUCTION AND USE OF SHORT-LIVED RADIOISOTOPES FROM REACTORS

HELD AT VIENNA, 5-9 NOVEMBER 1962

CHAIRMEN OF SESSIONS

I. L. G. ERWALL Isotoptekniska Laboratories Stockholm C . T A Y L O R Atomic Energy Research Establishment, H a rw e ll II. D. YASHIN USSR Academy of Sciences, Leningrad HI. D. YASHIN USSR Academy of Sciences, Leningrad P. C. AEBERSOLD Isotopes Development, United States Atomic Energy Commission, Washington, D.C. R.C. C O R N U E T Centre d'études nucléaires, Grenoble IV. E. SOMER Danish Isotope Centre, Copenhagen V.P. GUINN General Atomic Division, General Dynamics Corporation, San Diego, Calif. V. K. SCHEER University of Heidelberg W. JASINSKI Institute of Oncology, Warsaw VI. W. JASINSKI Institute of Oncology, Warsaw

SECRETARIAT OF THE SEMINAR

Scientific Secretaries: M . CO H EN Division of Isotopes, IAEA J.F. CA M ER O N Division of Research and Laboratories, IAEA E d ito r : E.M. COUNSELL Division of Scientific and Technical Information, IAEA Records Officers: T. J. JONES Division of Languages, D.J. M IT C H E L L IAEA Administrative Secretary: P. GHELARDONI Division of Scientific and Technical Information, IAEA

263 LIST OF PARTICIPANTS

N am e Institution Nominating State or Organization

ADLOFF, J. -P. Centre de recherches nucléaires, Dépt. de France chimie nucléaire, Strasbourg-Cronenbourg

ADLOFF -BACHER Centre de recherches nucléaires, Dépt. de France chimie nucléaire, Strasbourg-Cronenbourg

AEBERSOLD, P. C. Isotopes Development, US Atomic Energy United States of America Commission, Washington 25, DC.

AGELAO, G. Instituto di Applicazioni e Impianti Nucleari, Italy Université di Palermo

AKERMAN, K. Institute for Nuclear Research, Poland ul. Dorodna 16, Warsaw

ALBERT, P. Centre d'études de chimie métallurgique, France Vitry, Seine

ANBAR, M. The Weizmann Institute of Science, Rehovoth Israel

ANGOT, J. Société d'études chimiques pour l'industrie France et l'agriculture, Argenteuil (S et O)

ARTHUR, J.C . Jr. Southern Régional Research Laboratory, United States of America US Dept, of Agriculture. New Orleans, La.

BAKER, C. AERE, Bldg. C. 3. 7., Woolwich Arsenal, Woolwich United Kingdom London, S. E. 18.

BASOL, S. Université Technique du Moyen Orient, Turkey Faculté des Sciences, Section de Chimie, Ankara

BAUER. B. Osterr. Studiengesellschaft fur Atomenergie, Austria Vienna VIIL

BEELER, R. Institut de Physique Nucléaire, Switzerland Université de Genève

BENEDICT, G. Institut fur Anorganische Chemie und Federal Republic of Germany Kernchemle der Universitàt, Malnz

BILDSTEIN. H. Osterr. Studiengesellschaft fúr Atomenergie, Austria Vienna VIIL

BLANC, D. Centre de physique nucléaire, Faculté des France sciences, Allée Jules Guerda, Toulouse

BOCK-WERTHM ANN Hahn-Meitner Institut fiir Kernforschung, Federal Republic of Germany Berlin-Wannsee

264 LIST OF PARTICIPANTS 265

N a m e Institution Nominating State or Organization

BRUNS, K. Bundesforschungsanstalt fur Forst-und Holz- Federal Republic of Germany wirtschaft, Inst, fur Holzchemie, Birkenweg 1 Reinbek b. Hamburg

BUREAU, J. Société St. Gobain, 52 Bd de la Sillette, France Paris 19e

BUSSŒRE, P. Institut de recherches sur la catalyse du France Centre national de la recherche scientifique, 30, Bd de l'Hippodrome, Villeurbanne, Rhône

CICCARONE. P. Div. Biologica, Comitato Nazionale Italy Energia Nucleare, Via Be lis ario, 15, Rome

CIUFFOLOTTI, L SORIN, Saluggia (V ercelli) Italy

CLESS-BERNERT. T. Institut fûr Radiumforschung und Kernphysik, Austria V ienna IX»

COLONOMOS, P.M. Centre d'études nucléaires de Saclay, V enezuela Gif-sur-Yvette (S et O), France

COMAR, D. Centre d'études nucléaires de Saclay France Gif-sur-Yvette (S et O)

CONSTANT. R. Centre d'étude de l'énergie nucléaire, Belgium Mol-Donk

CONSTANTINIDIS, S. N.R.C. "Democritus”, Greek Atomic Greece Energy Commission, Athens

CORNUET, R. Centre d'études nucléaires de Grenoble (Isère) France

COURTOIS, G. Centre d'études nucléaires de Saclay, France Gif-sur-Yvette (S & O)

CUYPERS, M. Université de Liège Belgium

DAS, H. Reactor Centrum Nederland, The Hague Netherlands

DAVIES. J. W. L. Medical Research Council Unit, United Kingdom Accident Hospital, Birmingham 15.

DÊGOT, B. Bureau de recherches géologiques et France minières, 74, rue de la Fédération, Paris 15e

CRUZ, de la , F. Division de Chimica, Junta de Energía Nuclear, Spain Madrid

DOLAK, E. Ôsterr. M ineralôlverwaltung AG, Austria Otto-Wagner-Platz 5, Vienna IX.

DOMÍNGUEZ, G. Junta de Energía Nuclear, Madrid Spain 266 LIST OF PARTICIPANTS

Name Institution Nominating State or Organization

DOUIS, M. Centre d'études nucléaires de Saclay France Gif-sur- Yvette (S et О)

DOURNEL, P. Commissariat à l'énergie atomique, France 69, rue de Varenne, Paris 7e

DRAGUT, A. Ministry of Chemistry and Oil Romania Str. Scaune nr. 1, Bucharest

DUFTSCHMID, K. Osterr. Studiengesellschaft fur Atomenergie, Austria Vienna VIIL

DUGÎ3AN, M. Hammersmith Hospital, Ducane Rd., United Kingdom London, W. 12.

DURAND. N. Centre d'études nucléaires de Saclay, France Gif-sur-Yvette (S et О)

ELEN. J.D . Reactor Institute, Delft Netherlands

ELLEMAN, T .S . Battelle Memorial Inst., 505 King Avenue, United States of America Columbus, Ohio

ENGELMANN, Ch. Centre d'études nucléaires de Saclay France Gif-sur-Yvette (S et О)

EPHRAIM, K .H . Rotterdam Radiotherapeutic Institute, Netherlands Bergweg 232, Rotterdam

ERWALL. L. G. Isotope Techniques Laboratory, Sweden Drottning Kristinas vag 45, Stockholm O.

FELDMANN, A. Institut fur Biologie, Kernforschungsanlage Federal Republic of Germany Júlich, N.R. W.

FELIX, F. Hahn-Meitner Institut für Kernforschung Federal Republic of Germany Berlin-Wannsee

FELTEN, R .. Institut fur Medizin, Kernforschungsanlage Federal Republic of Germany Jülich, N. R. W.

FOA, E. Israel Atomic Energy Commission, Israel Hakirya, Tel-Aviv

FOGLIO PARA, A. CESNEF, (Politécnico di Milano) Italia Via Pascal, 3. Milan

FONTAN, J. Faculté des sciences, Université de Toulouse France

FRISSEL, M. Institute for Atomic Sciences in Agriculture, Netherlands W ageningen

FRUHAUF, K. Farbwerke HiSchst A. G. Frankfurt/Main-Hüchst Federal Republic of Germany LIST OF PARTICIPANTS 267

N am e Institution Nominating State or Organization

GASPAR, E. Institute of Atomic Physics, Romania Càsuta Póstala 35, Bucharest

GASPAR INI, G, Div. Biología, Comitato Nazionale Energía Italia Nucleate, Via Belisario, 15, Rome

GEBAUHR, W. Forschungslaboratorium, Siemens -Schuckert - Federal Republic of Germany Werke, Werner-von-Siemens-Str. 50 Erlangen

GETOFF, N. Reaktorzentrum Seibersdorf, N. Ô. Austria

GIBBONS. D. A. E. R. E .. W antage Research Lab., Berks. United Kingdom

GRÜNEWALD. T. Bundesforschungsanstalt fur Lebensmittel- Federal Republic of Germany frischhaltung, Kaiserstr. 12, Karlsruhe

GUINN, V. P. General Atomic Division, General Dynamics United States of America Corporation, San Diego, Calif.

GUIZERIX, J. Centre d’études nucléaires de Grenoble, France (Isère)

HAEGEMAN-GELADI, G. Centre d'étude de l'énergie nucléaire, Belgium M ol-Doak

HECHT, F. Analytisches Institut der Universitat Wien, Austria Vienna IX.

HERNE GGER, F. Institut fur Radiumforschung und Kernphysik, Austria Vienna IX.

HEYDORN, K. Danish Atomic Energy Commission, Denmark Research Establishment, Riso, Roskilde

HOGREBE, K. Isotopen-Laboratorium der Kernreaktor Federal Republic of Germany Bau- u. Betriebs Ges. m. b. H ., Weberstr. 5, Karlsruhe

HOSTE, J. 1 Université de Ghent Belgium

ITAHARA, K. Tohoku University Medical School, Japan Sendai

JASINSKI. W. Institute of Oncology, Ul. Wawelska 15, Warsaw Poland

JERCHEL. D. Organisch-chemisches Institut der Universitat Federal Republic of Germany M ainz

JURKŒWICZ, L. Institute of Nuclear Technique, Poland Academy of Mining and Metallurgy, Al. Mickiewicza 30, Cracow 268 LIST OF PARTICIPANTS

Name Institution Nominating State or Organization

KEPPEL, H. Isotopen-Laboratorium, Bundesallee 50, Federal Republic of Germany Braunschweig

KIM, C .K . Atomic Energy Research Institute, Seoul Republic of Korea

KIKNADZE, G. Institute of Physics, GSSR Academy of USSR Sciences, Tbilisy 49

KINELL, P.O. A. B. Atomenergi, Studsvik, Tystberga Sweden

KOHN, A. Institut de recherches de la sidérurgie. France 185, Rue Résident Roosevelt, St. Germain- on-Laye (S et O)

KRUSE, B. Danish Atomic Energy Commission, Denmark Research Establishment, Risü, Roskilde

KUYPER, E. Koninklijke/Shell-Laboratory, Netherlands Amsterdam (Nord)

LALÈRE, J. Centre d'études nucléaires de Saclay, France Gif-sur-Yvette (S et O)

LEDICH, A. Ôsterr. Studiengesellschaft für Atomenergie, Austria Vienna VIII.

LENGYEL, T. Institute of Isotopes, National Atomic Hungary Energy Commission, Budapest

LETTRÉ. H. Institut fur experimentelle Krebsforschung Federal Republic of Germany der Université: Heidelberg

LÉVÊQUE, P.C . Bureau de recherches géologiques et minières, France 74, Rue de la Fédération, Paris, 15e

LŒSER, К. H. Lehrstuhl fur Kernchemie, Eduard-Zintl-Institut, Federal Republic of Germany Technische Hochschule, Darmstadt

LOOS. R. Université Lovanium de Léopoldville Congo (Léopoldville)

LUCK. H. Deutsche Forschungsanstalt für Lebens- Federal Republic of Germany mittelchemie, Leopoldstr. 175, München 23.

MAILLE, С. Stein et Roubaix, 164 Av. Paul Vaillant Couturier, France La Courneuve, Seine

MALAMOS, В. Dept. Clinical Therapeutics, University Greece of Athens

MARCINOWSKI, H. -J. Isotopen-Studiengesellschaft, Federal Republic of Germany Karlstr. 21, Frankfurt/Main LIST OF PARTICIPANTS 269

N a m e Institution Nominating State or Organization

MATSUMURA, Y. Dept, of Biochemistry, Tokyo Women’s Japan Medical College, Kawada-cho. Shinjuku, Tokyo

MAXIA, V. Laboratorio di Radiochimica, Université Italy di Pavia

MEINKE, W.W. Dept, of Chemistry, United States of America University of Michigan Ann Arbor, Mich.

MENKE, H. Institut fur Anorganische Chemie und Federal Republic of Germany Kernchemie, Universitat Mainz

MILSZTAJN, J. Ateliers de constructions électrique Belgium de Charleroi

M1RNIK, M. Nuclear Institute "Rudjer Boskovií", Zagreb Yugoslavia

MOLNAR, F. Central Research Institute for Physics, Hungary Budapest

MORTREUIL, M. Centre d'études nucléaires de Saclay, France Gif-sur-Yvette (S et O)

MUHLBERGER, F. Bundesministerium fur Handel und Wiederaufbau, Austria V ienna I

NELSON, F. Oak Ridge, National Laboratory, Tenn. United States of America

NEMENZ, H. Zoologisches Institut der Universitât Wien, Austria Vienna L

OBER LANDER, H.E. Landwirtschaftlich-chemische Bundesversuchs- Austria anstalt in Wien, Vienna IL

O’DONNELL. A.J. US Mission to the IAEA, Schmidgasse 14, United States of America Vienna VIIL

OOSTERHEERT, W. Institute for Atomic Sciences in Agriculture, Netherlands W ageningen

ORLA, M. Institut des sciences et techniques nucléaires, France В. P. No. 6, G if-sur-Y vette (S et О)

OZENDA, P. Centre d'étude nucléaires de Grenoble (Isère) France

PARSIGNAULT, D. Centre d'études nucléaires de Saclay, France Gif-sur-Yvette (S et O)

PAUL, W. Dept, of Pathological Chemistry, Canada University of Toronto

PETEOU, G. Ministry of Chemistry and Oil, Romania Str. Scaune nr. 1, Bucharest 270 LIST OF PARTICIPANTS

N am e Institution Nominating State or Organization

PETERSEN, B.R. The Danish Isotope Centre, Copenhagen V. Denmark

PETERSEN, T. AB Atomenergi, Drottning Kristinas vag 47, Sweden Stockholm Ó.

PETIT, J. Centre d'études nucléaires de Saclay, France Gif- sur- Y vette ( S e t O)

PIERQUIN, B. Institut Gustave Roussy, Villejuif, Seine France

PUGNETTI, G. Laboratorio Operazioni Calde délia Divisione Italy Materiali, Casaccia CSN, Rome

RADOSZEWSKI, T. Institute for Nuclear Research, Poland ul. Dorodna 16, Warsaw

RAMOS, E. Sección de Medicina y Protección Spain Junta de Energía nuclear, Madrid

RENNER, R. Bundesministerium fur Handel und Austria Wiederaufbau, Vienna L

ROSA, U. SORIN, Corso Galileo Ferraris, 162, Turin Italy

SÂRBU, L Institute of Atomic Fhysics, Romania Càsuta Postalâ 35, Bucharest

SAUERWEIN, K. Isotopen-Laboratorium Dr. Sauerwein, Federal Republic of Germany Harffstr. 148, Dusseldorf

SCHEER, K. Czerny Krankenhaus der Universitât Heidelberg Federal Republic of Germany

SCHWANITZ, F. Institut fiir Biologie, Kernforschungsanlage Federal Republic of Germany Jûlich, N.R.W.

SELLERIO, A. Université di Palermo, Instituto di Appli- Italy cazioni e Impianti Nucleari

SELLSCHOP, J. P. F. Nuclear Physics Research Unit, University of South Africa the Witwatersrand, Johannesburg

SKJELBRED, E. Institutt for Atomenergi, Kjeller Norway

SOMER, E. The Danish Isotope Centre, Copenhagen V. Denmark

SORANTIN, H. Osterr. Studiengesellschaft für Atomenergie, Austria Vienna VIIL

SOREMARK, R. The Royal School of Dentistry, Box 3207, Sweden Stockholm 3.

STADLER, I. Landwirtschaftlich-chemische Bundesversuchs- Austria anstalt in Wien, Vienna II. LIST OF PARTICIPANTS 271

N am e Institution Nominating State or Organization

STANG, L .G ., Jr. Brookhaven National Laboratory, United States of America Upton, Long Island, N. Ÿ.

STAUB, M. St. Gobain nucléaire, 23, Bd. Georges France Clemenceau, Courbesoie, Seine

STAUN, N.J. The Danish Isotope Centre, Copenhagen V. Denmark

TAUGNER,' R. Physiologisches Institut der Universitat Federal Republic of Germany H eidelberg

TAYLOR, C. Radiochemical Centre, Amersham, Bucks. United Kingdom

TELLŒR, C. Gaz de France, 23 rue Philibert Delorme, France Paris 17e

TEMPUS, P. Institut fédéral de recherches en matière, Switzerland de réacteurs, Wurenlingen/AG.

TEOFILOVSKI, C. Institut "Boris Kidric", Vinca, Belgrade Yugoslavia

THOMAS, C.C. Jr. Western New York Nucl. Research Center United States of America Inc., State University of New York at Buffalo. N. Y.

TIMTCHOUK, B. State Committee on Coordination of the USSR Research Works of the Byelorussian SSR, Government House, Minsk

TITZE, H. Reaktorzentrum Seibersdorf, N. Ô. Austria

TOLMIE, R. Commercial Products Division, Canada Atomic Energy of Canada, Ltd., P. O. Box 93, Ottawa.

TOLUN, R. Université technique du moyen orient, Turkey Faculté des sciences. Section de chimie, Ankara

TOMAZIC, M. Institut "J. Stefan", Ljubljana Yugoslavia

TOUSSET, J. Université de Lyon, Institut de physique France nucléaire, 1 rue Raulin, Lyon

TROLY, G. Bureau de recherches géologiques et minières, France 74, rue de la Fédération, Paris 15e

VARGA, C. Isotope Institute, Csillebere, Budapest Hungary

VINCENT. J. Michelin Durin et Cie., Place des Carmos, France Clermont -Ferrand 272 LIST OF PARTICIPANTS

N am e Institution Nominating State or Organization

VOOGD VAN DER Laboratory of Experimental Histology and Netherlands STRAATEN, 'W. A. de Cytology, State University

VUORINEN, /V. Institute of Technology, Reactor Laboratory Finland O taniem i

WAHL, R. Société interchimique, 81 rue Escudier, France Boulogne, Seine

WARD, A. Royal College of Science and Technology, United Kingdom Glasgow, Scotland

WATT, J. S. Australian Atomic Energy Commission Australia Research Establishment, Sutherland, N. S. W.

WESTHOLM, S. AB Atomenergi, Studsvik, Tystberga Sweden

WOLDRING, 1Vi. Isotope Laboratory, Academical Hospital, Netherlands Groningen

WOLF, P. Kernforschungszentrum Karlsruhe, Federal Republic of Germany

WOLF, R. Électricité de France, Centre de recherches France et d’essais de Chatou, 6, Quai Watier, Chatou (S et O)

YASHIN, D.J\. Physico-Technical Institute, USSR Academy USSR of Sciences, 2. Politechnicheskay uliza, Leningrad

ZELLER, A. Landwirtschaftlich-chemische Bundesversuchs- Austria anstalt in Wien, Vienna IL AUTHOR INDEX

The ordinary numerals refer to pages in Vol. I and those underlined in Vol. II.

A dloff, J.-P. : 181 G ibbons, D. : 9J5 A d lo ff-B â c h e r, M. : 181 Gómez, M. Barrachina: 159 Aebersold, P. C. : 31 Grigorescu, L. : 393 Akerman, K. : 305 Guinn, V. P. : 3 A lb e rt, P h . : 53 Guizerix, J. : 383 Anbar, M. : 147', 227 Haegeman-Geladi, G. : 141 A rth u r Jr., J. C. : 247 Hart, D. M. : 275 Baker, C. A .: 39 Heydorn, K. : 123 B a rth o m eu f, D. : 79 Horan, R. F. : 275 Barrachina Gomez, M. : 159 Iravani, J. : 187 Berg, O. : 405 Itahara, K. : 175 Beyer, H. : 201 Ito, T. : 175 Bildstein, H. : 171 Jammes, R. : 201 Birnbaum, M. : 393 Jimbo, T. : 175 Bjerle, I. : 259 Jones, Elizabeth: 213 Blanc, D. : 415 Joplin, G. F. : 213 Bolt, G. H. : 261 Kim, Chong Kuk: 221, 73 Brafman, M. : 305 Kitala, J. : 305 B u s s iè re , P . : 79 Kohn, A. : 285 Chassagne, D. : 201 Кондуров,И.А.: 83 Chinaglia, B. : 127 K ra u s, К. A. : 191 Ciuffolotti, L. : 127 Laverlochère, J. : ^79 Cornuet, R. : 383 Ljunggren, K. : 229 Courtois, G. : 357 Loos, R. :.215, 45 D as, H.A. : Ш . McLemore, T. A. : 247 Deschamps, N. : j)3 Maille, C. : 415 D e y ris, M. : 53 Mallard, J. R. : 213 Douis, M. : 49 Malvano, R. : 127 Duggan, Mary H. : 213 Matsumura, Y. : 137 Dutreix, J. : 201 M einke, W. W. : 93 Elleman, T. S.: 319 Moinard, J. : 415 Engelmann, Ch. : 29 M ortreuil, M. : 201 Erwall, L. G. : 229 N elso n, F . : 191 Fasolo, G. B. : 127 Nowak, M. : 305 Felix, F. W. : 105 Oncescu, M. : 393 Fik, H. : 305 Pennisi, G. : 161 Fontan, J. : 415 Petersen, B. R. : 269 Forsberg, H. G.: 229 Petit, J. : 29 F o u rn e t, L . : 53 Pierquin, B. : 201 Frühauf, K. : 249 Pirrwitz, D. : 105 Galle, P. : 201 Poczynajxo, A. : 305 Gasnier, M. : 357 Rosa, U. : 161 Gaspar, E. : 393 Rupp, A. F . : 31 G et off, N. : 171 Sandru, P. : 393 Sato, T. : 175 Teitel, T.: 393 S c a s s e lla ti, G. A. : 161 Tellier, C. : 357 Simpson, H. : 95 Thomas, Jr.,C .C . : Somer, E. : 405 T itz e , H .: 171 S o ra n tin , H .: 171 Tominaga, T. : 175 Stang, Jr., L.G. : 3 Townley, C.W. : 319 Stiennon-Bovy, R. : 141 Valade, J. : 49 Sumner, M. E. : 261 Ward, A.: 113 Sunderman, D. N. : 319 Watt, J.S. : 343 Szabó de Bues, E. : 105 West, R. : 67 Taugner, R. : 187 Whiting, М.: 67 Taylor, C. : 67 Яшин, Д.A. : 83 OTHER IAEA PUBLICATIONS PROCEEDINGS SERIES

L’électronique nucléaire - Nuclear Electronics (1959) (2 Vols. ) STI/PUB/ 2 Medical Radioisotope Scanning 3 Large Radiation Sources in Industry (2 Vols. ) 12 Metrology of Radionuclides 6 Disposal of Radioactive Wastes (2 Vols. ) 18 Codes for Reactor Computations 24 Selected Topics in Radiation Dosimetry ' 25 Effects of Ionizing Radiations on Seeds 13 Small and Medium Power Reactors (2-Vols. ) 30 Radioisotopes in the Physical Sciences and Industry (3 Vols. ) 20 Inelastic Scattering of Neutrons in Solids and Liquids 35 Pile Neutron Research in Physics 36 Chemical Effects of Nuclear Transformations (2 Vols. ) 34 Nuclear Ship Propulsion 37 Radioisotopes and Radiation in Entomology 38 Radioisotopes in Tropical Medicine 31 Tritium in the Physical and Biological Sciences (2 Vols. ) 39 Nuclear Electronics (3 Vols.) (1961) 42 Effects of Ionizing Radiation on the Nervous System 46 Whole-Body Counting 47 Physics of Fast and Intermediate Reactors (3 Vols. ) 49 Plasma Physics and Controlled Nuclear Fusion Research (2 of 3 Parts) 50 Power Reactor Experiments (2 Vols. ) 51 Radioisotopes in Soil-Plant Nutrition Studies 55 Radiation Damage in Solids (2 of 3 Vols. ) 56 Reactor Safety and Hazards Evaluation Techniques (2 Vols. ) 57 Thermodynamics of Nuclear Materials 58 Corrosion of Reactor Materials (2 Vols. ) 59 Inelastic Scattering of Neutrons in Solids and Liquids (2 Vols. ) 62 Selected Topics in Nuclear Theory 67 Theoretical Physics 61 Treatment and Storage of High-Level Radioactive Wastes 63

IN PRESS

Diagnosis and Treatment of Radioactive Poisoning 65 Radioactive Dating 68 Radiation Damage in Solids (Vol. Ill) 56 Radiation Damage in Reactor Materials 56a Plasma Physics and Controlled Nuclear Fusion Research (Part 3) 50 Neutron Dosimetry (2 Vols. ) 69 A complete Catalogue of all Agency publications will be gladly supplied by any of the Sales Agents or directly by the Editorial and Publications Section, International Atomic Energy Agency, Karntner Ring, Vienna I, A u s tria . OTHER IAEA PUBLICATIONS ON RELATED SUBJECTS

PROCEEDINGS

Radioisotopes in Soil-Plant Nutrition Studies

461 pp. (16X24 cm) - STI/PUB/55 - US S 3.00; Elsewhere 54s. stg.

Proceedings of a symposium jointly organized by IAEA and FAO and held in Bombay, Feb. - M ar., 1962. Contents include: soils chemistry and physics; ion uptake and translocation; biological measurement of soil characteristics and fertilizer usage.

Radioisotopes and Radiation in Entomology

307 pp. (16x24 cm) - STI/PUB/38 - US $ 6.50-, Elsewhere 39s. stg.

Proceedings of an IAEA symposium held at Bombay, Dec., 1962. Contents include: ecology and general biology; labelled insecticide studies; studies on insecticide resistance; insect physiology and biochemistry; studies on feeding behaviour; using insects against themselves; and some insect problems in tropical countries.

Radioisotopes in Tropical Medicine

375 pp. (16x24 cm) - STI/PUB/31 - US $ 7.00; Elsewhere 42s. stg.

Proceedings of a symposium jointly organized by IAEA and WHO and held in Bangkok, D ec., 1У60. Subjects include nutrition, protein metabolism and deficiencies, tropical sprue, haematologicai problems, iron metabolism, etc.

Tritium in the Physical and Biological Sciences

Vol. I: 369 pp. (16x24 cm) - STI/PUB/39 - US S 7.00; Elsewhere 42s. stg. Vol.II: 438 pp. (16x24 cm) - STI/PUB/39 - US $ 8.00; Elsewhere 48s. stg.

Medical Radioisotope Scanning

Proceedings of a seminar jointly organized by IAEA and WHO and held in Vienna, 1959. Subjects include: theory of isotope scanning; collimation; photoscanning; basic problems of scintillation counting; scintillation cameras; liver, thyroid and pancreas scanning; bremsstrahlung in vivo; profile counting; coincidence scanning and diagnosis of intra-cranial lesions.

Radioisotopes in the Physical Sciences and Industry

Vol.I: 542 pp., (Vol.II: 554pp., Vol.III: 633 pp. (16x24 cm). Each volum e - US S 8.00; Elsewhere 48s. stg.

Proceedings of a conference jointly organized by IAEA and UNESCO and held in Copenhagen, Sept., 1960. It serves as a sequel to proceedings of earlier conferences in Oxford (1951, 1954) and Paris (1957) and emphasizes developments since 1957.

Large Radiation Sources in Industry

Vol.I: 438 pp.. Vol.II: 456 pp. (16x24 cm). Each volum e - US S 4.50; Elsewhere 27s. stg.

Proceedings of a conference held by IAEA in Warsaw, Sept., 1959. Special emphasis was on chemical processes. Contents include, inter alia, (Vol.I) large radiation sources and methods of use; cobalt-60 and other radiation facilities; fission- fragment recoil energy for chemical processing: ( Vol. П) radiation and chemical reactions, special applications, radiation in food preservation. REVIEW SEMES

Tritium: dosage, préparation de molécules marquées et applications biologiques (Walter G. Verly) (in French)

56 pp. (14.8X21 cm): Review No. 2. US $ 1.00: Elsewhere 6s. stg.

The Application of Radioisotopes in Biology (A.M. Kuzin)

64 pp. (14.8X21 cm): Review No.7. US $ 1.00; Elsewhere 6s. stg.

Radioactive Isotopes and their Production under Neutron Irradiation (N.E. Brezhneva and S. N. Oziraner) (in Russian and English).

72 pp. (14.8X21 cm): Review No. 15. US $ 1.00; Elsewhere 62s. stg.

MISCELLANEOUS

Use of Radioisotopes and Supervoltage Radiation in Radioteletherapy. Present Status and Recommendations

88 pp. (14.8x21 cm). Panel Report. US $ 1.50; Elsewhere 9s. stg.

Report of an 18-member study group under B.W. Windeyer as chairman convened by IAEAand WHO in Vienna, August, 1959. Published in English, French, Russian and Spanish editions.

Radioisotope Applications in Industry (Technical Directory)

(In press: prices on application). Approx. 100 pp. (16x24 cm)

Classification of industries and other economic activities in which radioisotopes have proved of value is used as the basis for a survey of the international literature. Within each industrial category the various applications of radioisotopes are listed in detail and provided with selected literature references.

International Directory of Radioisotopes (Second Edition). Technical Directory.

700 pp. (16x24 cm) 1962. US $ 9.00: Elsewhere 54s. stg.

This revision of the earlier IAEA two- volume directory has information on most radioisotopes and labelled compounds sold or distributed by major suppliers of the world.

Application of Isotope Techniques in Hydrology

31 pp. (16x24 cm). Technical Reports Series N o.ll. US S 1.00; Elsewhere 6s. stg. IAEA SALES AGENTS

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INTERNATIONAL ATOMIC ENERGY AGENCY, VIENNA 1963 PRICE; North America= US $8.50 Elsewhere= Sell 178,50 (51s.stg; NF 34,~ DM 29,80)