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IAEA-TECDOC-527

NEW TREND DEVELOPMENTD SAN S IN RADIATION

PROCEEDINGS OF AN ADVISORY GROUP MEETING ORGANIZED BY THE INTERNATIONAL ATOMIC ENERGY AGENCY AND HELD IN BOLOGNA, ITALY, 14-17 NOVEMBER 1988

A TECHNICAL DOCUMENT ISSUED BY THE INTERNATIONAL ATOMIC ENERGY AGENCY, VIENNA, 1989 TRENDW NE DEVELOPMENTD SAN RADIATION SI N CHEMISTRY IAEA, VIENNA, 1989 IAEA-TECDOC-527 ISSN 1011-4289

Printed by the IAEA in Austria October 1989 The IAEA does not normally maintain stocks of reports in this series. However, microfiche copie f thesso e reportobtainee b n sca d from

INIS Clearinghouse International Atomic Energy Agency Wagramerstrasse5 P.O. Box 100 A-1400 Vienna, Austria

Orders shoul accompaniee db prepaymeny db f Austriao t n Schillings 100,- in the form of a cheque or in the form of IAEA microfiche service coupons orderee whicb y hdma separately fro e INImth S Clearinghouse. FOREWORD

Radiation chemistry is a branch of chemistry that studies chemical transformations in materials exposed to high-energy radiations. It uses radiation as the initiator of chemical reactions.

Practical application radiatiof so n chemistry today exten mano t d y fields, including health care, food agriculturean d , manufacturingd ,an telecommunications. Relativel peoplw yrangfe e e awar th e ar f eo f eo contributions from this largely hidden branc sciencef ho .

e importanTh t advantag radiatiof eo n chemistr yabilits it e lieb n o i st y used to produce, and study, almost any reactive atomic and molecular species playing a part in chemical reactions, synthesis, industrial processes, or in biological systems e techniqueTh . applicable sar gaseouso et , liquid, solid, and heterogeneous systems combininy B . g different technique radiatiof so n chemistry with reactioe ,th n mechanis kineticd man f so chemical reactions are studied.

In November 1988 in Bologna, Italy, the IAEA convened an advisory group meeting to assess new trends and developments in radiation chemistry. Radiation from Austria, Canada, China, Denmark, Federal Republic of Germany, France, German Democratic Republic, Hungary, India, Israel, Italy Japan, Netherlands, Poland, United Kingdom, United States USSd ,an R attended the meeting.

The present publication includes most of the contributions presented at meetinge believes th i t I . d that this publication will provid usefuea l overvie presenf wo t activitie w trendne researcd f so san radiation hi n chemistry promoto t d ,an e better understandin potentiaf go l contributionf so radiation chemistry to other fields of knowledge as well as to practical applications. EDITORIAL NOTE

In preparing this material press,the for staff Internationalofthe Atomic Energy Agency have mounted and paginated the original manuscripts as submitted by the authors and given some attention presentation.the to The views expressed in the papers, the statements made and the general style adopted are the responsibility namedofthe authors. necessarilyviewsnot The do reflect those governments ofthe Memberofthe States organizationsor under whose auspices manuscriptsthe were produced. The use in this book of particular designations of countries or territories does not imply any judgement publisher,the legalby the IAEA, to the status as of such countries territories,or of their authorities institutions delimitationand the of or theirof boundaries. The mention of specific companies or of their products or brand names does not imply any endorsement recommendationor IAEA. partthe the of on Authors themselvesare responsible obtainingfor necessarythe permission reproduceto copyright material from other sources. CONTENTS

INTRODUCTION ...... 7 . V. Markovic

RESEARCH PAPERS

Pulse , a method of choice for the fast kineticist — past, present and future ...... 13 Sonntagvon C. New applications of pulse radiolysis in ...... 23 A.K. Pikaev, S.A. Kabakchi, I.E. Makarov, A.V. Gogolev From radiation chemistry to energetics via photoelectrochemistry — hydroged an s n liquidn i s s ...... 3 4 . SchillerR. Assessment of the radiation chemistry of and aqueous at elevated temperatures ...... 1 5 . G.V. Buxton Current status of radiation chemical studies with heavy ...... 69 R.H. Schuler, J.A. LaVeme Solid state pulse radiolysis ...... 9 7 . Z.P. Zagorski Immobilizatio asparaginasf no radiation ei n cured, thermally reversible hydrogels ...... 9 8 . Méchain,B. Yanhui Sun, HoffmanA. Some aspects of radiation chemistry of epoxies ...... 97 Singh,A. C.B. Sounders, A.A. Carmichael, V.J. Lopata The radiation chemistry of connective tissue; hyaluronic acid ...... 105 P. Myint, D.J. Deeble, G.O. Phillips The use of for solar . Application of methods for the binding of functional groups to polymers ...... 117 . Rabani/

REVIEW PAPERS

Recent developments in radiation chemistry at IRI-TU Delft ...... 129 HummelA. New developments in radiation chemistry applications in Japan ...... 141 5. Machi General surve f radiatioyo n chemistr Francn yi e ...... 7 14 . L. Gilles Concepts of radiation research in the German Democratic Republic ...... 157 J.W. Leonhardt Radiation chemistry at Harwell ...... 165 W.G. Burns An overview of some basic and applied radiation chemistry studies at Trombay ...... 171 P.N. Moorthy Radiation chemistry in China ...... 185 GuanghuiWu, Man Wang SUMMARIES

Intramolecular long range electron transfer reaction peptiden i s proteind san s ...... 5 19 . Faraggi,M. M.H. Klapper role f sulphueTh o r compound affectinn i s g radiation response: molecular aspects ...... 9 19 . TombaM. Some implication f studieso f electronso visualizatioe fluidn th si r fo s n of ...... 3 20 . G.R. Freeman Advancements of radiation induced degradation of pollutants in drinking and waste water ...... 207 N. Getoff The radiolysis of aqueous solutions of glycosides ...... 211 Rongyao Yuan, Jüan Wu Using multi-effects of chemical scavengers to study the radiolysis of cyclohexane-4-methyl-4-phenyl-2-pentanone system and cyclohexane-tributyl-phosphate system ...... 213 Zhang,Nan JüanWu crystallizatioe Th n kinetic f irradiateso d polypropylene with additives ...... 215 Wenxiu Chen, Shui Yu

SPECIAL TOPIC

Radiation chemistry in flue gases ...... 219 F. Busi

Lis f Participanto t s ...... 9 23 . INTRODUCTION

V. MARKOVIC Industrial Application Chemistrd san y Section Divisio f Physicano Chemicad an l l Sciences International Atomic Energy Agency Vienna

I. BACKGROUND

presentatione Th discussiond san thif so s advisory group meeting show that fundamental knowledge gained by radiation chemical methods is contributing in an increasingly important way to many and diverse areas of basic and applied chemistry, biology and . Of particular importance has been the development over the last two decades of a variety of pulse radiolysis techniques whic mads hha e availabl considerablea e amounf to kinetic and structural information on free radicals which is not readily available from other approaches. For example, a recent compilation [G.B. Buxton, C.L. Greenstock, W.P. Helman, A.B. Ross, J. Phys. Chem. Ref. 3 (1988)Data51 , ratf ,17 ]o e informatio reactione th n no hydratef so d , and hydroxyl lists ~ 3500 rate constants, almost all of which have been determined by radiation chemical methods. This rate information is extremely important to researchers interested in the application of radiation from environmental to biological problems, particularly to radiation therapy, and in modeling problems in radiation chemical processin reactod gan r technology. e fundamentaTh l knowledg radiatiof eo n chemistry foun numbea d f ro different applications in industry. Particular interest of industry has been in radiation modificatio polymerf no differenr sfo t uses. Radiation sterilizatio medicaf no l product pharmaceuticald san largels si ye baseth n o d knowledge and data provided by radiation chemistry. New developments in biomédical applications have recently occurred. Radiation chemistry of gases has become the subject of increasing interest due to potential use of radiation processing for removal of toxic components in flue gases. New development e likelsar tako yt e plac fundamentan i e l studie polymerif so c systems, radiation chemistr heavf yo y ions, biological system othed san r fields. n spitI thesf eo e facts radiatioe ,th n chemical community todas i y relatively small. There are today, worldwide, only a few hundred active investigators in the basic research and, perhaps, a similar number in the radiation processing industry. This unfortunate state results froface mth t that active practice requires to a considerable extent the availability of major, fairly sophisticated equipment, suc higs ha h energy electron accelerators. Because of this requirement most of the interest is concentrated on "national" laboratories end institutes and not on universities. There has factn i , recenn ,i t years bee declinna e rather than expansion a interesf no universitiese th n ti . Most chemistry faculty members and graduate students are, therefore, unawar onlr eo y distantly e awarth f eo contributions that radiation chemistry method makn theio sca et r effortst I . must als e recognizeob d thae impactth radiatiof to n chemistr quits i y e diffuse and many times information obtained by radiation chemical methodology is not recognized as such. II. OBJECTIVES OF THE MEETING Advisore Th y Group (AC convenes )wa d witmaie hth n objectiv reviewinf eo g the new developments and trends of research in radiation chemistry. A further objectiv adviso t rols Agence s promotinn it eth wa ei n yo advancemene th g f to radiation chemistry researc Membes it n rhi States.

IIISHORA . T SUMMAR INDIVIDUAF YO L CONTRIBUTIONS

A total of 35 individual contributions were presented at the meeting. contributione Mosth f to reproducee sar thin i d s report eithe fuln ri l texr to extended summary. The meeting has shown that, indubitably, radiation chemistry has evolved into a broad discipline of chemistry. The methods employed in radiation chemistry and accumulated knowledge have broad range of applications, not usually recognized eve professionaly nb correspondinn si g areas. Some more important developments were mentione differeny db t speakers: in general chemistry (organic, inorganic) - mechanisms of different reactions, identification of intermediates, solvated (hydrated) electron and its reactions; in chemical kinetic diffusios- n controlled reactions, rate constants determine thousandr dfo fref so e radical radicaln io , , radical- reactions, etc.;

in free radical chemistry - identification of free radicals, reactions, kinetic reactionf so s with further implication medicinen i s , nutritional sciences, , , etc.;

in biology (radiation). biotechnology, medicine - sterilization of human tissues;

in preservatio environmenf no purificatiot- fluf no e gases, waste water purification, drinking water (chemistrozonization)d an V U f yo ;

in industry - polymerization (curing), crosslinking of polymers, sterilizatio medicaf no l supplies, pharmaceuticals, spices;

in - nuclear reactors, high temperature radiation chemistry (coolants, moderators), corrosion and control of pH, degradation of organic materials in radiation environments.

The meeting has identified a number of important new areas of development: - radiation chemistr heavf yo y ions witimplications hit n i s and microelectronics ; - development of pol]rmeric systems for photochemical storage of energy; - high temperature (aqueous) radiation chemistry; - development of radiation sensitive/resistant polymers; - free radical reaction biochemistryn i s particulan ,i r reactionf so hydrox peroxd yan y radicals; - environmental applications (gas phase and heterogeneous reactions, treatment of pollutants in water); - the effect of irradiation on corrosion; - reaction of very low energy electrons and high LET particles; - immobilization of drugs and biologically active materials; - new detection techniques for pulse radiolysis study of transients as wel substantias la l increas sensitivitf eo existinf yo g techniques; - photochemistr fref yo e radicals;

- synthesi metaf so l aggregates; etc.

IV. MAIN CONCLUSION RECOMMENDATIOND SAN S Groue Th p concluded that, wit exceptionsw hfe , ther continuins ei g decline of resources allocated for radiation chemistry in most of the countries. Thi contrars si increasino yt g contribution radiatiof so n chemistr otheo yt r likels fieldi d resulto neayt e san th r n ,i future n ,i long-term detrimental effect. workere Mosth f radiation to si n chemistr eithee yar r base nuclean i d r sciences oriented institutions or have gained experience in these institutions sense on en I strengt.a thi s si h provides sincha t ei d excellent instrumental backing and access to radiation sources. This mode of development has also proved a weakness, since it has isolated radiation chemists from the broad stream of chemistry. Universities, generally, have kept pace no tth e with these development thein si r academic courses.

Groue Th convinces i p d that orden ,i gaio rt n maximum benefit froe mth advances made in radiation chemistry, it is necessary to integrate the information derived from radiation chemical investigations intvarioue oth s traditional branches of chemistry. The benefits of successful industrial applications of radiation technology have been directly derived frowidee mth r investmen radiation ti n chemical investigation. In developing countries the transfer of radiation technology is not often adequately covered by building the fundamental research base and in developed countries, once adopted by industry, there is a tendency to reduce the associated fundamental investigations. Unless both trend correctede sar , continuing benefi radiatiof to n technologe b t no y yma fully realized. The above has been illustrated throughout discussion by numerous examples bees ha nt I als. o pointe that Agence ou dtth y programmn ei the transfer of radiation technology is not adequately balanced with support to fundamental radiation research. It is considered desirable and necessary, in the future to promote: - dissemination of information about the manner in which radiation chemistr contributins i y othee th ro t g area chemistryf so , advanced education in radiation chemistry, transfe knowledgf ro developino et g countrie buildind san f o g infrastructure for fundamental studies.

Next page(s) left blank RESEARCH PAPERS

Next page(s) left blank PULSE RADIOLYSIS, A METHOD OF CHOICE FOR THE FAST KINETICIST — PAST, PRESENT AND FUTURE

C. VON SONNTAG Max-Planck-Institu r Strahlenchemiefü t , Mühlheim/Ruhr, Federal Republic of Germany

Abstract

e pastIth n , radiation chemistr s madha y e considerable contribution r presenou o t st knowledge of free-radical chemistry. This was largely due to the pulse radiolysis technique which has been established some 25 years ago. Although it is true that one of its most notable contributions, the establishment of reliable rate constants for the reactions of the water radicals ('OH, H- and e~ ) with a host of organic and inorganic compounds is losing in importance because this techniqu provides eha s witdu bodha f manyo y excellent data and a picture of the reactivity of various classes of compounds has now emerged, there developmente ar pulse th en si radiolysis technique itself which will make possible another breakthroug free-radican i h l research. These recent development briefle ar s y discussed.

1. Historical background

Before the early sixties, radiation-chemical studies were confined to low-dose-rate steady-state type experiments. Hence it was very difficult to obtain reliable kinetic data. The advent of pulse radiolysis constituted a "quantum jump n radiatioi " n chemistry whe t i becamn e possiblo t e characterize by UV/VIS intermediates such as the , and, even more important, to obtain absolute rate constants for many free-radical reactions which can be initiated by the action of ionizing radiation. There is now a wealth of reliable rate constants of reactions of radicals (e.g. n wateri H'H ~ [1]e ,'O : , HO^/O^ [2], organic (not ye t tabulated; for an example see Ret. [3]) and inorganic radicals [4,5] including metal ions in reactive valence states, cf. Réf. [6]). With many solutes unrivalled in scope by any set of similar physico-chemical data obtained other techniques. With this huge bod f informatioyo havinw no n g accumulated, it is sometimes asked whether this technique would not merely provide more of the same. This is certainly not the case, and it is the purpose of this brief article to show that pulse radiolysis with its famous past will have a brilliant future.

. Improvement2 e basith cf o s setup

Computerization and shorter time domain. The basic setup consists of an electron accelerator which delivers electron pulses (ca MeV3 . f abouo ) t 1 (is duration, linked with a UV/VIS-spectroscopic detection system. The typical experiment of the first two decades in pulse radiolysis research has been the determination of the rate constants of the water radicals ('OH, e~aq )

13 wit givea h n substrate, monitorin intermediate decae th gth f yo e whereever it could be followed owning to its UV/VIS absorption, otherwise by the competition method. This has implied the determination of the UV/VIS-absorption e resultinspectrth f o a g intermediate(s) e ratTh e. constant e bimoleculath f o s r deca f thesyo e intermediate(s) wer f courseo e also accessible in principle. These experiments were performed at one given temperature, "room temperature" e limiteTh . d sensitivit e detectioth f o y n system required high concentration f intermediateo s s (i.e. high doses)e Th . rapid bimolecular decay of the radicals often prevented the elucidation of reactions kineticall f firso y t orde n radicalsi re earlth yn I .day f pulso s e radiolysi recordee b o t e trace th sd d ha sphotographicall evaluated an y y b d hand. e meantimeIth n , technological progres s permitteha s d considerable improvement and rationalization. Data acquisition, processing and evaluation is now generally done with the help of the computer. Computerization also allows repetitive pulsing (improvement of the signal to noise ratio). This make dosew hencd lo t possibli s an se o increast eus o t ee lifetim th e f o e the radicals considerably with respect to their bimolecular decay. As a consequence, very interesting unimolecular free-radical processes remain to be discovered. With pulsed lamps that provide the high light intensities required for the easy detection of the intermediates, the 1-10 ms range had been the upper observation time limit. Now, more sensitive instrumentation f non-pulseo e allowus e th sd e longer-timlampth r fo s e range.f Thio s i s especial importance for the investigation of industrial and bio-polymers whose radicals intrinsically hav lona e g lifetime. Most modern pulse radiolysis equipment routinely deliver nanosecond pulses, and some of the older machines are now upgraded for doing this as well. These shorter pulses allo o studwt y unimolecular reactiona n i s new time domain e recenTh . t progress made becomes obvious wheo tw n investigations on the same topic are compared (e.g. the protonation of the adenosine radical anion by water), one published in 1981 [7] and one publishe n 198i d 7 [8]. e nanoseconTh d tim e smalleseth domait no t s i ntime-scal e thas ha t been reache n pulsi d e radiolysis studies n extensioA . o t n e dowth n i n picosecond rang bees eha n achieved some year [9]o t thiag s. A s time-scale "chemistry t tak" ye doee t placeno s t interestinbu , g phenomenae sucth s a h solvation of the electron can be studied. Computer-assisted data acquisition produces more data per unit time. Hence, experiments that wer time-consumino eto tacklee pase b th o g t n di are now possible. In former times, an experiment was done at "room temperature"; now, the temperature dependence of unimolecular processes can be measured with an acceptable effort. As a result much of the knowledge now taken for granted may have to be reinterpreted (e.g. Ref. [10,11]). With special constructions the temperature range may be extended o 200t [12C ° ] (see also pape G.Vy b r . Buxto n thii n s report). Conductometry. Although UV/VIS-spectroscop s ystilmosi e th l t widely used detection system conductometrie th , c method [13,14somn i y s ewa ha ]

14 meant a second break-through since it allows the detection, kinetic characterization and quantitation of charged intermediates and products. In principle, this method should also allow to study the kinetics of reactions that are not unimolecular in charged transients [15]. In this Institute, we make extensiv f thio se techniqueeus ; indee t dseemi s surprisin manw gho y t havye laboratorie et no thi so d s supplementarr believou o t e d an y indispensible facility. Light-scattering. e polymeth r Fo r e biochemischemisth d o an t wh t deals with biopolymers suc s DNAa h , detectio light-scatteriny b n g allows to measure strand breakage and crosslinking in the time-resolved mode. e introductioTh f low-angle-laser-light-scatterino n a considerabl s i g e improvemen f thio t s technique [16wild an ]l surely provid s witu e h data which can be interpreted more straight forwardly than the original method which measured light scattere ° [17]90 t .a d Often, -derived radicals undergo strand breakage. Provided that a polymer carries chared functions (e.g. poly(U) A [19[18]r o ]DN , hyaluronic acid [16]), strand breakag e followeb n ca econductometryy b d , sinc a numbee f o condenser d counter- e releasear s d froe th m polyelectrolyte upon strand breakage. Thus this technique supplements observations obtaine light-scatteriny b d g [20]. Polarography. Valuable informatio e redox-behaviouth n o n f freo r e radicals has been obtained by combining pulse radiolysis with polarography [21]interpretatioe Th . t alway date no th s a i f s no simpl e becaus numbea e r of parameters have to be considered [22]. Further developments of this method have been briefly reviewed [23]. Roman speciroscopy. The combination of pulse radiolysis and Raman spectroscop a relativel s i y fielw ne yd [24d onl]an y some comperatively simple systems have been investigated so far, e.g. Ref. [25-28]; cf. also pape R.Hy b r . Schule n thii r s report). However, this methoe d th wil n i l near future furnish an enormous set of Raman spectra of free radicals, and expecy ma e t thar knowledgon ou t e abou structure th t f suco e h short-lived intermediated wile considerablb l y increase n additio i de greath o tt ndea l f complementaro y information already gatherespectroscopyR ES y b d . ESR spectroscopy. The combination of the electron accelerator which produces frespectrometeR eES radicalse th r d theifo ran , r detectioa s ha n long tradition (e.g. Ref. [29-32] t globallbu ) y this techniqu s currentli e y available in less than five laboratories. As one might expect, it is quite tricky to shoot (charged) electrons through an ESR cuvette which is placed in a strong magnetic field. For this reason this technique is only used when other ways of generating free radicals within the ESR cavity fail. Such a situation may arise when strongly reducing radicals are generated by redox reactions. Then e radiolytith , c generatio e radical methoe th th f o ns i f s do choice. Even less frequen e facilitiear t s which allo e measuremenwth f o t ESR signals in the time-resolved mode, a technique which has yielded most valuable data (e.g. Ref. [33,34]; for a review see Ref. [35]). Fluorescence-detected magnetic resonance (FDMR). This methos i d not as genarally applicable as some of the other methods, but it has yielded

15 very valuable informatio n somo n e fundamantal processes occurine th n gi radiolysi f organio s c solvents (cf. Réf. [36-38]). Chemically-induced nuclear polarization (CIDNP).e CEDNth n I P method free radical e generatear s R dNM withi n e a cavitth nf o y spectrometer. Their selective decay o signalt s f enhanceo s d emission and absorption. Usuall e radicalth y e formear s d photolytically, e.g. wita h laser r thermallyo , alsn producee ca ob t bu , electroy db n beam irradiation. Since radiation techniques provide tools to produce some type of radical quite selectively [20] and in this respect is superior to other techniques, this method widens the spectrum of radicals which can be investigated. Thae CEDNth t P metho d pulsan d e radiolysis with opticad an l conductometric detectio givy enma complementary result t obtainablno s y eb either method alon s beeeha n shown hydratioe recentlcasth e th f e o r yfo n e acetyoth f l radical [39,40]. Pulse radiolysis combined with the rapid-mixing technique. In the case of radicals with a sufficiently long lifetime (> 1 ms), such as O^ (e.g. Ref. [41]) or radicals derived from polymers (e.g. DNA cf. Réf. [42]), it is possible to produce them by pulse radiolysis and subsequently (without negligible bimolecular decay) mix in a given substrate (even at high concentrations )t bee whicno ns subjectehha ionizine th o t d g radiation. This techniqu s yieldeha e d much informatio e reactivitth n o f nO^o y , whose reactions sometimes are not fast enough to be investigated by ordinary pulse radiolysis (for an example where this is still possible see Ref. [43]). This t exploitetechniquye s fult it lno o t dpotentias i ee real th f mo n i l . Some investigation e reactionth f o sf polynucleotido s e radicals with glutathione have give s alreadu n y valuable insight inte th o mechanism of the so-called chemical repair of [42]. An extensio f thio n s approach inte realth o f mradiatioo n biologs i y the rapid-lysis technique, [44] where living cell e irradiatear s y pulsb d e radiolysi enzymatie th d an s c repair reactions rapidly quenche a secon n di d step. Much of what we know about ultra-fast DNA repair reactions has been obtained with this technique [20]. In this contex e -implosioth t n technique shoul e mentionedb d . After a short pulse of ionizing radiation, anoxic cells are exposed to a burst of oxygen [45]. This techniqu s provideha e s witu d h most valuable data on the "oxygen effect" which is of major importance in radiobiology and cancer therapy [20].

3. Areas of research

e widelTh y hold belief (among outsiders) that radiation chemistrs i y a crude and undiscrimiriate method ("a shooting at sparrows with a tank gun") is certainly wrong. Over the past decades, radiation chemists have in particular develope radiolysie dth f aqueouo s s t whicsolutionar n ha o t s allow o generatt s e quite selectively almos conceivably an t e radical quite selectively [20] e solven.th Sincs i tt i ewate r which absorb e energyth s , absorption characteristic e soluteth f o ss whic importane har case th f eo n i t

16 photolytic generatio f radicalsno e irrelevantar , . Because th e yiel d th e an d nature of the radicals is practically independent of temperature, kinetic data obtainee b n ca d ove wida r e temperature range (which woul impossible db e y thermab l generatio f radicals)no . However onle th y, t watesolvenno s i r t for pulse radiolysis studies, and very interesting and far-reaching results are bling obtained in organic solvents (see e.g. papers by G. Freeman, A. Hummel and Y. Tabata in this report). Another misunderstanding prevailin n somi g e circle s i thas t pulse radiolysi s restrictei s e elucidatioth o t d f free-radicao n l reactions. This i s not so. In many cases the free-radical reactions are fast compared to the subsequent non-radical reactions o thas e followe, b e t th y both y ma b d above-mentioned detection systems (e.g. Ref . n als[46,47])e ca b o e Us . made of rapid oxidation of a radiation-induced radical by transition metal ions. This may lead to carbocations and related short-lived intermediates (e.g. Ref. [48-50]) e reactionth , f whico sn the e followedca b hn r Fo . example n intermediata , e postulate o e plaacid-catalyset d th a roly n i e d hydrolysis of ortho esters has been generated by such a technique [50]. Thus many problem f generao s l interes reaction i t n kinetice solveb n dca s in a straightforward manner, more easily than by any other technique. Inorganic chemists have realize r somdfo e tim e greath e t potentiaf o l pulse radiolysis in studying unusual oxidation states [6]. The solvated electron formed in the radiolysis of water is the strongest reductant availabl low-valend an e t metal iontheid an sr complexe e generateb n ca s d n homogeneoui s which otherwis n onl e produceca eb y e th t a d surface of an electrode. The pulse radiolysis also technique opens up the fielw f metalline o d c microaggregat e studth f theio yd an rs unexpected reactions. This is a recent development which is only starting to be explored (see e.g. . papeBellonJ y b r thin i i s report). Radiation chemists and radiation biologists know that our present concept n radiatioi s n biolog radiatiod an y n therap f canceo y e largelar r y based on results obtained with the pulse radiolysis technique [20]. For s followeanyonha o e literaturth dwh e n thii e s area ove e lasth rt decade it is obvious that enormous progress has been made in this field, and much more will be achieved in the near future. This, of course, also holds for such an important question as radiation protection. Less obvious than in the last mentioned area is the contribution of pulse radiolysi e environmentath o t s l sciences. Pulse f radiolysio e on s i s the finest tools to study the formation and the fate of peroxyl radicals in aqueous solutions (cf. Réf. [20], Chapter 4). These also play an important e degradatioth rol n i e f organio n c matter presen n drinking-watei t r upon ozonation (note for example, that in California in greater Los Angeles 15 million people are supplied with ozonated water). All the really reliable data e kinetic ensuine th th n f o o s g peroxyl radical reactions have been obtained by radiation techniques. A similar situation holds for some of the reactions occurring in acid rain (cf. Réf. [51-54]).

17 . Futur4 e trends

It is obvious that the aforementioned developments in pulse radiolysis have unlocke areaw f ne dresearco s e hmerelth w no where se e y w e beginning t otheBu . r development e alsar so expected. A cas e diffuse-reflectancn pointh i e s i t e method, which allowo t s undertake pulse radiolysis experiments with opaque samples. Although described already in 1984 [55] the potential of this method has not been explore furthery dan . This might eventually yield interesting resulte th n i s field of radiation biology and polymer sciences. With lasers more powerful than those used for it should be possible to photolyse radicals formed by pulse radiolysis. The photolytic products of the radicals may then be studied by any of the above-mentioned techniques photochemistre Th . f freyo e radical solution si n a woulver e yb d interesting e additiopresenth o t nt wide rangf o e possibilities. surm a e I tha e hart th wit dl woral h creativd an k e effort goinn i n go our field, further techniques are on the way to more then justify my opinium that pulse radiolysis has a famous past and a brilliant future, or as P. Wardman quoted it in his Weiss lecture: "Radiation chemistry is alive and well living in all areas where free radicals reside. Pulse radiolysis is now of age: let it put it to work" [56].

References

] [1 Buxton.G.V., Greenstcick,C.L., Helman,P.W., Ross,A.B., Critical revie f rato w e constants for reactions of hydrated electrons, hydrogen atoms and hydroxyl radicals (•OWO~ aqueoun i ) s solution . PhysJ . . Chem. Réf. Dat 7 (19881 a ) 513-886.

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Next page(s) lef1 t 2 blank NEW APPLICATIONS OF PULSE RADIOLYSIS GENERAN I L CHEMISTRY

A.K. PIKAEV, S.A. KABAKCHI, I.E. MAKAROV, A.V. GOGOLEV Institut f Physicaeo l Chemistry, Academy of Sciences of the USSR, Moscow, Union of Soviet Socialist Republics

Abstract The pulse radiolysis method is widely used not only for the stud primarf o y y radiolytical processese th alst r ,bu ofo solutio differenf no t problem generaf so l chemistry repore ,Th t is a short review of the new results obtained by us from the stud somf o y e application thif so s metho generan i d l chemistry. date kineticTh n ao fasf so t reaction hydrogef so n ionn si aqueous solutions including temperature dependenc reactiof eo n rate, reactivity of inorganic free radicals (SOT, HCU, Cig, COO etc.) towards ions of transition metals including ions of lanthanide actinided san aqueoun si s solution autooscilad san - tion processes in some irradiated systems (mainly in concen- trated aqueous solution halidef so alkalinf so alkalined ean - earth metals) are discussed»

1. INTRODUCTION At present the pulse radiolysis method is used mainly in two directions. It plays an important role in the study of primary chemical stages of radiolysis that is one of the main problem radiatiof so n chemistry secone .Th d directioe th s ni application of pulse radiolysis for the solution of different problem generaf so l chemistry (see e.g. Refs./î-S/). Kinetics of fast and superfast processes, properties of short-lived intermediate products of various inorganic and organic reac- tions etc. are studied by this method. It is widely applied investigatioe th r fo propertief no solvatef so d electrons, inorgani organid can c free radicals, anion-and cation-radicals, ions of metals in unusual oxidation states, carbanions and carbocations, excited states. The peculiarities of some physical-chemical processes: tunneling of electrons, transfer

23 of proton excitatiod san n energy, formatio colloidsf no , chemical induced dynamic electron polarization etc. are investigate dpulse th als ey o b radiolysi s method. The second direction is developed intensively by many researchers including the authors of the present review. Pulse radiolysin collaboratio(i s useu s i uses y db sr wa o d n with co-workers and colleagues) for the solution of the following problems of general chemistry; 1).reactivity of solvated electron differenn si t system meltn s (i alkalinf so e halides, concentrated alkaline methanol solutions etc.); 2) formation and properties of inorganic free radicals (SOT, (CïïS)ôj ClZ, HCU, CCÛ etc.); 3) formation and properties of ions of metals in unusual oxidation states (Tm(II), Pr(IV), Hg(I), Hg2(I), Pb(III), To(VI), U(III), Am(II), Am(IV) etc. aqueoun i ) s solutions reactivit) ;4 ionf yo uraniuf so transuraniud man m elements towards product watef so r radiolysis formatio) ;5 n and properties of organic free radicals and anion-radicals in wate ethyd ran l alcohol (free radicals from aromatic compounds, semireduced form rhodaminf so e dyes, free radical aniond san - radicals from spiropyran dyes etc.) generatio) ;6 properd nan - ties of aromatic carbanions in the solution; 7) kinetics of reaction hydrogef so n ion aqueoun si s solutions tunnelin) ;8 g of electrons in irradiated glassy alkaline ice and single crystals of alkaline halides; 9) generation of autooscillation processes and elucidation of their regularities. Some respec- tive result summarizee sar bookn di s /Î,â7 a*id review papers /2,3,5,8,10,117» In tiie Present review the data obtained in last years durin stude gth fasf yo t reaction hydrogef so n ions, reactivity of inorganic free radicals towards ions of transi- tion metal autooscillatiod san n processe somn si e irradiated aqueous system considerede sar .

EXPERIMENTA. 2 L

Two linear electron accélérâtors:U-12 and ELU-6 "Elektroni- ka n are used in our experiments. Their parameters are shown in Tabl. eI Two fast spectrophotometric set appliee sar d /8,10j7e .Th firs functione on tbasie th U-1 f sn o so 2 accelerator tims ;it e resolutio completels i yus1 t 0. .I s ni y automate meany db f so

24 Tabl Parameter. eI lineaf so r electron accelerators

Typ accef o e - Energy, Duration Maximum cur- Maximum dose lerator MeV of pulse,s rent in pulse, per pulse,Gy A

U-16 2(T 1 3x . 2 5 0.2 150 n Q Elektronika" 8 5x10- 15 20-30

microcomputer "Iskra-226". The automatization includes opera- tion of accelerator, photomultiplier, monochromator and light shutter, registration and accumulation of optical signal and data treatment e secon.Th d spectrophotometri functiont cse n so the basis of "Elektronika" accelerator; its time resolution is 5 ns. The detailpurificatioe th f so substancef no s usede ,th sample handling technique, the composition of solutions and the measurements are given in our above-mentioned publications. KINETIC. 3 REACTIONF SO HYDROGEF SO N IONS Three methods of determination of rate constants of H+ reactions were used /12-21/r firse i.Th t methoe bases th i d n o d S(ï study of the competition of processes (1) and (2) by micro- second pulse radiolysi tos i e compounS ( s d under study):

H ) 1 OH H aq +< a"q ~*° 2 " H+aq + S ——> Product (2) From the investigation of the competition it is possible to determine k^/kg values .knows i Sinc. value nk. eth /227f eo , from the ratio k^kg it is easy to obtain kg. The values of kg for some pH indicators and CrO, ions were determine thiy db s method (see TableH p case II)f th o e .n I indicators the optical density of the,solution at peak of optical absorption ban acif o d d indicatoH p for f mo r appeared as a result of reaction (2) was measured. In the case of reactions

Haq + Cr042~ —* HCrV <3>

25 + ——————Table II—« Rate constants of reactions of Haq ions

Solute k..s E , References

Pheno d re l (7.2*0.8)x1010 /Î2,13/ Bromophenol blue (1.6*0.2)x1010 /Î2,137 Bromothymol blue (8.8*0.9)x1010 0?hymol blue (alka- (1.0*0.2)x1011 /Î97 line form) CrO, 11 4 (3.1*0.4)x10 /Ï47 (3»0*0.1)x1011 /Î77 97x. 2 1 1 1O /217 HPO2- (I.8±0.2)x1011 /Î57 B(OH)- (1.4*0.2)x1011 /Î8/ MoO2" (2.6±0.4)x1010 /Î67

the decrease of optical density of the solution at peak of optical absorption, bandeters CrOf wa do ) .- nm 0 (i.e37 Ot .a mined« The second metho similas firsi de th to rt bases one i t d.I competitioe stude th o nth f yo reactionf no s (1)-(3 microy )b - second pulse radiolysis. This method was used to find the 2 2 values of k2 for HPO^ ^, B(OH)4~, MoO^ " and thymol blue (alka- line form). The values obtained are shown in Table II. The third method is direct. It was used for the determinati- on of k~. Its value was measured by nanosecond pulse radio- lysis directly from kinetics of the decrease of optical absorption of the solution at 370 nm after electron pulse. To calculate the value of k., from such data the computer ES-1060 was applied with usin prograe gth m pack "KINETIC" /217e .Th mechanism including 49 reactions was treated. It was found descriptioe th thar fo t kineticf no s sufficientli t si o t y

26 take into account only reactions (1), (3)-(6):

HCrO- —*> H+q + Cro|~, (4)

—*• H20 4- CrOj-, (5)

) (6 Hlq + OC..

The obtained value of ko is presented in Table II» It is seen that this valu value closs eth i eo et determinee th y db competition method. The consideration of the results obtained on the basis of the theor diffusion-limitef o y d reactions, developen i d paper /23/, shows thatheore th t y describe experimentae sth l dat case a th onle n wheyi n anions reacting with H* havo en aq any effect on the structure of water and their diffusion may be presente motioa s da chargef no d sphere isotropin si c medium aniof .I n occupie cavitiee sth waten si r structurr eo forms the substitution solution, the distance between reacting species when reaction occurs (i.e. reaction radius) is more than Onsager's radiu 1.5-2.y s(b HS~5, times)F~ ,. ~ .OH - ?- ?- ?— a^- B (OH)., HPCn , SCT and CrOT belong to such anions. To explain this phenomeno possibls i t ni proposo et e eth hypothesis base multiproton o d n transfer /24/ reactioe «Th n of H* with structuring anions consists of two stages. At the " + first stage ETa_q as a result of random motion approaches the microregion structure aniony db secone .Th d multi e stagth s -ei proton transfer insid microregione eth thin .I s case anion reacts not with proton approaching the microregion but with neighboring prot'on. In our opinion, this hypothesis may be tested by the study of temperature dependenc ratf eo e constan reactiof o t n between H"taq_ and any anion structuring water. According to the proposed hypothesis, apparent activation energy A B of the reaction is the sum: ) (7 , E

where E-^ is activation energy of the first stage limited by diffusion (it is equal to activation energy of self-diffusion of water activatios i Ed )an n chemicae energth f yo l reaction

itself structure .Th & hydrogef eo n bond weakenes si d with

27 increasing the temperature. It causes the decrease of probabi lit multiprotof o y n transfer, i.epossibls i .t i e s thai tB a negative. Moreover, it should lead to that à E < ED. We studie temperature th d e dependenc ratf eo e constanf to reaction (3) by means of nanosecond pulse radiolysis /20/. The values of k~ were determined from the curves of dependen- ceopticaf o s l densit resula s a f yo ta m decreas 0 37 t ea reactio timn o temperaturet ea ) (3 n s 278-32face Th t . 3thaK t reaction (3) is reversible was taken into account. The data obtaine e showdar n Arrbeniuni s coordinate n Figi s . 1 (kp o ^-B

the rate constant of reaction (3) at 293 K~and kT is the rate constant at given temperature). The value of A E is 8«4+1*0 kj/mole. It coincides within the range of experimental errors . o— with apparent activation energ reactiof yo 30+ ^ T nH measured in work /257. Pig. 1 shows also the temperature dependenc relative th f o e e coefficien watef to r self-

diffusion Vy/V2Q (D2Q is the coefficient at 293 K and DT coefficiene th s i givet ta n temperature) plottebasie th sn do of literature coefficienvaluee th f so t /26, 277. This dependence withi temperature nth e rang 273-32f eo nons i - 3K linear; activation energy of water self-diffusion within this

0 A LHCI],M 8 Fig.1. temperature dependences of relative rate constant of reaction 3(1 relativd )an e coefficien watef o t r self- diffusion (2).

28 rang changes ei d from 22.818.8o t 1 4 kJ/mole maid ,an n change takes place within the range of 273-285 K. It is possible to

regard that at temperatures higher than 285 K (to <-> 470 K) ED« 18.84 kJ/mole. Therefore, apparent activation energie reactionf so s , 2- 2- between HI„ and structuring anions SO, and CrOA are less | &\ *r *r than activation energy of water self-diffusion. Using the

values 4E, E,, and equation (7) we obtain that E& is negative and equal approximately to -10 kJ/mole. The negative value of activation experimentae energth s i y l r hypothesiprooou f fo s multiprotoe oth n n transfer mechanis aucf mo h H+ reactions. Hence experimentae ,th l data presente d discussedan n di this review show clearly that pulse radiolysis method allows to study successfully the fine kinetic effects not only in reaction fref so e radicals, ion-radical d excitesan d species but als reactionn i o stablf o s e species suc hydroges a h n ions.

REACTIVIT. 4 INORGANIF YO C FREE RADICALS TOWARDS IONS OF TRANSITION METALS IN AQUEOUS SOLUTIONS The dat reactivitn ao inorganif o y c free radicals towards ions of transition metals in aqueous solutions are of interest for radiation chemistry, photochemistry, , and . In the present review the results obtained durin stude gth reactivitf o y S07f yo , NO.,, Gig, Brg ,d CO 3-2an Z towards ion transitiof so n metaln si aqueous solution meany sb pulsf so e radiolysis method /2S-397 are shortly summarized. Respective literature data published befor investigatior eou n were collecte papen i d r /40_7. Free radicals were produce reactiona dvi solutef so s with primary products of water radiolysis and/or as a result of the direct action of ionizing radiation on solutes. As a rule, bimolecular rate constants were determined from the dependences of respective rate constant pseudo-firsf so t order reactions on concentratio metaf no l ions. With, this purpos time eth e variatio opticaf no l densitsolutioe th f yo n withi opticae nth l absorption band of free radical was measured. In some casas (e.g. in cases of Eu(II), Sm(II) and Yb(II)) the rate constants were calculate meany db computef so r simulatio radiolyticaf no l processes in the system.

29 fable III» Rate constants of reactions of SO"

Ion Medium k, M~1s""1 9 Ag(I) 2M H2S04 (3.6±0.7)x10

1.8 M MgSO,+0.4 2 M HC10.4 8 Ce(III) 2-10 M H2S04 (I.6±0.2)x10 HgSO,M 8 ^0. (2.0Î0.2)x109 7 Mh(II) 2-10 M H2S04 (I.6±0.2)x10 9 Mo(CK)^" 1 M LiC104 (3.oio.3)x10 Hp (III) 3 M H2S04

ffp(V) H2M 2 S04 i 9 Pd(II) HM 2 S04 4 (L5 0.2)x10

Pu(III) H5M 2 S04 8 Sb(III) 2-10 M H2S04 (8*0-0. 6)x10 a 7 + U(IV) 1.8 M H2S04 i 8 V(III) 2 M H2S04 (1.3 0.2)x10 V(IV) 2 M HgSO^, (3.3io.6)x106 7 V(IV) HM 2 S07 4 (I.8±0.2)x10 value ratTh f eo a e constant depend U(IVn so ) concentration, solutionM ïhi0 1 sr .valufo s ei

Tables III-VI shovaluee wth ratf so e constant typicaf so l reactions "between inorganic free radicals and ions of transition metals in aqueous solutions. The reactivity of free radicals towards ions of transition metals depends basically on different factors: the value of free energy of reaction (or difference's0 of redox potentials of reacting species), electrostatic interac- tion "between reagents change ,th structurf o e d compositioean n of reacting and forming ions, the formation of complexes etc. However, it is possible to make several general conclusions on the reactivit ionf o y s under consideration.

30 Tabl Rat. eIV e constant reactionf so , NO f so

Ion Medium s kM ,

i 9 Ag(l) 2-7 M HHÛ3 (1.9 0.3)x10 Affl(V) HÜTOM 5 - 2. (2.5-0.3)x108 6 Ce (III) 2-3 M HN03 (1.2io.2)x10 9 Fe(CN)£- JtfaN0M 3 3 (5.0±0.5)x10

Mn(II) 3 M HN03 (I.5±0.3)x10 6 Mn(II) HN0M 9 3 (2.2io.4)x10 6 Mn(II) 12 M HN03 (4.0-0.6)x10 8 Hp(V) HN0M 35 1- (8.oio.8)x10 9 Pd(II) 1 M HH03 (L5-0.2)x10 Pd(II) 6 M MÛ. (1.2io.15)x109 8 Pd(II) 9-1 HN0M 2 3 (9.oii.o)xio i 8 Pu(III) 2 M HI03 (2.5 0.3)x10 i 7 T1(I) HN0M 39 3- (3.7 0.7)x10 V(IV) 3 M HDTO- (6.6±1.0)x106 7 V(IV) 9 M HN03 (2.2io.2)x10

Firstly, if for reactions occuring via mechanism of outer- sphere electron transfe difference rth e AE sufficientlys °i - high (ca. 2.3 V and higher), the rate of such reactions is limited by diffusion or is close to this limit. Reactions: Ag(I) + S0~, Hp(III) + SO^, U(V) + Clg, Yl3(II) + Br~ etc.- belong to such processes. This conclusio valit reactionr no dfo s ni s havin complega x mechanism exampler reactior .Fo fo ° ,AE n vers i U(IV yT SO ) + high; however, its rate is comparatively low. The possible reasons were the formation of sulphate complexes of U(IV) in sulphuric acid medium whicn ,i rate hth e constan measureds twa , structure change anth th d f o e uraniuf o e durinn mio g oxidation of U(IV) to U(V).

31 Table V. Rate constants of reactions of halide ion-radicals

Ion Radical Medium k,M-V1

9 Bu(II) C1 0.3 EuGlM 3 1 3+0.HC M 1 6x10 i 9 Bu(II) Br2 0.3 EuClM 3 r 3+Û.KB M 1 2. 5x1 O 7 Bu(II) I ÎTaClM 9 OI 0. ,+0.K M 1 9x10 2 4 J?e(CîO£~ ci- NaCM 1 l (I.0±0.2)x109 Fe(CN)^"* ClJ 1 M HC1 (6.2il.0)x107 7 Pe(CH)4- Br2 1 M KBr (6.0±0.6)x10 Fe(CïOg- I~ 0.8 M KI (3.oio.5)x107 7 Mo(GN)*- Br2 1 M KBr (I.2io.1)x10 JSTp(III) ci- 1 M HC1 (I.6io.1)x109 Up (III) Br~ r HB M 1 (I.1-0.1)x108 6 Np(III) I2 0.9 M HC104+0.1 M Nal (5.0±0.5)x10 Np(V) ci- 1 M HC1 (3-1i0.6)x106 7 Np(V) C12 3 M HC1 (I.lio.2)x10 Pu(III) ci- 1 M HC1 (3.0±0.3)x107 8 Pu(III) C1i 3 M HC1 (1.2±0.2)x10 6 Pu(III) Br2 1 M HBr (I.6io.3)x10 10 Sm(II) iji ^"\ 0.9 M HaCl04+0.1 M KBr 1.1x10 9 Sm(II) I2 0.9 M NaClO +0.1 M KI 9x1 0 9 U(III) I2 HG10M 9 I 40. +0.K M 1 1.2x1 O U(V) ci- UO.-CCIOJv'-O.M 1 0. M I 9 0 1 HC14x + C. C ^f + 0.7 M HC104 9 Yb(II) Br" 0.9 M UaCl04+0.1 M KBr 9x10 9 Yb(II) I2 0.9 M NaCl04+0.1 M KI 8x10

32 Tabl . RateVI e constant reactionf so " CO f so

Ion Medium k, M""1 s"1

Am(III) 3 M K2CÛ3 (2.5±0.3W 7 Am(III) KM 2 CÛ6 3 d^iooJxio Ce(III) G0 (4.3i0.5)x107 0.75 M K2 3 7 Ce (III) 3 M K2C03 (9.oii.o)xio NaM C05 0. (5«oio.5)x108 Q 2 3 A ^ i 7 KHC0M 1 3 (6.5 0.7)x10 ± 9 Np(III) 1 M K2C03 (3.3 0.4)x10 9 Np (III) 3 M K2C03 (1.4^0. 2 )x10 7 Np(V) 0.5 M ÏÏa2C03+0.2 M HaOH (1 ,8-0.2)x10 7 Hp(V) HaM 2 C05 0. 3 NaO+M 1 H (4.4±0.5)x10 5 Hp (VI) NaM 2 C05 0. 3+0. NaO5H H ^ 9x1 O 8 Pu(III) 1 . 1 M K2C03 (5.6±0.6)x10 Pu(III) 4.3 M KgCO^ (6:7io.7)x108

Secondly rate reactionth f o e f ,i t limite no diffusions y si d"b , it depends ofte redon no x potential fres R/R~f i so eR "( radical) and respective pairs of metal ions. In many cases reactivity of

free radicals has the following order: SOT > ^03^ C12 > Br2 > Ig. For example, it is distinctly seen for reactions of Np(III) and Pu(III). The illustration of the influence of redox potentials of pair metaf so lrate reactionionf th eo s si Hp(III)f so , Pu(III) and Am(III) with ion-radical COO; it decreases with an increase of this potential. Thirdly structure th f ,i metaf eo l ions (and also free radi- cals reacting with them similars )i , thereactionsr nfo , whose limitet ratno s diffusiony ei db , therlineaa s ei r dependence of logarith ratf o m e constan differencn o t redof eo x potentials of reacting species. Such dependences were obtaine reactionr fo d s

33 0 t,jus

Pig.2.Dependence of logarithms of rate constants of reactions of ~ (1), Mo(CN)J'8 " (2), Eu(II) (3), Up(IIId an ) )(4 Pu(III) (5) with Gig (a), BrJ 0>) and Ig (c) on differences of redox potentials of reacting species.

-1000/T , K

Fig.3«Dependences of logarithms of rate constants of reactions of Ce(III) (1), V(III) (2), Co(II) (3), Ti(III) (4), Mn(II) (5), Pu(III) (6) and Pe(II) (7) with Cl~ on HOI concentration

34 of Bu(II), Np(III), Pu(III) and cyanide complexes of Fe(II) and Mo(I?) with Gig, Brg and l£ (see Fig.2). Analogous dependence observes wa reactionr fo d Ce(III)f so , Pu(III Am(IIId )an ) with COO. However value ,th ratf o e e constan reactiof o t n Hp(III)+ COo s outsiddependenc"e i th f o e e (obviously rate thif ,th o e s reactio controlles ni diffusion)y db . Fourthly, there is a noticeable influence of the formation of complexe reactivite th n so metaf yo l ions exampler .Fo rate ,th e of reactions of Fe(II), Mn(II), Co(II), V(III), Ti(III), Ce(III), Np(V) and Pu(III) with Gig depends considerably on concentration of Cl~ ions in the solution because of the formation of inner- sphere complexes (see Fig.3)« Fifthly, on the basis of data obtained it is possible to estimate redox potentials E° for S0~/S0?~ and NO^/NO" pairs. Radical SOT reacts with Ag(I) and 11(1) with rates close to the diffusion NO r limitfo , suct ,bu h high rat observes ei d only for reactions with Ag(II)/Ag(IAg(I)r fo value e ° .E Th f so d )an respectively, V T1(II)/T1(I2 2. d an 9 .equae 1. )Thus ar o lt , thvalu° eB NOyiTOr efo lV (probably pai2 closs 2. ri o 3 et ,2. valu° E S0~/so| r e efo th d mucs ~i an h, higherV) .

5.AUTOOSCILLATION PROCESSES IN IRRADIATED AQUEOUS SOLUTIONS importane th Onf o e t problem moderf so n physical chemistry elucidatioe th s i peculiaritief no autooscillatiof so n processes in homogeneous systems. The number of such systems is not much. We obtained the occurrence of autooscillation processe somn si e irradiated aqueous solutions /41-447e .Th applicatio pulsf no e radiolysi stude th thesf o yr sfo e processes vers i y effective pulse . Th ionizin f eo g radiation generates the required amount reactinf so g components during compara- tively short timalmosd ean t uniformle th bula f n o kyi solution and pulse radiolysis allows to carry out the direct observatio variatione th f no concentrationf so reactiof so n products. It was found that in concentrated aqueous solutions of halides of alkaline and alkaline-earth elements the autooscil- lations of XÔ concentration (X is halogen) were observed after

35 A X 8 v O ~

?

6 0 0.6 1.6 AE°,V

Fig.4. Formatio decad n an product f o y radiolysif so saturatef so d

aqueous solutio MgClf no aqueouM 25 (1-39* sd )an solutio n of LiCl (1'-3') after microsecond puls electronsf eo ; rn "~ 1 1 '• rn "" o o t • «"" _^^> C13 - 1,1, 012 - 2,2 , eaq - 3,3 .

the actio electrof no n pulseillustrates i t .I Fig.4y db , where autooscillation Clf so Z optical absorptio concentraten ni d aqueous solution LiC f MgCld so lshowne an ar 2 . Trihalidn eio X7 is one of three forms of "active halogen" which are in equilibrium: HOX H X (8) X" aaaq + " The formatio Xf Ôno occurs during millisecond reactionsa svi : OH + X™— -*- HOX~, (9)

HOX" H20 (10) X X" (11) HOX" X" OH (12)

d. *2 L3 (13) The further periodical variation of XI concentration is accompanied by decrease of its average concentration to the level determined by composition of the solution and occurs, obviously, with participation of .

36 Table VII. Period oscillationf so concentratioC s Bi ( f Oo n bromidn i e solutions after electron pulsd ean during permanent action of xenon lamp light

Bromide A^y,, M s> T Without light filter With light filter (250< X<370 nm) LiBr 12.3 60 300 LiBr 11.1 68 360

SrBr2 6.8 70 -

BaBr2 5.8 90 120 KBr 4.6 100 100

The autooscillations of XÔ concentration after the action of electron pulse were observed in saturated aqueous solutions of

LiCl, RbCl, MgOlg, CaCl2, LiBr, KBr, SrBr2, BaBrCsld an .I 2,K The period of oscillations depends on the nature of halide, the concentration of the solution and the intensity of light that is used for the registration of X7. The data obtained in the case of bromide solutions are shown as an example in Table VII. actioe Th necessart lighf appearancno e no th s ti r yfo f o e oscillations; however, it promotes considerably their stabiliza- tion (especially in solutions of bromides and iodides) because of more effective transformation of "active halogen" into hydrogen peroxide and vice versa. The action of ionizing radiation causes also the oscillation processes connected with mutual transitions of some forms of complex organic compounds in the solution. Such transitions were studiesolutione th n i d peroxidasf so e /44/» Puls gammad ean - irradiation of diluted aqueous solutions of peroxidase from horse-radish roots to the formation of oxygenated forms of this enzyme, whose concentration changee sar d periodically during several minutes.

37 REFERENCES

[\J PIKAEV, A.K., KABAKCHI, S.A., MàKAROV, I.E., ERSHOV, B.G., Pulse Radiolysis Applications ajiIt d , Atomizdat, Moscow (1980 Russian.)n )(i . / PIKASV/2 , A.K., Pulse radiolysi applications it d san , Vestnik m SSSR 1(1977. )54 /3/ PIKAEV, A.K. "Puise radiolysis in ", Physical Chemistry. Modern Problems (KOLOTYRKIN, Ya.M., Ed.), Khimiya, Moscow (1980) 121-158. / BUXTON"/4 , G.V., SELLERS, R.M. radiatioe ,Th n chemistr metaf o y l ions in aqueous solution, Coordination Chem.Rev. 22 (1977) 195. / PIKA.EV/5 , A.K., Applicatio pulsf no e radiolysi inorganin si c chemistry, Zfl-Mitteilunge a (1981n43 . )9 / BU2TON/6 , G.V., "Applicatio watef no r radiolysi inorganin si c chemistry" Stude ,Th Pasf o y t Processe Transiend san t Species by Elecyron Pulse Radiolysis (Proc.NATO Adv.Study Inst. Capri, 1981) (BAXEEDALE, J.H., BUSI, P., Eds.), D.Reidel Publ.Co., Dordrecht (1982) 267-288. /7/ SWALLOW, A.J., "Application of pulse radiolysis to the study of aqueous organic systems", The Study of Past Processes and Transient Species "by Electron Pulse Radiolysis (Proc. NATO Adv. Study Inst. Capri, 1981) (BAXENDALE, J.H., BUSI, P., Eds.), D.Reidel Publ. Co., Dordrecht (1982) 289-315. / PIKAEV/8 , A.K., Applicatio pulsf no e radiolysi generan si l chemistry, Khim.Vys.Energ. 17 (1983) 195. /9/ PIKAEV, A.K., SHILOV, V.P., SPITSYN, V.l., Radiolysif so Aqueous Solutions of Lanthanides and Actinides, Hauka, Moscow (1983 Russian)n )(i . /Ï0_7 PIKAEV, A.K., Modern trends in theoretical radiation chemistry, Khim.Vys.Energ (19859 .1 ) 196. /Î1/ PIKAEV, A.K., ERSHOV, B.G., MAKAROV, I.E., Influence th f eo nature of a matrix on the reactivity of electrons in irradiated systems, J.Phys.Chem (19759 .7 ) 3025. /Î2/ KABAKCHI, S.A., ZAWSOKHOVA, A.A., PIKAEV, A.K., Determina- tio ratf no e constant reactionf so hydrogef so n ions with pH-indicator aqueoun si s solution pulsy sb e radiolysis method, Dokl.AN SSS1 (1976R23 ) 653.

38 /î 37 PIKAEV, A.K., KABAKCHI, S.A., ZANSOKHOVA, A.A., Yields and reactions of hydrogen ions in radiolysis of water and aqueous solutions, Faraday Disc.Chem.Soc. 63 (1977) 112. fitj PIKABV, A.K., KABAKCHI, S.A., ZANSOKHOVA, A.A., Kinetics of reactions and yields of hydrogen ions from pulse radiolysis of aqueous solutions of potassium chromâte, Radiât.Phys.and Chem. 16 (1980) 125. /ï§7 ZANSOKHOVA, A.A., KABAKCHI, S.A., PIKAEV, A.K., Determination of rate constan reactiof to HPCr+ aqueoun i nTH s solution4. s P— by pulse radiolysis method, Khim.Vys.Energ. 16 (1982) 21. /Ï6/ KABAKCHI, S.A., ZANSOKHOVA, A.A., PIKAEV, A.K., The study of proton transfer in aqueous solution of mixture of molybdate and chromate, Khim.Vys.Energ. 17 (1983) 406. CM] ZANSOKHOVA, A.A., KABAKCHI, S.A., PIKAEV, A.K., Direct determi- natio ratf no e constan reactiof to hydrogef no n ions with chromate ion aqueoun si s solutio nanosecony nb d pulse radioly- sis, Khim.Vys.Energ (19837 .1 ) 503. /Ï8/ KABAKCHI, S.A., PIKAEV, A.K., On rate constants of reactions of hydrogen ions in aqueous solution, Dokl.AN SSSR 275 (1984) 106. /Ï97 KABAKCHI, S.A., ZANSOKHOVA, A.A., PIKAEV, A.K., Applicatiof no pH-indicators for the study of formation of hydroxyl ions from pulse radiolysi aqueouf so s solutions, Khim.Vys.Energ8 .1 (1984) 379. /20/ KABAKCHI, S.A., LEBEDEVA, I.E., PIKAEV, A.K., The study of influence of temperature on kinetics of reaction of hydrogen ions with chromate ion aqueoun si s solution pulsy sb e radioly- sis method, Dokl.AN SSSR 297 (198?) 883. /21/ BUGAENKO, V.L., KABAKCHI, S.A., ZANSOKHOVA, A.A., PIKAEV, A.K., Application of program pack KINETIC for description of reaction hydrogef so hydroxyd nan l ions during radiolysif so aqueous solutions of pH-indicators, Khim.Vys.Energ. 23 (1989) 9. /527 EIGEN KURTZE, ,M Reactionsmechanismum Zu TAMM, ,G. , ,E. r sde Ultraschallabsorptio wässrigen ni n Electrolytlösungen. ,Z Electrochem (19537 .5 ) 103. ^237 HONG, K.M., NOOLANDI, «T., Solution of the Smoluchowski equation with a Coulomb potential. II. Application of fluores- cence quenching, J.Chem.Phys (19788 .6 ) 5172.

39 /24/ SCHREINER, S., Theoretical studies of proton transfers, Ace. Chem.Res, 18 (1985) 174- /25/ COHEÏJ WEISSj, ,B. , Picosecon,S. d kinetic reactiof so n E^0+ + So| HSO- ~HgO—» J+ , J.Phys.Chem (19860 .9 ) 6275. /267 LUCK, W.A.P., DITTER Approximat, ,1. e method determininr sfo g the structure of HgO and HOD using near-, J.Phys.Chem (19704 .7 ) 3687. /277-GILLEN, K.T., DOUGLASS, B.C., HOCH, M.J.R., Self-diffusion in liquid water to -31°C, J.Chem.Phys. 57 (1972) 5117. /287 GOGOLEV, A.V., MAKAROV, I.E., PIKAEV, A,K., Pulse radiolysis of concentrated hydrochloric acid, Khim.Vys.Energ. 18 (1984) 496. /297 GOGOLEV, A.V., MAKAROV, I.E., PIKAEV, A.K., The study of reactivity of Cl£ towards aqua-and chlorocomplexes of Co(II), Pe(II) and Mn(II) in aqueous solutions by pulse radiolysis method, Izv.AN SSSR. Ser.khim. (1984) 1419. /307 GOGOLEV, A.V., MAKAROV, I.E., PIKAEV, A.K., The study of Brreactivitd ^an g towardGi f o ys vanadyl ion aqueoun si s solution pulsy s"b e radiolysis method, lav,AN SSSR. Ser.khim. (1985) 690. /3l7 GOGOLEV, A.V., SHILOV, V.P., PEDOSEEV, A.M., PIKAEV, A.K., The study of reactivity of neptunoyl ions towards inorganic free radical pulsy sb e radiolysis method, Izv.AW SSSR. Ser. khim. (1986) 456. /327 GOGOLEV, A.V., MAKAROV, I.E., PEDOSEEV, A.M., PIKAEV, A.K., Reactivit ITOf HSOd yo an ^ , radicals towards ion transitiof so n metal aqueoun si s solutions, Khim.Vys.Energ (19860 2 . ) 298. /33/ GOGOLEV,,A.V., SHILOV, V.P., FEDOSEEV, A.M., MAKAROV, I.E., PIKAEV, A.K., The study of reactivity of lanthanide and actinide ion lowen si r oxidation states towards Cl^, d Bran g 10 radical-ions in aqueous solutions by pulse radiolysis method, Izv.Aïï SSSR. Ser.khim. (1987) 1248. /34/ GOGOLEV, A.V., FEDOSEEV, A.M., PIKAEV, A.K., Reactivitf o y inorganic free radicals towards plutonium (III) in aqueous solutions, Khim.Vys.Energ. 21 (1987) 478. /35/ GOGOLEV, A.V., MAKAROV, I.E., PIKAEV, A.K., "Reactivitf o y inorganic free radicals towards ions of transition metals in aqueous solutions. Pulse radiolysis study", Proc.oth Tihany Symposium on Radiation Chemistry (Balatonczeplak, 1986)

40 (Hedvig, P., Nyikos, L., Schiller, R., Eds.), Akad.Kiado, Budapest (198?) 161-166. /36/ GOGOLEV, A.?., SHILOV, V.P., PIKAEV, A.K., She studf o y kinetics of palladium(II) oxidation by inorganic free radicals in acid aqueous solution pulsy sb e radiolysis method, Izv. AIT SSSR, Ser.khim. (1988) 1001. /37/ GOGOLEV, A.V., SHILOV, V.P., PIKAEV, A.K., Radiolysif so neptunium(VI) carbonate solutions, Izv.AKT SSSR. Ser.khim. (1989 press)n )(i . /38_7 GOGOLEV, A.V., SHILOV, V.P., PIKAEV, A.K. stude ,Th reacf yo - tio ozonidf no e ions with neptunium(VI) ion alkalinn si e aqueous solution pulsy sb e radiolysis method, Radiokhimiya 31 (1989) (in press). /39/ GOGOLEV, A.V., FEDOSEEV, A.M., M/LKAROV, I.E., PIKAEV, A.K., The study of reactivity of inorganic free radicals towards ferrocyanide and octacyanomolybdate ions in aqueoua solutions by pulse radiolysis method, Khim.Vys.Energ. 23 (1989) (in press). /40/ ROSS, A.B., HEIA Rat, ,P. e Constant Reactionr sfo Inorgaf so - nic Radical Aqueoun si s Solutions, HSRDS-WB HBS, S65 , ?/ashington (1979). /4l7 GRIGOR'EV, A.B., MAKAROV, I.E., PIKAEV, A.K., On concentra- tion oscillation productf so radiolysif so concentratef so d

solution MgClf so 2, Izv.AN SSSR. Ser.khim. (1981) 2654» GRIGOR'EV, A.E., MAKARÛV, I.E., PIKAEV, A.K., Concentration oscillations in aqueous solutions of MgClg initiated by the actio ionizinf no g radiatio lightd nan , Dokl.AH SSSR 2?6 (1984) 625. /43/ GRIGOR'EV, A.B., MAKAROV, I.E., PIKAEV, A.K., Concentration oscillation brominf so irradiaten ei d aqueous solutionf so bromides, Izv.AU SSSR. Ser.khim. (1985) 1919. /44/ MAKAREffKOVA, I.I., GOGOLEV, A.V., MAKAROV, I.E., PIKAEV, A.K., Concentration oscillations during radiolysis of aqueous solutions of peroxidase from horse-radish roots, Izv.AN SSSR. Ser.khim. (1989) 212.

Next page(s) left blank 41 FROM RADIATION CHEMISTR ENERGETICO YT S VIA PHOTOELECTROCHEMISTRY - ELECTRONS AND HYDROGEN ATOMS IN LIQUIDS

R. SCHILLER Central Research Institute for Physics, Budapest, Hungary

Abstract

The interrelation between radiation chemistry and photoelectrochemistr demonstrates i y y severadb l examples. The studies of electron injection into liquids by illuminating metal cathodes render informatio n o nexces s electron energies n electroo , n thermalization, transport and reactivity. Atomic hydrogee b injecte n ca n d e intaqueouth o s phase throug e illuminatiohth tungstef no n bronze cathodes immersed into acid solutions n e A outloo.th f o k relevanc f etheso d similaean r processe n o lighs t energy conversion is given.

1. INTRODUCTION mose th t f o importan e On t services radiation chemistry has rendered to chemistry as a whole is the discovery and description of a number of short-lived entities. Excess electron hydroged san n atoms plaa y central role in this respect. The optical, thermodynamic and transport properties of these basic species have been studied in much detail, the kinetics of their numerous reactions have been quantitatively describe weld an dl understood. Important as these achievements are the impact they have mad n eo chemistr n generayi l e seemb o st somewha maie th tn limitedf o reason e r thiOn .sfo s lies wit e intricathth expensivd ean e instrumentation of contemporary radiation chemistry. Short pulse length accelerators with high time resolution detecting systems, having reache sub-picosecone th d d rang y noweb , demand both lavish financial support and specially trained staff. Althoug s beeha nt i h realised that laser photochemistry can well complement pulse radiolysis, photochemical methods are necessarily specific, being limitee rangeth o t ds of optical absorption. In this report some result f o solvates d electro d hydrogenan n atom experiment reviewee sar d which were achieved by a fairly general, simple yet physically exact method called photoelectrochemistry. The gist of the method is an interfacial phenomenon. A metal or semiconductor electrode is immersed into a liquid, a voltage is applied between the two phases and the interface is illuminated. As a result of this charge carriers travers the interface. In the conceptually simples sucf o th experiments, whera e metal cathod s i illuminatede , electrone b n ca s

43 injected e liquidintth o , excess electron processes can be studied. The instrumentation of a standard electrochemical arisimpla d e optical laborators i y sufficien measurementr fo t thif so s kind. Despite its obvious financial advantages over large accelerator laboratories we do not want to creat e th false e impression that photoelectro- chemistry is just the poor man's radiation chemistry. There are certain processes which can be elucidatede •through photoelectrochemical studies. And, perhaps more important, photoelectrochemistry has some direct relevance to the contemporary problems of energy transformation and storage. 2. ELECTRON INJECTION INTO NONPOLAR LIQUIDS Photoemission of electrons from metal into vacuum has been a process well known for about a century e logica.Th l extensio thif no s phenomenos ni the photoinjection of electrons from metals into insulating liquids. Similarl vacuuo t y m photoemission measurements the analysis of the photocurrent as a functio f nwavelengto h determinenableo t e on se eth minimum energy needed for an electron to be transferred from the metal into the liquid. That quantit calles i y d work function. ,W From the point of view of electron chemistry mose th t f o importan e on t parameter e energth f s o i sy the excess electron in the liquid prior of solvation y rearrangemenoan r e liquith f to d phase.e th Thi s si e conductiobottoth f mo e nunperturbeth banf o d d liquid ,e worV0Th .k functio a metal/vacuu t a n m interface metal/liquia d tha an t ta , ,Wv d interface, Wi, gives a > sVe Vo = Wl - Wv . (1) l It is easy to see that V0, as given by eq.(l), is independene th e d metanaturth an f o l ef o t characterizes the electron-liquid interaction only. A series of experiments on liquid rare gases hydrocarbond an s have show ne d sigth an than y tb magnitude of V0 one can well predict the mobilities, radiation chemical yield d chemicasan l reactivities of excess electrons. Photochemical methods can also be used for the determination of V0 it is, however, impossibl o eobtait n thiparametey ke s y makinb r g exclusiv f higo he eus energ y radiation. Thibees sha n mose th t f o strikin e on g example e problemth f o s s launched by radiation chemical observations which were solved, however, through photoelectrochemical methods. These and related questions are reviewed e.gRefsn i . . [1,2].

3. ELECTRON INJECTION INTO WATER firse Th t experimen thin ti s field precedee th d discovere electroth f y o moryb n e than hala f century n i :183 9. BecquereE l observed thate h s ,a

44 illuminated one of two identical electrodes immersed into a dilute acid, electric current flowed across the cell. This early observatio photoelectroa f no - chemical effect was followed by extensive research into these phenomena. The great inherent interest in e probleth m notwithstanding cleas i rt ,i that this area of research obtained large impetus from the discovery of the hydrated electron. May we here refer to some reviews [3-6].

METAL ELECTROLYTE

FIG.1. Scheme of electron injection into water.

Our present day picture on electron photo- injection from metal int n aqueouoa s solutioe du s i n to Barker [7] and is summarized in Fig. 1. A photon, if its energy h is higher than a certain limiting value, can eject an electron from the metal and make it enter the aqueous phase. The electron usually has some kinetic energy t morno ,e than severa, eV l becaus e photoeth n energy will excee e minimuth d m value required. This extra energy is dissipated due o interactiot n wit mediume hth electroe ,th n becomes thermalize e vicinite th cathodeth n i df e o yTh . probabilit f o yfindin a gthermalize d electroa t a n distance betwee x+dd f(x)ds an i xn x x which givee th s average distancJ*x= f> (x)dx

45 solute reacts also wite "dryth h " electro thad an nt S~ gets oxidized in a conventional electrode reaction. One of the most advantageous aspects of a photoelectrochemical experiment is its variability: one can change the potential between metal and solution e ,th frequenc & , f o ylight e th * ,,u duratio f o nillumination e e metanaturth th , lf o e what amounts to the change of the limiting frequency, U>0 (referring to the (f -0 case) and can measure the density of the photocurrent, j. The primary current densit f o ycharg e injection s givei , y eq.(2nb jp , ) as

) (2 te f )- 5• /2 > j- A(nupnu - J wher denotee elementare sth y charge [6]. electronse Th , diffusing toware e bulth dth f ko solution after being hydrated, react wit e solutehth , S. The kinetics of this diffusion-controlled reaction obey eq.(3) which describes both the spatial and temporal variation of the electron concentration, ce, if the cathode is exposed to a light pulse of the shape G(t),

G>Ce/Px = D(2 2 ce/3 x2^ - ks Cs Ce - ke Ce 2 + f(x)G(t) .(3)

Here D is the diffusion coefficient of the hydrated electron, ks the rate coefficient of the solute reaction, and ke is that of the bimolecular electron processe findon sf I . ce(x,t y solvin)b g eq.(3)n a , intricate task eve f i nsimplifyin g assumptione ar s introduced, one can approximate the observed net current density as j = jp - D(9ce/,Dx) (4) a functio s a f p f0o j n d e knowan on Thus j sf i , and où > the electron rate coefficients and the thermalization length, e founb y n analysindb ca , g eqs.(2-4). The kinetic energy of photoinjected electrons usually falls between kT and several eV, an energy interval whic moss i ht difficul o t investigat y eb any other experimental metho d wheran d e e eveth n theorie f moderatioso n fail. Thermalization lengths have been found to be in the 10 to several times 100 A range obeying the empirical rule valid between 0.2 and 7 eV L = 100E5/3 (5) where L denotes thermalization length in angstroms an initiaE d l energ electron i y n volts [6].

46 4. PHOTOGENERATION OF HYDROGEN ATOMS AT A SEMICONDUCTOR/WATER INTERFACE Photocurrents are usually orders of magnitude higher, electrode reactions more versatile on f i e uses semiconducting photoelectrodes instead of metals. However, these advantages also imply more complicated e kineticusuallar d an ys accompaniey b d impaired stability of the solid surfaces. Semiconductors are either n-type or p-type materials, i.e. the majority charge carriers are electrons or holes, respectively. Hence, if appropriately biased and illuminated, they can inject either hole electronr o s s e intliquith o d phase. (Hole injection obviously consist f electroo s n transfer frosolid.e e liquimth th o t d ) Unlike metals the bulk of the semiconductor can be permeated by light, hencelectron-hole th e e pair e generatesar d also quite far from the interface. They diffuse within the solid, experience a potential drop near e interface th so-calleth n (i e d Debye layer) and, according to the sign of this potential difference, either hole electronr o s e injectedar s . n Thena f i , appropriate solut presents i e , diffusion controlled oxidation-reduction processes take place in . the aqueous solution. Energetically speakint l resulne al e f tth o g these phenomena is the transformation of light into chemical energy applyiny B . g appropriate conditions the oxidation and reduction reactions can be spatially separated what makes electric potential d electrian buil p u d c current flo wthin i i.es. case light energy is converted into electric energy. The vast result experimentaf so theoreticad an l l research in this field are summarized e.g. in Refs. [8-10]. n Aa exampls f eo semiconducto r photoelectro- chemistry in the service of radiation chemical research let the behaviour of hydrogen-tungsten bronze/aqueous solution interface be shortly discussed [11]. Compound generae th f lso compostion MxWOs r o severa, a wherN lM , denotee Li othe , H sr metals, are called tungsten bronaes. If x is lower than 0.25 the compound behaves as a semiconductor, above tha a tmetalli s i limi t i tc conductora f I . semiconducting H- or H-Na-tungsten bronze cathode, immersed intacin a od solution which contains also some appropriate solute illuminates i , d with visible light, photo-current flows across the cell. The kinetics seem to be somewhat non-conventional in the sense that stationary photocurrent is proportional to the square roo f to ligh t intensitcurrene th d tan y builds up as the hyperbolic tangent of time, j = const(4I)tanh(ßt) , (6) wher denoteeI s light intensity. The role of the solute seems to be more interesting radiatios a r t fa ,a leas ns ta chemistr y is concerned. Cathodic current involves reduction to

47 e aqueouth tak n i es solutio nobvious i thu t i s s that e preconditioth a cathodi f o n c e procesth s i s presence of a reducible solute. It was found, however, that solutes that react exclusively with

solvated electrons like NsO, Znor Cd2+ do not

+ suffice. In the presence of othe2 r substances, e.g. Fe3+, Fe(CN)s3+ , NO3 02 tetranitromethanr ,o - e which are known to react also with atomic hydrogen, considerable photocurrent e observedb n ca s . Hence, n onconcludca e e thae light-generatetth d species i s atomic hydrogen y knowinB . g thi e coulson d devis. ea simple reaction mechanism which resulted in the kinetics given in eq.(6). Some recent spin trap work [12] lends direct support to the role of H atoms in the photoelectrochemical transformations discussed. It shoul e merelb d y mentioned here that hydrogen economy being one of the great hopes of energetics for the not too distant future, one may hope that these types of systems and reactions might gain some practical use in the energy industry.

REFERENCES [1] Davis, H.T., Brown, R.G., "Low energy electrons in nonpolar fluids", Advance n Chemicai s l Physics, Vol.XXXI. (Prigogine, I., Rice, S.A., Eds.), Wiley, New York (1975) 329-464 [21 Nyikos, L. Schiller, R., "Excess electrons in nonpolar liquids" e ChemicaTh , l Physicf so Solvation. Par tC (Dogonadse , R.R., Kaiman, E. , Kornyshev, A.A., Ulstrup, J., Eds.), Elsevier, Amsterdam (1988) 329-351 ] Barker[3 , G.C.j Electrochemical effects produced by light-induced electron emission, Ber. Bunsenges (19718 5 7 8 . )72 [4] Brodskii, A.M., Gurevich, Yu.Ya., Theory of external photoeffect froe surfacth ma f eo metal, Soviet Physics JETP 27 4 (1968) 114 [5] Gurevich, Yu.Ya., Pleskov, Yu.V., Rotenberg, Z.A., Photoelectrochemistry, Consultants Bureau,New York, 1980 [6] Konovalov, V.V., Raitsimring, A.M., Tsvetkov, Yu.D., Thermalization length f "subexcitatiposo n electrons waten i " r determine photoinjectioy db n from metals into electrolyte solutions, Radiât. Phys. Chem. 32 4 (1988) 623 [7] Barker, G.G., Gardner, A.W., Sammon D.C., quoted in Ref. [5] ] Myamlin[8 , V.A,, Pleskov, Yu.V., of semiconductors, Plenum Yorkw Ne , , 1967 [9] Gerischer, H., "Semiconductor electrochemistry". Physical Chemistry Vol. IXA (Eyring, H., Ed.) Academic Press, New York (1970) 463-542 [10] Hamnet "Semiconducto, ,A. r electrochemistry", Comprehensive Chemical Kinetics Vol. 27 (Compton, R.G., Ed.) Elsevier, Amsterdam (1987) 61-246

48 f. 11] Nagy, G. , Schiller K, , Photoelectrochemical productio atomif no c hydroge tungstet na n bronze/aqueous solution interface. ,J Electrochem. (19882 Soc1 5 .)13 3022 [12] Raitsimring, A.M., Nagy, G., Bil'kis, I., publishee Schilleb o t , drR.

Next page(s) left 9 blan4 k ASSESSMEN RADIATIOE TH F TO N CHEMISTR WATEF YO R AND AQUEOUS SOLUTION ELEVATET SA D TEMPERATURES

G.V. BUXTON Cookridge Radiation Research Centre, University of Leeds, Cookridge Hospital, Leeds, Yorkshire, United Kingdom

Abstract

Recently obtained experimental data which are relevant to the chemistry of water-cooled reactors are sunmarised and assessed. Several reports on the yields of some of the primary radiolytic products fron wate broadle rar agreemenn yi t thae tth patter watef o n r radiolysis doet changno s e very markedly betwee yielde nTh roo radicalf s. o C m temperatur0 s25 . ca d ean (e , H, OH) increase smoothly by ca. 0.2 % per °C in neutral m d H2 S0l 4mo ' 4 T0. ^ en i C ° r pe % 1 0. . solutionca y b d ,an

HOd an sho H pK'wO f temperaturso e dependences typica weaf lo k 2 concludeacidss i t I . d that yield extrapolatee pK'b d sn an sca d to reactor temperatures with some confidence. Kinetic measure- ments reveal that some important reactions which are diffusion controlle t ambiena d t temperature become activation controlled at elevated temperatures.

1. INTRODUCTION

Although the effect of temperature on the radiation chemi- str watef y o aqueou d ran s solution always sha s bee intrinsif no c interest, its importance in the context of nuclear power opera- tions has stimulated research at elevated temperatures in the last ten years. The primary goal of this work, which is being

51 carried out in a number of laboratories, is to obtain data which can be used reliably to model water radiolysis at ca. 300 °C, the operational temperature regio water-coolef no d reactorst A . the sam knowledgw e ne time eth importans ei bettea r tfo r under- standin e fundamentath f o g l aspectradiatioe th f so n chemistry of water in particular, and the effects of temperature on free radical chemistry in aqueous solution in general. There are three main topics of interest, namely, the effec f temperaturo t G-value) primare (i th n o ef so y products (reaction (1)),

+ H20 -v^-* e~g, H, OH, H02, H2 H202, H (1)

(ii) acid dissociation constants of OH, H02 and HJD2 and (iii) rate constant r reaction fo sradicae th f so l species with them- selves, with each other and with solutes. The purpose of this paper is to summarise and assess the experimental data that have been obtained so far and to indicate where the main gaps in our knowledge exist with respect to nuclear technology.

2. G-VALUE PRIMARE TH F SO Y PRODUCTS

Measurements of G-values, expressed here as per 100 eV, of the species produced in reaction (1) have been made using steady-state (mainly Y~ra(3iolysis d pulsan ) e radiolysis methods. In each case the chemical systems employed to measure these yields must be well characterised and this inevitably broadens the scope of: the work beyond the radiation chemistry of water. Of particular importance, of course, is the thermal stabilit e selecteth f o y d systems and, since spectrophotometry is generally the method of product measurement, it is also important to knew how temperature affects the absorption spectrum of the species of interest.

52 2.1. Steady-state radiolysis

Two systems that are suitable for study in acidic solution are the ferrous sulphate and eerie sulphate dosimeters, and these have been the subject of a number of investigations in 0.4 molar sulphuric aci usefulnese d Th [I ]. thesf so systemo etw s is that their mechanism e welar sl established e radiolytith ; c changes in them are given by eqns (2)- (4)

3+ G(Fe ) aerated = 3(G - + G„) + G___ + 2GH _ (2) eaq H OH H2°2 3+ G(Fe )deareate) G(e~(3 d= G+ g G^ + Q 2GH+ fl Q

T radiatioLE w s lo i y-rayo C nu r yiele sucHC Fo sth s f a ho d negligibly smal thao materiale s tth l balance eqn, .is

Ge; + S + 2G - GOH + 2G = G (5) scj z £. £ £. e b ELCd n anan ca dL H hencO primare , th eH) + y ~ yield(e f so acj 2. 2. deduced. Data from a number of studies of the ferrous sulphate and eerie sulphate dosimeters have been compared by Katsumura et al. [1] . The yield of ferric ion has been measured up to 250 °C and shows a small positive temperature coefficient of ca. 0.03% per °C in aerated solution and 0.07% per °C in deaerated solution; a s thha ed yielan bee s C cerouf dha o n 0 n measure15 sio o t p du larger negative temperature coefficient of ca. -0.3% per C. From these result s] conclude Katsumur[1 . al dt ae tha e th t

primary yield of OH increases, and that of H„0 decreases, with 2

increasing temperature whilst the yields of ea q + H maintain mor lesr eo s constant values. Rather different results for the ferrous sulphate system were reported by Kabakchi and Lebedeva [2] who found that

53 G(Fe ) increased by ca. 0.4% per °C between 150 and 200 °C, although their results were in agreement with those of Katsumura et al. [1] at lower temperatures. Kabakchi and Lebedeva [3] also measured the temperature dependence of G and G„ ~ using oU-n j H O solutions of potassium bichromate in 0.4 molar sulphuric acid. e resultTh s indicate thatemperature tth e coefficient thesf so e G-values are ca. 0.32 and -0.10, respectively, compared wth ca. 0.21 and -0.07 deduced by Katsumura et al. [1]. The values of G~, calculated by Kabakchi and Lebedeva [3] depend on the values Un of G + G [2] obtained from their yields of Fe3+ in the eag H2 ferrous sulphate system the o s e expecte, yar highee b o t dr than the value f Katsumuro s . [1]al t e a. Elliot et al. [4] have measured G(H ) = 5.1 at 300 °C in

the deaerated ferrous sulphate system and also G(EL) = 4.3 and , respectively°C 0 30 mola4 d 0. an n r i ,C sulphuri° 5 2 t a c 1 5. acid solution containin 1 mola0. g r methanol eacn I .h case e latteth n i r d thean y u G + _ G + a measurG(H u s G i 0 )f o e e H n~ ^ aq 2 correspon temperatura o dt e coefficien. C 0.07f r to pe % The ferrous sulphate and eerie sulphate systems have also respectively, C 0 8 d an ,C bee usin 0 n 15 gstudie o fast p tu d —1 o C 0 15 m y o [2]t V p neutronke U .0 4 . sca witf o mea a hT nLE the temperature coefficients are 0.65% per °C for (e + H),

0.53 for OH and -0.45 for H202, but at higher temperatures the patter watef o n r decompositio estimates i n vere b yo t dsimila r o that r y-icaysfo t [5]. n importana Thi s i s t conclusion with regar modeo t d l calculation coolanf so t radiolysis because fast neutrons contribute significantl totae th lo t ydos e absorbey db the reactor cooling water. Less information is available from steady-state experi- ments (Y-radiolysis) in neutral water. Jha et al. [7] measured

54 th ee hydrate yielth f o d d electro solutionn i n s containing SF- D or KUO and found it to increase rather uniformly from 2.5 at 0 , correspondin°C 0 30 t a a o V t ge 8 molecule 4. 0 10 o t r C pe s° temperature coefficient of ca. 0.3% per °C. Kabakchi and Lebedevn i ] measure [8 C a° e yiel0 th d25 f H o „do t fro 0 2 m aerated 10- 3 mol dm- 3 KBr solution as 0.44 ±0.02 molecules per 100 eV over the whole range. Contradictory results were reported by Burns and Marsh [6] who obtained G(Hp) = 2 at 300 and 410 C. They interpreted this yield, which decreased with

increasing dose indicatins ,a 0 H d an H g , thayield~ e e~ tth f so . 2 g a are 0.4, 0.3 and 2.0, respectively, at 410 °C.

Recently, Elliot at al. [3] found the yield of H9 to have a negative temperature coefficient in KBr solution and a

slightly positiv NaN0n i e 2 on esolutio n overange th r e 20-300 C. They point out that in experiments designed to measure yields of H~ it is important to minimise the mass fraction of

water present in the vapour phase where G(H2) is ca. 7 at elevated temperatures.

2.2. Pulse radiolysis studies

e pulsTh e metho suitabls i d measurinr fo e yielde th g f so

the radical products of water radiolysis, ea~q , H and OH. A numbe f studieo r neutran i s l solution have been made recently [10-12], the results of which are in good agreement with the steady-state data of Jha et al. [7]. Shiraishi et al. [10,11]

«• f*\ direcy b C t 0 observ25 hav o t e - p measureu yiele e th df o d ag MV*s a +C ° [11] 0 20 , o t p u + [10d Cd an ]atios a r no

+ 2+ ) (6 Cd Cde+ > ~a- q 2+ + ) (7 MV- 4 ~ e -a*q MV* methy= (Mv l viologen)

55 and Buxto Wood nan d [120 ]20 o havt p eu measure G.G + ,+ - dG e__ n un solutionn i C formatf so methyd ean l viologen, H, OH + HCO~ 2 (8) OX MV24- MV (9)

benefie Th convertinf to o primare t th gH O yd an radical H , ~ se aq s M7thai * t MV s stabli * e s enougopticait r fo h l spectruo mt be characterised quantitatively up to 200 °C [11].

10

o H + H + e aq ^

H2°2 D-

I H2 0 100 200 300

FIG. 1 Measured G-values in 0.4 molar sulphuric acid ( ) and neutral water (O)

56 _ H S0 The G-values of the primary products in 0.4 mol dm 2 4 and in neutral water are summarised in fig. 1 as averages of data obtained in independent studies as described above. In 0.4 molar sulphuric acitemperature th d ) eG coefficien+ G ( f to ag H' is ca. 0.07% per °C which is markedly smaller than that of Ge- aq in neutral water e reasoknowt Th no .r thipresen t na s nfo i s t e associateb y ma n but i i dt H wit e conversioo t th h e f no acidic solution,

eaq+H H * (10) From the standpoint of reactor technology the important results

are tha. temperature ca th t e ar H n eG d coefficientan _ G f so aq OH n neutrai C ° 0 e ltemperatur th wate25 d o t an r p u eC ° r pe 0.25% . 0.16%ca coefficiens i . „ MeasurementG t f a o t G f o s H2 2°2 elevated temperatur neutran i e l wate t beerye havnt madeno e . In view of the smooth increases in yields shown in figs. 1 t i seeman , 2 d s reasonabl assumo t e eextrae b tha date n th t-aca polate o reactot d r temperatures (300-330 °C) f courseO . ,

H d an H0, value° K 2 OH p , ^f 2o 2 s°2 FIG.

57 measurement thest sa e temperature desirablee sar systemt ,bu n so whic mako t h edifficule b they mma fino t d becaus thermaf eo l instability limitations.

3. pK VALUES OF OH AND IKL

Apart fron water itself ionisable ,th e product watef so r

radiolysis are OH, H02 and H2O2 whose basic forms are 0*~, O2*~

and H02 respectively. Although H0_ is a very minor product under deoxygenated conditions, it is a major one when oxygen is present becaus rapie th df eo reaction s (11)-(13)

2 2 O H0 H+ - * (11)

e + 0 (12) lq 2 * °2*~ + H02 + 02*~ + H (13) In the case of OH ionisation takes place via the fast reaction (14)

~ -»OH O • H+ 0 2 0*H ~+ (14) importans Ii t knoo temperaturw t who e affects equilibria (13) and (14) becaus eacn ei h cas reactivitiee eth acidie th d f scan o basic radicale formth f so s differ significantly exampler Fo . ,

O*~ is a reductant whereas H02 is an oxidant, and OH is an ele- ctrophil nucleophilea whilss i ~ t0* e [13].

3.1

The temperature dependence of the pK of H02 has been determined spectroscopically because the absorption spectra of

Od 2an e significantl' ~ar „ H0 y different e stud[14]on yn I . Christense d Sehestean n d [15] converte e primarth d y radicals

forme reaction i dH0o t 2/O') reactiona (1 n ~vi s (15), (11d )an

58 hig(12t a )hL E usinpressur d mixturan ga 2 O e f (14-1eo 5 MPa),

OH + H2 -*• H + H20 (15)

At necessars ambienwa t 8 [14i 4. t o ]ys = temperatur K p s ha 2 eH0 to select buffer systems with pK close to 5 and whose temperat- ure dependence is known in order to control the pH of the solution. Phosphat acetatd ean e buffers provesuitable b o t d e and Christensen and Sehested were able to determine the pK of

H02 up to 285 °C. In another study, Buxton et al. [16]

converte 0o 2reactiont a * ~H vi d O s (16 (17)d )an ,

OH + HC0~ -> C0'~ + H0 (16)

2 0• 2C0 * -» ~+ C0 2 20 * ~+ (17) and also used format buffeo t e e systemth r . They obtaineK dp values up to 200 C. The results are averaged in fig. 2 and also include earlier measurements by Schwarz and Bielski [17] at 2 °C and 60 . TherC goos ei d agreement betwee three nth e set datf so d aan th eploe shaptypicas th i t weaf a eo f klo acid shoult I . e db noted that the experimentally measured quantity is the product of G-value and extinction coefficient for HO„ and 0 * , and this increases with temperature. Christensen and Sehested assumed

e independenar * 02 f temperd o tthaG-valuee an th t HO - f o s ? ature, after making a small correction for changes due to spur scavenging [15] , so that the change in eG was attributed to a change in e. Conversely, Buxton et al. [16] attributed the change in eG to a change in G-value. That the two treatments yield dat fairln i a y close agreemen HOr «fo becauss K i tp e th e is derived fron (18meg )

K i3 ' %-2 -V

at where A is the absorbance due to R(= H02 + 02*~) i

59 pH, and HO- or 02* at low or high pH, respectively. Since A is proportional to eG, changes in either of these quantities with temperatur n (18)e wort s eq teni n canceo .i t ht dI t notinlou g

here thatemperature th t e dependenc H0r acin i fo 2 dG e f eo

solutio s significantli n y less than thar 0 2*fo neutran t~i l solution [15,16]. This is in keeping with the temperature dependences of the radicals shown in fig. 1.

3.2. OH

determinee b n ca kinetia H y O db f o c K methop e Th d whereby a solut choses i e n whice hOn react. witt * no h0 st bu wit H hO such e carbonat solut. d Buxtoth [16 al an s i et n ]e n io e used . ConfirmatorC 0 20 o t p yu datH O thi adeterminf o o st K p e eth werC ° e0 8 obtaineuo pt Ellioy db McCracked tan n [17] usine gth same metho witt bu dh ferrocyanide soluteth e dats a .Th a n io e are shown in fig. 2 together with the pK's for HO« (v.s) and H„0

and H202 taken froe literatureth m eacn I .h case thera s i e smooth dependence on temperature so that extrapolation up to reactor temperature made b en witsca h some confidence.

. 4 RATE CONSTANT FRER SFO E RADICALS

modeo T e radiolysi th lprimare watee th th n i rf y so heat syste a nuclea f o m r reacto s alsi ot i rnecessar o knoe t y th w rate constant mane th y f sreactiono e freth e f sradicao l prod- ucts of water radiolysis, see for example refs. [9] and [19]. In several y nevecasema e possiblt rb i s measuro t e e reaction rates at ca. 300 °C because of experimental limitations and so the reliabilit extrapolatinf o y g data obtaine lowet a d r temper-

60 atures mus e assessedb t . Hitherto generalls ha t i , y beee th n practic o extrapolatt e e from near room temperature usine th g Arrhenius relationship, Aexp(-k= E ./RT) (19) ace but this is not a valid method when reactions occur at rates approaching diffusion control at room temperature. Under these

condition observee sth d rate constant gives i y , nb , ,k oos kactkdiff kobs= k+k.. _ <2°) act difff

where kac t. is the rate constant that would be observed if there

were no diffusive restriction on the reaction rate and k,.ff is

the rate constant for complete diffusion control. If kac t and k, .„ relate to processes having different activation energies then n i additio, o t pureln y activation-controlled (slow) reactions and wholly diffusion-controlled (fast) reactions, the situatio n arisca n e a k,.wher ambient . « a k e t temperature

but kob ,s * kac t. at reactor temperature. This will occur when the activatio ndiffusive energth r fo y e proces greates si r than that for the . These three situations have all been recognise recenn i d t work.

4.1. Reactions with k , = k .

By definition these are slow reactions at room temperature. A number of these have been identified which obey egn (19) and

Q listee ar tabln i d . eThe I characterisee 0 1 yar x s5 . k y db dm mol s~ at 20 °C, i.e. k . - 0.05 k,.„, but the values _ of E range from 4 to 24 kJ mol so it is not possible to 3CC reactioa valus basie o it assigt th ef . so n no valuna E f eo of k at room temperature.

61 TABLE I. Rate parameters for seme purely activation-controlled reactions [20].

Reaction k . (20 °C) aca t Eact Tmax 3 —1—1 dm mol s kJ mol °C

OH + Cu2+ 8 3.10 1x 13.3 220 OFeH+ 2+ 4.3 x 108 9.2 220 7 OHH+ 2 02 2.7 x 10 14.0 160 7 2 H OH+ 3.10 4x 19.0 230 O HCOH+ Z 8.5 x 106 21.2 200 8 OH + C03 4.2 x 10 23.6 200 5 H09 + HO 8.10 4x 20.6 285 7 TT 1 TT ^\ "" 5 x 10 16.6 80 8 ea qS2+ 03~ 9 1 x 10 4.0 200

a. Ref. [21]

4.2. Reactions with k,

For a truly diffusion controlled reaction between species Smoluchowsk e give,;,s . th i ;, k y nb B d an iA eqn,

kdiff where r and D are the reaction radius and diffusion coefficient, respectively, of the reacting species. If both species are ionic the righthand side of egn (21) is multiplied by the Debye factor So far, the only reactions that have been shown to be truly dif- fusion con toi led over an extended range of temperature (up to

q a 200 C) are those of q ea + nitrobenzene and e -f 1,1 '-dimethyl 4-4'-bipyridiniu whern e temperaturio m th e e dependence corres- ponds to the activation energy for the self-diffusion of water

[21].

62 3.5

FIG. 3 Temperature dependence of k(OH + OH)

TABL . II ERat e parameter f somo s e reactions whic e describear h d by eqn (20) [21].

Reaction C ° 5 k2 act ta Eact Tmax dm3 mol- 1 s-1 kJ mol"1 °C

OFe)CN)îH+ ~ 4.0 x 1010 7.0 120 D 9 OH + HCO2 6.10 5x 4.0 200 OH + OH 9 1.10 0x 3.7 200 10 2 0 H+ 3. 103x 6.3 200 10 e~ + 02 6.5 x 10 11.5 200 10 H e+ ~aq 3. 100x 14.0 200

63 4.3. Reactions wit ^hk n (20giveeq )y nb

Althoug havH hO e mand ratan ye H reaction , e f o s aq constants close to the diffusion limited value at 20 °C, those that have been measure elevateo dt d temperatures are, more often than not, described by egn (20). One example is shown in fig. 3 from evidens whici t i h t that extrapolatio f rato n e data from room temperature to reactor temperatures assuming diffusion- controlled behaviour over the whole temperature range can be very misleading. Rate parameters of some reactions which are described by eqn (20 notable e liste)Th ar tabln i d. e II efeature e th e sar generally large values of k at 25 °C and the small values of act Eac t,. Since many of the important reactions in water radiolysis appea diffusioe b o rt n controlle ambient da t temperatury ma t ebu t elevatea e b t d no temperatures s clearli t i ,y importano t t measure their rates wida ove s a rangea r f temperaturo e s a e possible to establish the rate parameters in eqn (20). Then it should be possible to extrapolate the data to the required temperatures with sane confidence.

. 5 CONCLUSIONS

A clear picture is emerging of the radiation chemistry of wate elevatet ra therC ° donl e 0 temperaturesear y25 . ca o t p U . relatively minor e decompositiochangee yieldth th f n o si s n products, mainly represente increasn a yield e e y dth th b n f esi o radicals. These datonlt ano y provid w informatioene n against which to test theoretical models of the radiolysis of water but also strongly suggest that they can be smoothly extrapolated to

64 temperatures pertaining to water-cooled reactors. Nevertheless, direct measurement e desirablar s f suitabli e e systeme b n ca s designed for them. alsIs ti o clear that reaction rates mus measuree tb d over a wide temperature rang f valii e d extrapolation o reactot s r temperatures are to be made. These kinetic data are also of fundamental importanc n understandina o t e mechanistie th f o g c details of reactions whose rates are limited by diffusion at ambient temperature. I am grateful to Dr. A.J Elliot for many helpful and stimulating discussions.

REFERENCES

[1] KATSUMURA, Y., TAKEUCHI, Y., ISHIGURE, K. Radiation chemistry of high temperature water. I. Degradation products in acid by gamna radiolysis. Radiât. Phys. Chem. reference 3d (19882 an 9 )25 s therein. [2] KABAKCHI, S.A., LEBEDEVA, I.E. Temperature dependencf eo e yiel th f reducino d g particles durin radiolysie th g f o s liquid water. High Energy Chem(19843 8 .1 ) 166. [3] KABAKCHI, S.A., LEBEDEVA, I.E. Temperature dependencf eo the yield of oxidative particles during the radiolysis of liquid water. High Energy Chem(19874 1 .2 ) 261.

[4] ELLIOT, A.J., OULLETTE, D.C., REID , MCCRACKEN,D. , D.R.

The G-values of the primary species in 0.4 mol dm HSO. ? . irradiateRadiât°C 0 30 .t da Phys . Chem. pressn ,i .

[5] KATSUMURA, Y., TAKEUCHI, Y., HIROISHI, D., ISHIGURE, K. Fast-neutron radiolysi f o acis d wate t a elevater d temperatures. Radiât. Phys. Chem(19894 3 .3 ) 299.

65 [6] ELLIOT, A.J., Atonic Energy of Canada Ltd., Chalk River Nuclear Laboratories, personal cotmunication.

[7] JHA, K.M., RYAN, T.G., FREEMAN, G.R. Radiolysis of H00 £

and D20 between 0 and 300 °C. J. Phys. Chem. 79 9 (1979) 868.

[8] KABAKCHI, S.A., LEBEDEVA, I.E. Effec temperaturf to n eo e yiel th f moleculao d r hydrogen during Y-radiolysif o s liquid water. High Energy Chem (19834 6 .1 ) 248. [9] BURNS, W.G., MARSH, W.R. Radiation chemistr f higo y h temperature (300-41 water) C 0Chem. J . . Soc., Faraday Trans (19817 7 , .I ) 197.

[10] SHIRAISHI KATSUMURA, ,H. HIROISHI, ,Y. ISHIGURE, ,D. . ,K Pulse radiolysis study on the yield of hydrated electron at elevated tanperatures. J. Phys. Chem. 92 10 (1988) 3011. [11] SHIRAISHI BUXTON, ,H. , G.V., WOOD, N.D. Temperature dependence of the absorption spectrum of the methyl viologen catio methyf o n e radicalus viologed an l a s a n scavenger for estimating yields of the primary radicals in the radiolysis of high-temperature water. Radiât. Phys. Chem. pressn ,i . [12] BUXTON, G.V., WOOD, N.D. Effect of temperature and scavenging power on the sum of G(e ) + G(H) + G(OH) in the range 20-200 °C. A pulse radiolysis study. Radiât. Phys. Chem. pressn ,i .

[13] BUXTON, G.V., GREENSTOCK, C.L., HELMAN, W.P., ROSS, A.B. Critical review of rate constants for reactions of hydrated electrons, hydrogen atom hydroxyd an s l radicals (OH/0*" aqueoun )i s solution Phys. J . . Chem. Réf. Dat7 a1 (19882 ) 513.

66 [14] BIELSKI, B.H.J., CABELLI, D.E., ARUDI, R.L., ROSS. A.B.

Reactivit H0f o y? /0?~ radical aqueoun i s s solution. J . Phys. Chem. Réf. Data 14 (1985) 1041.

[15] CHRISTENSEN ~ radical2 0 d an t SEHESTED, a s ,2 H. HO . ,K elevated temperatures Phys. .J . Chem(1880 1 2 ).9 3007. [16] BUXTON, G.V., WOOD, N.D., OYSTER . ,IonisatioS n constants of OH and HO- in aqueous solution up to 200 °C. J. Chem. Soc. Faraday (19884 Trans 4 8 ), . I 1113 .

[17] SCHWARZ, H.A., BIELSKI, B.H.J. Reactions of H0 and 0^ 2

with iodine and and the I2~ and I atom reduction potentials Phys. J . . Chem (19867 0 .9 ) 1445. [18] ELLIOT, A.J., MCCRACKEN, D.R. Effec temperaturf to n eo 0* reactions and equilibrium: a pulse radiolysis study. Radiât. Phys. Chem. 33 1 (1989) 69. [19] LUKAC. S.R. modelling of radiolysis of reactor cooling water A comparativ .- e study. Radiât. Phys. Chem3 3 3 . (1989) 223. [20] SEHESTED, K., CHRISTENSEN, H. "The radiation chemistry of water and aqueous solutions at elevated temperatures," Radiation Research (Proc Inth .8t . Congr. Edinburgh, 1987)

Vol. 2 (FIELDEN, E.M., FOWLER, J.F., HENDRY, J.H., SCOTT, D., Eds.), Taylor and Francis, London (1987) 199-204.

[21] ELLIOT, A.J., MCCRACKEN, D.R., BUXTON, G.V., WOOD, N.D. Unpublished data.

Next page(s) left blank 67 CURRENT STATUS OF RADIATION CHEMICAL STUDIES WITH HEAVY IONS*

R.H. SCHULER, J.A. LAVERNE Radiation Laboratory, University of Notre Dame, Notre Dame, Indiana, United States of America

Abstract

The histor f radiatioyo n chemical studies with heavy ion s briefli s y reviewee scopth f currend o e an d t activitie s summarizedi s . Attentios i n focused on the significance of these studies to discussions of track effect radiation i s n chemistry.

Recognizing that a large number of studies were carried out with a-particles during the first half of this century we will restrict the present discussion to work carried out since 1950 whe e generath n l availabilit f accelerateyo d heavy ions madt i e possible to examine the dependence of radiation chemical yields on the energy loss characteristics of the irradiating particle. Studies prio o 195t re summarizear 0 a variet n i d f booko y s such s thosa f Lindo e d Bac^d Alexander.^ an an )q 2) Reviews sucs a h tha f Burton*o t 3) t indicatimmediatelar e e statth th e f o e y after World War II. The present summary is based on a compilation by e Notrth e Dame Radiation Chemical Data e Centemorth ef o rrecen t work which appeared as a bibliography in Radiation Physics and Chemistr s n sinc1981i yha d ^e an bee^ n update e currenb o t d t through the third quarter of 1988.(5) A total of 515 papers coverin e perioth g d since 195 e include 0ar e 198 th 8n i d revision. The references are distributed between the different

The research described herein was supported by the Office of Basic Energy Sciences of the Department of Energy. This is Document Wo. NDRL-3145A from the Notre Dame Radiation Laboratory.

69 TABLE I

DISTRIBUTIO STUDIEF HEAVE NO TH YF SO

PARTICLE RADIOLYSI LIQUIDF SO AQUEOUD SAN S SOLUTIONS

References References Classification 1980a 1988b Water, Aqueous Solutions: Inorganic Solutes 165 221 Water, Aqueous Solutions: Organic Solutes 19 29 Liquids, Nonaqueous Solutions 97 118 General and Reviews 53 67 Theoretical _ 58 80 TOTAL 392 515

Referenc- 4 e - Reference 5

area f interesso s indicatea t Tabln i d . I Approximatele 8 y papers/year appeare e 1950'sth n i d. Since 1960 there have been 12-15 papers/year with f courseo , , considerable fluctuation resulting from prominent effort f individuao s l investigators. Whil e volumth e f reportt greato e no e muss i on ,s t kee minn i p d that studies are difficult and slow going because of limited access to appropriate experimental facilities. There is clearly a continuing interes n thii t s topic, particularl appliet i s a y s to areas of radiobiology. e firsW t examine some detailpublicatioe th f o s n historn i y this are f researco a d thean h n summariz e experimentath e l facilities availabl d approachean e e uses b o carr that dn t ca tou y studies with heavy ions. Finall e importancth y f theso e e experimental studies in discussions of track effects in radiation chemistry is briefly considered.

70 Publication History Studies of the decomposition of water by a-particles date back to the early 1900's and it was known as early as 1901 that substantially higher decomposition yields resulted from irradiation with a-particles than with X-rays.(°) In particular molecular hydrogen was shown to continue to be produced in a substantia le cas yielf th a-particlo e n i d e irradiations whereas it reached w steadonllo a yy state with e X-raystimth f o e y B . the Manhattan Project (1942)^ this difference was well recognized as resulting from the high density of energy deposition along the track of a-particle tracks which caused high rates for radical combination. The term Linear Energy Transfer e s radiobiologicacoineth wa (LET y )b d l community( o describ7)t e the energy loss alonn ionizin a pate f th go h g particlo t d an e give a parameter with which to characterize this energy loss. n facti / a give, is r identica T nFo e stoppinLE heav th n o io yt l g power (i.e. dE/dx). It was not until the development of experiments using accelerated ions in the 1950's that detailed studiedependence th f o s f radiatioo e n chemical reactionT LE n o s readily became possible. Essentially all the studies with heavy particles before 1950 were carrie witt ou dh a-particles, using 210Po produce decae th f radon o yn i d . With the post World War II development of heavy ion accelerator s becomha t i se possibl o stud et dependence th y f o e radiation yields on particle type and energy. Studies in the mid 1950s mainly used protons, deuteron d heliuan s m ions accelerated at cyclotron d employesan d absorber technique varo e t s th y particle energies. Much attentio s focuseFricke nwa th n eo d dosimeter. These studies provided particularly valuable datn o a the Fricke system for particles have LET'S up to ~ 25 eV/Â. In these studies compariso yielde th r oxidatio f fo so n f ferrouo n s

71 ion in aerated and deaerated systems and for reduction of eerie n provideio d informatio energe th n yo n dependenc H atom e th s f o e and OH radical yields. It was also shown as early as 1957 that e yieldth r radicalfo s s escapin heave n tracth g io y k were somewhat greate r heliufo r m ions thar protonfo n s havin e samth ge LET.<8> Studies were also carrie t durin ou de lat th ge 1950'n i s alcohol hydrocarbonsn i d san , with some emphasi e latteth n i sr cas n aromatieo c systems becausprojectee th f o f eo e us d aromatic organicn i s moderated reactors. e wasSucus n ,a hi

part ,e relativel baseth n o d2 productio H w yiel r lo y e fo d th n i n y-ray radiolysis of benzene and terphenyl. However, it has since

been recognized that H is only a minor product. Complications 2 demise th f o organieo t havd le ec moderatio practicaa s a n l

reactor concept. As it turns out, H2 is produced from benzene in relatively greater amounts in the tracks of heavy ions than in

electron radiolysis a resul s A .t H productioe b n ca n 2 used to monitor the importance of track processes. A detailed study with radiations up to 30 MeV carbon ions, having LET'S up

to 80 eV/Â, has since been carried out.(') In these cases the H2 yields approach 1 molecules/100 eV, or ~ 25 times that for fast electrons (0.04 molecule/100 eV). During recent years particles produce t alternatina d g gradient cyclotron d lineaan s r accelerators have provided radiations having energies greater than 100 MeV and LET1s up to 600 eV/Â. In these cases the initial energy can be varied by changing the accelerator parameters. This aspect is important because otherwise straggling and fragmentation problems make it difficult to define precisely the particle characteristics when absorber technique e usedar s . Currently there are, worldwide, some six heavy ion accelerators being used to carry out radiation 72 Chemical experiments and another eight which could be equipped readily for relevant studies.

Approaches Because one wants to compare yields for different particles with results from theoretical studies it is necessary to have radiations with well defined characteristic o thas t absolute differential yields can be determined. The differential yield represents the yields for a track segment at a particular energy. Where the particle is stopped in the sample, these

yields can be obtained from the slope of plots of GQEO as a

function of EQ/ where GQ represents the yield averaged over the

trac d EQan k represent particle th s e energentert i e s a yth s sample and i.e.

Since experimental uncertainties make it impossible to determine Gj_ directly from measurements over small increment n particli s e

energy we have found it convenient to plot GQEO as a function of

d thean En determine y takinGb ^ derivative th g polymoniaa f o e l Q fio suct t plot a hr particle Fo . s having 0 energie5 o t p u s MeV/nucleon, where the ranges are less than 1 cm, such an approach works quite well. For more energetic particles, such as e severath l hundred MeV/nucleon particles available th t a e Lawrence Berkely Laboratory BEVALAC, wher rangee th emane ar s y centimeter, differential yields can be directly determined for track segments. ' Unfortunatel' y such measuremente sar complicate y fragmentatiob d e initiath n whilf o nio l e passing throug e sampleth h .

73 Most measurements of yield are determined from the amount of produc te energ formeth d y an dinpu s determinea t d from knowledge e particlth f o e energ d measurementan y e totath lf o snumbe f o r irradiating particles. The latter requires monitoring of the particle current on an absolute basis. Since beam currents are small/ e.g .10~~ 9 amps strad ,an y current frequentle ar s y generated in the measuring apparatus as a result of secondary emission and scattering accurate measurement of the charge input is particularly difficult. The present authors monitor the current with a charge collection apparatus which is a Faraday cage. This apparatus is described elsewhere.^11^ Current integrators are sufficiently accurate to determine the total charge readilar % e1 y inpu ~ available o t t . Determinatiof o n particle energy requires correction of the energy of the particle produced by the accelerator for energy losses in the window system. At high energies the latter correction is relatively smal d reasonablan l e estimate e readilar s y mad o thas e t radiation yields can usually be determined as accurately as permitted by the chemical measurements w energielo t e correctionA .th s e ar s quite substantial and possible errors become quite large/ particularl e e Bragregioth th gf n o i nypeak . Typical particle energies for low mass ions and residual ranges have been summarized.^ We note that the quantity of particular interest

is not so much GQ but rather GOEQ the total amount of product at

energy EQ. This valu determines i e d frochemicae th m l

measuremen d doedirectlt an tno s y involve EQ.

Significance of Heavy Ion Studies Studiee energth f yo s dependenc r ferroufo e s oxidation i n e Frickth e syste a variet y b m f heavo y y particles havw no e provide a detailed d picture dependencth f o e f wateo e r

74 dissociatio atoH d m nan productio n traco n k structure.(f O ) particular importanc e verth y s i cleae r demonstration thaT LE t is, in itself, not a sufficient parameter with which to characterize track effect n radiatioi s n chemistry. This result mann ii s y ways expected becausparticle th a give T t a eLE ne velocity require produco t d a givee T increaseLE n s with masd an s charge. The density of energy deposition correspondingly decreases. As a result processes such as intratrack recombinatio f radicao n l becomes less importan a relativel d an t y greater fractio f reactivo n e intermediates diffuse inte bulth ok phase to enter into processes occurring at relatively long times. From time resolved studiew knono we w stha t intratrack processe spurn i s shundree occuth n o rd picosecond time scald ean e virtuallar y complet microsecont a e d times. Presumable th y predominant processes in tracks of heavy particles are even more rapid, i.e. considerably less than nanoseconds. The various studies carried out to date have provided a firm foundatio n whico n baso t h descriptioa e f intratraco n k processes waten i r radiolysis. Theoretical studie f Chatterjeo s d an e Magee,r examplefo ' ' , giv descriptioa e n largeln i y correspondence wite experimentath h l results n generaI . l there ia sreasonabl e understandin nature th f tracf o eo g k processen i s water radiolysis even though in some instances, such as HÛ2* production from water, one has yet to delineate the chemical mechanism involved. s cleaIi t r froe studieth m s already carried out, that even with the most densely ionizing radiations there are small yields H radicals.^H atomO d f o san 12^ This aspec particulas i t r important to radiobiological applications where many mechanisms are considered to involve radical intermediates. In general the information now available for aqueous systems provides

75 information on which to model radiobiological processes involving radicals in the tracks of heavy ions. The situation in non aqueous media is much less well defined and much work has yet to be done. Existing data is extremely limited and generally has only very qualitative understanding in substances such as hydrocarbons. t thia se meetinse e W a substantiag d expandinan l g interest in radiolytic studies with heavy particles n expecca e t On .tha t this interest will continue but that, because of the difficulties involved, experimental work will procee a relativel t a d y slow pace.

REFERENCES

1. S.C. Lind, "The Chemical Effects of Alpha Particles and Electrons", 2nd Ed., Chemical Catalog Company, New York, (1928).

. 2 Z.M .Alexander. P Bacd an q , "Fundamental Radiobiology"f o s , Butterworths Scientific Publications, London, (1955).

3. M. Burton, "Radiation Chemistry and Nuclear Energy", Chem. and Eng. News. 26, 1764 (1948).

4. J.A. LaVerne, R.H,, Schuler, A.B. Ross and W.P. Helman, "Bibliographie n Radiatioo s n Chemistry . StudieI e :th f so Heav n radiolysiIo y f Liquido s Aqueoud an s s Solutions", Radiât. Phys. Chem. r?,. 5 (1981).

76 5. J.A. LaVerne, "Bibliography of Studies of the Heavy Particle Radiolysis of Liquids and Aqueous Solutions" revised November , 198818 . Available froauthore th m s NDRa s L Special Report SR-124.

6. P. Curie and A. Debierne, "Sur la radio-activité induite et les gaz actives par le radium" Compt. Redn. 132, 768 (1901).

7. R.E. Zirkle, D.F. Marchbank and K.D. Kuck "Exponential and Sigmoid Survival Curves Resulting from Alph d X-raan a y Irradiatio f Aspergilluo n s Spores . CellulaJ " d Compan r . Physiol. 22' 75 (1952).

8. R.H. Schuler and A.O. Alien "Radiation Chemical Studies with Cyclotron Beams of Variable Energy: Yields in Aerated Ferrous Sulfate Solution" . ChemAm . ,J Soc. , 156,79 5 (1957).

. 9 J.A. LaVern d R.Han e . Schuler "Track Effect Radiation i s n Chemistry: Core Processes in Heavy-Particle Tracks as manifest by the ~&2 Yield in Benzene Radiolysis" J. Phys. Chem. 8£, 1200 (1984).

10. E.A. Christman, A. Appleby and M. Jayko, Radiation Chemistry of High-Energy Carbon, Neon and Argon Ions: Integral Yields from Ferrous Sulfate Solutions", Radiât 3 (1981). 44 Res , 85 .

. J.A11 . LaVern R.Hd an e . Schuler "Track Effect Radiation i s n

Chemistry: Productio Radiolysie th H0f n o i 2 Watef so y b r High-LET 58Ni Ions, J. Phys. Chem. 91, 6560 (1987).

77 12. J.A. LaVerne and R.H. Schuler "Radiation Chemical Studies with Heavy Ions: Oxidation of Ferrous Ion in the Fricke Dosimeter Phys. J " . Chem , 57791 .0 (1987).

13. A. Chatterjee and J.L. Magee "Radiation Chemistry of Heavy- Particle Tracks Frick. 2 . e Dosimeter System . PhysJ " . Chem. 84, 3537 (1980).

78 SOLID STATE PULSE RADIOLYSIS

Z.P. ZAGÖRSKI Department of Radiation Chemistry and Technology, Institute of Nuclear Chemistry and Technology, Warsaw, Poland

Abstract

The paper stresses the insufficient knowledge of solid state radiation chemistry contrasting with well developed radiation chemistr f o yliquids e basiTh . c difference between solid d liquidsan s consist rapin si d deca f o intermediatey n i s the latters and a long life of reactive species in the solid mobilitw lo a systef o o stateyt e mdu , constituentsr es o t e Du . investigation, radiothermoluminesce, lyoluminescence etc the knowledge is developing on comparatively stable species, but their precursors other ,o r short lived species decayin stablo gt e compounds remain unknown. In spite of experimental difficulties, caused mainly by a not sufficient transparency of samples, pulse radiolysis in the solid state is developing. Different approaches e presentear d with example resultsf so . They contribute th o t e knowledge of solid state radiation chemistry. Nonoptical methods of detection of intermediates in solid state pulse radiolysis (e.g. electrical conductivity) are not discussed in the present paper.

1. INTRODUCTION

Solid state radiation chemistry seems to be a not sufficiently explored field yet concerns A . condensee sth d phase, the majorit radiatiof o y n chemistry studies have been performed using liquid systems. Few papers only deal with the solid phase, especially if one discounts liquids frozen to the amorphous state. Radiation chemistry of liquids shows well defined situation of intermediate stabld san e mobilitth e productso f t o y e Du . molecules e unstablth , e products disappear usualln i y microseconds and the remaining stable products of radiolysis are detected and determined with usuall tools of analytical

79 chemistry. Cases of semistable intermediates are encountered in exceptional cases, like hydrogen peroxides reacting in the Fricke syste secondsr mfo , easy followed electrochemically. Limited mobilit reactivf o y e specie solie th n dsi stats i e the caus f moreo e complicated situatio f intermediateno n thai a t form of condensed phase. There are mare stages of reaching the thermodynamic equilibrium here and very often many intermediates survive for years and .may be easily detected long after the irradiation by esr, lyoluminescence, radiothermoluminesce etc. Electrons trapped in ceramics are case in point. They are stable enoug usee archeologicar b fo do ht l dating, because rather high temperatures only, exceeding those of crystalline transitions, may cause detrappin electronsf o g . Although som survivinf eo g intermediate solie th dn si state may be considered as the primary chemical species appearing just after the act of electron detachment, other surviving species may have their precursors. Therefore a tool is needed for the detection of short living intermediates in the solid phase and pulse radiolysi mose sth t seeme suitablb o st en ca method e On . realize alread firse th tt ya glance , that applicatio f o pulsn e radiolysis to the solid state will have its own features and difficulties, not encountered in liquid state pulse radiolysis.

2. EXPERIMENTAL APPROACH A proper experimental approach is crucial in the pulse radiolysis of solid state. Already the visual inspection of samples creates doubtss concerning application of optical methods of detection. Severe restrictions seem to apply in connection wit a hlimite d numbe pulsef o r e se applieb th whic y o t ma dh sample without causing chang f responso e estud th f o n yi e intermediates and their kinetics of decay. Let us discuss the first, most important problem of transparency. Figur show1 e s schematically different optionf o s pulse radialysis with optical detection of intermediates. Approaching pulse radiolysis of solid samples one has to make every effor applo t y conventional technique, i.e e bea.th f o m analytical light shining throug sample hth direcn i e t path. That

80 Xe tamp

FIG. 1. Pulse radiolysis of solid sample, a. Conventional arrangement in the case of acceptable trans- parency . Diffusb , e reflectance arrangement . Cerenkoc , v light self-absorption metho variao tw -n di tions denoteM . monochromatoe sth measurine th d an r g system.

approach has its own long history because it already had prepared difficulties in making ordinary spectrophotometric investigation an deep frozen samples of systems forming transparent glasses. Man yabandonee b systèm o t d deha because preparatio perfeca f no t glas s simplswa y impossible. Som ee modifieb system o t o d t sdha the extend in which answers to the problem could hardly be obtained. Even witpropee hth r e frozechoicth f no e systeme th , realizatio d reproducibilitnan s verywa y difficul verd tan y often calleo s d "cracked glasses" were obtained which most probably were partly crystalline materials. Anyway, the deep frozen glasses have a rather narrow application in pulse radiolysis, because products firse formeth tn i dpuls e practicallear y stable an dbleachede b hav o t e , befor nexe eth e t appliedb puls n ca e. Irradiation of glasses is important in the study of spectra in frozen matrices with intermediates of prolonged life and of their decays occuring in the time of minutes, hours and days. There are cases, in which preparation of polycrystalline material Is possible with such high transmission, that conventional measuremen f o tintermediate n pulsi s e radiolysis arrangemen possibles i t cas.e th Thae s i witt h aqueous clathrates [1] which easily may be obtained in perfect polycrystalline

81 aggregate consistin millimeter-sizf go e crystals wito voidn h s between them. Sample tetrabutylammoniuf so m hydroxide, fluoride, bromide oxalatr o , e hydrate preparee b y sma y b crystallizatiod n of carefully molten large crystals, directle pulsth en i y radiolysis cell. Sample thesf so e compounds resemble liquids a s concern e th transparencys . Unfortunatel e methoth f yo d preparation of samples by crystallization from melt finds application limited to few favourable cases. Usually it works with compounds of temperature of melting, slightly higher than ambient. Good result s beesha n obtained with samples melting below the freezing point of water. Examples are again in the field of clathrates. Another approac e preparatioth he b f o seem o nt s monocrystals t leasa f r o tlargo , e crystal conglomeratese Th . latters may be arranged in cells in a way in which they form an average laye f millimeteo r r deep thickness wit dominatioo hn f o n voids of gas. Some hydrates has been investigated in that way £2] , although the quantitative approach is much more complicated than in the case of samples filling completely the cell like liquid samples. Last but not least the technique of sample preparation used e infrareith n d spectroscop y help yma t consistI . n pressini s g crystals into pellets in conventional hydraulic presses used in the IR laboratory. However, the majority of compounds hardly succumb completela o st y transparent sample without additives. The IR-spectroscopist uses usually the mixture of investigated compound with KBr, obtaining transparent samples, suitablr fo e the preparation of spectra. The technique is perfect for IR measurement doubtfuf o s i t l sbu applicatio case f th epulso n i n e radiolysis. Intermediate r KB radiolysi n i y s disturma s b investigation of products to be studied. The same applies in an even higher degre liquido et whicn si h crystal f o investigates d compounds coul suspendede b d . e effecIth n f preparatioo t e f solino th df o sample e on y sb mentioned methods a partia, l transparenc s achievedi y e Th . question arises what opacity termn i , opticaf so l e densitb y yma tolerated e answeTh . r depend e opticath n so l qualitpulse th ef o y

82 radiolysis apparatu st fullusedno usage y.f Th o etransparen t sampl accompanies i e highey db r leve f noiseo l n thaI . t respect e propeth r acquisitio processind nan f o hel n i e b pf dat go y ama enhancing the signal to noise ratio. The experience shows, that in man . airyvs case,0 e opacit1. sth a c yf o expresse . D . O s da masuccessfulle b y y negotiated. Conventiona t lver no woryn o ktransparen t sampley ma s prepare difficultie interpretatioe th n si measurementsf no . With a satisfactory transparenc reae yth l pat analyticaf ho l lighs i t geometricae equath o t l l one. However ,w transparency witlo ha , close to the limits of possibility of obtaining a meaningful signal e rea,th l pat f ligho h s i longet r e thageometricath n l o internat onee ,du l reflections. Therefor e quantizatioth e f o n the O.D. has to be made with proper restrictions. The conventional pulse radiolysis equipment with the beam of analyzing light passing through the sample cannot satisfy all needs of solid state work. The first choice in pulse radiolysis of opaque samples seems to be the diffusive reflectance method ) investigate(Fib 1 g d e.g .Lany b d C3] diffuse .Th e reflectance spectrophotometr bees yha n applie de soli th firs n di t state photochemistry, mainly for investigation of stable products of photolysis. The technique is difficult in realization and interpretation and the present author prefers the method which Cerenkoe th f makeo ve sus ligh t emitted froe irradiatioth m n zone, attenuate absorptioe th o t intermediatey b d e du n s

83 radiolysis arrangement is exactly Identical with the time profile electroe oth f n pulse, measure solenoie th y b dr dcollecteo s a d the charge behind the cell. In the case of an intermediate absorbin chosee th t nga wavelength, onle lighyth e t th leve t a l beginnin t disturbeno s pulse enterei th s i ef d go an d into

calculations as IQ. The light level is diminishing with time and marecalculatee b y d inte opticaoth l density values, althouge hth function is more complicated than with usuall recalculation of transmission into CKD. in classical pulse radiolysis. The simple formul conventionan i a l pulse radiolysis: D = 10~I/I0 where I is the intensity of light in the presence of absorbing intermediate, I is the intensity of light before the pulse at the same wavelength, D is the product of molar absorptivity e and e lighth t pat, I h changes into:

D 0 1 u L - 10~~ D 1 < / > = I/Io

wher symbole eth s havsame th ee meaning D incorporatet bu , s I whico longen e s geometricai hth r l pat f o lighh t likn i e transparent samples. The light emitted in opaque samples travels a much longe thay shortese rwa nth t geometrical one e reaTh .l average pathlength may be estimated using samples of different thickness e transienIth f a lon s gt ha hal f life tim comparison i e o t n e pulsth e length s lineae buili th ,p u dr with time t whee bu ,th n decay time is comparable to the duration of pulse, the build up is leveled and the algorithm is similar to the case of activation of a short lived nucllde in the nuclear reactor of constant neutron flux. extensive Therth s ei e literature publishee th n o d method, allowing proper applicatio advantage nth [4,51s i t f I .eo the method in allowing an investigation of samples as opaque as aspirin tablet, but there is a serious disadvantage of the time scale limited to the duration of the pulse. Therefore the spectra are of perfect value, but decays may be estimated, if at all, in the case t f comparablso e lengtth pulseo f eht o .

84 The second difficulty connected with solid state pulse radiolysis is the possibility of formation of too much product of radiolysis during subsequent pulses, thus changin e systemth g . That difficulty is common to all versions of solid state pulse radiolysis shown on Fig.1. It has been proved experimentally that radiolysis products capacit f o majority f systemo y s higi s h enough to tolerate thousands of pulses. In unknown systems it is advisabl mako t e e repetitio f identicao n l initial pulses after serie recordf so different sa t wavelength experience Th . e gained with many of solid compounds has shown that frequent change of sample t needeno usualld s si dan accumulatee th y d dose tolerance is high. Only two cases has been noted

3. EXAMPLES OF RESULTS OF PULSE RADIOLYSIS IN SOLID STATE

Historically first applicatio f no puls e radiolysis method with Cerenkov light seIfabsorption has been focused on hydrates of alkaline metals hydroxides. An intensive absorption with maximum n (dependin 0 62 m betweed n concentratioo an g 0 n58 f o n water), observed at the room temperature has been easily identified as due to the electron trapped in aqueous moiety, because no influence of the cation, even of the

85 dry electron. E.g. in the case of hydrates containing NO as guest in the crystalline clathrate structure, there is a competitio electror nfo e pointh n t d betweean defect O nN a , specific vacancy of HO molecule. It has been found experimentally, that the dry electron reacts with N O very slowly trae anth dp shows much greater crossectio reactioe th r nfo n with e~dr . The most of electrons appear just after the pulse, but decay later faster tha e n samTh withouO-clathratN e. O N t e J 22 system in the liquid state does not show the hydrated electron at all becaus rapit i f deo reactio e reactione Th th wit. NO hf o n

dry electron with n liquiNi O d wate probabls i r t veryno y much Z faster than in the solid state. Interaction between water and NO is possibly changin e reactivit th e g th latter f o y. Pulse radiolysi solif so d hydrates helpe separato t d e sequenceth f o e reactions. The fact of small crossection for the reaction between dry electron and NO has to be taken into account in other system medid san a wher electroy dr e supposes ni o react d t with nitrogen suboxide. Pulse radiolysi solin i s d stat shoy ema w fine differencef so the structur matrixe th f eo . Pape present] C8 r s transformatiof no the trap wite electro th hmicrosecone th n no d time scal t 170Kea , corroborating with assumed relaxation of water molecules in similar systems. Another exampl f applicatioo e e solith f do n state pulse radiolysis is connected with looking for precursors of esr stable spectra observed long after the irradiation. Other intermediates which have no relation to esr spectra or products detected analytically, may be observed by pulse radiolysis during the pulse. E. g. the solid alanine, popular nowadays as dosimeter (wit detectionr hes radiation i ) n processing show a stransien t optical absorption spectru . Othenm m r wit0 maximue 52 hth t a m aminoacids show very different behaviour e resultTh . s wile b l published soon.

4. CONCLUSION OUTLOOD SAN K The comparatively young solid state pulse radiolysin i s i s the phas collectinf eo g experimental facts. Interpretatiof o n

86 experimental results will deman w loone k d a e intradiatioth o n chemistry of the solid state in general. Among problems unique to solid state are: micro- and macro heterogeneity of the material, the role of imperfections, spur phenomena in solid media, transportation of intermediates, specific energy transfer etc. Execution of solid state pulse radiolysis at temperatures different from ambient will be more important than in the case of liquids because of higher activation energies involved. It is hoped that solid state pulse radiolysis will gain importance in basic research. On the applied side, the developmen knowledgf o t solin i e d state radiation chemistry will stimulat applicationw ne e radiatiof so n processin d dosimetrygan .

ACKNOWLEDGEMENTS

The research is supported by the programme CPBP 01.19,02-12.

REFERENCES

[1] ZAGôRSKI, Z.P., Pulse radiolysis study on electrons trapped in aqueous solid clathrate Phys. J s . Chem 0 (19869 . ) 957.

CE3 ZAGORSKI, Z.P., Pulse radiolysis study on electrons trapped in semiclathrates and non-clathrate hydrates J. Phys. Chem. 91 <1987> 972.

[3] LAND, E.J., communication at the Gordon Conference "Radiation Chemistry'» 1986.

[4] ZAGORSKI, Z.P., ZIMEK Z., Cerenkov light selfabsorption as the indicato f o intermediatr e change n microseconi s d pulse radiolysis Int Radiât. J . . Phys. Chem 7 (1975. ) 529.

£53 ZIMEK, Z. , ZAGORSKI, Z.P., Cerenkov radiation as a source of analytical ligh n pulsi t e radiolysis experimental technique Hukleonik (19794 a3 ) 983.

87 [6) ZAGORSKI, Z.P., GRODKOWSKI, J. , ZIÄEK, Z. , BOBROWSKI, K., Pulse radiolysis of hydrates: Relation to the radiation chemistry of aqueous solutions Proc. 4th Symp. Radiation Chemistry, Keszthely 1976, Akademiai Kiadô, Budapest 1976.

3 E7 ZAGORSKI , Z.P., GRODKOWSKI , BOBROWSKIJ. , , TrappeK. , d electron spectra in hydrates of sodium, potassium and tetraalkylammoni\im hydroxides of varying HO content Radiât. Phys. Chera. IS <1980> 343.

£81 ZAGORSKI, Z.P., Thermal effects on the behavior of electrons trapped in aqueous solid clathrates J.Phys.Chera. 91 (1987) 734.

88 IMMOBILIZATION OF ASPARAGINASE IN RADIATION CURED, THERMALLY REVERSIBLE HYDROGELS

B. MÉCHAIN, Yanhui SUN, A. HUFFMAN Cente Bioengineerinr fo r d gan the Washington Technology Center, Universit f Washingtonyo , Seattle, Washington, United States of America

Abstract e havW e immobilized asparaginas a thermall n i e y reversible hydrogel by radiation curing solutions of N-isopropyl acrylamide mixed with monomer-conjugated enzyme and a crosslinker. We then measured the immobilized enzyme activitie a functio s a s f radiatioo n n dosd an e temperature. The immobilized enzyme is much more stable to radiation than the free enzyme or the monomer-conjugated enzyme. We have found that ablwe l abov ear cyclo ge beloet d e e an eth lowes w it r critical solution temperature, causin reversiblga e shrinkin occuo t l swellind rge gan e th f go in the aqueous environment, without significant loss of enzyme activity. The enzyme activity is "turned off in the shrunken gel above the LCST, but regains its activity when the gel reswells below the LCST. This system represents a novel way of preparing an immobilized enzyme reactor which smaly b f lof change turned e b an n n temperaturedn o ca si whicd an , h then may act as a temperature sensitive reaction "valve" for exothermic reactions.

. 1 INTRODUCTION Enzyme widele sar y use industrias da l catalysts diagnostin ,i chemicad can l assays and as therapeutic agents. Since enzymes are proteins, and liable to breakdown, they are often immobilized on or within various support materials in order to stabilize them and prolong their useful lifetimes, as well as to protect the environment from them. A variety of immobilization techniques have been use thir dfo s purpose, including physical adsorption, crosslinking, covalent attachment and entrapment (e.g. 1, 2). Radiation technique alsy usee osb ma immobilizo dt e enzymes (3), e.gcovaleny b . t attachment to a radiation graft copolymer (4-6) or by either covalent or physical immobilization within a radiation-cured hydrogel (7-13). Asparaginase is currently the principal therapeutic agent for treating acute lymphatic leukemia (14). However, this enzym n causca e e immunologie and toxicologie effects in its native form (15). These adverse effects can be reduced when the enzyme is immobilized. A variety of immobilization techniques have been utilize thir dfo s purpose (16,17). We have previously immobilized asparaginase onto a radiation graft copolymer of polymethacrylic acid deposited within the pores of a hollow fiber plasma filtration unit (18,19). We have also immobilized asparaginase onto a preirradiated cellulose paper by subsequent graft copolymerization onto the pre-activated cellulose backbones of monomer-conjugated enzyme plus acrylamide relate(6)n I . d studies have w , e incorporated monomer- conjugated asparaginase into chemically-cured thermally reversible hydrogels (9,10). These latter hydrogels were prepared from crosslinked copolymer N-isopropyf so l acrylamide (NIPAAm acrylamidd )an e (AAm), where each copolymer exhibit differensa t lower critical solution temperature (LCST). Such gels shrink significantly when warmed above their LCSTs,

89 which ranged from copplymee . 50°C32°th ca r Co fo t r gels studiede Th . gels reversibly reswell when cooled below their LCSTs (9,10) thin I .s study we have extended this approach by using radiation for the first time to cur thermallea y reversibl l containinege immobilizen ga d enzymee W . report on the effect of radiation dose, radiation temperature and gel reaction temperatur activite th n easparaginasf o y o poly(NIPAAma n ei ) hydrogel.

2. MATERIAL AND METHODS 2.1 Materials N-isopropylacrylamid obtaines ewa d from Eastman Kodak Co.. Methylene-bis-acrylamide (MBAAm d N,N,N',N'an ) - tetramethylethylenediamine(TEMED) were obtained from Aldrich. N- succinimidyl aery late (NSA) was synthesized following the method of Adalsteinsson et al. (20). L-asparaginase aminohydrolase (L-asparaginase) derived from Escherichia Coli was obtained as ELSPAR from Merck, Sharp and Dohme. Asparagine and Nessler reagent (Sigma Ammonia Color Reagent) were obtained from Sigma. PD-10 Sephadex Columns were purchased from Pharmacia. 2.2 Monomer Conjugation of Enzyme We have previously published this protocol (21) which was adapted from the procedure of Adalsteinsson, et. al. (20).

2.3 Radiation Curing of Poly (NIP AAm)-Asparaginase Hydrogels e followinTh typicaa s gi l protoco r preparinfo l enzymee gth - hydrogel 1.2A :M NIPAAms solutiowa 6 bufferS 8. 0.01 n ni PB H Mp , prepared with crosslinker (MBAAm) thao crosslinkee s , th t monomeo rt r molar ratio was equal to 1 to 300. The monomer solution was sparged for minute0 2 s using nitrogen enzyme th d an e, solutio addes n wa reac o dt ha molar concentratio 4.210'f mixturx e no 5 3 Th degasse.s ewa pulliny db ga vacuum usin ga standar d laboratory aspirator, unti bubblino n l s gwa observed mixture Th immediatel.s ewa y poured into glass molds (thickness polymerizatioe mm)Th 2 . initiates nwa d using gamma-irradiation from Co source (0.486 Mrad/day) for 16 hours at ambient temperature. The washes wa l d60ge three times wit Trito% h1 n X-10deionizen i 0 d watere on , time with deionize time d wateon e d witan r bufferhS 0.01 8.6PB H Mp , . The gel was cut into small discs and stored at 4°C in 0.01M PBS buffer, pH 8.6. We also synthesized a series of gels by irradiation at different temperatures from -78° to 20°C and at radiation doses from 0.12 to 0.486 Mrad. We irradiated native and monomer-conjugated enzymes in PBS buffer solution, treate forminl d exactlge e th g s ysolutionsa . In another series of gels, crosslinker concentration was varied by using four different ratios of crosslinker to monomer (1/400 to 1/100). The polymerizatio thir nfo s serie carries ambient a s wa t dou t temperature witha 0.32 Mrad radiation dose. The enzyme activities in all of these gels and solutions were tested using the Nessler assay, as described below.

90 2 . 4 Measurement of Enzyme Activity L-asparaginase reacts with L-asparagine to produce aspartic acid and ammonia. The amount of ammonia was determined by addition of Nessler reagent (65% solutio f mercurino c chlorid r mercurieo c iodide)e W . incubated 5 ml 0.06M L-asparagine solution in 0.01M PBS buffer, pH 8.6 for 5 min at 25°C. One gel disc was added and allowed to react 10 minutes. This reaction time correspond constana o st t rat turnovef e o enzym e th r rfo e reaction. (See Results). reactioe Th terminates nwa removiny d b l discge e . gth Followin g the enzyme reaction, 0.05 ml of the reaction mixture was transferred to a tube containin l deionizem 8 g1. d l Nesslewaterm 5 0. ;r reagen thes nwa t added sample Th . e absorbance agains blanta determinates kwa m n 0 42 t da (using a Bausch and Lomb Spectronic R 1001) after 10 minutes. The blank was prepare repeatiny db above gth e process without l discaddinge .e gth eacr Fo h sampl minimuea mthref o e discs were tested. native Th e enzyme solution activit determines ywa d usin similaga r procedure l .disc ge Instea ,e O.lmth f do enzymf o l e solution (0.72mg/ml) wa reactiose addeth stoppes d dnan wa addiny db g 0.0 Trichlorhydril 5m c acid (TCA) blanke Th thir . sfo s experiment were prepare addiny db e gth acid prior to the enzyme.

One International Unit (I.U.) of L-asparaginase releases one of ammonia per minute. The specific activity of the enzyme in LU. was calculated usin gstandara d curve obtaine reactiny db g Nessler reagent with ammonium sulfat sourca s ea ammoniaf eo .

I.U (Abs./0.562)(V/t)(ml/min= . )

. 3 RESULT DISCUSSIOD SAN N firse W t establishe mind0 1 tha e . timtth e chose measuro nt e enzyme activities in our gels was appropriate. We measured the ammonium aspartate product produced as a function of time by one gel at 29°C, in a 0.05M asparagine solution. It can be seen in Fig. 1 that the 10 minute time point is in the period of constant rate of turnover, which is desirable. Thus, all other studies reported here are for 10 minute runs. We then tested the influence of radiation conditions on the enzyme activity. Kaetsu and co-workers (8) have prepared immobilized enzyme systems by low temperature irradiation of supercooled glassy monomer solutions containing dissolved enzymes. They suggested that n -78°a s Cwa appropriate temperatur sucr eimmobilizatiofo n ha n process alse oW . varied the radiation temperature between -78° ambiend Can t (18°C measured )an d asparaginase activit t 29°ya hydrogelCn i s cured 4 witMra0. ha d dose. Figur showe2 s thaactivite th t vers yi y little influence temperature th y db e during irradiation. However mechanicae th , l variel ge strengt e dth f ho visibly with radiation temperature gele sTh . formed between -78°- d Can 15°C were very weak and opaque, while that formed at 0° was also opaque but stronger, but still easily torn. Only at ambient temperature did we obtain a strong, transparent gel. Thus chose w , e r thiou s f conditioo l al r nfo subsequent studies.

91 1200-

1000- 'S tf 800-

600-

400-

200-

I I 10 20 30 40 50 60 Time (min) Fig. l. Reaction kinetics for asparaginase immobilized in a radiation-cured poly(NIPAAm) gel. (Asparagine cone 0.05.= MPBSn i ; reaction temperatur 29"C)e= .

300-

I 250-

S> 200-

S 150-

50-

I I 0 -2 -80 0 -4 -60 20 Radiation temperature (°C) Fig. 2. Effect of radiation temperature on the activity of asparaginase immobilize a radiatiovi d n curin a poly(NIPAAm n gi ) gel. (Asparagine cone. = 0.05M in PBS; reaction temp = 29°C; radiation dose = 0.4 Mrad).

92 100.00

• Free enzym buffen ei r 20.00- ° Conjugated enzyme in gel * Conjugated enzym buffen ei r

0.00 0.00 0.10 0.20 0.30.400 0.50 Dose(Mrad) Fig . 3 Effec. radiatiof o t nrelative dosth n eo e activit f freyo e enzyme, monomer-conjugated enzym enzymd an e e immobilizea n i d poly(NIPAAm) hydrogel.

200-1

150-

100-

50-

• Temperature increase o Temperature decrease

20 25 30 35 40 Temperature (°C) Fig. 4. Effect of reaction temperature on the activity of asparaginase immobilize a thermall n i d y reversible poly(NIPAAm) gel. (Radiation dose = 0.32 Mrad).

93 We then investigated the effect of radiation dose on the relative enzyme activity (normalize initiale th o dt , zero dose activity threr )fo e types of asparaginase ) fre(1 :e enzym solutionn ei monomer-conjugate) (2 , d enzyme in solution and (3) immobilized enzyme in our LCST hydrogel. resulte Th showe sar Figurn i . e3 It can be seen that the free enzyme rapidly loses activity as dose increases, and retains less than 30% of its initial activity at 0.5 Mrad. Monomer-conjugation of the enzyme protects it somewhat from the radiation, as it retains about 50% of its activity at 0.5 Mrad. However, the most interesting result is that the hydrogel-immobilized enzyme is most stablradiatione th o et retain d an , mucs sa 80-90s ha activits it %f o y ovee rth whole rang dose f stabilizeo y ma sr l enzymo studiede e ge th e on y eTh b . more covalent attachments to the polymer network. Also, the effects of radiatio aqueoue th n no s phase insid gele eth , perhap combination si n with the polymer chains generaty ,ma lesea s reactive spectru mfref o e radicals, ion-radicals and other species which can attack and deactivate the enzyme. We then tested the effect of reaction temperature on the enzyme activity within the thermally reversible hydrogel. We prepared one enzyme- gel system by irradiation at ambient temperature to a dose of 0.32 Mrad. We men measured the generation of ammonium aspartate from asparagine afte minute0 1 r f reactioo s n wit enzyme-gee hth t varioua l s increasing temperatures from 25°C to 37°C. Following this series of increasing temperatures, we cooled the gel and remeasured the enzyme activity within same th r e fo serie l th edecreasinf ge s o g temperatures. Figur showe4 s these results. It can be seen that the activity of the enzyme increases with temperature up to about 32° C. This increase is due both to the increase in substrate (and product) diffusion rates as well as to the increase in enzyme- substrate reaction rate with temperature. This occurs despite the gradual shrinkage and loss of some pore water as the temperature approaches the LCShydrogee th f To l (9-12). However, onc LCSe eth passeTs i d (ca. 33° C) the gel rapidly shrinks and loses a large fraction of its aqueous swelling solution. This los porf so e volume significantly reduce ratee sth s of substrate diffusion in in as well as that of product out to the surrounding solution, where it is assayed. Thus, the measured activity rapidly drops as temperature rise 37°Co st cooleds i . l Whe activite ge e th , nth regaines yi d and rises to a maximum ca. 32°, then drops after that to 25°C, following the same curve as before. This shows that the effect is reversible and is due to pore collaps reexpansio warmed s i el an coolege d e dan th sequencedn s ni a . e havW e noted similar behavior with chemically-cured LCST hydrogels containing immobilized enzymes and cells (9-12, 23). We have also shown that bot diffusioe hth partitiod an n n coefficient thesn i s e gels drop rapidly at the LCST, especially the diffusivity, and this is due to the los f "free"so , bulk-lik l shrinkege watee th s s (23,24)ra .

4. CONCLUSIONS In conclusion have ,w e shown that: 1) Radiation may be used to form an immobilized enzyme-gel by curing an aqueous monomer-crosslinker solution containing a monomer-conjugated enzyme.

94 2) Neither radiation temperature nor dose have a significant influenc enzyme th l appearn eo ege activite gelo e sTh t th . n yi "protect" the enzyme from the radiation. enzyme-gee Th "turnee offd b ) an "y 3 reversibln do ma l y yb warming and then cooling through the LCST of the gel. 4) Such temperature control of hydrogel-immobilized catalysts may have wide biomédica industriad lan l uses.

ACKNOWLEDGEMENTS One of the authors (B.M.) would like to thank Mme. M.L. Martin, Faculté des Sciences, Univ. de Nantes, Frances for providing her the opportunit continuo yt D.E.Ar ehe Profn .i . Huffman's laboratory alse oW . gratefully acknowledge the support of the du Pont Co., Johnson & Johnson Co. and the Washington Technology Center.

REFERENCES [I] WINGARD, L.B., Jr. et. al., (Eds.), Immobilized Enzyme Principles, Academic Press, N.Y., N.Y. (1976). [2] LASHKIN, A.I., (Ed.), Enzymes and Immobilized Cells in Biotechnology, Benjamin and Cummings Publ., Menlo Park, CA (1985). [3] GOMBOTZ, W.R., HOFFMAN, A.S. , "Immobilization of biomolecules and cells on and within synthetic polymeric hydrogels," in Hydrogels in Medicine and Pharmacy, Vol. I (PEPPAS, N.A., Ed.), CRC Press, Boca Raton, FL (1986) 95- 126. [4] HOFFMAN, A.S.. al.et ,, Covalent bindin f biomoleculego o t s radiation grafted hydrogels, Trans. Amer. Soc. Artif. Organs, 18 (1972. 10 ) [5] HOFFMAN, A.S., "Ionizing radiation and plasma discharge treatments for preparation of novel polymeric biomaterials", in Polymers in Medicine, Advances in , No. 57 DUSEK , Ed.)K. , , Springer-Verlag, Berlin, F.R.G. (1984). ] [6 DONG, L.C., HOFFMAN w metho,ne r A.S.fo A d , immobilization of biomolecules using pre-irradiation grafting at low temperatures, Radiât. Phys. Chem., 28, (1986) 177-182. ] [7 DOBO , ActJ. , a Chim. Acad. Sei. Hungar. (19703 6. , ) 453. [8] KAETSU, I., et. al., Studies on the immobilization of biofunctional component radiatioy sb n polymerization, Radiât. Phys. Chem.7 2 , (1986) 245. ] [9 DONG, L.C., HOFFMAN, A.S., Thermally reversible hydrogels: III. Immobilization of enzymes for feedback reaction control, J. Contr. Rel. (19864 , ) 223-227. [10] DONG, L.C., HOFFMAN, A.S., "Thermally reversible gels. IV : Swellin d deswellinan g g characteristic d activitiean s f o s copoly(NIPAAm/AAm) gels containing immobilized enzymes", in ACS Symposium Series, 350, Reversible Polymeric Gels and Related Systems, (RUSSO, P., Ed.), ACS, Washington, DC (1987) 236-244. [II] HOFFMAN, A.S., "Thermally reversible hydrogels containing biologically active species", in Polymers in Medicine III, (MIGLIARESI . al.et , , Ed.)C , , Eisevier Science Publishers B.V., Amsterdam (1988) 161-167.

95 [12] PARK, T.G., HUFFMAN, A.S., Effec temperaturf o t e cyclinn go activit productivitd yan f immobilizeyo d ß-galactosidasa n ei thermally reversible hydrogel bead reactor, Appl. Biochemd an . Biotech., 19 (1988) (in press). [13] . KUGOal.et , , K. "Radiatio, n cured, thermally reversible hydrogel usefusA baseimmobilizer PV fo l n do d biomoleculed san cells." (Proc World 3r . d Biomtls. Congr,, Kyoto, Japan, Apri- l21 25, 1988) 108. [14] LIU , CHABNERY , , B.A., "Enzyme therapy: L-asparaginase,n "i Pharmacologie Principles of Cancer Treatment, (CHABNER, B., Ed.), W.B. Saunders Company, Philadelphia (1982) 435-43. [15] DOWOLY . al.et ,, Toxi W. anti-neoplasti,d an c c - effecL f o t asparaginase, Cancer , (198619 , ) 1813-1819. [16] WEETALL, H.H., COONEY, D.A., "Immobilized therapeutic enzymes", in Enzymes as Drugs, (HOLCENBERG, J.S., ROBERTS, J., Eds.), Wiley Interscience, N.Y., N.Y. (1981) 395. [17] SCHMER, G., HOLCENBERG, J.S., "Entrapment of enzymes and drugs," ibid, 385. [18] GOMBOTZ, W.R. . al.immobilizatioe et , ,Th L-asparaginasf no e on porous hollow fiber plasma filters, J. Contr. Rel., 2, (1985) 375-383. [19] HOFFMAN, A.S. . al.,et , Immobilizatio f enzymeo n d an s antibodie o radiatiot s n grafted polymer r therapeutifo s d an c diagnostic applications, Radiât. Phys. Chem., 27 (1986) 265-273. [20] ADALSTEINSSON, O., et. al., Preparation and magnetic filtration of polyacrylamid l containinege g covalently immobilized proteins and ferrofluid, J. Mol. , 16 (1978) 199-255. [21] SHOEMAKER, S., et. al., Synthesis of vinyl monomer-enzyme conjugates, Appl. Biochem Biotechnologyd an . (19875 1 , ) 199- 225. [22] PARK, T.G., HOFFMAN, A.S., Immobilization and characterization of ß-galactosidase in thermally reversible hydrogel beads. (Submitted to J. Biomed. Mater. Res..) [23] DONG, L.C., HOFFMAN, A.S., unpublished results. [24] ZHONG, Y.P., et. al., "The effect of bound and free water on the activity of enzymes immobilized in thermally reversible Hydrogels." (Proc. 3rd World Biomtls. Congr., Kyoto, Japan, April 21-25, 1988) 107.

96 SOME ASPECT RADIATIOF SO N CHEMISTR EPOXIEF YO S

. SINGHA , C.B. SAUNDERS, A.A. CARMICHAEL, V.J. LOPATA Radiation Applications Research Branch, Whiteshell Nuclear Research Establishment, Atomic Energy of Canada Limited, Pinawa, Manitoba, Canada

Abstract Epoxides can be radiation-polymerized using electron beam or gamma irradiation polymerizatioe .Th n process occurs mostly by a cationic mechanism. Water acts as an inhibitor of the cationic mechanism, and, therefore, monomers have to be carefully dried. Epoxie larga usee n sar i d e varietf o y products, including structural composites. Radiation polymerizatio f theio n r matrices offers some unique advantages, suc lowes ha r residual stresse ambieno t e sdu t temperature processing. Carbon fibre-epoxy composites are used extensivel satellitesn i y . Becausconcerne th f eo s abou integrite th t f satellito y e component outen i s r space, there is also considerable interest in the study of radiation effects on epoxies. Polymer matrices in the composites used in satellites in geosynchronous orbits get exposed to very high doses during their lifespan of ~30 years n thi.I s paper, radiation polymerizatiof o n cyclohexene oxide, as an example of the radiation polymerization of epoxides, radiation curing of carbon fibre-acrylated epoxy composite d radiatioan s n effectn so some epoxies are briefly reviewed.

1. INTRODUCTION Epoxies constitute an important class of plastics. Organic compounds containing the three-membered oxirane ring system, also known as the epoxides, are the starting points for the epoxy resins. The most common epoxies are the diglycidyl ethers [1] produced by the reactions of epichlorhydrin with derivativess bisphenoit d an lA . Epoxie e particularlsar reinforcen i e yus goor dfo d composite structures. They provide high strength-to-weight ratios and good thermal and electrical properties. In the aircraft and aerospace industries, carbon fibre-epoxy composites are being increasingly used. The industrial usefulnes epoxief so s continue encourago t s e further worn ko them [2-4]. Polymerizatio produco t n e epoxienumbea done b y eb n rsca of methods, including radiation curing [5,6] e exten.Th f o t radiation curing on the industrial scale appears to be small. However, because of the overall advantages of radiation curing [7], which include increased cure speed,

97 ambient processing temperatures, eliminatio chemicaf no l initiator d reducesan d residual stresse compositen i s s [8], its industria expectes i e lus increaseo t d e possibilit.Th y of this increase is further strengthened with the potential w 10-Mene e oVth f electron accelerators, which could cure thin composites (< 4 cm, unit density) with electrons and thicuni, cm t k 0 density2 one < ( s ) with X-rays [9]. The environment in outer space, where carbon fibre-epoxy composites are being used in satellites, is very severe. These composites have to maintain their integrity and function despite repeated thermal cycling (from -150 to 175°C) every day, and exposures to sunlight and a mixed fiel high-energf o d y radiations. Because radiation-cured composites contain no catalysts, they may offer better characteristics for use in outer space. This brief review focuse radiation so n polymerizatiof no epoxies, taking cyclohexene oxide as an example, radiation curin carboa f go n fibre-acrylated epoxy composited ,an radiation effect n somso e epoxies elucidato t , e th e behaviou compositef ro outen si r space.

2. RADIATION POLYMERIZATION Radiation polymerization of many epoxides, including cyclohexene oxide, has been widely investigated [6,10-12]. Cyclohexene oxide undergoes radiation-induced polymerization in liquid, glassy soli d crystallinan d e states [10,11]o ,t give a solid amorphous polymer. Convincing evidence for the inhibitory rol watef eo radiation i r n polymerizatiof no cyclohexene oxide has been reported [10], It was found that the additio 0.02f no % wate carefullo t r y dried monomer reduce rats it f polymerizatiodeo y 10%nb , whereae th s additio 0.5f no % water reduce factoa rate y th d b e 2.5f o r . For the dry monomer, the polymerization rate increased with temperature, from 4%/h at 0°C to 20%/h at 50°C. Polymerizatio s alsnwa o inhibite ammoniay b d , suggestinga cationic mechanism [10,12], starting witformatioe th h f no the monomer cation and an anion (electron or a solute anion):

C6H100 -> C6H100* + X- [1] The cation undergoes stepwise addition to the monomer, leadine formatio th polymere o th t g f no :

+ C6H100 +(n-1+ ] [2 ) C6H100 -» (C6H100)n

(C6H100)n+ + X- -» (C6H100)n [3] However, the growth of the cation can be inhibited by water or ammonia,

6H9° + H30+ [4]

NH 3 + (C6H100)n_(m+1)C6H90 V +N

98 chaiy b r no transfer (proton transfe e monomerth o t r )

- 06 H100)n_(m+1)C6H9+ 0

] [6 C6HU0+

Oxygen doe t inhibisno t cationic polymerizationd ,an therefore radiation polymerizatio epoxidef no e b n ca s carrieairn i .t Howeverou d inhibitioe th , f cationino c reaction y tracesb watef so r requires careful e dryinth f o g monomers, thus makin procese th g s unattractiv industryo t e . In comparison to the epoxides, acrylated epoxy resins lend themselves well to radiation polymerization [6] and do nos sensitiva t e b see o t mo inhibitio t e y moisturenb . Thus, radiation processing is a potentially useful technology for the manufacture of composites from acrylated epoxies.

RADIATIO. 3 N PROCESSIN CARBOF GO N FIBRE-ACRYLATED EPOXY COMPOSITES A resin system combinin epoxn ga y diacrylate oligomer (50mass)y b % ,polybutadiena e diacrylate oligomer (30%d )an the multifunctional monomer dipentaerythritol monohydroxypentaacrylate (20%) s beeha n user preparinfo d g carbon fibre-acrylated epoxy composites [8,13]. The polybutadiene diacrylate was included in the resin formulation to improve the flexibility and impact resistance of the epoxy diacrylate polymer. The dipentaerythritol monohydroxypentaacrylat s addee wa improvo t d e th e weatherabilit e flexibilitth d formulatioe yan th f o y n [8, 13]. r reinforcementFo ,plain-weava e carbon fabric, produced from polyacrylonitrile (PAN) precursor, was selected from an aircraft manufacturer's qualified products list [8,13]. Composites containing carbon fibres are particularly suited to radiation processing, since carbon fibres exhibit excellent radiation stability. The mechanical properties of carbon fibres are not adversely affected by electron beam treatment to a dose of 50 MGy [14]. For fabricating the composite material, laminates containing 14 plys, all in the same fibre orientation (±1°), were made using standard hand layup methods [8]. Both vacuum-ba external-pressurd an g 0 kPa60 )< ( e techniques were used during radiation processing with 10-MeV electrons from the AECL 1-10/1 linear electron accelerator. The key mechanical propertie composite th f so e produced compare favourably with the specifications of a leading aircraft manufacturer shows ,a Tabln ni . eI The gel fraction of the radiation-polymerized matrix was found to depend on the dose rate [8]. The samples irradiated with gamma radiation (dose rat kGy/h6 1 e , nitrogen atmosphere) reached a gel fraction of 97%, whereas those irradiated with 10-MeV electrons (dose rate 1300 kGy/h, nitrogen atmosphere l fractioge a 88%.f d e reasono n) ha Th s

99 8

TABL INDUSTRIA: EI L CARBON FABRIC-EPOXY PREPREG LAMINATE SPECIFICATIONS AND RESULTS

TEST SPECIFICATIONS EB-TREATED PREPREG TEMP. PROPER'1'IBS2 MINIMUM MINIMUM MINIMUM PROPERTY <°C) AVERAGE2 VALUE3 AVERAGE2 VALUE3 Ultimate Tensile Strength (MPa) 20-130 480 410 580 565 Tensile Modulus (GPa) 20-130 59 55 57 49 Tensile Strain (-cm/cm6 10 )x 20 7000 - 11,400 10,000 130 6500 - - -

laminate Th ) (1 e containsame th e n fibrplysi 4 s1 l e,al orientation (±1°). least A ) t (2 five specimens were tested. (3) For single samples. r thifo s dose-rate e knownt dependencth ye t n .I no e ear presence of air, the gel fraction decreased by about 8% in the case of gamma irradiation, but was unchanged in the case of electron-beam irradiation. This oxygen effect suggests that the radiation-polymerization occurs at least partially via a free radical mechanism. It is known that the inhibitory effect of oxygen on free radical processes in polymers decreases with increasing dose rate [15], primarily becaus dissolvee th e d oxygen gets consumediffusioe th d an d n f furtheo r oxyge slos ni w compare e ratee th th f so o t d radiation-induced reactions. Radiation polymerizatio essentialls i n adiabatin a y c process s importanti t .I , therefore monitoo t , e th r temperatur compositee th ris n i e s during irradiation.A dose of 42 kGy delivered at a rate of 1300 kGy/h caused a temperature rise of 39°C at the surface of the laminate and 46°C internally [8,16]dose th e kGy/h6 t 1 .ratA f o e, during gamma irradiation, the sample temperature rose by 19°C, both d thean n y surfacee internallkG th 0 3 dosa t a t f ,ea o d yan remained constant on further gamma irradiation [16]. Fourier-transform infrared spectroscope th f o y individually irradiated (100 kGy) epoxy diacrylate, polybutadiene diacrylate and dipentaerythritol monohydroxypentaacrylate showe amoune dth f tha) o t (i t unsaturatio s reducenwa eachn i d ; (ii) carbon dioxida s ewa radiolysis product in both the polybutadiene diacrylate and the dipentaerythritol monohydroxypentaacrylate d (iii;an ) the polyether structure was not affected by irradiation [16].

4. RADIATION EFFECTS The components of satellites in geosynchronous orbits are expecte receivo t d 1-MG~ e y dos thein ei r projected 30-year lifespan. Irradiation is known to induce crosslinking and degradatio epoxien i n s [17,18] case structuraf th eo n .I l composites, the aims of the irradiation studies include (i) improvement propertiee th matricese n i sth f so d (ii,an ) determination of the radio- and thermal resistance of the matrice t conditionsa s simila thoso t r outen i e r space. Ther e severaear l polymers, other than epoxies, thae ar t known to be radiation-resistant. For example, (i) polyetheretherketone is reported to have withstood doses up to 11 MGy without significant degradation [19], and (ii) polyetherimid fairls ei y resistan gammo t a radiation (94% retentio tensilf no e strengt irradiation o h y [20])MG 4 . o t n Unfortunately studiee th f ,o s ver w includfe y e detailf o s chemical changes (degradatio d crosslinkingnan ) that take plac n irradiationeo . generaln I , les knows si n abou basie th t c mechanismf so crosslinking in epoxies than in polyethylene [21,22]. It may be assumed that, as in the case of polyethylene, radiation- induce dH bon epoxiebreakagn C- i de th sf eo woul d plan ya importan tcrosslinkine th rol n ei g reactions:

101 RCH2OCH2R -* (RCH;,OCHR)- + H- [7]

2 (RCHjOCHR)- -> RCH2OCHR [8]

RCH2OCHR Tilman Krokoskd an s y [23] investigate effece th d f o t radiatio mechanicae th n o n l propertie a thermall f so y cured epoxy system consistin Epof 8 epoxgo 82 n y resi phenyd nan l glycidy lreactive etheth s a r e diluent (Shell)e th d ,an curing agent EM 308 (Thiokol). Their results suggest that crosslinking, which enhanced the strength of the composite, was predominant up to a dose of 20 MGy. However, the strength decrease highet a d r doses, presumably becausf eo degradation. Sykes and Bowles [24] investigated the effect of electron beam (1 MeV) irradiations (1 MGy) of two epoxy- graphite composites under vacuum at about 30°C. One was the commercially available T300/CE339 systems, which is probably a dicyandiamide-cured diglycidyl epoxy with carboxy- terminated butadiene-acrylonitrile elastomer copolymer and the other its modification in which the elastomer had been omitted. They reported tha) durin(i t g thermal cycling (-150 to 175°C) ther s significanewa t microcrackine th f o g irradiated samples dosew MGy1 d e (iilo < )( an sth ,t ) a sample containin elastomee th g r exhibited more microcracking. Netraval coworkerd an i s [18] investigated irradiation of a crosslinked epoxy resin formed by the reaction of tetraglycidyl-4,4'-diaminodiphenyl and

the curing agent diaminodiphenyl sulfone. The irradiations were done with 0.5-MeV electrons (dose up to 4 MGy) Coor60 gamma radiation (dose up to 1.6 MGy). Differential scanning of the cured samples showed a large exothermic pea 272°Ct ka , suggestin exothermin ga c curing reactiof o n the unreacted epoxy groups. Irradiatio resie th nf o nreduce d this exothermic peak (~ 85% of the unirradiated at a dose of ~ 2 MGy). Infrared spectroscopy confirmed the reduction of the residual epoxy groups on irradiation.

CONCLUDING REMARKS The requirement to carefully dry the monomers has discourage industriae th d f radiatioo e lus n polymerization of pure epoxide systems. The current alternative to extensive drying of the epoxides is to incorporate catalysts [6], acrylics or other monomers in the formulations [6,8]. A radiation-curable carbon fibre-acrylated epoxy composite has been prepared that meets the typical physical d mechanicaan l property specification aircrafe th f o s t industry [16](Table I). Optimization of the formulation used y providma composita e e material with improved properties for use in aircraft and satellites. To understand the effects of mixed radiation fields and thermal cycling in outer space, it would be useful to supplemen experimente th t e changeth n relevann o ssi t

102 mechanical properties, with studie simultaneoun so s chemical changes. The studies should also be extended to mixed radiation fields, including electrons, gamma radiation and heavier energetic particles, know bombaro t n d objectn i s outer space. Materials used in outer space are also exposed to a wide spectrum of sunlight, with a bigger component of ultraviolet than that reachin earth'e th g s surface. Thus further research on radiation effects on composites should also incorporate appropriate photolysis studies. Simultaneous irradiatio matricef o n s with high-energy radiation and ultraviolet light is likely to increase their degradation s compare,a radiolysio t d s alone.

REFERENCES

[I] HANDLOVITS, C.E., "Epoxy", Modern Plastics Encyclopedia, Vol .3 (AGRANOFF6 Ed.), ,Y. , McGraw- Hill, New York (1986) 21. ] [2 THOMPSON , SONG,D. , J.H WILKESd .an , G.L., Structure- property behaviou f electroro n beam cured bis-GMA, Polym. Mater. Sei. Eng 6 (1987.5 ) 754. ] [3 PACANSK WALTMAN, YJ. , R.J., Electron beam curinf go poly(perfluorinated ethers) used as lubricants in the magnetic media industry: poly(perfluoropropylene oxide) , (Radcure '86, Baltimore, 1986, Conf. Proc.), (1986) 6-1. [4] KRETSCHMER, J., Composites in automotive applications arte - statth , f Mato e . Sei. Tech .(19884 ) 757.

[5] WHITE, H.J., "Epoxy curing agents" Encyclopedie ,Th a of Basic Materials for Plastics, (SIMONDS, H.R., CHURCH, T.M., Eds.) Reinhold Publishing Corp., New York (1967) 159. ] [6 DICKSON L.W., SINGH Radiatio, ,A. n curin epoxiesf go , Radiât. Phys. Chem. 31 (1987) 587. ] [7 RIE BEREJKA, ,J. , A.J., "Radiation curing" ed.d 2n , , Association of Finishing Processes of the Society of Manufacturing Engineers, Dearborn, Michigan (1986).

] [8 SAUNDERS, C.B., DICKSON, L.W., SINGH CARMICHAEL, ,A. , A.A., LOPATA, V.J., "Radiation-curable prepeg composites", AECL-9560 (1988). ] [9 McKEOWN "Radiatio, ,J. n processing using electron linacs, IEEE Transaction Nuclean i s r Science NS-32 (1985) 3292.

[10] CORDISCHI, D., LENZI, M., MELE, A., Radiation-induced polymerization of 1,2-cyclohexene oxide, J. Polym. Sei., Part A 3 (1965) 3421.

[II] HIRAMOTO ISHII, ,T. HAYASHI , ,M. OKAMURA, ,K. , S. , Termination mechanism in the plastic crystalline state polymerization of 1,2-cyclohexene oxide, Polym. Lett. 10 (1972) 511.

103 [12] AIKINS, J.A.,, WILLIAMS, F., Radiation-induced cationic polymerizatio limonenf no e oxide, a-Pinene Oxide and ß~pinene oxide", ACS Symp. Ser. 286 (1985) 335.

[13] SAUNDERS, C.B., DICKSON, L.W., SINGH CARMICHAEL, ,A. , A.A., LOPATA, V.J., Radiation-curable carbon fiber prepreg composites, Pol. Comp (19889 . ) 389.

[14] FORNES, R.E,, MEMORY J.D., NARANONG Effec, ,N. f o t gammV Me 1.3electronV a3 Me radiatioe 5 th 0. n so d an n mechanical propertie graphitf o s e fiber composites, Appl. Polymi Sei. 26 (1981) 2061.

[15] DICKSON, L.W., McKEOWN "Radiatio, ,J. n interactions with linac beams", (Proc. Working Meeting on Radiation Interactions, Leipzig, E. Germany, 1987) 21.

[16] SAUNDERS, C.B., CARMICHAEL, A.A., KREMERS, W.,. LOPATA, V.J., SINGH, A., "Physical and mechanical characterizatio f radiation-curablno e carbon fibre composites", Proc. 19th Ann. Conf. Canad. Nucl. Soc., Winnipeg, Manitoba, 1988) pressn ,i . [17] LEE, H., NEVILLE, K., "Handbook of Epoxy Resins", McGraw-Hill Yorw ,Ne k (1967).

[18] NETRAVALI, A.N., FORNES, R.E., GILBERT R.D., MEMORY, J.D. Investigations of water and high energy radiation interaction n epoxya n i sAppl. , J . Polym. (19849 2 Sei. ) 311. [19] DILLON, H.J., "Polyetheretherketone", Modern Plastics Encyclopedia, Vol. 63 (AGRANOFF, Y., Ed.), McGraw- Hill, New York (1986) 52.

[20] BARTOLOMUCCI, J.R., "Polyetherimide", Modern Plastics Encyclopedia, Vol. 63 (AGRANOFF, Y., Ed.), McGraw- Hill, New York (1986) 50.

[21] DOLE, M. (Ed.), "Free Radicals in Irradiated Polyethylene", The Radiation Chemistry of Macromolecules, Vol. I, Academic Press, New York (1973) 335. [22] MANDELKERN , "Radiatio,L. n chemistr lineaf o y r polyethylene", The Radiation Chemistry of Macromolecules, Vol ., (DOLEI Ed., ,M. ) Academic Press, New York (1973) 287. [23] TILMANS KROKOSKY, ,A. , E.M. effece Th , radiatiof o t n n somo e mechanical propertie epoxn a f yo s system. ,J Mater. 6 (1971) 465. [24] SYKES, G.F,., BOWLES, D.E., Space radiation effects on the dimensional stability of a toughened epoxy graphite composite, Int. SAMPE Symp. Exhib 1 (1986.3 ) 657.

104 THE RADIATION CHEMISTRY OF CONNECTIVE TISSUE; HYALURONIC ACID

. MYINTP , D.J. DEEBLE, G.O. PHILLIPS North East Wales Institute of Higher Education, Kelsterton College, Connah's Quay, Clwyd, United Kingdom

Abstract

Aqueous solution f hyaluroniso c acid have been irradiated under various condition amoune th d stranf to san d scissio determines nwa d viscometrically. OH radicals were found to be some 1.5 times more potent tha atomH n t inducina s g breaks, methanol, propan-2-od an l t-butanol radicals produced relatively little breakage (potency less than 3% that of *OH). Tetranitromethane (TNM) has been used to measur e yielth ef reducino d g radicals produce H radicaO n o d l attack n hyaluronio c acid hyaluronie th , f arouno % c80 d acid radicals reacted witM (ie TN hreducine .ar g radicals) wit rata h e x constan 5 4. f o t 1 — 3 1 ~ 1 08 mol dm s .In contrast similar measurements on the polysaccharide model, £-cyclodextrin, indicated that all the radicals formed were reducing. The presence of TNM or oxygen during radiolysis caused a 3O% fall in chain breakage. The majority of radicals produced in both hyaluronic aci(S-cyclodextrid an d e eithear n dihydrox2 1, r r o y 1-hydroxy 2-alkoxy type radicals, both of which form £-carbonyl radicals by the acid {and base) catalysed elimination of water or alcohol. These e-carbonyl radical e considerablsar y less reducing than their parent <>(-hydrox t expecteyno radicale ar o reac t dd an st with TNM. By determining the extent of reaction with TNM as a function of TNM concentration, the first order rate constant for the formation of £-carbonye th l radical e calculateb n ca s n applyino d g simple competition kinetics e rat e abou.Th s founb e wa o constant 4 d H p t a t 4 x 10 s in the case of hyaluronic acid radicals, with the J3-cyclodextri e ratn th systee 8 constan2. mH p eve s lest a tnwa s tha2 n x 103 s"1.

105 1. INTRODUCTION Hyaluronic acid is a pclysaccharide and a member of the group known as mucopolysaccharides or glycosaminoglycans. The monomeric repeating unit in hyaluronic acid is D-glucuronic acid fc-1-3 linked to N-acetyl D-glucosamine, these subunits are then linked together by £-1-4 glycosidic bond s. Hyaluroni (Fig1) . c majoa aci s i dr constituenf o t loose connective tissue although its presence in nature would seem to be considerably more widespread in that it has been found, often in very small amount n ev€>ri s y human tissu s beer whicha fo e n t i h analysed [1]. Ionising radiatio uses i no sterilis t d e human tissu r storagfo e n i e tissue banks, where it is then available for transplantation. Much of the most useful tissu connectivs ei s importani e t tissui d tan e that the effects of radiation on the tissue components is well understood. Hyaluronic acid particularle seemb o t s y sensitiv radiatioo et ] [2 n prima ans i de candidat r studyfo e . In diseases such as arthritis, hyaluronic acid in the synovial fluid is degraded and free radical mediated processes are believed to be responsible [3]. The application of standard radiation chemistry techniques permits the detailed study of many of the reactions involved. Hyaluronic naturall s acidit n i , y occurring state higa s h,ha molecular weight (several million Daltons) and when dissolved in water forms viscous solutions. Indeethis i st i dpropert y whic s thoughi h t o confet hyaluronin o r c aci biologicas d it muc f o h l usefulness [1]. Relatively simple methods can be utilised to measure viscosities and since viscosit s quantitativeli y y relatee moleculath o t d re th siz f eo solute, these data enabl e averagth e e solute molecular weighe b o t calculated. This procedure has been applied to hyaluronic acid solutions irradiated unde varieta r f conditiono y n ordei s measuro t r e e chaith n breaking potenc f selecteo y d attacking radicals. numbea Ther e f possiblar eo r e site hyaluronin so c acid wherea free radical could be formed. A very elegant technique was developed

106 COOH CH2OH

NHCOCHa

Figure 1. Repeating unit of Hyaluronic acid.

to distinguish the two major radicals formed by "OH addition to pyrimidines [4], This metho differine bases th i d n o d g redox potential e adductsth f o se 6-y ,th l radical (the reducing radicals )i able to reduce the oxidant tetranitromethane (TNM), while not reacting with the reductant N-N-N'-N'-tetramethyl phenylene-diamine (TMPD). In contras 5-ye tth l radical (the oxidising radical) reacts with TMPt bu D not with TNM. The concentrations of the products of these reactions, TMPD from TMPD and the nitro-form anion (NF~) from TNM, can be readily determined spectrophotometrically. In the past few years this metho bees ha dn used with great succes determino t s e specific radical yield numbea n i sf system o r s wore [5]th k n .presenteI ds hereha M ,TN been used as a probe to examine hyaluronic acid radicals. The effect n freo eM oTN radicaf l mediated hyaluronic acid chain scissios nha also been investigated, p-cyclodextrin is a cyclic polysaccharide consisting of seven jS-l-4-linked glucose molecules and provides a n infinitela mode r fo l y long linear polysaccharide chainr .Fo comparative purposes, TNM has also been used to measure the radiation yield f reducino s g radicals forme n irradiatei d d £-cyclodextrin solutions.

107 MATERIAL. 2 METHODD SAN S Hyaluronic acid (highly puregifa s t )wa from Pharmacia, Uppsala, Sweden. All other chemicals were of "Analar" or equivalent grade. Water was triply distilled, the final distillation being from alkaline permanganate. Viscometry and the evaluation of viscometric data were performed as previously described [6]. Steady-state irradiations were performed with o eithe(0.0C 6a r s (0.0C 1Gy/s Gy/sa r )o ) irradiation source. Fricke dosimetry s employedwa . Pulse radiolysi e PatersoTh carries t a wa s t n ou d Institute for Cancer Research, Manchester, U.K. [7], To ensure internal consistency, a saturated 1 x 10 mol dm formates solutiowa M containin, 7 TN H p n m d l g mo 0.5-1. 0 1 0x — 3 — "î use s dosimetera d , taking molecules/lOOe6 G(NF~ e b o )t e th d an V extinction coefficient of NF at 35Onm to be 14600 mol dm cm [8] M concentration.TN s were determine e additioth a y b df o n known volume of concentrated hydrazine solution (so that there was a large exces f hydrazino s o e (t ove ~ rNF TNMo t o )converM t TN e tth ensure a rapid reaction the final pH of the solution was made ca. 9.5 e additiobth y f sodiuo n m hydroxide). Possible contaminatiof no unirradiated solutions by NF~ was avoided by making use of the volatility of TNM. A pre-gassed (N„O) solution of 1 x 10— "~? mol dm T sodium bicarbonate pH 9 was saturated with TNM and nitrous oxid s thewa e n passed through this solutio d inte samplan noth e solution (also pre-gassed) wher M vapouTN e 0 rN_ carriee th n i d dissolved.

3. RESULTS AND DISCUSSION Dilute aqueous solutions have been irradiated and under these

H20 VVAA* 'OH, "H, e~aq, H, H202, H2 (1)

conditions almost all of the energy deposited is in the water and water derived radicals and products are formed (reaction (1)). The

108 radiolyt:c yields (G(values)) of these species have been established as being 2.7, 2.7, 0.6, 2.7 7 molecules/lOOe,0. 0.5d an 5 r *OHfo V ,

e~aq , *H, H , H~& and H-,0£ -£ .respectively [5]. By varying the experimental conditions made e systeb ,th en ca essentiallm y uni-radical (reactions (2)-(5)) and the attack of selected radicals on chosen substrate e studiedb n ca s reactio n I . RR'CHO) (5 n H represents

) (2 0 N + H 0 ~O 0 N + + eH a~—q *"O 4 z e~aq + H* —* *H (3)

'OH + t-butanol —» H20 + t-butanol* (4)

'OH('H + RR'CHO) » H— H2 0(H ) 2+ )RR'CO(5 H

aliphatic alcohol d propan-2-oan ) sH suc= = methanos R ' a h( R l = R ( l ^ R = CH,). The rates of reactions (2)-(5) approach the diffusion controlled limi d unde e conditionan t th r s chose r thifo n s wore ar k complet n les i en nitrou I s . thas 1 sn oxide saturated solutioH "O n majoe ith s r initial attacking radical (reaction (2)} e yiel.Th f o d e enhanceb n * ca Hy lowerinb dH (reactiop e th g ns bee ha (3))n e Us . made of the large difference in the reactivities of 'OH and "H with t-butanol (the bimolecular rate constan s r lowe"i a Hfo t y b r factor of 5,000) to selectively scavenge the former (reaction (4)) and hence enable the reactions of "H to be studied. In nitrous oxide saturated solutions of alcohols, all the primary water radicals are converte alcohoo t d l radicals (reaction (5)). Table I shows the average number of strand breaks produced per hyaluronic acid molecule per Gray on irradiating aqueous hyaluronic acid solutions under various conditions. In order to compare the potencie e variouth f o ss radicals produced with regar o theit d r abilities to cause chain scission, the data is also expressed in Table I as breaks per molecule per attacking radical. As can be seen "OH is more potent than "H, while both methanol and propan-2-ol radicals produce relatively little breakage. Previous measurements seemed to indicate that t-butanol radicals were significantly more potent than methanol radicals at strand breakage [6]. There is no good reason for

109 a Tabl . ChaiI e n breakage induce hyaluronin i d c acif d M {1. O 1 5 x viscosity average molecular weight 2 megaDaltons) in aqueous solutio e attacth f y variouo kb n s radiation produced radicals (values calculated from yield-dose plots)

Irradiation Major Attacking I0x(breaks/molecule) I018x (breaks/ Conditions Radical per Gy molécule)m ,d per attacking radical

e pH I , N20 *OH 4.0 1.2 pH 2.66 1. , N 'H 0.78 0.5M t-buéanol

e pH I , N20 methanol 0.098 0.026 0.5M metnanol radical

C pH 7 , N20 propan-2-ol O.013 0.0035 0.5M propan-2-ol radical

e pH 7 , N20 t-butanol 0.07 0.019 IM t-butanol, radical 0.05M propan-2-ol

pH 7 N-0/0 'OH 2.9. 0.87 (4:1)

p7 H N,O 'OH 2.5 0.75 O.5mM TNM (a) in terms of repeating subunits. G('OH) (b )= 5.4 ; G('H )3.3= ; G(methanol radicals )Gtpropano= l radicals) = 6; G(t-butanol radicals) = 5.4 molecules/lOOeV. phosphatM 2m ) (c e buffer.

suc differencha possibla d an e e explanatio s apparenit r fo n t existence might be that in the t-butanol system some *H reacted with hyaluronic aci o givt d e breaksmethanoe th n I . l werH syste* el al m scavenge methanole th y b d n attemp.A mads twa o allot er stranfo w d breakage due to *H attack, however uncertainties in the relevant rate constants could easily apparene th lea o t d t differencen i s potency n irradiatin.O t-butanol/propan-2-ol/hyaluronia g c acid mixtur whicn i emajorite givH th h "O e f t-butanoo y l radicald san e completel"ar H y scavenge e alcoholsth y b d , hardl y stranan y d breakage occurs (Table I). Consequently in common with the other two

110 alcohol radicals, t-butanol radicals produce very little chain scission at the dose rates employed (0.01 Gy s ). It may be that at much lower dose rates or with the low fluxes of radicals likely to be encountered in biological systems when self annihilation reactions are much slower, "secondary radical" attack on hyaluronic acid could lead to strand breakage. "OH and *H react rapidly with hyaluronic acid (rate constants, 9 x 108 and 6.4 x 107 mol"1 dm3 s respectively [9]) and are expected to abstract H-atoms (reaction (6)) to form radicals

HA-H + 'OH(-H) ——* HA" + H20(H2) (6)

centred at carbon atoms. In the case of *H attack (pH 2, O.5 mol dm" t-butanol, degassed) full yield werH n facf i eo s t obtained. 3 2 In solution f simplo s e suc s ribosa h r glucoseo e H *O , attac s essentialli k y random f hyaluroniI . c acid behaves similarly e radicalth mos f o t s produced woul ^-hydroxe b d fî-alkoxr o y y radicals and these would be expected to react with TNM to produce NF [5]. However from NF yields in irradiated hyaluronic acid (1 x 10

mol" dm , N20, pH 7) solutions containing TNM, it appears that only 82% of the hyaluronic acid radicals are reducing. In contrast similar experiments using p-cyclodextrin in place of hyaluronic acid gave 100% reducing radicals e mai.Th n difference primarn i s y structure between hyaluronic acid and ^-cyclodextrin are the C-6 carboxyl group

(-CH2OH in cyclodextrin) and the C-2 acetamido group (-OH in cyclodextrin). acetamide Directh n o t H attaco*O grou f o k p shoule b d small (the rate constanreactinH "O r tfo g with acetamid s lesi e s tha e tentnon s reactioh it thar fo tn with glucose) .A radica l located at C-2 of the N-acetamido glucose subunit is similar in structure to the C-6-yl radical in uracil and so, by analogy, would be expected to be reducing. Thi hyaluronie sth leavef o radicae 5 th scC- acit a l d glucuronic acid residue as a possible "oxidising" radical. Random radical production by H-abstraction from hyaluronic acid would mean

111 that the yield of each of the possible eleven radicals would be 9% of the total radical yield. Since the measured yield of reducing radicals is 82%, the inference is that either two types of radical do not react H attack'O r secondare o , witth M perhap o TN ht e y du s structurf eo hyaluronic acid, is not entirely random. A third possibility, the rearrangement of an initially formed reducing radical into an oxidising radical cannot entirely be ruled out, however such a reaction would e extremelb hav o t e y rapid (rate constant greater than sinc) s concentrationM e TN evem d t a n x l 1 mo f O o s1 x 1 m o significand thern s ewa l mo t0 1 increas e yielth f n o di e ~ (thNF e rate constanM reactinTN r fo t g with hyaluronic acid thi , measures swa s m d d puls l mo e 0 1 x radical 5 4. s i s Û _ 1 "3 _ 1 radiolyticall y determininb y e pseudth g o first order rate constanr fo t ~ formatioNF a functio s a n f [TNM])o n . One of the main features of the free radical chemistry of simple carbohydrates is the elimination of water from 1,2 dihydroxy radicals wite formatio th hcorrespondine th f o n g R-carbonyl radicals (reaction (7), R = H) [5], In glucose, for example, of the six possible radicals

-COHCHOR- —————* -COCH- + HOR (7)

f thio fouse ar typer . Howeve ß-cyclodextrin i r x si e th f no onlo tw y possible radicaldihydrox2 1, e ar s y radicals hencd ,watean e th e r elimination reaction in polysaccharides will be relatively less important than for simple sugars. l-Hydroxy-2-alkoxy radicals can eliminat e alcohoth e l again formin e correspondinth g g -carbonyl radicals (reaction (7), R = alkyl), this reaction has a lower rate constant thaequivalene th n t water elimination reaction, both reactions are acid (and base) catalysed [10,5]. Out of the eleven possible hyaluronic acie dth radicalf o 6 C- sd thosan 4 C-2t a eC- , acetamido-glucos e glucuronith f o 3 C- c d e an moiet 2 d thosC- an yt ea acid are l-hydroxy-2-alkoxy type radicals. Alkoxy elimination from all of these radicals wit6 radicaexceptioe C- th h e s strani th l f o nd breakage (the alkoxy group is the adjacent sugar subunit). In the case

112 CHOH CHAIN

NHCOCHs

NHCOCHg

Reaction Scheme 1. A possible mechanism to account for the lowering of free-radical-induced hyaluronic acid chain scission brought abouy b t the presence of oxygen or TNM.

of the C-6 radical ring opening would occur with the formation of a hemiacetal at C-l, this would be unstable and would also give a strand brea s showa k n reactioi n n Schem 1 e(th 4 acetamido-glucoseC- e radical could similarly ring open as an alternative to eliminating the adjacent sugar e finath , l result would)in both instances,be chain 3 glucuroniC- d breakage)an 2 cC- acie .Th d radical2 dihydrox1, e ar s y radicals and thus might in fact be expected to preferentially eliminate water rather thae adjacenth n t sugar whicn i , h case three out of the eleven hyaluronic acid radicals would produce breaks by ^-alkoxy elimination. The formation of chain breaks has been found to follow first order kinetics although more than two component reactions appeae involvedb o t r neutrat overale ,a th H p ll half-lifr fo e breakage was found to be ca. l ms [11]. A value of this order of magnitud s quiti e e compatable wite possiblth h e involvemenf o t

113 elimination from 1-hydroxy 2-alkoxy type hyaluronic acid radicalse ,th rate constant for which would seem to be less than 3 x 1O mol ~ s d(sem r oxygen)e below)(o presence th M n TN i , , f theseo e radicals would be oxidised to give the corresponding carbonyl derivatives preventino ,s g chain breakage {see exampler fo , , reaction Scheme 1). As shown in Table I the presence of TNM or oxygen does indeed reduce breakage, similar "protection* by oxygen against chain scissio s reporteradiolysie nwa th r fo d cellobiosf so e solutions [12]. If it is assumed that the four hyaluronic acid radicals based at the carbon atoms involved in the glycosidic linkages are hydrolysed to produce breaks [5], then in the absence of oxidant seven of the possible radicals would lead to breaks. In the presence of oxidant all of these radicals would be oxidised, those based on the "glycosidic" carbons would thus be converted (via solvolysis of the intermediate carbocation) to hemiacetals which would decompose to give breaks, the other three radicals mentiones ,a d above, woul e converteb d o stablt d e aldehyde r ketone o sw lea breakso no would t dt san no d . Hence, accordin o thit g s simple model e additio th M ,shoul TN f do n reduce breakag 7 (43%)factoa 3/ y seee eb b f ,o rnn whicfroca s ma h TablI e is approximately the case (the experimental value for the decrease in breakage is 38%). As already mentioned «/.-hydroxy £-hydroxy-alkyl or «<-hydroxy jS-alkoxy radical e reducinar s d reacan g t with TNM, however the resulting /^-carbonyl radicals formed in reaction (7) are less reducin wely t reacma no ld tan g wit M (theTN hnoto yd r example,fo , react with methyl viologen [10]). Consequentl measuriny b y F N g yields as a function of TNM concentration, and applying simple competition kinetics t shoul,i possible b d obtaio t e e firsth n t order rate constane eliminatioth r fo t n reaction. Preliminary experimentn so hyaluronic acid at neutral pH indicate the rate constant to be less than 4 x 10 s~ . Since the elimination reaction should be acid catalysed the experiment was repeated at pH 4 when a value of ca. 4 x s foundwa .similaA s m d r experimenl mo 0 1 t performed with £-cyclodextrin at pH 2.8 indicated that here the rate constant

114 for conversio £-carbonyo nt l radical s s lesi s 0 s1 thax 2 n Th edifference reasoth r fo n e between £-cyclodextri d hyaluronian n c acid coul thae e locab d tth + concentratioH l vicinite e th th n i nf o y hyaluronic acid is elevated due to its being a negatively charged polyelectrolyte. Further experiments are currently being undertaken to extend and clarify these results.

REFERENCES

] [1 LAURENT Biochemistr, C. . ,T hyaluronar.f o y . Acta Otolaryngol (Stockh.). Suppl. 442, (1987), 7-24. [2] EDWARDS, H. E. and PHILLIPS, G. 0., Radiation effects on human tissue and their use in tissue banking. Radiât. Phys. Chem. 22, (1985), 889-90O. ] [3 McCORD Fre, M. e . ,radicalJ inflammationd an s , protectiof no synovial flui y Superoxidb d e dismutase. Science 185, (1974), 529-530. [4] FUJITA, S. and STEENKEN, S., Pattern of OH addition to uracil and methyl and carbonyl substituted uracils. Electron transfe adductH O f o r s with N,N,N',N'-tetramethyl-p-phenylene diamine and tetranitromethane. J. Am. Chem. Soc. 1O3, (1981), 2540-2545. n SONNTAGvo , "Th,C. e] [5 Chemical Basi Radiatiof so n Biology." (1987), Taylor and Francis.

[6] MYINT, P., DEEBLE, D. J., BEAUMONT, P. C., BLAKE, S., and reactivite PHILLIPSTh , 0. variouf o . y,G s free radicals with hyaluronic acid. Steady-state and pulse radiolysis studies. Biochim. Biophys. Acta 925, (1987), 194-202. ] [7 BUTLERSWALLOWd an Reactivit, , HOEY. J. M ,J. . . ,A ,B f o y semiquinone free radicals of antitumour agents with oxygen and iron complexes. FEBS Lett. 182, (1983), 95-98.

115 ] [8 RABANI pulse MATHESONd Th an MULAC, , e . . ,J. A S . . ,W ,M radiolysi tetranitromethanef o s Rat.I e constante th d san extinction coefficien e solvateth f to d electronI .I Oxygenated solutions. J. Phys. Chem. 69, (1965), 53-70.

[9] BLAKE, S., DEEBLE, D. J., BEAUMONT, P. C., PARSONS, B. J. and PHILLIPS, G. 0., Influence of Cu ions on hyaluronic acid free radical chemistry n "Frei , e Radicals, Metal Iond an s Biopolymers" (Proceeding e Summeth f ro s Meetine th f o g Society for Free Radical Research, Bangor, (1988), Editors Beaumont, P. C., Deeble, D. J., Parsons, B. J. and Rice-Evans, C., (1989), Richelieu Press. [10] STEENKEN, S., DAVIES, M. J. and GILBERT, B. C. , Pulse radiolysis and electron spin resonance studies of the dehydratio f radicalo n s frodiol2 1, related m an s d compounds. J. Chem. Soc. Perkin Trans I (1986).I , 1O03-1O1O.

[11] DEEBLE, D. J. , PHILLIPS, G. 0., SCHUCHMANN, H.-P., BOTHE, E. n SONNTAG ankinetice vo d Th / ,C. f hydroxyl-radical-induce so d strand breakage of hyaluronic acid. A pulse-conductometric study . NaturforschZ . , (1989),c , manuscript submitted. [12] SONNTAG n effece SCHUCHMANNvo Th d f oxyge, an to ,C. . N n . ,M on the OH-radical induced scission of the glycosidic linkage of cèllobiose. Int Radiât. .J . Biol , (1978).34 , 397-4OO.

116 THE USE OF POLYMERS FOR SOLAR PHOTOCHEMISTRY. APPLICATION OF IONIZING RADIATION METHODS FOR THE BINDING OF FUNCTIONAL GROUPS TO POLYMERS

J. RABANI Energy Research Center and Department of Physical Chemistry, Hebree Th w Universit f Jerusalemyo , Jerusalem, Israel

Abstract e applicatioTh f polymero n r photochemicafo s l energy storags i e described syteA . ms reportei d which enable storage sth f energeo a r yfo time period in the range of minutes. Such systems require polymers covalently linke specifio dt c functional groupso t , whice only th ywa s hi achieve linkage betwee a specifia npolymeri d an c n grouio c p which possess the same electric charge. In systems where the binding is a result of electrostatic interactions only locaa , l opposite field site existf th eo t sa e reactionth n sucI . h cases e retardatio order3 th , 2- f magnitudy so b s ni e s comparea d wit7 order6- h s whic s observei h a covalentl n i d y linked systems. A method based on application of ionizing radiation for the formation of covalent links between a polymer, and a functional molecule is reported t I require. s pulse radiolytic investigation e chemicath f o s l kinetic polymen i s r solution e solution th e functiona n th s weli a s f s o sa l l molecules. The advantage of the radiation induced method is that it enables the use of natural polymers. It can be applied to fields other than photochemical storage of energy, such as preparation of model systems for biologica d medicaan l l research n lino , e analysi d specifian s c interactions.

General background Polyelectrolyte e knowar s havo t n a considerable ee rate effecth sn o t of chemical reactions [1]. Thus, reactions between ionic species possessing the same type of charge are enhanced by polyelectrolytes which possess an opposite charge. This effect is because of the concentration of the reactiv epolymee th ion n i s electrostatie r th domain o t e du , c interactions. Reactions between oppositely charged e ionar retardes y b d polyelectrolytes, sinc e electrith e c field f theso s e polymers attrace th t counte e samth et r a timionsd ean , they repe e ionth ls which have th e same e polymerchargth s a e . Consequently e reactivth , e speciee ar s differently distributed in the solution volume, and their reaction rate is changed. This featur f polyelectrolyteo e s beeha sn investigated with special emphasis on retardation of photochemical back electron transfer reactions. Such reactions a solar-photochemica n i , l assemblye ar , responsible for the energy losses after the primary stages of photoabsorption and electron transfer. The understanding of the nature of

117 such reactions may assist with the optimization of future solar photochemical storage systems. Kinetically (relatively) stable redox systems which stor ee combineb energ y ma y d with appropraite catalystr fo s hydrogen and oxygen formation from water, A typical photochemical conversion and storage system involves the following reactions:

o (1) S* A (2) + + 4S + 2H2O4H + 2 O 4 S+ (3)

2A- 2H2O 2A + H2 + 2OH- (4)

Reaction (1) represents the excitation of a photosensitizer S. The excited state S* must possess the appropriate energy and a sufficiently long lifetim able b transfe o et o t e electron a accepo racceptoe t th r o (o nt A r an electron from a donor; these two cases are symmetrical). Reactions (3) and (4) produce O2 and H2 respectively, and may require appropriate redox catalysts. The net result of the reaction sequence (1X4) is the decomposition of water to H2 and O2. It is not possible to store all the energy absorbed in process (1) since reactions (2X4) requir ecertaia n driving force. Energy storage means that the products formed possess higher free energy than the reactants. An activation energy barrier must exist between the products formed and the initial reactants, and this can be achieved only if part of the absorbed photon energy is "lost" by its conversion to heat. Therefore a partial loss of the absorbed energy cannot be avoided. Since a spontaneous process proceeds in the direction of lower free energy, the possibility of losing e excesth s free energ e intermediatth y f o durin y an ge e stageth y b s so-called "back reactions" is very likely.

(5) complex formation S* + A ? . . > .SA* (6) charge rearrangement S+A-* (7) charge separation

(8) diffusion to bulk

back reaction + A «- (12) s

Figurel: Reaction sequence in photochemical electron transfer.

118 In common with ordinary chemical processes, photochemical electron transfer takes plac n severai e l steps e firsTh .t step involves excitation (reaction (1)) followed by the formation of a photochemical pair (reaction (5)). These species, after charge rearrangement (reaction (6)), produce the photochemical cage (pathway (7)) from which the electron transfer product e buldiffusy th kma so t e(pathwa y (8)) e bac.Th k reactionsn i , which the original ground state reactants are formed, may take place at e stepsth eac f .o h Thi s showi s Figurn i n . While1 e deactivatioeth d nan spontaneous self decay of S* can be suppressed in many systems by using sufficiently high concentration , reactionA f o s s (9X12) remai e maith n n obstacl achievino et g direct photochemical energy storage with reasonable yields.

Use of Microassemblies The overall efficiency of photoinduced electron transfer systems such as those described above may vary considerably in an organized assembly. The rates and yields of reactions occurring in these microheterogeneous e systemdramaticallb n ca s y changed accordin e e naturth th f o o t eg microenvironmen photoredoe th d an t x systems. e wilW l restric r discussioou t e effectth f polyelectrolyteso nt o s , which are polyionic molecules, usually with a high charge density. In many cases there is a charge on every repeating unit. The high charge density of the polyionic molecule provides a strong electric field which may be exploite r acceleratinfo d r retardino g g reaction f chargeo s d specied an s usefue b henc y controllinn i l ema g photoredox reactions. e abilitTh f polyelectrolyteo y o enhanct s r retaro e e rateth df o s chemical reactions is well known.

Retardation Reactionsof Between Oppositely Charged Species The inhibiting effects of polyelectrolytes on reaction rates between ions possessing opposite charges s beeha , n studied [2-8]e inhibitioTh . s ni generally due to the combination of electrostatic attraction of the ionic reactants with the electric charge opposite to the charge of the polymer, and repulsion of the ions with the same charge as the polymer. The retardation factor e usuallar s y much smaller than thos f accelerationeo n i ; most cases they are only 1-2 orders of magnitude. Retardation effects cause y factorb d s other than electrostatic attractio repulsiod an n n have also been reported.

Enhancement of Photochemical Electron Transfer Between Small Simple Ions s expectedA , when bot e exciteth h e quenchedth statd e ionan e ar r s which posses e samth s e charge e additioth , polyelectrolyta f no e witn ha opposite charge enhance e quenchinth s g rate. Ther , howeveris e n a , important difference when quenching of an excited state is involved, as compared with an ordinary reaction between counter ions. This difference is due to the relatively short lifetime of the excited states, particularly when aqueous solutions serve as the reaction medium. Compounds presently being use s a redod x photosensitizers include heterocyclic complexes of some transition metals such as Ru, Ir, Os, Rh, Cr, polynuclear compounds, heterocyclic derivatives such as thionine,

119 10 l l I I I t I I I 1 I I

1.0

ro S; O

0.1 10 100 1000 Fe(in)/(polynner molecule)

Figure 2. Dependence of & (PVSXcorr) on [Fe(III)]. Open points are for q l 1 kq(PVS)(corr). Solid r kpointsqfo (PV e ar SXcorr 10.73x10* Af" , f where e th latter limitingtermthe is rate constant extrapolated infiniteto dilutionthe in polymer field. Reference 10.

méthylène blue, phenothiazine, aromatic compounds and segments such as phenanthrene, some simple ions suc uranys ha wels a lporphyrins s a l e Th . e solubilizeb latte n ca r s sulfonatea d r pyridiniuo s m saltse mosTh . t popular photosensitize Ru(bpy)|e th s i r + which absorb svisible lighth n i te rangtriplea s e ha nm)0 t(pea d lifetim45 an ,t ka f abouo e JJLS6 0. t. Meisel and Matheson, [9] reported the effect of PVS on the photoinduced electron transfer from excited Ru(bpy)2+ to Cu2+ ions. A pronounced enhancement of the quenching rate of the lowest charge transfer stat f Ru(bpy)|o e y Cub + 2+ ion s i observes A quenchind g reversal phenomenon was reported at higher Cu2+ concentrations owing to the displacement of Ru(bpy)2+ from the potential field of the polymer by the Cu2+ ions. No net electron transfer products could be observed, perhaps because of an enhanced back reaction. The phenomenon of quenching reversa s alsi l o observe systee th n mdi Ru(bpy) 2- Fe(III+ n i ) e presencth f polyvinylsulfateeo e enhanceTh . d quenchine g th effec d an t quenching reversal are shown in Figure 2.

Charge Separation Assisted by Poly electrolytes In the particular case where the photochemical electron transfer product e ionar s s which possess opposite charges e additioth ,a f o n polyelectrolyt havy e yiel effecn th ema ea f product do n o t n s welo a s s a l the rate of their back reaction. Such an effect was reported by Meyerstei . [11]al t ,ne using Ru(bpy)| photosensitizea s a + neutrae th d lan r molecular species Fe-Nitrilo-three-acetate or Co-acetyl-acetonate as electron acceptor quenchers. Addition of the negative polyelectroly polyvinylsulfate induced a remarkable increase of the quantum yield for electron transfer. Similar results have been reported by Sassoon and Rabani [12] for the Ru(bpy)2(CN)2 ferricyanide system.

120 time c) d)

t r**'11*« R8 /- / t 1 •-BOO ns-* 20% f\ ••-800ns-» 18.5% f f t time time Figure 3. Oscilloscope traces (superimposed 10-15 times) of emission at 600 nm and bleaching at 440 nm. (a) Quenching of the emission of Ru(bpy)2(CN)'2 by Fe(CN% in the absence of polybrene, and (b) in the presence of polybrene. (c) Bleaching ofRu(bpy)2(CN)2 following laser pulse with Fe(CN% in the absence of polybrene, and (d) in the presence of polybrene. RB is the residual bleaching observed after all Ru(bpy)2(CN)'2 has decayed away. When corrected for the self exciteddecaythe complex,of Ru correspondsit quantuma to the yieldfor 1 5 electron transfer products. [Ru(bpy)2(CN)2] = SJxlO' M, [Fe(CN%] =

3.0x10^ M, [polybrene] = 134xlO~2 M (in monomer units). The number of

15 photons r laser deposited3pe cm pulse, 9,13,17)xl0 r (9 pe s i r (a),fo (b), (c), respectively.(d) and

The polymer used in the latter case has a relatively low molecular weight with only eleven monomer units e negativTh . e ferricyanide ions e confine ar volume positive th th o t df eo polymee th fiel f o d r while eth photosensitizer Ru(bpy)2(CN) 2e bulk th possesse n .i s o i chargn s d an e Typical result showe sar Figurn ni . e3 The back reaction between the photochemical products Fe(CN)g~ and + 9 1 Ru(bpy)2(CN)2 proceeds wit hrata e constan f 4.5xl0o t M'V . This value is not much lower than the diffusion controlled limit. The lack of a large inhibition effect on the back reactions is quite general for small heterocyclic complex molecules.

Retardation Backof Reactions Polymersin Covalently Linked Rutheniumto Bipyridine e lac f stronTh o k g inhibitio e bacth kf o nreaction polyelectrolytn i s e systems involving non-polymeric electron donors and acceptors calls for the consideration of two effects. Firstly, it is possible that a fraction of the counterions is the bulk at any given time. The back reaction, in this casetaky ema , plac a thivi es fraction. Secondly ther a neutralizatio s i e n effect of the polymer charge at the site of reaction, when one of the reacting species is a polymer conversion.

121 The polymers are usually poly salts with inert monovalent counterions. In the presence of ionic photosensitizers or quenchers, the total ionic charge of the counter ions is larger than the polymer charge so that part of the counter ions must be in the bulk. Although photochemical reactants whic e multichargear h d ionse expectear , o replact d e th e original monovalent counter ions of the polymer, the question arises as to whethe e dynamith r c equilibrium between boun "freed dan " ions doet sno leave a fraction of the reactant counter ions in the bulk. Even if this fraction is very small, e.g., 0.01, this sets an upper limit of 102 for the retardation effect by the polymer. Formation of a covalent link between the reactant and the polymer may be exploited in order to combine photochemical reactants and polymers which possess the same charge signs. In this way, the partial neutralization effect is avoided, while the appropriate reactan polymee keps th i t n i t r field

Two Polymer Systems Sassoon and Rabani [13] studied the decay of polybrene radicals by pulse radiolysis. In the presence of N2O at near neutral pH, the hydrated electrons produced by the pulse are converted to OH radicals. The OH and H abstract hydrogen from the polybrene and produce polybrene free radicals. Therefore, in this system, practically all the radiation primary radical convertee sar polybreno dt e radicals. Monomeric radicals similan i r structur e polybrenth o t e e radica e expectear l o decaa t diffusiod y b y n controlled bimolecular reaction. However, the combined effects of the electri e slowecth field r an ddiffusio npolymee th rat f eo s expectei r o dt slow down the decay. Comparison between the rates of decay of the polymeric and monomeric radicals serve to estimate the maximum retardation factor s e obtaineb whic n ca hn suci d h systems. Indeede th , lifetim polybrene th f o e e radica bees ha ln measure severae b o dt l seconds (Figure 4). This is more than four orders of magnitude slower than the corresponding reaction of a monomeric model radical.

2%

0 4 0 3 0 12 0 tim) e(s Figure 4. Decay of polybrene radicals measured at 302 nm. Initial radical concentration 11 jxM, polybrene concentration 0.73 mM (in monomer units).

122 Figur . 5 e Photosensitized electron transfer systems containingo tw polyelectrolytes. (a) The photosensitizer Pl bound to a negative poly electrolyte transfers electronan neutrala to quencher Q^produceto Q^~ which repelledis by the negative poly electrolyte to a second negative polyelectrolyte. (The back reaction between oxidizedthe photosensitizer reducedthe and acceptoris drastically retarded a result as theirof covalent attachment negativeto polyelectrolytes.) (b) An analogous system with electron transfer finally + yielding a reduced photosensitizer P2~ and an oxidized donor species D on separate positive polyelectrolytes.

e resultTh s describe e constructioth d o abovt d le ef photochemica o n l redox systems with very large retardation e bacfactorth kr fo reactionss . This is shown schematically in Figure 5.

a specifi n I c model syste r phtochemicamfo l energy storag e usew e d two positive polymers. One of the polymers is covalently linked to ruthenium-tris-bipyridine, while the other one is linked to tetramethylphenylenediamine (TMPD). Both polymer e dissolvear s n i d n i additiowater d e solutioan th ,n n contains methoxydimethylaniline [1,14,15] e rutheniuTh . m compound absorbs lighproduced an t e tripleth s t e ruthenium-tris-bipyridinth stat f o e e accordin o equatiot g n (13), where poly-Ru(bpy)|+ stands for the linked ruthenium complex. The excited molecul a lifetim s eha f abouo e t hal a microsecondf , whic s enoughi o ht alloreaco t wt i t wit methoxydimethylaniline hth e (reaction (14)).

pory-Ru(bpy)f poly-Ru(bpy)|+ (13)

NMe, NMe9 j poly-Ru(bpy)|+* —— poly-Ru(bpy)+ m + (14) OMe OMe

The reaction involves electron transfer from the methoxy dimethylaniline to the excited ruthenium compound, with subsequent formation of a

123 Ru(I) compoun a methoxy-dimethylanlin d an d e positive radical ion. This positiv s repellei e positiv th n io y eb de electri e cpolymer th fiel f o d , e buldiffused reactth an ko t s s wite poly-TMPth h D accordino t g equation (15).

NMe2 NMe2

+ poly-TMPD —— ry + poly-TMPD+ (15)

OMe

Reaction (15) takes place since the oxidized methoxy-dimethylaniline has a redox potential which is more positive than that of TMPD. The positive ion radical of methoxy-dimethylaniline is relatively stable (with respect to dismutation or recombination) and therefore lives long enough to react with poly-TMPD despite the positive field of the polymer. The back reaction between poly-Ru(I) and the methoxydimethylaniline positive radical ion is prevented by using an excess of poly-TMPD which successfully compete e oxidizinth r fo s g species. Thuss possibli t i , o t e obtain a pair of photochemical products which cannot back react quickly, since each of the products is linked to a different polymer molecule. The strong electri e cpolymer th fiel f o d s combined wit e relativelth h y slow diffusion rate retards the back reaction by more than six orders of magnitude. Recent results obtained in our laboratory indicate that covalent linking of the reactive center to the polymer chain is an essential condition for strong retardatio e photochemicath f o n l back reaction [16]. Electrostatic bindine polymeth o t gs alsi r o possible n casei , s wher e reactinth e g specie e oppositelar s y charged. However n suci , h cases, exchange with other counter ions may take place, and even a very small bulk concentration of reactive molecules may enhance the overall back reaction rate. If the reactive species are multi-charged ions, particularly if they possess 3 or more charges, it is possible to obtain a system where practically all the reacting species are in the volume of the polymer field. This can be achieved by applying polymers where the original coutner ions are monovalent and therefore unable to exchange with a significant amoun e multivalenth f o t t counter ions. However, eve sucn ni h systems, the back electron transfer reaction cannot be retarded by more than 2-3 orders of magnitude, as indicated by the recent experiments [16]. The reaso r thi nfo s proba.bli s e existencyth locaa f eo l opposite fiel thao (t d t of the polymer) at the site of the back reaction. Therefore, a most effective retardation of the back reactions can be achieved only when the polymer and the reactive moiety possess the same charge so that the polymer field remains uninterrupte e reactioth t da n site. This requirea s covalent link, otherwise the reactive species might be repelled to the polymee e effecth th bulk f d o t an r, woul decreasede db .

Synthesis The development of simple synthetic techniques for specific functional groups pendant on polymer chains is important for photochemical energy storage as well as for other fields of science. Of particular interest is the

124 possibility to modify existing polymer molecules by linking specific segments. In collaboration with D. Behar, V. Markovic, P. Neta and J. Silverman [17,18 e havw ] e demonstrate e possiblf radiatioth o d e us e n chemistry for such modifications. The principle is based on radiation induced formation of polymeric free radicals, which react with free radicals derived froe specifith m c molecules whic e chosee ar b h o t n linked to the polymer. Thus, aqueous solutions of polyethyleneglycol (neutral), polystyrenesulfonate (negative d polybrenan ) e (positive, repeating alky n unia s i lt quaternary ammonium salt) produc organin ea c free radical upon irradiation in the presence of nitrous oxide. In the absence of other solutes, such radicals decay by a second order process (the polystyrene sulfonate exceptionn a s i e mechanisth , m ther s muci e h more complicated). Free radicals produced by OH addition to ruthenium-tris-bipyridine or iridium-tris-bipyridine react with the polymer free radicals and produce a covalent link. Pulse radiolysis is a powerful tool for the investigation of the radical radical kinetics in the various systems e understandinTh . e kineticth f o g essentias i s r optimizatiofo l f no e linkinth g process e photophysicTh . e photosensitizater-polymeth f o s r linked system is very similar to that of the free photosensitizer. The radiation method is not selective. The OH attacks the polymers at various different sites. It also produces a variety of OH adducts upon its reaction wite photosensitizeth h o thae s producrth ta mixtur s a i largt f o e number of similar compounds. This may not make a great difference concernin e propertiegth e photochemicath f so l redox systems t addi t sbu , difficulties to the basic investigations. e e advantagmetho th e existinTh s us ha dn gca e polymerse thaon t , which are only slightly modified. This enables the linking of reactive segment o t naturas l polymers r examplefo , , whic s i difficulh r o t impossible to synthesize. Such a technique may be valuable in fields other than photochemcial energy storage, wheneve linkee b polymea r o t d s ha r a specifi o t c functional group r eve o r o ,differen linkinfo ntw f o g t polymers. Application can be found in specific interactions, model system r biologicasfo medicad an l l researc on-lind han e analysis.

REFERENCES

) Rabania d 1Sassoon. an . J , , R.E . PhotochemJ . , (1985)29 . . 7 , b) Rabani Thotoinducen i . J , d Electron Transfer" . M.A, Ed Par , . B t . ChanonM d an , x EisevierFo , Amsterdam 1988. 2. Okubo, T., Ueda, M., Sugimura, M., Kitano, H. and Ise, N. J. Phys. Chem. 87 (1983) 1224. 3. Okubo, T., Maruno, T. and Ise, N. Proc. R. Soc. London, ser. A, 370 (1980) 501. 4. . PhysZ Kunugi Ise d . ChemN an , . S , . N.F (19742 9 . . 69 ) 5. Morawetz Shaferd an . H , J.A . PhysJ . . Chem (19637 6 . ) 1293. 6. Ishiwatari, T, Maruno, T., Okubo, M., Okubo, T. and Ise, N. J. Phys. Chem (19815 8 .. 47 ) 7. Mita, K, Kunugi, S. Okubo, T. and Ise, N. J. Chem. Soc. Faraday Trans (19751 7 , l ,) 936.

125 8. Okubo, T. and Ise, N. J. Am. Chem. Soc. 95 (1973) 4031. 9. MeiselMathesond an . D , . Chem, M.SAm . J .. Soc (19779 .9 ) 6577. . 10 Meisel , RabaniD. , , MeyersteinJ. , Mathesond an . D , , M.S . PhysJ . . Chem. 82 (1978) 985. 11. Meyerstein , RsibaniD. , , MathesonJ. , , M.S Meiseld . PhysJ an . . .D , Chem. 82 (1978) 1879. 12. Sassoon, R.E. and Rabani, J. J. Phys. Chem. 84 (1980) 1319. 13. Sassoon, R.E. and Rabani, J. J. Phys. Chem. 88 (1984) 6389. 14. Sassoon, R.E. J. Am. Chem. Soc. 107, (1985), 6133. 15. Sassoon, R.E. and Rabani, J., to be published. 16. Behar, D. and Rabani, J. J. Phys. Chem. 92 (1988) 5288. 17. Neta, P., Silvermari, J., Markovic, V. and Rabani, J. J. Phys. Chem. 90 (1986), 703. 18. Behar , Neta D. , SilvermanP. , Rabanid an . J ,. J ,Int . .RadiatioJ n Phys. Chem. 29 (1987), 253.

126 REVIEW PAPERS

Next page(s) left blank RECENT DEVELOPMENT RADIATION SI N CHEMISTRY AT IRI-TU DELFT

A. HUMMEL Interfaculty Reactor Institute, Technical University Delft, Delft, Netherlands

Abstract e researcTh radiatioe th n hi n chemistry grou IRI-Tt pa U Delft comprisee sth following activities: a. Fundamental radiation chemistry Charge separatio nonpolan ni r liquids; ionizatio recombinatiod nan n non- homogeneous kinetics, computer simulatio spurf no s Thermalization Primary species; holes, electrons and excited states

b. Application researco st varioun hi s fields Polymers Catalysis Biological systemsA ;DN Solar energy

c. Developmen experimentaf to l facilities GraafPulsee d n fdVa accelerator Optical detection, absorption and emission; conductivity, DC and microwaves Product Analysis Data treatment and automatization The development in the various research projects will be discussed.

Introduction

The Interfaculty Reactor Institut Technicae th (IRI f o ) l University Delft (TUD) operates as a main research facility a 2MW swimming-pool reactor, which is used for neutron-beam research, radiochemistry and reactor physics research. In addition there is a 3MeV pulsed Van de Graaff electron- accelerator {which is the main radiation source for the research in the radiation chemistry group a variabl) e energy positron source Febetro,a n electron-accelerator, a Co-60 irradiation facility and various other

129 o carr t researct ou s yi I hsources IR wit e e hmissio Th th .thes f o en facilities, stimulate the use of the research facilities by the Dutch scien- tific communit d providan y e educatio varioue th n ni s disciplines thae tar covered. The IRI is operated by the Technical university Delft and is governed by a board of trustees with a representation from the TUD, other Dutch universities and industry.

Radiation Chemistry

The basic philosophy of the group has been to carry out fundamental radia- tion chemistry research on the one hand and on the other to provide a broad basi collaboratior sfo n with worker othen si r fields, both theoreticalld yan experimentally. The IRI group is the only one in Holland where fundamental radiation chemistry research is carried out. Through the years work in col- laboration with Dutch universitie bees s ha fieln e th donradiatiof do n ei n damage of DNA (with the Department of biophysics of the Free University Amsterdam), on various aspects of photochemistry (with photochemistry groups of the Universities of Leiden and Amsterdam) and in the field of polymer- modification and grafting (with the Universities of Twente, Groningen, Eindhove Delft)d lase an th nt n fiel.I d occasionally industr alss yha o been involved e fundamentaTh . l wor mors ki e internationally oriente severad dan l research projects have been carried out in collaboration with laboratories abroad e internationaTh . l collaboratio bees nha n stimulated greatle th y yb employment of post-doctoral fellows with a background in radiation chemistry in foreign laboratorie summer-visitord san s from abroad. The permanent staff of the radiation chemistry group consists of 4 scien- tists (dr. J.M. Warman, dr.ir. L.H. Luthjens, dr. M.P. de Haas and the author) and 6 technical assistants. In addition on the average 4 to 5 posi- tions have been available throug yeare post-doctorar hth sfo l fellowd san Ph.D students. Also Ph.D students and staff members from the universities (and also undergradute students) come to the IRI at regular intervals to carry out experiments with the accelerator, in collaboration with our staff members. The research in the radition chemistry group may be subdivided in the fol- lowing three activities

a. Fundamental radiation chemistry b. Application researco st varioun hi s fields c. Development of experimental facilities.

130 The research effort in each of these sections in our group is comparable in magnitude. Most of the research on basic problems (a) and on experimental facilitie dons i IRI-personely eb ) (c s wore application,n th ko mostls si y n collaborationi carrie t ou d s wilA . show e lb n below developmen- ex f to perimental facilities (accelerator, detection techniques, data treatment) has been crucial for the progress in both fundamental radiation chemistry applicationse th researcn i followine d th an n h.I shale gw l briefly review some e recenaspectth f to s progres e abovth n eaci ef s o mentioneh d activities.

Fundamental radiation chemistry

The research has been directed towards gaining an understanding of the charge separation resulting frointeractioe th m high-energf no y radiation ni nonpolar liquids, witemphasin a h liquin so d saturated hydrocarbons, CCl^. alst bu o Cf-Fc: and liquid noble gases .broaA d spectru experimentaf mo l tech- niques has been used: observation of transients by means of pulse radiolysis with optical absorption and emission, dc and microwave conductivity, but also product analysis and escaped ion yield measurement. The development of the microwave conductivity technique in our laboratory has been crucial for this work . Also the development of a fast pulsing system for the Van de Graaff accelerator (300ps), in combination with fast sampling techniques (lOOps) and fast digitizers (700ps, 50ps) has been of great importance (see under Development of experimental facilities). In this way we have been able to study the nature of the transient primary charged specie nonhomogeneoue welth s sa s la s kinetic charge th f eso . Although some doubt has been cast in the literature on the existenc fasf eo t electron-hole movemen cyclohexanen ti proposes ,a y db us years ago, recent experiments with cis-and trans-decalin (optical emis- sion, microwave conductivity, product analysis) have shown convincingly that the phenomenon exists in these liquids. Mobilities and chemical reactivities of the holes have been studied. There is good evidence that the phenomenon (2 ) 34 is of a general nature, although the lifetime may often be limited . r effortIou n fino st d charge migration with electron-attaching molecules, y analogouwa electron-hole a ith n o t s e movement have ,w e shown that fast electron migration exists in C^F,- and moreover that the electron in somewhat C? R fi\ delocalized1 '. 5' t The microwave conductivity method enables us to study charge migration in solids without the necessity of electrode contact (Ib) . Fast electron and proto s been ha nCharg migratio. e studieic ' e n migratioi nd n ni ( 7 A Q ^

131 teflon* 'and more recentl polyethylenen yi alss ha o' bee* n observede .Th transport of charge is of obvious importance for the ensueing chemistry. We shall retur thio nt s below. Nonhomogeneous recombination of oppositely charged species, in single pairs and in clusters of pairs is a predominant process in nonpolar liquids, but even play significansa t rol polan ei majore th systems rf o stum e .On - bling blocks in the interpretation of the experimental data involving nonhomogeneous kinetics has been the difficulty of the mathematical treat- ment of the problem of the movement of more than two charged species in each other's field. Even in the track of fast electrons however the majority of the ionizations takes place in groups of more than one event, giving rise to group pairf so oppositelf so y charged specie eacn si h other's Coulomb field. An important break-through has been achieved by us recently in the treatment (12) e multi-ion-paith of r casy meanb ef computer-simulatioo s . Thins development is an immediate result of the progress in computational facilities. Single ion-pair kinetics applies to an important fraction of the ionizations (fros phasga m e dat estimate aw relativelr e fo 30# d )an y long times, when the multi-E>air clusters have decayed to single pairs. The problee formatioth f o m singlef no d tripletan t excited state recombinan so - tiof chargeo n d species, direcwhicf o s hi t importanc resultine th r efo g chemistry, has been considered by computer simulations and compared with ex- perimental results on singlet formation in the decalins (3). Several aspects of the nonhomogeneous kinetics of clusters of ion pairs are being studied. Thus far we have discussed only the recombination aspect of the charge separation problem, startin momene th t thermalizatiof tga o chargee th f no d species. Study of the phenomena before thermalization is a great challenge. Experiment thermalization o s liquin ni d noble gases, using subnanoseconc d and microwave conductivity techniques have shown that thermalization can Thermalizatiodirectl. observee ' b y heatinCoulomd e dn an th n gi b 15) field is an important process to be studied, especially for high mobility liquids .

Applications to research in various fields

The study of the chemical effects of high energy radiation in matter touches on a large variety of problems that may be considered as subjects of long existing fields in physics and chemistry or that have developed more recently into separate disciplines. The field of radiation chemistry is in- terdisciplinary in itself and rather ill defined. The subdivision into fundamental radiation chemistr applicationd yan otheo st r field theres si -

132 fore somewhat arbitrary. In the following we discuss some of the application have sw e been involve. din

Polymers e mentioneAw s d abov microwave eth e conductivity method provide exceln sa - o measurt leny wa et charge migratio solidsn ni , withou necessite th t f yo electrical contacts. Measurements with powder therefors si e also possible. We have shown that charge migration occurs in teflon, which we ascribe to charge transfer of the electron from one fluorine atom to another, without dissociation occurring^ . Recently we have also measured charge migration in UHMW polyethylene, during ca 6 ns after the irradiation pulse, with an indicatioknot ye holwe t r th whetheeo no s f o i anisotropo d n t re i W . y the electron tha observeds ti phenomenoe th onlt s .No yi chargf no e migra- tion an interesting material property, it is also of great importance for the nature of the chemical effects of high energy radiation. High energy radiatio alss nha o been use groupy db s from Dutch univer- sities (see above) in order to study cross-linking in stretched UHMW, polyethylene cross-linking and scission in polymer blends, and grafting on f\1 \ 1 polymers. Some work on coatings has also been carried out

Catalysis e microwavTh e conductivity techniqu bees eha n use studo t dionizatioe th y n in semiconductor particles (CdS, Ti02 relation )i catalysiso t n e Th . v ( 17) kinetics of the disappearance of holes and electrons after pulsed irradia- tion, with and without dopants, is studied and compared with the catalytic properties. This wor carries collaborationn ki i t dou . We have just starte projecta d whicn ,i h pulse radiolysi uses si o dt study transient species formed by reaction of excess electrons with transi- tion metal complexes in relation with homogeneous catalysis, in collaboration with the university of Athens.

Biological systems, DNA For several years we have collaborated with the Free University, Amsterdam on several aspect radiatiof so n damag DNAn ei . Pulse radiolysis experiments radicalA onDN solution si n have beeshows ha n nd carrie an evidenc t dou r efo 11A \ charge migration . Charg^ e migratio n DNA/ici n e system alss sha o been studied by means of microwave conductivity, which has shown that fast electron migration with substantial lifetime occurs eve thin ni n layerf so . moleculA DN e th e waten i t r no (icet bu )A arounDN e th d ) (120 9 Substantial progress has been made in the non-homogeneous kinetics of the (21) reaction of radicals in water with DNA 133 Photochemistry, molecular electronics s beeha Itn laboratorr showou n ni y that measuremen microwave th f to - eab sorption provides a unique method to determine the dipole moment of solute excited states forme pulsey db d laser excitation nonpolan ,i r liquids (22) Usin n excimea g r laseintramoleculae th r r charge separatio specialln ni y synthesized donor-acceptor compound have been studied. This wor bees kha n carried out in collaboration with groups of the university of Leiden, Amsterda Sydned an m y (Australia)*23' 24> >25

Developmen experimentaf to l facilities

Van de Graaff accelerator A passive pulse shaping device has been developed which, in combination with a delay line, o t obtaienable a s u 300pn s s pulse e froth m \ O p / py accelerator . The length of the pulse is determined by the losses in the long dela yacceleratoe th lin n ei r terminal whic necessars hi - ob r fo y taining a sufficient delay between pretrigger (also developed at IRI) and (29) electron pulse . It is expected that the pulse can be shortened to ca lOOps after installation of an improved delay line system. Researc carries increasinn hi o t dou beae gth m current durin pulse gth e by studying various aspect cathodf so e behaviou collaboration ri n wit- hin dustry (Philips). Production of large currents with short duration by means of photo emission resulting from illumination of the cathode appears to be promising and pilot experiments are planned. In connection with this project laser-development wor carries ki alsot dou .

Detectio pulsn ni e radiolysis A new high-intensity pulsed Xe-lamp system has been developed for optical absorption measurements. Using the Digitizer with 50ps time response the time resolution of the equipment is limited by the pulse length of the electron pulse. For optical emission experiments we measure the fluorescence e directioth in n opposit thao et electrof to n beam combination ,i n witha special cell, in order to minimize the contribution of Cherenkov light. Emission is measured either with a sampling system (lOOps time resolution) transiene th of ro t wite digitizeron h s (Tektronix 7912, 700p 7250d san » 50ps) . Fast DC conductivity measuring systems have been developed in col- laboration with the Mount Vernon Hospital. The time resolution of the equipment user aqueou fo nonpolar d fo d s an rsolution, solutions 6n s i s s

134 e metho Th r determininfo d e (DCth g ) conductivit measuremeny yb e th f to microwave absorptio bees nha n develope laboratorr ou n di Equipmen . y t with X-ban wels a Q-bans dla availables di time .Th e resolutio approximatels ni y 0.5ns (Q-band), limited by the time response of the diode used for the measurement of the intensity of the microwaves. In a recent experiment where the microwave fiel directls di y appliefase th t o digitizerdt , withoue tth s beediodeha nt i ,show n thaoscillatine tth g microwav- ob ee b fiel n dca served directly and that a time resolution of about 200ps has been reached .

Computers All pulse radiolysis datobtainee ar a digitan di storee b n ldca ford an m centramemore e eitheth th f n yo i l r IRI-computer (VAX 8350) and/o tapen ro s or floppy discs for each experimenter individually. Data treatment can be carried out with the central facility and with Atari's. Kinetic plots and spectra can be observed with graphic displays and can be registered with plotters A .logarithmi c cloc availables ki , whic especialls hi y usefur lfo disperse kinetics. Signal averagin carriee b n eithet gca dou r automatically or manually. Various parameter acceleratoe th f so detectioe th wels ra s la n equipmene tar controlled by computer. Application of computers for data aquisition and handling has proved to be of great value, not only for increasing the efficiency of the use of the equipmen t alsincreasinr bu tofo possibilitiee gth interactivr sfo f o e eus the pulse radiolysis equipment. In a number of cases automatic control of experimental parameters however has proved to be indispensable.

Concluding remarks

Important progress in our understanding of the chemical processes resulting frointeractioe th m higf no h energy radiatio bees nha n mad recenn ei t years. Applicatio f radiatioo n n chemistr d experimentaan y l facilitie otheo st r fields of fundamental and industry oriented research continues to increase, and wil enhancee b lincreasinn a y db g understandin basie th cf g o radiation chemical processes. The growing complexit necessare th f yo y experimental facilities resultn si an increasing investment in capital and running cost and results in a grow- g criticain l mas manpowern si .countriew Onlfe ya s wil able lb supporo et t the most advanced facilitie internationad an s l collaboration seeme b o st needed woult .I d appear thaIEEe tth A could pla roleya .

135 REFERENCES

1.a. Warman, J.M., "The microwave absorption technique for studying ions and ionic processes", in: The study of fast processes and transient specie electroy b s n pulse radiolysis Baxendale. ,ed , J.M., Busi, ,F. Reidel Publishing Company, Dordrecht (1982) p.129. b. Warman, J.M. Haase D , , M.P., "Time resolved conductivity Techniques, DC to Microwave", in: Pulse radiolysis of irradiated systems, CRC Press publishede b Tabata . o ,t ed , reporI ,Y. ;IR 134-88-01r tn . . 2 Warman, J.M., "The dynamic f electrono s d ionnonpolan an si s r liquids", in: The study of fast processes and transient species by electron pulse radiolysis . Baxendaled , , J.M., Busi Reide, ,F. l Publishing Company, Dodrecht (1982) p. 433. 3. Luthjens, L.H., De Leng, H.C., Appleton, W.R.S., Hummel, A., "Fluorescent solvent excited states from hole-electron recombination in cis- and trans-decalin inrradiated with high-energy electrons", Rad.Phys.Chem. publishede b o ,t reporI ;IR 134-88-05r tn . e D Haas, . 4 M.P., "Rapid positive charge migratio n liquii n d hydrocarbons", Proceedings International worksho liquin o p d state electronics, West-Berlin 1988; ed. W.F. Schmidt, p.73. . 5 Nyikos n Endede , ,n L. C.A.M.Va , , Warman, J.M., Hummel "Hig, ,A. h mobility excess electron n i electron-attachins g liquid hexafluorobenzene", J.Phys.Chem. 84_ (1980) 1154. 6. Van den Ende, C.A.M., Nyikos, L., Warman, J.M., Hummel, A., "Mobility, reaction kinetic opticad san l absorption spectrue th f mo excess electron in pure 0,-F,- and admixtures with nonpolar liquids", Radiât.Phys.Chem. 19_ (1982) 297. e HaasD 7,. M.P., Kunst , WarmanM. , , J.M., Verberne, J.B. (VU), "Nanosecond Time-Resolved Conductivity Studie Pulse-Ionizef so d Ice, 1. The Mobility and Trapping of Conduction-band Electrons in H20 and 0 ice"D2 , J.Phys.Chem. 8_7_ (1983) 4093- . 8 Kunst , WarmanM. , , J.M., "Nanosecond Time-Resolved Conductivity Studie f Pulse-Ionizeo s d Ice ,. 2 "Th e Mobilit Trappind an y f go Protons", J.Phys.Chem. 8_7_ (1983) 4093- . 9 Kunst , WarmemM. , , J.M. e HaasD , , M.P., Verberne, J.B. (VU), "Nanosecond Time-Resolved Conductivity Studies of Pulse-Ionized Ice, e ElectroTh Prob a . 3 Defectr s na efo Dopen si d Ice", J.Phys.Chem 8_7_ (1983) 4096.

136 n LithVa . . (INRMeiD L ,. HummelZ ,). , 10 "Charg, ,A. e migratio- ir n ni radiated polytetrafluoroethylene, studied by means of microwave absorption with nanosecond time resolution", Radiâ tPhy. sChe. 6 2 m. (1986) 373. e D Haas11. , M.P., Hummel , "ChargA. , e migratio n irradiatei n d polyethylene, IEEE publishede ,b Trano Insu. t l , E reporsI l. ." ;IR r tn 134-88-13. . 12 Bartczak, W.M. (TUL Hummel), "Compute, ,A. r simulatio recomn io f -no bination in irradiated nonpolar liquids", J. Chem. Phys. 8? (198?) 5222. . 13 Sowada , Warman. U , , J.MHaase D ., , M.P., "The density dependencf eo hot-electron thermalizatio n liquii n d argon, krypto xenon"d nan , Chem. Phys. Lett (19820 .9_ ) 239. 14. Sowada, U., Warman, J.M., De Haas, M.P. , "Hot-electron thermalization in solid and liquid argon, krypton and xenon", Phys. Rev. B 23 (1982)

. 15 Warman, J.M., Sowada Haase D , ,. , U M.P ."Transien, t negative mobility electront ho f o gaseoun si s xenon", Phys. Rev .3JA ^ (1985) 1974. . Dijkstraa . 16 , D.J., "Entanglement d cross-linkan s n ultra-higi s h molecular weight polyethylene" , thesis University of Groningen (1988). b. Van Aerie, N.A.J.M., Crevecoeur, G., Lemstra, P.J., "Cross-linking of oriented polyethylen y E.Bb e . radiation". Influenc morphologf eo y induce drawingy db . Polymer comm 9 (19882 ., ) 128. . Warmana . 17 , J.M. Haase D , , M.P., Wentinck, H.M ."Th, e Stud Radiatiof yo n Induced Conductivity Change Microheterogeneoun i s s Materials Using Microwaves", Radiation Physics and Chemistry, in press; IRI report nr 134-88-02. b. Warman, J.M. , DE Haas, M.P., Graetzel, M., Infelta, P.P., "Microwave Probing of Electronic Processes in Small Particle Suspensions", Nature 310 (1984) 305. . 18 Visscher, K.J. (VU), Horn, M.L., Loman . (VU),H , Spoelder, H.J.W. (VU), Verberne, J.B. (VU), "Spectral and kinetic properties of inter- mediates induce y reactiob d f hydrateo n d electrons with adenine, adenosine, adenylic acid and polyadenylic acid; a multi- component analysis", Radiât. Phys. Chem. , in press. n Lith Va , WarmanD. , . ,19 J.M. Haase D , , M.P., Hummel "Electro, ,A. n micratio hydraten Collagend i an temperaturesw lo A dDN t na Effec. ,1 t of water concentration", J.Chem.Soc., Far. Trans. l 82 (1986) 2933.

137 Lithn EdenVa , WarmanD. , ,J. . 20 , J.M., Hummel "Electro, ,A. n migration in Collaged hydrate an temperaturesw lo A t nDN a d e effecTh . f ,t2 o additives", J.Chem.Soc., Far.Trans. (1996_ l82 ) 2945. 21. Verberne, J.B., "A pulse radiolysis study of the electron reaction n aqueoui witA DN sh solutio d ice"an n , thesis Free University, Amsterdam (1981). 22. De Haas, M.P., Warman, J.M., "Photon-induced molecular charge separa- tion studied by nanosecond time-resolved microwave conductivity", Chem.Phys. 7_3_ (1982. )35 23. Weisenborn, P.C.M. (RUL), Varma, C.A.G.O., De Haas, M.P., Warman, J.M., "Contribution from dipolar electronically excited moleculed san mobile charge carriers to photo-induced transient dieletric loss of solutions of some aniline-derivatives", Chem.Phys. 122 (1988) 14?. 24. Paddon-Row, M.N. (UNSW), Oliver, A.M. (UNSW), Warman, J.M., Smit, K.J., De Haas, M.P., Oevering, H. (UvA), Verhoeven, J.W. (UvA), "Factors affecting charge separation and recombination in photo- excited rigid dorior-insulator-acceptor molecules "J.Phys.Chem., , 9_2_ (1988) 6958. . 25 Weisenborn, P.C.M. (RUL), Varma, C.A.G.O. (RUL) Haase D , , M.P., Warman, J.M., "Dipole moment electronicallf so y excited state- 4 f so N, N-dimethylaminobenzonitrile and related compounds deduced from transient dielectric losses", Chem.Phys.Lett 9 (1986.12 ) 502. . 26 Warman, J.M. ,e HaasD , M.P., Oevering . (UvA),H , Verhoeven, J.W. (UvA), Paddon-Row (UNSW), Oliver, A.M. (UNSW), Hush, N.S. (US), "Donor, acceptor d self-quenchinan , giant-dipole th f go e a sta f to rigid, sigma-bond separated, donor-acceptor molecular assembly", Chem.Phys.Lett. 12_8_ (1986) 95- 27. Luthjens, L.H., Vermeulen, M.J.W., Horn, M.L., "Remotely controlled passive pulse-shaping device for subnanosecond duration voltage pulses with stepwise selectrable pulse length", Rev.Sci.Instrum. 5_3_ (1982) 4?6. . 28 Luthjens, L.H., Horn. M.L., Vermeulen, M.J.W., "Sub-nanosecond pulsing Graafe d n f Va electro V 3M noa faccelerato meany passivra b f so e coaxial pulse shaper", Rev.Sci.Instrum. 4_9_ (1978) 230. 29. Luthjens, L.H., Horn. M.L., Vermeulen, M.J.W., "Electronic analyzing light signal substractio measurind nan g devic transienr efo t absorp- tion spectrophotometry", Rev.Sci.Instrum. 5_5_ (1984) 495.

138 30.a. Visscher, K.J., De Haas, M.P., Loman, H., Vojnovic, B., Warman, J.M., "Fast protonatio radicas it denosina t a f l o d nanio ean n formey db hydrated electron attack", Int.J.Radiât.Biol. $2_ (198?) 745-753. b. De Haas, M.P., Warman, J.M., Vojnovic, B., "Geminate ions in nanosecond pulse irradiated CCL^., detected by DC conductivity", Radiât.Phys.Chem (1984_ .23 ) 61-65- c. Vojnovic, B. De Haas, M.P., unpublished results. e HaasD , . M.P.31 , Warman, J.M. Ewijkn Va , , C.R., Varma, C.A.G.O., "The Use of a Multi-Gegahertz Digital Oscilloscope as a Full-Wave Microwave Detector for Subnanosecond Time-Resolved Microwave Conductivity Measurements", Revie f Scientifio w c Instruments- ,ac cepted for publication; IRI report nr. 134-88-11.

Next page(s) left blank 139 NEW DEVELOPMENTS IN RADIATION CHEMISTRY APPLICATIONS IN JAPAN

S. MACHI Takasaki Radiation Chemistry Research Establishment, Japan Atomic Energy Research Institute, Watanuki-machi, Takasaki, Gunma, Japan

Abstract

Industrial applicatio radiatiof no n chemistr firss ywa t achieve 196n i d 0 and has grown since then in mainly polymeric materials and medical products sterilization. Nowadays abou electro0 t18 n beam machine usee r sar dfo radiation processing. Researc developmend han t haven been carrien i t ou d governmental institutes such as JAERI and private companies, and new applications have been commercialized.

Environmental conservation is an important task in Japan and application stud radiatiof yo n processin thir gfo s purpos alss eha o been conducted. Radiation chemistr alss yi o playin importann ga t rol estimato et e eth life-tim organif eo c materials use nuclean i d r plants under radiation exposure. This paper reports overvie up-to-datf wo e radiation applications futurs anit d e trend Japann i s .

Polymew Ne . r1 Applications

1.1. New Drug Delivery System

Since radiation induced polymerization can be carried out even at room temperature, drugs can be capsuled in polymer matrix by the polymerization withou degradations tit their ,fo r controlled delivery. Anti-cancer drugs have been immobilized and successfully tested in clinics. Recently a new drug delivery system which is sensible to temperature was developed by our Institute. Schempreparatioe th f eo shows ni Figurn ni . eThi1 s polymef ro proline methyl ester is swollen at 4 C and insulin release rate is increased while at 35 C it shrinks and the release rate is decreased as shown in Figure 2.

141 CH2H =C I 0=0 .COOCH3

60 Co , r-ray Acryloyl-L~proline methyl ester Polymer formulation containing insulin

Insulin

Fig. 1. Model schem r preparatiofo e f temperature-activateno d mechanochemical polymer formulations containing insulin for drug delivery systems

4°C 4°C 4°C 4°C

250 37°C 37°C 37°C 37°C X) CD U)o 200

150

100 01 a. 50

0 1 2345678 Repeated run (times)

Fig. 2. In vivo release profile of insulin from a poly(acryloyl-L- proline methyl ester) formulation between d 37°4°Can C at 24-hour intervals

1.2. Battery Separator

Graft Polymerization by pre-irradiation method has been used for manufacturing battery separators, in acrylic acid grafted polyethylene. This technolog developes ywa grour transferred ou an py b d industryo t d e Th . separator is used for silver oxide battery and other secondary batteries and shows excellent lif commercias e it time d an , l productio increasings ni .

142 1.3. New Deodorant

New deodorant has been developed by our institute by using radiation graftin f styrèno g d chloromethyean l styrène onto polypropylene fiber followed by sulfonatio quatemizationd an n . These products have much higher capacity as deodorants and adsorb efficiently acidic and alkaline pollutants. Commercial production will be started in 1989 in Japan.

1.4. Crosslinked Polymers

Radiation crosslinkin widels i g y usepolyethylenr fo d wirr fo ee insulation, heat shrinkable materials and foamed polyethylene. New products of radiation crosslinked materials have been develope e Sumitomth y b d o Electric Industries (crosslinked polyurethane and nylon). The hot water resistance of the radiation crosslinked polyurethane, used for cable of antilock brake sensor of automobile, is greatly improved.

Radiation crosslinking of natural rubber latex has been studied within IAEe scope th th A f eo regiona l cooperation projec South-Easr tfo t Asid aan Pacific. Better qualitie manufacturef so d product termn i s transparencyf so , smaller amount of ash and sulphur dioxide formation at incineration as well as smaller hazar skio advantagee t d nar thif so s process.

TABLE I. EB CURING PROCESSES IN JAPAN

Year Product Company Remarks 1988/89 Precoated Steel Nisshin PVC -Laminated Steel 1987/88 PCB(electro- CMK conductive ) 1986 Micro Floppy TDK Discs 1986 Plastic Sheet Mitsumura A m 5 keV 0 17 30 , Printing Printing 1985 Juice Carton Tetrk Pa a 2 lines Printing Japan 1984 Gypsum Tile Achilles A keV0 m 28 0 4 , 1982 Precoated Steel Dai-Nippon 300 keV, 80 mA Ptg. Ellio 2 lines 1979 Cement Roof Tile Nakazato 300A m keV 0 ,10 Sangyo 1973 Motorcycle Parts Suzuki 300A m keV 0 ,10 - 80 (steel, ABS, PP) Motor (2 heads)

143 1.5. Curin Surfacf go e Coating

This application is most widely used and still expanding in industries. Major application listee sar Tabln i d. FurtheI e r developmenw ne f to application expectes si findinn i d w formulatiogne coatingf no substratesd san .

2. Environmental Conservation

2.1. SO and HO Removals from Stack Gases £+ X

Stack gas treatment to remove SO and NO by electron beams was first studiejointe th y ,db researc JAERf h o Ebard Ian a Mfg year.7 1 s ago. Based on this research the US Department of Energy had carried out pilot scale experiment studo st y commercial feasibilit thif yo s technologr yfo purificatio coaf no l combustion gases resulte Th . s indicate technology reliability and economic merit in comparison with conventional chemical treatment.

JAERI group has carried out basic research in support of US DOE Project in orde furtheo rt r elucidate detailreactioe th f so n mechanism. Recentlt yi was found that NO is partially reduced to Nitrogen in addition to the conversion to nitric acid,. Reaction mechanism so far elucidated is summarized in Figur. e3

demonstratioA n plan commerciaf to l scale shoul operatee db studo t d y engineering terms and to show long time operational reliability.

2.2. Waste Wate Wated ran r Treatment

Waste water containing pollutants not degradable by biological treatment ca treatee nb radiatioy db reduco nt CODs eit . Chlorinated organic compounds polluting efficientle wateb n rca y remove radiatioy db presence th n ni f eo ozone. This technolog usee treatmenr b fo dn yca drinkinf to g wate wastd ran e water. Extensive studie conductee sar JAERn i d I Takasak thin i s important field.

144 FLUE GAS

Active Species Main Components / Ac1 ^\AAA- 0,OH,H0O, ( 2,N N2,02,H20 //////////, L/ Pollutants /c ^ '^ S0 ,NOx 2 v T Acid cid

Ammonia [\jf-J3

' ule fat Nitrogen, ,N itrate

Fig. 3. Reaction process of electron-beam flue gas treatment.

2.3. Sewage Sludge Treatment and Its Composting

In Japan more than 200 million tons of sludge is disposed from sewage treatment plant year lanso pe ocead rt an dincinerater no d (contributin) gto environmental pollution. Only 20% of sludge is used for farming land. Our grou s studiepha technologe th d disinfeco yt t sludg electroy eb n beamd san compos efficientlyt ti . Pilot experimen bees tha n carrieshoo t wt ou d technical and economical feasibility of the technology.

3. Ion Beam Applications

New project of ion beam applications and chemistry has been initiated in JAER foud bean Ian io r m accelerators includin cyclotroF gAV n wil e installelb d in four years. Major research projectmateria) (1 e sar l science under space environment materia) ,(2 l scienc nuclear efo r fusion environment, (3) biotechnology application, (4) development of new functional materials.

145 TABL NUMBE. EH ELECTROF RO N ACCELERATOR JAPAN SI N

Power Application Field Number Energy(MeV) Current (mA) Research & Development 64 0.175 - 3.0 100 Curing 50 0.2 - 0.3 600 Wir Cabl& e e Insulation 38 0 2. 0. - 3 100 Pre-Curing of Tire Rubber 9 0.5 - 0.8 220 Shrinkable Tube & Sheet. 8 0.3 - 3.0 100 Polyolefin Foam 6 0.5 - 1.0 100 Others 5 0.5 - 2.0 60 Total 180

e radiatioTh n technology B applicationbaseE n o d s beeha s n very well establishe n Japani de tota Th . l numbe machinef o r s user differenfo d t application s showi s n Tabli n . II e

146 GENERAL SURVEY OF RADIATION CHEMISTRY IN FRANCE

L. GILLES Institu recherche d t e technologiqut e de développement industriel, Commissariat à l'énergie atomique, Centre d'études nucléaires de Saclay, Gif-sur-Yvette, France

Abstract

A récent symposium held in France allowed the meeting of about a hundred french speaking scientists, fundamenta applied an l d researcher wels s a industrials s a l , interesten di e fiel f radiatioth o d n chemistr e frenc y- Mosth f ho t laboratories and/or groups were represented.

Afte glimpsa r theif eo r activity, pointin t morgou e precisely their main domai researchf no , the tools employed depending upon steady state studies or pulsed sources, the importance - number of people employed - in each group, five principal axes will be considered :

1. Studies on the primary effects of the interaction of radiations with matter for which a strong correlation appears between radiolyti photolytid can c studie understano t s e dth solvation proces electrof so n;

2. Studies of chemical reactions induced by radiolysis for which the use of heavy ions can give a new impulse ;

. Studie 3 effecte th radicalf n so o s biochemistrn si whicr y fo radiolyti e hth c methods appear the best way to produce radicals involved in biological mechanism as, for instance, the respiration ;

. Studie4 e biologicath f o s l effect f radiationo s d moran s e particulary some effectf o s hydroxyl radical;

5. Some industrial applications of radiations in view of destroying pathogenic germs in food, for graftin reticulatiod gan polymersf no .

The fate of water and solutes used in nuclear reactors as well as the effects of irradiation on nuclear wastes will be also considered.

Amongst the multitude of questions arising from the obvious interest of scientists for Radiation Chemistry, various way f reflexioo s n coul e developeb d d considerine th g stagnation of this discipline in the context of the present time, the studies for which radiolytic method irreplaceablee sar wayw studief ne so e th , s offeredevelopmene th y db f o t nuclear power. Finally the contribution of teaching and the necessity to maintain a high level of education will be emphasized.

PRELIMINARY

In orde o present r a comprehensivt e survey t appearei , d advisabl o request e t written contributions fro mane mth y laboratories, group industriad san l firms involve radiation di n chemistry in France.

147 I wish to especially thank those who have assisted me with this survey through their contributions or advice : J. BELLONI and B. HICKEL, french observers at the above- mentioned meeting, R.BENSASSON, D. BRAULT, J. CADET, A. CHAPIRO, Y.CHELET, G.DUPLATRE FAVAUDON. V , . C FERRADINI, GAUSSENS. G , , Y. HENON, J. MARCHAL, J. POTTIER, J.RAFFI and R. TEOULE.

INTRODUCTION

A recent symposium held at Marly-le-Roi, France (14-17 June 1988) hosted a meeting of abou e hundreon t d french-speaking scientists, either fundamenta r applieo l d researchers, involve fiele radiatiof th do n di n chemistry. participantSome th f eo s were also very activn ei teachin universite th t ga y level.

This symposium provided the. second opportunity withi nvera y short perio revieo dt e wth research conducted and to consider the future of radiation chemistry in France. The preceding event was a one-day workshop organized in 1987 by the CEA at the Institut National des Sciences et Techniques Nucléaires (INSTN) at Saclay, in commemoration of Jack SUTTON papere Th . s presented durin symposiue gth m were publishe Januare th n di y 1988 Journa e issuth f eo Chimie d l e Physique, together wit revieha f somwo e ideas which emerged durin workshoe gth p devote future th radiatiof o deo t n chemistry.

Finally survea , y entitled "Glimpse Ninetn si y year Radiatiof so n Chemistr Francen yi . C y "b FERRADINI and R. V. BENSASSON will be published in the near future. In this survey, the authors present an extensive review of the activities of the main groups in France at the beginning of radiolytic studies : HAISSINSKY's group at the Institut du Radium/Laboratoire Curie, MAGAT's group at the Laboratoire de Chimie-Physique in Paris and Orsay, HERING's and SUTTON's group at the CEA's CEN Saclay (Nuclear Research Center). The interaction between the various laboratories is also presented and the current activity of each french group is reported, including radiation chemistry at Strasbourg (Universit Centrd yan Recherchee ed s Nucléaires, Centr Recherche ed s le r esu Macromolécules), Toulouse (Centre de Physique Atomique), and thé CEA's nuclear research centers at Cadarache and Grenoble. In addition, applications of radiation chemistry considerede ar , particularl activite laboratoriee yth th f yo CEA'e th t a ss Saclay cented an r some future opportunities relatin instrumentationo gt wels a ,interdisciplinars a l y exchanges with chemistry, biolog medicined yan .

. CURREN1 T STATU RADIATIOF SO N CHEMISTR FRANCYN I E

Research into the effects of ionizing radiation on the three states of matter (gas, liquid and solid) is being conducted at Universities, the Centre National pour la Recherche Scientifique (CNRS), and the CEA's principal nuclear research centers.

It would be tempting to make an effort to classify each of these major research entities into well-defined categories ranging from fundamental research to industrial applications. In fact, althoug e researcth h h performe t universitiea d s generalli s y fundamental e greatesth , t variet f activitieo y s clearli s y bein e CEAgth carriey ,b whict ou d s involvei h n boti d h researc developmentd han .

Regardin e developmength toole th f s o trequire r thidfo s research e radiatioth , n sources, onl ya handfu f frenco l h industrial firm e activar s thin ei s market. This situation prevails clearly because the radiolysis market is and probably will continue to be too small.

None the less, some french industrial firms are now contemplating the use of radiation hi very new fields as, for instance, sterilization. As a result, the traditional radiation chemistry environment may eventually change and thus create additional requirements, both intellectual and technological, stemming from new directions in research.

148 As in any scientific field, the "logistic" support for radiation chemistry is provided at the educational leveranga n i lf course eo s offere t Universitiesa d Conservatoire th , e National des Arts et Métiers (CNAM) and the CEA's INSTN. Seminars and workshops are organized alloo t w researcher engineerd san mee o sexchangt d an t e their experience.

e followinTh g presentatio f researco n h program d projectan s s conducte y frencb d h laboratorie groupd san divides si d into four main categories: - activities mainly concerning fundamental research conducted by Universities and the CNRS; GroupA - activitieCE e , th rangin f so g from fundamental research conductee th t da nuclear research centers to industrial applications; - industrial applications and development by Companies in France ; educationa- l activities.

1.1. Research at Universities and the CNRS (Table I)

Université R, DESCARTES/Paris - Laboratoire de Chimie Physique.

e MedicaBaseth n i d l School 6 member1 e tea th f , mo s heade y Professob d r C.FERRADINI is specialized in the study of biochemical reactions. It is particularly interested in the reactions of oxygen radicals (hydroxyl radicals, Superoxide ions, oxygen singlee th n i t state) with antitumor drugs, vitamins, protein peptidesd san e wels th a ,s a l chemistr f bioradicalso y e resultTh . s obtained using pulse radiolysi d gamman s a irradiation illustrate the importance of improved understanding of radiation effects on treatmenlivine th n go cell d cancerf o ts an . The moreovee yar r highly promisin mann gi y areas of biology and hi the treatment of diseases in which the role of radicals is increasingly evident laboratore Th . cobala s sourc0 y ha Febetro6 a t d f ~10eo an i 0nC 708 electron gun for its own pulse radiolysis research requirements, but the researchers have often collaborated with other laboratories, particularly wit "Febetroe hth n teamt "a the Saclay nuclear research center, for almost 20 years, and more recently with the Universit Sherbrookf yo Canadan ei .

It should also be mentioned that Professor C.FERRADINI and Dr. J.PUCHEAULT have publishe a dboo e biologica e studth n frenci th k f o yn o h l effect f ionizino s g radiation.

Muséum National d'Histoire Naturelle, Paris

Dr. R.BENSASSON and Dr. R.SANTUS have concentrated their efforts specifically on the study of biomolecular photolysis. They have nevertheless performed pulse radiolysis investigations concerning the same molecules using the facilities of the Christie Hospital at Manchester in the United Kingdom. A new collaborative effort was recently initiated with the Institut Curie Biologie. R.BENSASSON is co-author with EJ.LAND and T.G.TRUSCOTT of a book entitled "Flash Photolysis and Pulse Radiolysis : Contributions to the Chemistry of Biology and Medicine". For his part, Dr. D.BRAULT has investigated the reactions of certain porphyrines using pulse radiolysi n collaboratioi s n Washingtoi nS wit r NB P.NET D d he an nth t Aa L.K.PATTERSOr D Radiatioe th t Na n Laborator e Universitth f yo f Notryo e Dame (USA).

Institu Biologie td e Physico-Chimique, Laboratoir Biophysique ed ePari- s

The team headed by Dr. Y.HENRI and Dr. A.GUISSANI is conducting research in close collaboration with the Saclay nuclear research center (Febetron team). This research is focused on two main areas : the chemistry of copper-based proteins and the reaction radicalf so s with treatmen e drugth r sfo cancerf o t .

149 TABLE I.

FUNDAMENTAL AND BASIC RESEARCH

Primary events moderation X X X X heavy tons APPLIED X X X RESEARCH Alcoholic solutions oleflns X X X. X X sugars Initialing canters grading * X. membranes micelles aggregates * X INDUSTRIAL Bio Chem. & Phys. biological systems X X X X X DEVELOPMENTS biomédical research X X Fruit membranes X Nuclear qualification X Orthopaedics Gynaecology hntmocomoullbllllv X X X Laboratoir Chimie ed e Macromoléculair eTHIAI- S

During the last 4 years, the studies of this laboratory, headed by Dr A.CHAPIRO were concerned with: - polymerization and copolymerization of monomers engaged in associative complexes, - preparation and proterties of perm - selective membranes, preparatio- hydrogelf no graftiny sb polymerf go solutionn si . Besides such applied researches, fundamental studie e conductear s nature th f n o edo initiating centers created under radiation.

Institut Curie - Biologie, Centre Universitaire d'Orsay. e radiobiolobTh y research conducte e Instituth t a dt Curi - eBiologi e concernee th d analysis of nucleic acid lesions induced in the genome of encaryotic cells by ionizing radiation, including neutrons e mechanism th s wel a ,s a l s governing their repaid an r regulation e ultimatTh . e goa f thio l s researc furtheo t s hi e understandin th r e th f go molecula cellulad ran r biolog cancersf yo . The laboratory recently acquired a 4.5 MeV linear electron accelerator (Kinetron) manufacture CGR-Mey db cobalt-6a alsd s Van oha 0 source. Unde supervisioe th r f no Dr. J.M.LHOSTE and Dr.V.FAVAUDON, it is now focusing on a new area of radiotherapy research addressing two complementary themes : - fundamental research, particularly analysie actioth f f antitumoo o ns r drugr o s radiosentizers ; - radiotherapy, e.g. the study of metabolic modifications of tumors grafted in animals following radiotherapy and chemotherapy treatments. Special collaborative projects have been initiated with the Laboratoire de Chimie - Physique of the R.DESCARTES University (under Professor C.FERRADINI) and the Muséum National d'Histoire Naturelle (under Dr. R.SANTUS and Dr. R.BENSASSON) to conduct research into the effects of ionizing radiation in the field of biological and medical applications.

Université de Paris-Sud (ORSAY) - Laboratoire de Physico-Chimie des Rayonnements

Primaril stild yan l concerned wit effecte hth electronf o s non-aqueoun si s environments to enhance the understanding of ion-electron recombination probabilities, and with the determination of the most probable parent ion-electron distances in various solvents, the main are f researc membera6 o teae 1 th f mr o hfo s heade. J.BELLONDr y db e th s i I reductio metaf no resultine lth iond san g aggregation dynamics laboratore .Th thus ywa s abl produco et e subcolloidal metal aggregates.

Intensive research into the control of aggregate size, the understanding of aggregate structure, as well as the redox potential and the resistance to catalytic poisons is being conducted instancr fo , simulato et photographie eth c development proces achievo t r so e a radiolytic synthesis of metal "nanoaggregates" in ion-exchange fluorinated membranes. Thus activity of this Laboratory covers now a very wide range of topics from fundamenta applieo t l d research. laboratore Th panoramia s yha c sourc Febetroa cobal f ed o (300an 0 6 t) n0Ci electron whicn gu electrohV emitke 0 ns60 pulse Snsef so J/pulse)4 c( .

Institu . SADROCh t N (Strasbourg - Laboratoir) e Dégradatio t Stabilisatione s de n Polymères.

. J.MARCHADr s currentlLi y usin panoramio gtw c irradiation units equipped with gamma radiation sources to conduct research into the oxidizing degradation of olefins, an aging factor, and into the origin of olefin photostabilization by steric hindrance amines.

151 Laboratoire de Chimie Nucléaire, Centre de Recherches Nucléaires (Strasbourg)

Dr. J.ChABBE and Dr. G.DUPLATRE are conducting innovative research into fast radiolysis reactions in liquids using probes sensitive to numerous properties and structure f matteo s r (posito positonium)d nan . This research specifically concerne th s dynamic f solvatioo s liquidsn i n , phase change phenomena and, more generallye th , detection and characterization of defects. a resul s f numerouo A t s collaborative efforts mainly conducted abroad with such countries as Poland, Spain, Mexico and Brazil, the laboratory team comprising two full- time researchers has undertaken and is pursuing a wide variety of research themes. The laboratory is equipped with three spectroscopy installations for the positon life time with time psec 0 resolution30 .o t p u f so Experiments are under way for the comparison of data derived from pulse radiolysis method specifid san c laboratory methods develope studo dt y fast reactions.

GrouA . ActivitieCE 12 p e Nucleath f so r Research Centers (Tabl) eI

Owing to the type of R&D conducted in these centers, the CEA is chiefly endeavoring improvo t understandine eth effecte l kindnuclead th al an f radiatiof f g o so o s n r ma n no components therefors i t I . t surprisinno e g that numerous engineer techniciand san t a s these centers are involved in wide-ranging radiation chemistry research in dosimetry, fundamenta applied an l d research industriad an , l applications Group'A , sincCE e seth Compagnie Oris-Industri industrian a s eha l mission.

Researc) a dosimetrd han y Grenoble Nuclear Research Cente IRF/Départemenr- Recherche d t e Fondamentale

Dr. J.CADET and Dr. R.TEOULE are investigating the principal mechanisms governing the radiation-induced degradation of nucleic acids and their components, as effecte welth ionizinf s a lo s g radiatio isolaten no r in-celdo l DNA. They have extended their researc photosensitizatioe th o ht n reaction nucleif so c acids. The main domain of interest of this group of 8 people covers three axis : mechanistic e radiatiostudieth f o s - ninduce d decompositio A modeDN lf o ncompounds , photosensitizatio componentsA DN f o n , determinatio f radiation-induceo n d lesions within cellular DNA.

Cadarache Nuclear Research Center - IRF/Département de Biologie laboratore Th y wit personsh6 equippes ,i d wit gammha (13i C 70 a Cs) sourc60 8 .1 f eo e RadioagronomTh y Department develope n earla d y interese degradatioth n i t f o n polysaccharides groue .Th researcherf po s working wit . J.RAFFhDr I demonstrated that products formed by irradiation are not fundamentally different from products formed by thermolytic methods t shoulI . d als e mentioneob d thae departmenth t s involvei t n i d food irradiation researc developins i d han g method identifyinr sfo g irradiated foodstuffs. Active collaborations have been than i buil tp u tparticula r field with Universitief o s Marseill LESGARDS. G r e(P Cardifd )an J.K.EVANS)r (D f . This group, heade r SAIND y db T LEBE Researca s ha , h Agreement with IAEr Afo identification of ionized foods.

Saclay Nuclear Research Center

- FEBETRON TEAM IRDI/DESICP- / Département d'Etud Physico-Chimi a Lasers l e de d t se e

Since 1969, when the Febetron team was established, the laboratory of Dr. B.HICKEL bese th ts suiteha mosd dan t available equipmen liquir fo t d phas condensed ean d matter research e pulseTh . d radiation source employe Febetroa s di n electro whicn s ngu hha been modified to emit 2 MeV electron pulses during 20 nsec.

152 In addition to his specific area of interest encompassing anion solvation phenomena, the propertie f solvateso d electron polan i s r solvents suc s alcoholha s (and more recently anhydrous ) structure th , f micelleeo instabld san e oxidation statef so meta HICKE. l B ions . Dr , maintaininLs i g close collaboration with teamCNRe th t sa S (unde e supervisioth r f Professoro n s C.FERRADINI, M.P.PILENI, BALPERT), together with long-standing cooperation wit Rise hth o laborator Denmarkyn i .

Laboratoire Primaire de Métrologie des Rayonnements Ionisants/ ORIS-DAMRI : This laboratory is in charge of reference standards metrology. Accordingly, it performs measurement of high radiation doses at high dose rates and established a procedure for manufacturin checkind gan qualite gth f alaninyo e dosimeter 1987n si t alsI . o designed and engineered the automation of an EPR spectrometer instrumentation system. The CEA thus has the expertise required to calibrate and assess radiation standards. Related service d productan s e suppliedar s , particularl r hospitalfo y d clinicsan s , industrial firms and research laboratories.

b) Applied Research and Industrial Applications

- Radiation is used primarily for industrial applications but also for more general activities. Accordingly, for several years the CEA has been making its skills available to e Frencth h Culture Ministry, French museum d regionaan s l authoritiee th r fo s treatmen preservatiod an t artifactsf no regionaA . l artifact preservation center (ARC- Nudeart) is being established at Grenoble and will pool the CEA's know-how with other protection and renovation techniques.

Laboratoire d'Applications Biologiques des Rayonnements/ ORIS-I : Base t Saclada y unde Compagnie th r e Oris-Industrie, this laborator2 3 stafa f s o f yha extensivn peopla d an e e arra f irradiatioo y n facilities. These facilities includo tw : e gamma irradiation unit)unitq B curie0 s, (on00 0 1 0 , e2 x cobalt-6 7 3. e 0on unid an t two electron accelerators, one of which is a VAN DE GRAAFF unit. scope Th applicationf eo s encompasses medical applications (orthopaedics, gynaecology, haemocompatibility), energy applications particularly for nuclear qualification (qualification of equipment for Electricité de France, studies performed for Framatome r nucleafo d an r safety organization Francn si abroad)d ean industriad an , l applications suc radiosterilizatios ha cross-linkind nan polymef go r films. Numerous collaborative effort e beinar s g implemented with research laboratoriet a s universities CNRe th ,hospitals d San . These efforts cove followine rth g areas:

. gynaecology, orthopaedics, haemocompatibility ; . human and veterinary pharmacy (time-delay drugs, intrau-terine devices, hip and knee prostheses).

Département d'Electroniqu t d'Instrumentatioee n Nucléaire/IRDI-D.LETI In the area of radiation generators, construction of a model has been initiated to validat desigelectron w a r ne nfo ea n accelerator withi e LETnth I Departmene th f o t Industrial Research and Development Institute at Saclay. Short-term testing projects are being carrie develoo t t dou pmachina industriar efo l food processing.

. Industria13 l Application Developmentd san Companiey sb Francn si e

firse Th t patents filed bac 195n ki A.CHAPIROy 5b , M.MAGA J.SEBBAd Tan N quickly attracte e attentioth d f companieo n s suc s Pechinea h d Sainan y t e Gobaith r fo n industrial development of polymer grafting using radiation techniques.

- COMPAGNIE FRANÇAIS E RAFFINAGD E s i Ecurrentl y pursuing industrial production using this techniqu graftinr efo acrylif go c aci polyolefinn do . - Founde Lyon di year5 n2 s ago, CONSERVATOM producinEs i g 1200 tonne r yeaspe r of a cross-linked polyethylene film known as Girolène using radiation techniques. The

153 specific property of this product is its ability to shrink under the influence of heat for packaging applications. Conservatome is also using ionizing radiation for medical equipment sterilizatio food nan d processing. GAMMASTER, a company established in 1968, is a leading European firm active in toll processing using gamma radiation techniques t I alread. s brancheha e y th n i s Netherland Wesn i d t san Germany wild an l, ope nplana t Marseilla t Marcn ei h 1989. s businesit Mos f o t s concern e radiosterilizatioth s f medicao n d surgicaan l l instruments. Gammaste t involveno s i r researchn di t occasionallbu , y participaten i s short-range scientific projects such as the development of dosimetry systems or the testin polymerf go s use medican di l products. Founded in 1966 by the Thomson Group, the Corbeville Ionizing Radiation Applications Center (CARIC bees ha ) n supplying industrial irradiation service subsidiara s a s f yo the Perouse Group since 1985 involves i t .I thren di e area businesf so stol: l processing, experimental testin f compositgo e material foodstuffsd an s engineerind an , e th r gfo constructio irradiatiof no n units. CARIC has two irradiation units located at Orsay. Each unit is equipped with a CGR- MeV linear electron accelerator, one installed since 1966 and the other in 1987.

The industrial development of radiation sources for research needs is virtually non- existen Francen i t .advene Thith t f pulssa o t situatioe explainee eus b y e th n ma y db technology in France, at the end of the sixties, of exclusively electron guns of the Febreton type, which were employed in research laboratories for a variety of reasons (ease of use, cost).

It should nevertheless be emphasized that a new demand may emerge in the future. Furthermore, it has to be noticed that be the new radiation source which will employed e Instituth y ab tt Curie Biologi a Kinetro s i e n linear electron accelerator recently developed by CGR-MeV.

1.4. Educational Activities

The rapid survey presented supposes a substantial effort to train researchers, engineers and technicians. This training is offered in the form of specialized courses, and also in seminars locally organize e laboratorieth y b d s involved. Educatio s providei n y b d definitio t Universitiesna t als accreditey bu ,ob d Institution sConservatoire sucth s ha e National des Arts et Métiers (CNAM) and the CEA's INSTN.

. GENERA2 L CONSIDERATIONS

Many of the research laboratories are located in Paris or the surrounding area. Notable exceptions to this rule are the laboratories based in Strasbourg, Grenoble and Cadarache.

Numerous collaborations have been buil. up t laboratore Th y heade Dr.B.HICKEy db Saclae th t La y nuclear research cente pertinena s ri t exampl f thieo s situation e researcTh . h team there participate activitiee s th full n a i y f o s joint research unit wit CNRSe hth additionn I . , traditional collaborative effort e beinar s g pursue n i particulad r wite Laboratoirth h e Chimie-Physiqud e R DESCARTE( e S University) and the Institut de Biologie Physico-Chimique. Moreover occasional collaborative projects are also created to carry out specific research subjects (e.g.with LOUVAIN LA NEUVE University). t shoulI d als indicatee ob d that, afte lona r g perio "mutuaf do l ignorance" radiolysie th , d san photolysis laboratorie w ofteno sn collaborat n problemo e s e thaactuallar t y quite complementary or similar. Many examples of this collaboration are to be found at the Saclay nuclear research center, the Muséum National d'Histoire Naturelle and other Institutions. Many researchers also do not hesitate to use techniques calling on radiolysis and radiolytic- induced specie r specifisfo c investigations employing ionradicald san s and, more generally, to study the mechanisms due to redox reactions.

154 Another significant trens followa s di : witsexceptioe hon n relate f heavo e dy us wit e hth contrasn i ions situatioe d th an , o t n abou year0 2 t s ago investigatioe ,th primarf no y energy deposit phenomena is no longer in vogue. As a result of technological advances, interest has now converged on the determination of reaction mechanisms through the detection of transient determinatiospeciee th d san producf no t appearance/disappearance kinetics. This trend may involve the risk of losing the previously gained knowledge, which educators should attempt to prevent. Research int photoionizatioe oth molecules ga f no s using synchrotro r laseno r radiatios nha contributed so extensively to the understanding of the primary mechanisms governing the productio dissociatiod nan f ionno s thas radiolysiga t becoms sha e virtually non-existenn i t France. The many laboratories and the wide range of research themes adressed in France actually mas a kdegre f stagnatioo e turnoverw n lo reflecte e n researci th y b d he th team d an s decreasing numbe "domesticf o r " students educate radiation di n chemistr trained yan d with the use of radiolysis techniques ; nevertheless considering the relatively constant number of publications concerning pulse radiolysis throughout the world, our national situation does not appea exceptionals ra .

3. TRENDS

Regarding areas of research, the recent radiation chemistry research symposium (JECR) hel t MARLY-LE-ROda 14-1n Io 7 June 1988 identified curren futurd an t e target frencr sfo h researchers: a) modelling Theoretical scientists continue to express interest in the dynamics of electron solvation owing particularly to the recent contributions of photophysicists and the results obtained with "femtosecond" lasers. b) contribution of radiolysis to reaction mechanisms research Experiments such as those aimed at forming silver aggregates using pulsed radiolysis and enabling measurement of the aggregates redox potential, could improve a better understandin photographie th f go c process particularn I . , helthey explaio pyt ma y nwh a critical size of latent image germs must be achieved for its development. c) biological mechanisms probed using radiolysis Researchers know exampler fo , , that some radical formee sar biologicay db l processes suc s respirationha . Radiolysi suitabla s i s e metho r producindfo g these radicald an s investigating then- chemical reactivity. It can also be readily demonstrated that the reduction of heme in hemoproteins by hydrated electrons does not occur directly. d) biological effects of radiation Despite extensive research biologicae th , l effect f radiatioo s e stilt completelnar no l y understood appearw no t .I s certain thahydroxye th t l radica mose e th th s ti n l i toxi e con case of indirect effects, that is the effects resulting from one of the products of water radiolysis. e) radiation applications Non-medical application f ionizino s g radiation require dlona g tim r developmentefo . Current trends nevertheless appear promising, namely : - irradiation to destroy pathogenic bacteria in food ; - techniques for grafting and cross-linking polymers used particularly for manufacturing biocompatible materials to make prostheses ; nuclea- r qualification.

The development of nuclear energy to a mature stage in France will help to maintain teams of versatile researcher experte ar o radiolysin si swh CEAe t leasth sa t a t. Typical research targets thus include achieving a precise understanding of the mechanisms governing the radiolysis of water and aqueous solutions, particularly at high temperatures hi connexion with the corrosion phenomena in nuclear reactors. Spent fuel reprocessing requires a comprehensive investigation of valence changes and hydrolysis for ions exposed to radiation.

155 Disposa nucleaf o i r waste deen si p geological formations (granite, clay, salt hundredsr )fo r o even thousand f yearso s raises difficult questions concernin resistance gth f materialeo o st radiatioe releasth d f hydroge o ee dissociationan th d oxygeo watey t an ne an f rdu no n present. Finally, such releases mus preventee b t d durin transportatioe gth radioactivf no e solutions.

- Furthermore a curren, t research e investigatiotrenth s i d f phaso n e influencee th n o processes involved : the dissociative attachment and auto ionizing resonance processes in the gaseous phase, as well as the solvation of ions in the liquid phase.

- Finally, numerous applications will require investigatio f radiolysino s using heavy ions sa well as protons on radiobiology and radiotherapy, and using electrons at energies below 15 MeV (to avoid activating the target materials) for food irradiation research.

Prospect- technologw ne r sfo emergine yar simultaneoue th r gfo s implementatio severaf no l research methods. These methods include : absorption and emission spectroscopy, Raman resonance, electron paramagnetic resonance, polarography and conductivity.

- The findings of the workshop in commemoration of Jack SUTTON are still pertinent. The priorities identified at that time were : - reinforce existing research teams; - train new researchers ; - modernize equipmen; t - strengthen ties between fundamenta applied an l d research.

Accordin theso gt e prioritie frence sth h scientific community would nee creatioe dth a f no fast kinetics research center which would combine research teams, comprising photochemists and radiation chemists, from the CEA, Universities and the CNRS. Such a center could provid eplaca accommodatinr efo g researcher holdind san g meeting muca f so h larger community.

156 CONCEPT RADIATIOF SO N RESEARCHN I GERMAE TH N DEMOCRATIC REPUBLIC

J.W. LEONHARDT Forschungsbereich Physik, Akademi r Wissenschafteede r DDRnde , Berlin, German Democratic Republic

Abstract

Current status and actuel1 projects of radiation application in GDR are described. Basic research is discussed.

I.FVWORDS

Accelerators, application, beam, cable coating, curing, electrons, evaporation, facility, gamma radiation, hardening, heating, industry, lasers microelectronics, polymers, pulse radiolysis.

1, INTRODUCTION

Radiation application has a long tradition in G.D.R. A 2uO I-..Ci—gamma facilit s installewa y n Radeber i 197n i dO r fo g sterilisatio medicaf o n l supplies 0 groun76 . d water wells were equipped by means of barslaped radiation sources with a total amnount of Co-60 of 42 F'Bq. The gamma radiation protect aquiferse th s ' channels agains e depositiotth f o n unsalable iron and oxide hydrates by biological action [l}. Studies of irradiation treatment of onion due to sprout inhibitio a beeinw n no starten i d g an 19&n di J pilot production scale usin speciag2 l gamma facilities [2]. e radiatioTh n induced chlorinatio alsC FV o f arriveno e th d industrial pilot scale e advantagebecausth f o en i s comparision wath conventionally treated material [ 3]. The first application of a 1,5 MeV-High-Voltage 6O KW- accelerato FE—crosslinr fo r cabln i g et in industr G.D.Rn yi . was installed in 1975. There are treated 10-30 KV-cable insulations [43. The research projects relate e havb o et suco t d h application fields, which have future prospect countrye th n si . Thas ti the reason, industriathae th t l applicatio f electroo n n accelerators was getting pronounced since 1980.

PROJECT. 2 S USIN GENERSW 20-5LO V Y0 Ke ACCELERATOR S r industriaFo l implementation Type serie f higo s h power electron beam guns were develope Forschungsinstitue th n i d t

157 . Ardennev . M , Dresden, providing beam range powe»th en "i between 5 kW and 12OO kW. The length of the beam path in the working vacuum chamber at pressure of ca. lO"* Pa varies beae Th m deflectio. m 3 d an realizes betweeni m 5 y 1, b nd means of a 1OO kHz radiofrequency. The main application of Electron beams (EB) is the thermal surface modification. As applied in the heat treatment of subsurface rones of metal parts EB enhances the physical and/o chemicae th r l propertie highlf so y stressed surface regions in order to improve performance in service. Hardness, resistance to wear and corrosion get increased. Because of the high thermal conductivity of metals, the confinement requires energy sources of high power density. EB meets these requirements as well as other demands of modern technology better than laser beams e bea(LB)th mf ,i powe greates ri r. thakW n3

2.1 Hardening [5]

Homogeneous hardenin surfaca f go e layer with thicknesh s requires that the material be heated to a temperature above the austenizing température throughout the1 none avoiding the surface fusing. The hardness can be increased by more than a factor of 2. EB~hardening hae been used increasing!v since 198 heavn i 4 y engineerin machine-makind gan g enterpricef o s the G.D.R mosn I .t cases EB- performes Hi multa—purposn i d e plants, which also perform EB welding. Typical items are quill's, harvesters' mower blads e lif,th e tam whicf eo t hgo twized.

2.2 Fusing [5]

Despite to difficulties due to the specifity of liguid phase processes (convection, surface tension etc B offer)E o t s enhanc e stres&abilitth e marginaf o y l rone n sordei o t r improv tribologicae eth l propertie partf so addition si o t n an improved resistanc abrasiveo et , corrosiv d rollinean g wear. Favorable effect attainee b n sca d especiall steeln yi , grey cast, iron, aluminium alloys titaniud ,an m alloys.

Wearing zones of rockers, camshafts, pistons can be succèsfully heated. Automated production plant engineered for EB-Fusion treatment of pistons with diameters in the rang excamplS>-32r f o epe m u m equippes ei dW K wit C h*2 1 electron guns, allowing produce 220000 pistons per year.

Annealin3 2. 3 [6 g

The homogenous heatin metaf go l strip annealee sb d with heat up—rates of 10s I- /S can be easely done by means of EB. Withou speciaa t l heat-treatment program cold-rolled strip

158 e improveb s steemechanican it ca n ldi l propertied an s processing features. Ther suggestee ear d various plantd san equipment for EB-anneal ing for strip steel and non-ferrous metals on industrial scale.

.4 Evapora t ion /Coating [73

The Physical vapor Deposition - FVD - in vacuum is the most important technology to procuce thin layers or coatings. The EE has stimulated this technique very much, because of direct heating of the évaporant surface in a water cooled cruicible laver f higso h producee puritb n 5o n ur 0t y ca p du separatee b s"-electroe n Th 1-.ca n d ngu fro evaporatioe mth n flux usin transversga e magnetic fiel magnetid dan c lenses for beam guidance.

Applicatio realizes i n standarn i d d evaporation plants (EB) for electronic d opticaan s l industries. EB-coatxnf o g piastres, paper, tapes and metal strip allow high production speeds of 2OO m min~"x, strip with &X> mm using 2?; 600 KW- preheatinr e fo th W unitK evaporatior f O o fo gs6O x 2 d nan strip.

Z0 I.- 20 eV-ACCELERATQPROJECT E TH R SFO R (LEA)

This low energy electron accelerator was developed as prototyp r technologicafo e a l studies i CIIRe t th I .n s i single gap accelerator using a Linear cathode as an electron emitter. As design principle that of the "Electrocurtain"— processor f Energo s s yadapted wa Science«3 S e £ Th .c In ? accelerator consist heae th d f sconnecteo higa y hb d voltage powee th cablr o supplyt e n a hige Th .o h t voltag d fe s ei electrical optical svstem consistin e tungsteth f o g n falament cathod d lenseean ? formin electroe th g n stripe Th . filament is located in the center of an cylindrical vacuum emittee th chambe d d an electronr acceleratet sge e th o t d ground potential of the camber. After penetrating the 10 urn Ti-window they reac irradiatioe hth n zone. Electron energy varies between 15O-2OO 1-eV, maximum current: 3O mA, the beam uniformite Th curren e . widtth cm f yO o th7 ovecathode rth e is ± IS"/.. The longitudinal uniformity of the current is monitore v meanmeasurina b df o s g grid e windoTh .s ha w dimensiond containx an JLOO20 m m On f o boto s h sides channels for water cooling. Thin parallel copper strips suppor foile tth . Energy loss withi windoe th n less wi s than 107. at 200 ^eV. A maximum dose rate of 1,1 mGy per second s arrivedwa . That mean sproduca t spee 120m/mif do 0 1 t na I By-dose level £10].Tha O t20 )• eV-accelerator mainls wa y designe curingr fo d , graftin dryingd gan , whic operatee har d at normal pressure.

159 1 Curin3. Woodef go n Production

The accelerator LEA is now woriing as part of a pilot line whic s builwa r helectro fo t n beam curin f furnituro g e elements. The line is operated under contract with the industry t consistI . f followino s g major parts: fully inertizable conveyer section, lacquer curtain coating machine, accelerato A witLE rh self-shielded radiation protectio inerd nan units conve/oe tga Th . divides ri d into three sections with independent speed controllers. Thus, lacquer coating, condationing and curing can be done at different speeds conveyoe Th . rvariee b spee n ddca fro0 1 m to 80 m/min and special entrance and exit elements of the conveyor section minimize inert gas consumption s inerA . t nitroges ga u&es ni d whic generates hi d from liquid nitrogen containing typicall oxygenm pp 0 tvpicaA 1 .y l iners ga t consumption is 3D ~ 25 nfVh. f coatingo C advantages EE sha e Th n comparisioi s n with conventional chemical methods of curing, especially energy savings and minimal air pollution using solventless binders. R werSD In e studie behavioue dth f rbindeo r systems a s polyesters, epoxies, polyurethanes and also vinyl monomers [11} . The aim of research was the formulation of acrylic binder systems with curing dose f-GwitO d 5 an ys h pendulum hardness value 10_ Of so immediatel y after irradiatione Th . influence of oxygen on the EEC in given systems was investigated [12],

. PROJECT4 SO t eV-^CCELERATO 5O USIN E GTH R TYPE "AURORA"

The evV> (-eV-high- power acceJerator (4O~oO teV) AIRORA is manufactured in the Efremov-Institute in Leningrad, Soviet Union. Thi curinr sfo textilet typR ga GD uses ei n di d san the irradiatio fluf no e gases.

4.J Curin f Textilego s

As a pa Jot plant in the textil industry was installed an 5Oj leVHslectron accelerator (50 Hd) of AURORA Type. The Institute of Fibre's Technology developed the so called particularly cured textile structuratiof o m sai wate th h f no textil surfaces. Using the fibre property of shrinl-ing after curing the textile is covered by a thin 1 mm—aluminium mas^ wath holes during .irradiation. An other technology developed stronusee th s g dependenc radicae th f eo l concentration o n temperature f selecteI . d irradiatee areath f so d material are heated by means of a special roller, no radicals mal-e curing over there. It was observed, that the behaviour of irradiated textile electrostatio t e sdu c charge uptake th , e of moisture and dust was improved D-33.

160 4.2 Irradiation of flue Gases

A pilo exhause t th plancleanins r tga fo t y meanb g f o s electron beams is under consideration. The main purpose is to chec EBFAR-principle kth e LlOl, which combine- EB e sth induced oxidation of SCfe and NoM with a plasmachemical reactor. High energy electron injectee fluse ar s th e ga n i d strea d producan m e electrical carriers e thermalizeTh . d electrons are accelerated up to excitation energies of wished radicals by means of the electrical field. If ionisation collision can be avoided the specific energy per radical can be decreased in comparision with the B-values.

5. BASIC RESEARCH

Fundamental research projects have to be related to such application fields, which have future prospects in the country. Radiation chemistr wela s lyi developed fielt bu d only a few technological processes arrived an industrial scale in chemical industry.,, p. e. the chlorination of FVC. e importanTh t benefit camR GD e n s i frocabe e d th mwir lan e and plastic industries, frosterilizatioe mth f medicano l supplies and also from the radiation induced prevention of the ochre deposition in wells.

5.1 New application lines to be considered

5.1.1. Application of the EB-curing in furniture and printing industries

5.1.2. Environmental applications, especiall flue s yth ega cleaning, waste water treatmen d degradatiotan n of toxic compounds (halocarbons) 5.1.3. Irradiation of food and fodder

5.1.4. Applications in the electronic industry

5.1.5. Application of radiation in biology and medicine

In preparation of these and in feedback of the applied research the basic research program is suggested as follow:

Researc2 5. h projects

5.2.1. Studie f fasto s , excitatio d chargan n e transfer processes in the ns-ps-range (pulsed electrons & photons)5 especially to the "fast hole" interaction in nonpolar hydrocarbons, primare th f ,o y processen si aIcylhalogenides, alcanes, polymers etc. 1143.

161 5.2.2. Radiolysis studies in polar media at high temperature and pressure related tc the safety of pressurised water reactors

5.2.3. Study of the radiation induced decomposition of macromolecules, p. e. FVC, cellulose etc. in respect to problems of recycling

5.2.4. Thermal ization, excitation, ionization, negative ion and cluster formation, especially interactions of products like dinners, trimer systems e ga th n d si san investigatio e SCta/NOth f o «n oxidation mechanism includin e influencth g electricaf eo l fields 115}.

5.2.5. Time resolved studies of the radiation induced electrical carrier d an theis r behavioun i r semiconductors e defectth f f o n o ,solidsi d an s carrier n i spacs e charge d superconductinan s g s I a i mar .te

5.2.6. Studies of fast charge and energy transfer in macromolecules induced by ps-electron pulses and fs- photon pulses Ci6l.

5.3 Experimental equipment for basic research

e experimentaTh l techniqu e s locatei Centrath e n i dl Institut Isotopf eo Radiatiod ean n Researc Leipzign hi e Th . following facilities are available:

5.3.1. The 4-11 MeV LINPC "ELECTRQxilCA'1, giving 1 ns-pulses witKra3 ha d us-regime dose poweW th k n .5 ri e optical analysi range th en s i 200-120 , emissio0nm n (1 ns) and absorption (2 ns) Use of 30 ps-fine structure pulses and a conductivity preparation i cele ar l n

"ELIT"V Me 1 5.3.2, e singl.Th , e ps pulse O 3O s dowo t n optical analysis 2OO—12OO nm, beam coupled ESR with time resolutios u f no

5.3.3. The 23 MeV MICROTRON, 20 uA electrons, us-pulses, up to 0.5 kW power, irradiation with electrons of 1, 2, 3 ... 23 MeV or bremsst rah lung 5.3.4. The 500 keV "AURORA", 20 kW beam power for applied research

162 REFERENCES

[l] WISSEL , LEONHARDTD. , , J.W., Applie BEISETh , -,E. cation of Gamma Radiation to Combat Ochre Deposition in Drilled Water Wells, Radiât. Phys. Chem. 25 , (1985) 57. [2] DÖLLSTÄDT GRAHN, R. , , CH., HaBNER REINHARDT, ,G. , ,I. SCHUNKE, H.-W., SFRINZ, H.,WINKLER Oniow Ne nA , ,E. Irradiator. Proc. II.Work Meeting Rad.Applic.aRad,, (1981) Leipzig. [3] EOF:, M., FRIESE, K., REINHARDT, I., Radiation Induced Chlorination of FVC, lAEA-Conf. Ind. Appl. Radioisot. Rad.Tec hn., Grenoble, (1981) (Ex tended Synopsis). [4] PQSSELT, K., FLÜGGE, D., HEINRICH, H.-J., NIESNER, CH., SCHINKE F'roc, , F. CME f .o A Symp. Rad. Chem. Mod., Warshaw (1977). [5] SCHILLER, S., PANZER, S., Thermal Surface Modification by electron beam high—speed scanning. Ann. Rev. Mater. (1988: Sei18 ) 121-4O. [6] SCHILLER, S., PURSTER, H., Hötzsch, G-, JäSCH, G., ODRICH ANTON, ,D. , K.H., Annealin metaf go l strip with electron beams h Internationa8t . l Conf n Vacutio . m Meta11urgy, Lin z, Austria (1985). ] SCHILLER[7 , HEISINGS. , FRACH, H. ,Electro, ,P. n beam evaporation : SurfacinIn . g Technologies Handbook (T.S. Sudarshan Ed.), Marcel Dekker, Inc Yorw Ne .k (1988). [&] AARONSON, J.N., NABLQ, S.V., Nucl. Instr. Meth.in Physics Res., B 10/11 (1985) 998. [9} LEONHARDT, J.W., SCHQTTKA, A., KŒNERT, P., MEHNERT, w ElectroNe , R. n Irradiation Facilite CIIRth ,f yo Leipzig, Proc Conf. IV .. Radioisot. Appl. Rad. Proc. Ind., Leipzig, (1988) (in Press). [lOJ LEONHARDT, j!.W., BOB , GROSSEJ. , , H.-J., FOFP, ,P. Radiation Induced SO^-Oxidation, Proc. V. Tihary Symp., Siofok (1982). [ll] SCHMIDT, J., MAI, H., DECKER, U., SAALBACH, B., Acrylates with higher Malmesses far EBC, Proc. 4th Conf.Radioisotop.Appl.Rad.Proc.Ind., Leipzig (1988) (in Press). tl2'] SCHMIDT , MAI J. ,, SAALBACH . H , , InfluencB. , f eo f Coatingso C EB Oxyge. n o Procnh Conf4t . . Radioisotop. Appl. Rad. F'roc. Ind., Leipzig (1988) (in Press). [13] DORSCHNER, H., HEGER, A., FUTZGER, D., Praktische Erfahrungen beim Einsat r Elektronenbeschleunigerzde - anlag s Instittttede e Technologir fü s r Fasernde e , Dresden, für die strahlenchemische Modifizierung Hocn- polymer, Faserforschung- Lind Textiltechnik (19783 9 ,2 ) 199.

163 [14] BFEEË , Zentra,0. l institu Isotopenr tfu Strahlend -un - forschung, Leipzig, personal communication [15] EŒS, .T., Zentralinstitut fur Isotopen- und Strahlen— forschunq, Leipzig, personal communication rd-^ERT, R., Zentral inst i tut für Isotopen- und Strah- forsn le c l Tung, Leipzig, personal commuinication

164 RADIATION CHEMISTR HARWELT YA L

W.G. BURNS Harwell Laboratory, United Kingdom Atomic Energy Authority, Harwell, Didcot, Oxfordshire, United Kingdom

Abstract Radiation Chemistr pursues yi Harwelt da orden li o rt provid basiea advicr fo s e nucleae giveth o nt r industry where the efficiency and safety of its operations, with respect both to workergenerae itn th sow d lsan public, could potentialle yb affected by radiation chemical effects. For example we advise the fuel reprocessing organization, (BNF pic nucleae th ) r reactor construction (NNC operatind an ) g organizations (CEGB)d ,an undertake relevant contract work for external customers. We undertake specific investigations involving experiments and their interpretation, including predictions involving scaling from laboratory experiment largo st e scale systems pureld ,an y modelling projects. The types of system investigated are varied. In gas phase radiolysis they include high dose rate fission fragment irradiation of caesium iodide vapour in helium at ca 400°C in the fuel clad gap, where iodine atom concentrations can affect stress corrosion crackin Zircaloe th f go y cladding. Anothe phass rga e investigation addresse gamma/neutroe sth n irradiatio C0f no 2/CH4/H20 mixture advancen si d gas-cooled reactors, where carbonaceous deposits on surfaces can affect reactor efficiency wore W .systemn k o s relatestorage th o t de and transport of irradiated aqueous or wet materials, including the radiolysis of plutonium nitrate solutions. Important topics are the effect of irradiation on corrosion, and the speciation of the actinides in long-term repository storage. This speciation is normally calculated using thermodynamic principles which do t applradiatioa no n yi nevaluate w fiel d dimpacan e eth f to radiolytic reactions by establishing the rates of the forward and reverse reactions which contro notionae lth l redox equilibrid aan potentials so that reactions of radiolytic species can be allowed to compete with them. Our current main effort is directed towards understandin radiatioe gth thermad nan l chemistrf yo dilute iodide solution provido st basiea advice r th fo s n eo safet pressurisef yo d water reactor certain si n fault conditions.

Studiee effectth f radiatioso f o s n chemistr beine yar g pursued in many of the Divisions of the Harwell Laboratory. This reflect importance sth radiatiof eo n chemical effect mann si y operation nucleae th f so r industry mors A .e detailed attention is paid to the safety of the industry's workers and of the general publi widespreae cth d influenc thesf eo e effects becomes clearer. We wish to discuss the work of the Radiation Chemistry Section, whic pars hi Reactof o t r Material Radiatiod san n Chemistry Grou Chemistrn i p y Division provido t rols s It i e. e advice to the British nuclear industry in matters where radiation chemical effects impinge on aspects of the safety and efficiency of operations. In addition the section performs relevant fundamental work and contract work for external customers [1],

165 The radiation chemistry section undertakes specific investigations involving experiment theid san r interpretation, including predictions involving scaling from laboratory experiment largo st e scale systems pureld ,an y modelling projects e investigationTh . s cove widra e rang systemsf eo , including gas phase and aqueous phase radiolysis, and liquid/ solid interactions. Some of the principal areas of study are now described. Our main effort is currently directed towards understanding the radiolysis of very dilute iodide solutions [2,3,4,5], This interesf topio s ci t since iodin fissioa s ei n product whose radioactive forms may constitute a significant potential radiological hazard if released in a PWR or BWR reactor fault. In som thesf eo e fault condition aqueoue sth n si mediue b n mca the form of aerosol droplets at 100 to 150°C from which volatile iodin readiln eca y partition inte larg spacs th oa ga ef eo reactor containment.

somn I e type reactof so r fault e caesiu,th m iodide released into the water from the fuel can take part in thermal and radiolytic oxidation which can cause molecular iodine to be formed. This can partition into the vapour phase if the reactor vessel is breached, giving access to the containment space. Laboratory studie relevanf so t aqueous therma radiolytid lan c chemistry of iodine species [4,5] are being carried out internationally and modelling procedures are being used to apply laboratory result predico st t effect n fulsi l scale plantn A . important effect in full scale prediction is that because of the large vapou liquio rt d volume ratio iodin removes ei d efficiently by partitioning from the liquid and this has significant consequences for the total amount of iodide which can be transferre vapoue th o rdt phase [5] interestin.n A g poins i t that insid operatinn ea g reacto iodine r th fuen eca l exists mainly as caesium iodide vapour.

Consequently our studies have included computer simulation of gas phase radiolysis in the fuel clad gap where high dose rate fission fragment irradiation of caesium iodide vapour in helium occurs at ca 400°C, and iodine atom concentrations can affect the possibilit stresf yo s corrosion crackin Zircaloe th f o g y irradiates i x intensn mi a cladding s y dga b ee Th (5w/g. ) fission fragment irradiatio solid/vapoue n th fiel d an d r interactions between the iodine and metal and oxide species present are important [6]. Another gas phase radiolysis investigation addresses the gamma/neutron irradiation of C02/CH4/H20 mixtures under the conditions pertinent to the coolant gas mixture of an advanced gas-cooled reactor. In AGRs the coolant gas carbon dioxide, although itself radiation stable, when under irradiatio 20-4t na 0 bar, 600-900K, dose-rate ca. Iwg"1 (reactor conditions) it could erode and weaken the graphite moderator. Carbon monoxide and methane are added and they minimise this unwanted effect. However transiene , th som f o e t species formed radiolytically from the methane react catalytically with the surface of the stainless steel fuel claddin producd an g carbonaceouea s deposit which reduces the heat transfer froe fue gasmth o lt , lowerin e reactor'th g s

166 efficiency. To understand and eventually to alleviate this difficulty Norfolk et al [7] and Marsh et al [8] have developed a computer simulation of the chemistry of the AGR gas mix. Studies at Harwell [9], [10], have extende simulatio e scope th dth f eo n e cyclinbule tth oth k f o gflowin througs ga g n irradiateha d core sectio unirradiaten a d nan d sectio whicn n i concentration e hth s of CO, H20 and CHA, are restored to their required values, as occurs in the reactor circuit. We have also developed a quantitative method for analysing the mass transfer of transient specie surfaca o fasa st n tei flowing medium whic sucr hfo h specie improvemenn a s si usuae th ln to approximat e methoa f do mass transfer coefficient. Studie water-coolen so d reactor systems have recently focussen o d Boiling Water Reactors. In BWR systems high temperature aqueous radiolysis produces hydrogen and oxygen which partition into the water vapou two-phasa n i r e annular flow coolansysteme th s A t. proceeds at high speed up the fuel channel the steam fraction and fluid linear velocity increase, preservin constana g t mass flux along the flow path. Work at Harwell [11] simulated these effects for the Winfrith steam generating reactor, and suggested that Zircaloy cladding corrosion might be lessened by adding hydroge e feedwaterth o nt . Such addition beinw no ge sar mad e worldwide in BWRs, not to protect Zircaloy cladding, but to protect stainless steel (eg 304L) components from intergranular stress corrosion cracking (IGSCC) which is assisted by irradiation Generae Th . l Electric pumt serieje p f sreactoro s shows interesting features in the concentrations of dissolved oxygen and hydrogen in the recirculation loop water, where they dissolveb pp al0 l30 contaido t oxyge 0 varyinnd 20 nan g concentration hydrogef s o absenc e th n deliberatelnf i eo y added hydrogen. Those reactors which produce lower hydrogen concentrations when no hydrogen is added need lower additional hdyrogen to suppress oxygen concentrations below a given level [12]. This problem has been addressed by computer simulation by Japanese and British workers [13] [1A] [1]. It appears that radiolysis in the downcomer region outside the reactor core is important. Crucia suco t l h chemical calculation reliable sar e values for the high temperature yields of aqueous radiolytic product higd san h temperature ratequilibriud an e m constantr fo s their reactions, and work is proceeding here and elsewhere to gather these data [15-17]. We wor systemn ko s relatestorage th transpord o dt ean f to irradiated aqueou materialst we r so , includin radiolysie th g f so plutonium nitrate solutions. Important topics are the effect of irradiatio corrosionn no speciatioe th d e actinide,an th f no n si long-term repository storage. This speciatio normalls ni y calculated using thermodynamic principles and we have to evaluate e impacth radiolytif to c reaction attemptiny sb establiso t g e hth rates of the foward and reverse reactions which control the notional redox equilibriu potentiad man thao ls t reactionf so radiolytic species can be allowed to compete with them. Note that equilibrium thermodynamic principle applt a no n i yo sd radiation field have W .e modelle effece th d radiolysif to n si changing the speciation, usually by oxidation, of radionuclides. In some cases agreement with laboratory irradiation experiments has been achieved. The importance of this subject is due to the easier permeability through rock formatio highee th d rnan

167 solubility of oxidised species, especially anions such as pertechnetate [18]. We have also studied the effect of irradiatio leacn no h rate vitrifief so d highly active waste [19]. fundamentae th n O l sid collaborativr eou e work with Oxford University [20,21,22] compares the results of stochastic and deterministic calculational route primarr fo s y yield suggesd san t possibly thaearlye th t effect gammf so a irradiation water molecules to be dissociated together in linked groups of several molecules rather tha smallen ni r group unlinkef so d molecules. Our studies also include radiation effects in the corrosion of stainless and mild steels. It is intereting to note that in modelline th e largth ef o g scale effect boundarf so y reactionn si turbulent flow, and electrochemical reactions in corrosion, we are using, with different timspatiad ean l scales, similar methods to those used to model the diffusion kinetic processes of spurs and tracks. expece W continuo t provido et e sound advice base goon do d basic science and our considerable skills in the simulation of large scale radiolytic effects. This latter activity is as rewarding intellectuall basis ya c science involvin desige gth n and interpretatio laboratorf no y experiments ,fiela whicn i d e hw also expec continuo t e contributing high quality relevant work. WalterS preparatioe W th helr r D n sfo pi o t e Thankndu e sar of this paper.

REFERENCES

1. LIN, C C, RUIZ, C P, ROBINSON, R N, CURTIS, A R, BURNS, W G, "Model Calculation Watef so r Radiolysi PrimarR BW n si y Coolant", Water Chemistr Nucleaf yo r Reactor System. s5 (Proc.Int.Conf. Bournemouth, 1989), Vol.1, BNES, London (1990 pressn )i . . BURNS2 MARSH, G "Th , ,R W e ,W decompositio aqueouf no s iodide solution induced by f-radiolysis and exposure to temperature 300°C"o t p su , Water Chemistr Nucleaf yo r Reactor Systems 2, (Proc.Int.Conf. Bournemouth, 1983), Vol.1, BNES, London (1983) 89-101. 3. BURNS MARSH, G "Th , ,R W e, W Chemistr iodinf yo accidenn ei t conditions", Water Chemistry of Nuclear Reactor Systems 4, (Proc.Int.Conf. Bournemouth, 1986), Vol.2, BNES, London (1987) 125-136. 4. BURNS, W G, MARSH, W R, "The thermal and radiolytic oxidation of aqueous I" and the hydrolysis and disproportionation of aqueous I2", Proc. Specialists' worksho iodinn po e chemistr reacton yi r safety, Harwell 1985. (DEANE POTTER, M ,Ed)A , E , ,P CSNI OECD Steering Committee for Nuclear Energy, AERE-R11974 (1986) 121-136.

168 5. BURNS, W G, SIMS, H E, "Computer modelling of the radiation chemistry of aqueous iodine solutions in laboratory LOCR PW conditionA a usin n FACSIMILe i th gd san E computer program", Proc. 2nd CSNI Workshop on iodine chemistry in reactor safety, Toronto (1988) pressn ,i .

6. BALL, R G J, BURNS, W G, HENSHAW, J, MIGNANELLI, M A , POTTER, P E, "The chemical constitution of the fuel-clad gap in oxide fuel pinnuclear fo s r reactors", proh Int.Symp7t c . on thermodynamics of nuclear materials, Chicago (1988) J.Nucl.Matl (1988) pressn ,i .

7. NORFOLK D J, SKINNER, R F, WILLIAMS, W J, Hydrocarbon chemistr irradiaten yi d C02/CO/CH^/H20/H2 mixtures, Radiât. Phys. Chem 21, 3 307.

. MARSH8 NORFOLK, R ,G SKINNER, J ,D "Theoretica, F ,R l modellin carbof go n deposition processes", Proc.Confn .o performance, Stratford-upon-Avon, BNES, London 235-241, (19851 l )Vo .

9. BARTON, R A, Chemistry Division, Harwell Laboratory, Oxfordshire, 0X14 ORA, personal communiction.

10. BURNS BARTON, G GOODALL, W A ,R , JAB, MARDON Mas, ,T s transfe reactinf ro g chemical species exampln :a e froe mth radiation chemistry of AGR coolant gas mixtures, Nucl. Energy 27, 2 (1988) 109.

11. BURNS MOORE, G "Radiatio, ,J W ,B n enhancemen zircalof to y corrosion in boiling water systems", Water Chemistry of Nuclear Reactor Systems (Proc. Int.Conf. Bournemouth, 1973), BNES, London (1974) 229-237.

. COWAN12 INDIG, L KASS , ,E R LAW, SUNDBERG, N ,J M ,J ,R , L ,L "Experience with hydrogen water chemistr boilinn yi g water systems", Water Chemistry of Nuclear Reactor Systems 4 (Proc. Int.Conf. Bournemouth 1986), Vol .BNES1 , London (1986) 29-36.

13. IBE, E, NAGASE, M, KARASAWA, H, SAKAGAMI, M, UCHIDA, S", Radiolytic Environments in boiling water reactor cores", Water Chemistr Nucleaf yo r Reactor System s4 (Proc . Int. Conf. Bournemouth 1986), Vol.1, BNES, London (1986) 37-42.

14. TAKAGI, J, KATO, I, ISHIGURE, K, FUJITA, N, "Simulation study on water radiolysis in BWR primary systems", Water Chemistr Nucleaf yo r Reactor System s3 (Proc . Int.Conf. Bournemouth 1983), Vol.1, BNES, London (1982) 381-384.

15. BUXTON WOOD , DYSTERV , D ,G , N "lonizatio, ,S n constantf so aqueoun i H0 d sO Han solutio 200°Co t p n u puls, a e

2 radiolysis study, J.Chem.Soc. Faraday Trans 1,84 (1988), 1113 paped an ,thio t r s meeting.

16. BURNS MARSH, G Radiatio , ,R W ,W n Chemistr higf yo h temperature (300-410°C) water Par Reducin1 t g products from gamma radiolysis, J.Chem. Soc. Faraday, Trans, l, 77 (1981) 197, and unpublished work.

169 17. SEHESTED, K, CHRISTENSEN, H, "The radiation chemistry of wate aqueoud an r s solution elevatet sa d temperatures", Radiation Research (Proc Inth .8t . Conf Radnf .o . Research, Edinburgh, 1987), Vol.2 (FIELDEN FOWLER, M ,, E F ,J HENDRY, J H, SCOTT, D, Ed), Taylor & Francis London (1987) 199-204.

. WALTERS18 WISBEYreviee literaturA , " S th , W f J wo , S e relating to radiolytic oxidation", Ref, AERE R11964, Harwell Laboratory (1986).

19. BURNS HUGHES, G MARPLES, W E NELSON , ,C A , A S , J , R STONEHAM, A M, Effects of radiation on the leach rates of vitrified radioactive waste. J.Nucl. Matls.107 (1982) 245.

20. GREEN, N H B, PILLING, M J, CLIFFORD, P, BURNS, W G, Stochiasitc and deterministic models of spur kinetics, J.Chem. Soc. Faraday Trans 1,80 (1984) 1313.

21. CLIFFORD, P, GREEN, N J B, PILLING, M J, PIMBLOTT, S M, BURNS, W G, Hydrogen and hydrogen peroxide yields in the radiolysis of water: a comparison of stochiastic and deterministic models, Radiât, Phys. Chem2 (1987 0 ,3 ) 125.

170 AN OVERVIEW OF SOME BASIC AND APPLIED RADIATION CHEMISTRY STUDIE TROMBAT SA Y

P.N. MOORTHY Chemistry Division, Bhabha Atomic Research Centre, Trombay, Bombay, India

Abstract Radiation Chemistr d relatean y d aspects con- stitut d programmebasie R& th ef so mann i s y groupt sa the Bhabha Atomic Research Centre (BARC t Trombay)a . e presenTh t paper give n overvie a se recenth - f o re wt searches carrien thii st e Chemistr ou fieldth n i d y Division of BARC.These comprise : (i) studies on the generatio d reactionan n f transienso t speciee th y b s pulse radiolysis technique, (ii) charge migratiod an n reaction in glassy matrices, (iii) radiation induced polymerization, (iv) radiation protection of vitamins, (v) radiation effects on lubricants, (vi) biomédical application f radiatioso n crosd an sl linkege A PV d (vii) effec f higo t h energy <»C- particlee th n o s catalytic propertie f oxides.Somso e topicth f o es propose e investigateb o t d e neath rn i dfutur e ar e also mentioned.

1.INTRODUCTION

In the Bhabha Atomic Research Centre (BARC) at. Trombay near Bomba nuclea, y r related d worha k startee earlth n yi dfifties.A s this involved handling of different type f radiationso d radioactivan s e substances/the importance of a thorough understanding e effectoth f f radiationso varieta n o s f systemo y s s recognisewa d almost frobeginning.The th m e subject had its formal beginning with the studies on the chemical effect f neutroo s n induced nuclear transfor- mation n transitioi s n metal complexes,primarily aimed at producing high specific activity isotope a (n,vi s O reaction e nucleath n i sr reactor.I e earlth n y sixties we had to tackle the problem of deposition of radioac- tive chromiu e reactoth n i mr coolant water pipes.As the coolant water contained trace f Ko s2CrO ^ addeo t d prevent the biofouling of the coolant water, inves- tigations were directe o asset de rol th sf radiatioo e n chemistry of chromate solutions under conditions prevalen e reactorth n i t . This activity later evolved into systematic studiee radiatioth n o s n chemistrf o y aqueous systems bot t rooa h m K temperatur 7 7 t a d an e wite objectivth h f o elucidatine g radiolytic mechanisms.The possibl f terphenylo e us e s coolanta s s in heavy water moderated organic cooled reactors [1] spurred interes e radiatioth n i t n chemistr f organio y c

171 molecules,particularly those that undergo polymeriza- tion initiate y radiationb d . Som f theseo e activities have culminated in developments of useful products and processes such as wood plastic composites [2,3], sul- fochlorinatio f hydrocarbono n o product s e biodegra- dable detergents [4], modification of textile fibres etc] [5 .

2.PULSE RADIOLYSIS 2.1.Experimental setup This is shown schematically in Fig.l and has been described earllier [6].The electron beam pulse from a 7 MeV LINAC ( Ray Technologies U.K.) irradiates the sample contained in a rectangular "Suprasil1 m opticacuvettc 1 f o le pat htransiene lengtth d an h t species generate e celth ln i contentd monitoree ar s d by employing "white1 light beam from a 450 W pulsed Xeno lamc perpendiculan ar ni p r geometr e detecTh . y- tion of transient light intensity changes is done using a R-955 (HTV Co.Japan) photomultiplier tube, the output of which is fed to a fast digital storage scope (Iwatsu Electric Co.Japan Mode S 812T l 3 ).The digital

SAMPLE CELL

SOLN OUT SHUTTER CUTOFF FILTER 1 I L l

SAFETY CHECK

FIG.1 SCHEMATIC DIAGRAM OF PULSE RADIOLYSIS SET UP

172 data from the scope are read and processed by an IBM PC/XT system to give kinetic and spectral parameters e transienoth f t species.The same system (wite th h monitoring light alss switchei e ) oth usef r of dfo d stud f e-beao y m induced transient light emission. 2.2.Systems studied 2.2.1. Excited states in solutions of coumarin dyes 7-Amino coumarin dyes (Schemwele ar l ) know1 e n s lasea r dyes.Fo n efficiena compounra e b o t dt laser dye the probability of intersystem crossing from the singlet to the triplet state should be as low as possible,s oe unde thady re t th higlos f ho s intensity pumping light through chemical reactions of long lived triplets is minimised.For this reason triplets of these dyes canno e populateb t d with significant yield y photoexcitation.Neverthelesb s i importan t i s o t t hav a gooe d knowledg e photophysicath f o e l properties of these compounds to be able to choose proper con- centrations and additives in the dye solutions so as to minimis e triple th e losa dy e vi st path, however small.We have therefore explore e feasibilitth d f o y studyin e tripletth g f theso s e compound y pulsb s e radiolysis. Radiolysi f benzeno s e produces triplet benzene with G-valu2 [7] 4. s triple. A f o e t energf o y benzen k cal s hig2 i es (8 hmol" e triplet1)th f mano s y solutee generateb n ca s y energb d y transfer from benzene. By this route, we were able to produce the triplets of all the coumarin dyes enumerated in Scheme 1. The authenticity of these triplets was confirmed by energy transfer from other known triplets which in turn were generated from benzene triplets by energy transfer [8]. Their energies were estimated by energy transfer from other donor triplet f knowo s n energd an y energy transfe o acceptort r f knowo s n triplet level. o significanTw t findings froe th m ) thi(a s: wore ar k T-T absorption spectra of these dyes are broad and overlap the flourescence spectrumyhence if not scavenged,even a low concentration of triplets can significantly affect laser performance;(b e triple)th t energie 50-6( s 0k cal l "-1-smo )are much higher than tha singlef o t t 0 henc; 2 e molecular(triplet) oxygen should be a good scavenger for the dye triplets.

C1 : R = CH3 C102: R = CH3

C1F =CFR : 3 3 C153CF = R :

SCHEM . E1 7-AMIN O COUMARIN DYES

173 Intense emission signals were also observed in solution f theso s e dyen varioui s s solvents under pulsed e-beam irradiation. The emission spectra, in all cases were identical to the photon excited fluorescence spectra in the respective solvents.From a detailed study of one of the dyes , viz. C 153, in cyclohexane s concludewa t i , d e emissiothath t n originates from the first singlet excited state of the e whic dy s producei h y energb d y transfer froe th m excited solvent molecules, greater part of which arise from excitation by Cerenkov light produced by the electron beam passing through the medium [9], 2.2.2.Redox reactions of thiazine dyes in aqueous solutions Thiazine dyes have the phenothiazine ring as the common structural unit.Som phenothiazinee th f o e s are important as drugs,while others such as thionine have been studied extensively in the past for their potentia n photogalvanii e us l e cdirec th cell r tfo s conversion of light to electrical energy. As redox reactions of these compounds are thought to play a key role in both these areas we have studied the one electron reduction and oxidation of thionine,méthylène blud toluidinean e ; blu n aqueoui e s solutioe th y b n pulse radiolysis technique [6,10-12], All the three compuonds undergo ease electroon y n reductio y e~b n acf and other reducing radicals.The transient absorption spectra of the semireduced dye species(D~)exhibited absorption bands red shifted with respect to those of the parent dye(D).Oxidizing radicals suc s Cl?a h , " T1(II), Br2~ and ^ were found to bring about one electron oxidation of these compounds to give semi- oxidize e speciedy d s (D+) with absorption maxima blue shifte s comparemolecules.The a d dy e o thosth t d f o e e standard potentials for the D/D~ and D+/D couples were estimate e respectivelb o t d 3 Volt 1. + 0.0 s d v ~ sy 5an NHE. OH radicals also react with these compounds to give a mixture of species , one of which is , in acid solutions , the semioxidized species.

3.GAMMA RADIOLYSIS 3.1.Charge migratio d reactioan n n frozei n n matrices 3.1.1.Aqueous matrices Our detailed investigations e reac[13th ]n -o tions of trapped electrons and 0" radical ions in V- irradiated frozen alkali hydroxide matriceK 7 7 t a s revealed that radiation produced mobile electrons can react with dissolve o beforO d e being stably trapped. The product of this reaction, Q*^ is also formed when the trapped electron made ar s e mobil y warminb e o t g 160 K or by light excitation in their absorption band (photobleaching) followe y reactiob d n with 0?.This species was identifiable by its charecteristic ESR spectrum and its yield was found to be directly

174 proportiona concentratioe th o t l f dissolveo n d oxygen e matrixith n . Further annealin e matrith t f a o x g various higher temperature s founwa s o leat do t d interestin gR spectra.Thu ES change e K th 8 n 17 i s t a s an entirelR patterES w ne ny distinctly different from that of 02~ was observed which on annealing at higher temperatures gradually got retransformed to the original pattern of the 02~ species/the retransforma- f o e tious e n th bein y B g. fasK d complet 5 an t 24 t a e selective scavengers for mobile electrons (precursors holed an shows s) wa ~ (precursor nt ot e fi ) 0" f o s that both these species are essential for the forma- tion of the species observed at 178 K. This , coupled with the interconvertibility of this species and 02~ o infet lea s u rd thae forme a th loost s i re complef o x 02~ and 0~ such as 02~ .... 0~ . 3.1.2.Alcohol matrices The reactivity of trapped electrons produced y b /-irradiatio K toward 7 7 t sa n various solutes wa s studied as a function of trap depth by employing glassy matrices consistin f mixtureo g f methanoo s d an l isopropanol.In such mixtures the ratio of the two com- ponents can be varied over a wide range ( 90:10 to 10:9, thereb) 0 y changin e trappine naturth th g f o e g sites substantially [14,15] e percentagth s .A f o e isopropanol in the glass increases, the absorption max- imum of e^r~ was found to be red shifted ( 518 to 585 nm) showing that the trap depth decreases. The various solutes studied were acetone,uranyl nitrate,carbon disulphid d benzyan e l chloridA . e solut n lowe e yielca th r f Q^ y o reactindb r~ g with electron either befor r o eafte r trapping e molaTh . r concentratio f scavengeo n r require o reduct d e th e yiel value f e o th dtro hal t ~ef o fobtaine e th n i d absence of any scavenger ( S-[/2 ) , was determined for various solutes. It was observed that for the effi- cient scavenger {e.g. U02(NC>3)2 },the Si /2 value does t changno e significantly ovee entirth r e rangf o e glass composition. However , for the less efficient scavenger (e.g.acetone) , the S-, /? value decreases as the concentration of isopropanol increases indicating that less efficient scavenger becomes more efficient as the trap depth decreases.These results support Miller's mode f o lelectro n tunnellin n i glassg y matrices [16]. 3.1.3.Hydrocarbon matrices Reactions of radiation produced mobile electron d holean s s wit a varieth f soluteo y s have also been investigated in glassy hydrocarbon matrices. •V-i r radiated CH2I2 in 3-methyl pentane glasses [17] showed absorption maxima at 385 and 570 nm ;the inten- e absorptiositieth f o s n increased with increasing concentratiopeam n k5 disap38 solute e th Th -f . eo n peare presencn i d f catioo e n scavengers suc s MTHa h F

175 while the 575 nm peak was reduced in intensity by typical electron scavengers such as biphenyl.The 385 nm peak was therefore assigned to the solute cation solute th peam n o et k0 57 radica e anth d CH( l 2) I produced by dissociative electron capture by the + solute.Whereas the CH2I2 yield was found to increase linearly with CH2I2 concentration,that of I2 (measured after thawing the irradiated matrix ) increased much more rapidly.Similarly addition of benzene did not + affect the CH2I2 yield but lowered that of I2 , the

effect being more pronounce highet a d r CHI concen- 2

tratio Thes. n e results were interprete suggestins a d2 g the existance of CH2I2 in clusters in the 3-MP matrix at 77 K.In support, of this interpretation it was found that in the radiolysis of CH2I2 in 3-MP in the liquid matrix at 300 K where aggregation is not expected to occur , the I2 yield was linear with solute concen- ration. Anion radical formation and its conversion to ketyl radica y protonatiob l n were studied with both protiated and flourinated organic solutes in 2-MTHF and 3-MP glasses 118].The irradiated matrices showed optical absorption maxima in the visible and in a few caseV regioU e s th alsn n attributabli o e anioth no t e radical.Acetylacetone showed modified spectral fea- tures on warming the irradiated matrix for a few seconds and recooling to 77 K,the change being attri- butable to the protonation of the anion radical to give the ketyl radical.Spectra attributable to presol- vated anions (solvent dipoles randomly oriented) were observe e cas th f benzophenon o en i d d perfluoroan e - benzophenon resulte Fro. e th m thermostimulatef o s d current measurement irradiate- y~ n i s d 3-MP glasses containing C^Fg as solute,electron attachment to this solut nondissociative b shows wa eo t n e [19 Als. ] o perfluoro 2-butyl tetrahydrofuran glas s founswa o t d be a very useful matrix for the stabilization of solute cations.

3.2.Studie n vitamino s s 3.2.1.Radiation protection studies in aqueous solution The vitamins of the B-complex group are water soluble organic compounds with complex organic structure,but most of them contain heteroaromatic nuclei , such as pyridine ( in nicotinamide and pyridoxin ) , pyrimidine ( in thiamin,folic acid and riboflavin) , thiazole ( in thiamin ) , pyrazine ( in riboflavin and folic acid ) , benzene ( in riboflavin) and porphyrin ( in cyanocobalamin ).Although they also contain side chains and groups of varying complexity attached to these nuclei,the known reactivity of the above mentioned heteroaromatic compounds,coupled with the activating influenc e sidth e f eo chain s would make e expecon t these molecule e b highl o t sy reactive toward primare th s y radiolytic species from water.

176 Therefore these compound e expecteb n ca so underg t d o extensive degradion when irradiate n aqueoui d s media. It was found that even at a dose of 50 krads there is considerable destruction of these compounds when irra- r diatesaturateai n i d d 10~ l dm"-4mo 3 aqueous solutions.Under this condition/of course the destruc- tion is largely due to reaction with OH radicals as the eaq~ and H atoms are scavenged by O2.ln order to show conclusively tha H radicalO t wels a ss e a laqd ~an H atoms contribut e radiolytith o t e c degradatioo tw n set f solutiono s s were irradiate compared an d) (i : d N20 saturated solution where the eaq~ are quantita- tively scavenge y N^b o dgivt O H radicalO e d hencan s e e effecth s expectei t e almosb o t dt exclusivelo t e du y OH radicals { as G(OH)=Gea(.j~ + GQH } and (u) argon saturated solution containing 0.1 mol dm t-butanol as a selective scavenger for OH radicals . Under the latter condition_the effect is entirely due to the reactions of eaq~ and H as the ^-hydroxyl radical e reactioformeth H wit O y b df h o n t-butano s unreaci l - tive towards the vitamin molecules.In both cases there was appreciable depletion of the vitamin molecules in- dicating the importance of eaq~ , H and OH in the radiolytic degradation of these molecules.From this it is clear that inorde o protect r e vitamith t n molecules from radiolytic degradatio n aqueoui n s solutione on s must use scavengers for both OH radicals and e_q~. We have explored the feasibility of using glucose/N20 and glucose/0 s suc2a h scavengers.Here glucose serves a s the H atom and OH radical scavenger,the product radi- l beinca g unreactive towrd e vitamins.Nth s n O d 20an serv electros a e n scavenger e productTh . s f o radios - lysi f glucose,notablo s y gluconi d glucuronian c c acids and dihydroxy acetone have been shown [20] to be non- toxi o mammals.Frot c e absorptioth m n spectre th f o a different vitamin solutions irradiate w doselo n o i st d presenc glucosf o e 0 2 glucosr con0d N o 2d an e an -e clusive evidence protectioth r e fo vitamieth f o n n molecules was obtained.In order to find out the use- fulnes f thio s s procedur e w have e further studied these systems up to the normal sterilization dose of 2.5 Mrads[21].It was found that in all cases,although the above additives inhibit the decomposition of the vitamin as compared to solutions containing no glucose there is no complete protection particularly at high doses.Thi e limiteth s largelo i st d e solubilitdu y f o y these gaseous additives and hence their depletion with increasing dose.More detailed investigations revealed that a real competetion is involved between 02 and the vitamin molecule for eaq~ and between the vitamin and glucose for OH radicals and H atoms. 3.2.2.Reactions of vitamin radical intermediates with hydrogen peroxide A systematic investigation [22 f solution]o s irradiated under conditions such that the initial reaction is exclusively with either eaq~ ( argon saturated solution with t-butanol as OH scavenger) or

177 OH (®2° saturated solutions) both in the absence and presenc f initiallo e y added H202 reveale e importh d - tance of radical - H2C>2 reactions.Thus the radical in- termediates produce y b ed aq~ reaction e witth h vitamins were foun o reactt d : efficientl e casth en i y of thiami d nicotinamide,lesan n e casth f o en i o s folic acid and not at all in the case of pyridoxin.In the cas f riboflavio e e electroon e th n n reduction produc e full th s wela tys a lreduce d form were found to react with H202.Similarly the data on G (-vit.) and G (H 0 ^ -*-n N2° saturate<3 solutions with and without added2 H202 revealed thae vitamith t n radicals formed

by the reactio2 n of OH with these molecules are reac- tive toward se cas Hf th pyridoxin,folio 2 e0n 2i c acid, cyanocobalamin and thiamin but not so in the case of riboflavi d nicotinamide.Ratan n e constant valuer fo s some of these radical-H20 reactions have been deter-

mined and reported [23], 2 3.3.Polymerization Extensive work has been carried out on the radiation induced polymerization of acrylates and methacrylates [24,25] . The number average molecular weights were found to be much lower than the molecular weights expecte e basith f kinetio sn o d c chain length. This strongly suggests chain transfer from the growing polymer radical to the monomer leaving behind terminal unsaturation whic s confirmewa h R spectre I th y b df o a polymers obtained.Wheneve a growinr g polymer radical meets a polymer molecule with terminal unsaturation ,a branched growing polymer radical results leading to rapid propagatio e polymerizatioth f o n n process- Be . cause of such branched polymer structure the polyacry- lates and methacrylates are more amorphous in chare- cter.In our view it is this chain transfer to the monomer followe y branchinb d s observea g d above that is responsibl e autth or acceleratiofo e n experimen- tally observed rather thae viscositth n y effect hitherto postulated.Also the polymers obtained in the initial stages of polymerization from thoroughly purified monomers exhibited bimodal distribution of molecular weights.The molecular weights of the polymer were found to be lowered to a much larger extent in presence of compounds such as benzoquinone which acts s bota h free radica d electroan l n scavenge s coma r - pare o biphenyt d l n aniowhica s i hn scavenger.Hence contribution of both anionic and free radical mechanism e radiatios inferre th e casswa th f eo n i dn induced polymerizatio f acrylateo n d methacrylatesan s . 4.APPLICATIONS

4.1.Radiation effect n lubricanto s s e extremth f Radiatioo e e environmenton s i n s encountered in nuclear technology . Lubricants and hydrolic fluids exposed to radiation are known to un- dergo radiolysis and produce degradation products or

178 polymers which can drastically affect their physical and chemical propertie d alsan so impair their performance. An evaluatory cum development programme was un- dertaken wit a vieh o indiginisatiot w f lubricanto n s and oils for the nuclear power plants [26,27] . In a number of oils irradiated to doses upto 109 rads the molecular weights were found to increase up to 67 % kinematie anth d c viscosities upte th o n 100O . 0 % e resultbasith f o f sradiatioo s n exposuren i d an s situ tests withi e poweth n r reacto s wela s a rl outside n indiginoua , s blen e fuellf greasth o d r -fo e ing machine head of our PHWR was developed ;this blend e morb s founwa eo t d radiation resistant thae th n imported e brandearlierus n i s .

4.2.Biomaterials from radiatiqn_crosslinked PVA A numbe f usefuo r l application f so V-radiatio n crosslinked polyvinyl alcohol (PVA hav) e been deve- r laboratorlopeou n i d 28,2[ y 9 ].An inexpensivd an e fas te detectiomethoth r fo d f bilirubio n n urini n e was developed by encapsulating a detecting agent in the crosslinked PVA.Th l allowge ee selectivth s e dif- fusion of bilirubin and keeps other pigments out,thus providing a simple method for the diagnosis of infec- tive hepatitis. The same material has also been found e usefuimmobilizatioth r fo l f o nenzyme s sucs a h ureas d glucosan e e oxidas d offeran e a nontoxis c alternative to polyacrylamide gel immobilized systems. Similarly adsorbants suc s activatea h d charcoal encap- sulated in the radiation crosslinked PVA gel have been found to be useful as oral sorbates and hemo perfusion e removadeviceth r f toxinfo o l s s from human systems. Yet another application is for the encapsulation of the bacterium Bacillus Sphaericus effective for the killin f mosquito g o larva n stagnani e t waterd an s hence useful n controllini l g malaria.

4.3.Radiolytic reductio f metao n l ion n aqueoui s s soluticm 4.3.1.Productio f metalo n n fini s e powder form Iradiation of aqueous solutions of divalent metals suc Cus a h 2Co, + 24" ,Ni Cdd 2an 2++ containing formate ions to convert OH radicals to the reducing C02 species was found to form a precipitate of the respective metal precipitat[30e Th . ] e consistef o d fine particles of the metal and was very reactive towards oxygen.By using hypophosphite ion as the OH scavenger,an autocatalytic reduction coul e broughb d t abou d thuan t s mor e% conversio tha0 9 e n th f o n divalent ion to the metal form was achieved with V- doses of -1 krad.The metal powder obtained in this case had a narrow particle size distribution,contained -2% phosphorus and was stable towards oxygen.

179 4.3.2.Separation of Eu from rare earth mixtures In acidic ( ^SO/^ ) solutions containing iso- propanol and Eu-Sm/Pr mixture, the Eu3+ ion was found to be selectively reducible by the isopropanol radi- cals to give a precipitate of EuSO^ , the other rare earths being unaffected [31] . This provides an easy metho f separatioo d u froE mf o nsuc h mixtures.

4• 4. "f- irradiation effect on the catalytic activity of oxides Irradiation of metal oxides with ionizing radiation n lea productioo ca st d f atomio n s wela cs a l electronic point defects.The atomic point defects such as interstitial vacancie, s d dislocationan s e ar s produced more effectively by energetic heavy particles such as neutrons, <<-particles and protons, ft- and •/"- rays produce mainly electronic defects sucs a h electrons and holes.Ionizing radiations can also lead e productioth o t f differeno n t oxidation e stateth f so metal e cas th f transitioiono en i s n metal oxides.The introductio f theso n w entitiene e y irradiatiosb y ma n n increasa lea o t d r decreaseo e concentratioth n i e n of pre-existing catalytic centre r introduco s w ne e one n thesi s e compounds.One would therefore expeco t t find changee catalytith n i s c propertie f theso s e com- pounds as a result of irradiation.In our work [32] on e V effecjü th Me -particl 0 4 t e irradiatio- ac e th n o n tivit f /?-Mn0o y r H20fo 22 decompositio observee w n d that the catalytic activity increased with increasing dose and reached a plateau when low beam currents ( < 0.8/*A) were employed.At high beam currents (> 2 /£ A) e catalytith c activity reache maximua d m with increas- ing oL- dose and then decreased.The catalytic centres appear to be Mn , both existing prior to irradiation as welproduces a l y b irradiatiod Experimenta. n l results indicated the latter to be of two types , one easily annealabl d hencan e e inferre e produceb o t d y b d reactio f radiatioo n n produced mobile electrons with Mn4 + e othe(MnOoth rd an )requirin g higher temperature for annealing and hence inferred to be produced by displacement collision e

5.Future programmes In our future programmes in radiation chemistry there will be greater emphasis on the study of systems f radiobiologicao d biomédicaan l l importanc d alsan e o those that are of relevance to conversion of light to chemical energy and viceversa . We also plan to initiate studies on the transient and permanent radia- tion effects on solid state electronic devices and on radiation chemistry at high temperatures and pressures relevant to our PHW power reactor programmes.

180 ACKNOWLEDGEMENTS

verm a yI gratefu Dr.R.M.Iyeo t l Directo, r , r Chemical Dr.J.P.Mittad Grouan , p Hea, l Chemistr, d y Divisio BAR, nr thei fo C r encouragemen d supporan t , t numbea ano t df colleague o r t Trombaa s o werwh y e helpfue preparatioth n i l f thio n s pape y conb r - tributing material from their respective areas of research interest and offering useful suggestions.

REFERENCES [1] Narayana Rao K. et al , Studies on the pyrolytic and radiolytic stabilities of organic coolants , Rep. AEET/CD/20, Bhabha Atomic Res.Centre , Bombay (1963) [2] Rao K.N. et al , A study of wood plastic combinations , Rep. BARC-331 , Bhabha Atomic Res.Centre , Bombay (1968) Woo, l K.Mdo a Ra plastit e . ] [3 c combinations Part . AcryliII c ester d theian s r copolymer Rep, s . BARC-369 , Bhabha Atomic Res.Centre, Bombay (1968) [4] Rao K.N. and Moorthy P.N., Radiation induced sulphochlorination of hydrocarbons ,Rep. BARC- 420 , Bhabha Atomic Res.Centre/Bombay (1969) [5] Rao K.N. ,Rao M.H. ,Moorthy P.N. and Charlesby . ,RadiatioA n induced graftin f acrylio g d an c methacrylic polyesteo acidt n o s r (terylen) e fibres., Polyme. J r Sei.(Polymer Letters Ed.) 10 (19723 )89 [6] Guha S.N. ,Moorthy P.N. ,Kishore K. ,Naik D.B and Rao K.N. ,0ne electron reduction of thionine studied by pulse radiolysis. Proc . Indian Acad . Sci.( Chem . Sei. ) 99 (1987) 261 [7] Baxendale, J.H. and Fiti/M., Yield of triplet state of benzene in the pulse radiolysis of some aromatics. J.Chem.Soc. Faraday II 68 (1972) 218 ] Priyadarsini[8 , K.I .Naik, , D.B Moorthd .an y P.N., Triplet state of C 153 studied by nano- second pulse radiolysis. J.Photochem. and Photobiol. Part I Chemistry , In print (1988) ] [9 Priyadarsini, K.I. Naik, , D.B Moorthd .an y P.N., Pulse radiolysis studies on the formation of singlet excited states of coumarin 153 in cyclohexane solution. Radiât.Phys.Chem.In print (1988)

181 [10] Kishore, K ., Guha, S.N. and Moorthy, P.N.,Pulse radiolysis study of one electron oxidation of thionin aqueoun i e s solutions. Proc.Indian Acad. Sci.( Chem.Sci.) 99 (1987) 351 [11] Kishore, K., Guha, S.N., Mahadevan, J. and Mittal, J.P.,Redox reactions of methyleneblue : A pulse radiolysis study. Radiât.Phys.Chem.In print (1988) [12] Mahadevan, J., Guha, S.N. and Moorthy, P.M.,One electron reductio f toluidino n e blupulsA : e e radiolysis study. Proc.Indian Acad.Sei. ( Chem.Sci.) In print (1988) [13] Moorthy, P.N., Rao, K.M., Mishra, K.Pd .an Singh, B.B., Radiation effects in oxygenated frozen aqueous alkali hydroxide systems. Rdiat.Effects 22 (1972) 243 [14] Kapoor, S., Gopinathan, C. and lyer, R.M. Electron scavengin methanol-isopropanon i g l glasses at 77 K in presence of benzyl chloride DAE Symp. Radiochem. and Radiation Chem. Tirupati (1986) [15] Kapoor , GopinathanS. , d lyeran ,. , C R.M e .Th trapping and reactivity of electrons in methanol-isopropano. l K glasse 7 7 t a s J.Radioanal d Nuclan , . Chem prinn I . t (1988) [16] Miller, J.R. Scavenging kinetics of electrons produced by irradiation of organic glasses; experimental evidenc r lonfo eg range tunnelling. J.Chem.Phys. 56 (1972) 5173 [17] Mohan, Hari, Rao, K.N d lyeran . , R.M., Identity of intermediates formed on photolysisis of C^^ and CHIo in 3-methyl pentane at 77 K . Radiât.Phys.Chem 3 (19842 . 5 )50 [18] Shoute, L.C. Mittald Tan , J.P., Matrix isolation studies of transients produced in the gamma radiolysis of decafluorobenzophenone.Spectral relaxation of anion radicals and ketyl radical formation. Radiât.Phys.Chem. 24 (1984) 209 [19] Shoute, Lian C.T d Mittal.an i P.,AbsorptioJa , n and conductivity studiee transientth n o s s gen- erated in the gamma radiolysis of perflouroben- zen n rigii e d matrices. Radiât.Phys.Chem. 30 (19875 )10 [20] Schubert, J.Proc.V Intern.Congress Radiât.Res. Seattle (1974) Paper E-17-4 p.271 [21] Kishore , Moorthy,K. , P.N d Raoan . , K.N., Radiation protection of vitamins in aqueous sys- tems Part I,I d III.,Radiât.EffectIan s 27 (1976) 167, 29 (1976) 165, 37 (1978) 98

182 [22] Kishore Moorthy, ,K. , P.N d Raoan ., K.N.,Rolf eo ^2Q2 ^-n tiie ^adiolysi f vitamino s n neutrai s l aqueous solutions Parts I and II ,Radiat.Effects Letters 67 (1982) 153, 161 [23] Kishore, K., Moorthy P.N. and Rao,K.N.Reactivity of ^2(->2 with radiation produced free radical: s Steady state method for estimating the rate constants. Radiât.Phys.Chem. 29 (1987) 309 [24] Raghunath , Rao,S. , M.H Raod an ., K.N., Radia- tion initiated polymerization of phenyl metha- acrylate. Radiât.Phys.Chem.22 (1983) 1011 [25] Kumar, M., Rao, M.H. and Rao, K.N., Radiation polymerization of cyclohexyl methacrylate I and . Radiât.Phys.ChemII 0 7 (19873 2 . , )21 [26] Thomas, V.G., Srivastava, S.B. and Karkhanavala, M.D. ,Effec f Co-6o t 0 radiatio n certaio n n physical propertie f somo s e lubricantd an s oils. Indian J.Technolog 6 (19871 y 6 )32 [27] Srivastava e indiginisatioTh , , l S.Ba t e . f o n Lubriplate 630- d developmenan 2 f Servo t o nucleas M assembl2 greasF/ - W e PH r fo f eo y power reactor. Rep. BARC-1087, Bhabha Atomic Res.Centre, Bombay (1980) [28] Amonkar, S.V., Vijayalakshmi , Rao,N. , A.Sd an . Gopinathan . SustaineC , d release formulatiof o n Bacillus Sphaericusd.S Species -5-WHO-2173r )fo control of cutex fatigous larvae. Current Sei. 57 (19880 )53 [29] Gopinathan A metho . ,C f makin o d a chemicallg y three dimensionally crosslinked polyvinyl alcohol P 15379I . 7 (1984) [30] Shastri L.V. Reaction COOf o s " radica witn io lh M+ and M states produced in the radiolysis of aqueous solutions. Radiât.Effect 7 (1971s 3 )28 [31] Shastri, L.V., Mittal, L.J Mittald an . , J.P., Radiation chemical separatio f europiuo n m from aqueous lanthanide mixtures. Radiât.Phys.Chem. 29 (1986) 359 [32] Kishore d Moorthyan . ,K , P.N.,Radiation effects on the catalytic activity of ß- MnO? . Radiât. Effects 105 (1988) 257

Next page(s) left blank 183 RADIATION CHEMISTR CHINYN I A

Jüan WU, Guanghui WANG Departmen Technicaf o t l Physics, Beijing University, Beijing, China

Abstract

Radiation chemistry in China has a short but remarkable historys evolvedha t I ., first, froe interesth m r chemistrfo t y e technologrelateth o t df nucleao y r reactor d radiatioan s n effects on polymers or induced polymerization. Several universitie Chinn i s a introduced radiation chemistry into academic curriculum, undergraduat graduatd ean e level earln ,i y 1960s. At present ther 10-1e ear 5 centre Chinn i s a actively involved in fundamental and applied research in radiation chemistry, at universities, nationa locad lan l institutions. The research programmes cover a broad range of topics from primary processes in radiation chemistry to various applications in industry, biology and medicine. f 198Ao se Journa3th f Radiatioo l n Researc d Radiatioan h n Processing is regularly published.

1. HISTORY IN BRIEF The branch of radiation chemistry in China was first founded in about 1957 .t beginninA g s developewa stage o t tw i ,n i d directions: the first was radiation chemistry which related to the technology of nuclear reactor and after treatment of nuclear fuels; the secon s polymewa d r radiation chemistry whic s focusehwa n o d e fronth t lin f o researce t a thah t time suc s studieha f o s radiation initiated polymerization in solid state, ring opening polymerizatio f o triformaln , explosive polymerizatiof o n acetaldehyde and thermal oxidation of irradiated polyethylene. e achievementTh n thai s t period were presente firse th tt a d radiation chemistry meeting of China held in Changchun, Nov.20-31, 1963. Since 1978s furthewa ,t i r develope w fieldne d san d were seen in radiation chemistry in China. Systematic, fundamental studies e werfiel th f eo energ dn i carrie yt ou transferd , radiation chemistr f o organiy c compound d theoran sf o y crosslinking and more attention was paid to radiation processing. On July 3-7, 1981, Radiation Research and Radiation Processing Societ s foundeywa Shanghan i d d organizeian firse th d t meeting of radiation research and radiation processing. In Oct. 1983, Journal of Radiation Research and Radiation Processing started publicatio Chinesn i n d Journaean f Isotopeo l s in June 1986. At now a stronger researcher team is involved in the most fields of radiation chemistry.

185 . 2 EDUCATION It was in 1960 that we started to foster scientists specilized in radiation chemistry in Beijing University. The programme include: training courses and training undergraduate d graduatan e students presentt .A , several universities including Beijing University, Universit Sciencf o y Technologd ean Chinaf yo , University of Science and Technology of Shanghai and Beijing Normal University have ability to offer B.S. and M.S. degrees in the field of radiation chemistry. Also there are Ph.D. programmes in this area in Beijing University and University of Science and Technology of China. In addition all above-mentioned Universities have carrie t scientifiou d c research work n radiatioi s n chemistry.

3. INSTITUTE , RADIATION CENTRE AND FACILITIES With respec f o radiatiot n facilities, more n thate n radiation centre d institutean s s have thei n Co-6ow r 0 gammy ra a sources with a capacity over 3.7 x 10 15 Bq (105 curie)- There are 4 no less than 46 Co-60 sources with capacity over 10 curi n i Chinae . Among these centre d institutesan s som f theeo m possess a researcher team in radiation chemistry such as Institute of Atomic Energ t Beijinga y ; Shanghai Institut f o Nucleae r Researc , Academih a Sinica; Changchun Institut f o Appliee d Chemistry, Academia Sinica; Shanghai Research Institutf o e Chemical Industry; Institute of Physics of Xinjing, Academia S\nica; Institut f Biophysicso e , Academia Sinica; Chenguang- institut f o chemicae l i LongjianIndustrHe d an gy Institutf eo Technical Physics. The pulse radiolysis machine is not well equipted in China but a 10 sec. pulse radiolysis machine is under adjusting operatio n i Institut nw Energ Lo f yo e Nuclear Physic Beijinf so g Normal Universit a 10~ d undes *i an secye r on .constructio n ni Shanghai Institute of Nuclear Research.

. 4 ACHIEVEMENT 4.1. Fundamental Studies 4.1.1.Studie f o radiatios n energy transfe d mechanisan r f o m radiation protection (a) By concerning the primary radiation processes of DNA and radiation modifiers a fast radiation protection mechanism - charge transfer protection has been explored. Studies of some binary molecular mixtures such as thymine-cysteine, thymine-histidine, dTMP-hydroxycinnamic acid derivatives, DNA-caffeie acid etc. showed that the charge transfer protector is a substance with higher EA but lower IP than the target molecule, and the charge transfer sensitize a substanc s i r e higheP witI hd rbotan thaA hE n the target molecule. Furthermore, H transfer repair mechanism also bees ha n discussed. (b) A new idea of application of scavengers was developed in e whicmultiplth h e effect f o chemicas l scavengers were successfully used to investigate radiolysis of cyclohexane. By usine exciteth g t onlno d y e singlew hav t P ego TB td proban P eMP the yields of excited singlets of Benzene ( 1.4±0.2 ), cyclohexane geminat e yielde th th 1.4±0. f ( sd o ( e P 1.5±Q. an ionTB ) 3, s) 2

186 of cyclohexane (3.8 alst )bu o utilize multiple th d e effectP MP f so and TBP successfully in the research of different transfer processe n radiolysii s cyclohexanef o s . chemicaa s uses wa a d WheP lTB nprob studyinn ei g energy transfer kinetics t performei , accepton a s a d becaus. rs it f eo very small molar extinction coefficient the Förster type energy transfer process can be avoided. The rate constants of the energy transfer for TBP- binary systems were determined and it was found that energy transfer proces controlles i s y diffusivb d e e reactinmotioth f o ng species. Morever unusualle th , y high rates of energy transfer from excited alkanes to solute, which had been reporte y b somd e groups elucidatede b n ,ca . Furthermors wa P TB e used as a probe for detecting the excited states of cyclohexane and more reliabl G evalu f o cyclohexane e were obtainen I . d a additioprobe b usedetectinr s a t ealsfo di n ca no e th g geminate ion pairs of alkane. (c) The probability of positronium formation in molecular substance s investigatewa s d e froviewpointh m f o radiatiot n chemistry. That is effect of radiation protection on the probability of positronium formation. A new conception so called "radiation protective function proposes wa correlativa ) d "(F dan e equation with e botprobabilitth h f Ps-formatioo y d an ) I ( n \> radiation protective functio s derive" wa idean n i ld binary systems" accordincompetitive th o t g e reaction mechanise th n i m spur. It was found that systems containing positive hole scavenger pyrrolidine possesses a larger radiation protection ability comparing with dioxan d trimethylaminan e n-heptano t e d thaean t for anion aqueous solutions the order of radiation protection of the anions to watei is r>SCN~>S2~>Er~>Cl~>F~ .

4.1.2. Radiolysis of organic compounds fiele th Ind dealing with dependenc f radiatioeo n stability e moleculath n o r structuie, radiation chemistr f organophoso y - phorus compounds has been investigated in detail. It was found P bondC- dialkythan e si th t l alkylphosphonate wels sa dialkys la l arylphosphonate e weaar sk bond d theisan r radiation stabilities are less than that of C-C bonds in the ester alkyl chains. The bond scission of C-C bonds of ester alkyl group is by no means completely random durin e irradiatioth g CW.-e d CU-Cth an H d ^an n bond more sar e readily broke nC bonds thaC- d n. an othe H C- r Other studie f o radiolysis organif o s c compounds donn ei China include: radiolysis of important organic solvents such as CCI and ethanol in which new results have been obtained, 4 radiolysi f o organis c aqueous solutio whicn i n h attentions were attacH O e glycosidef th kpaio o t d .

4.1.3. Chemical Evolution Being contrary with traditional f o conclusion y wa w ne ,a chemical evolutio s advancedwa n : undee primitivth r a se e condition H 8.0-8.5(p ssalts wateit n i s,r o r 50-100°N HC ) C bodies coul o g bacdo atmospher t ke morb ed effectivelan e y converted into biological organic molecules under the action of electric discharge than in liquid by the action of ionizing radiation. It may be an important pathway which converts HCN into biomolecules on the primordial earth.

187 4.2. Radiation Chemistr Polymerif o y c Systems Most of investigations in the area have been proceeded in the polymer chemistry. e influencTh ) f moleculao e(a r configuratio degradation o n n e procesdegreth f n o i radiatiose n crosslinking reactions swa studied e rigiTh . d chain polymer with higher glass transition (hindrancf temperaturf d an eg T efacto f internao r l rotatio) n value and the polymer containing some structure unit of radiation degradation type obey Charlesby-Pinner relationshi branched an p d polymer and flexible chain polymer with lower Tg and tf value obey Chen-Liu-Tang relationship consideration I . deviatioe th f o n f no experimental results from Charlesby-Pinner's and Chen-Liu-Tangs expressions relating sol. fraction to radiation dose, an exponent ß concerned with the structure and property parameters of a introduces wa fd ) an assumed polyme an dg (T dr thafracture th t e density is proportional to R (R is radiation dose). Thus, a general formula relating sol. fraction to radiation dose was derived. When 6=0.1 arid 0.5 this expression is reduced to Charlesby's equation and Chen's equation respectively. broaa s i dt I fiel f radiatioo d ) (b n crosslinking that thers i e in China. Some works about enhanced radiation crosslinkinf go polymer have been done theoretically. According to the two models of enhanced crosslinkin usiny b methoe d th g an probabilitf go d y the theoretical relationships between crosslinked structure parameters and sol. fractions of crosslinked polymers were derived. In practice, enhanced radiation crosslinking of polymer (effec f polyfunctionao t l monomer n radiatioo s n crosslinkinf go LDPE) and heat shrinking behaviour of gamma radiation crosslinked polyethylene have been systematically studied. f worko t slo havA e been performe detain i d n crosslinkino l g of siloxane copolymer, fluoropolymer, polysulfone and polyamide, a multiple-phase syste polydimethylvinylsiloxanr fo m d copolymeean r of ethylene-vinyl acetate which was crosslinked by means of radiatio s gooha n d heat-shrinkage properties preparation I . f no e th system PDMVS a sensitize acte s radiatioa th s f o r n crosslinking of EVA. The studies of radiation-induced crosslinking of siloxane copolymers with various contents of vinyl group is another progress. The existance of vinyl groups in the copolymer macromolecules could reduc gelatioe th e n dos hencd ean e increases the G value of crosslinking because vinyl group is very sensitive to radiation induced crosslinking. In another work the high temperature property of radiation crosslinked F-46 shows beneficial improvement s discoverewa t I . y b meand f x-rao s y photoelectron spectroscopy thadifferene th t t crosslinking bonds were formed in polysulfone irradiated at different temperature. With polyamid e crosslinkinth e f polyamido g e b 101n ca 0 characterize y b crystallizatiod n temperatur electricas it d ean l propert d an thermay l resistanc e improvear e y b radiatiod n crosslinking. Additive effect on radiation crosslinking of PVC and polypropylene has been investigated. It was found that the additio difunctionaf o n l monomer, diethylene glycol diacrylato et PVC improved its insulating and mechanical properties. (c) The important works about radiation polymerization are radiation polymerization of acrylamide and the preirradiation polymerization of vinyl monomers.

188 A pilot process of polymerization of acrylamide in concentration 30-35% by weight of aqueous solution with the additive disodium EDTbees ha An reported. Preparatio f o supen r water absorben - polyacrylamidt e hydrogel f higo s h water retentio y radiatiob n n techniqued san hydrolysi alss i s o successful. Polyacrylamide hydroge (PAM-HGII l ) which retains distilled water (350g/g) has been prepared by radiation crosslinking f o polyacrylamid 1 x 10* 8 6 9. ). w (M e Polyacrylamide hydrogel II (PAM-HGII) was made by alkaline hydrolysis of PAM-HGI to enhance its hydrophilic character. Radiation polymerizatio f acrylamido n solin i e d state also has been described and unfortunatly tl» polymers formed by radiation polymerizatio f o acrylamidn n i solie d state were insoluble due to intermolecular crosslinking. When the chain transfer agent, isoproyl alcohol addeds wa , , which effectively inhibit e crosslinkinth s o givt g e water soluble polymer% ,95 conversion and molecular weight more than 5 x 106 polyacrylamide were obtaine monomea t da r concentratio bathe ic .n i % n65 The preirradiation polymerization of vinyl monomers has been studie detailsn i d somn I . e cases some vinyl monomer radicaln sca be stored in peroxide form. When used, it can be decomposed by different methods to liberate free radical and causes polymerization immediately e wholTh . e proces e oftes b ha o snt carried out at place off source, and polymerization proceedes in more mild condition. The study on the kinetics of the radiation synthesis of poly-2-hydroxyethyl methacrylate (,PHEMA) hydrogel shows that a t first the HEMA is polymerized by radiation and then the PHEMA gel

is formed after 20% conversion . The polymerization-crosslinking of HEMA proceedes as a free radical mechanism: Voo^I'0 ^ This radiation-crosslinking process only nee suitabla d e irradiation dose sucs a lesh e sb , x n thu10tha Gy ca ^1 hig a s nl hge obtained. It has been succeeded in applying above principle for preirradiation polymerizatio manufacturo t A MM f o ne thick block PMMA and for the preirradiation copolymerization and crosslinking f o another vinyl monomer o prepart s e soft lense d releassan e polymer drugs. Plasma discharg anothes o initiati t e y wa r e polymerization. Plasma polymerized film of hexafluoropropene has been prepared and more attention will be paid to this area. (d) Radiation grafting is another branch of China's radiation chemistry. Preparation of permselective membranes of high performance by radiation graft copolymerization of hydrophobic and hydrophilic monomers on different polymeric substrates has been performed polymee th e mosf Th ro . tfilm d monomeran s s usee ar d Teflo P (F46)FE n , polyethylene (PE), styrène (St), acrylic acid (AA), methacrylic aci d ddivinylbenzen an (MAA) e (DVB)e Th . radiation induced graft copolymerization of pre-irradiated F-46 and PE film with St and DVB in vapor phase has been carried out in orde o prepart r e variou sn exchangsortio f so e membraness wa t I . found that graftin gaseoun i g s phase caused less homopolymen i r th equalite systeth d f obtaineo yan m exchangn d io F-46 e membranes might be improved. A thin permselective membrane was prepared by the radiation induced graft copolymerization of pre-irradiated PE film with MAA in toluene. The resulting membrane shows good chemical inertness and fine permselectively and thus has been used satisfactorily as cell separator material of the Zn-AgO batteries.

189 e studieTh n o radiatios n graftin f acrylio g c acid onto polypropylen e hydrophilicityth e ongoinar d ean g , gas penetrability and dying ability of grafted product were all improved. In the research of radiation induced graft copolymerization of polytetrafluroethylene-styrene-fumaric acid relation between surface structure arid adhesive property has been discovered. In the case of surface grafting, the adhesive strength was found U> be above 100 kg/ein^ . On the contrary, the adhesive strength was found to be lower than 4& kg/cm In modificatio e naturath f o ln polymer materials good filling effect can also be achieved in the radiâtion-induced graft copolymerization of n-butyl acrylate onto chrom-tanned skin, (e) Not only scientific research in polymer radiation chemistry was widely operated in China but also practical applications. Main radiation polymeric commercial products are listed as following: radiation crosslinked polyethylene shrinkage tube; radiation crosslinked silicone rubber; radiation crosslinked wir d cableean ; preirradiated PE grafting film with MAA (cell separator material of the Zn-AgO batteries); radiation polymerized acrylic amide; radiation copolymer of acrylic acid and acrylic butyrate; radiation grafting acrylic aci n PTFmodifyino r d fo E g adhesion; radiation degraded PTFE wax and radiation resistance polypropylene. 4.3. Radiation Chemistry Related to Nuclear Technology Radiolysis of various home made cation and anion (exchange) resin have been studied and the inhibition of the gamma radiolysi polystyrene th f o s e sulfonic acid resi y somb n e solutes has been found. In these reactions the relative rate constants between inhibitor and excited water were calculated. Radiation chemistr f o tributyy l phosphat s beeha e n investigate n detaili d e naturTh .d structuran e f o strone g complexing compounds, long chain acid phosphate and complex compoundP containinTB f o s g nitrogen forme gammn i d a irradiated TBP-dodecane system wer s founewa studiet di thad dan t stilbens i e a very effective inhibitor for the radiolysis of TBP in the TBP- dodecane system. studiee Ith n s ralatin nucleao t g r technology some radiation resistance polymers have been got. 4.4. Dosimetry At present, many specilis e involve e radiatioar tth n i d n dosimetry e water-calorimeteTh . d ferrous-sulfatan r e dosimetee ar r e b accepteto nationas a d l standards e high-dosTh . e measurement systems of gamma-ray from cobalt-60 are being established. For the transfer dosimeter systems alanine (ESR), ceric-cerous sulfate solutio choicee th e radiochromie Th .nar e filmscdy , persped an x visual dose labels woul e recommendedb s routina d e dosimeter.

5. PROSPECT e Th radiatio ) n(a chemistry related with substancef o s biological interest wile developedb l , suc s radioprotectioha n mechanism of synthetic sinapic acid amine salt derivatives, radiolysi chiee th ff o components f Chinesso e herbal medicind ean radiolytic kinetics of transformed protein molecule.

190 ) (b Fundamental stud n radiolysiyo typicaf so l organic compounds wile proceedeb l o solvt d e such problems:(1) exact radiolysis mechanis f o typicam l organic compounds ) makin(2 . g clean o r multiscavenger effect kineti) (3 . c behavio electrof o r atoH d man n in organic medium. (c) Enhancing the studies of effects of various additives on radiation crosslinking of PE for wire, cables and shrinkage tube with different characteristies. (d) To approach the possibility to construct a pilot plant to treat the fuel gas by electron beam with international cooperation and support from UNDP. (e) Advanced Studies on radiation technology for immobilization of bioactive materials may be proposed as (1) introducing pnsirradiation polymerization method to immobilize bioactive material. (2) to inquire the reason of deactivation of enzymes with increasin f graftino g e quantitgth yield f bounan o yd d protein when we immobilize enzymes onto films through radiation grafting . (3) to study the possibility of using peroxidase in initiating polymerization in organic phase. ) (f Electron beam curin f oligomero g r magnetifo s c media coatings. ) (g Establishmen higf o th dose measurement system electrof o s n beams.

REFERENCES

[1] Journal of radiation research and radiation processing (China) radiatiot 1s ] n[2 chemistry meetin Chinn i g a (1964, Changchun) e selectioTh ] proceedingf no [3 nationat 1s f so l conferencn eo radiation research and radiation processing (1981, Shanghai) [4] The 1st, 2nd and 3rd China-Japan Bilateral Symposium on radiation chemistry (1983, Shanghai; 1985, Osaka; 1987, Changchun)

Next page(s) left blank 191 SUMMARIES INTRAMOLECULAR LONG RANGE ELECTRON TRANSFER REACTIONS IN PEPTIDES AND PROTEINS*

. FARAGGM I Departmen f Chemistryo t , Nuclear Research Centre Negev, Beer-Sheva, Israel M.H. KLAPPER Divisio f Biologicano l Chemistry, Department of Chemistry, Ohio State University, Columbus, Ohio, United State f Americso a

Until recently thoughe ,th t that electrons might migrate over long distancewithi) A 0 1 singla n > ( s e protein or between proteins within a complex was en- d dismissew an tertaineno w e fe w y most b dy t b dBu . have numerous reports, based on flash photolysis and pulse radiolysis experiments f Lon,o g Range Electron Transfer (LRET n proteini ) d othean s r organic mole- cules, and we recognize that LRET may be important in photosynthesis, respiration, and radiation induced radical damage to proteins and nucleic acids. In explanatio f theso n e long range transfers many researchers have designed experiments to test the prediction a theor f o sy associated with R.A. Marcus. This semiclassical argument postulates that upon the proper nuclear rearrangement, treated in n activatioterma f o s n energy e electroth , n tunnels from dono o acceptort r e subsequentlTh . y derived prediction e LRE e th that Tar s) i :rat e constant, k(et), decreases exponentially with increasing dis- tance between redox centers; i.e., k(et) « exp[-ßr], a dampin s wheri ß e gedistanc th constan r d e an t between centers; ii) as the potential energy diffe- rence, AG°, becomes more negative, k(et) first in- creases, reache maximua s m valu thed an en decreases; i.e."invertee th , d region" effect; iii) k(et) should vary wit geometrie hth c orientation between donod ran acceptor ) k(etiv ; s )influencei .thy b d e solvenn i t whic e electroth h n transfer occurse transfeth ) v ; r rate should become constant and finite at low tempe- ratures where nuclear motion is no longer signi- ficant.

* A more detailed review of long range electron transfe proteinn i r polypeptided san s will appear in "Excess Electron Dielectrin si c Media", eds. .C Ferradini and J.-P. Jay-Gerin, CRC Press.

195 o datT e LREs beeha T n studiet leasa 0 n 3 i td proteins, generally of known crystal structure and modified so as to establish a suitable electron donor/acceptor pair separate a presumabl y b d y known distance r examplefo , .We , have converte e singlth d e cysteine sulfhydryls of both the hemoglobin a-subunit e hemerythrianth d n subuni o mixet t d disulfides. Upon reduction of the disulfide bond with the formate radical e producth , t disulfide radical anion becomes a dono r electrofo r n transfe e iroth n o t raccepto r already in the holoprotein. As a further example, others have replaced protein heme groups with a zinc- porphyrin that upon photoactivation becomes the elec- tron donor. e basiO th nf thes o s e many studies o thern s i e doubt that LRET occur proteinn i s s over distances a s long as 30 A; whether these results are explainable in terms of Marcus theory is still unclear. There are apparent trends in that k(et) does roughly decrease as distance increases and equilibrium driving force decreases. However, when all the results obtained with different proteins studied in different labora- torie e consideredar s e correlationth , s become more labored othee th rn . O hand , results obtained froe th m cytochrome c/cytochrome bf- protein complex that con- tains various mixed metal heme centers [McLendon, G. (1988) Ace. Chem. Researc 160, 21 h] sho "inverten wa d region"e ratth e K d belo constan;an 0 17 w r elecfo t - tron transfer o metalloporphyrinbetweetw e th n f o s the [Zn,Fe(III)] hybrid hemoglobin becomes tempera- ture independent [Peterson-Kennedy . (1984al t . )e J , Am. Chem. Soc. 106, 5010]. However, researchers have still not isolated potential complications due to the relative donor/acceptor geometries and to the influ- ence of the environment around the redox pair. Moreover, additional questions have arisen. Does electron transfer occur "through space" ovee th r shortest straight line throug proteie hth n matrixr ,o does it occur via a best path composed of covalent and/or hydrogen bonds? Do protein structural ele- ments e ß-sheete ,a-heli th th suc d s a han x , modulate electron transfer rates? These question e imporar s - tanr botfo th chemica d physiologicaan l l reasons; e.g., it is reasonable to propose that the rate at which an electron negotiates through the protein is biologically significant and, hence, becaus f evoo e - lutionary pressures, subject to the imposition of path specificities on the LRET process. Because proteins are inherently complicated, we and others have begun studying LRET in oligopeptides. Our initial pulse radiolysis experiments have been wite tyrosinth h e phenolic side chain electron donor e tryptophaanth d n radical indolyl side chain accep- tor, separated from one another by an oligoproline spacer. With Förster energy transfer experiments, Chiu and Bersohn [(1987) Biopolymers 16, 277] have

196 shown that each proline located between the trypto- phad tyrosinan n e linearly increase e separatioth s n of the aromatic side chains. In the tyr-(pro) -trp serie f approximatelo s e d witoveA an a a hr V m 5 5 y distance up to approximately 20 A ln[k(et)] decreases linearly with the proline number, as predicted by Marcus theory,. However,_the damping factor, ß, is unexpectedly low, < 0.3 A 1. Moreover, the compar- ison of our data with those of others [Isied, et al. Chem(1985. Am .. ) J Soc 7 743210 . ; Schanz Saued an e r (1988) J. Am. Chem Soc. 110,1180] who used different donor/acceptor pairs at the oligoproline ends suggest that the magnitude of ß may decrease as the redox potential differenc e paith r f o edecrease s [Faraggi, et al. (1989) J. Am, Chem. Soc. Ill, in press]. This observation, not yet addressed in terms of Marcus theory, suggests tha proline tth e chain "resistivity" migh e reduceb t d even furthe y arrangine b rA a r fo g of zero. In conclusion, the now well documented long range electron transfer in proteins and peptides frees us from the requirement for close physical proximity of electron donor/acceptor centers; whether this LRE s explainei T n termi d f Marcuo s s theory remains to be established.

Acknowledgement: This work was supported by grants no. 85-00217 and 86-00206 from the United States- Israel Binational Science foundation (BSF), Jerusalem e Nationath , y Israeb ld an lInstitute f o s Health Grant GM-35718

197 THE ROL SULPHUF EO R COMPOUND AFFECTINN SI G RADIATION RESPONSE: MOLECULAR ASPECTS

M. TAMBA Istituto di Fotochimica e Radiazioni d'Alta Energia (CNR), Bologna, Italy

Cellular thiols, almost entirely consisting of glutathione (GSH), have been much implicated in determining the radiosensitivity of cells and the level of the oxygen effect in response to radiation [1/2]. Current ideas postulate that cellular thiols and GSH in particular exert the function stated above mainly throughout radiation chemical mechanisms e figurTh . e shows schematically some possible mechanism f radiatioo s n damag d protectionan e . Centrao t l this model is the target radical, T", and its fate, which is critical in determining deleterious biological consequences. Thiol positiveln sca y interfer frey eb e radical protection. Whether protection occur scavenginy sb hydroxyf go l radicals hydrogey ob r n ato r electroo m n donation, thiyl radicals, RS', will be formed.

H20,H2

Recent results make the thiyl radical much more reactive than commonly believed. In fact the radical, which has an oxidising nature, has been observed to react rapidly with antioxidants, to abstract carbon bound H atoms and to add rapidly molecular oxygen [3,4]. In this paper are presented some recent results on the interaction of thiyl radicals of different naturee th wite fat th f ho e n oxygeo d an n resulting sulphur peroxyl radical, RSOO*.

199 The results can be summarized in this way: 1) RS' rapidly reacts with oxygen (^y 2xl09M~1s~1 producin e correspondenth g t thiol peroxyl radical RSOO" through an equilibrium reaction

RS- 4 o2

2) RSOO f o differen' tl al origicharacterize e nar a y b d weak transient absorptio e 540-56th n i nm spectra n 0 l region ;

3) for GSH, the decay of GSOO' occurs with a first order kinetics suggesting intramolecular rearrangement with formatio f carboo n n centered radical, *G(-H)SOOH, and/or sulphynyl radical, GSO';

4) GSOO' efficiently accepts electrons from several natura d man-madan l e antioxidant (D), including Vit. C, NADH, ABTS, at a rate comparable with that of GS'

RSOO' + D ———— »-RSOO" + Dt

5) RSOO' inactivates some enzymes, like lysozymd an e trypsin, while RS' is often almost completely harmless to the enzyme C£italytic activity.

Despit e difficulth e o establist t h unequivocally what happens within cells presene ,th t results suggest thae tth fast conjugatio wit' RS h f no oxyge n leadin potentiallo t g y harmful thiol peroxy e factore th b l f o o radicalst e on s i s carefully considered in the context of the oxygen effect and chemical repair processes.

ACKNOWLEDGEMENTS

This work has been supported in part by a grant from the Italian National Research Council, Special Project "Advanced Technologies and Metodologies in Radiochemistry".

REFERENCES

[1] M. Quintiliani, The oxygen effect in radiation inactivatio f DNo nenzymesd Aan . Int . .J Radiât. (1986)3 57 Biol , .50 .

200 [2] M.B. Astor, M.E. Anderse. MeisterA d an n , Relationship between intracellula levelH d GS an rs hypoxic cell radiosensitivity. Pharmac. Ther. 39, 5 (1988)11 . [3] C. von Sonntag, (Ed.), The Chemical Basis of Radiation Biology, Taylo Francisd an r , London, (1987). . Tannba M . [4SimoneG ] . Quintiliani, M , , Interactionf o s thiyl free radicals with oxygen: a pulse radiolysis study. Int. J. Radiât. Biol. 50, 595 (1986).

Next page(s) lef1 t blan20 k SOME IMPLICATIONS OF STUDIES OF ELECTRONS IN VISUALIZATIOE FLUIDTH R SFO QUANTUF NO M MECHANICS

G.R. FREEMAN Chemistry Department, Universit Albertaf yo , Edmonton, Alberta, Canada

r studieOu f electronso n fluidsi s have been accompaniey b d attempts to visualize their behavior. This has assisted in the visualizatio severaf no l quantum mechanical processes ha d san led to modifications of their traditional interpretations. For example, the intensity of atomic fluorescence that- follows the

photodissociation of Ca2 molecules is modulated in time [1]. The modulation is due to the interaction of single photons with two dissociating atoms and has been said to be analogous to the interaction of single photons with two Young-type slits [1,2], However, the modulation is mainly caused by resonant radiative coupling between the two atoms and is not analogous to diffractio slitso tw y .nb + Grangier, Aspec Vigud photodissociate] tan 1 [ e d Ca2 molecule spulses p wit0 f lase12 hso r photon d measuresan e th d time dependence of the fluorescence. Ca* + Ca-~-j . ^"^7^0 + 2Ca ^ + Ca*

The Ca2 dissociate atome th sd separatedan d wit relativha e velocity of 1060 ± 60 m/s. Fluorescence was measured at right angles to the laser beam. By passing the fluorescence through a polarizer they selected photons emitted along the axis of the line of flight of the separating atoms. This fluorescence displayed a time modulation during the first nanosecond after excitation.

e modulatioTh f emitteno d intensit functioa s a y f timno e correspond decreasea o st d probabilit f emissioyo n whee th n atoms were numbed separateod haln f a o r fy db -wavelength e th f so photons wit2 / relativela oddhn \ ,n d an , y higher emission probability s evenwhe emphasizwa o T n . e this relationshie pth emission intensitie n Refi s hav] .[1 e been replotte n Figi d 1 . as a function of the distance between the separating atoms in units of XQ/ the time required for the atoms to increase their

separation by XQ = 423 nm was 0.40 ± 0.02 ns. The observed intensit f ligho yI t emitten a y b d electronically excited populatio N nondissociatin f no g species C(-d= iI s N /dt) detectioe , th wher s i eÇ n efficiency. Hence,

where T is the decay constant and N * is the number at time t = 0.

203 r(ns) -0.4 0.0 0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2

0 ^ — 1

Fig. 1 Parallel polarized fluorescence intensity as a function o fd interatomi timan u e- 3 c42 distanc= 0 n unit\ (i f o sed nm)experimental, • . , background subtracted Ref, —- . [. 1] right side of eq. (3), with T 2.3 x 1O8 s~1. ———, eq. (3) filtered by a sliding Gaussian with a 180 ps (0.45 X ) full widt halt a h f maximum e experimentaTh . l plo Refn ti show] .[1 s T = 0 at the first maximum, which is equivalent to shifting the theoretical e responscurveth y b s e system. th ps tim 0 f o e18 ,

photodissociatine Ith n g Ca2 systes i value F th mf eo affected by resonant radiative coupling between the separating atoms [1,2]. s replaceTimi t e time y tdb ,th e after dissociatio e molecule th e timescal f th o ne n th O . f o e measurements, dissociation is instantaneous after photoexcitation [1]. The rate of detection of II polarized light, I||f is determined by the following equations (see eqs. (16), (23) and Appendix I of Ref. [2]]). T 1 1 1 I,,/Ç||N0* = T (T) expC-/ T (t )dT' ] (3) o ) (4 r'(T = )rt f*(u)+ i i

where u is the distance 6(m) between the atoms at time -u divided e radianlengtth y b ? h emittee \= o/2ith f to d photons, (radiansu vt/f= ) ÔA«= d c an , U u n si ; .si3 _nu (5) 2 ( 3 u u Eq. (4) represents the effect of resonant radiative coupling betwee atome th nthes a s y separate [2] value .Th f eo the right side of eq. (3) is plotted against T in Fig. 1.

204 e experimentaTh l detectio Gaussiaa nd systeha ] n[1 mtim e resolutio s fulp n0 l wit18 widt ha hal t ha f ) maximum(4 . Eq . s thereforwa e processed wit slidinha g Gaussian filter factor 2 2 2 )2] whic h ave exp[-(T'-i:) /(108 ps) ] = explXd'-d) /(0.270 ko ' 9 e ar 2 / X 3 e fuld th an l 2 lin/ e minim Fign X Th ei t . a 1 quantitatively explained by resonant radiative coupling between e atomsth greatet A . r separation undulatioe sth dominates ni d by noise. The value F = 2.3 x 1O8 s~1 was used, which corresponds to a mean lifetime of 4.4 ns, compared to the reported atomi cs [1,2]n lifetim 7 .4. f o e

The emission minima at atom separation distances equal to an odd number of half-wavelengths of the photon indicates a tendency to form a localized state of the photon between the atom thost sa e separations e emissioTh . n maxim atot a m separations equal to integral numbers of complete wavelengths might indicate that a photon can have a physical length of one wavelength. Conventional quantum mechanics give informatioo n s n about the length of a photon, but we would like to know it.

In the first paragraph of p.789 of Ref. [2] the intended statement appears to be A|?a - P,J = 8.8 x 10 kg»m/s > 28 10~x 5 2. kg»m/s= o •f/\ i , rather tha » h/X n | b A|?QP . - a Furthermore displayee th , d relation &|R R- ab |AJP P^- a j > s simpl*fii reformulatioa y f theino r relation (32), which

reduces to A|Pa - P^ | ~-îî/A|Ra - Rjjl* It was suggested [1,2] that the oscillating emission probability from dissociating Ca^ molecule effecn a s twa s analogous to that of single-photons interacting with two slits. "This experimen thus ti s analogou single-photoa o t s n Young's slit experiment whicn i ,e 'slits th h ' (the atomse )ar moving" [1] e 1-sli.Th d 2-slitan t interaction singlf so e elementary particle mucs a subjeca he sar f livelto y debatw no e as they were sixty years ago d thee importanan ,ar y e th o t understandin e foundationth f o g quantuf o s m mechanicse Th . separating pai atomf o rs vacuusha m between them o slittw e ; sar separated by an opaque material. Fig. 1 demonstrates that the effect is due to resonant coupling; the experiment was therefore not analogous to a single-photon two-slit experiment of the Young type.

Finally, the Heisenberg limitations of information are a facto f 2io rt less severe than suggested [1] d measuremenan , f to XQ to an accuracy of 1 pm would permit one to say which atom emitte photone th d . That remain challengesa .

REFERENCES

[1] GRANGIER ASPECT, ,P. VIGUE, ,A. , Quantu,J. m interference atomo effectw sr radiatinfo t singlga e photon, Phys. Rev. Lett , (1985)54 . , 418.

s» ] [2 GRANGIER , VIGUE,P. , Quantu,J. m interference effecr tfo two atoms excited by molecular photodissociation: a theoretical analysis, J. Phys. (Paris) 48, (1987), 781.

Next page(s) lef5 t blan20 k ADVANCEMENT RADIATIOF SO N INDUCED DEGRADATION OF POLLUTANT DRINKINN SI WASTD GAN E WATER

N. GETOFF Institute for and Radiation Chemistry, Universit f Viennayo , Vienna, Austria

designatee watee b Th n mose rca th t s a importand t foodstufl al r ffo living systems including man. The development of various industries as well as increased use of chemicals in agriculture and daily life etc. resulted in great problems of the water resources. The radiation induced degradation of pollutants, especiall halogenatef yo d hydrocarbons, offer efficienn sa d tan economically acceptable possibility in the future (Getoff, 1989 and réf. therein).

The decomposition of several biological resistant pollutants in water suc: dichloromethanehas , chloroform, 1,1,1-trichloroethand ean trichloroethylene has been studied as a function of dose in aerated solutionstakes indicaton a wa decompositioe s nth a ~ yiele Cl r Th rf .fo o d n degree of each individual pollutant. The formation of aldehydes and simple carboxylic acids were observed as intermediate products. They can be completely decompose increaset a d d dose.

addition I theso nt e studies, also various mixture chlorohydrocarbonf so s _3 mg/d1 wer36 ) mo et (0.irradiate2 (19y dkG 0 wit 9 krad dos1. ha n f )i eo presence th airf eo shows .A Tabln ni completa eI e degradatio thesf no e substances is achieved.

The radiation induced degradation of aqueous pollutants in technical scale can be easily realized by means of powerful electron accelerators. At present they can provide an electron beam (2-10 MeV and more) with rather high power (30-300 kW and above). A meaningful and efficient performance of the method is shown in Fig. 1, where the electron treatment of the polluted water is followe conventionaa y db l biological purification.

Finally, the absorption spectra and kinetics of CH , CH,0_, CJA^ O J £. £. J C H and 2 50 species were reinvestigated Fign spectre I .th . 2 a with their characteristic data are shown. For explanation of the results probable reaction mechanisms are presented.

207 Tabl . eI Radiatio n induced decompositio somf no e chlorohydrocarbons m ) presence wate* th r n ai i r f eo Applied dose: 1.9 kGy

Sample Pollutant n water/ijg.dm"I s 3 Nr. Treat- CH C1 CHClj CCI,, C1 C-CH C1 C=CHC1 ci c=cci ment 2 2 3 3 2 2 2 1 unlrr. • ~ 3 7 — — Irrad. n2d -- n°id 2 unlrr. — 25- 0.2 — Irrad. .- nd _ 3 unlrr. 48 — 107 1.1 Irrad. rid — 0.8 nd _ 4 unlrr. 23 2.3 1.1 0.2 Irrad, rid nd 0.1 nd _ _ 5 unlrr. — 2.5 0.2 4.5 361 0.2 Irrad. nd nd nd nd nd

The GC-analysis were performed with "Vista 6000", Varlan Ltd., by Doz.D Bauer. .u . Traceable limit1 ug.dnf0. < : 3

n detectablno n= d e C13C-CH ,1,1-TrIchloroethane CH2C1 Dlchloromethan= 2 e C12C=CHC1 Trlchloroethylene CHCl jChlorofor= m C1 C=CC1 = Tetrachloroethylene CCI,, = Carbontetrachloride 2 2

waste water

River

Fig! Schem1 . radiatiof eo n Induced decompositiof o n pollutant wastn I s e water. (CR) Collecting reservoir (T) Tank for adjustment of the water layer thickness and flow velocity (EA) Electron accelerator (CBP) Conventional biological purification.

f Radi \ "•(IK ^ 6 cals y s ,* * „•W™-') Mo ^max.-1 -1 " 2000' m c M (nml H0 1 * 2 230 U30 1 204 lOOO 245 2150 '500- 1500- 2 248 1350 6 1500- n 1000 } H0'V. \ ^' /\ , T ^j>/jpt—b

to H02 and 02"/ (B) and C2Hg02 In aqueous solutions.

208 ACKNOWLEDGEMENTS

authoe Th r thank Federae sth l Ministr Sciencf yo Researcd e ean th d han Jubilee Funds of the Austrian National Bank for financial support as well as the MPI of Radiation.

REFERENCE

Getof Appl, fN. . Radiât. Isot.(A) prinn ,i t (1989)

Next page(s) left blank 9 20 THE RADIOLYSIS OF AQUEOUS SOLUTIONS OF GLYCOSIDES

Rongyao YUAN, Jüan WU Departmen Technicaf o t l Physics, Beijing University, Beijing, China

Glycoside e widelar s y distribute naturen i d e studTh .f o y radiolysis of giycosides may provide the criteria for enacting the hygienic safety standard of irradiated foods and sterilization of pharmaceuticals. In this paper three types of aqueous solutions of giycosides, glycyrrhizin, baicali d an 1,8-dihydron - xyanthraquinone-ß-D- glycoside have been investigated. The yields of decomposition of giycosides are determined. When high dose is applied their G values decrease as doses increase. Some radiolysis products are identified. The influences of radical scavengers, 0 , NO , KCNS Lf & and isopropanol, are observed. Radiolysis is mainly caused by OH radical. The OH addition compound of l,8-dihydroxyanthraquinone-ß- D-glucosid s beeha en found. Radiation induced hydrolysif o s glycosidi e maith cn t processlinkagno s proportioe i e,th f no dissociated aglycon to total radiolysis products are less than 10% for giycosides. As the medicinal property of aglycon is always similar to that of the original glucoside, so we must put the separatioe stresth n so d identificationan compounde th f no , which is formed by addition reaction or oxidative reaction with OH radical under gamma irradiation of glycoside.

Next page(s) lef1 t blan21 k USING MULTI-EFFECT CHEMICAF SO L SCAVENGERS TO STUDY THE RADIOLYSIS OF CYCLOHEXANE- 4-METHYL-4-PHENYL-2-PENTANONE SYSTED MAN CYCLOHEXANE-TRIBUTYL-PHOSPHATE SYSTEM

ZHANGn Na , JüaU nW Department of Technical Physics, Beijing University, Beijing, China

w ne conceptioA n about applicatio f o scavengern s i s developed e multiplTh . e effect chemicaf so l scavengers have been used in the investigation of radiolysis of cyclohexane. Using the excited singlet probe MPP and TBP, we obtained the yields of excited singlets of benzene (l.4±0.2), cyclohexane (1.5+0.2), TBP (1.410.3) thermae yielde th ,th f so l hydrogen atom cyclohexanf o s e (1.5) which come mainly frogeminate th m yielde th ions f d so ,an the geminate ions of cyclohexane (3.8). The atom detachment of excited singlet cyclohexanf so littles ei multiple Th . e effectf so P werTB ed successfullan P MP ye researc th use n i ddifferenf ho t transfer processes in the radiolysis of cyclohexane. The kinetics f hydrogeo n atom captur d protoean n transfe s alswa ro discussed. e multipleTh , effect f scavengero s alwaye sar s unavoidable but useful in figuring out the whole picture of the radiolysis if one or two processes are unique and easily detected. A lot of unexpected information can be approached after a careful selection of such scavengers.

Next page(s) left blank 213 THE CRYSTALLIZATION KINETICS OF IRRADIATED POLYPROPYLENE WITH ADDITIVES

Wenxiu CHEN, Shui YU Departmen f Technicao t l Physics, Beijing University, Beijing, China

The flexibilit radiatiod yan n toleranc f polyo e - propylene(PP) havrelatioe th es crystallinity it o nt . PP with various additives, forming in different con- trolling and other treatment have the effect on its crystallinity and also on its crystallization kine- tics paramatere Th . f crystallizatioo s n kineticf o s PP were changed by mixing additive or irradiation. The Avrami exponent(n value) of PP were decreased from 3.49 to 2.71 with the increasing of isothermal crystallization temperature(valun e eth t bu , ) T increased from 2.5 to 3»98 wi£h T during less phtha- locyanine green dye (^0.3$ w/w) mixing into PP. The crystallizatio nwitP increasee P ratdy h f o e d almost two times as the PP without dye and the crystalliza- tion heat (AH, J/g) were changed (Pig.l). After irra- decreasediatioH valun d e an enth d wit e increahth - sing of dose (Pig.2). By means of IR and electronic microscopy techniques, the charaterist of PP under the influence of additive and dose were evaluated.

215 AH

100

90

80

70

60 ______125 127 129 131 133 135 137 139 141*C(T ) o Fig.l The crystallization heat(AH) of PP under different isothermal crystallization temperature (TJ. curve 1, isotactic PP without additive 3 ,i~P d curvPan 2 e with dye 0.1# and 0.3#(w/w) respectively.

0 30 400kGy(Dose 0 20 ) 0 10 0 Pig. Avrame 2Th i exponent crystallizatiod an s nP P hea f o t under various doses. Solid curve ——— *3 witC 13 h= signaT , lx Dash curve ----- with signal* , T = 125 *C c 216 SPECIAL TOPIC

Next page(s) left blank RADIATION CHEMISTRY OF FLUE GASES

. BUSF I Istituto di Scienze Chimiche, Université di Bologna, Bologna, Italy

Abstract

A chemical mechanism for the radiolysis of combustion gases produced in fossil fuel power plants, in agreement with a large body of experimental results is presented. The process represent an exampl f successfuo e l applicatio f radiatioo n n chemistro t y the control of air pollution problems.

Introduction In spite of the extensive studies reported in the recent years, fundamental questions on the relationship between the formatio f acio n d precipitatio e chemistrth d an f o ny sulfu r dioxide, SO , and nitrogen oxides, NO = NO + NO , in the pol- L- AL. luted atmosphere remaianswerede b o t n . d formatioan O N f acidio d n Oxidatioan c9 nitratS0 f o nd an e L. X sulphate aerosols e gas-phasoccuth n i r d liquid-phasan e e atmo- spheri c-mi crodlopl ets. e gas-phasIth n e oxidatioth e n reaction e initiatear s y b d e absorptioth f sunligho n t which inducee e formatioth th s f o n oxidizing radical d HO*an . s, Reaction-0 'OH ,e primar th f i o sox y c. • — dizing radical d secondaran s y organic peroxide radicals yield sulfuric and nitric acids [1]. The results obtained by field mea-

surements on the rate of S0? oxidation cannot be completely explained by reactions with light induced primary and secondary radicals since rapid conversion of sulfur dioxide has been obser- vet nigha d t time, under condition f higo s h humidity. Catalytic autoxidatio aqueoun i O sS microdlopletf o n s beeha s n suggested as a nonphotolitic patway for the rapid accumulation of H SO. in humid atmospheres e reactio .Th O witS f ho n oxygea varietd an n y

219 of inorganic and organic compounds can be accelerated in the pre- senc f transitioo e n metal ions, suc s Co(II)a h , Co(III), Cu(II), Fe(II), Fe(III), Mn(II), and Ni(II) [2,3]. The determination of the catalytic autoxidation mechanism of SO- has been, for many years, the goal of researches in many fields. The results reported are characterized by serious disa- greements on reaction rates, rate laws, and pH dependence [2,3]. High energy irradiatio s mixture samga th ea f o composjf eo n _ tio f polluteo n r induceai d s oxidation processes initiatee th y b d

radical , -OH '0 s' (organi , RO H0' d ;,an c peroxides d reductio)an n processes due to reactions of N- radicals [4-24]. Radiation stry studies can, therefore, help understanding the many fundameri tal gas-phase processes related to acid rain development. Impor- tant results for the determination of the SO- autoxidation mecha- nism have, also, been obtained by pulse radiolysis studies of sulfur dioxide aqueous solutions. The experiments have identified e natureth e physico-chemica,th l propertie decae th yd kinetican s s of the intermediates but the initial step of the autoxidation process catalysed by trace metal ions still remains to be cla- rified [25]. The radiolysis studies of power plants flue gas, which is an example of highly polluted air, has shown that, upon addition of a basic compound, SO- and NO can be removed with yields thatmake L- A the process economically convenient [24]. e presenIth n t communicatio e illustratw n e chemistrth e f o y the radiation induced SO and NO removal from fossil fuel power L. A plants stock gases in the presence of stichiometric amount of am- systee addes th i n o i mt dH N e Th . ]) moniO [N a+ 2[S= ] ([N] O H O L. A O order to form ammonium salts which can be removed in situ by electrostatic precipitators or filters.

Primary processes The radiolysis of stock gas yield reduction and oxidation of the pollutant components as final result of a complex chain of

220 processes whic e initiate ar he energ th y yb d e depositioth f o n incident radiation. e fractioTh f energo n y absorbe y eacb d h s componenga a f o t mixture is proportional to its concentration and stopping power.

In the N2 (68%), H20 (10%), C02 (12%), 02 (8%), NO (360 ppm),

N02 (10 ppm), SO (1000 ppm), and NH3 (2380 ppm) mixture, which rapresents a typical flue gas system with added NH , the compo- G nents which significantly interact wite radiatioth h e nitroar n - gen, water, carbon dioxide, and oxygen. We have developed a gene- ralise e calculatiod th mode r e radialysifo lth f o n s yields under different experimental conditions. The calculated yields are in good agreement with a large body of experimental measurements [18-21]. e primarTh y processes induce y radiatiob d representee b n ca n d by [18]:

+ N2 ->HH. N*, e", N , N', N*, N* 2.27= G , 2.96, 0.69, 1.90, 1.15, 0.29

+ 02 *++ 02, e", 0 , 0*, 0* 6 = 2.07, 3.30, 1.23, 1.41, 1.90

+ + + H20 +-~ H20 , e", FT, 'OH, 0', OH , H , H£ G = 1.99, 3.23, 4.15, 4.25, 0.45, 0.57, 0.67, 0.45

+ + C02 +++ O)!", e", C0 , 0 , 0', CO G = 2.24, 2.96, 0.51, 0.21, 0.51, 0.21

The primary species, X. are produced at a rate given by:

0 10 x N D/ dX./dx G = t

where D, eV l s , is the dose rate, G is the number of molecu- les produced per 100 eV of energy absorbed by the parent compound and N is the Avogadro's number. The species undergo fast reactions for which the following mechanism was assumed

221 a) ion-molecule reactions.

O S fy\Jl t A* 1 /X

r\ 1 1 v f\ 1 1 i M \o 0 2 H > 0 2 H + N ; 2 + N

+ 3) 0* + H20 ——— > H20

4n \; uf\ +i HI 1 ur\ - s>. Hl | Uf\ + 0

+ +

6) H 0+ + H 0 ——— > H/ + OH 2 2 «; + 11 \ 1-1"*" . r>n v fo ! + U L / L,U+ ö„U ^

+

' wU j \ j y rf x o—, u o ' /O ** rt 2

10) e" + C02 + M ——— > C02

S U_ M + —— 0 ~ UI 1 0 + 'I — _ ~ > e C J ) . J 11 1

12) 0 + C0 ——— > C0 2 2 2 + 02

b) neutralization reactions. + —X —* —+ X >—r " p >e ) 13 oduct:

H > 1 1 v U H + „ tü \ r \ ; n n r"*n 14 1 t ~ L, O

+ 0 + O C — > —— 2 C0 + 15 2 )0

) unchargec d species reactions.

— N > —— N + N ) 16

2 — H0 > —— 2 0 17+ )H O — >H —— H O + 18 H )O

19) H02 + H02 20) 0 + 0 + M

21) OH + OH ——— > HO + 0

22) N* + 02 ——— > NO + 0 0 + O — >H —— O H + 23 H )O

222 e modeTh l e systegivesth r m ,fo unde r consideration, 6(*OH)=

= 3.26, G(H02) = 3.60, G(N-) = 1.53, G('N*) = 0.90, G(O') = 1.02, and 6(CO) = 0.24, in good agreement with experimental results [18]. e reactioTh f exciteo n d nitrogen radical, -N( D)+NN *= , P) ( 2 2 with 0» produces NO during radiolysis with a yield of G(NO)=0.90 and increases the yield of oxygen radical.

Reaction of primary radicals with low concentration components e minoTh r mixtures componentga e th , f SO-o sd NO-, an ,NO , NH-, cannot compete with neutralization reactions and most of the ion-molecule reaction n scavenca t e 'OHbu sth g , HO", d *N*an 0, radicals. e followinTh g mechanism e flus compositioth ga e r fo , n pre- viously defined, n irradiatiorefea o t r n temperatur f 80°Co e . O radicaH Thwhile N -O eth d ean l O N react , O sS , wit H N h O L. L- HO* radical reacts predominantly with nitrogen oxide:

———H -O >O + H -N+ H HN ) 24 0 L- C.

———H -O >+ 252 HOSO)S0 * 26) NO + -OH ———> HNO

———H -O O >+ HN 2 N0 ) 27 H O + O N HO;+ 28> O ;)—— N

0 ———H + 29 >0 )N

e dosth Reactio e3 Mradn i o rangt , p u converte28 n s over 70% of HO* to -OH radical, figure 1. The yields of 'OH radical reactions change during the radio- lysis wite concentratioth h e reactantsth f o n , e calfigurTh - . 2 e culated yields give due account for the desappearance of SO by heterogeneous thermo-based processes.

223 NO

NO2* HOj

1 d Dosra M e,

. Calculate1 Fig. d e yieldHOth ^ f radicao s l reaction . dosevs s .

3

OCX) OH

t Dose.Mrad 2

. Calculate2 Fig. radicaH "O de lyiel th reaction f so . dosevs s .

224 e -NTh H radical, produce reaction i d , reduce24 n s nitrogen oxide and dioxide according to:

30) -NH2 + NO

0 N ) -N+ H31

yielde O N reduceTh f o , scalculate reactionn 31 i d d an 0 3 ds X for different doses, figure 3, indicate that the reduction proces^ sess •fully account for -NH radical decay in the dose range exami- ned. The decay mechanis produce th f f reactioo mo t - , HSOra 25 n' dical s beeha , n extensively e studiefollowinth d an d g mechanism has been proposed [1]:

H *O + O HS ) 32

2 H + 3 — >S0 —— 33 )H HSO"O ^+

34) HSO' + N02 ——— > HOS02ONO

35) HSO; + H00 ——— > H0SOC . d O £3 36) HSO: + o —— > HOSO o: ô L. L. C. 37) 2 HSO ——— > 38) HSO+ HOS : — ;HSOOo — >2 : 3 C. L. *T

39— >) —— 0 HSOHOS0N ^+ O N 2 0+ 2

— > —— HOS0 HOS0) O 40 2N ON02 0+ 2 2

41— > )—— 0 HSO S HOS0 2 ^+ S0 2 0+ *

42) HSO^ + NO ——— > HOS02ONO

43) HOS0202 + N* ——— > HSO^ + NO

The calculated product yields of reactions 32-43, figure 4,

give G(HSO;) = G(HSOl) = G(HSO;) + G(HOS0ON0), which indicates

0 o b 4 L0 c.

225 1.8

1.0

•NH24 NO2

Q (X)

0.5 _

0.0 3 1 Dose,Mra 2 d 0

Fig. 3. Calculated yields of the -NH2 radical reactions vs. dose.

1.0 .

0.8 -

0,0 1 Do*e, Mrad 2 Fig. 4. Calculated product yields of the HOSO^ radical decay pro- cesses vs.. dose.

226 e relevanar tha, 41 t e t d onlpr undean e y0 th r4 reaction , 39 , 36 s sent experimental conditions. The yields of reactions 26 and 27 change with the ratio [NO]/[N(L], figure 2. The nitrous acid, produced primarely in reaction 26, undergoes back reactions 44-46:

+ HN0O + — >N O —— 2 HN ) 44

45) HN02 + HN03

) HN046 2 +*OH

yielde Th f bace negligibleo s ar k 6 reaction4 d d an an , 5 4 s that of reaction 44, calculated at different doses, is shown in figure 5. The results have been obtained giving due account to he terogeneous reaction O whicHN f HNOo sd h an »dissolv aeroson i e l L. O microdroplets according to the mechanism discussed later.

1.0

0.8

0.6

GCX)

0.4

0.2

O.O

1 Dose2 , Mrad

Fig . Calculate5 . d yiel r HN0dfo back reaction 2HN0 N0+N0= + 2 2

t differena O +H t doses.2

227 1.5 _

OCX) _

N.

N,O

0.5

0.0 Dose, Mrad

Fig. 6. Calculated product yields of -N radical reactions vs. dose.

grounThe d state nitrogen radical reacts wit trogehni n oxides according to

- O N 47+ N )*

48) 'N + NO - -> NO + NO

- . NO + 49N )' f. i- e producTh t yield f reactiono s s 47-4 e show9 ar figurn i n , 6 e

228 2 increas2 d Reactionan e9 4 considerabl , 47 s yiele f o th y d oxygen radica a valu o t le which only slightly depende dosth en o s absorbed by the system and for 1.0 Mrad is 6('0) = 3.30. The *0 radical undergoes reactions with 0_ and the oxides present. The reaction with molecular oxygen yields 0_ which gives •\J the some oxidation processes as *0 does:

0 ' ) 50

51) '0 + NO ——— > N02 52) '0

2 2 ———0 + N0 O + >N 53 0 )"

54) "0 + S02 ———> S03

e bacTh k reactio 3 reduce5 n e removath s l efficienc_ ra 0 ' f o y O N proceeds e oxidatioo dicat th e O s th e yieldN a l Th . f f o no s relevant '0 radical reactions, at different doses, are shown in figur. 7 e e nitricTh , sulfuric d nitrou,an s acid vapors produce- du d ring the radiolysis of the gas mixture condense together with wa- ter molecules, mainly on existing aerosol particles which serve e phas s nucleth a er fo transitioni e neutralizatio.Th f sulfuo n - ric acid and nitric acid aerosol by ammonia gas occurs at a rate lower than the rate expected if the diffusion of NhL to the aero- sol e ratdropleth e s determininwa t g - stepae d depende ,an th n o s rosol particle sizd concentrationan e . Experiments performea n i d laboratory flow reactor indicate that partial neutralization to NH.HS s relativeli O y fast unde e conditionth r - sE presen e th n i t -Beam treatment, but the complete neutralization to (NH ) SO. is a slow process [26] .A complet e physico-chemical understandinf o g the aerosol acid neutralization by ammonia gas is not available, but the results obtained indicate that the rate of the process ijn creases with particle concentration and size. Therefore addition

229 OCX)

1 Dose, Mrad

Fig . Calculate7 . d yieldradica0 - f o s l reaction . dosevs s .

f powdero y material should significantly contribut o acit e d aero- sol neutralization reaction. The nitrous acid absorbed in liquid droplet, in the presence f dissolveo d SCL(H O'SOJ, undergoes chemical processes according e followintth o g 5 [3]reactions3- := H p t ,a

K, -l 0 HN ) 55 2(g) HK02(1) H = -9.49 Kcal mol K (56_ 56) HNOr = -2.0 H 0 Kcal mo l 2 N0

where K, = 49.x 0M atn f (Schwart d Friebergzan , 1981)d an ; . ) H1/lrrl55 M [21] ;0 1 x 1 7. K,,, = (56A)

230 PPM

300 >

200 _

100 _

O.O 0.4 0.8 Dose, Mrad 1.6 2.0

Fig . Calculate8 . d removal yield r EBARfo s A flue gas 0 Mra1. ; d s"1 dose rate.

) 2HN57 0 -> 2HSO + NO + HO + 2H

) 2HN58 0

The contributio f w reactiono lo s e i negligibl th 8 5 n o t e edu rat f reactioneo producte e post-irradiatioTh th . f o s n procesf o s nitrous acimainle dar y nitric acinitroud dan s oxide value Th e.

yiel0 ? N calculated e produce th modee 8 Mra r th 1. f fo y o dt l b da d energy absorbed by the system is 83 ppm which compares satisfacto ry with the measured value of 76 ppm [27]. injO ^N f o m pp mixtures Th0 ga e36 calculate e r th fo , n i O dN X tially present, afte 8 Mra f 1. energro d y absorbed, amount8 13 o t s ppm (N0„, 107 ppm; NO, 31 ppm), figure 8, which compares well to the experimental value of NO , 128 ppm, measured in the EBARA pi- /\ lot plant afte e procesth r s vessel [27] e valu.Th e measuree th t da

231 EBARA d systethereforan m mpp outlee9 6 post-irradiatios i t n remo val reactions must occur. Since significant pre-irradiation mainl , remova O , N NO yf o l A was not experimentally observed, except when powdery material is added to the gas mixture, we assumed that the post-irradiation re

o liquid-phast e movadu s i l e reaction f N0o s ?, accordino t g

H(59) 2(1)

= 1 x 10"2 M atm"1 [21], and

60n ++ ) M SO"— > M—— 2(n '1} + SO" 6i) so: + o — > so: b c. à 9 : SO SO"+ — >2 62" —— 2) SO 4 o b — > —— "OSO OO ON N + " SO ) 63 . - - H2° 64) OS0ON0 — ^-> N0 + HS0 + H

where reaction 60-64 are based on the metal catalized autoxidation mechanism proposed [2] to explain the results obtained by Hayon and co-workers [25]. e presencIth n f liquid-phaseo e , sulfur dioxide undergoes the following equilibrium reactions

I/ (65) 1 65) SO-2(g,) . ————- — 2 H.O'SO2(1)oMv AH = -6.24 Kcal mol"

3.9- = 8 H A Kcal mol" O HS 1+ + H ) H0'S066 - ,

i/ -2.9= H SO+ A • + 82 (67H " ) HSOKca ^67 l" mol"1 0

where Ku,-n> = 1.24 M atm is the Henry's law constant, K„ = o b n\oy;? = 1.23 x 10 M and K ., = 6.61 x 10 M are the first and the se- oc / cond dissociation equilibrium constants, respectivelye Th .

232 fraction of SCL which is absorbed in the liquid phase strongly de s givei y d [2]b nan :H p e pendth n o s

(K= H(65)/a)xP(St)2)

where

+ 1 + 2 K+ 66Kx 1 67/[H ( 6 /[H 6 = K ]+ ]a" )

In the pH range 2-6, ammonia is strongly absorbed in the lv quid phase [21]

1 ) NH68 0 ,. -8.1= 3(g H ) A 7 Kca———NH,,.l mol"»— 3(1]

where Kufcn^ = 58.9 M atm . Therefore, the presence of ammonia n(bo) in the gas-phase increases the pH of the liquid phase and the fractio O S absorbed f o n . In additio o ammonit n d sulfuan a r dioxide, other components s mixtur e absorbega b e liquid-phasen e th ca th en i df o r examfo ; - e presencth ple, f oxygef greao eo s i tn importance:

I/ H(69) 1 . 69, 2 )0 -3.5= 0 H 2(1A 7 Kca)l mol"

Oxygewher. m en at K..,..- reactM = 1.2^0 s1 6x with sulfu-3 r -l dioxide accordin e followinth o t g g simple stoichiometr] [2 y

,(2-n)- OS0" H ———_ 0 ) 2 70 SO>H 1/ j "+ n 2 2 n 4

where n varies from 0 to 2 depending on pH. Autoxidation process e reactio th acceleratee b slo s t i n bu w, e presenc ca n 70 th y b d e whic, V h r o , n M f trace-meta, o i N , e lF ion, se F suc s a h 2+ 3+ 2+ 2+ 4+

233 have been detecte e particulatth n i d e release d coald an frol - oi m -fired power plants. The metal catalyzed autoxidation is not ful- ly understood but empirical equations for the reaction rate have been derived under different experimental conditions. As for Fe3+ 2+ and Mn catalyzed autoxidation, the expression which can be ap- plied to the flue gas system, in the presence of NH , is (Jacob O and Hoffmann, 1983):

2 + 71) -d[S02(aq)]T/dt = 4.7 x [Mn Y/[H ] +

7 3+ 2 + 1 x 10 x ([Fe ] [S02(aq)])

for [SO , .] > 10"5 M and pH = 3-5; and

[S°2(aq)] TCH= 2°'S°2 ~ ][HS+ °3 ]+

Quantitative evaluation of the removal of SO- in theaqueous- -phase requires, in addition to the purely chemical pathways, the knowledge of various parameters, such as the physical process of nucleation scavenging, the droplet size and growth of condensa- tion nuclei, the concentration of major aqueous-phase species,the e dropletth f po H , etc e valueTh . f theso s e - parametera t no e ar s vailable and strongly depend of the quality of the fuel, the cha- racteristi e poweth f ro c plant e flus coolin,th ga e g system, etc. Therefore o quantitativ,n e analysi t presenta , is s , possible- Ne . vertheless, the suggested chemical pathways can explain the re- sults obtained under different experimental conditions.

Conclusions

The competitive thermal processes in the radiation treatment

of S0? give the major contribution to the final abatement yield. The nitrogen oxides are essentially removed during the irradia- tion step. The efficiency of the process can be enhanced by the

234 addition of powdery material which increases the water nucleation process and the amount of NO absorbed in the liquid-phase. A

References [1] CALVERT, O.G., and STOCKWELL, W.R., "Mechanism and rates of the gas-phase oxidations of sulfur dioxide and nitrogen oxi- atmosphere"e th den i s 2 OxidatioN0 ,d S0an 2O ,nN Mechanism: Atmospheric Consideration, (CALVERT, J.G., Ed) Butterworth, Boston (1984) 1-69. ] HUFFMAN[2 , M.R. d JACOBan , , D.J., "Kinetic mechanisd an s f o m e catalytith c oxidatio f dissolveo n d sulfur dioxidn i e aqueous solution n applicatioa : o nightimt n g watefo e r chemj[ stry", S02, NO and N02 Oxidation Mechanism: Atmospheric Con- sideration, (CALVERT, J.G.Butterworth) Ed , , Boston (1984) 101-171.

[3] HUFFMAN, M.R., and CALVERT, J.G., Chemical Transformation Modules for Eulerian Acid Deposition Models. Vol. 2: The Aqueous-Phase Chemistry. Interagency Agreement DW 930237. Project officier, DDGE, M.C. Atmospheric Sciences Research Laboratory Offic f Researco e Developmentd an h , U.S. Enviro- mental Protection Agency Research Triangle Park, NC 27711 (1985).

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] KAWAMURA[5 AOKI, K. , KAWAKAMI ,S. HASHIMOTO, ,W. d an , ,S. MACHI, S., "Radiation for a Clean Environment", IAEA-SM-194/ 707, Vienna (1975) 621.

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[12] KAWAMURA , KATAYAMA d KAWAMURAK. , an , , "Th,T. K. , e pilot plant experimen f electroo t n beam irradiation procesr fo s removal of NOX and SOX from plant exhaust gas in the iron and steel industry", Radiât. Phys. Chem. 18 (1981) 389. [13] t al.MACHIe , , S. "Radiatio, n treatmen f o combustiot n gases", Radiât. Phys. Chem. 9 (1977) 371.

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[27] EBARA, Data from the report prepared the D.O.E. of U.S.A., and personally comunicate . FrankN y b d.

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Prof. N. Getoff Mr. L. Gilles Universit Viennf o y a Division d'exploitation des reacteurs Institute for Theoretical and prototype expérimentaut e s x Radiation Chemistry CEN Saclay Wahringer Strasse 38 91191 Gif-sur-Yvette 1090 Vienna FRANCE AUSTRIA Dr. B. Hickel Freema. R . G . n Dr Servic e Chimid e e Moléculaire Chemistry Department Département de Physico-Chimie University of Alberta CEN Saclay Edmonton, Alberta 91191 Gif-sur-Yvette CANADA T6G 2G2 FRANCE

Dr. A. Singh Prof Schille. .R r Atomic Energy of Canada, Ltd. Central Research Institute Whiteshell Nuclear Research Establishment for Physics Pinawa, Manitoba ROE 1LO 9 4 P.Ox Bo . CANADA H-1525 Budapest 114 HUNGARY Prof. Wu Ji-lan Departmen Technicaf to l Physics P.N. Dr . Moorthy Peking University Head, Radiation Chemistry Section Beijing Chemistry Division CHINA Bhabha Atomic Research Centre Trombay, Bombay 400 085 Prof. Chen Wenxiu INDIA Department of Chemistry Beijing Normal University Prof Raban. .J i Beijing Hebrew University CHINA Department of Physical Chemistry 99904 Jerusalem Prof. Sun Dakuan ISRAEL Shanghai Institute of Nuclear Research Academia Sinica Dr. M. Faraggi Shanghai Israel Atomic Energy Commission CHINA Departmen Chemistrf to y P.O. Box 9001 Mr. E. Bjergbakke Beer-Sheva 84190 Chemistry Department ISRAEL Risö Rational Laboratory DK-4000 Roskilde Prof. F. Busi DENMARK Istituto Fotochimici 'd Radiazione a i d'Alta Energia (FRAE C.N.Rl )de . Sonntan Profvo . .C g Via de* Castagnoli 1 Max-Planck-Institut für Strahlenchemie 40126 Bologna Stiftstrasse 34-36 ITALY D-4330 Mülheim/Ruhl r FEDERAL REPUBLIC OF GERMANY Dr. H. Tamba Istituto Fotochimic Radiazionae i Prof Leonhard. .J t d'Alta Energia (FRAE C.N.Rl )de . Akademi Wissenschafter ede R DD r nde Via de' Castagnoli 1 Forschungsbereich Physik 40126 Bologna Rudower Chaussee 5 ITALY Berlin GERMAN DEMOCRATIC REPUBLIC Dr. Qu.G. Mulazzani Istituto Fotochimica e Radiazioni Mr. J. Belloni d'Alta Energia (FRAE) del C.N.R. Physico-Chimi Rayonnements ede s CastagnolVi' ade 1 i Université Paris-Sud 40126 Bologna Bât. 350 ITALY 91405 Orsay FRANCE

239 Prof. Y. Tabata Dr. R. Nohr Department of Nuclear Engineering Long Term Research Tokai University Kimberley Clark Corporation 1117, Kitakaname, Hiratsuka-shi 1400 Holcomb Bridge Road Kanagawa Roswell, GA 300 76 JAPAN 259-12 USA

Dr. S. Machi DrOlejni. .T k Takasaki Radiation Chemistry Chlc-opee, Research Division Japan Atomic Energy Research Institute 2351 U.W. Rt. 130, P.O. Box 940 Research Establishment Dayto 08810-094J nN 0 Takasaki, Gunma USA JAPAN Prof Silverma. .J n Dr. A. Hummel Universit Marylanf yo d Intel-university Reactor Institute Lab. for Radiation and Polymer Sciences Mekelweg 15 Departmen Chemicaf to Nuclead lan r Engineering 2629 JB Delft College Park, MD 20742 2111 THE NETHERLANDS USA

Dr. Z. Zagorski Prof. A.S. Huffman Institute of Nuclear Chemistry Universit Washingtof yo n and Technology Bioengineering, FL-20 . Dorodnul 6 1 a Seattle, WA 98195 03-195 Warsaw USA POLAND Prof. R.H. Schuler W.G. Dr . Burns Radiation Laborator Departmend yan t UKAEA Harwell of Chemistry Didcot Oxon 0X11 ORA University of Notre Dame UNITED KINGDOM Notre Dame, Indiana 46556 USA Dr. G.V. Buxton Cookridge Radiation Research Centre Prof. A.K. Pikaev University of Leeds Institute of Physical Chemistry Cookridge Hospital Academy of Sciences of the USSR Leeds LS16 6QB Leninski Prospekt 31 UNITED KINGDOM 117915 Moscow GSP1 USSR Prof. G.O. Phillips The North Wales Institute of Higher Education Dr. V. Markovic (Scientific Secretary) Kelsterton College IAEA Conna Quay. hS R , 4B Clwy 5 CH d Wagramer Strasse5 UNITED KINGDOM P.O. Box 100 A-1400 Vienna AUSTRIA

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