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STELLINGEN BEHORENDE BIJ HEJ FROEFSCHRIffT VAN R. FURLER 1. De episoomtheorie over het ontstaan van het mitochon- drion is weinig plausibel. R.A, Ratt and H.R. Mahler, Science 221 O972),575 2, Doordat S. Cirendini et al. de dragergassnelheid aan 'aet einde van een chromatografische kolom gebruiken, ontstaat een geflatteerd beeld van de weergegeven re- sultaten. Tevens is het niet mogelijk een dragergas- snelheid te berekenen zonder dat men de interstitiële porositeit kent» S, Cirendini, J. Vermont, J.C. Gressin and CL. Guilleain , J. Chromat. 84 (1973),24 3. De in de mode zijnde bepaling van RNA-moleculair ge- wichten door metingen aan formaldehyde behandelde RNA's berust op dubieuze aannamen. J.M. Kaper and M.E. v/aterworth,Virology 51 (1973),183 T.O. Diener and D.R. Smith, Virology *£ (^973), 359 M.M. El Manna and G. Bruening, Virology 56 (1973),198 4, Op grond van de zeer grote verschillen in stralingska- rakteristiek van de isotopen 1-131 en 1-123 is het streven van isotopenproducenten om een zo 'schoon' mogelijk 1-123 voor diagnostische doeleinden te leve- ren in strijd met de volksgezondheid, doordat de ver- tragingen#die dit oplevert onnodige stralingsbelasting voor patiënten veroorzaakt. H. ïlishiyama et al. J.Nucl.Med. 1£ (1974),261 5« De analogie die Gilbert et al. opmerken tussen de "exchange peak" in de kolom vloaistofchromatografie met behulp van ionenwisselaar en de luchtpi.ek bij gaschromatografie is twijfelachtig. T.W. Gilbert and R.A, Dobbs, Analyt.Chem. 45 (1>73), 1390. ~^ 6. De aanname dat Rhizobia een tumorvormende bakterie als evolutionaire voorouder hebben gehad, die een plasmide met stikstoffixatiegenen verwierf is aan- trekkelijker dan de aanname van Dilworth en Parker dat zij een zelf-voorzienende stikstofbindende bakterie als voorouder hebben gehad. M.J. Dilworth and CA. Parker, J.Theoret. Biol. 2£ (1969),203 7. De verwijdering van thallium matrices door middel van extractie met 2,2' dichloorethoxyethaan ten behoeve van sporeanalyse levert een onvoldoende decontamina- tiefaktor. P.I. Artyukin,E.N. Gil'bert and V.A. Pronin, Trudy Kom. analit. Khim. 16 (1968)^69
J'L... INFLUENCE OF CH&MELWIDTH IR GAMMA-RAY SPECTROMETRY and two other contributions to activation analysis
ACADEMISCH PROEFSCHRIFT
ter verkrijging van de graad van doctor in de wiskunde en natuurwetenschappen aan de Universiteit van Amsterdam, op gezag van de Rector Magnificus Dr. A. de Froe, hoogleraar in de faculteit der geneeskunde,in het open- baar te verdedigen in de aula der universi- teit (tijdelijk in de Lutherse Kerk, ingang Singel 411, hoek Spui) op woensdag 12 juni 1974- des namiddags te 4- uur.
door ROBERT FURLER geboren te amst^rdam PROMOTOR : Prof.Dr. G. den Boef GOPROMOTOR : Dr. H. Poppe CO-REFERENT: Dr.Ir. H.A. Das CONTENTS
page
Voorwoord I
Introduction II
Summary IV
Samenvatting VIII
A statistical approach to the choice of 1 channelwidth in gamma-ray spectrometry using empirical relations between resolution and gamma-ray energy
A statistical approach to the choice of 20 channelwidth in gamma-ray spectrometry II. The use of semi-empirical relations between resolution and gamma-ray energy for Nal(Tl) scintillation detectors
The exchange behaviour of inorganic thallium compounds on hydrated antimony pentoxide
Electrodeposition on copper powder as a means 37 of separation for trace analysis of noble metals in activation analysis, a tracer study
-I-
VOORWOORD
Dit proefschrift beslaat mijn werk dat in de tijd dat ik op het laboratorium voor Analytische Scheikunde heb gewerkt tot een afgerond resultaat is gekomen. Diegenen die hun heel direkte bijdrage aan de verschillende delen van dit werk gegeven hebben zijn vanzelfsprekend co-auteur van de artikelen. Anderen zijn promotor, copromo- tor en coreferent, één heeft een dubbelfunktie. Dat heeft tot gevolg dat al diegenen die op iets minder di- rekte manier hebben geholpen niet worden genoemd. Daar zou ik iets aan kunnen doen door iedereen persoonlijk in dit voorwoord te bedanken. Maar ik ben bang dat ik niet in staat ben dat te doen zonder dat het onecht klinkt. Ik doe het daarom liever niet, in de hoop dat ik iedereen die me hielp direkt heb later, merken dat ik daar blij mee was. Als dat niet altijd duidelijk is geweest, dan spijt me dat en dan wil ik alsnog zeggen dat ik iedereen voer allo hulp erg dankbaar ben. : . ••••. •' •'• • • '•• •-...: . •-il—"- •' •••. ' • • "• •-•.••;• ••' - :••••: •
INTRODUCTION ! i . i i The content of this thesis can be divided into tv/o parts. The main part, consisting of two papers, deals with the influence of the choice of channelwidth on the overall i resolution in gamma-ray spectrometry. The other two papers : describe separation systems for activation analysis. In all the studies we have made, our aim was to ensure a relative simplicity in the actual application of the subject under consideration. This simplification applies to the separation systems as well as to the influence of channel- width on the gamma-ray spectrum. In analytical chemistry it is quite common to consider those factors that affect the precision of spectrometric systems. Thus, in gamma-ray spectrometry using multichannel analyzers, the influence of the radiation detectors and the electronics involved on the broadening of the gamma peak is widely recognized. Although the influence of the finite energy content of a channel of a multichannel analyser on peak-broadening is known in a qualitative way, a systematic and quantitative v treatment may be helpful in the optimization of the spectrometric system for a specific problem. We dealt with this problem for Ge(Li) and Nal(Tl) detectors in our first and second paper, using two different relations between detector resolution and gamma-ray energy. i The need for a knowledge of the precision of the measured j peak as a function of the gamma-ray energy exists especially when it is necessary to measure at the same time higher and lower energy gamma rays with a multichannel analyzer with small memory capacity. This occurs especially when one wishes to determine , palladium, silver, platinum, gold and mercury in one step by activation analysis using Nal(Tl) scintillation detectors ( and a low cost multichannel analyzer for reasons of simplicity \ and wider applicability. A separation system for these metals I b,7 means of electrodepositiön on copper powder is described h in ïthé,;- fourth paper. •.':••• ,. • .: • "' • •.
'it. -•'••. .... V/hen this separation system is applied to a thallium matrix the need arises to ensure/better matrix decontamination than can be attained by eiectrodeposition. Therefore we evaluated the possibilities of Hydrated Antimony Pentoxide : for different thallium compounds, the description of which can be found in the third paper. All research described in the four papers which form this thesis originated from the problem of determination of noble metals in thallium matrices. We hope that this contribution is a step forward towards the solution of this problem. -IV-
SUMMARY f. A STATISTICAL APPROACH TO THE CHOICE OF CKANNELWIDTH IN ' GAMMA RAY SEECTROMETRY USING- EMPIRICAL RELATIONS BETWEEN" RESOLUTION AND GAMMA-RAY ENERGY
R. Furler and H. Fcpp.e
J. Radioanalyt. Churn. (197*0 in press
In gamma-ray speetroinetry, the finite channelwidth of a multichannel analyz.er influences the resolution of gamma peaks obtained from the detector. In deciding which number of channels to USG for a certain energy range there are always two compromises to be made: first that between the largest possible energy range and the smallest number of channels, and secondly that- between the too small number of channels for the low energy gamma peaks and the too large number of channels in the high energy region. . Both compromises can be made when the influence of the choice of the channelwidth on the broadness of the registered gamma peak is known. This influence can be estimated by comparing the registered peak in the histogram form as obtained from the multichannel analyzer, with the gamma peak delivered by the detector system itself. As a measure of comparison the normalized central second moment is Used. Prom this comparison it is possible to derive an expression for the extra peak-broadening " 'caused by the channelwidth and also for the channelwidth, .. once the value for the extra peak-broadening is accepted as bolerableV This expression also contains the relation between the detector line width and the gamma energy., ; For four types of Nal(Tl) scintillation detectors we' constructed; graphical straight line fits to the resolution data. Each detector was represented by two lines: cne for the lower energy and another for the higher energy part.
...t-.....-j.t ".1M-.L- •'•{ •• ...-«Slf. .L.fe.i. _._ _.. . i/ƒ • For GeCLi) drift 'detectors we derived an empirical logarithmic, relation between the;energy and resolution. Graphs of the percentage of extra peak-broadening.as a. function of: channelwidth and energy are constructed as : examples of the.possible applications. Eased upon estimates it is' then-possible to test the reliability of standard' spectrum catalogues and of specimens from the literature on-activation analysis* It appeared that the extra peak-broadening is sometimes unnecessarily large and sometimes-completely negligible» in the latter case causing a rather inefficient use of spectrometer
: •• •"• capacity. : . :•;'.. ..'^ "-' .'••. '•'. -• ••'. • ;.. • • <•./.•;.• . "• It is also possible for the .analyst to. achieve the ; compromise; mentioned, in .the first line in a.relatively simple way-, based on an estimate of necessary error.
2 o A STATISTICAL APPROACH TO TOE CHOICE' OF CEANNELWIDTH IN - GAMMA-RAY SPECTROMETRY II the use of semi-empirical relations between resolution and gamma-ray energy for Nal(Tl) scintillation detectors
R. Furler
J. Radioanalyt. Ghent., submitted for publication
In the first "paper on this subject we have developed by statistical means equations describing the percentage of extra peak-broadening caused by the finite channelwidth ' 'in multichannel- gamma-ray, spëctrö'metry. For application - of these'equations, it is; necessary,tó have a"relation •.. between debeetor ,r/esolution,, and gamma-ray energy* . . , ,, In this paper, we „apply this treatment 'to a semi-empirical ~ second-order equation fitting thé experimental resolution data of Nal(Tl), scintillation detectors, instead.of two • graphic ally/ fitted straight;; li-nes. In .this, way the ..' -:
disadvaritage that%two functions are used to describe '' , onjè detector has been overcome; . The general ;=f óï-mula ,of the; secönd-rrder equation was obtained by combining a statistical consideration of the - electron multiplication ."process in thé photoaultiplier
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y'',.J*'":'V: "• -VI-
with the empirical energy dependence of photon production in. the scintillator and photon transfer from the scintillator to the photomultiplier. This general formula is fitted to the data by means of a least-squares.fit. Three simplified fitting methods are presented» each one involving less work but also showing decreasing precision. It appeared that for many cases where only rough estimates of thé channelwidths are desired, no detecor specifications are required to estimate the percentage of extra peak-broadening. We recommend to use the mean values of the constants determining the second-order equation obtained from our detectors. A graph representing this case is given for general use.
3• THE EXCHANGE BEHAVIOUR OF-INORGANIC THALLIUM COMPOUNDS ON , HYDRATED ANTIMONY PENTOXIDE- ; ; .:. .• '• ,
R. Furïèrj Ingrid E.C.P.M. Licht and J.P.M, van Heijst
Radiochem. Radioanalyt. Lett* (1974)» in press
In the study for inulti-element trace: analysis and the
analysis of mercury and .some:noble metais in thallium matrices by activation analysis, the possibilities of hydratéd antimony "pentoxide (HAP) as bulk activity remover and as,matrix decontaminant are evaluated. We studied the behaviour of five different thallium compounds in six different media in column experiments. It appeared that 14- M HNO, and 6 M HCIO^ arèrünsatis- ' fac'tory media for the adsorption of thallium compounds '- on HAP. In 6 M HC1 this applies only to TlpO,. In 7 M. and 1 M HNC^,/l M HClO^ and 6 M HC1 a single-st^p exchange is|quite useful for the removal of bulk activity.
Multi-ötep exchange permits analysis of traces in all
thallium compounds, studied. ;_ :; : '. • • . ' :.•••"• -VII- • •'• •;•:.. .•;.%' ••• v..:/- '""•'•-••':
4. ELECTRODEPOSITÏON ON POPPER.POWDER.AS A MEANS OF SEPARATION FOR TRACE ANALYSIS OF; NOFLE METALS.IN ACTIVATION ANALYSIS/A TRACER STUDY
R. Furler,'Ingrid E.CP.M. Licht, J.K.L, Offenberg and
H.L. Polak •-••'• :
J. Radioanalyt. Chem., submitted for publication
This paper describes a tracer study of the electro- deposition on copper powder of metals with abnormal potential above that of the Cu(li)/Cu couple. The conditions which the deposition system was supposed to •fulfil,;1 e.g. simple arid quick performance, the use of a simple chemical environment and the possibility of application of NaI<[Tl) detectors, are all met, . The deposition was performed by sucking the tracer solution through a column filled With copper powder. It appeared possible to obtain nearly complete deposition of palladium, silver, platinum, gold and! mercury,whereas ruthenium, osmium and iridiuin were hardly deposited, probably due1 to kinetic barriers. .The medium for this : . exchange was 1 and.: 1,5: M HNÖ, and Ce(IV); carriers were, added at about 100 /«g quantities for each element.
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SAMENVATTING
1. EEN STATISTISCHE BENADERING VAN' DE KEUZE VAK' DE KANAAL- B3EEDTE BIJ GAMMA SPECT5ÖMEIRIE M.B.V. EEN EMPIRISCH VERBAND TUSSEN HET OPLOSSEND VERMOGEN BH DE GAMMA ENERGIE
R. Furler en H.Poppe J. Radioanalyt. Chem. (197^), in druk
De breedte van gamma pieken, zoals die wordt gemeten in de gamma spec-trometrie wordt beïnvloed door de eindige breedte van een kanaal van een meerkanaalspulshoogte- analysator. Bij de keus welk aantal kanalen moet worden gebruikt voor een bepaald energiegebied moet daarom al- tijd een compromis worden gesloten. Dit compromis behelst twee dingen: ten eerste zal men een zo groot mogelijk energiegebied in zo weinig mogelijk kanalen willen meten, waarbij, ten tweede, verdisconteerd moet worden dat er aan de lage energiekant te weinig en aan de hoge energiekant teveel kanalen per piek zullen worden gebruikt» Een dergelijk compromis is te sluiten als de invloed van de kanaalbreedte op de piek bekend is. Dit probleem kan worden bekeken door vergelijking van de door de detector gemeten piek met de geregistreerde piek. Als vergelij- kingsmaatstaf is het genormaliseerde centrale tweede moment gekozen. Daarmee is het mogelijk een vergelijkijag af te leiden waarmee het percentage extra piekverbredtng wordt gegeven terwijl ook een vergelijking is te geven voor de kanaalbreedte wanneer een bepaald percentage verbreding acceptabel wordt geacht. In deze vergelijkin- gen zit het verband tussen de detector piekbreedte en de gamma energie opgesloten. 3ij yier typen Nal(Tl) scintillatiedetectoren werd gra- fisch een rechte geconstrueerd door de gemeten resolutie waarden. Elke detector was door twee rechten gerepresen- teerd, één voor het lage en êên voor het hoge energie deel. Voor Ge(Li) drift detectoren leidden we uit de meetpunten ._ *ni ^ .. , * -IX-
een empirisch logarithmisch verband tassen energie en resolutie af. Ter illustratie van de toepassing construeerden we een aantal grafieken, waarbij de piekverbreding als functie van energie en kanaalbreedte, dan wel kanaalbreedte als functie van energie en toelaatbare fout werd weergegeven. Het is dan mogelijk de betrouwbaarheid van standaard- spectrum catalogussen en van de spectra van literatuur- artikelen te controleren. Het blijkt dat de extra piekverbreding in sommige ge- vallen onnodig groot is, en in andere gevallen volledig verwaarloosbaar» In dit laatste geval kan soms worden gesproken van een niet efficient gebruik van de meer- kanaalsanalysator. Het is dus voor de analyticus mogelijk op een tamelijk eenvoudige manier het compromis, in het begin genoemdj te sluiten.
2, EEH STATISTISCHE BENADERING VAN DE KEUZE VAN DE KANAAL- BREEDTE BIJ GAMMA SPECTROMETRIE II het gebruik van een semi-èmpirisch verband tussen het oplossend vermogen en de gamma energie voor Nal(Tl) scintillatie detectoren
R. Purier
J. Radioanalyt. Chem., ter publicatie aangeboden
In he,t eerste artikel over dit onderwerp leidden we d.m,v. een statistische behandeling vergelijkingen af voor het percentage extra piekverbreding dat ontstaat tengevolge van de keuze van een eindige kanaalbreedte bij gamma épectrometrie met behulp van een meerkanaals- pulshoogteanalysator. De toepassing van deze vergelijkin- gen vereist de kennis van het verband tussen detector resolutie en de gamma energie. In <üt artikel wordt een semi-empirische tweede orde vergelijking afgeleid om dit verband weer te geven voor Nal(Tl) dstectoren» Dit vervangt de twee rechte lijnen . die wij eerder voor hetzelfde doel gebruikten* zodat het nadeel dat één detector door twee vergelijkingen moest worden beschreven, kan worden ondervangen. De algemene gedaante van de tweede orde vergelijking is verkregen door een statistische beschouwing van het electronvermenigvuldigingsproces in de photomultiplier te koppelen aan de empirisch gevonden energieafhanke- lijkheid van de fotonproduktie in de scintillator en overdracht van het foton naar de fotokathode. De konstanten van deze algemene vergelijking zijn be- paald door de vergelijking aan de meetpunten aan te passen door middel van de methode der kleinste kwadraten. Ook zijn er door ons drie eenvoudiger methoden aange- geven ter verkrijging van de konstanten. Deze vereen- voudigde methoden vereisen veel minder werk, wat ten koste gaat van de precisie. Het blijkt dat,, in die gevallen waar een grote precisie niet vereist is, zelfs geen enkel specifiek detector gegeven noodzakelijk is om een acceptabele schatting van het percentage extra piekverbreding te geven. In een dergelijk geval bevelen we aan de gemiddelde waarden van onze detectors te gebruiken als de konstanten voor de energiecurve. Een grafiek voor algemeen gebruik op basis hiervan is gegeven.
3. DE UITWISSELING VAN ANORGANISCHE THALLIUM VERBINDINGEN OP GEHYDRATEERD ANTIMOON PENTOXIDE
R. Furler, Ingrid E.C.P.M. Licht en J.P.M, van Heijst
Radiochem. Radioanalyt. Lett. (1974), in druk
Ten behoeve van multi-element sporeanalyse en van de ana- lyse van kwik en enkele edele metalen in thallium d.m.v. aktiveringsanalyse zijn de mogelijkheden van het gebruik van gehydrateerd antimoon pentoxide (HAP) ter verwijdering van grote hoeveelheden matrix aktiviteit onderzocht. Hiervoor is de adsorptie van vijf verschillende thalliua souten in sea verschillende media in met HAP gevulde -XI-
kolommen onderzocht. Het blijkt dat 14- ïï HNO, en 6 M HCIO^ niet voldoen als medium. In 6 M HCl blijkt alleen Tl^O-, niet aan HAP te adsorberen. Een enkelvoudige uitwisseling in 7 M en 1 M HNO,, 1 M HCIO^ en 6 M HC1 blijkt uitstekend te vol- doen om de grootste hoeveelheid thallium te verwijderen. Om een redel.i jke matrix decontaminatie ten behoeve van sporeanalyse te bereiken is herhaling van het adsorptie- proces noodzakelijk.
DE ELECTRODEPOSITIE VAN EDELE MEPAKEN OP KOPERPOEDER ALS SCHEIDINGSMETHODE IN AKTIVERINGSANALYSE, EEN- TRACER STUDIE
R. Purier, Ingrid E.C.P.M. Licht, J.K.L. Offenberg en
H.L. Polak
J. Radioanalyt. Chem., ter publicatie aangeboden
In dit artikel wordt een tracer studie naar de electro- depositie aan koperpoeder van metalen met een normaal potentiaal boven die van het Cu(II)/Cu koppel beschreven. De eisen die aan het uitwisselingssysteem zijn gesteld zijn alle vervuld. Gedacht wordt hierbij aan een snelle en eenvoudige uitvoering, het gebruik van een eenvoudig me- dium en de mogelijkheid om Nal(Tl) detectoren te gebrui- ken.
De uitwisseling werd verkregen door de oplossing met de te bepalen elementen door een met koperpoeder gevulde kolom te zuigen. Het blijkt mogelijk om een vrijwel volledige reductie tot de metallische toestand te verkrijgen van palladium, zilver, platina» goud en kwik. Ruthenium, osmium en iri- dium worden nauwelijks gereduceerd, waarschijnlijk ten gevolge van het optreden van kinetische belemmeringen. Het medium waarin de uitwisseling werd gedaan was 1 en 1,5 H HHOi en Ce(IV:); de gebruikte hoeveelheden carrier zijn ongeveer 100 pg per element*
A STAI'LSriCaL APPROACH TO THE CHOICE OF C.HA11HELWIBTH IN GAMMA-RAY SPttCTROMETRY USING EMPIRICAL RELATIONS BETWEEN RESOLUTION .SAD GAMMA-RAY ENERGY
R. Furler and H. Poppe
Laboratory for Analytical Chemistry, University of Amsterdam, Amsterdam, The Netherlands
SUMMARY The problem of extra peak-broadening, caused by the finite channelwidth in multichannel gamma-ray spectrometry is discussed, using empirical equations for the relations between resolution and energy in Nal(Tl) scintillation detectors and Ge(Li) drift detectors• Relations are derived and graphs designed to estimate the extra peak-broadening at a certain energy, caused by the compromise necessary when using a chosen energy scale in as few channels as possible.
INTRODUCTION In gamma-ray spectrometry the finite channelwidth influences the measured resolution of the gamma peaks. In deciding which number of channels to use for a certain energy range, there is always the compromise between the largest possible energy range and the smallest possible number of channels in order to take full advantage of the possibilities of modern pulse height analyzers. It would be convenient to have the means to judge which percentage of extra peak- broadening arises from a certain compromise. The problem statea is complicated by the,fact that the resolution- defined as Full Width at Half Maximum (FWHM) divided by the gamma-ray energy (E)-mcreases at decreasing energy in a non-linear way. When it is necessary to measure at the same time low (e.g. 0.05 MeV) and high (e.g. 2.5 MeV) energy gamma-rays when channelwidth is constant, a great number of channels is required to avoid deterioration of the intrinsic detector resolution at the lower energy end. This problem can be overcome by using multichannel analyzers with non-equal channelwidth. Kelley describes a system with a channelwidth proportional to v/Ë. AS a result the number of channels for each peak is about constant. The -2-
disadvantage of this system is the relatively complicated p channeiwidth adjustment. Maeder describes three different systems : a linear, a square root and a logarithmic energy scale* The first has the disadvantage mentioned above. The last system has the reverse disadvantage. The second system equals the one described by Kelley. More recently Tunnicliff* describes a system using a linear amplifier, followed by a logarithmic compressor eoupled with an equal-channelwidth multichannel analyzer. This makes it possible to measure 0.04 - 5 MeV in 255 channels with equal PWHM .for each peak. However, all systems using non-linear amplifiers and/or compressors have the disadvantage, in comparison with ?.inear systems, that the parameters are more susceptible to time and temperature change. This, and the fact that all commercially available systems work with linear amplifiers and equal-channelwidth multi- channel analyzers, causes the need for a simple tool in deciding which number of channels is necessary for an . energy scale of a specified range when accepting a specified loss of resolution. The purpose of this paper is to give such a tool, using empirical relations for the energy dependence of the resolution for both Nal(Tl) and Ge(Li) detectors. This is combined with a statistical analysis of the effect of channelwidth on the gamma-ray peak-broadening.
GENERAL CONSIDERATIONS The gamma-ray spectrometer is considered as a given system; the only variables being the detector and the channelwidth (implicating amplifiergain and conversion of number of channels to pulse height). When using a Nal(Tl) detector as an integral assembly, the intrinsic pc\k-broadening is for about 50# due to statistical fluctuations in the interaction between radiation and matter in the crystal, and for the other, half to statistical fluctuations in the electronmultiplication in the photomultiplier . The electronic devices make a negligible contribution to the peak-broadening. The total abs rption gamma peak is to be considered as gaussian iri^shape-5»6> • • -3- "• "• ' ' • ' :•
When using a Ge(Li) drift detector the peak-broadening is also partly due to the interaction between radiation and matter, but the role played by the contribution of the electronics of the preamplifier to the peak-broadening (mostly with a FET first staged is considerable'. Although there is a .linearrelationship between the FWHM and VE for the crystal, this relationship is seriously affected, especially at lower energies, by the preamplifier. Because the analyst is interested in the complete detection system, he has hardly any advantage of this knowledge'. Consequently we decided to neglect the physical background of the phenomena observed, and refrained from explanation of' the shape of the graphs obtained. ' •
STATISTICAL APPROACH When measuring a gamma-ray spectrum, the total absorption peak is considered as gaussian, having a standard deviation o-j.. The spectrum is measured with a multichannel analyzer with a channelwidth W. This finite width causes an uncertainty in the exact value of the measured E. This uncertainty will increase with increasing W and decrease with decreasing W, the limiting case occuring when W is infinitely small. In all normal cases a histogram instead of a continuous gaussian curve is observed: the count rate distribution curve. The problem is now how to compare this histogram in terms of peak width or resolution with the original gaussian curve. For this we need a measure in which the peak width of both gaussian curve and histogram can be expressed. This measure can be found in the square root of the normalized central second moment of the curves. We will denote this ff measure by rjiAp and we have thus defined:
| — ot>" M ƒ* C(E)dE —oo where C(E)dE is the count rate between E and E + dE. —if—
The choice of this measure for the peak width has a number of advantages, of which we mention: a) It is unambiguous- and relatively.easily manipulated mathematically,, b) For gaussian curves it coincides with the standard deviation. c) When different processes contribute to the width of the distribution curve, this width, expressed in the measure mentioned, can be found in most ce-ses by adding the contributions of all processes quadratically. d) If the distribution curve is gaussian, the amount which has a certain minimum distance from the mean can be found from tables for the areas under the standard normal curve. If the distribution curve is not. gaussian, an upper limit to such an amount.ia set by Tsjebyschew's inequality.
All this is well documentated in standard texts on statis- tics. For a number of cases we calculated o^p, defined above, expressed in cv,. We chose, values for W from 0»5°f up to 6(7. Further we distinguished cases A, where the . separation line between two channels coincides ..with the peak maximum of the gaussian curve, and eases B where the middle of a channel coincides with the maximum. These are the two extreme cases. The results are presented in figure 1. W For values of -^— < 2 the points are expressed accurately by the expression o%&p = a\ + \~ ' [2]
The relative channelwidth q is defined as W ' .- • iKserting [5] in [2] gives:
1 + -5-
Pig. 1 Application limits of statistical - approach with central second moment. O cases A * cases B. Straight line according to . aTAP " °\ + h
Although q. is more apt for calculations, it is more convenient to use the percentage of extra peak-broadening, caused by the choice of W. This percentage will be denoted by the symbol Q.
Let the relation between and E be: [6] Combination of [3] , [5] and [6] gives for values — < 2 the generally applicable formula: [73
In order .to measure «^ it is necessary to make Q as snail as possible. This has been done for the determination of X(E) in ars many channels as possible. The choice of the number of channels/peaJc is made in such a way that Q < 0 -6-
APPLICA'JION TO Nal(Tl) DETECTORS The resolution Nal(Tl) detectors is usually expressed as
To obtain a relation between 17 and E it is customary to 2 14 plot rj vs Ij Plots have been made for,four different sizes of Nal(Tl) crystals. An example of such a plot is given in fig. 2.
800-
Harshawa X3 w«Htype+EMI 3708 PM
Pig. 2 i?2.vs E~1 for 3"x'5" Harshaw ,. well type crystal; well 0 25.4 mm, deep 52 = nun coupled to EMI 9708 photomultiplier, All measurements are made with a Quartz & Silice pre- amplifier AS 02, Elrón baseline restorer BLR-N-1, and an Intertechnique DIDAC 800 Multichannel analyzer. Details of the detectors are the first four'entries in table "i. " ; • ' 8 Q 10 11 The agreement with other similar experiments '•*' is yood, differences be'.ng due to technical differences between —7—
TABLE:1 Constants-^ è, p /.. rësp. V , /$• for lower and higher . energy.^straight; line;fits for Nal(Tl) detectors
•. a 3(M E(IïeTD- detector ref.
: 7 •3.. 10-3 1 .92 .10-3; < 0 .333 1) 7 .6 .10"3 1 .24 ..ib"5-v < 'O .200 present 10~5.. 3) authors 5 5 ••••, • 6 .9 ..10" -. ';. "1.38. ^.io" - < 0 .140 4) 5 5 1 0 * .7 .10- ;; •29 .:io~ -.' • 5) 9 ; 1Ö"3 .• 2 .4 . .•••;;'1-' '4.172 6) 8 •• ~3 ••• 5 •1; 4 .50. .ib"' '' '-•.<• 0 .8;' 7) 10 5 4 .28. 10" ' .. •'* 1 . .91 0 .&!" •"• 10 ,10-? ^<- 7) 3 ; IQ- .08 ••'•<'- .8 >' • 2 10 .70. ... . • b. 5 • " . ^ 7) 5 4 .80. 1Q- ' 1 ,67, 1 1 \j/' b..8: • ?) 10 V 6 .03. : .-.I',62 , v< Q?,3 ••'••.;• 7) ' 10 8;'•' •• . 34.iS' : 1 •76. ;.<• 0, 7) 10
a' (MeV) •••;•'-. •".. E(MëY) detector , ref.
' '"?•'•
1 .4 , 10-3 :$, .85. ••••>'; 0.
1 •7 . ,64. :•••• '2) i present *• 2. ö;. 1' 3) ! authors 5 5 1 iov -..-.: 38. 1;b" 0. 25Q • 4) 0 *3'V 10"5 0. w.10"5 <• 5) 3 1rO""3 f 1 .7 .'10" 2. 5 . > 0. 275 ] 6). • [ 10-5 4; 06. 10"5 - 8); -1 11;:
* 'not specified
1) 3"x3" Quartz',&,,Silice ,+ RCA PM 2) 3"x3" Harshaw ..welltype + E^I _. ,9708" ! 3) '2"x2 i' Ilarshaw ,,,•• " , : +- EMi.A. 9656 •PM,' 4) 2''x2:üra Harsha'// •'-•. ..EMI/." 9656 PM'"' 5) 1i"x1" , * ' , ..+ 'DuMont 6292 ' PM ' 6) 3"k3" '-.-*V- « iiuMont 6363 PM 7) different siues • of crystal,: ' details not specified ;;;- , 8) + DuMoht 6292 PM
• •*) .
* 'i'? cietectors.. The only exception, are the 'data of Bernstein As indicated- by Bissl and Zappa and Bernstein" it is Ï to fit the lower energy with a straight line of the ground. formula n - <*. + 4 ..The experimental data of Kelley afford the same possibility. Por the higher energy part it is also possible to give a straight line fit,as has been done, by Kelley and Julke . When using the above general formula the constants a andp will be denoted with a prime. The constants <*,/> resp. or1, /J' are-summarized in table/?, together with earlier data. Reference numbers are given in the last column. Having three variables (Q, W and E) it is possible to approach the problem of how to choose the energy range relative to the number of channels in two ways. The first, which will be dealt with in this section and the next is to choose first the maximum tolerable value of Q» . It is then possible to plot a graph that gives W at each energy E. • , ' ' . . : : The second is to plot Q, at a given value of W, as a function of; E. This approach will be dealt with later. The plots of-W against the photon energy E were constructed for the values of.Q and corresponding values of q which are presented in table 2. '.'. . .
TABLE 2 Q values and q values used in constructing plots of figures 3 and 4
30 2.03 10 1.12 0.60 1 0.35, 0. 3 Oil 9 - 0.1 0.11
*•.•«.-.:•: .A:-.!-. -9-
The empirical relation GO was £ound for the Nal(Tl) detector.
Recalling that r, = 1™. and that aE = 0.425 PWHM for a gaussian peak shape, the function a_ = x(B) is:
Jf(E) = 0.425 \/aE2 + /JE [9]
Using eq« [3] the expression for W becomes;
W = 0.425.103.q where a factor of 1Cr is introduced in order to obtain W in keV instead of MeY, Equation pO] is plotted for different values of Q for the lower and the higher energy range, plotted in one graph (figure 3).
<*- 30 10 3 1 as 11 W 90 5 18 180 29 • 80 7 4 TO 40 20 «0 40 too 30 S 3 t SO IS 4 40 I 2 20 K» 30 a S
20 3 10 9 1 10 1
Fig. 3 W for four different values of Q as a function pf £
. Jit -10-
APPLICATION TO A Ge(Li) DBIFQ? DETECTOR The resolution of a Ge(Li) detector is usually expressed in terms of FWHM. Experiments' have led to the conclusion, that about 80$ of the apparent resolution is due to the FET- preamplifier noise. The theoretical relation between FWHM and E would be
FWHM = constant . E*
In measuring the features of a complete detector system, this relation does not apply, with the greatest deviation at the lower energy part. The relation between the resolution and the gamma-ray energy is usually plotted as FWHM vs log E. The behaviour of the detector system we used (Quartz & Silice true coaxial Ge(Li) detector + Nuclear Diodes preamplifier 101 A, Elscint amplifier CAV-N-1 and Nuclear Dicdes "Kicksort" 4-056 channel analyzer) was plotted in the same way. This plot is in good agreement with the 7 ' curves reported by Heath •• This plot, however, is not easily converted into a handy tool for analyst's for the choice of the channelwidth in the same way as the Nal(Tl) resolution/energy plots. We there- fore recommend a plot of log »? vs log E, which gives a linear relationship for both lower and higher energies, similar to NaI(!Tl) detectors (figure 4-).
woo
100 -vW
W
i,
Fig» 4- log n vs log E""1 for a Ge(Li) detector -11-
The empirical relationship for the two straight line fittings will then be:
log ri = log p - r log ~- [11] E° The energy E° is introduced to acquire a logarithm from a dimensionless quantity. E° is chosen 1 MeV. The advantage of this will be seen later, ! When E = E° s 1 MeV log 17 = log p Using the definition of »j, the relation
n Trr PWHM = 2-^ [12] E°" can be derived.. The function A"(E) for a Ge(Li) detector will be then:
Combination of [3] and [13] multiplying by 10* in order to have W in keV, and inserting E° = 1, gives:
W = q.105.0
The values of p, r and p•, r' (for higher energy) are given in table 3»
TABLE 3 P> ^ and p', r' derived from fig
T = -0.J538 E< 0.5MeV p1 = 4.36.10,-3~ r' = -0.8259 E >
In the same way as for Nal(Tl) detectors, plots are made for the Ge(Li) detector with W as a function of Q vs E (figure 5).
fc' . '. L t -12-
30 03 ai
Ge(Lt)drm dttoctor
00)004 031
03 003
OM
003 oo;
««oot
1.0 1.9 20
Fig. 5 W vs E for four different, values of Q for a Ge(Li) detector
GRAPHS OF Q vs E AS A FUNCTION OF IV As indicated earlier it is possible to plot the three variables in another way. Which way is more convenient is up to the analyst. In gamma spectrometry, using a given multichannel analyzer, a reverse approach can often be made to the problem of choosing the channelwidbh. When a certain energy range has to be analyzed with a given analyzer it is possible to give in advance sx\ estimate of the possible values of W. It is then more convenient to have a graph giving the relation between Q and E as a function of W. This can be done with eq. [7] and [9] for Nal(Tl) detectors and [?] and [13] for Ge(Li) detectors, using the appropriate constants <*, p resp. a1, /$' and p, r resp. p', r'. In figure 6 such a plot is made for the. lower energy range of one of the Nal(Tl) detectors used. Plots like this are very system dependent, so we give only one graph as an example. -13-
XJOOi
1O0C
woo I OMl
owe
coo» OO3O 0300 , — O30O 0300
Fig. 6 log Q vs E for four different values of W for the lower energy part of si Nal(Tl) detector
APPLICATION OF THE CRITERIA DEVELOPED The criteria derived for estimating the extra peak- broadening due to the choice of the chumielwidth are not only useful for the analyst in his direct work (the main purpose of this study) but can also be applied to spectra mentioned in the literature in order to judge their reliability. >.'.'• We have selected the standard spectra published by Heath1^. 1-5 14 Crouthamel , Adams and the criteria for Ge(Li) detectors developed by Heath . The Nal(Tl) spectra compiled by Heath12 are plotted with a value of W, varying between 0.5 and 2 keV, with the en exception of -"Co, with W = 0,25 keV. The most frequently used value of W is 1 keV.
Using the criteria for W » 1 keVt the values of Q at E = 0.025 MeV are between 0.1 -0.3%. In the 1 MeV-regron Q is-"smaller than 0.001JK. The conclusion is that the spectra are very accurate, but the use of the «pectsropieter is rather inefficient. In the spectrum catalofeu» coapiled by Crouthamel^^, which
. -14-
14 are also included in the work of Adams , there is a different value of VI for each spectrum, probably to ensure more efficient use of the multichannel analyzer. In table 4 a small number of isotopes are chosen for assessment by the present criteria.
TABLE 4 Peaks in some Nal(Tl) spectra from the Crouthamel catalogue
Isotope E(MeV) W(keV) (aw , , . . i • ft 7Be 0.480 2 .75 ca 0.21 38 K 0.511 6 • ca 0.7 2.167 ca 0.1 Fe 0.141 5.7 ca 3 0.191 ca 2.3 1.100 ca 1 1.290 ca 1 600o 1.17 12 .9 ca 1.2 1.33 ca 1.0 0.032 3.2 ca 8.4 0.662 ca 0.14 •05Hg 0.077 2 .9 ca 2 0.279 ca 0.3
The conclusion is that this catalogue was made with an acceptable compromise between accuracy and efficient use of the analyzer. From the Ge(Li) spectrum cataloque included in the work of 14 Adams the same isotopes-are selected; two isotopes are . added, having low E and/or X-rays (table 5)» The conclusion of this brief survey is, that the spectra have a much greater peak-broadening than those recorded for Nal(Tl) detectors. This may be acceptable, due to lack of memory capacity of multichannels especially when spectra with both higher and lower energy are recorded at the same- time (e.g. ** Fe). But in cases where this is not necessary (e.g. both Hg-isotopes), a smaller value of W should have been selected for a standard catalogue. It should be noted that for Ge(Li) detectors with even better resolution than TABLE 5 The Q value of peaks in some Ge(Li) spectra from the Adams and Dams catalogue
Isotope E(MeV) W(keV)
Be 0,4776 0.97 ca 8 0.5110 1.0 ca. 8 2.1668 ca 18 0.1425 1.01 ca 24 0.1925 ca 18 1.0986 ca 15 1.2915 ca 13 60, Co 1.1731 0.97 ca 15 1.3324 ca 13 60ra Co 0.0585 0.5 ca 0,0322 0.69 ca 9 0.0364 ca 9 0.6616 ca 2 197m Hg 0.0688 1.00 ca 13 197 0.0776 ca 13 0.0780 ca 13 0.1339 ca 11 0.1914 ca 10 203'Hg 0.0729 1.01 ca 13 0.0826 ca 13 0.2791 ca 10 our detector, the values of W used by Adams lead to greater values of Q. Next we made a comparison between our criteria and those mentioned by Heath' for Ge(Li) spectra. Heath states that for obtaining adequate information a given peak must have a value of 5 channels FWHM. This criterium corresponds with '•' 15 FWHM, i.e. T-TTTnJïT • "F» giving Q = 2.3*. Applied to an energy range between 0.1 - 2 MeV, and Q = 2.3, for the 0.1 MeV peak in this range 12,000 channels of equal width (0.15 keV)are needed. The need for a compromise is evident. Heath suggests values for W as a function of each range, which are summarized in table 6. In the third column the value of Q for the highest value of E in the first column is given, in the fourth Q value for 0.05 MeV, which is taken to be the lowest energy in the range. -16-
TABLE 6 Q values for W values for Ge(Li) detectors recommended by Heath
E(MeV) W(keV) Q for E Q for E = 0.05 <*) (#) 0.05 ca 13 ca 13 0.10 0.15 ca 12 ca 13 0.30 0.20 ca 12 ca 16 0.60 0.2? ca 15 ca 18 1.00 0.34 ca 14 ca 21 2.00 0.46 ca 11 ca 26
Conclusion: The rule of thumb given by Heath is useful for values Q in the order of magnitude as Adams uses for standard spectra, but gives no insight into the exact nature of the compromise. As a last application we checked a random selection of gamma spectra in papers dealing with complex spectra in activation analysis. This is not easily done,, because most papers do not give sufficient information for the calculation of W. In table 7 this survey is given. Especially in the investigation described in ref, 15 and 1?» in our opinion, the compromise between use of multichannel capacity and accuracy is not quite adequate. In all comparisons made in this section, the value of Q is an estimate, because the exact value will depend on the detector used. TABLE 7 Application of our criteria to some papers detector W(keV/ch) lowest energy highest energy Re*. subject used ______. _p_eak peak "isotope" E(MeV) isotope E(MeV)
Ge(Li) 2 0.1584 ca 30 «So.' 0.8894 ca 15 15 noble metals in lead beads, matte platina ores Ge(Li) 0.5 0.1033 ca 12 0.9535 ca 6 . 16 rare earths elements with group separation Ge(Li) 2.9 198AU 0.4-10 > 30 2.110 ca 15 17 trace elements in atmospheric pollutants Nal(Tl) 11 19a__ ca 12 12*Sb 1.690 ca 0,7 18 gamma spectra of irradiated Rh- sponge
Nal(Tl) 5 0.069 + ca 6.5 2O5Hg 0.279 ca 1 19' simultaneous 0.077 determination of Ag, Au and Hg in S Pb -18-
CONCLUSION . The approach to the choice of channelwidth made in this paper enables the analyst to make a good estimate of the percentage of cxtx'a peak-broadening as a function of the energy, OI1CÓ the channelwidth is chosen, or to choose the channelwidth*when a certain extra peak-broadening can be tolerated. When a compromise is necessary and the per- centage of peak-broadening, especially in the lower energy region is large, he will have an exact value of the error made for each energy, when using graphs such as figure 6.
In our opinion values of Q up to 5# at lower energies are acceptable for complex spectra up to 2 MeV. In gamma-ray spectromstry errors of the kind described here are in- avoidable. It is believed that up to now most spectra have been recorded by virtue of much experience.and a certain percentage of intuition. It is probably better to exclude the intuition and replace it by the percentage of necessary error.
REFERENCES • 1, G.G. Kelley, Nucleonics 10 (4) (1952) 34 2. D. Maeder, Rev.Sci.Instr. 26 (1955) 805 3. L.D. Turinicliff, R.C. Bowers and G.E.A. Wyld, Modern Trends in Activation Analysis, MBS Spec.Publ. 312 Vol. II p. 1049 (1964) 4. J.:?. Birks, The Theory and Practice of Scintillation Oounuing, Pergamon Press, Oxford (1967) 5. B.R. Kowalski and T.L. Isenhour, Anal.Chem. 40 (1968) 1136 6. K.L. Heath, R.G. Heimer, L.A. Schmittroth and C.A. Cazier, Nucl.Instr.Meth. 4£ (1967) 281 7. R.L. Heath, Modern Trends in Activation Analysis, IBS Spec.Publ. 312 Vol. II p. 959 (1969) 8. G.G. Kelley, P.R. Bell, R.C. Davis and K.H. Lazar, Kusleonics 14 (4) (1956) 53 9. W. Bernstein, Nucleonics 14 (4) (1956) 46 10. A. Bissi and L. Zappa, tfucl.Instr. j5 (1958) 17 11. H.T. Julke, J.E. Monahan, S. Raboy and C.C. Trail, i Argcnne National Laboratory Report ANL-6499 (1962) j -19-
12. R.L. Heath, Scintillation Spectrometry; Gamma-Ray Spectrum Catalog AEC-Report No: IDO-16880-1 2nd ed. (1964) 13» C.E. Orouthamel, Applied Gamma-Ray Spectrometry, Pergamon Press, Oxford (1960) 14. F. Adams and R. Dams, Applied Gamma-Ray Spectrometry, Pergamon Press, Oxford (1970) 15. J« Turkstra, P.J. Pretorius and W.J. de Wet, Anal. Chem. ±2 (1970) 855 16. P.M. Graber, H.R. Lukens and J.K. Mackenzie, J.Radioanal.Chem. 4 (1970) 229 17. K.K.S. Pillay, ö.C. Thomas Jr, J.Radioanal.Chem. 2 (1971) 107 18. J.P. Francois, D. de Soete and J. Hoste, Radiochimica Acta 8 (1967) 192 19. J.P. Op Ds Beeck and J. Hoste, Anal.Chim.Acta (1966) 427 -20-
A STATISTICAL APPROACH TO THE CHOICE OF CHAKNELW-DTH IB GAMMA-RAY SPECTROMETRY II The use of a semi-empirical relation between resolution and garama-ray energy for Nal(Tl) scintillation detectors-
S. Purler
Laboratory for Analytical Chemistry, university of Amsterdam, Amsterdam, The Netherlands
SUMMARY .;•••: Previously equations giving the percentage of extra peak-broadening caused, by the finite channelwidth in multichannel gamma-ray spectrometry are developed by means of a • statistical treatment. Empirical straight line fits for the energy vs resolution curves were used. Xn this paper this treatment is applied, using instead a semi-empirical second-order equation for Nal(Tl) detectors. The disadvantage of the use of two equations to describe one detector is thus overcome. We present four different ways to estimate the extra peak- broadening as a function of channelwidth, depending on the degree of precision required» A statistical consideration giving the precision of each estimate is included. It appears that, for many cases, no specific detector information is required. For these cases a generally applicable plot is given. INTRODUCTION ______In a previous paper we dealt with the influence of the choice of channelwidth of a multichannel analyzer on the total absorption peak width in gamma-ray spectrometry. The finite channelwidth gives rise to an additional loss of resolution in the spectrometric system. In order to compare the contributions of the detector resolution and the channelwidth to the overall resolution of the count rate distribution curve, the normalized central second moment was chosen as a measure of peak width. In our treatment we assumed the gamma peak as measured by the detector to be gaussian in shape. The normalized.central second moment then coincides with the standard deviation «r_. In this case the equation for the percentage of extra peak- broadening Q is: •-. V '.• •' •
where W is: the channelwidth arid jf(E) is the function. . describing: the depëhdeiibe; of et. on the gamma energy- Ë* V Equation [i] holds f or values ~-< 2.
Rearrangement of equation; fi]; gives: •••'_: :
For; Nal(Tl) scintillation detectors, the standard deviation Is usually expressed in- terms of deteptör resolution, being the Fulï Width ;£t lïa^ divided by the gamma-
ray ' ' :' ' '"•• '' ' '"" ''"'" " •••••- -
In order to obfeairi a relation between IJ and E it is- customary
; ; ;: v: •.'.•to• plo• ••••t p:^ vs; \ |••' •. It•..••;••'' appear• . •. 4, p s•'"' 5 ?*4 v5 »»<"•'••••• tha' t•-•-•.•••.•• th• •'•-e curv ••-•'•' e can. be fitted by means-, óf two straight Jirie fits, one f or the lower energy part and! one for the higher one• : < o ' ' • ' jj' • "'•'• ' •' :' •:•'• -..:,%•-•• • • •• •; . ••';••• : • •
In our'previous paper we used this straight: liheiit to compute Q and W for four differerit NaïCïll^d^ graphical adjustment is simple; however, -in general^wo sets of a and ƒ$ values1 are necessary to cover;the whole energy
: range. . -. \ .-- '" . •'•'"" • i :... ' •• : -,' ., •,• '.. -u ••••'"-
In this paper we describe a method to Overcome this ; , disadvantage, "usingpa, least-squares fit with, a quadratic function.
The method is more-, elaborate, sobthat thp straight line f it, may sometimes be preferred;,, we have been able to outline three simplified procedures, involving a ^slight Iq'ss of precisian.
GENERAL COHGIDERATIÖHS,, .,*;''": -. , ' - < : Four processes contribute to the line width of a Nal(Tl) -
; detector asjsembl^.*-^=4;^—'-... .:_=l-—^--.-'-•. =.-=^='^~"" •••• - •,. . ,-==^f '":'". , '"••• c 1. The „emission of pkotóns byüthe öcintillator. • 2. The collection of \ photons by the photocathode. '! 3* The emission of p^oto-electron8 at the photocathode ^-. The electron multiplication process. -22-
Although statistical treatment of all these factors can "be carried out separately, it is difficult to estimate the individual contributions from the experiments. Usually the processes 1 and 2 together "are; seen as a contribution to the line width arising from the scintillator, its package and the non-uniformity of the photocathode. The processes 3 and 4 together represent the phötomultiplier contribution. Thus the overall detector assembly resolution can be represented
where, tj is proportional to the relative variance and index S stands for the scintillator contribution, whereas index T represents the contribution of thé transmission in the photomultiplier. ' A detailed,discussion of the theoretical variance of the output pulse of a detector assembly is given in standard
Co .' ' ' . ••'•••• \ • •"' -••'• • • • •:•• •• •: •• • • textbooks *',.. '..•".
: It can be• show• • • n tha'. t•• • >?p m • ~ 1 s . Ï2 Q can•' b•'•••e ' obtaine' .•••'•••-•d • by sub-
:X 2 • 2 ••••••'• '•'• 2 •''' • ••'•••• '••••" tracting i^ from y .It appears, that 170 is independent of . the; number of. photons, but dependent on the energy E. . T; Kelley observed that «^ -w E .. . ;r -.-• «72c = —^rB - . ca• n'"' V It is necessary to add a constant C to represent phenomena which give rise to a constanti the pulse amplitude, e.g. var,iat4;9%^;in_ gain voltage and change-of temperature in the dynqdes. Thus equation [5] :
: i^i, obtained. V • • -•••--• •"•'"•''' .,t -^z~-" ' '"V/, "''' This is^''in agreement with the empirical f it' for séyëra^ï, ' y
second-order equations by Zerby . •-"/.'•' v" //, v( The function Jf(E) will then be:
*(E) = 0.425 \OE-+ BEVË + CE? ƒ '
i'-< ' ••.-.'.>jv.. •«. rJi"* -23-
To obtain the values for, A, B and C, which are system- dependent, a curve fit to the experimental 7 vs E is necessary. : = . • After inserting equation §6] in the equations [1] and [2] the relative peak-broadening and the channelwidth can be obtained, provided the constants A, B and C are known. Thus: 1 + — W A - 1 V.100# 1.08(AE c-f; BE \/Ê + CE*) / and; • • •'••' •" '. '. •• . '• •
w = 1.08 I { «&.; + 1J - 1 [ AE + BE \/Ë :+ Cir] [8] TV • ••:•,' /•••l.l. * Por Nal(Tl) recorded spectra one usually has Q < 2%. In these cases W can be simplified to
W = ; V/ö.Ö216Q/AE + BÈi/Ê + CE^J [93-
EXPERIMENTAL integral detectors used are the same as in our prevfous paper, viz. a 3"x3" well type^detector -(Harshaw), .'•#.;3-"K5'IJ detector (Quartiz & Silice),°a 2Hx2'! and a 2"x2 mm
.^fer ^detector (both Harsnaw); They represent the most; commonly used Kai(Tl) detectors. All measurements were made with a Quartz & Silice preamplifier AS 02, Elrq.n-baseline restorer i^LR-N-1 and an Intertechhique DIDAC,800 multichannel analyzer* The isotopes and gamma energies used to obtain the experimental curves are indicated in fig. 1. )•' The choice of the number of channels/peak was made in such a way that Q < 0.01#. r. •
CURVE FITTING * '" •• '.. - ' '" ' • . """• " '.. ^ The derived quadratic curve n = g + -^=- + C was "fitted to 2 the set of points (* , E1),(«?2i,E2),. X? .^ (^'^"b^. means of the methods of the least-squares. Thet>cohstajnits'A,. & and C are determined-by solving simultaneously the normal equations for the least-squarps quadratic curve, . * • The number of data is 16, excep.t for the^S^até mm detector, for'which it is 10. I
Aa a measure for the goodness or fit, the standard error of .ïöt;iniate was taken as:
In this equation if stands for the computed and n for the c • e experimental resolution. The values obtained are given in table 1 * first section. As an example the computed curve and the measured data of the 3"x3" well type detector are shown in fig. 1. For a knowledge of the extra peak-broadening or for the i choice of channelwidth* the level of precision ensured by j the rather elaborate least-squares fit is often not required. For these cases we developed simplified methods to achieve a fit. The precision of these methods will be compared with the standard error of estimate of the curves fitted by the least-squares method»
Three is the minimum number of data necessary to obtain the constants of a quadratic curve. After comparing a large number of sets of data, we selected the 0.032 MeV peak of 1pCs, the 0.279 MeV peak of 20%g and the 1.110 MeV peak of
-'Zn. The values of A,, B, and C7 can be obtained from
A 3 - °-°582.?§.O32 " °-286.^2?9 - 0.228.
E3 = -0.166 .,§>o32 + 1#B7 .
^ - 1.51 .^2?9 + 2.41
Index 3 refers to the number of data. The results are given in table 1, second section. As an example the curve of the 3"x3" well type detector is shown in figure 1. j '; ' i
! • •• !
• i
X- ;-. TABLE i Values of A, B and C for the resolution vs energy curve tf » 4 .+ -J~ + 0, obtained in four different ways of curve fitting, included standard error oTEestimate of each fit Nal(Tl) detector used 3"x3lf Quartz 2"x2" Harshaw =2"x2 mm Harshaw section well type & Silice with EMI with RCA with EMI with EMI 9708 PM 8054 PM 9656 PM 9656 PM A (MeV) 0.0008020 0.001373 0.0009238 0.0009387 least-squares B O.OO39SS O.OO55S1 0.002907 0.003793 fit C -0.00011^-2 -0.001364 -0.0008127 -0.0002381 0.001520 "Ö7ÖO1167 "070057896"" 0.001967 4 (MeV) 0.0005920 0.001072 0.0007880 0.001000 fit with (MeV*) 0.005463 0.006062 0.003824 0.002260 B3 3 isotopes -0.001824 -0.002800 -0.001722 0.002009 0.001217 "Ö.ÖÖÖ8748" 0.002248 I (MeVj 0.0009999 0.0008875 0.0009587 0.0009537 fit with B 0.004094 0.003563 O.OO4454 0,004158 1 isotope i 0.0005394 0.001830 0.002482 -O.OOOIOI9 Ö7ÖÖ281Ö~" 0.006430 0.004811 0.0034-58 4 X (MeV) 0.0009999 0.0008875 0.0009587 0.0009537 fit with 5 0.004094 0.003563 0.004454 0.004158 mean values C 0.0008119 0.0003883 O.OÖO579O -0.0007706 ~O7ÖÖ267O"~ ÖTÖO527Ó' O.OO55O.O 0.002260 -26-
11 i
tii t
•: experimental data OM :lcasl aquaralit
A:fttan«fMi«eiop* • :fM onmaan valtM
oo:
oa
ooi
,0 to
Pig. 1 T,2 = 4 + -7^.+ C for 5"x3" Harshaw well type V E Nal(Tl) scintillator detector with EMI 9708 PM, Experimental data and calculated curves
I
• A -27-
A rough estimate of the resolution curve of a Nal(Tl) detector can be obtained by taking the mean value of the A's, E's and C's of all our detectors (A, B and C), computed with, the least-squares method. A correction of this method for an individual detector can be made by the use of a value of C, obtained from the resolution of the 0.662 peak of -"Cs by solving: . , ,,
• C11 "" '066'0.6622 "^I A- 1.229 B The value 7Q CCO can be measured or taken from the detector specification of the manufacturer, Recommended values for A and B are given in table 2. We calculated the precision of this method for each detector when using the mean of three mean values from A and B (A" and B) of the other detectors and calculating the value of Ci of the detector under consideration. The results are given in table 1, third section. As an example the curve of the 3"x5" well type detector is shown. in fig. 1.
2i_curve_fit_based_on_mean_values_of_Ai_B_and_C Omitting the correction used in the method described above we calculated the precision for each detector when using the mean of three mean values for A, B and C (A, B and C) of the other detectors. The results are given in table 1, fourth section. As an example, the calculated curve for the 3"x3" well.typs detector is shown in fig. 1. Recommended values for A, B and C to use witn the methods 2 and 3 are given in table 2. They are the mean of the values of the four detectors described. INFLUENCES OF STANDARD ERROR ON Q AND W j The general formula for error propagation of the function Y = aXb, is SY u SX
Applying this to the equations [ij and [3] results in: j sw f *¥ " ! VT = To obtain the relative error in Q ruid W it is thus necessary to use the relative standard error of estimate of the fitted curves, given by:
The values for -ff-- , ^ and ^ of each curve fit are tabulated in table 3.
TABLE 2 Recommended values for A, B and C for the 2 A B resolution vs energy curve 7 » ^ + —r=- + c for Nal(Tl) detector ^
A 0.0009499 MeV B 0.004067 MeVT C -0.0006375
As can be seen, comparing table 1 and table 3» the relative errors of the least-squares curve fits do not differ much from the relative errors of the fit with three isotopes.
GENERAL GRAPH OP Q VERSUS E Based on the mean values for the resolution curve constants A, B and C, we plotted in fig. 2 a graph of Q vs E for a number of values of W. This graph can be generally used when quick spectrometer adjustment is necessary and there is no time for more refined treatment. We used a set of commonly used W values, corresponding with an energy adjustment of 0.125, 0.25, 0.5, 1.0, 1.5 and; 2.40 MeV in 256 channels. TABLE 3 Relative standard error of estimate of each curve fitted on the equation ~~ _2 A B + c
for Nal(Tl) detectors (%)
(.. Fit ! 3"x3" Harshaw| 3"x3" Quartz •! 2"x2O"- " Harshaw | 2Mx2 mm Harshaw mean well type & Silice least-square 10,06 8.98 5.69 . 7-89 8.2 3"isotopes 9.88 8.96 5.48 7.45 7-9 1 isotope 9.97 24.75. 16.13 45.62 24.1 mean value 9.73 45.15 12.91 52.23
s -30-.
The relative error in Q.is represented by a shaded area. We
used for Sn/Q the mean values of the relative errors of estimate from table 3*
a W=7.B1 keV (2.00 MeV/258 channels)
0.001
Fig. 2 Generally applicable plot of the extra peak- broadening ~(Q) as a function of E for different values of the channelwidth (W) for Nal(Tl) scintillation detectors. Shadedareas indicate relative standard error of estimate
CONCIUSIOH . As can be seen from the standard estimate of error in table 1, the least-squares fit is only slightly better than the fit based on three data (with the fit for the 3"x3" well type detector as an exception). The estimates of error of the fit obtained using one isotope and that attained on the mean values of A, B and C are of the same order of magnitude. However, these fits show a lower precision compared with the fits mentioned above. -31-
Two practical recommendations can be made. a) When no great precision is required in determination of extra peak-broadening, fig, 2 can be used to estimate, it in the energy region under consideration. b) When greater precision is called for, adjustment with the use of three isotopes results in a sufficient precision. The values obtained for the constants A, B and G can be inserted in equations [7], [8] or [9] giving the extra peak-broadening and channelwidth as a function of the gamma energy.
Laboriousness of a least-squares fit is not in proportion to the results. The use of such a fit in this paper served mainly to provide a reference for other methods of' adjustment.
REFERENCES 1. R. Furler and „H. Poppe, J. Radioanalyt. Chem. (1974), in press 2. G.G. Kelley, P.R. Bell, R.C. Davis and M. Lazar, Nucleonics 14 (4) (1956) 53 3. W. Bernstein, ibid 14 (4) (1956) 46 4. A. Bissi and L. Zappa, Nucl. Instr. _5 (1958) 46 5. R.T. Julke, J,E. Monahan, S. Raboy and C.C. Trail, Argonne National Laboratory Report ANI-64-99 (1962) 6. J.B, Birks, The Theory and Practice of Scintillation Courting, Pergamon Press, Oxford (1964) 7. F. Adams and R. Dams, Applied Gamma-Ray Spectrometry, Pergamon Press, Oxford (1970) 8. CD, Zerby and H.S. Moran, Oak Ridge National Laboratory Report ORIIL-3169 (1962) -32- ' , •
THE EXCHANGE BEHAVIOUR OF INORGANIC THALLIUM COMPOUNDS ON HYDRATED ANTIMONY PENTOXIDE (HAP)
R. Furler, Ingrid E.G.P.M. Licht and J.P.M. van Heijst
laboratory for Analytical Chemistry, University of Amsterdam, Amsterdam, The Netherlands
SUMMARY The exchange behaviour of 5 inorganic thallium salts towards HAP was studied in 6 different media in column experiments. Single-step exchange appeared useful for the removal of bulk activity. Multi-step exchange permits analysis of traces in thallium compounds.
INTRODUCTION In the course of the determination by activation analysis of traces of noble metals in analytical grade and specpure inorganic thallium compounds it proved difficult to obtain a sufficiently low decontamination factor for the thallium matrix. The same problem arose in the multi-element trace analysis by high-resolution gamma-ray spectrometry of the same- compounds. One of the methods tried for matrix decontamination was the separation of thallium on hydrated antimony pentoxide (HAP). HAP as decontaminant for bulk activity was first mentioned "1 2 by Girardi » . Although the use of inorganic separators is only afc its beginning and the knowledge of the processes 2 ^ involved very limited » , the potential use is very extensive. The most striking feature of HAP is the very high retention capacity for sodium (I), This has been applied to biological j and geological samples ' » . Girardi tested the behaviour of j more than 60 elements on several inorganic separators, one of them being HAP5»6»7. j Thallium was not among the elements tested. The resemblance hetween thallium (I) and the alkali metals '° led us to -che use of HAP for thallium matrix decontamination. EXPERIMENTAL The chemicals used were: Hydrated antimony pentoxide: HAP Erba (Carlo Erba, Italy)
T1IIO5, T12SO4, T1C1, Tl-Acetate, T12O3 (British Prug House, England) - ; ' .
IS ,;.jk :,;_,. -33-
TlpSO^, tracer solution (The Radiochemical Centre, Amersham, England). All experiments were performed in polythene cylinders, internal diameter 5 nim. The columns were prepared by putting a teflon wool plug at the bottom and filling the column with 4- cm HAP (about 0.55 g)« On top of this another teflon wool plug was placed. The solutions were sucked through the column by means of a peristaltic tube pump, at a. rate of about 2 ml/min. The procedure is the same as that described by Girardi * , except for a difference in the diameter and the length of "Che column, and a preliminary wash. First a preliminary wash with double distilled water was performed until the filtrate was clear. The column was then conditioned by passing a 5 ml portion of the eluent through it, whereupon a 5 ml adsorption step and two succesive elution steps were passed through. The adsorption and first elution step were collected and diluted to 50 ml. The second elution step was also diluted to 50 ml. 3 ml aliquots from both diluted solutions were counted in a 2"x2" well type Nal(Tl) detector coupled to a sample changer, and single channel analyzer. Counting was performed by gross gamma counting of the X-rays and bremsstrahlung. This was justified because gamma-ray spectrometry of the first elution step showed no significant contamination of the tracer. In order to avoid counting problems due to the fact that 204 Tl is a pure ^-emitter, the percentage of thallium in the elution steps was determined by comparing the original amount of tracer in a chemical environment approximating the elution steps as closely as possible. The total retention capacity for thallium was determined in column experiments. Batch retention capacities were not determined in view of the great difference between batch and column experiments*. The retention capacity was measured for three thallium (I) compounds in 1 M HNO,. The three solutions, containing 100 mg Tl(I)/5 asl, labelled
-•,-_•• to. •• • -• : -aA. -34-
with 2 Tl, were sucked through.the column in the way described before. Results are given in table 1.
TABLE 1 Retention capacity of HAP for three inorganic
thallium (I) compounds in 1 M HNO7 in columns
Comp. Retained on column (mg Tl(I)/g HAP) T1NO 3Z
Tl Acetate
The other solutions used for determination of the adsorption behaviour of HAP towards thallium were prepared by heating the thallium salt including the. tracer in a high concentration of the eluent to ensure chemical homogeneity. After cooling and appropriate dilution, a solution con- taining 0.5 mg Tl/5 ml was obtained. The results are given in table 2. - Thallium can be eluted from the column with a solution of ammonium cerium (IV) sulphate in dilute UNO, or HC1 (probably by oxidation of Tl (I)), or with concentrated HC1 only (probably due to complex formation of Tl (III)). The HAP cannot be reused. The percentage of thallium bound to HAP is not sufficient to warrant the use of this technique for matrix de- , contamination in the case of trace analysis in the ppm region. For this purpose we recommend a multi-step exchange with twc successive adsorption steps, adding between each step a thallium backhold carrier, and using a technique which assures chemical homogeneity. This appears to be un- successful in 6 M HC1, probably due to stabilization of Tl (III) by €1". • •'•••[ • • Preliminary experiments in 7 M HNO, and 1 M HQIO^ are being made* The results are promising, the ratio of thallium retained to thallium elutèd being about 10 to 1» In the case of the analyjsi.8'. of traces of noble metals other decontamination steps af ber the HAP adsorption step are TABLE 2 Percentage of -adsorption of some inorganic thallium compounds to HAP. • Value mentioned is. mean of three experiments
Eluent ...
Gomp, 14M HNO5 7M UNO-, .1M HNÖ 6M. H(3104- 1M HCIO^ 6M HCl - •
• 5c(# 5( ^X .x(SK) Bx Sx x<*) Sx • 6J 3.2 99 : 4 .8' 0.2 0.3 99.8. 0.2 84.2 0.1 ,- -r i ,2.\ % 99 0.5 VM n vn 15. 7-.. 3-7 87 0. 99 '.< i 0.2 1.0 O..3:.-...99.8-:;o.2" "99.4 0.1 . 11 i9, 1-.-1 98 ,3 ^.0.%,.^9; V.9;;4.6' 0.8 99.7 0.2 97.6 0.3 •: Tl-Acetrate 21,*94-1 ^9''""99 .8 ; o.3 '99 .9! 0.2 6.9 1.6. 99.4. 0.5 98.4 0,2 2 6-| 1.1' 98•7-!,2«i;;;K99 .8;.. 0.2 .0.2 :.0.1 ,99.9 0.2 0.4 0.3 ..
f '••• -. • r" • . '.••••.• '•<:.' •... • . v'< ' • • • 10 "11 possible, e.g. . elect rode/pos itji-pn on copper powder ' •••. . The limits of this system are ;imder investigation in this
laboratory. •'•'•.• i/••"'''\.' .•'•'. CONCLUSION ••.. . . '. -f^y'% , " ' , ' ; . ' ' Ejctendlng' the iri^i'C:0ivè;'f^përiments of Girardi, more detailed data are^necessary to determine the use of HAP ' for decontamination purposes. In the cases • studied^'14- M HNO, and 6 M HCIO^ appear, to be unsatisfactory media for the adsorption of thallium compounds., In 6 M^ HCl this "applies only to TL^O,.. In all ..other cas.es single-step exchange is quite useful for the
removal of bulk activityv but multi-step exchange permits analysis-öf-traces in all thallium compounds studied.
5EFERENCES . '. v..:'V; ••.:•.•• . • • ' : 1» .¥,' Girardi, Proc.IAEA Coiif. Nuclear Activation. Techniques in the Life .Science,: Vienna (1967)^,11.7 . 2. ..-F, Girardi, E. Sabbioni, J.Radioanalyt.Chem. 1_ (1.968)
3» Ï1» Adams, J.P.'Op.De Beeck, P.: van den.Kinkel, . R. Gybels, D. deSoete, J. Hoste, Crit«Rev.Analyt.
! : Chem. i_ (197D '*5$. :- !, - /: '[.". ^ ••:-.•' ••••••••^ . • 4. S.F.. Peterson, A.; Travesi-and; G.H.' Morrison, Modern • Trend's in Activation Analysis, NBS:,Spec.Publo 312 : (1969) 624 5. F. Girardi, R. Pietra and E. Sabbioni, ibid 639 " 6. F. Girardi, R. Pietra," E. Sabbionif J, Radio ana lye. Chem, ^ (1970) 141 .• , • . ..-'">: 7. F. Girardi, R. Pietra,,.E^ Sabbioni, Eur. 4287;.e (1969) 8. I.M. Korenman, The, Analytical Chemistry of Thallium,
^9* A.G. Lee, The'Chemistry, of .Thallium, Elsevier^ Amsterdam "V:2i97i0 " T"; '::' " ' :' ' ' '"~ " 10.: 5".!. Kim and J. Hoste, Analyt.Acta ^ "(1966^61 11. J., Op De Beèck and J. Hoste,, ibid ;5£ (1966) 427
* ...\i.i ••.•;'-• ELECTRODEPOSITIOM ON COPPER POWDER AS A MEANS OF SEPARATION FOR TRACE ANALYSIS- Off -H03LE METALS IN ACTIVATION ANALYSIS, A TRACER STUDY •
R. Curler, Ingrid E.C.P.M. Licht, J.K.L. Offenberg and
H.L. Polak
Laboratory for Analytical Chemistry, University of Amsterdam, Amsterdam, The Netherlands
SUMMARY A tracer study of the electrodeposition on; copper powder of metals with a normal potential above that of the Cu(ll)/Cu couple was performed. It appeared that in a quick and simple way nearly . complete deposition of palladium, silver,platinum, gold and mercury, can be, attained-, whereas ruthenium osmium and iridium are hardly deposited. ... The chemical environment was chosen in such a way. (1 M and 1.5 M'nitric acid and Ce(IV) ) that problems arising irr theJapplication of the system to different matrices are minimized.
v INTRODUCTION ;. - . '•; . • / ' .:. As a part of the determination of trace elements in thallium compounds by activation analysis, we devised :a-;system for the group separation of mercury and some*noble metals, ful- filling a number of conditions: - simple procedure, to avoid the need for highly skilled ;
. labour. • < • r - quick procedure, so that -fche system is not restricted to--
the determination of the ^"long living" elements as Ru, Agv Os, Ir, Au and Hg, but also applies to the "short living^ Pd and Pt. The determination of Rh, due to the very short half live, requires manipulating near the reactor .
- simple chemical environmentv thus airximising the problems arising in the application to different matrices, including those resulting after appropriate destruction of organic '•• matrices and»samples from the biosphere. - the use of Nal(Tl-) scintillation detectors and a multi- channel spectrometer with a small number of channels, thus extending the use of the method to laboratories not equipped with high resolution spectrometers.
,L -38-.
We chose therefore a method based on the determination of mercury by Evans ?:>, using coarse copper powder. Copper powder was used in the separation of mercury, gold and silver by Kim and Op De Beeck- . Park et al. studied the- behaviour of six noble metals towards amalgamated copper powder. Considering the normal potentials, ruthenium,rhodium, palladium, silver, osmium, iridium, platinum, gold and mercury ions can be expected to be reduced to the metallic state by copper powder in an acid solution (see table 1). Kinetic barriers can present an obstacle to this reduction.
;GENERAL CONSIDERATIONS
Although preliminary experiments showed no significant difference between HG1 and HNO7, as solvents, HNO7 was taken in order to minimize problems with certain matrices. The lower limit for the concentration of HNO-, is determined by the necessity to avoid the codeposition of copper, bismuth and antimony^' , and by the instability of the carrier solution at 'HNO, concentrations below 0.7 Hi An upper limit is set at 2.5 M by the incomplete deposition of the elements involved, due to quick dissolution of the copper powder. We therefore considered 1.0 and 1.5 HNO, an appropriate choice.
To avoid chemical problems in multi-element trace determination in activation analysis, it is sometimes preferable to omit carriers for the elements to be determined. We thought this undesirable for the present elements, mainly because of the instability inherent to very dilute solutions. Especially dilute mercury solutions proved to be unstable. The valency state of noble metals in solution is often 9 10 subject to rapid changes ' , due to mutual oxidation/ reduction processes and disproportionation reactions both accompanied by complex formation^ I+; appeared that a stock carrier solution containing RuCl,,
Rh(HO3)2, PdCl2, (NH)0Cl (NH)Il H
_. • i LIAJ .- -.. ... -39- . . • •
TABLE 1 Redox potentials of some compounds in acid solutions, according to Latimer'
Reaction LwJox pot.CV;
Cu2+ • + 2e~ - Cu + 0.357
+ 2e~ ! + 1.25
T1+ + e~ - Tl : - 0.356
RuCl2" + 5e" - Ru v 501" j + 0.60
Rh5+ + 3e~ - Rh :ca + 0.80 RhCl2" . + 3e~ ~ Rh v 601" ; •" + 0.44-
+ 2e~ - PdClj-" -1- 2C1" + 1.288 + 2e~ .- Pd + 0.62 Pd2+ - Pd . + 0.87
+ Ag ••* Ag + 0.7991 + 2e~. - 2Ag «••BOJ- + 0.653
+ OsO^: + 8H + 8é"~ -* OS HH. 4H2Q' +.0.85
+ I.OI7 irci|" - Ir H1- 601" + 0.77
ptci|- + 2e~ h 2C1" + 0.68 PtCl2" + 2e~ » Pt Hv 401" + 0.73
-* Au + i.5O Au+ -» Au ' +1.68
2+ 0.920
2e~ - 2Hg Q. 739 -40-
Hg(CH,C00)2, in a quantity of about 100^g/ml of each element, can be used over a period, of two weeks. The silver carrier, AgNO-,, has to be added prior to use.
EXPERIMENTAL
1. 3"x3" Nal(Tl) detector (Quartz & Silice) or 31lx3" well type Kal(Tl) detector (Harshaw), Quartz & Silice AS 02 preamplifier, Elron BLR-N-1 baseline restorer and Intertechnique DIDAC 800 multichannel analyzer. 2. 1 j/4rtx2" Nal(Tl) detector with radial bore (Nuclear Enterprises), Quartz & Silice AS 02 preamplifier and Tracerlab Spectro/Matic 535 AM single channel analyzer» The choice of the system used depended on the radiochemical purity of the tracer end the counting efficiency required. chemicals_used The- tracers used are: Hg'^OsClg + H^^OsClg in diluted
2O3 10 HC1, Hg(CH5COO)2 in aqueous solution, ^RuCl5 in 4 M HC1,
192 19S 11Om (NH4)2 IrCl6 in 3 M HC1, AuCl5 in 4 M HOI, AgNO3 in 0.1 M HNO^, all manufacturated by the Radiochemical Centre, Amersham, England. Pd, Pt and also Au tracers were obtained by irradiating an appropriate solution of the carrier salt by means of the pneumatic rabbit system 1 of the High Flux Reactor of the Reactor Centrum Nederland, Petten, The Netherlands. Although rhodium carrier is used, thus enabling determination of rhodium, no rhodium tracer was used for the reason given in the introduction of this paper. i The copper powder was a 200-400 mesh fraction of laboratory I quality copper powder, obtained from Carl Roth 0}lG, Germany. f The other chemicals used are manufactured by the British Drug House Ldt (Analar), England, E. Merck AG (pro analysi), Germany and Drijfhout & Zn, The Netherlands, I A glass tube (internal diameter 2 mm, length about SO mm) . at the lower part conical in shape, is filled successively with an acetate fibre filter, 4-50 mg copper powder of the selected fraction and another filter to prevent backlash of the powder during the suction of the tracer solution. The upper part of the glass tube is connected with a PVC tubing to a 50 nil separation funnel. The lower part is connected to the tubing of a peristaltic pump.
Shortly before the experiment the tracer solution is prepared by adding 0.5 ml AgNO, in 1 M HNO, (about 100 Ag(I) )» 2 ml 7 M HNO, and the tracer to 1 ml of the above -mentioned stock solution in a 50 ml Erlenmeyer flask. To obtain chemical homogeneity between the tracer and the corresponding carrier, the Erlenmeyer flask, covered with a watch glass, is heated at 80°C during 15 minutes. Tracer experiments registered no losses during this process. After cooling a 20 ml portion of a Ce(IV) solution (64 g ammonium cerium (IV) sulphate in 1 1 1 M HNO,) is added. The function of this addition is to prevent reduction to the metal prior .. to electrodeposition, and also to prevent reduction of ''.••
2 • • • • • • PtClg to Ft(II), which causes a precipitate of unknown composition. The solution is then heated again during another 15 minutes; double distilled water or concentrated HNC* J.S added to obtain the HNO, concentration required.
The electrodeposition system is washed with 3 ml double distilled water. During this wash the flow rate is adjusted to 2-3 ml/min. After washing, a 1 ml portion of 3 M HNO, is sucked through the glass tube to remove copper(I)oxide from the copper surface, followed by a 1 ml portion of double distilled water, slightly acidified, in order to reduce the HNO, concentration in the powder. Thereafter the tracer solution is sucked through. It is essential to avoid air being sucked in, as it oxidizes the wet copper surface, immediately forming CuO. After completing the electrodeposition, the separation funnel is thoroughly
! -42-
rinsed with 10 ml 1 M MO;, and two 10 ml portions of double distilled water, The rinsing solutions are also sucked through. The glass tube is then prepared for counting by sealing it in thin plastic foil.
The results of the tracer experiments are listed in table 2, To obtain the value for 100 °/o deposition (the reference value) two methods are used. 1. ïï-orth e elements with a nearly complete electrodepositio: a number of glass tubes, filled with copper powder ax-e coupled, one after another, connected with PVC tubing. The deposition is performed iv] the way described above. All glass tubes are counted separately, and the net couütrates of tSie glass tubes 3umiiK.irir.eci. The S;ÏIS is considered to be the reference value. As a rule two or three tubes are sufficient. 2, When the electrodeposition if! sma.il, the reference value is determined by wetting the upper part of the copper powder with the same amount of tracer as that added to the tracer solutions. The precision of this •method, although acceptable, does not equal that of the method described sub 1.
TABLE 2 The elecurodepcsition of mercury and the noble metals on copper powder. Percentages given are the mean of four experiments.
Element UNO-, concentration | 1 M ! A".5 H meanOO j standard j raean(#) standard j '. deviation I deviation- L .. . — ... Ru 1.3 0,05 | 1.4 0.08 Pd 98.1 0.1 ! 96.0 0.3 Ag 99.8 0.3 100.0 0.0 Os 4.8 0.3 5.1 0.14 Ir 4.2 0.1 4.4 0.05 Pt 96.1 0.3 95.0 0.2 Au 100.0 0.0 95.5 1.2 Hg 100.0 0.0 100.0 0.0 -43- \ , .-. ...:•.:... :
CONCLUSION . •' • • Separation by means of electrodeposition, performed in the way described, is satisfactory for palladium, silver, platinum, gold and mercury. The precision of the method is good as compared with the precision normally attained in activation analysis at the trace level. Ruthenium, osmium and iridium are hardly reduced to the metallic state, obviously caused by the low rate of reaction. In our case this is an advantage, because of the rather complicated nature of the gamma spectra of thermal neutron- irradiated osmium and iridium. In the application to practical problems of the system described in this paper, several difficulties may-arise. Firstly, it may be'possible to prepare a stable solution of . the matrix under the conditions for the- electrodeposition, secondly the relative quantity of each noble metal trace present may obstruct severely the calculation of.the peak • areas of the gamma spectrum, and lastly the possibility of attaining satisfactory matrix decontamonation may be .. limiting. . . .
REFERENCES • , 1. R. Gijbels, Talanta 18 (1971) 587 • 2. B.S. Evans, Analyst £V( 1926) 229 3. B.S. Evans and S.G. Clarke, ibid %\_ (1926) 224 4. J.I. Kim and J. Hoste, Analyt. Chim. Acta ££ (1966) 61 5. J.P. Op De Beeck and J. Hoste, ibid ££ (1966) 427 6. K.S. Park, R. Gijbels, J. Ëoste, J. Radioanalyt. Chem. I (1970) 43 7. W.M. Latimer, Oxidation Potentials, Prentice Hall Inc., Englewood Cliffs, N.J. (19%) j 8. T,Y. Toribara, C.P. Shields, Larysa Koval. Talanta XL (1970) 1025 9. P.E. Beamish and J.C. van Loon, Recent Advances in the Analytical Chemistry of the Noble Metals, Pergamon Press, Oxford (1972) 10. R. Gilchritt, Chem. Rev. ^2 (1943) 277