ATOMIC EEttEY AGEECY STUDY GROUP oar KSSSARCII RSACTOR UTILIZATION -."Casa'ccia, Italy, 2-6 February 19?0
PRODUCTION 01? RAJDIOISOTOSCS IK RESEARCH REACTORS V.V. Bochkarev, V.i. Levin
Radioactive isotope producee sar researcn di h reactorr sfo nearly a quarter of a centurjr* Is addition to the increase in number of these reactors their geographic location has been rapid- ly expanded* At present in the whole world we count already several hundreds of research reactors, many of them having neutron from'1012 to 5-10*15 c/cm2.scc. The proble researcf mo h reacto productioe th r usr efo f no radioisotopes and labelled compounds is therefore of much signi- ficance especially as related to short-lived isotopes and to medi- cal preparations of these isotopes primarily for countries and areas remoted from the main v/orld centers of isotope production* Recently many countries have commenced isotope production, organi- sing isotope radio chemi-cal laboratorie theit sa r research reactors Production of isotopes in research reactors (as a rule being mul- tipurpose) however is not -she only task of these facilities and even usually not the forst one. Taking account of all said above IAEA already in November 1962 held a seminar on short-lived isotopes production in small research reactors and their use. In 1966 IAEA, published a special manua isotopn lo e production (Manua Radioisotopf lo e Production, Technical Reports, Serie s6J)N whicn , i basi e hth c aspectf so this problem arc discussed* Radioisotope productio researcn ni h reactor mans sha y diffe- rent aspects whicf o l h ,al canno discussee tb singla n di e paper*
243 However, some "basic aspects might be difined and illustrated by examples* In the p^eofcnt paper we do not consider purely engineering problems connected with desig maintenancd nan variouf eo s auxi- liary loadin unloading- g (and other) devices. These problems requir separatea e discussio probleme welth s n a s la s o« protecti\ boxes and othor specific equipment used in further procesci^s of irradiated materials* considet no V.'o d e r method technologd san productionf yo , control and certification of labelld compounds and specific pr*;?:-- rations with radioactive compound thess sa independene ear t prob- lems. V/o concentrate our attention on the very process of isotope production in research reactors. generan I l nearl radioisotopel yal producee b n a sca n di nuclear reactor although productio neutron-deficienf no t ivaclides requires the bombardment of initial targets v/ith charged particles This procedur raann ei y more caseb en seffectivelca y performed acceleratorf o e us e bcyclotronthaa l yth firsd f al ts o an f to * Altogc-cher 1500 raaioisotopes are know, out of them for regular productio availabls ni mort eno e than 155-14-0 oneo- ,in cluding abou p~educe0 t10 nuclean di r reactors obvious i t .I o that the choice of isotopes for production is determined by locc.1 r.oeds and its operation program. In addition it should be notec. that out of the great number of reactor isotopes the folio-wins 25 may be asevii"l '~ to the cost widely used in industry, agricul- ture, biology and. medicine /except the transuranium elements/1 1 52 35 42 *B, *0, «fc, P, S, K, *5Ca, 51Cr, 55*,,
244 652n,
icierejf o Besids s i noto t tt si e a. grou short-:f po . tvcd isotopeo use therapn di y a&i dia&ioctic 'T?s( , '''c^, 'yfl'ic, , 1*1, Wat) and in other fields C28^, "
main propsrtieo of fcb.e a'oove isotope & are presented in Sables 1b d l.aan 2h.es groupo tw e s aal:e up A-0 pe- rl isotope cenal f to s i:ore or less regularly produced in nuclear reactors. By their pro- duction volune (total activity, cost, the numb a r of supplies; an dassortneAe alsth y ob compoundf to sourced san s they probably exceed 98 per cei.t of the total production* Ail these isotopes can bo produced in research reactors of medium povre productiot rbu oojsf no theif o e a (tritium^ corbon-14, long-lived isotope fissioa f so n product group and. cobalt-60n )i these conditions is practically unreasonable. The general schema of radioa.ctive isotope production in a reactor consists of 5 n&li. stages. 1. The choice of a suitable target snd its irradiation conditions* Targ. 2 e v preparatio irradiatiod nan n i reactor£a . 3* Processing of the irradiated target and production of necessara y compound or drug. 4. Analysis, measuremen necessarf i d tan ybiologicaa l con- trol and certification of a ready-aade product. 5* Packin deliveryr gfo *
245 considee w w Ho r sbiae question relation si tho nt e firso ttw thstageo t e d primarsan y processin irradiatef go d targets* Sine target choice« 2he choice of initial chemical materials - targets for irradiation, plays an important role in the whole matter of isotope production* 3te initial materials should meet Many serious and often contradictory requirements* .She first one is quite certain irradiatio wf no e targe reactoa n ti r shoul2 d0 safe* Vhe second requirement is related to the rational choice of a type Of irradiated naterial f^on the point of view of obtaining an optimum yield and specific activity of the necessary isotope; third is related - to the production of necessary isotopes wi'sl sh radioisotpic purity choice th £ort e o e;t th hof- . necessary isotopes from the point of view of convenience o.f further proces- sin irradiatef go d material (separatio necessara f no y isotope frotargee mth direcr to t pi-oa-.ctici labellea f io d compound). As for the second requiresent, i.e. effective use of neutron fluxe exposurd san e tim o"stainind ean g larger isotope yields, it eight appear that irradiation «.£ necessary material in an ele- mentar fore th ym n fori ol r amostlo y compact compounds wite hth maximum content of the principal, elexent is of greater advantage* But the fourth requirement (prccarcing of the target) forces one to reject such.choice and to us» suitable compounds even at the expense of significant vrorsenirg in the utilisation of the useful volume in a reactor* She third .requirement (radioisotopic purity of the product) is usually settled by compromise in relation to other conditions tar satisfo et y tris requiremen rula s s eti a very difficult* 246 generan I propee lth r target choic achievo et necessae eth - ry specific activity in the irradiation and to obtain the least quantit radioisotopif yo c impuritie connectes si d ttit nocace hth - sity to consider nany factors and essentially depends on the irra- .diation conditions. If we consider only tie simplest v/ay of isotope production by neutron capture reaction than v/e should distinguish at Itast three source radioisotopif so c impurities: radioactive impurities by activation of other chemical elements contained in the irra- diated material, formatio differenf no t radioactive isotopef so the principal element and, ilnally formatio othef no r radioactive isotopes by paralell and secondary processes in isotope activatioi in a nuclear reactor. Naturally the materials to be irradiated should be of grea- test chemical purity and chemical compounds selected for target preparation should introduc lease th et quantity of. radioactive, at any rate - long-lived impurities into the principal radioioo- tope. Certainly, often it is possible to eliminate radioactive impurities of other ic-otopes by radiocheraical methods but thic procedur mors ei e difficul sometimed tan s even practically it^js- feible wit isotopee hth same th e f selemento * Therefore radioiso- topic futurpurite th f eyo radioactive product shoul providee db d for beforhand, These questions v.'il discussee lb mora n edi detailed Torn considerinn i processee gth targef so t irradiatio reactora n ni * Isotope,production ways* Of practical value for isotope productio followine th e nar g nuclear reactions excite neuty db - reactorr^',a n 3i : 247 1« C&tV - reactio) n c£ 'radio. iiv$ sout^on capture C-* c-iccci.w/ capture of two aud xacre aotttrossu* 2» (n,1^ ) v.'ith subsequent isotope de.cay leading ti v';.c- formation of secondary radioactive product* 3* Eeac-cicns -.7ifti charged particles cr^issios:: (n, %) cr«i
Cnsct ) and (n, 2^:} rd&ction*
4, Secondary reactions (t, r;) ;^-:d (t, n) v/ith taltcns fo;r:'.c~ ^ by neutron reaction cX;i(*i.,ol), and clso :-;->cc:idAr7 -.vitii roccil protons jrciousec «i'rc.di&.-;:in i . c i:yf :o d rials \vith i'sct re&ctor noutrons. $* Mission rcacticn ln,-y }* A nors deudlsd di.scv.ssio.-. ^cilc;7o. fi;otopc G of She noct part oi' v?:.3.v.s-.ts be oouained "by VR,^) reactic-i. 2ho yields cf this se^ct*c>i; uav al- decreasy l e v/ith tlae iricr.-;aso ou* aa'a^rML inersy* Irradiation of tho target- therefors ?i e performe reacton di r channoie *./itn prc- do^inatic thermaf ao l neuvrons* In cUoooinc irradiation conditions oosides activation croineutrons, e. e* to use resonance
248 instea thermaf do l ones. Accumulation of the radioisotop irradiatioe th n ei n process is expressed by the following equation.
M where A activit2- y of the irradiation product, £,~ decay cons- tan thif to s product, S activatio,- n cross-sectio inie th -f no tial isotope, cit- < s abundanc irradiatee th n ei d element,' I. - I molecular weight of the irradiated compound, 6"^ - activation cross; sectioradioactive th f no e product, <£> " J&eutron flux expo- ,t - sure time, A'^ - Avogadro number. uJhe first -cer bracketn ni s shoves consumptio "burn-upr no " initiae ofth l stable isotope secone ,th d ter adeca- "burnd yan - up" of the produced isotope. Isotope activity in the target increases with exposure tine, reaches a naxiiauia and then again decreases as a result of "burn- up" of the initial isotope. Therefore increase in the exposure tine abov value eth e require tHr edfo achievemen maximuf to - nac tivity \vill result in decrease of the necessary isotope yield. SJais phenonenon is especially noticable in the production of long-lived isotopes with large activation cross-sections. As an example we take the irradiation of cultural iridiuia with theraal reactor neutjo^s to obtain radioactive ° Ir. 'j)he activation cross-section of the initial isotope ^^ Ir by thermal neutrons barns0 is96 . '"Ir neutroformee th n di n irradiatio iridiuf no a decays with half-life 74»4 days. DBesides this isotops it n ei turn capture neutrosa turnd nan s int stabloa e ?"Tr crosse ,th - /1QT section of this process being 700 barns. If iridium of natural 249 isotopio composition is irradiated in the thermal neutron flux O of 1.10 ^ neutron/cm .sec then accordin tho gt e calculation 2a activity of J Ir is reached already in 13,1 days. !2hus v/hile half-life of *^2Ir is 74»4 days zaeximua possible activity of this isotope in these conditions is reached in 12*1 days and further irradiation is unra&sonable* I£.g. 1 shews accumulation curves of this radioisotope in target irradiation* 2he ti&e required achievemene th r fo naxjbauf to a activit functioa s yi neutrof no n flux level §\6 !>>i, * ^ , *"i (2) In aany other cases v/lien turn-up of the initial isotope i be neglecte possibls i t di assuzxo et e tha activite tth thf yo e target v;ith the increase of ozposui-ur tino tends to the lioit (activit saturationt ya ; e^xxalao dt A - ~ This equation is often used in practical calculations* With the increase of neutron flux level the maxima yield of radioactive product increase £ tending to a certain linit. After this liaiit is reached further increase of the flux having -c aore influence on t^ rux.-:iaur yield reduces the ti&e, required for 'its achievement* I'ins in tli@ neutron irradiation of natural cobalt the aaxinun yieli ox* Co expressed as a fraction of available Co nuclei from the number of initial Co nuclei approxiaiate centr pe ,0 7 'Ixansformatioo st n rate e closth o et maximu cenr malreadpe s t i - 1 6 y achieve irradiatioe th y db n :• u the neutron flux of 10 ^ n/cci2. *sec, this process requiring 1«52 years of irradiation* Increase of the flux by 10 times
250 increase pe3 onlo C ry yiele yb cen sth t f do etbu exposure tim reduces ei days6 6 o d.t Further increas neutroe th f eo n practically doe influenct sno yielde eth * In the above consideration v/e regarded the bum-up as a "hamful" process but in seme cases of isotope production it ir.ay be useful. Kv.ltlple neutix5n-C£i3tu:?8 rag-.ctiov', In favourable conditions the proces multiplf so e neutron capturradioisotope th y eb e forced course inth reactio f eo deca e th yy n b produc (n,r o f thi) f to s productioe th isotop usee r b necessarda fo n f eca no y isotope. This process is determined by the following two requirements: firsi primare lyth y produc reactiof to n (n, T ) aust hav largea e enough neutron-capture cross-section and secondly of great value is the neutron flux level sinco the yield of secondary neutron irradiatioi products significantly increases v/it increase th h neutronf eo - flux irradiatiolevele th f .I n lasts long enoug ratie h th seconda f oo - producy r t activit activite th primare o th y t f yo y product v/ill be praportional to §*. $ . For the sake of illustration Sable 2 gives the calculated activity values of oone isotopes forced by the double neutron- cap-inire reaction. The presented data indicate that the production of 28instanc^!r .gfo thiy eb s reactio unreasonables ni e th n .O contrary :y4d ^f. producee 0'an sar d v/ibh large yields (hundreds iaCi/p: whe neutroe nth n0 c/c1 flu f mxo .se used)s ci . Satisfacto- ry yields can be also obtained for ^La and ^U. Reactions (n,^" )•£ of higher order than double capture are used on practice for the production of transuranium elements in the neutron fluxes of high intensity. 251 In soae cases the reaction of aouble neutron capture leads to undesirable results, i»e* with the- accumulatio radioactivf no e and stable impurities (iinpuritifcs of ^*~«.u to ' Au, see belov/)* Reaction (n,T> v/il/b, subssrvent daca:/* chain* Heactions Cn,*^) and (n,^f)x considered cxbovo permit to produce rcdioisoto- pas of the same element as the initially activated isotope* I'hc radioactive product Jbtore i& produced v/ith .carriera * In prodv.c$ins ca;?riar-fro6 radioisotopes it is possible to use any naci^&r proces sV v;hicJ radioiso-ccpia anothef eo r elosent is produced froii the aatiiral isotope; this process permits chemi- cal separation of the carrier-free radioactive product* Out; of nuclear reactions occurring in £he reactor for the production of carrier-free radioisotopes it is possible to use neutron reactions with e&ission of charged particles and secondary reactions* She simplest *.7ay of carrier-free radioisotope productic is uhe reaction CnV) v/ith a subsequent nev/ly formed radioisotope decay leadinfora&tioe th o gt n o fsecondara s y radioactive product* After irradiation ths formation of the secondary product continues as a result of initial rc^clioiso-cope decoy- -She cjaaatity of the secondary product after irradiatio '3n 3n ca increase cere th -o dt tain maximu 'oherd man * decrease decayresule a th s da f *to therefore before the? cbordcal reparation it is necessary to coo irradiatee lth d t&r^ecertaia r tfo n perio accumulato dt e tLe secondary product. 1^ the irradiation lasted long enough when idle quantitie primare th secondarf d so y an y products approa- ched their maximum values thin *I s casmaximue eth m quantitf yo the secondary product is accumulabed already at the end of irra- diation* 252 Now v;c tal-:e as an cxasiple "cho accumulation of 49'Sc in the neutron irradiation calciue ofth m targets* 'Sformes ci d4 7accord- followine th in o gt g scheme:
If target irruaiation lasts for 5 days thc-a the storage of the target for 4 fiay requires si d mid durlas this perio quane dth t of 2L'o9 c increases by 40 ^r cent. If the irradiation continues for 10 day* then the uaxirnaa activit f y'So accumulates ci r dfo 2 days of storage and differs frora the initial one only by 10 per cent. Tabl citee5 s other examples fca-e3st-9 processef }o #", )s(n v/ith subsequent decay v/hic appliee radioisotope har th r dfo e pro- duction.* them the following transformation chains
productioe th use r dfo tv/f no o nostly important radioisotopes should be noted and also the prococses •
v/hich are J-he baoe for l}:o v/idospread isotope generators In SOF.C case-;: of carrier- free isotope production it possible to uso uore complicated chains of nuclear reactions. Neutron irradiation of tungsten is associated v/ith the double
253 neutron-capture re suiting in the formation of radioactive by j* -decay of which radioactive X|83Re is foraed. Sbutron reaction.? \yi>h enlsnio chargef no d particles. threshold raactlftaf;* Huclear reactions v/ith emission of charged particles (n, p) and (a, of ) can "bo used for tno- production of pure carrier-free radioisofccpes* Q&© usual voy oi trltiua production; is the reaction Li (n,oC ) ^H» I5&dioactive carbon is produced reaction A» (n> p) '{4C. In order to produce carrier-free 2 reaction (n) *S p ss ? usedi * Kadioactive sulphu s producei r d "by reaction 55CI (n, p^ 55S. fi— ' She reaction \Li Cn,cC ) -'li haj a large Sdiem^l-neutron cross- section* Sheru&l-nfeutron reactions give also significant yields Reactio. C of 55d Snan (r.. ) -ch,d p ? ean majorit f otheyo r reactions (n, p) end (n,oC } require fast neutrons* Hany of these reactions give satisfactory yield fission so n spectruw neutronn si a nuclear reactor* In order to increase the yield of the product the target placee sar d insid fuee eth l elemen tlarge wherth es esi fraction of unaoderatod fission neutrons* The significant numbe rcdioisouopef ro s whic impore har t ant for practical use can oo produced V>y reactions Cn, p) and (n,eO* Tiie cross-sections of these reactions in tho majority of cases largt no s-easured e an ar .Jjai^sn di * j-Iocrevdr often <&e yield of reaction (n, p) is comparable with the yield of reaction (n,y) on natural isotope tcrset or even e:-:ceods this yield* Thus the cross-section of flssion-asutron reaction ^Sc (n, p according to various data ecu&ls to 10-40 nbarns whereas the cross-sectio reactiof no n ^~hCa (n, ^^C) a calculatine th n go element equal 1o 4st mbarns. Analogical value reactionr sfo s
254 51? (n, p)51Si sna 5°Si (n,^)^1Si equal to 51 and 5*4- rabams respectively 4 It saould "be noted that with reactions (n,' p) and (n,o distine^is~es Oa d froir. reaction (n,*< carrier-fref) e radio- isotopes can bs produced* In soiae- cai>e-5 reactions (n, 2n) can "be also used. These reactions also requiring fast neutrons cLo not give a direct possibilit t^r eyfo productio carrier-fref no e radioisotopes. However sometimes due to the secondary decay process such pos- sibility does occur. ?or instance one of the ways for the produc- tio followine f n^ttth o s pi g reactions:
The advantage of reactions (n? 2n) lies in the possibility to produce neutronrdeficient radioiso topes which is impossible «• when using reactions (n, (n1. ^d , )p) an 5?o facilitate, the purification of a radioisotope produced by 1 > threshold neutron reaction measures shoul takee db reduco nt e eth » * » number of undesirable (n,y*) - produced isotopes* For this purpose before the irradiation the targets are wrapped up by cadaiun foil absorbing thermal neutrons irradiatioe andth performes ni - din sidfuee eth l eleaent v/her relative th e e fractio thermaf no l neutrons is smaller • •«_... , " . « ,'• Secondary reaction.0*. Charged partccles which are fonaed * * * * * i nucleana r reacto possesn rca s enough energ produco yt a e * / - secondary nuclear reaction. During the thermal neutron irradiation ^ * .lithiuf o m compound reactioe sth n °Li (n, t <£result) forr:e th -n si « , atioa of alpha-particles and tritons anons which the reaction
255 energy Ic distributed* S2ie energ tritonf yo s equa 2.7$o t l IleV is enough to produce soae nuclear reactions in which processes 16 2£ 26 18 i.Id ) 0p gan (t, u,g(t n ) E found practical application thn i e production of ;*8 an^- "'8i:« '•&« targets containing atoc;s o* Li and fc°Jg 02 bLi tmd '0 respectively are irradiated with :;heraal neubron a '-Jiiesan n subjected vO chemical processing for oeparation and purification of the necessary isotope. In general alpna-parUlcle proto&d san s forao reaotoa n di r c&n be used for the production of r&dioisotopes, e. g« according to the reaction 55C1 (n, p) 55S or 103
256 chiefly long-lived isotopes such as Sr, Cs, Ce and others* The most part of these isotopes are separated in the process of cocplex waste reprocessing providin complets ga possibls a e e use of fission products* Short-lived radioisotopes usually are not present in wastes from fuel reprocessing thei o plant e rtdu complet e e decath t ya end of reprocessing. But at tho same time some short-lived fis- sion products are of certain practical value and therefore for their production short neutron irradiation of uranium targetn si reactor is used. ffhe exposure time and the duration of a subse- quent cooling of the target are calculated in such a way that the necessary fission product could prevail in the nixture. This significantly facilitates cheaical separation and purification of the product. numbee 5Dth o fissiof ro n product radioisotopes routinely produced by special irradiation of uraniua targets belong the following: isotop*
M>«9 «••«•••» • 66.7 hours 6.1 77 hours 4.4 3; 05 ds.ys 2.9 5 6. 20.8 hours 5 6. 5*27 days 9.1 hours 6.2 12.8 days 6.3
257 and Ba can be produced in a reacfccr only by fission reaction 0 tn,-f )• llte othors are also formed by re^c
and 2e US6£ ^ |^e preparatio isotcpif no c •sors and **OCe used in medical diagnostic belong to iLost Xarly produced ones* Accumulation of radioactive an** stable impurS. tie s in the Irradiated i/arget; aann I .y cases tho irradiated targat conbcJ.ns different isotope same th e f selemeno thn tI »e irradiatiof no such, targets a mixture of radioisotopes of this element is c^i&s f oraed. Soiae of these isotopes decaying, foria daughter radioisoto- of another clement. Thus in neutron irradiation of tin . with isotopic composition 0»hich consists of ten stable isoto- pes), nine radioisotope formedc ar isomcr d n san *ti 2v;f so o o> them transform into other radioisotopes. resula **3 s na t o* orbital-electron capture transforms into radioactive x 12^5 y decay turns into radioactive b which in its turn forms
jjjs ^n irradiated by neutrous contains apart from staui- radioactive isotopes of tin, radioactive isotopes of indium.. and tellurivjou In addition as a result of radicisotopt decay, stable isotope indiurf so , antimon telluriud yan e sar .rormed* Similar phenomena take place in the neutron irradiation of calcium, iron, sine, tellurium, ceriu othed nan r elements v:ivl natural compositon. The possible sourc« of impurities in the target (oven it 'it consist initiae on f so l isotope nucleae th s )i r reactio seccr.f no - dary neutron-captur radioicotope th y eb stablr eo e proaue *?f bo & decay* Natural gold, for instance consists of one isoto;;^ "19-".Va7 . In the irradiation of gold targets neutron capture by the 258 initial nucleus gives withalf-lif°u e A hth 2.f eo ? days.
Au is characterised by a lai'fao neutron-capture cross-section (26000 barns) exceeding the cross-section of the production of this isotope (99 barns). This nuclear reaction of secondary neutron-capture gives another radioisotopo of gold, ^Au, wit half-life hth pf .eo 1 5 days resula s .A thif to s chaif no nuclear reactions (se schemee eth ) besides radioactiv°u A e alss 19i 7o97 accumulate targete th n di .
lfr In the irradiation of targets for 3-4- half-liveQ s of tyo^IQO ratie th tlies f oo u A e isotoped an s activitie accordancn si e wit cross-sectione hth s values wil expressee lb followine th y db g equation:
We see that the ratio: >:?7Au activity to ?0Au activity is a functio neutrof no n flu:: leve changed lan s accordine th o gt above equation frora ^0*9/5 in -che exposure flux of 10 12 n/cm 2.sec to 88Q# if the flux level is increased to 10* n/cm2.sec. Vrfhan the presenc f °'Aeo cenf r n uabovundesirable*u i s pe A i c 0 e1 , the irradiation shoul fluxemore t th nadno e e db f n so ethai n 10^ n/cm2.sec. Suc neutroha n flux leve quits li e enough since it gives the activity of 198Au equal to 80 Ci/g which is quite sufficient for the most cases of radioactive gold use. 259 A slmilc^r phenomenon is observed in che high neutron flu irradiation of calcium "carpets. Radioactive ^Ca foraod fi-ora na- JIA •uurat_-ar.sforza C l resulta s a cf "bet o - a decay int oa stabl e /|C•'Sc. This isotope of sosjidiura captures neutrons v/ibh large crcsc section* Sriis result for^abion si radioactivf no emittinc S e g ZL'" i. /• hard ganuaa radiabion. The presence of s Sc in the preparation of pure beta emitter AC^Ca is ratter uidt-cirable. If the irracLLa- tion is performed in the neutron flux of L^IO - n/ era2 . sec /. f for 175 days then 1.1 per cent of 3c i^ formed in calciun targets. Experiraeircal jtudy confirmed the calculutions. Significant radioactive contamination of the target can %o caused by nuclear reactions (n, p) a»id (n, da^s ^d P)an C^/j/2 a 1*»28 day&)» irof I irradiates ni d "by neu-ron*~ produco st e X5Te then 5Q besides ^"2^*"r'd an e long-lived isotop manganesr eo fornes ei d reactioe byth ^) np ;.fc ^thin , I .jB' (n se case th« tarcet storage
onls i y harmful sinc half-life eth f eo M n (l?/j / = 2°3 days), 2 is larger than the half-life of 5°l?e C^/j/g = *5«& days), there- fore to produce pure (without manganese ; preparations of radio- active iron chemical soparTGion froia uanganeiJ suitables i C .
260 e samInth e v/ay e irradiatio"bth y formes i u C y zinf ndb o c . on o cass e nickef d th o e en n i o ^l - C , p) reactio, (n n Z n In the majority of cases only fast neubron give noticable (n,cOd reactione an yieldth ) p ;r , Impuritiefo ss(n s formation by this way depends therefore on fission neutron fraction in the thermal flux. orden I reduco rt e impurities from secondary neutron-capture reactions in many cases it is better to perform irradiation at smaller neutron flux levelgivet i f ssi sufficient valuef so specific activity concernt .I obove sth e case f s-^Ao u impurity to 198Au, 46Sc impurity to45 Ca, 126I impurity to125 I and many others. The formation of impurities by secondary neutron-capture reactions can be sometimes reduced by the neutron energy modifi- cation produco t o preparatioe .S eth withou u f A yno iapue tth - •OQQ rity of •"]Gl?:?QAu it is possible to irradiate gold targets by reso- nance energy neutrons neutroe th n .I n energy range o frot m2 1000 ev a number of resonance maximums is observed for the reac- tion °"Ay), .U(n Jtesonacce integra golf lo d activatio 155s ni 8 barns practivallt °u A *Bu resonanco n s yha e absorption. There- fore if gold targets wrapped up by cadiaiura foil of sufficient thici^ifcss (to absorb neutrons with energies less than 0.4- ev) are irradiated then only ° Au but not *^Au r/ill be formed. •She ratio of isotope activities in the target can be modi- fied in the desirable direction by the selection of appropriate tim exposurf eo storagd half-livee ean th f ei thesf so e isotopes are sufficiently different. V/hen natural indium is irradiated by neutrons two isotopes are formed, In (E^ AJ » 50 days) 116m and ln 0^/2 = 54 tar£e e ain)th irradiates f t.i I 3r ' dfo hours *1* ' I &mnl n is formed with the impurity of *1 "1 /}THIn which does 261 not exceed 0.003 per cent at the end of irradiation'. But if tne irradiation lasts for 50 days and then the target is stored for one day H&ia In is produced with, imparity of 'llfim In approxiiiatc-d to 10"* per cent. In general it should "be noted that in producing short-lived isotopes in order to reduce the accumulation of long-lived im- puritie e exposursth e time should -chf "bo e e least possible duraric limited only by the required values of specific isotope activity. Irradiatio isotope-enrichef no d tnrp;ets« '£he irradiatiof no isotope-enriched targets permits for the purpose of obtaining the usual yield and specific activity to use lower neutron flux level, shortea r exposure time smalle,a r siz targetweighe r eo th f to , in other words, to compensate for any of these parameters or to increase respectively the specific activity and yield in proportio contene t isotope oth enrichee th th f to n e i d target usine gth same flux level, exposure time and the weight of the target (that espicialls i y importan low-power tfo medium-powed ran r research reactor). But still greater advantag thif eo s methopossibilite th s di y to produce the necessary products of hieher radioisotopxc purity. IChis method is applied ;vhen ii; is impossible to produce a prepa- ratio sufficienf no t raoioisotopic purity fro naturae mth l isoto- pic materials since the accumulation of radioactive impurities in the target is caused by the presence of several isotopes in the natural mixture. At the same time the specific activity of the pre paration increases. When irradiating, for example, the natural iron by neutrons, two radioactive isotopes: ^Pe and ^ Fe are pro- cq duced in the target. In this case the produced activity of "Pe it- usuan (i ver lw yneutrolo n contene fluth xs r a levelsto r fa s )a iron-5targee th onls n ti i 8 y activatioe 0.5 centth r 1d pe ,an n
262 cross-section of the isotope is also snail. It is not possible also to obtain the preparations of calciu&-4-7 v/ith a small quan- long-livetita f yo d calcium-4-5 by neutron irradiatioe th f no natural calcium. 4.9'Ca specific activity in such targets is negligible (the content of calciura-46 in natural isotopic mixture is 0,005 produc y cent)r ma 3 pe e .eOn both iron-5 calcium-4d 9an ? sufficientl higyf o purhd specifiean c activity when irradiating t neutrons iron-58-or calcium-46 - enriched targets respectively. When the exposure time of a natural iron target is equal to one half-life of 59Fe, the ratio of 5%e activity to ^9Pe activity is about 550 per cent. But if we use the enriched iron containing 82 per cent of 'CD Fe and only 0.5 percentC oAf ^Fe as a target, the above mentioned activity cenr ratipe t onls o1 i unde y0. same rth e condition irradiationf so ^J?e .Th e specific activit thin yi s case will increas factoe th 164f y ro eisotopicaHy-enricheb w .Ho d target appliee sar produco dt largea e numbe isotopef ro s (see Table 4). The separation of isotopes and the production of enriched materials are rather expensive processes. Therefore the more is ths enrichment of the target by the isotope which will bo activated, che more is the cost of the target and consequently that of a produced isotope. On the other hand the increase in the enrichment decree of tho target raises yield of the isotope and thereby reduces tue irradiation expenses relate unie th t o dt produce ofth t activity. In many cases isotope-enriched targets aro applied despite the high cost of the preparation because the high highe s lattepurite it th d rf yro an specific activity make this preparation much more valuable. Thus, the greater value
263 of the preparation compensates for its hi£h production coci;. Under certain conditions, however radioactive ,th e prepara- tion produced from enriched targets iaay be not only of higher quality but also no more expensive (or even cheaper) than the prepa- ration obtained frotargete mth naturaf so l isotopic composition. Eie use of isotope-enriched targets is suitable from the econo- mic point of vie?; if the degree of enrichment is either equal or exceeds the ratio of tho cost of oho irradiated target mass unit to the respective value for the normal target. If the degree of enrichment exceed above sth e mentioned ratio radioisotope ,th e production from enriched targets is cheaper than from the targets of natural isotopic composition. Under certain conditione us e sth of such rather expensive enriched material , Ca ^f bs sa does not practically affect the cost of the produced isotope. As far as the production of •''T59 o and Tl•'S <5 n is concerned it appears even cheaper. As a rule it is not advantageous to use enriched target producinr sfo g relatively short-lived isotopes. In some cases, however, the preparation of necessary quality may be produced only by using the isotope-enriched target. It concerns for example productioe ,th short-livef no d isotope 7'Hg (Tyj/g s "Q7 65 hours) contene .Th f °°Hto naturan gi l mercur onls yi y cenr pe t0.1 whil5 29.s r i centefo r H8t gi pe ; therefort ea prvo irradiation together with "• Hg a large amount of rKg with, half-lif 46.f eo 9 day produceds si reductioe .Th exposurf no e time in orde decreaso rt long-livee eth d impuritie effectivt no s si e in this case for it affords no chance of producing the necessary specific activity of "'Hg ( in particular, required for medical preparations). Similarly 'Ca - preparations of satisfactory
264 qualit relation yi tho nt e impuritie long-livef so d radioactive ^Ca, can "be produced pnly fron enriched targets.
Irradiation schedule of the .targetL and its cooling* Among the factors affectiag the quality of tlio obtained radioactive products tine exposure conditions are of great importance. As it has already been mentioned, exposure time and neutron flux level determine yield, specific activit rs-dioisotopid yan c purity of the final product* The cooling of the target after the irradiation allows to get rid of the shortcat-lived component of the irradiated target. Exposure time and cooling period should be specific for each case. Buatonis ta c reactors have certain operating cycles, loadee b target t unloader do no n sca ant da y time this operation being connected wit shutdowe hth reactof no r thro e interruption of some other works. This circumstance restrict choice sth f eo irradiation condition isotopef so reacton si ofted ran n does not permit to choose optimal ones, therefore in the cases when isc tope productio no-s ni c the' principal purpos r&actorf eo necess i t ,i - sary tc adjust the isotope production to the operating cycle of reac-cor* There ic another circumstance also affecting ohe organization resultane dtn isotopf so e productio re&earcn ni h roactorsn .I many thcases i o t intermittesi sometimed dan s "broken" schedule reactof o r operating cycle (shut&o.m week-ene atth d ox" afc sone other periods, functioning thnor etlo v/uole 24 hours aid so on). Th4.« ci'wUtifcicfl fcttlii coai>j.i(pA»$a too aNjj^ulnj? i>?^auotio?i of isoto- pes calling for acijur.tins to it, -for additional calculations and for v»r/ ooa.pl.sx sch.ocl.uler, of irradiation to produce naverSheleoc an isotope v.i-ch nocossory cbar?>etcrisvies, particularly of a
265 certain specific activity. In such aituacion one should take into account that the interrupted schedule increases the total time necessary to achieve the needed specific activity in compa- rison with the uninterrupted schedule of irradiation* Besides due to the isotope decay occurring during reactor shutdown, the in- terrupted characte reactof ro r operating cycle doe permit sno c tt obtain maximum specific activity, achieved usualsame th e t ya neutron flux at uninterrupted irradiation; this is especially appreciable for short-lived isotopes. Therefore it is necessary determino t l firsal f eto whethe reactoe rth r operating cycle allows for producing one or another isotope in general and in particular in connection with the accumulation of long-lived radioisotopic impurities. For this purpose special formulaes tables, and diagrams are used. To illustrate this we shall consider irradiation schedules at the following weekly reactor operating cycles:
I - operating 7 days a week, 24 hours/dayttotal useful work hours/week8 16 , without interruption. operatin- I I dayg5 weeksa hours/day4 ,2 , . shutdowr nfo week-end e hour8 4 th t sa , total useful wor hours/week0 k12 . III - operating ? days a week, 16 hours/day, shutdown for 3 hours/day; total useful work 112 hours/week. Ioperatin- V dayg5 weeksa hours/day6 ,1 , shutdowr nfo 8 hours/day and for 43 hours at the week-end, total useful work 60 hours/week. i'iie x'ol 1 ••VL.Aj '.able givc^. the vuluea of apeolfio for -*'X and ^2 (in mCi/g oi the target) at neutron flux 101 3' n/c2 a «soc and 4 week - operating cyclo under the above mcntioiiod conditions.
266 xeui/ujpe auu. . .cixpusure V Continouc. Intcrruoted targe : timt e , :480 use— J^-48 use— \ 320 use- t I s : hours ful hours .fui hours! ful hour. . il+•!••*l• * IV • • H • •
W I 672 70 •* «• -
(2e02) 480 64 45 - 448 62 45 - 320 55 ' . 29,6
52P 672 325 . -
0 48 (P20c) 271 221 - 448 258 214 - 320 209 - 146
At tne figuro 2 tne diagram of acti- vity accumulation bot continuout ha interruptet a d san d schedules (II) is illustrated. Specific activities at saturation for the above mentioned irradiation schedules will be respectively as follows (mCi/g)* - 77(D, 50(11), 50(111), }p(IV); . 435(1),296(11), 287(111), 195(IV). use of nuclear recoil energy* In reactors v/ith relative- ly low neutron flux some isotopes, especially short-lived ojie-s may be produced with sufficiently high specific activity using nuclear recoil energy*
267 Atoms, produced by nuclear reactions or by radioactive trans- formation, possess immediately after their formation such a high energy (from doaeas electron-volt severao st l I.!eV )sufs thai -t ti ficient to break its chemical bond. 1'his energy is used to sepa- ratradioactive eth e isotopes fro stable ath e oneunded san r certain conditions it is also used for the introduction of radio- active isotopes into the chemical compound we need. The liberated atom having lost the energy at the interaction wit environmente hth , again stabilize somn si e chemical form which may differ from the initial one. She recoil atom reactivi- ty is influenced by its kinetic energy and besides by its electric charge. The v;eil-knovm Sciilard-Chalitors method of concentrating radioactive isotope bases si chemican do l separatio frace th -f no tio radioisotopef no , stabilized afte nucleae rth r reactioa n ni chemical form different from the initial one* It is usually the compounds with stable covalent bonds that are used as initial substance; suc element-organis ha c compounds, complex compounds and anions in which the atom which will be activated is the cen- tral one. Scillard-Chalaers method was applied to produce the enriched preparation radioactivf so e iodine, bromine, chlorine, chromium, molybdenum, arsenic, copper, iron, cobal othed an tr elements 'by neutron irradiatio suitable th f no e compoundn si reactor. The enrichment decree achieved by Scillard-Chalmers method determines i ratie th oy d b betwee araoune nth radioactivf o t e isotope transformed by irradiation to the chemical iorm separable anoune th fro initiastable d f to mth an e el on isotop f she(o sane element) transformed to the saiae chemical fore; owing to
268 radiation-chemical degradation initia e cfth l compoun reactoy db r garnna rays and neutrons• Hie enrichment degree decreases with the increase of exposure time and neutron flux. Therefore Scillard- Chalmers method is suitable for producing email quantities of radioisotope, mainly short-lived isotopes eacr .Fo h particular system optiman thera s ei l neutron flux most favourable th r efo usScillard-Chalnerf eo s enricnment method somn I * e cases isotope yields were above 50-4-enrichmene th cenr 0t pe ta t factof ro several orders. She productio carrier-fref no isof o -e e us isotope e th d san topically-enriched targets (wherpossibles i t competie ei b y )ma - above th tiv eo et method rula s e.A v/hon the neutron fluxef so 10*Tt ^-1 0/l/ i n/cmO .sec are available, Scillard-Chalraers method for the regular production of isotopes is unreasonable. *3ie accumul- radioactive atioth f no e wastefore non-enrichichef th mo n si d disadvantagee th f o targemethode e e paron th th s f f tsi o o . nucleaf o The eus r recoio .productioe energth - r yla fo f no belled compounds was known long ago. The irradiation of the mix- tur lithiuf eo m compounds with some organic compounds resulten di the production of these compounds labelled by *H (reaction ,ot ) ^H)« The similar way is known for the production of com- 2 pounds labelled b: G% ^S, ^ P, halogens and other elements. case Inth e of'carbon atom labelling, nitrogen compound their so r mixtures with other organic compound exposee sar neutroo dt n ir-
radiation* Labelling _ i> s the result of the reaction of \f14/ aoo, -*..m _ forme cas e nucleay compoundf dth b eo n i r; C ;reactio ) p , n (n 'N labelled by "s reaction "ci (n, p) "s is used and so on. Methods of synthesis with the use of nuclear recoil energy are the object of numerous theoretical studies. However the prac-
269 tical value of these methods is limited* It is due to complex technology of these methods, i.e. that in siosfc cases a complex multi-component mixtur labellef eo d compound e formes sth i d dan separation of the necessary compound out of this mixture is often rather difficult and the yields are not large. In addition, the radioisotop distributes ei tLn di e &ol&«ul labellea f eo d com- pound randomly aud nonunifcrmly uLerea me&hode bth chemicaf so l or biological synthesis cake it possible to obtain a strictly specific labelling* 'J3ie Primary chemical processing of Irx^aciiatgd targets* In the simplest case the target subjected to neutron irradiation in a reactor is either directly used as a radiation source or delivere "irradiated n usea e tos th ra d portion" thesn .I e cases the target reprocessing is significantly simplified produce :th t is removed fropackage mth e (irradiation container whicn )i t hi was irradiated and then it is packed in parcels, convinient for the user. The most part of the targets however, after irradiation is subjecte speciao dt l chemical processing lattee .Th aimes ri d productioe atth radioisotopa f no requiree th n ei d chemical form or at the synthesis of a definite labelled compound. In a number of cases chemical processin necessars gi productioe th r yfo n initiaf o l radioisotop sufficientle th n ei y pure statee th f ,i target contains noticable radioactive and stable impurities* Chemical radioisotope separation frotargee mth necessars ti n yi the production of carrier-free preparations when the separation of a radioactive product from the bulk of targes and radioactive impuritie requireds si productioe th cas.e n 2hith ei s si f no
270 mostly important radioisotcped an S , P s productioe Forth ^f 2no P cither 52? (n,^) r Po n, p) * P reaction is ussd ae tney afford obtaining a carrier- free jP« '.There are F.eny methods for ^ 'P separation from the irradiated sulphur -barest* 2hose of siosb widely use "belong to the following three groups: Method. 1 p!?o£?phor-5f so 2 leachin watoy gb r solutions from raeltcd or finely ground sulphur- 2. Method :.»hosphor~3f so 2 extractio watey nb r solutions fror. sulphur completely or partially solved in organic solvents. Method. 3 phosphor-2f so 2 separation fron sulphu subliy rb - mation of the latter at elevated temperature. Radioactive sulphu produces ri thy db e reaction "ci (n) ,p ^S. For this purpose potassiu sodiur mo m chlorid usualls ei y subjected to irradiation. For the separation and purification of carrier-free sulphur the follcv/ias methods are used: 1* Methods cabio e baceth n dno absorption (potassium sodium) catioe byth n exchange coluan wit subsequene hth t purification from p P by ad&orption. 2« Methods in which sulphate separation (^S) from, potassium and phosphate ion carries anionitsy i b t dou e absorption. 3« Seduction of radioactive sulphate to hydrogen sulphide and separation of the latter from isipuribies by distillation.
Seductio. 4 sulphatf no e (^S )o separatiot S0 d 2an f no the latte distillationy rb . The nost comnon waproductioI f Jy o "\7/\ neutros ni n irradiation of tellurium compounds whor i'ollov/ine eth s chai nucleaf no r reac- tions occurs: 271 Elementary tellurium, tel.iuriun dioxid tellurid ean c acid are used as targets. Most methods of 1V^11 separation from the targets can be divided into tv/o large groups:
1« Ijethods of distillationL_fi*on the solution* After the solution of the irradiated target in acid or alkaline water so- lution, radioiodine is stabilized in the elementary state and distilled off into the receiver filled with alkali. Iodine dis- tillatio carries ni frot solutioe dou mth sulphurif no c acid dan in recent years fi»om that of phosphoric acid. 2. Methods of dry sublimation. Direct iodine sublimation from the irradiated target make possiblt si excludo et e operations connected with target solution. Irradiated tellurium compounds are heated in special leak-proof equipment and iodine-151 is gas-carrieblowey b t dou r current. Chemical isolatio carrierf no - free radioisotopes froe mth target is also used in the production of 'Sc, }>\ * Co and othen i r cases iit I *, necessar radioisotopr yfo e extraction from the mixtur fissiof eo n products too. The primary chemical processing of the targets is usually the last stage in the production of radioactive isotopes. It is followed by their transformation into some or other compounds or products wit hele appropriathf th po e synthetica technologid lan - processesl ca onn .I e case hov/ever productioe ,th radioisotcpef no s
272 is accomplished after the primary processing of the targets and even outsid reactore eth *case isotopf Sucth eo s hi e gene- rator use. Isotope generators* In many cases it is more convenient and safe to use short-lived radioisotopes with half-life in the range from several minute severao st l hours possibls i t .I o et introduce these isotopes In Isrge quantities as tracers into some material without fear TO arise difficulties in further use of the material originating from residual activity. Short-lived isotopes v/hen introduced int bode diagnostir oth y fo c purposes arspeciaf eo l advantage. short-livef o e us Bue tth d isotope certais sha n linitaitons. These isotopes canno storee lona tb r g dfo time transportation I * n over long distance usuay sb l means substantial, losses resulting from isotope decay occur. Simultaneously their quality is worsened increase th durelativa o et f eo e fractio long-livef no d impuri- ties. Therefore the use of short-lived isotopes is mostly effective near the place of their production. In some cases however, tho successful use of short-lived isotopes is quite possible at a long distance from reacto cyclotror ro n sitin wells ga . These are the cases when the required radioisotope is a daughter pro- duct of another radioisotope with greater half-life. An "isoto- pe generator" prepared from tho nother isotope makes it possible to produce the short-lived daughter isotope repeatedly by its che- mical separation (milking) froa long-lived mother isotope. The daughter isotope activity which can be obtained from the generator at a given moment is defined by the following equation:
273 <*>
Where A th2- e activit daughtea f yo r isotope eth whicn i s hi generator at a given moment; AQ/J - initial activity of a mother isotope at the moment o? generator loading or at the moment when time reading begins tir.- ;t 3 elapsed frcmomene ath t when time reading begins to the $re cc.it RO^C^; *~C - time elapsed from the moment of preceding daughter isotope separation (out of the generator presene th o )t t supposeuoiaens i t (i t d tha thin ti s separation the daughter isotope is completely removed); and decay constant mothef so daughted ran r isotopes respectively* Afte separatioe rth daughtee th f no r isotop activits eit y increases with timreached ean maximue sth t ma X*, (5) and then decreases according to the equation She ratio of daughter isotope activity to the activity of the mother isotope is expressed in the following ways it A, At the moment of maximum activity of the daughter isotope . Further rati A oincreaseA s withe tendtimd th o ean st
value
i_ (7) *h.v. v^v X^-Xt
274 tha e maximuV/e se etth m value Is somewhat more tha Thi. n1 s means tha equilibriun ti activite mth daughtef yo r short-lived isotope is a little more than the activity of mother isotope. Fig* 5 shows ^/^Sp accumulation after the milking. majorite inth casef yo isotopie sth c generato sorpa s ri - tion column filled by suitable packing on v/hich the mother isotope is fixed, '.flic eluting"solution of appropriate composition passing ~, i • - • • i* .' • » • through the coluisn separates the- dou&hter isotope. Tables 5a and 5b present genetic pairs of isotopes v/hich basare knov:eenoraf n eth o ei r no l possible isotope generators. In conclusion it should bo"noted that as a result of inten- sive study nade recently in nany countries a marked progress has been achieve developmene th n di radioisotopf to e production ni nuclear reactor. At present it is rather difficult to achieve essential impro- vement in the production technology of radioisotope preparation and essentially increase its quality or to develop a method for the productio isotopew ne a t evef n,o no r being under production.. technicaw Thine sf o require e l us mean e sdevelopmenth r so f to new technological methods. In"particula increase rth neutrof eo n flux level user dfo isotope production v/ill «j.lov; the numbe doublf ro' e neutron-cap- ture, threshold ano. secondary reaction essentalle b o st y enlarged* She sam trus isotope-enriche f ei wideo f e o e rus d targets especially of those with higher enrich-aent degree. £his way in addition gives the possibility to increase radioisotopic purity and specific activity of radioisotope preparations. In some cases it is advisable to use radioactive.isotopes as targets.
215 promisine Th opinio r e developmengou th \va o s nt i yw ne f to generator systems, e.g. those presented in Table 5b. Of some interest are the attempts to find naw methods for the production of carrier-free radioisotcpes e.g. by use of such chains:
Apart from this tLvirnumbea s i eimportanf ro t problems re- quiring more precise kaoulad&e ^iid v,-ork in connection v;ith the production of most widely used and short-lived isotopes in re- search reactors. It is useful to struce/ in detail and select targets and also to find optimum radia-ion scheuules for the most important groups «• of isotopes; to perform calculations, to make up tables and noao- determinatioe Gramth r sfo n of basic characteristic irrae th -f so diated targe different ta t radiatio coolind nan g schedulee th n si specified reactor operation seleco ;t bese tth t schedule ir rsfo radiation of fission meterials and develop complex methods for separatio thesf no thosr eo e group short-livef so d isotopes from fission debris; to develop now systems and methods for isotope separation by use of nuclear recoil energy, etc. Finally much study is.require furthee th n di r development of chemical processing of irradr'ated targets and improvement of chemical processe.'hics h are the base of isotopic generator work
and also in the developmentv ; of new labelled compounds special preparations.
276 Captions
S - -10' yfI.
400 &00
Fig. 1. Accumulation o£ Ir at the irradiation in different neutron fluxes. 277 Accumulatiof no in the irradi- ation of tellurium by the neutron flux at different operation schedules of re- actor. Tiie upper r continuoucurvfo - e s irradi- ation/ Tne worky loweda -5 r r curvfo e- ing week.
87 Y 87m Sr 50 100 <50 Fig. 3« Accumulation of "nSr in the isotope generator after milking. The upper line shov/s decrease in activit mothef yo r ?Y Lower curves show accumulation (growt decayd han f )o daughter 8^°Sr after the 1st, 2nd and 3d milkings: 1, 2 and 3 - growth 87mSr after milking, m - milking. 278 Table 1a CHARACTERISTIC HOS5 2 TP SO WIDELY USED HADIOISCX20ECS * : specific Radio- ;Principal IPyp f o e Qso-.ce * : activity isotope t of the p/ reaction of decay and initial 'O, :the clo- V. •»«•» **i*mmmHmit ••M».»I mmwmmmmm mt mmt imtm*+»m**ttmmm *K 6Li(K,«O f 7.45 294 12.262 yrs C.?. 1*C 14H (n,p) f 99-635 1.75 5730 yrs C.?. jN'a %a(Hty) f^ 100 s hr 0.53 6 9 4. 14 3900 32,« 31 , v P ^ ^(w,YP ) v- 100 0.19* 1GOO 14.28 days T.1 S (n,p) * 95 0.05 C ' i » 35s ^Cl(n,p) f 75.53 0.19 87-9 days C.P. 42K 41K(«,^) fif 6,83 1.3 12.36 hrs 370 ^5Ca ^CaC hr ) f>~ 2.06 0.7 day5 16 s 57 27.8 days 2100 i cX.^^X^f 4.31 15.9 "PO 54Pe(n,^f) E.C,X 5.Si{- 2.9 2.60 yrs 490 59pe ^®?e(h||r) ^ib" 0.31 1.06 45.6 days 9.6 58Co 58ili(n,p) E»C ., p.* X> ^ 67 . 88 0.1 05*71-3 days C.P. 60Co 59Co(K,r) ,JT, Y" " 7 3 100 5.263 yrs 10600** 64-, 63« / , x c Cu ^Cu( to^y) '7- «j^,£,{f 69.5 4. 1 12.s 8hr 7€00 65Zn 6V(K,r) &C, ^CT^ 48.89 0.46 245 days 300** 82Br 81Br(h^) 35.34 hrs 3500 85sr 1 V^/T 49.48 3.3 ^i ^ jv")T 56.90 0.16 10,76 yrs 11V 2** Sr UC ^-iT* ) JT - « s 27.yr 7 C.F. Qf\ fiO yV^y Qry~r f u ^*\ \A ^$4 y X r O^\ li O^ 100 1.2664.0 hrs 2300 QO QQ J^lf 23.75 0.51 66.s 7hr 200 (h.x.5 ) •* vw 279 "5 U ( U (fejf) &"/£")tf" " "~ 5°'° ^s C':i?' U(Vi,i) - p- 2.6 s 2yr C.F. i-u(^jf) friary 10° 93*8 2.697 days 8COOO OOP HsCh.y*x ) ft'iTv 29»80 >.8 46.0 991 days 29.50 8 3.81 ypG 1900 Note: * for i'ission spectriiE. neutrons ** during I year exposure 280 able 1b MAIN CHARACTERISTICS O 'GPOUPA P OP SHOitfJ-LIVED ISOT'OPSS addition (i thoso nt e cite Tabln di e "a") . --. • « « • :; At,un- .""" ;!.Iec:i'.;ua specific Principal : ?ypa of : ! ! m £adio-; ι dance ' ! 6-, : T [activity, mCi/c, • s 8 ! decay and -die ini- > ' 1; V2 e !olc&on[oth f t •*reactio: f no :tial i&o-;: "barns : ;[for the flux oi isotope: •; radiation :tope; % , : ; ! (Lrs! ) • ^ Λ ο * production ·1 > 1 * > * 4 4• t ' tlO'^u/cii . sec __ 1£F 160(-fc,n) w^*.r 99.759 1.83 C.P, 28-,, 26 Ulg Ms(t,p) f>eT>T 11.29 21.2 4 99.6 O.S3 1.83 2150 *U °A Ch%r> ΪΛ r 46 ^Ca Ca( ν,,ρ) ^r 0.0053 0.3 131.8 0.04 5Sto 55L!n( 'Λ»^) ^ T 100 13-3 2.576 39000 69m 68 Zn Zn(v,,y) Ί.Τ.,€Γ,Χ 18.50 0.1 13-8 45 6 75 ? As Αε(^) 100 5.A- 26i8 -9200 ^.Y * 26,4 87*sr 86Sr(h,y·) ir.,?^x,y 9.86 1.65 2.83 290 99mTc "MO^C IT^eT, Xtf 6,049 C.P. '°^d 108Pd(h^> f* ^>Τ 26.71 12.2 13.4-7 4950 r 11 '5Cd ^Cd(V) F'^T 28.95 1.1 55.2 470 1-.5m.fc 1^a*23*to iT.,c,r 1.66 C.F. 132j ^2Tc^2J f,r 26 »2 C.P. ^°La 159La(v>,^) i^r 99.91 8.2 4-0*22 9600 WHS 196 0.146 880 3600 Ηδ(νι·Γ) ΒΧ,ίΓ,Γ 65 281 Table 2 MAXIMUM ACTIVITIES OP SOME ISOTOPiSS < Ci/g of the pure initial isotope i.e. target) FORMED AS A HE3ULT OP DOIT3L2 NEUTRON-CAPTURE * * • • 'Activation cross- lActivtiy : :Secon- T ! section (baiT.s^ Half-lives • 1/2 ,:( Ci/g) Initial: Primary: a Ife oth r • . | initial 5 prir.ai-y initial ! secondary ' neutron isotope : product: product • : : IfllDC Of iisotopsiproduct product ' product • *V' O • • • « • jlO^r/nsf..^ 2 26 272? 2828 55 3 9 sHgg MMgg Uuge 27x1CT27x1 0~ 5Cx10'"5Cx10~2 mi0 1 n0 min 21.11.122 hra 4*7x10~4.7x10~ 66% 6 Ni i <*^ » *% 66Ni 1.54- 60 2.55 nrs 554.4«8 8 hrs 5.4x"iO""5.4x"io""5 5 ''^L'^La a 11^°L*°Laa WWLLaa 8.22 3.3.11 40.2^•0.22 iirs 5.85 JITixrSs e^cio"6.2:c10-5 186^ 18? tSSg, 11 187Ww -188^ 54 90 26 4 hrs 69.9*55 teIi3?ss 5*4xno""5.4x10" 22 195 1 1 ^ Qs0s ^O0s ^O^0ss 1.66 6000 'fA51 22LTlirsS yr9 s1. 9 yrs 1.5X10""1.53C10"" 282 Tabl3 e SOME ISOTOPES FORKED BY REACTION ( n,) Y/ITH SUBSEQUENT DECAY InitialtPrimary .'Type of -decay of J Dau^ter J Type of- debay of stabl radio: e - *+.%,.•'. 4^4-^™ QVs/-? * • isotope fioo-copo ! l;°, **• padiQisotop *| thi s isotope and ^c* *7 4· 5 days Jf 5.4 days Ca f' *7So ? 98ao 9^ %o F· 2,8 days c Ι.Φ., 6 hrs W •"°Pd ···"» f,aΪ2 min AS day6 7. rfs l) 11 11*Cd 5oa f· 2.5 days 115-^ 1.0?., 4.5 fcrs ΊΊ1Ί29 ΛΛ>-ί 8η π 3η £*C« . 118 days 113aTIrn, Ι·Φ·. 1··7 days 130 1 1 1*1j Τβ 5 Ce (^24*8 nin 1 day(ίΤ8. , s 12*,, ''25 * 125^ιρς j Λβ γΛ6 S.C., 18 hrs 2.C., 60 days 1 1 1 1 "'5°3* 5 Ba E.G., 11.7 days 5 CS B.C. ,9.6 days 2 °9Bi ^•Ofii 9 day(Γ4. , s ^^o oL, 1J8 days 283 Table 4 ISOTOEE-EKRICH23) T/OIGLT3 USED POR RADIOISOTOEB PRODUCOJIOH Produs- : I Content of activated isotop then ei - tion j Isotope (target) ! ts isotop$ e : norsial : enriched 31% ^28^ 6Li 7.52 95 2^s ?^:e 11,92 87 33p p$s 0,74 98 42K ViK 6,91 92 ^Ca '^'Ca 2,06 90 *7Ca ^Ca 0,0033 20 51 (jr 50Cp 4,31 95 55^ 54?3 5.81 95 5 %e 53?Q 0,31 80 6%i S2l«?i 3.66 97 6^Hi ^BTi 1,'<6 92 58Co 58s:i 67.76 99 6^a2n 682n 13.56 93 75Se ^*5e 0,87 33 ^85Sr 84Sp 0,56 64 J^Cd j^Cd 0.875 68 |X i/l2 " »5Sn " Sn 0,95 80 5.98 1> 95 123I 122^ 2.4-6 83 *> "*A 4 XA *X *T '2^*ttie* 34,5 99 ^?Ba ^%a 0.097 12 Ga 152Ga 0,20 35-7 168 169^ yb 0.14 17 185 , V ? 1B »/ 30,6 96 197.^ 9 l^n* 0.1$ 40 w<•-> «• a pc>? cent is given according to catalogue data o£ .rji-blvi isotope production firms. 2d4 gable 5a GSKSTICAL BABIOISOTOK; PAIHS POKING IHSJ SOOJOP^ C22CHAGJO.TS isotope generators) * Isotope pair :- mr-lfxrfts nol' sr• isotope : daughter isotope 28 **•* -> .u 21.2 hrs ni3 n2. 82Sr -^82Sb 25 days 1.3 min 275 days 68.3 min "*°S• ^ r — >./^SC ^ t 27.7 64.s 0hr 87y —^^S r 80 hrs 2.83 hrs "LIO -^"^c €6.7 hrs 6.0s 5hr 105?d~^"to3:r3h 17 lays 57-5 nia 11 5cd ^.H^ 2.23days 4,s 5hr 115Sn ~-^115ciIn 115 days 1.7 hrs 152Te —— 1523 77.7 hr-s 2.3 hrs 137Cs -*• "57ciBa 30 yrs 2.6 min 12.8 days 40.2 hrs ^ OO ^ O Q iH i— ^?o 69.4 days 16.7 hrs 285 Table 5b GEEETICAL RADIOISOTOPE PAI3S PORIUHSTHS BASE OF ISOTOPE G2SEI&TORS (possible isotope generators) Isotope pairs : Half-lives : mother isotop : daughtee r isotope 650 ;TS 14.28 days 33 yrs 12.4 hrs 'r days 3*43 days yrs 3-92 hrs 66Ki—^66Cu 54.8 hrs 5*1 min ?22a —>- ?2Ga 46.5 hrs 14.1 hrs 8.4 dsys 26 hr*s 83 days 1.8s 6hr 39«5 days 57*n mi 5 368 days 30 sec 4.0 days 20.8 hrs 10^ yrs 12.5 days 4.68 days 38 hrs 2.4 days 3.8 ain n mi 5 6. s hr 2 —>7 1^lia 4 —>28 day1Zf4s Pr 17-3 6 day4. s 0 5 days 57.6 days 7*7 too 5 yrs 6.7 days 6 yr& 17.4 hrs 1.9 yrs 39*5 hrs 202Pb —>202 T1 2 1 day3x10s 5 j'rs 286