JOURNAL OF CHEMICAL EDUCATION
NUCLEAR CHEMISTRY AT THE UNIVERSITY OF CALIFORNIA I. PERLMAN m d G. T. SEABORG University of California, Berkeley, California N o w and agnin in the evolution of science a new field concerned with the interpretation of nuclear reactions of st,udy emerges. I t is usually neither possible nor im- and IIWS the first chemist's work to identify the products portnnt t o point out a partirular dny or ycnr in which of the.% reactions. The first chemist is enpngml prithe new branch was born; instead, reflection will show marily in a special kind of annlyticsl prohlcm, the that it took root in a number of existing brnnches and mcond in studies which in mnny qrtnrterrr wonld not be grew along with and finally away from its pnrents. As called chemist,ry a t all but nuclenr physics. We shall the body of knowledge expands in hrendth nnd depth spcnrl some time discu~qingthe chemist's position in the aggregate techniques and concepts require longer this latter field; whether it is culled chemistry or physpriods of time to master nnd become a subject for irs h a . no more relevnnce than an nl~strnctdiscussion sprcinlizntion. Such, in our opinion, is the body of of whether spectroscopy is chemietry, physics, or nsknowledge and field of study which me choose to call tronomy. I t in more profitable in the c n . ~nt hand t o nnrlenr chemistry. diacuw what chemists an! doing. This is the basis ~vhich It is perhaps easiest to envisage the mope of nuclear we use for defining the field of nurlrsr rhemistry. .kt chemistry in terms of the ways in which a p e m n with present then nuclear chemistry \voulrl hr the study of broad basic background in chemistry can effectively nuclcnr renetions nnd t l ~ r~ w w i n t r ~rhrmicnl l studies contribute t o the study of nuclear phenomena and in neccled to elucidate t.hese reactions or d ~ i r htnkc nclterms of the training which a chemist will find advanta- vantam of nurli-nr react ionu. geous in utilizing the tooh provided by nuclear phenoml'hc use of chemistry in nuclcnr studie.s has an early enn in the solution of many chemicnl p r o l h n s . I t is history. Soon after the discovery of rnrlionctivity, the the aim of this paper to provide a discussion of these observation that pitchblenilr hns highcr specific radiosubjects, in particulnr the present method of operating activity than uranium was the stinl~~lrts for chemicnl our laboratories nnrl teaching at t,hr University of frnctionation of the ore. The chemical .wpnrations by California. the Curies which rcsulted in the discoveries of polonium In attempting t o define nuclear chemistp it should and rndium cnlled for a distinctive type of chemist^ first of all be renliced that this same term may refer to which has ever since been nn earmark of the chemird quite different studies in different lahoratories. Such p l ~ a w sof nuclenr chemistry. This rhnrnctrristir fendifferences are not unique to this field 11ut are common tun, has to do with chemical opcrntions on invisible to nll. An inorganic chemist in one place may be in- amounts of mnterial-invisible in nll respects except. to terested in analyt,ical problems, another in m c t i o n instruments and materials which can detect radionrtivkinetics. Sirnilnrly, in one lnhoratory a nuclear chemist ity. Almost all of the natural and nrtificinl mclioacmay be atudyinp the behavior of minute amount,s of tivities arc encountered in "weightless" concentrntions material which ran be followed by virtue of their mdio- and the special type of analyticnl chemistry whirh has activity, while another nuclcar chemist is primarily evolved to cope with t h r e quantities ha* l m n termed
JANUARY. lSSl
rrrdinchrmislrg whir11 1vr no1v ronsider as n hrnnrh of the l~roaderfield nuclmr chmisln~. The methods of radiochemistry nlrendy wrll estnl~lishnltwenty nnd thirty yenrs ago were uwtl in the Inl~orntoryinvestigntions of the nnturnl radioni.tivitirs an11 inclustrinlly for rndium sepnrntion. The cliscovrry of nrtiticinl rnrlionctivity nnd the development of accelerators for inducing r:dioactivities in all of thc elements greatly wirlmetl the mope for rndin141emirnlinvestigntions. During the puqt lvnr these methods lrramc of vital importance in extrncting plutonium frnm urnnium nnd fis-ion pmducts, and the clevclopment of the complrx process whir11 renulterl \vw hy far the most rxtrnsive use yet mnrle of such mrthorls. Rewnrrh nncl ilrvrlopmrnt chemists numbrring in the hundreds ~vorkerlwit 11 trchniques nnd instn~mrntsknown prrvirrusly only to n hnndful of research workers. From their rcsultn were built huge rlrrmical plants costing ovrr S100,000,000 while the mnintennnw nnd extrusion of this program now employs more chemists thnn during the 1vnr. Kndiochemistry, which has been defined as the study of suhstnnres nt extreme dilutions mnde possihlc hy measurement of t,he radionrtivity, is a mpidly expanding field \vit,hrnpidly inrreasing numhem of n e s in resenrrll nnd inclostry. The t.rncrr method and its mnnifold npplicntions is cleatined to heeome more and mow widely used as the nvnilnlility of radioactive mnterinls and the training of p ~ t m t i n lusers permits. The applirations of trncrm to t l ~ csolution of prnhlems in rla-mistry, I ~ i o l o ~and v , othrr firlrls are, of wurse, not inclotlnl in our rlefinition of nwlrar chemistry. I t should 1% pointed out. I ~ f o r eturning to nnot,her subject tlmt rscliochrmistr?. is Onwl on a funilnmmt.nl knowleikf! of rhrmieal lrhnvior such as nolubility properties, surfnrr d~rmistry,and reaction kinetirs, to name but a few phnses. I t is 1)asienlly a chemicnl field in which nurlrnr inst.ntments plny the secon(1ap role of permitting one to follow thr rnrlionctivity through the chemicnl scparntions. A nnturnl consequence of the nhility to separnte radionct.ivities in t.hnt complrx niixtu~rsmay often he r~.solveclinto simple pure rnclionet ivc speries. Indeed, a s we shnll .w, this is the goal for thr rndiochrmicnl separations when 1ve wish to pmpnrP simple mixtures or pure rndionctive specirs for st1111yof thrir 1111r1rarp r o p erties. This hrings 11sto the d i w ~ s i n nof a large m d fruitful outlet. for the nuclear rl~rnmistwhirh hns led him far afield from what we u w l to consider chemistry and into the forrfront in the clewlopmrnt of mnny aspects of nuclear theory. Many exnmples of this work ~vouldIF nerrswry to proprrly clrsrrihe its scope, hut only n frw rnn IE givrn hew. One nslrrt h m to do with the di.srovrry of new nurlrnr plwnomrnn by identifying the products of nurlrnr reactions. One of the most astounding discoveries made by this method wn.s that, of nurlrnr fission in which the itlrntification of certain fission proilurtn by rndiochemirnl methocls Id to the intr.rprek~tinn of the renction. It mny he argued t111rt fis-ion could hnve l m n discorem1 by Home otlwr technique, for example, mensuremrnt of the large elec-
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trical pulses in an ioniznt.ion chamber. However, there are many studies which cnn best he pursued by chemiral methods and some in which they are indisprnsnhle. In pnrticulnr, t,he last few yenrs have seen developments in whir11 there can bc little progress without employing chemical sepnrations. The new high energy range of accelerated pnrticles is produring such cornplcx mixtures of reaction prorlucts that it is hqwless to attempt to dingnose the reactions without rhxnical wpnrnt,ions. In a single irradiation with partivles in the 100-Mev range thirty or more rerogniznhle radionctive species mny be formed, thnt is, they are recognimble if t.hey are first fractionated into the fifteen or so elements of which they are isotopes. To mnke these srpnrntions nit11 speed and st,ill ohtnin in most ewes rkqremely high purit,y is n first-clnu4 nnalytical joh rrquiring a goid knowledge of inorganic chemistry and the spocinl skills of r:rrliochcmirnl methods. Onre the separations have 1-n mnde, t hr rnrlionrtivities identified, nnd their yields n~c:~~urerI. one may then hegin to picre bogebhrr the nuc1e:ir rrnrtionn \vhich prrwlured thrse produrts nor1 011t:iin informntion n~ to what happrns w l ~ mnorlri am r s c i t d to extremely high e n e ~ i e s . Thew exitmplrs whir11 could be expnnded greatly indirntr how tlw nuclear cl~rmistuses rl~emiatryto ohtnin information on nuclear reactions that hnve occurred. Sometimes the ohject,ive is somewhat different but still in the direction of studying nwlenr phenomena. During the pn.st yew. for example, severnl in our lnhoratory hnve l ~ c o m einterested in extending our knowledge of nlp11:r-n~lliowtivity. This wns n ~ a d epoliqible by the nrwly nrquiml nhility to prorluce mnny new nlphn-pnrticlr rmitters hy making wr of the high energy ryrlotrons nncl the nuclear rrnrtors or piles. Many new trrhniqurs in rhemicnl sepnrntion and rnrlioart ivity merrwremrnts were developed for t 11e.wstudies. The interest in nlphn-rndioactivity is severid-fold. Ily menns of a large anlount of nlpha-decny dnta we are ahle to reconstruct the energy re1ntionships of the whole heavy element region; thnt is, it is possil~leto construct an enerm uurface in n thermodynamic senm relating the norlrnr binding energirs of all parts of this region. Secondly, hy using the quantum mrchnnicnl trrntment for the nlpl~a-decayprocess we were nhle to mnke some funrlnmrntnl changes in nlpha-decny theory and to mlculntc in n mrnnincfol fnshion the nuclear rnclii in this region. (~.ert:~in:rlmrpt cl~angesin nurlcnr rndius are furthermore interpretwl, dong with chnngen in nlpha-enerp?., in terms of regions of grent nuclear ntnhility. We have outlined this pnrticular study :IS it illustrateq r:lthrr well t,hr information whir11 can he nhtainrd hy charncterizing ratli~m-tive properties of a lnrge clmq of nuclirlcs and thnt the most. povr.rrful tool for examining these radionctivit.irs involvrs n grent cleal of cl~emistry. There is another major brnnch thnt we include in nurlrnr clamistry, and this consists of chemicnl investignt ions of t.he synthetic nnd rnre roxlionct ive elements. The unique fontures of this work are t,hat a t leaqt up to now the investigntor must ohtnin or recover his own
12 starting mnterinl by rndiwhemical methods; the chemical experimentntion is either on n micro or ultrnmicro scnle, nnd t l ~ experimentntion e is heset with the peculinr difficulties of working with intenwly rnrlionctivc sub~tnnces. While much informntion on chemical properties cnn Ix ohtnined on the t rnrcr ~ c d e there , nre brond e l m s of mensurrments which can only IE mnde st mncro conccntrntions or with the pure element nnd itR compounds. Thermoclynnmic properties nnd phgsicnl properties of the metnllir stnte nnd its compounds. nbnorption and emision slxctrn nntl certain nuclenr properties fall into this rntrgory. Even in the cn.se of propert,ies which cnn IF drduced by rndiochemicnl metl~odsexactmeasurements rnn only hemade with the element in mncro concentrnt ions. For example, we may get npproximnte vnl~wsfor solubilities nnrl oxidnt,ion potentinls with only trnrrr nrnount,~of mnterinl, hut nrcurntc values cnn only be ohtnined by more conventionnl rhemistry. The importance of determining the chemicnl nnd physical properties 11- led t.o the isnlntion of nll of the synthetic and rnrc rntlionctive elements for which there rnn lw nny hope of olltnining in pure state. Only rndium nnd protactinium (elements 88 and 01) hncl been ixolnted hefore the wnr, but .since 1912 technetium (43), promethium (Gl), polonium (84), nctinium (R!l), neptunium (03), plutonium (M), americium (05), and rurium (96) hnve nll hrrn seen nnd worked with in the purr stnte. Two other elements, nstntinc (8.5) nnd francium (8i), hnve no isotopcs of sufficient. hnlf-life to permit prrpnrntinn nnd isolntion. 0lwi1,urly the isolntion within the lnst few yenrs of eight new elements (to be sure of limited avnilnbility a t prr.%nt) o p m u~p wide new areas for study. There nre two great difficulties with this work, howver. First, the limited avnilnhility of most of t h e e elements mnkrs it mnndntory to work on R milligrnm and evrn microgrnm scnle. The nltrnmicrorhcmirnl techniques which hnve now been hrought t o a condition of genernl uwh~lnrsnhnve become an rnrmark of this hrnnrh of nurlrnr chemistry. The ot.her difficulty is the intrnse rn~li:~tion assorinted with even microgrnms of nlmost nll of thew elemrnts, making neces-nry apecinl terl~niques.nnd in some rnses remotecontrol cquipmrnt is nerrssnry. The forraoing explnnntion of whnt we include in nuclenr rhemistry \vns indulged in ns it. will help give reason for the suhjert mnttrr of our lcrture COIIIWS and m c ns n I~nckgrounclfor outlining the resenrrh progrnm in our lnhorntory. Two lrct,t~rrcoursrr in nuclenr chemistry nrr oflered in the Drpnrtmrnt of Chemistry, one rnch wmester. The first is a two-hour courw with nn undergrndunte numlxrdwignntion nlthough up to this t,imenl~outtwothirds of thaw enrollrcl hnve hren grndunte students. The object of this course is to provide n dmcriptivc survey of nuclear theory and methcils inrlutling nn introduction to rncliochemicnl methods and properties of rndintion. The ~ t u d e n t swho tnlie this courw nppnrenbly d o so for a numlxr of reasons. The lnrgest ~ i n g l e group consists of grndunte students who expect to tnke part in some phnw of nuclenr wrrnrrh or nre nlrendy
JOURNAL OF CHEMICAL EDUCATION doing no. Thisgroup includeschemistn in nuclear chemistry, physicists, nnd n wide vnriety of students in the ngriculturnl nntl life sriencvs. Other students tnke the cour.w na an elective premmnhly with nothing more in mind than to lrrome ncqunintd with n new and interesting field. Thc subjects covered in the undergrnduntc c o n m start with nn historicnl development and the current pictnre of nuclrnr structure including nuclenr forres, conditions for stability, nnd n qunlitntive nonmnthemnticnl trentment of the qunntum mrchnnicnl properties. This is followed with n flexription of the rndioactive decay prwesvs, the theories of Ixtn- and nlphndecay, and the properties of the rndintion. Induced nuclear reactions nre next treated, nncl this suhject. includm reactions with charged pnrtirlrs nnd neutrons, nnd the instruments whirh prodore them IU wcll ns the factors which govern yields. Sprrinl wnctions like the fis-ion process nncl the nuclear chnin rrnrtion are also dealt with. A brief survey of rcliwhrmistry then follows in \vhich no attempt is m d c to devclop n system of nnnlysis, but t.he prinriples of epnrntion nnd identification of rndionctivit ies from irrntlinted or nnturnlly occurring substances nre o u t l i n ~ l . Other suhjecte t r e n t d nre the clwmirnl nnd physicnl effects of rnrlintions on matter, \vhic+ is termed rndinlion chemialr!l, a survey of t.he nnturnl rntlionctivities, nnd the rhemiral properties and plncc in the perindir system of the new synthetic elements. In gcnernl, we hnve nttempted in this r o u w to give aturlents with a hnekground in chemistry n fwling for the n n t u n of nurlenr wnrtions and to indirnte .wnw of the t h i n e whirh chemists rnn do in the lirld. The grnduntr lerturr courw given the srrwncl remester is n i n ~ r ~more l sperifirnlly for grclunte students engngwl in nurlrnr \vnr!i. The outline of the subjerts covrwl in this rourw is not grestly different from thnt already mentioned for the un(lergrndnate courrc. Thrre are two mnjor dilfrrrnres, I~owevrr. In the ndv n n r d c o u w we build upnn the clcsrriptive pict,ure givm in the elcmrntnry rourse nncl give a more rigorous trentment nnrl n grrnt den1 moredetnil. %-rondly, since this course is primnrily for thowrngnged in wsenrrh we mnke a determined effort to keep it strictly up to date by the inclusion of npproprinte new work whirh comes out nlmost \vwk hy \vcek. Other clifferrnces in this course nw: (1) R more detailed trmt.mrnt of rndiochemistry including specifir renrtions for :dl of the clcmmts, (2) n brief survey, for the student's genernl interest, of curwnt idens on surh sul~jertsn- nstrwhemistry, cosmic rays, nnrl meson theory. In the grndunte cortw we also require ench student t o prepare n review paper on n sul~jertof his own choosing. This IIIU the importnnt purpose of nrquninting him with the originnl liternture nncl also testing his nl)ilities for cliscriminntion nnd correlntion. It mny Ix mentioned thnt n numher of the grndunte studmts evm nt, this early stnge in their cnrerrs prepnrc very rreclitnhln pnpenr which with minor editing \vodd probnhly conform to the standnrcls of the rrputnble journnls.
JANUARY, 1991 I t may be well to inclicnte why we offer no formnl Inborntory c o u m in nuclenr chemistry. At the present time surh n course would he of vnlue only to a smnll minority. For grndunte students in nurlrnr chemistry the policy of the dcpnrtmmt is t,o h g i n r e w r c h the first semester, nncl the fnrilities and instmct.ion by tlie research dirrctom nncl stnil m e m l ~ r sof the Rndintion Lnhorntory nre much l ~ t t r thnn r roulcl IE provided i n n formnl c o u w . Mnny of the other grnclunte xtu~lrnts are 1ikewi.w doing rrsenrrh in other depnrtmcnts, and lwmtles this t,lie merlirnl physics clivision of the physics department does offer n course in rnrlionctive mensnrements. Finnlly, the research lnhorntorirs are open to qunlifird undrrgrnrluntes who con thus ohtnin better instruction and hnvc nrcesq to better fnrilities than they rould in n formnl course. The rhemishry depnrtment does o f i r nn instn~mrntscoursr in which rnclintioncounting equipmrnt is one type whir11 s t ~ d r n t unre tnught to unilrmtnnd and use. It may t ~ rmentionwl thnt the physirs depnrtment gives niwlrnr physirs ns two C O U ~ S one , undergrndunte nnd one pmcluntr, nncl nlso otTers no formnl lnl~orntory courses for physirists. For ndvnnced students doing nuclenr m n r r h thew is nlso given in the c h n i s t r y depnrtment n wninnr which mrcts \\.cekly nnd the physics depnrtment similnrly hn.7 n nurlenr seminar which a nomlwr of chemists nt.tend. Other specinl meetings surh n s those held by the Rndintion Lnhorntory are open to qunliliecl students. , I he m.wnrc11 proprnm for grndunte students in nurlmr chrmistry nt the rniversity of Cnlifomin is of ronsidernblc hrendth and probnl)ly differs in n number of rrsperts from that nt other s(.hools. First of all, nn explnnntion mny IH? in order for the functions of the Rndintinn Lnhorntory nnd Drpnrtment of Chemistry in the t.rnining of grndunte xtuclmts. All students in nuclrnr rhrmistry nre rnrollrcl in the Ikpnrtment of Chemistry nnd must sntisfy the ontrnnce rrquirrments, pas.. the examinations, tnke the r o u w s , and otherwise fulfill nll of the rcquirrmwts demnnded of nny other rhemistry grnclunte stutlent for nn ndvnnmd degree. The degrw? whrn ohtninrcl is nrrorclingly granted in rhemirt ry hy the Grnrluntc Division of the Lynivrrsity. The Rndintion Lnhorntory on the other hand, is nn orgnnizntion whir11 offers no formnl instnwtion and gives no degrrrs, but proviclrs rrwnrrh fncilitirs for it,s own staff mrmlwrs nncl for the depnrtments of the universit.y. hlwt of t l ~ senior e staff memlx-rs of the Rndintion Inhorntory nre also memlws of one of the ~cvernl departments suc11 ns pl~ysics, rhcmistry, mnlirel physics, nml engineering. The grnrluatc students mny either hold tencl~ingnssistnntsl~ipsin the Drpnrtment of ('hemistry or part-time rrsrnrrh positions in the Radintion I,nborntory, whirh nrc in eswnce resenrch frllowships. Howevrr, all students are expected to do Rome tenrhing during their grndunte years. An entering sturlcnt mny selert nny of a lnrge variety of snhjrrts for his resenrch. Those intmwted primarily in the applicntion of tracers mny, asnn emmple, elect to xvork with Professor >I Calvin . on bio-orgnnic studies
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13 such a s Ci4 work on photaqmthesiq or with Professor R. E. Connirk, w h w main fields of intereqt are renrtion kinetics and complex ion formntion. On snhjects somewhnt closer to nurlenr work, l'roferwor 1%.B. Cunninghnm is primnrily concernrd with tile chemistry of the t.rnnsurnnium nnd rare enrth elements nncl is the authority on the oltrnmicrorhemin~lmethods a . d in these chcmirnl stuclies nncl snme nuclenr studirs. Proh on nuclenr fessor D. H. Tcmplrton, l ~ s i rnrrying m.vnrrh with the nrrelerntors, operntcs n Inhorntory for X-ray diffrnction studies of crystnl structure wl~ichhe npplies to the synthetic: elements nnd to other purposes. Another memher of the stnff is Dr. I
