Asaro, Frank

Perlman, Isadore.

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Lawrence Berkeley National LaboratoryRecent WorkTitleAN ISOMETRIC STATE OP URANIUMPermalinkhttps://escholarship.org/uc/item/0kh776m7AuthorsAsaro, FrankPerlman, Isadore.Publication Date1957-05-01eScholarship.org Powered by the California Digital LibraryUniversity of California·j· ' ~,.. . ' {· ·: UCRL 3774 UNIVERSITY OF CALIFORNIA TWO-WEEK lOAN COPY This is a Library Circulating Copy which may be borrowed for two weeks. For a personal retention copy. call Tech. Info. Diuision, Ext. 5545 .BERKELEY. CALIFORNIA /'-w /BC:-ii DISCLAIMER This document was prepared as an account of work sponsored by the United States Government. 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UNIVERSITY OF CALIFORNIA Radiation Laboratory Berkeley, Callfornia Contract No. W -7405 -eng-48 AN ISOMERIC STATE OF URANIUM-235 Frank Asaro and I. Perlman May 1957 Printed for the U. S. Atomic Energy Commission UCRL-3774 UCRL-3774 Frank Asaro and ! . Perlman Radiation Lahori'il.tory end Department of Chemictry University of California, Berkeley, California. There 'lias been an a.p-pa.ren t :i.ncon::;istency 1n tb.e data concerning the energy levels of if35 e1."er since lt was noted tb.a.:t: (1) The groUnd st.ate spin ~f u235 ·determined from op·t1ca.l spectrum . . . . I 1,2 h:Y)»+fine .structu.re ·iB T z, and thic is in agreement with ·Coulomb excitation stu.dies.3 . 2''5 (2) The l.o'dest lying st.ate of ·u J populated in the al.pha-deca:y of Pu23~ a..p-f)ar~tly ha.G spi.n-l/2,. since it and tlte se<;tuence of lllvels .fibO'lfe ,it have the characteristics o.f a Bohr-Mottelson rotation~ band wlth ~pih-1/2 baoe ·state. 4-,5,6 (3) 9llere is ·no obv-ious gamma .. ray trm:miti(jn from the 1/i. s>t.ate ?:~9 . to th~ 7/2 state, e'i:'en though virtually aJ.l· Pu'"'_. a.lpha.-·tra':lsiti.on popu.la:te directly or indirectl~l to the a:pixl-1/2 staiie. . ?~0 Thls in:f'or.nation sUGgest.~• that Pu "' ... u decays to an isomeric state of' ~35 \iihich is either very long lived (to explain the f'a.ilare to find the abu..."ld..ant ~/'2. -> 1/2 ·glillmla-transition) .or t-wo states lie s.o close together tlia;t tl:l.e radiation i.s nG:t ob~ervable by u.aual. methods. For a.n E3 transition in a heavy element it .is jjuprobable that the llfetir!ie ca..lrl b~ long, since, as will .be pointed out at 'the end of thi.s note, no matter how low tiLe ener~ . I · bec.ames 1 the c.c.nvers:i.on coe:f'fic:lent becomes correspondingl;y large. .Nevertheless, ml the sup;pos.i tion 'that the radiation t.;a.s IOOa.surable but lo~g lived, care:fu.l r-ray and conversion el.e~-tron measu.rem~mts7 were made il:l this laboratory on a. smxwle of ni'!39 t>lb.i'ch l:iOO. .aged· for severaJ. years and failed to show ~ rs.diations other than those l,}reviou.sly seen. In addition, a C'.lten1ical. separa:tion of :uranium was made; this aJ.so gave ·no evidence fOl• tile . . . . . 1~ Very r(!cen'tly Huiz;enga, .lfugelkemei.r and To:npk~ ) have . ?~ . . . . 2~ spectrum of U'"'J · removed from Pu j and fo'Uild only the l<f\~r limit of six .months for the half-life of au isor.aer ' •:i i . 4·- i' . v sOlll'Crl.c w_,ans. \il.on. looked at the optical '7/2 st;.ate 1 setting· a of spin i/2. Th~ alternate explanation that the radiation WRG too soft t.o be detected under the means ~~~oyed t~ere~ore seemed more attractiv~; same evidence for this ~peared to ~erne? from ·the measurement o:f the conversion electron spectrum 0:f .shllagin9 who found 2 kev electrons 1~hich w·ere fairly prau:i:Irent·. .:..s \>.riD. / ·"'~---.. ---·-·- -- . / . 1 UCRL-3774 -2-. vt::;r;· soft electronlil,. b-u:t these seem to be of even lower energy than thoBe l"elXJrted b;)~ s.t;U.ia;gin. Tile ii:somerl;c ~tate confu•nung theae concJ~unlons wus found by collec'f.~ing · ·' .,.,9 . 'J>"5m recotla from the ~-,ha ... decay of.Pu."'5 . a.nd counting t..~e tr<; · in a windowless pro;portienal · tU>unter. · The. l':Jsnrp.le:s were fir.ert collected Ol:l aluminun foils, -~ing (JOO volt negative potenti.aJ. to dfr{.tO:s·1 t the ions mlich had: dissipe.teCi. t.l:ieir recoil ent::r6t¥ in air. :Seve-ral <>ample a zo collected contedned about 3000 counts per minute, ·wniclt ck::ea.yed t-o the b~kground of 20 c-vunts wi';;h. e. half-life· of ·r:!6.5 ±. 0.2 ntin.. In o~ e~riment a chtl!micaJ. separation of uraniura from ·piutonium :,<1-elded ·e ~npl.e with i:Jlr.~ aek'ilE'! decay chartil.Cteristic·s, b~tt th;,;!: a:ppe:r~mt ·yie.ld was low- bees-use . of u~:tf ... absor1''tioo of: the extremely soft ele(:trons. Bjr ~ recoil. method froru a s.a;.uple of P..X~j9 wbiclt had .a !:>~f~e density of 1.5 ~,., . .~.. ·~3.5m . ~ .. • n1·cro~ejcm ... , tae yield of soft elect-rons from ooe U' con-espondeu wivh 1 - - ·;!!-::'\ ...... \ elect~oo for et:leh five Pu"".J~ alpha-emissio-n eventz. ,';, oa;•apie of :plutunium •:1. . crO?Jlc~t -l.illl.c.k-er ("" ·7 :tif!Jn/'ar{') t,"'C\V'e an inteus1 ty of' ooft electrom; of only l;f,, '>'1'>0 so it is entirely .reasonable that every Pu~s? dec£\)' eYent goea t.lu-ough thiG iSuu1erlc tr~iticn. ~~ r<tue;h .measure of th.e e.n<:?l"'g;y of the el~!ctrotls was F...ade ~.Y an. absorber 'l;echniqtle in Which recoils trere ca~:t on thin plastiC fJ.lti'm end Ct;t.i.t}ted, With the ·s&l.¥~ aJ.ternnte,4"' f'acirv.; upward end dQt>n:nlfnrd. The ~range'' so .de'ternined j,nd~ca:ted that_ the energy o.f the elect.ronJ? is les~ than 1 kev. i;. plast.j;c film of 2~5 1J.Jicro~amsjc:A2 t.hicl"'-"leES cut dm,.'U the counting rate by a fs.ctor graater t...~ lOQ., so there &,e-s not seew. to be ru1 appreciable !HJmbcr of ele~tr<u"lS '!<rith energy even o.s hi~1 as 2 kev. 2~•5 t.l,Il exemina'Q.o-.a .0£ possible BS'Si!PltlieDt.G Of the two U :J leve·J..:; according ~-~ cr-,u·· ·"'--···"·'·n. par;-l.·-e··· 1·' ·.-- eta· te~fr·.o .. :·.·-11 .;,... ;,~"" ~"' 11 t. ·h · ........ __ ·· tAJ ~~ ;::.::;..., -;:: ......:: · :.; • " .w.• a. \A.I::.kO!'fficu \,re 1 Bl1G•9'eS ·S z; a~ w= .l'JOG't. . ' . • 0 ~ likel~ .. as·si~nts consi.etet!t with all in:formation a.re l/2+ { aa)'i'trp.tct.ic t,tuan.ttl!'J num~rs N ::;:. 6, n :t: 3) and 7/2.- {Z>T = '7, n.., = 4). The isomeric tren-<.;ition 1roul.d ·~ ~ ~ tr.anir:it:i:.on eneriW is deduced to "b;; 2.2 kev or les:;; USE\.mD.lig N11 , n:1Il conversion ac:cordi,ng to the follm'i'i.ng rear;;oning: If' the el.ect~ons are te.ken to be 1 keY and they r.e.suJ.. ted fran M shell conversion ( la.rgely s~1 and f-L. levels) there should aloe be CiGea:b1e numbers of d.ectrons froi!1 N ghell " \~ J.U . ' ~._I ,· 1 , .. '~ UGRL-3774 -..)-conv;:;rsion; the:Je !tould hav~ .energies of about 5 kev. Neither Shliagin' e electron spectr;.Xtil nor our abc:orptio.n !F."-!a,sure.ment;s ge··re evidence for such electrons. Con.:;Je<:;;ue:n:t.ly, the sof't. electro1w must com.e fr.orJ conversion :L'1 l{ Hhell or h.ig..lier. With les:J C(JD!id.ence the sim.iler argument c.&l be made tJ::s.at the e.lec·trons ~«e not converted in the 11 :;~hell becauze t:he N and 0 ed-&tec. <U.ffer b:,.• "' 1 k(;n'. If tb,e ohse:r,.r.cd electrons come from 0 .shell conver::>ion, the tran:::ition energy \<TOuld be l. £-~ kev or l.ess. Obviously, In·ter.en·dngly enou,gh, the ccl.cul.a.ted lifetime f<;.l• till.s transi~cion i;~ a.llrtOd'G :L.'lde:r;.e:rtdent of \12:ca.;y energy i.u t;he E!'il'..'}I'g}F ra.n.t.,re of in~erest. 'rne ($mnme.-ray emission oo.l.f Uv:;:;~; ha.r.ed o:n the 1singL2 pro~wn r,ran:.;:Ltion· relations , ··~ ~ . _, oi' l~adcmr.;ki are :shovm in 1fuble ! for a series of <..;;a.,lli:la er.tergi~s, U..\'ld ~.so l'·' listed are internal eonw.:rsion eoeffieient.s oiy;:;aiHC!d. l)y extrapolatj,ng Rofie' s ..1 H chell oo.2fficientz and aGSlt.ing 3-fold decreaGe for the t~ ~hell and for by an order of ma6iJ.it.ude for a chan"Je in energ,y of c. facf;or of 10. If 1-re th fo. l' ·;-·r··l.n rqZJ5m .~ "'-<·' ·~ • -" '~-., ~ li ~ h 'ld 1. ~ as sumc · . til;t v ~ ~ ~"""""" t;i:le 1~a.:sureu l..tl:w..::.:- · x e ;; ou~ i..>e :;.:;eco.."lc., 'l.'abl.e I Cale-u.lated hal:t'-lives and emrrersion coe:ffic:ients B,..j -~ansi-~ion in i.i!'at!.iUUL Energy -~ Partial y -decay c0n"fersion --(kev) half-life (sec) coefficient .,:_o=.;:......J_:.______ . ___.......,:- ~---·-10 1.1 X 107 q 5 l.J~ X 10" l ~ 1 1.1 X 'rrl.. '~-..1..'· 11.' 1 1(. 1'' 0 -· X i.J 0.5 0.1 1.1 X 1"31 i,} --'I'ota.i half -life . __ .....,{_s_ec __ L __ .1 .1 1 1 10 f UCRL-3774 1. K. L. V·ru'J.der Slui s &nd J • R. M.cNal.ly 1 Jr. , J.. frvt. Soc • .~!J.ne:r. ~ 65 (1955). z. c. ':,. rfutchison, Jr., :1?. H. Lle1itel.l:yn, E. \long, and: P. Dora.in, Phy;:; .• Rev.~' 292 (1956). 5. J. 0. lf0•.rton; Nuc. Phys. Vol. 3, 1957 (in press). :\. E.o~, P. o. Fr&m.n, and 'D. R. .f.bttelson 1 Dan. i•iat. Fys. !oodd. £2., l~o. 10 (1955). 6. L. L. Gr:d.'din, E. I". ':i:Tet'ys.kov, and G. I. NcYikcva, Cv·nf. Aca:d. Sci. U~'38R on Pea.c~ful Usc of Atomic Etlel•gy, Pllyo. l..,rath. Sei. li 226 {1955) .. " 7. The conversion \?.lectrons l>tere measured tti:th e perm:onent magnet spect::ro-B. ,~;n experiL\lent by D. 'west, S. K. D!31vson, and C. J. f:.ia.:tldleberg (British ,1.tomi.c L"'nergy Research Estel1li•>bruent, report /\ERE N~R 902 (195-2)) on 9. K. N. z:hliagJn, J. Exptl. 'l'heoret. J?hy~,:. { U0SR) :1l; 8r{ ( 1956} • 11. I. Perllaen and J. 0. Rasmussen, Uuiv0rsity of Ca,lifon:da Radiation I..nhora:tory R~:port UCRL- j424. \'F~'16) j', • 1~~.. S. A. }.1o~r.koi·r:,;l::.i, Chaj!ter XIII in ''B'..::ta and Gamma Ray D.I,~ec·trosccrpy," K. Sie~ahn, Editor, ( L"'lt:erGc.ieD:Ce FubliBhe.rs !fie. ( 1955)). ,,., -.). 1). J. R. Hui~:.enga, :0. ¥.. ~--elke.":n.t?ir, and .!:<"'. s. 'lbt.'1pldus, Bill. >:In. Phyr->. .Soc. £., 190 ( 1957) • 

AN ISOMETRIC STATE OP URANIUM

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