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\7" Radiation Laboratory University of California Berkeley.. California
Contract No. 1J-7405-eng-48
LRTIFICIAL Rt.DIOACTIVE ISOTOPES OF CERIUN PJJD L.L\.NTHANUM
James B. Chubbuck Special Review of Decl•uified Reports Authorized by USDOE JK Bratton Unclassified TWX Pl82206Z May 79
REPORT PROPERLY DEClhSS!F;ED ~~~N~G~ru~~~--~~~L rized Derivative Classi ier lf~Date ~~< ~~.zAt-(1-j_ May 17, 1948 UCRL-109
(.'i'-.!i.J.)!;lFlCA'HI)N C 1\.i~C!:'c.i)" .::> ,,r,y AU1'.Y.0,'1~TY . OF' Td.E Di5T£ Standard Distribution Copy Nos. Argonne National Laboratory 1-8 A:rmed Forces Special Weapons Project 9 Atomi.c Energy Commission 10-11 Battelle l\A:emorial Institute 12 Brookhaven National Laboratories 13-20 Carbide & Carbon Chemical.s Corporation (K-25 Area) 21-24 Carbide & Carbon Chemicals Corporation (Y-12 Are a) 25-28 Columbia University (Dunning) 29 General Electric Company 30-33 He.nford Directed Operations 34-38 Iov.ra State College 39 Los Alemos 40-42 Mon-santo Chemical Company, Dayton ( '43-44 National Bureau of Standards 45-46 Naval Radiation Laboratory 47 NEPA 48 New York Directed Operations 49-50 Oak Ridge National Laboratory 51-58 Patent Advisor 59 Technical Infonnation Division, Oimo 60-74 UCLA Medical Research Laboratory (P!arren) 75 University of California Radiation Laboratory 76-80 Universi~ of Rochester 81-82 Declassification Procedure 83-92 Chemistry Department 93-97 97 Information Divis ion Radiation Laboratory Uni ve:rsi ty of California Berkeley, California / 1 ~"~;::~~~;gk~~:',~~t~}~,'?;,> c ARTIFICIAL RADIOACTIV:d: ISOTOPES OF CERr"D1v1 1~IID L.AJ'f;'_HiJNUM - ---·~~·-'~;, ,'~~j}J Radiation !8b o~:~:; y~ 'u~~ ~:~ ~~~Y of ~~~ :,;o ~:~:;: ,;, ~~~~'::''"' Bcrk eley, Califol'nia \ ABSTRACT A description of some bombardments performed with the 60~inch and 184-inch cyclotrons at Berkeley• These bombardments resulted in the production of the following isotopes: 19.5 hour Le1 35 which decays by orbital electron captur.e and emits gamma radiation of 0.76 Mev energy; 2.1 hour La 136 which decays by positron emission, the positron having 0.84 Mev energy; La137 which has a half-life greater than 400 years; 16 hour ce135 which decays by positron emission; 36 hour Ce 137 which decays by orbital electron capture emitting conversion electrons of 0.18 Mev energy and garn.rn.? radiation of 0.28 and o. 7.5 lv1ev energies; and 140 day Ce139 which decays by orbital electron capture emitting conversion electrons of 0.1.5 . Mev energy and gamma radiation of 0.18 and 1.8 Mev energies. To be used as ~hesiso Contract Noo W-'7405-eng-48. '~ ; ' -:--, ARTIFICIAL RADIOACTIVE ISOTO:iJES OJ!' QiE.#~,i:AtJ:BNh00Bi~1_NiiJidy ~ui'HORITY' ,:; OF T, 12 I:WHi::U ;T ENGI. .:E£R '--".J-.:..Y BY THE D.ECLASSIFlCA TION COMMITTEE James B. Chubbuck Radiation LabQratory, University of California, Berkeley, California INTRODUCTION In this thesis are described some studies of the radioactive isotopes of cerium and lanthanum lyi.ng on the light or neutron deficient side of stability. It was only with the development of the large acoelerstors at Berkeley that it became possible to inves tigate isotopes far on the light side of stability and these are, of course, of interest as new nuclear types. The nigh energies required for the bombarding particles were not heretofore available. The production of cel3.5 by bombarding stable La13 9 with deuterons, for example, requires knocking out ' six neutrons, the (d, 6n) reaction. A further point of interest for the particular isotOIJes investigated here lies in the fact that the fast particle fission of bismuth has produced neutron-deficient radioactive isotopes in this region and the studies in this paper have helped to identify some of these. Finally, these studies fill a few gaps in the table of isotopes and thus eive a better picture of the distribution o~ half-lives and decay properties on the light side of stability. In these studies radioactive isotopes of cerium were produced by bombarding lanthanum VTi th deuterons in both the 60-inch and 184-inch cyclotrons. Those of lanthanum were produced both by bombarding cesium with helium nuclei in the 60-incn cyclotron and by- the decay UCRL-109 Page .5 of orbital electron capture or p·ositron-emitt1. .ng isotopes. 135 In Chapter I, two isotopes of lanthanum, La and La13 6 are assigned characteristics previously assigned to La137 and La13·8 respectively and further characteristics are reported for each. Lal37 is discussed briefly. Evidence is pr~sented for the mass assign ments made. Both La l3 .5 and La 13 6 w~r e produced by bombardments in the 60-inch cyclotron. Lal3.5 was also produced by the decay of the positron-emitting cel3.5. 135 Chapter II is concerned with two new isbtopes of cerium, ce and ce137, and evidence is given for their mass assignments. Both '• cerium isotopes were produced in the 184-inch cyclotron. Further characteristics of cel39 are given. This isotope was produced in bom bardments with the 60-inch cyclotron. Chapter III consj_sts of a summary, and y·ield. dc;ta for the various bombardments are tabulated. These experiments were performed under the direction of Dr. I. Perlman, to whom I am indebted for his continued interest and assis- tance. ·I wish to thc:nk Dr. G. Wilkinson, Mr. Ho Hicks, Mr. R. H. Goeckermann, Mr. M. Lindner and other members of the chemistry section for their help and suggestions. I wish also to thank Dr. J. G. Hamilton, Dr. D. C. Sev- 1ell, Mr. Jo T. Vale, Mr. T. Putnam and l1r. B. Rossi for cooperation in operating the 60-inch and 184-i.nch cyclo trons. This rese[.rch v·m s conducted under Contract No. W-7 40.5-eng-48 in connection wit.t'l the Atomic Energy Co~ission with the Radiation Laboratory, University of California, Berkeley, California. UCRL 109 Page 6 CHAPTER I ARTIFICIAL RADIOACTIVE ISOTOPES OF LMTTH.AN1JM James B. Chubbuck Radiation Laboratory, University of.California · Berkeley, California INTRODUCTION On the neutron-deficient side of stability two radioactive 2 3 is ot o_pes of lQnthanum, Lal37 (l, ) and La138 ( } are reported in· the ( 4 ) 138 literature but more recent evidence shows La to be stable and present in nature to the extent of 0.089 per cent. No lighter 137 isotopes of lanthanum have previously been reported. La is re- ported in t4e references above to decay by orbital electron capture with a 17.) hour hal.f~Jife and to have'gamma l,'adiation of 0~88 Mev energy. It was pre due ed by the reaction Ba ( d, xn). Since barium has ) five stable isotopes, this mass assignment could easily have been in error. Evidence will be presented below for assigning these charac 135 teristics (with some changes) to the mass assignment La • La138 reported above is assigned.a half-life of 2.2 hours but no othe~ characteristics are given. Evidence will be given below for the as- 1;;6 sir:nment of an activity of this half-life to La _, and further oharac- teri~tics will be given. It is not clear that La13 6 could have been (3) J?rod uc ed in the bombardment of Pool,. Cork and Thornton ·In all bof!lbardments of lanthanum with deuterons to produce 140 cerium isotopes by the (d, xn) reaction appreciable amounts of La , were produced by the (d,p) reaction. This isotope is so well- ()) known that it has not been discussed in this thesis. UCRL-109 Page 7 The higher energies now available v'li tl1 the 60-inch and 181.~-inch cyclotrons permit the bo.mbardment of cesium with helimn nuclei to produce lanthanum isotopes by the reaction (a,xn). Since there is only one isotope of cesium present in nat u:re, difficulties of working with an element like barium with its five stable isotopes are avoided. EXP.~RIM:i;NTJ~L The cesium sanples used were in the form of CsNo , .prepared by 3 A. D. Mackay Co~ and stated to be of gree;ter than 991o purity. Spectro- ( 6 ,. . graphic analysis showed rubidium to be present to the extent of leffi than 0.51o so the cesium was as.surned to be of sufficiently high purity .. Any appreciable content of rubidium would have greatly complies ted the chemistry by producing isotopes of yttrium in tho bombardment. The separation of yttrium and lc:nthanum is time-consuming, and since short-lived lanthanum isdtopes wer'e sought, it was essontial that the cesium be of high purity. Cesium in the form of 1,13 gms. of dry, powdered CsNo was 3 mounted on a copper backing plete of the 60-inch cyclotron and covered 2 with a 28 me/ cm aluminum foil. This foil was chosen of proper thick ness to reduce to 30 Mev the normal beam of 37 Mev helium nuclei. The dry, powdered crystalline CsN0 was pressed into the central depression 3 of the backing plate and the Al foil placed over it. With the Al foil cemented along the edges of the central depr8ssion, no displacement or lo,ss of the target mat erial due to handling was observed. The sample was bombarded VJith 30 Mev helit.llll nuclei for two hours. In:uuediately after the bombardment the target ms.terial was dissolved in UCRL-109 Page ~ water and barium and lanthanum carriers were added. The solution was then saturated with HCl gas in an ice bath,, ethyl ether was added and the solution shaken, The precipitated BaC1 was filtered. out, ' I 2 both the precipitate and filtrate being retained. The filtrate was diluted with 10 ml. H2o, made alkaline with concentrated NH40H and the lanthanwn precipitated as the hydroxide. The La (OI1} was washed 3 several times with cold H and dissolved in a few milliliters of 2o concentrated H.Cl. Barium carrier was added again and the precipita- tion of BaC1 with HCl ga3 and ethyl other was repeated. This cycle 2 was repeated a third time and tho lanthcmum again precipitated as the hydroxide. After washing several times again with cold H20, the La(OH):z was dissolved in thr~;e ml of 6N HCl and this solution used as ,./ stock solution for preparation of' samples for decay curves and absorp- tion curves. The chemistry of this bombardment would have been more precise, and loss chance for contam.ina tion of the lanthanun~ introducel, if the lanthanum had been precipitated as LaF • However, no compli 3 cations were evident. The BaC12 from the first precipitation was retained so that its activity might be checked. Results are discussed below. COU1\fTING K~UIPMJ£NT Electrons and -Jlect":ornagnetic radiations were counted with argon-ethyl alcohol filled Geiger tubes having mica windows of about 3 mg/cm2 tllickness. The pressure in the tubes was 10 em of Hg, 951. of the pressure being produced by pure areyn and 51o by the ethyl (7) (8) alcohol vapor Geometry factors ·were assumed as follows first shelf 30~, second shelf 101., third shelf 51., tourth shelf 21. and_ fifth shelf 1~. UCRL-109 Page 9 Positrons t:-:md negative ele ctrcns were differentiated VJi th a ·magnetic counter, with which the paths of emitted particles are bent by a magnetic field so as to direct the particles into a Geiger tube • .. Reversal of the direction of the rr0gnetic field permits the differ- entiat ion of posit j_ve and negative electrons. The mo gnetic counter also permits an estimation of the .anergies of ~he particles. By varying the magnetic field from zero to some maximum value, at the same time recording the number of counts for the applied magnetic field at that particular time, a curve is produced starting at the count or bacl~ground, rising to a peak (p~int of maximu_rn counts) and desc•.:mding to the backgrou.."ld. In this paper energies of positrons .•. have been taken as the energy at the vi.sual end point of the magnetic cou.p.ter curves. Visual end points selected· are indicetted on the appro.J?riate figLU'es. Calculc tions oi' energies were mode from the 4 2 1 2 formula Ji e (in gauss-em) :::; (10 /3} (E + l.02E) / , where E is in Mev. The energy of conversion electrons from orbital olectron capture isotorles was taken as the en :,rgy corl"esponding to the peak of the curv·e, since these electrons are homogeneous in energy and net dis- tributed as are the energies of ~~ pc.rticles. The magnetic counter also shows vrhen there are no chc:rged particles being emitted from a radioactive isotope. The use of this function of' the magnetic counter will appear in thG results to be discussed below. The energies of positrons and conversion electrons were also determined by beryl- liu..rn absorption curves. In foot, the enr.::Jrgies as determined from absorption curves are probably more accurate, since the ma~snetic counter has not been caJ_ ibrated. Counting efficiency of electrons was taken as l001o. UCRL-109 Page 10 - The energies· of electromagnetic radiations (x..,rays and gamma rays} were determined by absorption in aluminum and lead. The determination of the presence of L x-rays was made in only one case, Lal3.5, since their energies in this region of the periodic table are so low, about .5.2 Kev, that they are usually masked by electr.on. radiation. K x-rays and. gamma rays up to 0 • .5 1VI0v energy were asswaed to have a counting efficiency of 0 • .5~. For energies greater than 0.5 ~fiGv, the counting efficiency in per cent was assumed eq_ual to tho energy in Mev, i.e., a gamma ray of 0. 7 5 Mi3V energy was as 9 sumed to have a counting effici~ency of o. 751,( ). For all absorption curves reproduced in this paper, correction has been made for the mg/cm2 equival-ent of the counter window, the air gap botw.:oen window and sample and the materiel covering the sample. The samples are assumed to ha.ve been suffic1ently thin to require no correction for self-absorption. CROSS SECTION L:I:Li:i~SU::mHENTS Cross sections wore calculated on the assumption that the target was thin and that the beam intt3nsity was not diminished appl'eciably by the ssmple. The total beam current for the bombardment was ob- tained from the cyclotron records, the number of ato~ns bomberded was calculated from tho known we1ght of the sample and the number of atoms · tl"ansmuted was estimated from counting data. RESULTS 2.1 hour La13 6• A sample of thG 1anthanv.m fraction from the irrad1ation of cesium 1Nith 30 Mev helium ions was followed in its decay, resulting in the decay curve shown in Figure 1. This resolved 6 .. ··--- ... -::.::r:.::_.::. :::._.: --·-·· .. ------.----· UCRL-109 lJage 11 into 2.1 hour and 19 • .5 hour half'-lives. Both of those periods,. there fore, must belong to isotopes of lanthanum Of mass nun1ber 1.36 or lower. Immedistely aftor the le~1thanum was separated a sample was placed. on the megnet ic counter and a well-defi.ned positron peak was observed. This peaJ-;: is reproduced in Figure 2. The same sample showed no ne:;gative particles. The visual end point corresponded to an energy 6f 0.82 M.::;v. A beryllium absorption curve, corrected for decay of the sample during the time necessary to t-::1ke the absorption data, is shown in Figure .3. .A part of the curve does not appear but . tho lino indicating the gamma background is as shown. The high gamma background is caused by the gamma radiation of t.ho 19 • .5 hour Lal3 6 also prosent. A Feather analysis of this curve gives a range 2 in beryllium of 310 mg/cm , correspond.i.Gg to an energy of 0.84 May. Allowing more weight to the range dot0rmined by the Feather analysis, we take the energy of the positron as o. 84 Mev. An aluminum absorption curve corrected for decay was also taken ahortly after the bom.bardment, whilo both components wore still present. This curve, Figure t~, could not be accurately resolvod in so far as the ga1ililla radiation w:,c,r-3 concorned. Estimating the position and drawing the line for thG ganJ.ma radiation at. the proper slope for the 0. 76 Il/lev ga(1nma determined in the le;ad absorption curve, Figure 6, 1 rosol ve K x-ra ys of about 3 4 Kev. Part of tho curve is off the paper, but tho curvature continues so the missing pa-rt is of no help. Tho 0484 Mbv positron causes the CUI'Ve to rise so steeply at the left, \ ancl. on an expanded scale tho positron could be resol voo.• ! -~~~-· ~+-:L-t. ~--_-t_l ~-t:"":~.: --t- ~-~-•---~--- zesB - 35zB 0 1792 Gotf.l.ss-cm .: ======~~~---~.....,.-,.--,--.:-,--! 1: -:---:--...--::~·,..,...__ ·.,--_: __ .,...,~~.,..,: -':L-c-•; . ...,.·: ~-==::.,..., .. ~ :}~r~,~~""};.~::;=:k=:::-~:::ro' -~}:--:'_ ---,-,,_ ,.._ ': '...,..>'<--_j-:-:r:~;-:-::_ :·-::::;;::::c~:?::~:::-~~:_:r:;:::~;:::~~:=:~:~-o::1t'1~ l--::::::i~-:·:~0:.':_"~::::::-; -~r- ·~~l~: s __~----~---~~~--~_:~;_:.+J~_;:~---~-~~-~~:~0~:.~~;~Pt:~~~~~~~~0~:.:~~:~.~~:.~;:~:~~+--t~~~~=~~:~.~~:-b~-~:~~:~0~-;~~?:-~~~~~~~-~~~~~~=~~~~;~-~=~--~=--=~:::?.~ b :~: ~:: :< _+1: .:.....--=~---:.__;+. :----~--:.~~:-::~:-:-::}J~;;~,c:c ~-:;~~ :;.;;~~ "; :_1'( ~~~''~i ~'< ; ''f;i~"c'c .- -. :~4~~'";"'= 5--~~---;----__ ,______·L ::: •.:- __ :-:,_. __ ,_~-·--- -~----·--·~---·--···------····:---·-·-·-· Be absorpt1on C(lrve 4 3 ~-·-·..:.... ... 6 4 ...... :. 1.: I· 0 100 zoo lG=r==r==r==s=:w·::wm~~-9 - ~ ~-~~~PTI:IIIIJ~~~~- J.::·~~FT~~~~ s --+-'-.,--i----:+..:.....:...-:-:--+--:-~-'-t.....,.-',-'_-'-:-r_'-:-~:c-.. :c-_.:-r.,--· ~-:-:-t.,...-_-=-:_.,..._ AI a. b s ",.-p f i o n c ur ve before decay of 6 ! 1 6 --+-:-_;:_.:_+.:.._:_::~:..:-:-::-~r=::-::-::-:r:--:-:-:-~-:-:-:-:--:~-::::--:::=:-t-:--.--::11 2. I hI" L a ~ 5_-+--:-.:.:..:.:.:...... :...:+....:...: ...:..:..:.:..=-t-.:...... :..._---1----t---:-- +·--=-· =-=-·-=-· r-·:-:--:·-:-··•-j:~-== rlj (j re £{ -.:·=~:::-t~~~=:~ ---+-~-~-- ·-'··-· ~- _·::..:·-· ····-::..:: -l ··-···~------'--~--- 4_~~~~~~~~~~~~~~~~~~~~~~t7~=t~~~~i7 ~~...::~~:_:.:~-=,.:-::::_.:c.;;-=--:~~ .. =-=-=-:::::~::_.:...... ::.·~ ::i ~-'--.:~r;~:· ~c. ;_~=~~d~==-:...:.._~~---·, __._=:-=~- ~~~- .. -~ -~-: -:_ ~:_:- ..:·C::·~t=t--~--::_~ ·::=~.:::::=~t:.:.:~-: :.-? ~ .f ~ i:· i·~ . ~-l:: ~--i<: .-: ·:·: ~~ -~;-:-_::-~ 3---4r=-~:-=~~:....:...._=: -=:: _=t=+, =.::.::-.::._-~=--=: -=-=. _::t==--==- --===~-·_= .._._..:::::~:£_ r-=_:-·=::=-_:-=::-~==.~::=t_-.::==-:::=~ ~-=:~::=::-t_f=··=:~· ::=_-:-=:_==-~:+=:....:_;;:.~ •. ::-:~_~::-~ir-:-:~-:::~~:-:_ .• =~-=~-::r~ ~-::-::::~_il-=-=---:_ :=-=-=-_- ::~~~t-- -:-:_~--:·_~--:-=-:-:-_~-=--~ :tl_::::_ :·=·~=_=:.~~::-:_·r~---=-~ ~------~-----·~ ~---·.·-~·.:·l·: . j •.•. -~~-=== -=----::=::-=. =-:=~==t=.=-~-: .:=-~-=-=-1 : : ; . : r=-=~-=--~ 2~~-~~~:+_.~~-=~-~~-F__ ~---~--~~~-~+r~~~~t~:~~r~~~~~ ~-~---·------~-----'·--~--4----·_-_-_-_-,~~···_·_·__ +------T-----~----~------~-----r-----1------t------r- 1-1------t------~- ~ j. r:-·: ·-,-r-·-,- ·-· ~----·~-- (- --+--·--:-1--;- ' ' -'- '-~-- r--~--- - . f . t-· f---~- -=-~~ ·::- ::.-· - ------+ • -----, --,-·- -- .... ·- --·-·------~: ! i UCRL-109 Page 12 A beryllium. absorption curve was taken about twenty-four hours after the bombardment, whon tho 2.1 .hour activity had decayed through about eleven half-lives and could b.e asswned to have disappear-.od. This b,;ryllium absorption curve is shown in Figure .5. It is im-' mediately avparont that there aro no particles present in the radia tion. The cur;vat~e is seon to be due to L x-rays. The countJ.ng efficiency of particles, too, is so much higher than that of gamma radiation that the curve would have dropped much mor9 before leveling out at the gam.rna. be ckground if any partiCle racUat ion had b eon present. It is evident from this curve that the positron belongs to the short- lived component. A comparison of the beryllium absorption c urvG containing both lanthanum componGnts, Figure 3, with that· containing Lal3.5 alone, Figuro .5, shows that all the electrome.e;netic radiation in Figure 3 belongs to the Lal3.5. :tn arriving at this conclusion allOi!vance was made for difference in sample size and decay of the Lal3.5 during the tJ.me between the tald.ng of the tvw curves. Thus the 2.1 hour La13 6 has no electromagnetic radiation. · A lead absorption curvo taken at about this same time is shown in ]figure 6,. A small part of this curve does not appear. ·This curve resolves into two components, the K x-rays and a gamma radia- tion of about 0. 76 Mev. I conclude, therefore, that the 2.1 hour activit~ is the · .rositron-omittcr, and that no other radiation is associated vdth it. It V·Iill be noticed that x-rays are more abu.l'J.dant tllan gamma rays by a factor of about .50. In oth Gr ·words, thore is only about one gamma ray for each 50 disintegrations. = 9 . :_=±=-;- t-::~ ::--~ 8 -j- _;--:-::.~ ~=: 7 .--· 6 5 1 •__ , ' _...;...... _ R-:--:--!- ~--'- . . : -~ ~ ~ ~~~~~~--+-~- 2~ 0 0 . . - ! - - ~-·-·-·- '. I ''' ~ l I ' I I I •• . 9. . : ' :::-~---~~:::::_·:.":"~1:;:: ~-~-~,-~""~~::::,; ":l-:_ i' :..:~- . ;: : ·: :i:: ::.:-.~~- -~~ ~="'~~=--- :·:-:~-~--= -=-~ o.d ~~-- ;=::j:.j=-x~-=:;_:-~:_c.::- ~+j:"~: /000 /~00 ' ~ ~ I • • t ~---r---_ ---i~--·--1.----r~~-1----·;---:--~~~- ·j ~ 0 y•~c.-s- ?J UCRL-109 Page 13 The Table at the end of this pap~r shows the yields in terms of cross sections for the vz.rious bombz.rdments performed. From this· 136 table it appears that La {2.lhour acti;ity) wz.s- formed in about 135 1/100 the yield of the La (19.5 hour activity). With the energy of helium nuclei employed, the (a, 2n) reaction is more pro],.ific than (10) tho (a,n) reaction • I conclude that the 2.1 hour activity was formed by the (a,n) reaction and assign it to mass numbGr 136. The fact that La~36 is an odd-odd isotope is further evidence that the mass assignmvnt is correct, since odd-odd radioactive isotopes in this region of the periodic table may be expected to have greater decay ' energy and therefore to dacay by positron emission and to have shorter half-lives than adjacent odd-even isotopes. 136 La is, therefore, a positron-emitter, the positron has an energy of about 0.84 Mev and there is no other radiation associated '.dth the isotope. It has a half-life of 2.1 hours. 136 19.5 hour Lal35 ~· Tho discussion of La above has brc..ught out I ' 135 the characteristics of La • It is asswned to decay by orbital electron capture, although tho proper absorbers were not avaiJ.Bble to determin~ the element to which tho x-ra ys belong. This same activity, or at least an activity .of the same half- .. - life was fou..YJ.d in the decay of a cerium isoto)e, Ce135, to be discus- sed bo1ow. Successive separations of tho lanthanum daughter of Ce135 6 all showed the 19 • .5 hour activity. Since ce13 is stable the 19 • .5 hour activity could not have been its daughter. I conolude,thorefore, that the 19.5 hour activity decays by o.t."'bital. electron ca]Jture and emits tnc following radiation: J.., x-rays and K x-rays which arc in agreement v·1ith values for barium, and gamma radiation of a bout 0. 7 6 Niov energy. I assign it to mass UCRL-109 Page 14 number 13.5. tal37. In dhapter II, the radioactive isotope of cerium assign ed to mass number 137 is discussed. The lanthanum daughter of this isotope was v The b ari urn activity prod uc od in this bombardment was followed in its decay and found to have a ha1f-lif e of about 3 9 hours. This is obviously Ba 133 produced by· the reaction csl33(a,p3n)Ba133. {.5) This isotope is so v-Ioll-known that it· is not discussed here. I calculate a cross section of 0.00073xlo-24 cm2 for tho formstion of this isotope. This is probably a combination of two reactions, Ba 133 formed directly by the (a, p3n) reaction, and Ba133 produced by tho decay of Lal3.3 formed b~T the {a,4n) reaction. Lal33 is probably vory short-lived and ·would have decayed to Bal33 before Geiger counts were taken. UCRL-109 Page 1.5 CP..APTER II ARTIFICIAL RADIOACTIVE I30TOJ?ES OF C~RIUM INTRODUCTTON Soaborg? s Table of Isotopes (,5,) reports cel40 to have an excited state, decaying by isomeric transition to the ground state with a half-lifo of 140 days, emitting gar:ma radiation of 0.21 Mov en3rgy. (11) More rocont evidence shows that x-rays also .emitted are those of lanthanum, and that, therefore, this isotope is properly assigned to Co139, iNhich decays by orbital electron c:~p~ure to stable La 139. Evidence will be given below to show that this isotope also omits conversion elect;rons and that the energy of the gamma radiation is ( 12) more nearly 0.18 Mov. cel39 is reported to .be a positron emitter with a half-lifo of 2.1 minutes but this is believed to be in error. Two now isotopes of cerium, ce13.5 and ce137, are discussed and evidence is given for their mass assignments. Radiation character istics are given for Ce137. As will be seen belovv, ce13.5 was produced in such low yield that it was impossible to determine its characteristics, other than to say that it is a positron emitter of about 16 hours half-lifo. It should be remarked ti.1a t cel36, Cel3S, Ce140 ·and cel42 are ( .5 ) all stable E:xJ?ERIMENTAL Tho lanthanum samples bombarded with deuterons to produce cerium isotopes by tho (d,xn) reaction wore in tho form of La 2o3, prepared by roasting La 2 (c 2o4 )3. The lanthanum. oxalate was prepared UCRL-109 Page 16 by Daane at Iowa State ,College and is stated to be "believed very pure''·· It is stated that the lanthanum oxalate might contain as much as 11.. Coo • Vlhen bombarded in the 60-inch cyclotron the 2 La 03 was mountod as described above for CsNo • When bombarded in 2 3 the 184-irtch cyclotron the La o wa~ mounted on an aluminum plate 2 3 which in turn was attached to the probe of the 184-inch cyclotron, For bombardments irt the 60-inch cyclotron a o. 0002.5 inch thick tenta lum foil was used to cover tho target material. In the 184-inch cyclotron bombardments a o. 001 inch thick aluminum foil was used. Imrnodiately ai'tor the bombardments tho target matorial was dis solved in a bout three miililitors of 6N HNO~ .1 Cerium carrier was added, the solution was made up to eight ml with concentrated HN03 and solid KBro3 wns adr7.od (and dissolved) to oxidize tho corium to the eerie s tete. Tho solution we,s placed in an ice bath,, HI0.3 was added and ths corium pro cipi ts t;;;;d as Ce(I0 } • Aft or stirring 3 4 in tho ice bo.th for· two minutes tho eerie iodate was centrifuged out and washed with H o. The eerie iodate was then dissolved in dne 2 drop concentrated HCl, one drop H2o2 and eight ml of concentrated HNo • Lanthanum carrier was added and the oxidation and precipita 3 tion of the cerium wos repeated. This cycle wss performed five times to insure the purity of tho cerium fraction. After the fifth pre cipitation and waf.:hing of Co(ro ) , tho eerie iods.to was dissolved 3 4 in one drop of conce.q.tratod HCl, one drop of H202, and four ml of concentrated mro • The solution was diluted to ten millili tors with 3 H20 and Ce(OH) vvas precipitated v1ith concentrated NaOH. The 4 hydroxide was washed with H20 ~nd dissolved in one ml of 6N HCl. UCRL-109 Pag13 17 The solution was diluted to ten ml and residual 1.oc1atc was r.educ ed to iodide by bubbling so 2 gas through the solution. The cerium was precipitated as the hydroxide with concentrated W.d OH, the 4 Co ( OH) . was washed with H o and then dis solved in throe ml of 6N 4 2 HCl. This last solution was used as. stock solution from which aliquot portions wer0 taken for decay and absorpticn mec: Ri~SULTS .J-40 day Ce139. La o , 0.8.5.5 gms, was bombarded for tvw hours 2 3 with 20 Mev deutc~ons in the 60-l.nch cyclotron. A ·sample of the ceriwn fraction was followed in its decay. resulting in the decay curve shown in Figuro 7. :It will be seen that points are v'Jide1y scattered. This is believed ·due to having to use some six dif- ' ferent Geiger tubes during tho time of the decay. Soaborgrs Table ( .5 ) of Isotopes reports tho half-lifo to be 140 days. This was assumed correct and the line representing the long-lived ·component was drawn vvith this slope. The decay curve rusolves into two componcmts, tlio 140 day Cel39 and a 36 hour ~ctivity which is assigned to ce137 and discussed in detail below. A sa::.,;,ple of the 140 day activity was ple.ced on thG nr:, e;notic counter two months after the bombardment. A well-defined convorsion electron peak was formed. No positron activity was indicated. Tho :nagnetic counter curve is shown in Figure 8. Taldng the energy at the peak as the enorgy·of thG conversion GlGctron, I find 0.1.5 Mev. :I:. Decay cvrv~ of ceril.lhf /rctc f-/on -- reso/Ve cf info if..S f"Wo COI!HjOOH~II.'I-.s - -~- /Jf-0 tlt:MJ Ce '39 etn a' 36 hi"' Ce /~ 7 F/:; :. I ' > - j : : :: ~ - I : - - 1 . -.- .. . . -- . -- . - - .. . .. -- . . . . ·-· .. . - ·-··- ~- . ---I-: •---· --~- l~ -·-- ... !:..,_____ -··..- ..-···- ·-- - ·-· ·----- .:.:.::·~I ___ :_-~-----· -~------...4-!..- -:.-.! ... - '. ·-. . ... --- -·-- t::--- --'--· ~.,..... Ma~11efk c'ounfer· conver.s1~-,.. -~lecrYol"t. cvrve · of' l'rCJ tla:f Ce /.3': - peQt' at" a 10 MeY' .:::::::: _,_:::: -~i~ ~~:: ::.::-::::: ::::::: =-~-= =£"2' :~~=~ r1 (/r.i..· B :::.::.. :-;-:--:: -~·- - .... -.--- == 9 ' '. =::_ ~.::: .. : _::___~ ----=-=~- -• ~--= ":.: :. -- --- ·---- ~ , __:__ -:::--::::- ::...~:- -:::::=--· ::: ... : -·- : - -- --.. -:::--_::.::::·:.-::.:------~--:-::::::: ---=-~ :=' ___,.: . ~~~:.-_::~+-_:_-:::.~:-~~:~~t~r=~,~-:~ ·j:::. -- -!--"--- :.:-.:.:·:::::-.:::::·--::::-:·t::::::: :::::::..=:·:.-::=::::-: ,\:·~ ~ ~ .. -., ./--- -' .·-ji- : • ! " -:·I·::_ --·-·· ----! --- :.·i:.: _:_:_::-~J.~~-~~ :~= 0 Gerus.s- em UCRL-109 Poge 18 From a beryllium absorption curve takon sfter decay of the 36 hour activity, Figure 9, I estimate tho range of the conversion electron 2 to be about 30 mg/cm • This also corresponded to an energy of about 0.1.5 Mev. A lead absorption curve takon aft(;r docey of tho 3 6 hour activity is shovm in Figure 10. In this curve sufficient bc;ryllium was placed below tho load to absorb tho conversion electrons and suf ... ficient beryllium was p].aced a bovo tho load to absorb photoelectrons knocked out of tho loo.d by gau..ma rediation. This load absorption curve ro sol vos into K x-rays, gamma radiEt tion of about 0.18 Mev and gammn radiation of about 1.8 Mev energy. A bombardment of lanthanum with 40 Mov dcut orons, ·discussed below , produced the 36 hour activity in far gre::t or yield compared to tho 140 day activity than did thG 20 Mev dcut.::;ron bombardment. Tho two cerium activities cannot, thel1 cforo, be isomers. I conclude that tho 140 day activity is formed by the (d, 2n) reaction and assign 13 it to Ce 9• 0 cel39, then, do cays by orbital electron capt ur J w;i th a ho.lf-life of 140 days and emits c onvcrsi on l:>loctrons of 0.15 Mev, K x-rays of lanthanuJn and gaiP..... "lla radiation of 0.18 Mev and 1.8 IvLv energy. 137 36 hour Ce • ;r..a 2o3' o. 250 gms, was bombarded for one hour and forty minutes with 40 Mev deuterons in the 184-inch cyclotron. A sample of tho ceri\lm fraction was followed in its docay, resulting in tho decay curve shown in Figure 11. A sample of the samo cerium fraction placed on tho magnetic counter gave a woll-defined conversion elec_tron peak, sb.o· ·n in Figure 12. There was no positron activity with t~is isotope. Taking tha energy at the peak as the energ~ of the conversion electron, I f~nd ab.~ut o. 23 Mev. 9 ·8 7 f: i ilZO .zo ~==~~~~-:-'--- T..i---:-,----:-:==';=~~~!":=~~~~2- _:;]__;:;.-::.~- ;-;~~:E--!- -:.!:-~~I~""'--ZJ--:-1·'- ~:~2·~=<--:-)--:tr-__:-:- :-:-~""": .,....:' t--:-;, "'""; ...,..._:_-,-:'t-,-~-=-:'"'"'".:-,_,~=--=--!r-:-' B----t-~~--~~.~~~~--~~-t~~~-~--f~-~-~---~~-~:~.f·~---7-~~'~-~~~~--~,~:~~--~-~-~-~· F'h ab:sorpt/on cvrve. 7 ----i-~~~--t~--~-7__ ~-~~~~--~-r~7----~--=t~--~--~--~~~~~-~-7·~--E-~:~-~~~-=--~-~--t-~7: or l'rO -+-~ ... --- -· r-;----'- 5 - ·-·-;-t--.:.. . - - }- . - ·----~-~ ------jf-~-+----j------'---t--" --...------f- ---+ --~ ~-..!... rJ- . I ·.z:tc· :"': i I t, ·=' -+------t- -~- :I . I ;q~--- -~------·--+ --~-- --- .-- if.o- 0 /.0 3.0 lJe.cc:ry cu-rve of .36 hr. Ce /$7 . - ... ,::-:-;·,')' '. • -· +- -- • -.-. /;' ' . ~ . . . . - .. . . . - ... . ----·-"------. ~~ ---. ------. -- - ··----- .. -- : . :\ - . --~- . --- --· ------· ------. . --- ·-· ------ ~ ...... \ L_... __J_I·---=--Jt-1 -~-+--~_::_:__-+-----+--:-:-~~:_:~·----:-~:·:-:----~··:t: u~r---t-.--t---~\ ·~ 1- . j- ·--~-+---+--__ ------~------ [\ I' I . I . ~~~~·-~·~~+-~~~'~\\~·~ I ._._E_~~-+~-~····~-~~r::~:•-~•·~- 8 I ' I ...... !~L....+---:--+------r-·r-- \ _L_-+---J---1-~-+-_:_r-:--:--:---r _j.....:.....;__:...-+:----'---t-- _i I l 6 ~__.;-+------:-----:-. +--+------1 1~ l __ i._!_-~---+-____.:.-+--=· "=' :±:~--~-1'--:- 5 1\ --~ ~ : ~ :-: =-~-: -- - . -~ i \ ... ------·------.- ··-· -· --- - ·------~ - ... --- ·:::·· --=-- -. ·:_:------_------·- JC ,.,. I& D Mag11etic covrrter conver.sicl1. electr~n CVYI/e or 36 hr Ce /,g~ peer~ af 0/~S /deY: rig-~rc:. ;;:_ ·---~-·- .... --- .------~- . - --~-- -~·- - ... -- ---,.- --- ,. ___ -··· _.,. ______~---. - . - .. :·:::. =~::J.::~: ~:::-: ·:::~-~ r • • - • ·- .. ~--l-..--.- · =~~~ ::::: ·::-::~~= :::::.~ =-=~ :::: ·::--:--:-:::: :-::~. ::· :: :.::~: =-= ~=-~=----:: -~:_;_ ...... ·-··- ~--- ~. ·- ~ ...... -·-··-- -- ..... ,__ ... - ... ·------.. ·--- .. ~------__ ....._._ -... ------'- -~------· ·t -- - -.-- -· ... '"-• ..• ----. "-- ~------.. =~: ~ ::~:: :: :~ =:.:::. :-: .. :- :-:: :_> :-.. :-:~-:- -:_.: :~ .:~; : ~: : ---- -l -, ------· • - ..-- ---. --·---- ...... ------.. - ---- :~~: : . .--: -:-::·-. :·:::·:~:::-.=:: ::;:-_ .: ~ I I I,. t J I j.· I l ' -~ . I . t . . -f- -- . :.:: _:- ;_-- .:-.:: . -:-::- I· 1 - I I .·:1:.:: ::::. :.:~ ::·: ~--_-_ ! ·- I . l I· i l I ' I I ' . ! :.-: ., :. ::. . -.·:. ·-:~. :·.: i . I i'· . ·t· ·:·.·::: ... ·t:::: :::~ ....:._! . -~:. . .l_-,--- -~-~:ii_· -+-+-+--·.;_J!....:·--+·....:·.--11~-·-=-·:t:~::-+1~- :f4~1::':t::r-:::;::_ :.::: ~- 1-:..:..+--+--+.~11-:-:-: ..-r-----r-:. l ,. l : .J . - . - ' _/: • • • ~. j ... j .. ~, . : :...... ::!\ 1 --:.r . I ·I : . :i ·I ...... -~'~ . - . . . i. . ,. ... OL_~_L--'--l-~'J.f"':j'Z.-':I_·~_::_._:_::~: _:~~~~~~~ ~_:_ _::: J~~~,;; ... Gt:uJ.S:J- em UCRL ... l09 Page 19 A beryllium absorption curve is shown in Figure 13 • .A part of this our~e does not appear, but the missing part does not affect the figure or r esoluticn th ore from. From th:Ls curve I estimate the. range of the· conversion electron to be about ·4.5 mg/cm2, corresponding to an energy of about 0.16 Mev. Allowing more weight to the energy determined f'rom the beryllium absorption curve, I take the energy of the conversion electron to be about 0.18 Mev. An alum:Lnum. absorption curve i.s shown in Figure 14. A part of this curve does not eppear 1n the figure. From this curve I resolve 34 Kcv x-rays. A lead absorption curv(; for this isotope is shown in Figure 1.5. This curve resolves into two components, gamma radiatio.c. of 0.28 Mev and 0. 7.5 Mev en 0rgy. ce137, then, decays by orbitc.l electron C<:-;ptur c vri th a half-life of 3b hours, emits conversion electrons of about 0.18 Mev, ~ x-rays of lanthanum, and gamma radiction of o. 28 M.:.;v cind o. '7 .5 Mev energy. It was formed by the ( d, 4n) resc tion • .16 hour 13 La o , 0. 2.53 gms, was bombarded for two hours Ce ~ 2 3 v:ith 60 I!Iev doutGrons in the 184-inch cyclotron. It .was hoped that 135 an ap,prcciable yield of Co might be obtained by the (d,6n) reaction 137 b u t rcsLLlt.. s were d isappoJ.n· t·J.ng. The·-- 36, hour ce ac t·J. vi t y was .L"" orme d in such high yield that the col3.5 activity was completely mnsked in the dece.y curve. a gross decay curve of tho ,cerium fro.ction of this bombardment was exactly lilw tha·t shown in Figure 11. A sa.~i.plo of the corium fraction placod on the I!lBgnotic countar showed positron activity, llOiNCvo.r. A ropresentative mngnotic counter curve is shown in Figure 16. The hi&~ backg~ound is due· to ~~::_'j,'< =i==~ -~ ~ ~•c.= AI crbsor~fion CV.I"Ve or N==L..,::-H-· .3/J hr Ce 137 6 ri vre /'f 5 +-+--:--= -· t±::ci=_~- . I ' I ---+-' 4 -'- 3 I I I 2 I ; I ' I ! t : ' --j--1- ; I I ! H -·r- r-P.--t- ----t~ i I I I I ! I L...!-. ! I I I ~ i 1+--+- :-~ lf I ,.. I ! I I I I :'ti_, jll I ; ' I ! ! I I i I ! I 1 I '_l ;---r--r--; L'ki I i i J I i ~_j-H I_J J I I I I I I~ 1_.1_1 I j_l!_l I i 1 I ·1 .' ; ' I . I I ' i ll 1\.l'a I U I I l I I I : I l I l l I I I (_(). I I ! I I I ! I I ! I 'l ! I 9 FF~ ~-· .____.____, 5 I I 1 I I -+-+-c± :: . .;: - "--'---7------t I I ! i 1 ~-: : -~~-~- -~ --~'""~·,-~-i;; ' ;-t-IT-~ I ·I ij_ 1 t---;'1!! 11 I1 _;-·--~-;-;··- :~_:_j_: ~-~ 1 u_j--:--j1f-i-l+-t-lh!i--t-JTI iII ---l---·-~------~-"-"-J - ~ ; , ;----:--' i 'J i .. ITI l I I I ! j ! !-1 ~ : : I ------~J- . !""~.. i i : I ; '. I I ' '~ I . -~ • I 1 I ' .& ·-'- lf.L i I ' i ; i I "~--_,':== _- . - -''--·- :. __---=-===~ :±:::: :t ' I I 4 ::::: c.~-~.., :~-- 1-4--c-'---'--+ !::± -::. ::::.'::'.:: :± --+-+-t---+ = --. ,-- .-:-- ·- 3 -~- ~=-. ·-=~-' =+ •--: . .:. .::::~J;:~. .,-- •. j • ---' I~- -___:- 2 ~~ ~~~---;+- ~=~-=~ ___ j_ .. --; i.~ _-;:_- ... ! ·-·-·· . ------I::~ i.O . 0 ·-·. ,.! . -·:.~-:. -- :.;:· _: ... .:·r.:-.i::. :--::·.::: 9 8 7 6 5 ... ! 2 0 .. ·- J... . ~ . . . . -· ...•.. ;~:t:::r:~-1~-~l> ~.:u~-:~;-~::=ni~~H-· .r~·l_. : ~: "!." ..... : -"T ••. ll.fag·nc_ f/c c. oun-lc r 10o~ tfrcw :'"'''T . /~ ' ~- 1 .:.:r: --- -- •• ----1 CijYvc p/ /b ,1r. c-.; 3f "/t..:;j ·/~ 1 . -~ -~-·' .... . ~-- --···· . . -.. t'l1 d poi.'?f-. a 0 . ..:: i /i /:.· ;( --~ ---~- ... r . -· -~-· J=';j~,-2 16 ~----- :..:;_:._ !"-...l~~- ::·.:: .:::.; !.. --· J.!- - --- ... ---.., .. ...... : ·--- . -- -. -··-··rl······...... ·-· . --.... -.-- ----r.- "' .. ·-,:...::: '1 .... ~ ,__. ___ - ~-t-· ·--~ ···--- .... -···- ~:.::.if:-.: - ~------~ -- . \'-_ .;~~~-~~~ :J= -:\- -·-' ·-:-: _;:- .. :::.::: ;-_ .. ... - + ..-·r:: .oy-···· ---;.. ~-::::-t:::::= ·.;-:::;::; .--· ::.:: ---:-.7 .:: -· --- ··- ..;. - -~=- ___ ...... __ ·- ~---1 • : j.:.. ~ ... -~·- .::~ :·~- ~::=,·: -'~ ..__,· ..... ;:::).::· -----~:.___ · • f • r• .:.: :. ~ · .... -----·-- __-- .._._-.. .:.. -_.4..--=:: ~ ---- • • L. • . . ~ ...... --~- ....._-- __ :::::: +---·i-· __ ...... --···· - ··~··· ::: I: ... • :.:.0:: -•. ::.:. ·.·. t. _: ·:··.·.· .···.__ ·_. _·_ it . -. -. . .:. ---·r:~-. i . . T. .--. . - -! _ ··:-(:·- ..... --· --:-- ··-- ·• ', -· ~.-' 0 UCRL-109 Page 20 sea tt cred radiation. The decrt';o sc in background as me gnct c urront increo.sod is duo to crwrgod pcrtici•3S being curved into smc.ller and smaller circles so that thoy no longor roached tho counter tube. Tho generally high background, much higher than in other ID2,:;notic counter curves shown, wes also caused by tho usc of a high counting rato. This high r a to was noccssc.r y 11'1 order to rosol vc tho positron peak. Taking tho energy of the positron as that at the visual end point, I cstimnto tho positron to be of about 0.39 Mev energy. Successive mcgnctic counter curves were talccn for approximately two days. Integration of the '-~r,Jas under tho positron peaks 2s tho activity doccyed result cd in tho scattering of points shown in Figure 17. Through these points ::r: hDvo drawn tho representative line shown and estimate the hclf-lifo to be .: bout 16 hours. It VJas impossible to det0rmino any other charc.ctoristics of this isotope. This activity is assigned to Cel3.5 bocause it had not appeared in bombardments at lower onergios. Furth~, r evidence for this mass assignment appeared when tho lentho.num dcughtcr of the activity was sopai·atcd. This daughter activity docayed with a 19 . .5 hour half-life, exactly that of th.J l.snthanum activity assigned above to La13 5• .. 10 9 '·-'"o;::=t . ~~=~-;--~-- ~ :~~~~ =t:: ~ 8 •~-t--<-··· - . -- :· ~ . --+=t=F:: 13 7 --~:.~ :· . : . -:;'::t:::}_ E5flnrarion or half-life 0~ Ce. r. lro»r. Jlo'"t!JI"'I:l f-/ox o T crrecr s i./ M tl e,.. ''•. 6 posi -f"rol't. ~ectK 5 or .3.VCC. e ssJ l"e... .. 5 J-Haynet-/e c.ovn rer t; vrve s. 1 4 . FiJ /'f. /7 . J; ' ··- .: ; :r· ... - --'-"-:.... ___;__:__-:::: r=:- -- ~....,.....,.... --i-++-+ . -i- ' ' ' ~ '---1 -}-- H- : ' I I ---=-+-+-+ ·~ jt ! ' Ill II _j--1-.J. j ~ If 2 I. t I J ' : I I_; i I I I > .l._..:..:...i_L _:_j I I I I I I I I I .J_ f_.J. , ~- .LJ_j _L_ __,--.l_t. ~- .-J.....:__._j , ; _L:±=·t' ±=t±::l~-j l'tj 't ••t't:ti:I'=t'=!:::tttt:t:t_.=tl::tl4(±]±·-jl~....;_t__j_j' I _j__j ~~ :-17.1_ __! I I t ·~- I l , I t ' ' ' t I j j' I ! t 'I I I '--1-L.. '· j I :' ---L-.L...! i I • t __J 1 i l : l -1-!-l...... !_J---!- H-,--+'_,_!_~---;·, II __). tl· -1--i---!--H-t---t--l--t--H" --4 I II· !I . 1 I I .l....i_L H_j_j I ' . ' . I L..l_LL..L -4---!--!---'-- _L . ! • .. l I I ,--r-r-: . ! I 1 I i I I J 1 I ! I -T -l: -- ~ I I ' ; f t I I . I I ; ' 1 • ; ' I ; L ~ '.....!_j__f-1- 1-++'+-J-+-+,-If--+.l. ...JI-+-Hi!-+1 +-f-++411++-, -tl-if--H 1--t-~f-+--t--lf-+-+1 ·t-1--J I i I 1 i I 1 I : ,' I j 1 -+'-H'+I1 -1-lt--1-l!f-+1++-'-l'-HI+-Hf-t'' --ll-1--t'-Hii_IH-+-Hil-41-+-H'~·~-+-' ~_lj_J_ __;_j ' I i I I i ! ! r l i I l I i f-. ; ' ' ' ' l 1.1 i ' ' I 1 1 I i l--!-l....:t...i.+-1,-+-+l:...,'f:-''+-11'-+~H-+-H-+H-+-+1 +I H ' ! i ; I ' I I ' I '-t- r-!-, I I : ! 1 ; ' . 1 ' I ! I l ! ! -1-t--:IT! I I :. I : I 1 ; i~:. 9 8 ...:·-·;_. ,. "7 . . ' '· 6 --+-+--',.- ~--;---;- -- . .~ ;. _:. f ·~-~~---'II' II _; -=r-:-g--,-:...-; ... -+--•_ ~ ~= .::r....;_;_,_f--H__, 5 : : . ' -,- -: , . ~- H· ::;~ : : ~--t- --' ; , I I -t-++-t- --l -~ ··~-~ ·~ _, ·-~· .-H+ ~ ~ -~ -~ ' -~ '~ 9 8 6 . -1-- 5 -+ ~-++-+ I I 4 2~~~~~~~~~~-~~-~--~.±-~~~-···-!--- ·-'---~ :·. . ~-' j·...... ~~.~-~:_: .. ~--=----=--i---~--~·2.+:~~±E~~G=~ -·- ::.:::.-:: ~~~:.::.::::L ~;:=H± =t~r~a=~::~~:::~~-~-:~.-;-~-~:.·:~: ,__ --- _, ___ _1_.; _: : -~- -··-·---· ---- ·-~-.. - •· I _..;_~ tc:_J__;_·~-~~!.....~· ~~_-_IL~~~.-·~;_::,~~J-~~P~~-~-~:~-;_j" _:~.·-·-c ~-·~'k::,~-~....:..:.:·__ ~·....J..I ___ :--_~~~'l: z·-~oox_ ,···. TfL:~.,o: :·, ~· ~:o2' :. ~T: ~~: 8 Mt"nu t e .s ..;,. :.::. ~'·- UCRL-109 Page 21 CF.J~PTER III SLJI;.'1MARY In the ~able at the end of this thesis is a tabulation of the data obtained in tho various bombardments discussed above. In genoro.l, cross sections wcro calculated on the basis of tho K x-.re ys 0mi tted. Counting effici;:,ncy was assumed, as montionod above, to be o.Y/o. No calculation of cross section could be mr..:.do 1.3 .5 for Co bocsuse of its low activity and lack of knov.rledge of tho decay schomo. It is apparent that bombardments· of cesium v:ith high'·'r energy helium nuclei in tho 184-inch cyclotron would probably produce still lighter isotopes of lanthanum vdth ha lf-liv os which could be observed. Lo 134, an odd-odd isotope, would probably be a positron emitter and might be· very short-lived. La133 , how0Vor, would probably have an ens ily observable hu lf-lif,:; of an hour or tvvo. Compoting reactions, spallation fo.r· cx<::mple, might reduce the yields of those lighter isotopes •Ni th bombardments at onergios of o.bout 100 .Mev or higher. Similarly, bombardments of lanthanum with higher Gnorgy deuterons would probably produc o light or cerium isotopes. with obscrva ble half lives. cel.34, for oxc.mple, might be expected to ha vo a half-lif.e of sovore.l hours. .Again, competing r.ca ctions would probably rod uc e the yields. UCRL-109 Page 22 Table lrsotopej Type of Half.,..life Enerr,y of Radiation! Isotope Produced by ICross se~tion in Mev I i xlo24 em I HRadlationl I . :Partie 1e Electro• I I magnetic ,La 136 ~ ~+ 2.], hrs 0.84 None Lal36 cs 133( a., n ) 0.0003 l I I . 135 133 La 135 1K, y 119.5 hrs None 0.76 La Cs (a, 2n) 0.03 . ! I I La 137 I 400 yrs La l37 decay of I ' ceJ.37 I i lc 139 I - 139 8 140 dnys 0.15 0.18 ICel39 La (d,2n) 0.09 l K, Y, e I I L8 t 137 I . - Ce137 139 Ce IK, (, e 136 hrs 0.18 o. 28 w (d,4n) 0.06 I ';, I 0.75 I ! Ce135 1 c 135 139 I~+ I e La (d, 6n) 116 hrs I I 133 l Ba 133 Cs (a, p3n) 0,00073 I and decay of 133 La pro .. duced by I 133 l Cs (a,4n) j .. I - UCRL-10'9 Page 23 REFERENCES (1) Mounce, K. E.' M. L. Pool and J. D. Kurbatov, Phys. Rev. _,61 ' 389 (1942). ( 2) Weimer, K. E.' M. L. Pool and J. D. K~u·batov, Phys. Rev. 63, 67 (1~4.3). (3) l?ool, M. L., J. M. Cork and R. L. Thornton, Phys. Rev. .2.£., 23 9 ( 193 7) • (4) Inghram, M. G., R. J. Hayden and D. c. Hess,Jr., Phys. Rev. 72, 967 (1947). (5) Seaberg; G. T., Rev. Mod. Phys. 16, 1 (1944) ~ (6) The analysis was performed by J. G. Conway and co-workers in the Radiati_on Lab oratory, University of California, Berkeley. (7) H. P. -Robinson, private com...rnunication. (8) R. H. Goeckermann, private communication. {9) I. Perlman, private commun.J,cation. (10) G. Wilkinson, private communication. (11) Matthews, D.E., andM. L. Pool, l'hys. Rev. ]1._, 163 (1947). (12) Pool, M. L., and L. L. Q,uill, Phys. Rev. 2.?.., 437 (1938). .· .. - ' '' :~ .... ·,Cl..ASglFf"' \Tf~'l ,-. '~·~-: ;~ ... { ..