Campbell, E.C.

Harvey, J.A.

Slaughter, G.G.

Weitkamp, C.

English

Harvey, J. A.

Slaughter, G. G.

Campbell, E. C.

KITopen

August 1969Institut für Angewandte Kernphysik- E it e d c 204 1 - 206~_ - -.'Low-Lying .xc rt e States 01 T and 11 l-'opulacedin Thermal Neut r on CaptureKFK 1099C. Weitkamp, J.A. Ha r ve'y, G. G. Slaughter, E. C. CampbellReprint fromrrNEUTRON CAPTUREGAM-MA=RAY S-PECTROSCü1?ynINTERNATIONAL ATOMIC ENERGY AGENCYVIENNA, 1969LOW- L YING EXCITED STATESOF 204Tl AND 206Tl POPULATEDIN THERMAL NEUTRON CAPTURE*C. WEITKAMPInstitut für angewandte Kerntechnik,Kernforschungszentrum Karlsruhe,Karlsruhe, Federal Republic of GermanyandJ.A. HARVEY, G.G. SLAUGHTER, E.C. CAMPBELL.Oak Ridge National Laboratory,Oak Ridge, Tenn., United States of America(Presented; by D. Ranger)AbstractLOW-LYING EXCITED STATES OF 204 TI AND 206 TI POPULATED IN THERMAL NEUTRON CAPTURE.New Ievel diagrams of 204TI and 206TI are deduced from thermal neutron capture measurements on isotopi-callyenriched sarnples, The agreement of the 206TI level scheme with theory is poor, This is attributedto the attempt of all cornputations to reproduce a Iow-Iying 1- state for which no evidence could be foundexperimentally.When capture of thermal neutrons was first used as a methodto study the properties of partieular nueleides, it proved a powerfulmeans to obtain new and most valuable information on nuelear strueture,and the first data on the odd-odd isotopes of thallium were obtainedvia this reaction almost twenty yeary aga L-1~.Considerable improvement of these early data in bothaceuraey and completeness has been aehieved during the past decade bythe applieation of a series o~ other proeesses the most im~o~tant ofwhieh are, fpr the ease of 20 Tl, the reaeti8ns 203TI(d,p) 0 Tl and205TI(d,t)20~TI~2~ and, for the case of 2 °TI, the reactions205TI(d,!?)206Tl 1:2 ••• 4 7 20~Pb(d,a.)206Tl L5J and the a. and ß-deeays L 6 ••• 9, 10~ of~10mBi and 206Hg, respeetively.Despite these efforts, many details of the level struetureof the two nucleides have remained either unknown or poorlyestablished. For 204TI, a big step forward was aehieved by Prestwichand eollaborators L-11~ who used a Ge(Li) deteetor to observe thegamma speetrum from eapture of thermal neutrons, but, beeause of thenatural isotopie composition of the sample~ attributed some r rays to204Tl that did not arise from capture in 20JTl.For 206Tl whieh,beeause of its simpler nucleonie structure,is of more direet use as a test ease for different shell-model typeealculations, a somewhat controversial situation had arisen whetheror not a level with spin and parity 1- existed a few keV above theground state. This 1- state, predieted by Sliv, Sogomonova andKharitonov L-12J, was tentativ_ely introdueedinto the measur-ed level~, Research sponsored by the US Atornic Energy Commission under eontract with the Union CarbideCorporation.421xYsl. fI.JiJ \""NN11111 I II I203TI(n, y)204n2-5 MeV",~_J"lo'"''~ 20 , T "', "'--..:1 _. 'u(Xl03)i-T--;;~~I-l-'I~I--;----'-"--~~ -FIG.l. i High-energy, part of thegamma spectrum fromneutron capture in 203Tl.>E;8~"0~~10001000900900800BOO700700400 500 600CHANNEL NUM~ER400 500 aOOCHANNEL NUMBER300300200200100tOOI-I205 T 1(n,r) 206 T12-5 MeVI .Ii ' II~~ ~! ~lw,J, ~ l ' . I1 \ !I ~"""''''--~, ".,A... ., ~I 'I I\.I! ~,i 'li' ~'-"'''''''''''''''''''/' ';"..f..•".,-}..,:,." ....,-,~)..i;.. l,.J.lv\.Av" ••, 11.;,1.,) ,~~.j '\"..".. \t~}1 \,1< J \.!i fI I.,r' ~-_._~~_.Jl..__~~~.:.KG~:OUND W]TH CARBON SCATT:RER j':••/ ••.. 'Y':';.::,,:.;.}I,d: .. :!tt.~~-'t-i" ,l ,"'\,!' '<, y..i.' ........-........... ..-, .....)tN' ...["' ___' , ...~___' -v___• - ••1,. j""''VM ' •oo0,1 I I I il! I I Io30J!! 20s8(Xt03FIG.2', High-energy part of the tOgamma spectrum .fromneutron capture in 205T1•LOW-LYlNG STATES OF 2"'TI AND zo'TI 423diagram of Rusinov et al. ~7~, and the authors of subsequent theo-retical papers then tried to reproduce that level in their com-putations.These calculations of systems with two nucleons outside aclosed shell usually proceed in two steps. On account of the Pauliprinciple only the triplet-odd and singlet-even components of theresidual nucleon-nucleon interaction contribute to the wave functionsof those nuclei that are two like nucleons off a doubly magie "core"nucleusj so step 1 consists in an attempt to vary the magnitude ofthat half of the parameters until a best fit cf the resulting levelschemes with experiment is obtained. In step 2 the remaining para-meters are fitted to the level diagrams of the nuclei that differfrom the core nucleus by two different nucleonsj to do this use isnormally made of the unchanged parameters from step 1.In the region of 208pb this procedure works weIl if tgeparameters determined for the even-even nuclei 210po, 21Opb, 208Pb,and 206Hg are used to fi t those of the odd-odd nuclei. 219.13i, 20 Bi ,~nd_20ElTL I-t f"ai-l-s, -however ,-togive an aae-quate description of20bTl.It was this failure that led us to a reexamination af theproperties of the odd-odd isotopes of thallium, particularly 206 TI•Our main interest centered on the following questions:) 206 (. -1 Is there a level in Tl presumably 1 ) 10 keV or lessabove the ground state, or is it possible to establish asmaller upper limit for such a hypothetical state?2) Are there other levels observable in the energy rangeo to 800 keV in addition to the ones previously known?3) What is the excitation spectrum of 206 Tl in the energyrange between 0.8 and 2 MeV which is not accessible fromdecay measurements?4) Are gamma transition probabilities and branching ratiosfrom the (n,y) reaction compatible with the known spinvalues of the levels?5) Is the "anomalous bump'", i. e , the unusually intense groupof gamma rays around 5.5 MeV in the (n,y) and (d,py)spectra of nuclei with mass numbers between 180 and 208,observa ble for either of the two isotopes separately?The experiment was done with Ge(Li) detectors of 6 and 30 cm3and isotopically enriched sampIes of 203Tl (96.69 %) and 205TI(99.46 %) in an external thermal neutron beam of the ORR reactor.Let us first look at Fig. 1 and 2 to get the answer toquestion 5. Fig. 1 shows the high-energy portion of the y-rayspectrum from capture in 203Tl which is very similar to the spectrumfrom natural thallium and clearly exhibits the group of intensepeaks around 4.5 MeV (corresponding to y-ray energies around 5.5 MeV),with few y rays presentbetween 2 and 4 MeV.The spectrum from capturein 205Tl is shown in Fig. 2. Despite the high enrichment of thesampIe, about 30 %of the counting rate of this spectrum is due tocapture in 203Tl , but an evaluation shows that th~ gross behaviour of200Tl does not differ appreciably from that of 204TI, in completeagreement with theconclusions from Bartholomew's recent explanationoT the effect- L13J.-nr T!h<::> T ~I't-J!h'" .:s."."..'SI.6335U.2.16/.2-6/&S602.5!nasess:$64"'S6roSS~.S.~-z.S"'OJS2.T.IS2.$'S17,,>S13.JSO,..• ~lJS+-''''05+~/7J,,8,,3.40&.75$~70f'.6~1lt60SI,S73'-S.S11500*"'''34403~,J8043371t37342.1.74/'84/6."11 g4077ltOJ3'":3::j..:::l'"B..°re l3 dWV)i.LI3M 1'Z1'LOW-LYING STATES OF 2"'TI AND 206TI 425~IC>I426E(HeV)&0WEIT KAMP et ai.2DS77+ n~ ~ ~ = ~ : ~ ~ ~ : ~~ :;; :0 l; ~ ~ ~ ~ : ~ .. 6504.1..........__.. ··T· -.. ·_·-r···2.5!- - i- - - i-- !-2.01.$- ---~~~I .!!!!..2..:.!J11· -T--'-~-'-c'" t; 1+8:1.8 (0-,'-,2-)-- 0 b· --..... /~3.0...x__~-.:,~;."--;~;- IJ60:S(0-,'-,2)1.00.5-_-!.~~___-"It::.;~7.:.:.:;J ('-,2)~2­~(r,zJ--"...2.!:9480U' s:650.0 r~2-o_1..-_ .J~=...i-==...i-======::::::~JQ~..~.9 r266-1 z-o206 TI111 (QSFIG.4. Transition diagram of 206Tl •LOW-LYING STATES OF 204TI AND 206TI"Thotüum427...1!!.-C3-'600 (2-)3 levels above1.9MeV1550720 (2;3"'~C3;T)36 levels above2.5MeV22 levels above 9982.5MeV649.5 cn634.5 C2")-i4Sä8CO;I: 2")~(0;1;2-)J~.Q.~"111'Z3 11;2")1079.9 2-19.KCJ;2")94Q2801.6 3-650.0 I"635.3 2--lQQ..C1") .JQL.Cr) .JQL. ~I" -1QLI 304.8 (1") ..12L1" 304.9 1"26ilCz-) 26'2C2") 262 ""'2632 265.7 (2"' 266.1 2"-60 (1").10 Cf) _0_ _0_ _0_0" _0_0 _·_O-CO") _0_0- _0_0"~CO-) =10")sv:Golonetzldjetal. LlRusinov et a. S.Miche!ettl etal. GAKorolev et aI. P.Mukherjee J.RErsklne E.H.Spejewski GKWolf PresentJETP37I1959l560 JETP13I1961I707 NP37I1962J201 BuU.AcadSci. USSR N.P 62(1965) 541 P.RI38Il9651 8 851 NPAlOOI19671236 NPA116 119681387 Work21OmBi~Tl a 21OmBi~Tl 2OSpt, Id,11]6TI26(1962) 233205n1d,pj06Tl 205n Id,~Tl 21OBi~Tl 206Hg~Tl 205n In,~6Tla,y a;v.cE a 210mBi i~n p p y ß,Y,CE YComparison of Z'~llevel diagrams as measured from different reactions,The transition diagram of 204Tl is given in Fig. 3. Exceptfor astate at 553 keV which was not observed in our measurementsthe agreement with the level diagram of Prestwich et al. L-11-! isperfect. No evidence could be found for the ex~ence of a long-lived metastable state in 204Tl; thisis not amazing, however,because if such astate existed fts excitation energy must be low,its spin high compared to the 204Tl ground state spin ( 2 ), and theprobability of feeding it via neutron capture by a spin 1/2 targetnucleus would be small. Horrock's half life measurement L-14~ istherefore a ~tronger argument againstthe existence of a long-livedisomer in 20 Tl.Fig. 4 shows thg level diagram of 206Tl• The presence of a10w..J.ying 1- level in 20 Tl should manifest itself by a splittingorbroadening of at least some of the y rays feeding the ground state.This broadening, if present, should be best visible forlow-energyy lines. To answer question 1 an analysis of the widths of thecorresponding peaks was therefore done, and no evidence for a level~2.3 keV above the groundstate was found.206 . The answer tdquestion 2 arid 3 is given by Fig. 5 in whichthe Tl level diagram as determined from the present work is,compared tothe results from other nuclear reactions. No new levelsshow up below 900keV, butabove, aseries ofpreviously unknownsta:f;es could be found.For question 4 let us once more look at the transitiondiagram of Fig. 4. As the energy dependence of the 205['1 capture cross428 WEITKAMP et al,206Thallium1:"---Pair only Pair and 0 -0 Interaction~=W ~=W H H W W ~v, =20 v,=20 25 35 35 20 27 ExperimentC=10oo 1000 1000 1000 2000 1000LA.Sliv.GASogomonova. Vu.1Kharitonov.JETP(USSR)40 (1961)496Y_1.58 0.79 0FiOInter-action1-0- 48.25 4825 4a25 24.13.,,=24.13 32.50 32.50 32.50 32.50Vs.= 16.25 vr.=-14.40 "rr-4.83vs.=-8.12 -16.25 +16.25 -1625 0c=O.07OL5ilverberg. Arkiv Fysik 20 (1962)341o0.113ExperimentExperimentK.B.Baktybaev et. al. V.E.KimSovjet Journalof Nuclear P.R.138(1965)PhySics 6(1968)196 B 851R.SnowThesis NashvlUe,TN(1966)Kln-D.6 Kex=3.8Lin=1.2 Lex=-2SB.L.Birbrair.G.M.Bukat.\lN.GumanSovletJournal of NuclearPhysics. 5(1967) 193FIG.6. Comparison of calculatedlevel diagrams of 206 Tl .section is not well-known, both spin values of the capturing statemust be admitted, and 0-, 1- and 2- states can b~ fed by primaryelectric dipole radiation. Both ,feeding anddeexcitation of the groundand first three excitedstates is consistent withErskine's assign-ment of s pd na , The 650 keV level, however, .is strongly populated fromthe capturing state; as it feeds both the 0- ground and 2- 266 keVstates the only possible spin value is 1 if dipole transitions areassumed. The absence of a primary transition to the 802 keV level,on the other hand, and the deexcitation of this state tothe 2- 266 keVLOW-LYING STATES OF 204TI AND 20GTl 429level only is strong evidence for the 802 keY state being the 3candidate that is expected in this region from theoretical con-siderations. This assignment of spins, although in contrast toErskines interpretation, is but little outside the error bars of hisdata.Fig. 6 shows a comparison of the results of differentcalculations ~12, 16, ••• 19-7 with experiment. For simplicityonly the ground and lowest five excited states of 206 Tl are givenwhich correspond to the proton-hole neutron-hole configurations(sl/2 P1/Z) , (d3/2 P1/2) , and (sl/2 P5!2)' It follows from Fig. 6that there has been no really good agreement so far although a greatvariety of shapes and of range and strength parameters were tried.This may be due to the fact that all calculations were biased by theendeavour to reproduce an almost degenerate 0--1- ground state doubletwhich tiII now was not established experimentally. It might be pro-mising to try some of the approaches that worked so weIl in the caseof other nucle~ ground 208pb with the newer experimental data nowavailable for 0 Tl.Referencesf1J G.A. Bartholomew and B.B. Kinsey,Ganadian Journal of Physics II (1953) 1025{"2.l P. MUkherjee, Physics Letters 13 ( 1964) 238L3.7 P. Mukherjee, Nuclear Physics ~ (1965) 541f4J J .R. Erskine, Physical Review 138 (1965) B 851f5.l S. Micheletti and J.B. Mead, Nuclear Physics 11 (1962) 201f6.lf7JL8JS.Y. Golonetskii, L.I. Rusinow, and Yu.I. Filimonov;JETP (USSR) 11 (1959) 560; Soviet Physics JETP 12 (1960) 395L.I. Rusinov, Yu. N. Andreev, S.Y. Golonetskii,M.I. Kislov, and Yu.I. Filimonov;JETP (USSR) :±9. (1961) 1007; Soviet Physics JETP.12 (1961) 707G.A. Korolev and G.E. Kocharov,Izvest. Akad. Nauk SSSR, Sero Fiz. 26 (1962) 235;Bull. Acad. Sei. USSR, Phys. Sero 2~(1962) 233E.H. Spejewski, Nuclear Physics~ (1967) 236L10J G.K. Wolf, Nuclear Physics!...:!.1§. (1968) 387L:11J W.V. Prestwich, L.B. Hughes, T.J. Kennett, and H.J. Fiedler,Physical Review ~ (1965) B 1562~12J L.A. Sliv, G.A. Sogomonova, and Yu.I. Kharitonov,JETP (USSR) 40 (1961) 946; Soviet Physics JETP 1l (1961) 661430 WEITKAMP et al,[" 13 J G.A. Bartholomew, Bull. Am. Phys. Soc • .:Q. (1968) 1416~14-1 D.L. Horrocks, Nuclear Physics~ (1968) 238["15J L. Silverberg, Arkiv Fysik 20 (1962) 341["16-7 B.L. Birbrair, G.M. Bukat, and V.N. Guman;Yadernaja Fizika 5(1967) 274;Soviet Journal of-Nuclear Physics 2 (1967) 193["17 J Y.E. Kim, published by J.R. Erskine in Ref.I4]~18J R. Snow, Thesis, Vanderbilt University, Nashville,Tennessee (1966)["19-1 K.B. Baktybaev, I.M. Band,L.A. Sliv, and Yu.I. Kharitonov,Yadernaja Fizika 6 (1967) 270; Soviet Journal of NuclearPhysics ~"(1968) 196

Low-lying excited states of ²⁰⁴Tl and ²⁰⁶Tl populated in thermal neutron capture

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Low-lying excited states of ²⁰⁴Tl and ²⁰⁶Tl populated in thermal neutron capture

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