Transition probability studies in 175Au

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T ansi ion p obabili y s udies in 175Au G ahn, Tuomas; Wa kins, H.; Joss, Da id; Page, Robe ; Ca oll, R.J.; Dewald, A.; G eenlees, Paul; Hacks ein, M.; He zbe g, Rol -Die ma ; Jakobsson, Ul ika; Jones, Pe e ; Julin, Rauno; Juu inen, Saka i; Ke elhu , S e en; K öll, Th; K ücken, R.; Labiche, M.; Leino, Ma i; Lumley, N.; Maie beck, P.; Nyman, Ma kus; Nieminen, Päi i; O'Donnell, D.; Ollie , J.; Paka inen, Janne; Peu a, Pauli; Pissulla, Th; Rahkila, Panu; Re ill, J.P.; Ro he , W.; Ruo salainen, Panu; Rigby, Sa ah; Sa én, Jan; Sapple, P.J.; Scheck, M.; Scholey, Ca he ine; Simpson, John; So i, Juha; Venha , Ma in G ahn, T., Wa kins, H., Joss, D., Page, R., Ca oll, R.J., Dewald, A., G eenlees, P., Hacks ein, M., He zbe g, R.-D., Jakobsson, U., Jones, P., Julin, R., Juu inen, S., Ke elhu , S., K öll, T., K ücken, R., Labiche, M., Leino, M., Lumley, N., . . . Venha , M. (2013). T ansi ion p obabili y s udies in 175Au. In 11 h In e na ional Con e ence on Nucleus-Nucleus Collisions (NN2012), 27 May o 1 June 2012, San An onio, Texas, USA (A icle 012047). Ins i u e o Physics. Jou nal o Physics: Con e ence Se ies, 420. h ps://doi.o g/10.1088/1742-6596/420/1/012047 2013 This con en has been downloaded om IOPscience. Please sc oll down o see he ull ex . Download de ails: IP Add ess: 130.234.75.141 This con en was downloaded on 15/01/2016 a 11:09 Please no e ha e ms and condi ions apply. T ansi ion p obabili y s udies in 175Au View he able o con en s o his issue, o go o he jou nal homepage o mo e 2013 J. Phys.: Con . Se . 420 012047 (h p://iopscience.iop.o g/1742-6596/420/1/012047) Home Sea ch Collec ions Jou nals Abou Con ac us My IOPscience T ansi ion p obabili y s udies in 175Au T G ahn1, H Wa kins2, D T Joss2, R D Page2, R J Ca oll2, A Dewald3, P T G eenlees1, M Hacks ein3R-D He zbe g2, U Jakobsson1P M Jones1R Julin1S Juu inen1, S Ke elhu 1, Th K¨oll4, R K ¨ucken5, M Labiche6, M Leino1, N Lumley7, P Maie beck5, M Nyman1, P Nieminen1, D O’Donnell2, J Ollie 6, J Paka inen2, P Peu a1, Th Pissulla3, P Rahkila1, J P Re ill2. W Ro he 3, P Ruo salainen1, S V Rigby2, J Sa ´en1, P J Sapple2, M Scheck2, C Scholey1, J Simpson6, J So i1, J Uusi alo1and M Venha 8 1Depa men o Physics, Uni e si y o Jy ¨askyl¨a, P.O. Box 35, FI-40014, Finland 2Oli e Lodge Labo a o y, Uni e si y o Li e pool, Li e pool L69 7ZE, Uni ed Kingdom 3Ins i u ¨u Ke nphysik, Uni e si ¨a zu K¨oln, D-50937 K¨oln, Ge many 4Ins i u ¨ Ke nphysik, TU Da ms ad , D-64289 Da ms ad , Ge many 5Physik-Depa men E12, TU M¨unchen, D-85748 Ga ching, Ge many 6STFC Da esbu y Labo a o y, Da esbu y, Wa ing on WA4 4AD, Uni ed Kingdom 7School o Physics and As onomy, Uni e si y o Manches e , Manches e M13 9PL, Uni ed Kingdom 8Ins i u e o Physics, Slo ak Academy o Sciences, SK-84511 B a isla a, Slo akia E-mail: [email p o ec ed] Abs ac . T ansi ion p obabili ies ha e been measu ed be ween he low-lying y as s a es in 175Au by employing he ecoil dis ance Dopple -shi me hod combined wi h he selec i e ecoil-decay agging echnique. Reduced ansi ion p obabili ies and magni udes o ansi ion quad upole momen s ha e been ex ac ed om measu ed li e imes allowing d ama ic changes in nuclea s uc u e wi hin a low exci a ion-ene gy ange o p obed. The ansi ion quad upole momen da a a e discussed in e ms o a ailable sys ema ics as a unc ion o a omic numbe and aligned angula momen um. 1. In oduc ion Unde s anding he mic oscopic s uc u e and dynamics o mesoscopic sys ems emains a key challenge in con empo a y physics. The a omic nucleus has p o ed o be a unique labo a o y o s udies o he in e play o undamen al o ces o na u e. Fo ins ance in he neu on-de icien Z= 82 egion coexis ence o many collec i e s uc u es has been obse ed. Neu on-de icien iso opes a and nea Z= 82 p esen us wi h he mos ex ensi e mani es a ion o he shape coexis ence. In he e en-mass iso opes his phenomenon has been well es ablished wi h mo e de ailed nuclea s uc u e da a eme ging. Howe e , in he odd-Znuclei spec oscopic inge p in s ha e been sca ce. Only ecen ly due o he de elopmen o sophis ica ed echniques ha e he spec oscopic s udies been ex ended o odd-mass nuclei a and beyond he neu on mid shell a N= 104 (see Re . [1] o a e iew). 11 h In e na ional Con e ence on Nucleus-Nucleus Collisions (NN2012) IOP Publishing Jou nal o Physics: Con e ence Se ies 420 (2013) 012047 doi:10.1088/1742-6596/420/1/012047 Published unde licence by IOP Publishing L d 1 175 177 179 181 183 185 187 Mass Numbe 0 500 1000 1500 2000 Ene gy (keV) 96 98 100 102 104 106 108 Neu on Numbe 13/2+ 17/2+ 21/2+ 25/2+ Mid shell Figu e 1. Pa ial ene gy-le el sys ema ics o he p o on-pa icle i13/2bands in he odd-mass Au nuclei nea he neu on mid shell. The ene gies a e ela i e o ha o he 11/2−s a e a ising om he p o on-hole s uc u e. In cases whe e he 11/2−p o on-hole s uc u e is no i mly es ablished, an es ima e has been made. The da a a e aken om Re . [6]. A s iking example o he shape coexis ence can be ound in Pb nuclei esiding nea he neu on mid shell a N= 104, whe e h ee shapes (sphe ical, obla e and p ola e de o med) ha e been iden i ied o o m he h ee lowes -lying s a es [2]. In he shell-model pic u e he de o med con igu a ions appea ing as local minima in po en ial ene gy su aces o he mean ield a e associa ed wi h mul ipa icle-mul ihole exci a ions ac oss he Z= 82 shell gap [3]. Simila ly o he neu on-de icien Pb nuclei, whe e a beau i ul minimum o in ude s a es is obse ed a he neu on mid shell, he shape coexis ence has been obse ed in he odd-ZAu nuclei in he icini y o his egion. The p esen a icle discusses he iple shape coexis ence in e ms o he indings o he ansi ion p obabili y measu emen s in 175Au [4]. Figu e 1 shows he ene gy-le el sys ema ics o he odd-mass Au iso opes nea N= 104. In 175Au, he posi i e pa i y y as bands obse ed in he neu on-de icien odd-mass Au iso opes ha e been associa ed wi h a p ola e shape and assigned o eme ge om π(i13/2) in ude exci a ions [5]. Fu he mo e, he lowes 13/2+s a e has been associa ed wi h he obla e con igu a ion. Toge he wi h he sphe ical Iπ= 11/2−α-decaying s a e deduced om α-decay cha ac e is ics hey o m an ene ge ically close-lying shape iple . The pa ial le el scheme ele an o his s udy is shown in Fig 2. 2. Expe imen al conside a ions and esul s The ecoil dis ance Dopple -shi (RDDS) li e ime measu emen s in 175Au we e ca ied ou a he Accele a o Labo a o y o he Uni e si y o Jy ¨askyl¨a, whe e he 92Mo(86S ,p2n)175Au usion-e apo a ion eac ion was used in o de o popula e he exci ed s a es in 175Au. The 86S beam a an ene gy o 401 MeV was deli e ed by he K130 cyclo on wi h an a e age in ensi y o 2 pnA. The 1 mg/cm2 hick iso opically en iched 92Mo a ge and he 1 mg/cm2 hick Mg deg ade oil we e housed in he K¨oln plunge de ice. The ecoiling e apo a ion esidues en e ed RITU gas- illed ecoil sepa a o [7] and subsequen ly we e sepa a ed om he backg ound mainly 11 h In e na ional Con e ence on Nucleus-Nucleus Collisions (NN2012) IOP Publishing Jou nal o Physics: Con e ence Se ies 420 (2013) 012047 doi:10.1088/1742-6596/420/1/012047 2 Figu e 2. Pa ial le el sche me o 175Au. The da a a e adap ed om Re s. [4, 5]. Table 1. Elec omagne ic p ope ies o he low-lying y as ansi ion in 175Au. The alues a e aken om Re . [4]. Eγ(keV) Ii(¯h)τ(ps) B(E2) (W.u.) |Q |(eb) 997 13/2 300-11000 294 17/2 44(4) 130(10) 4.8(2) 323 21/2 11(2) 340(60) 7.6(7) 380 25/2 7(2) 240(70) 6.4(9) a ising om ission p oduc s and sca e ed beam. The 175Au ecoils we e iden i ied h ough hei cha ac e is ic αdecays in he GREAT ocal plane spec ome e [8] and subsequen ly co ela ed wi h p omp γ ays eco ded wi h JUROGAM II γ- ay spec ome e su ounding he a ge posi ion. Gamma- ay singles spec a agged wi h he 175Au αdecays we e collec ed a en a ge - o-deg ade dis ances wi h wi h he JUROGAM II Ge de ec o s loca ed ei he a 158◦( i e de ec o s) o 134◦( en de ec o s) wi h espec o he beam di ec ion. Mean li e imes τwe e ex ac ed o he s e ched E2 ansi ions o igina ing om he 17/2+, 21/2+and 25/2+s a es acco ding o he p inciples o he di e en ial decay-cu e me hod [9]. In addi ion, i was possible o es ima e he limi s o he li e ime o he 13/2+→11/2−E1 ansi ion om he obse ed Dopple -shi ed componen and he absence o he deg aded componen o he de-exci ing γ ay. A de ailed desc ip ion o he expe imen al me hods is gi en in Re . [4]. The esul ing mean li e imes τ, educed ansi ion p obabili ies B(E2) and absolu e alues o ansi ion quad upole momen s Q a e gi en in Table 1. 11 h In e na ional Con e ence on Nucleus-Nucleus Collisions (NN2012) IOP Publishing Jou nal o Physics: Con e ence Se ies 420 (2013) 012047 doi:10.1088/1742-6596/420/1/012047 3 17/2 21/2 25/2 0 1 2 3 4 5 6 7 8 0 100 200 300 400 500 Ii (h) |Q | (eb) B(E2) (W.u.) Figu e 3. T ansi ion quad upole momen s |Q |( illed ci cles) and educed ansi ion p obabili ies B(E2) ( illed ba s) as a unc ion o he ini ial spin in 175Au ex ac ed om he li e imes measu ed in Re . [4]. 3. Discussion Fo a igid o o nucleus he alues o he ansi ion quad upole momen |Q |can be ex ac ed om he measu ed B(E2) alues using he o a ional model (see, o ins ance, Re . [10] o de ini ion). In Fig. 3 he |Q |and B(E2) alues a e plo ed as a unc ion o he ini ial spin o he ansi ions. While he |Q | alues o he Ii= 21/2 and 25/2 ¯ha e cons an wi hin he e o ba s, he alue o he Ii= 17/2 ¯h ansi ion is conside ably lowe . This is also e lec ed by he B(E2) alues and ep esen s ypical alues o collec i e o a ional bands in he icini y o Z= 82 [11]. The educ ion o collec i i y o he 17/2+→13/2+ ansi ion can be unde s ood wi h he change in in insic s uc u e o hese s a es. A simila d op in collec i i y be ween low-spin y as s a es has been obse ed in 188Pb [11] and in 180,182Hg nuclei, in which he he ansi ion connec s he wo s a es wi h di e en s uc u es [12]. In Re . [5] he obla e con igu a ion has been p oposed o he 13/2+s a e, which is in ag eemen wi h he p esen obse a ion. The change in he in insic s uc u e om he p ola e y as band a highe spin o he obla e s uc u e o he 13/2+s a e hinde s he ansi ion a e and he e o e esul s in educed collec i i y. A quali a i e es ima e o he mixing ampli ude o he obla e componen o he wa e unc ion o he 13/2+s a e can be deduced om he ex ac ed quad upole momen s. Assuming he 21/2+and 25/2+s a es o be pu e o a ing p ola e de o med s a es as sugges ed ea lie [5], he quad upole momen o he p ola e s uc u e can be ex ac ed as an a e age o he |Q | alues om hese s a es. Fu he mo e, as he |Q | alue o he 17/2+→13/2+ ansi ion is hinde ed by he change in he in insic s uc u e be ween hese s a es, he obla e ampli ude can be de i ed simila ly as in Re s. [11, 12] and is on he o de o 50%. The ob ained ange o he li e ime o he ansi ion om he 13/2+s a e o he α-decaying 11/2−s a e yields o an uppe limi o he B(E1) alue a he 10−5W.u. le el. This is 11 h In e na ional Con e ence on Nucleus-Nucleus Collisions (NN2012) IOP Publishing Jou nal o Physics: Con e ence Se ies 420 (2013) 012047 doi:10.1088/1742-6596/420/1/012047 4 175Au 178P 180Hg 186Pb 182Hg 187Tl 196Po 194Po 195Po 2+ 4+ 6+ 2+ 4+ 6+ 8 , +10+ 2+ 4+ 6 , +8+ 10+ 25/2+ 17/2+ 21/2+ 29/2+ 2+ 4+ 6+ 8+ 2+ 4+ 2+ 4+ 6+ 17/2+ 17/2+ 21/2+ 25/2+ |Q | (eb) 7 8 9 10 11 12 1 2 3 4 5 6 0 P o on Numbe 79 84 80 81 78 82 83 P ola e P ola e- P ola e Obla e- Obla e Obla e- P ola e Sphe ical- Figu e 4. Expe imen al Q alues as a unc ion o Z o he exci ed s a es nea N= 104. The ansi ions a e labelled wi h he ini ial spin Iπ. The da a a e aken om Re s. [11, 12, 13, 14, 15, 16]. consis en wi h he single-p o on ansi ion om he mixed obla e-p ola e collec i e s a e o he 11/2−nea sphe ical s a e, in ag eemen wi h he sugges ion in Re . [5]. The e o e, hese esul s indica e he exis ence o h ee ma kedly di e en s uc u es and e olu ion o nuclea s uc u e om non-collec i e single-pa icle s uc u e h ough he de o med obla e and inally o he de o med p ola e s uc u es wi hin less han 2 MeV o exci a ion ene gy. The e olu ion o collec i i y can also be conside ed as a unc ion o Zin he egion nea N= 104 and a o nea he Z= 82 shell closu e. Figu e 4 compa es he |Q | alues ex ac ed om li e ime measu emen s as a unc ion o Z o exci ed s a es in his egion. The |Q | alues indica e ha he high-spin s a es in 175Au a e simila o p ola e s a es in his egion. Howe e , he ansi ion o igina ing om he 17/2+s a e in 175Au has a lowe |Q | alue as discussed abo e, and is e y simila o obla e s a es in his egion. In pa icula , he y as bands in 194−196Po ha e been discussed as ep esen ing a he pu e obla e bands [11, 13, 14] and he |Q | alues o hose bea close esemblance o ha om he 17/2+s a e in 175Au. I is in e es ing o no e ha he |Q | alues o he p ola e s uc u es end o inc ease sligh ly wi h he inc easing Z, while he co esponding alues o he obla e s uc u es emain a he cons an . On he o he hand, his seems easonable as he minimum o he in ude con igu a ions ha e been obse ed o mo e away om he neu on mid shell o ligh e iso opes. This can be seen in he Au case om Fig. 1. To conclude, he li e imes o he low-lying y as s a es in 175Au ha e been measu ed using he RDDS me hod aided by highly selec i e adioac i e agging echnique. The ex ac ed B(E2) and |Q ] alues p o ide e idence o a iad o coexis ing shapes a low spin. The measu emen s indica e ha a collec i e p ola e y as band a highe spin coexis s wi h he obla e s uc u e, which is mixed wi h he p ola e con igu a ion o o m he 13/2+s a e. Fu he mo e, he e idence o non-collec i e E1 13/2+→11/2− ansi ion e lec s he single-pa icle nea sphe ical s uc u e o he α-decaying 11/2−s a e. 11 h In e na ional Con e ence on Nucleus-Nucleus Collisions (NN2012) IOP Publishing Jou nal o Physics: Con e ence Se ies 420 (2013) 012047 doi:10.1088/1742-6596/420/1/012047 5 Acknowledgmen s Financial suppo o his wo k has been p o ided by he UK Science and Technology Facili ies Council, he EU 6 h F amewo k P og amme, In eg a ing In as uc u e Ini ia i e- T ansna ional Access (EURONS, Con ac No. 506065), he Academy o Finland Finnish Cen e o Excellence P og amme 20062011. T.G, P.T.G, C.S., and P.N. acknowledge he suppo o he Academy o Finland (Con ac Nos. 131665, 111965, 209430, and 121110). We hank he GAMMAPOOL o he loan o he de ec o s. R.K, T.K., and P.M. acknowledge he suppo by he DFG Clus e o Excellence O igin and S uc u e o he Uni e se. M.V. acknowledges he suppo o Slo ak g an agency VEGA (Con ac No. 2/0105/11). 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C 71(5) 054324 11 h In e na ional Con e ence on Nucleus-Nucleus Collisions (NN2012) IOP Publishing Jou nal o Physics: Con e ence Se ies 420 (2013) 012047 doi:10.1088/1742-6596/420/1/012047 6