Isomeric decay studies using a recoil mass separator

Abstract

Microsecond isomers in the exotic proton-rich N = 82, 83 nuclei 153Yb, 153Lu, 154Lu and 154Hf have been identified by y-ray spectroscopy following mass analysis of m;Pd+245 MeV 54Fe reaction products using the Daresbury Recoil Separator. The decays of the isomers, interpreted as ~h~/2 and rch~/2 vfT/2 states, are characterized. The reduced E2 transition rates indicate that halffilling of the ~ h~m subshell occurs just below Z = 71, and results for the N= 83 odd-odd isotones are also consistent with this finding.

Decay of a 19− isomeric state in Lu156

“…The lowering of the [πh −1 11/2 ⊗ νh 9/2 ]10 + state relative to the [πh −1 11/2 ⊗ νf 7/2 ]9 + state has been attributed to the strong attractive interaction between h 11/2 protons and h 9/2 neutrons [5]. Reduced transition probabilities measured in N = 82 isotones indicate that the half-filling of the πh 11/2 orbital occurs just below Z = 71 [15,16]. Therefore the interaction should be strongest in Lu isotopes and could be manifested in the reversal in the relative energies of these states in 156 Lu.…”

Fine structure in the α decay of Lu156 and Ta158

“…This may be assumed due to the consistency of the α-particle energy with those previously measured and that it is not observed in coincidence with any γ rays. It is proposed that the (6021-keV α-particle)-(22-keV γ -ray) coincidences in panels b(i) and c(i) are associated with the α decays from 158 Ta which populate a J π = 8 + state in 154 Lu which has previously been identified 22 keV above the 9 + ground state [26,27]. This assignment is made from the comparison of the total decay Q value of this α decay, Q T = 6200(4) keV, with that of the α decay to the J π = 9 + state, Q T = 6198(4) keV.…”

“…Detailed level schemes of high-spin states in all four of the N = 83 daughter nuclei of the α decays discussed are known. These were constructed from spectroscopy of γ rays emitted promptly following the production by fusion evaporation of 148 Tb [22,23] and following internal isomeric decays in 150 Ho [24,25], 152 Tm [25], and 154 Lu [26,27]. All four of the schemes were built on a (π h 11/2 ν f 7/2 )9 + ground state.…”

Blurring the Boundaries: Decays of Multiparticle Isomers at the Proton Drip Line

“…The excitation energies, spins, and parities of yrast states that could be populated by proton emission from the new isomer in 158 Ta and the multiparticle isomers in 157 Ta and 153;154;155 Lu are known [16,[30][31][32][33]. Partial half-lives for proton-decay branches from the multiparticle isomers in 155 Lu and 157;158 Ta estimated by using a simple formula that reproduces measured proton-decay half-lives [34] are presented in Fig.…”

“…In 153 Lu, the πs 1=2 isomer at 80 keV would have the shortest partial half-life, with those of the isomer decays and the πh 11=2 ground state being comparable. The excitation energy of the 154 Lu isomer is not known [32].…”