Multiparticle configurations of excited states in Lu155

Abstract

Excited states in the neutron-deficient N = 84 nuclide 155 Lu have been populated using the 102 Pd( 58 Ni,αp) reaction. The 155 Lu nuclei were separated using the gas-filled recoil separator RITU and implanted into the Si detectors of the GREAT spectrometer. Prompt γ-ray emissions measured at the target position using the Jurogam Ge detector array were assigned to 155 Lu through correlations with α decays measured in GREAT. Structures feeding the (11/2 − ) and (25/2 − ) α-decaying states have been revised and extended. Shell-model calculations have been performed and are found to reproduce the excitation energies of several of the low-lying states observed to within an average of 71 keV. In particular, the seniority inversion of the 25/2 − and 27/2 − states is reproduced.

Excited states in the proton-unbound nuclideTa158

“…+ states are πd 3/2 ⊗ νf 7/2 and πh 11/2 ⊗ νf 7/2 , respectively [18], while those of the sequence of yrast states from the 10 + state to the 16 + state are πh 11/2 ⊗νf 2 7/2 h 9/2 [16]. This sequence fits very well into the systematics of excited states of N = 85 isotones that are plotted in + state in odd-odd isotones [10,[29][30][31][32][33][34][35][36].…”

“…An alternative mechanism for generating spins greater than 16 is through the creation of higher-seniority states by breaking a pair of πh 11/2 protons and aligning their angular momenta, with the neutrons remaining in νf 7/2 or νh 9/2 orbitals. The full alignment of the six valence nucleons in this case would produce a state with spin and parity 25…”

“…In ref. [16] the stability against proton emission of the 19 − isomer, for which Q p = 3261(14) keV, was considered. Some of the excited states presented in this work lie at even higher excitation energies and could potentially have proton emission branches.…”

“…Prompt γ-ray transitions measured in JUROGAM that populate the 19 − isomer (t 1/2 = 6.1(1)µs [16]) were also identified. Fig.…”

“…Prior to the discovery of the 19 − isomeric state and its decay by α-particle emission and γ-ray emission [16,17], only two states were known in 158 Ta, both of which decay by α-particle emission: the (2 − ) ground state and a 9…”