New isomer found inSb8951140: Sphericity and shell evolution betweenN=82andN

Abstract

In this article we report on the first spectroscopic information on 140 51 Sb89 and the observation of an isomer in this nucleus with T 1/2 = 41(8) µs. It is located in a close proximity to 140 Sn for N =90, where the νf 7/2 orbit is being completely filled. The possible origin of the isomeric state is a πg 1 7/2 × νf −1 7/2 coupling configuration, resulting in a (6 − ) or (7 − ) spin/parity. This is likely caused by an inversion of the πg 7/2 and πd 5/2 orbitals at N = 89. The existence of such an isomer far from stability is discussed extensively in the context of shell-model calculations and compared to results from mean-field calculations performed using a deformed Woods-Saxon potential. Both approaches suggest the observation of a single-particle excitation mode at an extreme neutron number. I. INTRODUCTION

Evolution of proton single-particle states in neutron-rich Sb isotopes beyond N=82

“…This feature was already discussed in Refs. [47][48][49]. In the first, the effective SPE were calculated, showing a decrease of the proton gap with increasing neutron number with the inversion taking place at N = 90.…”

First lifetime investigations of N>82 iodine isotopes: The quest for collectivity

“…[46,47], respectively. The N3LOP effective interaction was successfully used before in describing the spectroscopic properties and collectivity of nuclei in the vicinity of the 132 Sn nucleus [5,7,8,15,28,48]. The diagonalization of the considered systems 135,137,139 I is achieved using the ANTOINE shell-model code [49,50].…”

“…Above Z = 50, the evolution of the low-lying proton π (1d 5/2 ) and π (0g 7/2 ) orbitals as a function of neutron number, N, is of particular interest. An indication for the inversion of those orbitals was observed in a long-lived (6 − ) isomer in the 140 Sb nucleus [15]. In the odd-odd 136,138 I isotopes longlived isomers [13,16,17] were suggested to result from the drastic lowering in the position of the π (1d 5/2 ) orbital [13,18].…”

New nuclear structure data beyond 136Sn

“…Several experimental investigations were recently performed using various methods, as on the very neutron-rich nuclei -in isomer and β-decay spectroscopy at EURICA, the less neutron-rich in prompt γ-ray spectroscopy at EXILL and in purely β-decay measurements at LOHENGRIN. Details of these studies were discussed elsewhere [2,5,11,16,17]. The strategy in these complementary measurements is to find a common description of the entire region on orbital evolution and collectivity, while searching for single-particle and collective excitations and their persistence with the addition of particles.…”

“…More monopole corrections are needed e.g. at the end of the νf 7/2 shell, around N=90, to describe our recent experimental data on possible crossing between πg 7/2 and πd 5/2 orbitals [11]. Even if some of these descriptions do reasonably well close to 132 Sn, they show discrepancies e.g.…”