New isomer found in $_{51}^{140}Sb_{89}$ : Sphericity and shell evolution between $N = 82$ and $N = 90$
Résumé
In this article we report on the first spectroscopic information on 14051Sb89 and the observation of an isomer in this nucleus with T1/2=41(8) μs. It is located in close proximity to 140Sn for N=90, where the νf7/2 orbit is completely filled. The possible origin of the isomeric state is a πg17/2×νf−17/2 coupling configuration, resulting in a (6−) or (7−) spin-parity. This is likely caused by an inversion of the πg7/2 and πd5/2 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.
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