1p(3/2) Proton-Hole State in Sn-132 and the Shell Structure Along N=82

摘要

A low-lying state in 131In82, the one-proton hole nucleus with respect to double magic 132Sn, wasobserved by its γ decay to the Iπ ¼ 1=2− β-emitting isomer. We identify the new state at an excitationenergy of Ex ¼ 1353 keV, which was populated both in the β decay of 131Cd83 and after β-delayed neutronemission from 132Cd84, as the previously unknown πp3=2 single-hole state with respect to the 132Sn core.Exploiting this crucial new experimental information, shell-model calculations were performed to study thestructure of experimentally inaccessible N ¼ 82 isotones below 132Sn. The results evidence a surprisingabsence of proton subshell closures along the chain of N ¼ 82 isotones. The consequences of this findingfor the evolution of the N ¼ 82 shell gap along the r-process path are discussed.