Evolution of the N=82N=82 shell gap below 132Sn inferred from core excited states in 131In

The γ-ray decay of an excited state in 131In, the one proton hole neighbor of the doubly magic 132Sn has been measured. A high-spin, core-excited isomer with T1/2=630(60) nsT1/2=630(60) ns was identified following production by both relativistic fragmentation of a 136Xe beam and fission of a 238U beam. This state deexcites by a single γ  -ray branch of 3782(2) keV from which direct evidence for the size of the N=82N=82 shell gap is inferred. The results are discussed in comparison to a shell-model calculation including configurations across the closed shells at N=82N=82 and Z=50Z=50.