Investigation of a 290 ns 23-/2 isomeric state in 117Sb and evidence for shape coexistence

A 290 ns23-/2 isomeric state has been identified as 3230.6 keV excitation in 117Sb populated in the 115In(α,2n) reaction at Eα = 27 MeV. The decay scheme was investigated by pulsed beam γ-ray spectroscopy. From TDPAD measurements on molten and solid metallic In targets, the g-factor, g=+0.437(5), and a lower limit for the electric quadrupole moment, vertical strokeQvertical stroke > 1,7 b, have been determined. The experimental data indicate that the 1g-19/2 proton shell-model intruder excitation responsible for coexistence in odd-mass Sb nuclei is present in the structure of some high spin states in 117Sb. The [π(1g-19/2)xν(1h11/22d3/2)-7]23/2- configuration has been assigned to the isomeric state on the basis of the measured g-factor. The enhanced E2 isomeric transition probability and the lower limit established for the electric quadrupole moment indicate an increased collectivity associated possibly with a deformation of the 290 ns 23-/2 isomeric state in 117Sb. (orig.)