Sn116Levels Populated by the Decay of 54-Minln116m

Abstract

The decay of the 54-min ${\mathrm{In}}^{116}$ isomer was reinvestigated by means of scintillation singles and coincidence spectroscopy techniques. Angular-correlation measurement of four pairs of successive $\gamma$ rays served as a basis for the assignment of the spin and parity of all levels, and the multipole order of all transitions. The excitation energies (MeV, relative to the $0^{+}$ ground state) and characters ($j^{\pi }$) of the observed levels were 3.06 ($4^{+}$), 2.78 ($4^{+}$), 2.53 ($4^{+}$), 2.38 ($4^{+}$), 2.12 ($2^{+}$), 1.72 ($0^{+}$), and 1.29 ($2^{+}$). In addition, two new transitions with energies of 0.385 and 0.435 MeV (previously unreported in this decay) were observed to feed and depopulate, respectively, the level at 1.72 MeV. The relative intensities of all transitions are presented. The experimental results are compared with previously reported work and are discussed in the light of recent pairing-force calculations. All levels populated in this decay, with the exception of the 1.29-MeV first excited state, were found to be distinctly different from those populated in the same nuclide by the decay of 1-h ${\mathrm{Sb}}^{116}$. These findings are discussed, and arguments are presented to account for these differences.