116In level scheme and p-n configurations

Abstract

The low-energy and high-energy γ-ray spectra associated with the reaction 115In(n,γ) 116In have been measured with Ge(Li) detectors and a Ge(Li)-NaI(Tl) pair spectrometer. A γ-γ coincidence study has been performed using a Ge(Li)-Ge(Li) coincidence system. Combining these measurements with the results of (d, p) and other (n, γ) studies, a level scheme for 116In up to 1.4 MeV is proposed. In particular, seven states of the (π( g 9 2 −1, v h 11 2 ) multiplet (3 − to 9 −) are unambiguously identified and the anomalous high isomeric cross-section ratio of the second isomeric state is explained. The binding energy B n of the last neutron in 116In has been determined to be 6784.2±1.2 keV. From the energy splitting of the fairly pure high-spin states of the (π( g 9 2 −1, v h 11 2 ) multiplet, the coupling constant of the quadrupole part of the residual proton-neutron interaction k 2 is calculated in a spherical basis. The k 2 obtained is about 5 times larger than the one normally used in calculations of quadrupole oscillations in doubly even nuclei. This discrepancy is discussed, and an explanation in terms of an isovector component of the quadrupole interaction is proposed.