Discovery of a nonyrast K-pi=8(+) isomer in Dy-162, and the influence of competing K-mixing mechanisms on its highly forbidden decay

Abstract

The Gd-160(Be-9,alpha 3n)Dy-162 reaction has been used to study high-spin states in Dy-162. Pulsed beam conditions were utilized for enhanced isomer sensitivity. An isomer at 2188.1(3) keV with a half-life of 8.3(3) mu s has been discovered and assigned K-pi = 8(+) with a two-quasineutron configuration. Among 11 gamma-ray decay branches, an E2, Delta K = 8 transition to the ground-state band was observed with a reduced hindrance of f(v) = 35, agreeing well with systematics correlating f(v) with the product of the valence neutron and proton numbers (NpNn) over an extended N, Z range. Small deviations from NpNn dependence are analyzed for a range of two-quasiparticle isomer decays and interpreted as arising from a weak dependence on the isomer excitation energy relative to the yrast line.

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