Discovery of a nonyrast Kπ=8+ isomer in Dy162, and the influence of competing K-mixing mechanisms on its highly forbidden decay

Abstract

The Gd160(Be9,α3n)Dy162 reaction has been used to study high-spin states in Dy162. Pulsed beam conditions were utilized for enhanced isomer sensitivity. An isomer at 2188.1(3) keV with a half-life of 8.3(3) μs has been discovered and assigned Kπ= 8+ with a two-quasineutron configuration. Among 11 γ-ray decay branches, an E2, ΔK=8 transition to the ground-state band was observed with a reduced hindrance of fν=35, agreeing well with systematics correlating fν 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.