K-mixing in the doubly mid-shell nuclide Dy-170 and the role of vibrational degeneracy

Abstract

A detailed study of the structure of the doubly mid-shell nucleus View the MathML sourceDy10466170 has been carried out, following isomeric and β decay. We have measured the yrast band up to the spin-parity Jπ=6+Jπ=6+ state, the K=2K=2γ -vibration band up to the 5+5+ state, a low-lying negative-parity band based on a 2−2− state that could be a candidate for the lowest energy octupole vibration state within this nucleus, and a candidate for the Kπ=6+Kπ=6+ two quasi-particle isomer. This state was determined to have an excitation energy of 1643.91(23) keV and a half life of 0.99(4) μs, with a reduced hindrance for its decay to the ground-state band an order of magnitude lower than predicted by NpNnNpNn systematics. This is interpreted as being due to γ -vibrational mixing from a near degeneracy of the isomer and the 6+6+ state of the γ band. Furthermore, the parent nucleus 170Tb has been determined to have a half-life of View the MathML source0.91(−13+18) s with a possible spin-parity of 2−2−.