Nuclear structure of Th229

Abstract

Lifetimes of excited states in Th229, populated in the β decay of Ac229, have been measured using the advanced time-delayed βγγ(t) method. Half-lives of 14 states have been determined including 11 of them for the first time. Twenty-seven new γ lines have been introduced into the β-decay scheme of Ac229 based on results of γγ coincidence measurements. Reduced transition probabilities have been determined for more than 70 γ transitions in Th229. Average |D0| values of 0.029(1), 0.077(3), and 0.024(5) e fm have been deduced for the lowest Kπ=1/2±,3/2±, and 5/2± parity partner bands, respectively. Excited states in Th229 and experimental transition rates have been interpreted within the quasiparticle-plus-phonon model. The half-life of the 3.5-eV, 3/2+ isomeric state is predicted to be about 10 h. Potential energy surfaces on the (β2,β3) plane for the lowest single quasiparticle configurations in Th229 have been calculated using the Strutinsky method. © 2006 The American Physical Society.