Feeding times of high-spin states in 152, 154Dy: Probes of nuclear structure above the yrast line

Abstract

Measurements of feeding times of high-spin yrast states up to spin 30 ℏ in 154Dy and 36 ℏ in 152 Dy were utilized to obtain information about possible spin-dependent shape changes. The reactions 25Mg( 134Xe, 5n), 124Sn( 34S, 4n) and 25Mg( 132Xe, 5n), 122Sn( 34S, 4n) were used to populate the high-spin states in 154Dy and 152Dy, respectively. Feeding times as well as lifetimes were determined with the recoil-distance technique. In 152Dy only long feeding times (⩾ 10 ps) could be identified, indicating that the aligned-particle yrast states are fed through configurations of similar character, with little direct population from collective cascades in the continuum region. In 154Dy discrete states with I ⩽ 30 ℏ have lifetimes which are characteristically collective, whereas the preyrast cascades exhibit both fast (≲1 ps) and slow (∼10 ps) feeding components. The latter imply a change with increasing spin from collective to aligned-particle character, probably associated with a prolate to oblate shape transition.