Decay of high-spin isomers in Os nuclei by barrier penetration

Abstract

A decay scheme for the 130±20 ns high-spin isomer in 182Os has been established. The excitation energy of the isomer is 7049±1 keV and it has Iπ = 25(+). A 2.4% decay directly to the yrast 24+ level at 5988 keV is observed. In 184Os a 20±5 ns isomer is observed at 2366±1 keV excitation energy with Iπ = 10+. Again, direct transitions into the yrast 8+ and 10+ levels are observed. Contrary to previous speculations, there is no compelling evidence for stable triaxial shapes in the structure of the levels through which the isomers decay. The abnormally short half-lives observed, as well as the unusual decay patterns, are best understood in terms of a γ-soft nuclear potential. Motion in the γ-direction allows the isomer to decay via barrier penetration from an axially symmetric prolate shape with the angular momentum along the nuclear symmetry axis (deformation aligned state) via oblate shapes to another prolate shape with the angular momentum perpendicular to the nuclear symmetry axis (rotation-aligned state).