Shapes, Softness and Non-Yrast Collectivity in 186W

Abstract

Non-yrast, excited states in neutron-rich ${}^{186}$W were populated via inelastic-scattering reactions using beams of ${}^{136}$Xe nuclei accelerated to 725 and 800 MeV. Levels populated in the reactions were investigated via particle-$\gamma$ coincidence techniques using the Gammasphere array of High-Purity Germanium detectors and the compact heavy-ion counter, CHICO2. The $K^{\pi }=2^{+}$ ($\gamma$), $K^{\pi }=0^{+}$ and $K^{\pi }=2^{-}$ (octupole) rotational side bands were extended to spins $14\hslash$, $12\hslash$, and $13\hslash$, respectively. A staggering pattern observed in the energies of levels in the $K^{\pi }=2^{+}$ band was found to be consistent with a potential that gets softer to vibration in the $\gamma$ degree of freedom with increasing spin. The odd-even staggering of states in the $K^{\pi }=2^{-}$ band was found to exhibit a phase opposite to that seen in the $\gamma$ band; an effect most probably associated with Coriolis coupling to other, unobserved octupole vibrational bands in ${}^{186}$W.

Comments: 14 pages, 16 figures