Negative-parity structures and lifetime measurements in 71As.

Abstract

High-spin states up to (29/${2}^{+}$) and (29/${2}^{\mathrm{\ensuremath{-}}}$) in $^{71}\mathrm{As}$ have been studied via the $^{58}\mathrm{Ni}$${(}^{19}$F,\ensuremath{\alpha}2p) reaction at 62 MeV using in-beam \ensuremath{\gamma}-ray spectroscopic techniques. Based on a particle-\ensuremath{\gamma} coincidence measurement a new decay sequence of negative parity has been assigned to $^{71}\mathrm{As}$. Lifetimes for some E2 transitions were extracted from Doppler-shifted line shapes observed in coincidence mode, and experimental transition quadrupole moments were determined. They indicate a moderate to high collectivity in both the positive-parity yrast band and the new negative-parity decay sequence at high spins. Total Routhian surfaces calculated for states of both parities reveal strong triaxial shapes at high spins. A noncollective structure of 19/${2}^{(\mathrm{\ensuremath{-}})}$ and 21/${2}^{(\mathrm{\ensuremath{-}})}$ states is interpreted as a three-quasiparticle excitation.