Evolution of Collectivity with Spin in $^{70}$As

The high-spin decay of $^{70}$As was studied using the $^{55}$Mn($^{18}$O, $3n$) reaction at 50 MeV and a Compton-suppressed Ge array consisting of three Clover detectors and seven single-crystal detectors at Florida State University. Based on prompt $\gamma$-$\gamma$ coincidences and $\gamma$-ray relative intensities measured in the experiment, several previously proposed $\gamma$-ray transitions have been confirmed and additional transitions have been placed in the level scheme. In particular, members of a ``missing'' negative-parity, odd-spin band were observed. The yrast positive-parity band shows similarities to those of neighboring odd-odd isotopes, including signature splitting and large alternations in the $B(M1)/B(E2)$ ratios. Kinematic moments of inertia were calculated for each observed high-spin band and roughly indicate a convergence to the expected rigid-body value. Theoretical shape calculations indicate a nearly prolate shape at high spin, as well as a possible oblate shape associated with some low-spin, negative-parity states.