Evidence for Multiple Negative-Parity Band Structure in $^{71}$Se

The negative-parity bands of $^{69}$Se and $^{73}$Se indicate a stark contrast between strong single-particle ($^{69}$Se) and collective ($^{73}$Se) behavior over a wide range of spins. However, only one negative-parity band has been observed so far in $^{71}$Se, making it difficult to see where it lies between these two very different cases. Thus, the goal of the present work was to extend the level scheme of $^{71}$Se as much as possible, with an emphasis on finding new negative-parity states. $^{71}$Se nuclei were produced at high spin following the 80-MeV $^{54}$Fe ($^{23}$Na, $\alpha pn$) reaction at Florida State University. $\gamma-\gamma$ coincidences were measured using an array of 10 Compton-suppressed Ge detectors which included three Clover detectors. From the coincidence relationships, new states were found that formed candidates for perhaps two new negative-parity bands. Cranked-shell model calculations indicate that one new band is associated with rigid- body rotation at high spin.