Accurate Lifetime Measurements of Superdeformed Bands inA∼80Nuclei

Comparative measurements of the lifetimes of yrast superdeformed (SD) states in ${}^{80--83}\mathrm{Sr}$, ${}^{83}\mathrm{Y}$, and ${}^{84}\mathrm{Zr}$ have been performed using the Doppler-shift attenuation method. Thus, the transition quadrupole moments ( ${Q}_{t}$) of these structures have been determined accurately. The yrast SD bands in ${}^{80--83}\mathrm{Sr}$ possess ${Q}_{t}\ensuremath{\sim}3.5e\mathrm{b}$, while the ${}^{83}\mathrm{Y}$ and ${}^{84}\mathrm{Zr}$ cases display ${Q}_{t}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}4.4e\mathrm{b}$ and $5.6e\mathrm{b}$, respectively. Intruder orbital assignments based on these results demonstrate a previously unnoticed transition in the structure of the SD bands when the proton number changes from $Z\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}38$ to $Z\ensuremath{\ge}39$.