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 $Q_t\sim 3.5e\mathrm{b}$, while the ${}^{83}\mathrm{Y}$ and ${}^{84}\mathrm{Zr}$ cases display $Q_t=4.4\mathrm{}e\mathrm{b}$ 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 $Z=38\mathrm{}$ to $Z\ge 39$.

• Received 10 May 1999

DOI:https://doi.org/10.1103/PhysRevLett.83.5447