The ground-state band up to the $4^{+}$ state in the even ${}_{}{}^{74-82}{}_{}{}^{}\mathrm{Se}$ isotopes was studied by inelastic scattering of polarized protons at 65 MeV. Both the cross-section $\sigma \left(\theta \right)$ and the analyzing-power $A\left(\theta \right)$ measurements leading to the $4^{+}$ state in the light ${}_{}{}^{74,76,78}{}_{}{}^{}\mathrm{Se}$ isotopes show quite different shapes from those in the heavy ${}_{}{}^{80,82}{}_{}{}^{}\mathrm{Se}$ isotopes. Coupled-channels analyses show that both the $\sigma \left(\theta \right)$ and $A\left(\theta \right)$ distributions are well reproduced with a positive deformation parameter ${\beta }_4$ in ${}_{}{}^{74,76,78}{}_{}{}^{}\mathrm{Se}$, but with a negative ${\beta }_4$ in ${}_{}{}^{80,82}{}_{}{}^{}\mathrm{Se}$, indicating a hexadecapole-shape transition between ${}_{}{}^{78}{}_{}{}^{}\mathrm{Se}$ and ${}_{}{}^{80}{}_{}{}^{}\mathrm{Se}$.

• Received 25 July 1983

DOI:https://doi.org/10.1103/PhysRevLett.51.1741