Extreme Prolate Deformation in Light Strontium Isotopes

Multiple-particle, $\ensuremath{\gamma}$-ray coincidence techniques have been used to study neutron-deficient isotopes near $N=Z=40$. Results are presented for $^{77\ensuremath{-}80}\mathrm{Sr}$. Levels in $^{78}\mathrm{Sr}$ were seen to $J=10$ with $E({2}^{+})=278$ keV and ${T}_{\frac{1}{2}}=155\ifmmode\pm\else\textpm\fi{}19$ ps. The results suggest that this region contains some of the most deformed nuclei known, with quadrupole deformations ${\ensuremath{\epsilon}}_{2}\ensuremath{\approx}0.4$. These data resolve conflicting theoretical predictions of nuclear shapes and emphasize the important contribution of hexadecapole deformation in determining the most stable shape.