Evidence forY4Deformation lINNe20and others−dShell Nuclei

The sign and magnitude of the haxadecapole deformation in ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ is determined from measurements of the inelastic scattering of 24.5-MeV protons. A coupled-channels analysis yields a value for ${\beta }_4$ of + 0.28. A similar analysis of other available data in the $s-d$ shell suggests a large hexadecapole deformation in ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ (+0.25) and ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$ (+0.25); ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ is found to have a $Y_4$ moment close to zero.