Molecular Alpha-Particle Clustering inRa218; Dipole Collectivity in the Vicinity of Nuclear Shell Closures

Evidence for the presence of alpha-particle clustering in ${}_{}{}^{218}{}_{}{}^{}\mathrm{Ra}$ comes from a number of observables: binding energy, $S_{2n}$, $Q_{\alpha }$, $E_x\left(J^{\pi }\right)$, ${{\theta }_{\alpha }}^2$, and $F_{\alpha }$. That this clustering is a signature for the new dipole collectivity suggested by Iachello and Jackson follows from observation of simultaneous enhancement of selected $E1$, $E2$, and $E3$ deexcitation transition matrix elements; of these the $E1$ enhancement is most pronounced as would be expected for dipole collectivity.