Molecular Alpha-Particle Clustering in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi mathvariant="normal">Ra</mml:mi></mml:mrow><mml:mprescripts/><mml:mrow/><mml:mrow><mml:mn>218</mml:mn></mml:mrow><mml:mrow/><mml:mrow/></mml:mmultiscripts></mml:mrow></mml:math>; 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, ${S}_{2n}$, ${Q}_{\ensuremath{\alpha}}$, ${E}_{x}({J}^{\ensuremath{\pi}})$, ${{\ensuremath{\theta}}_{\ensuremath{\alpha}}}^{2}$, and ${F}_{\ensuremath{\alpha}}$. 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.