Level structure and deexcitations inRa220and their systematic behavior as a function of neutron number

The level scheme of ${}_{}{}^{220}{}_{}{}^{}\mathrm{Ra}$, constructed from ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}({}_{}{}^{14}{}_{}{}^{}\mathrm{C},2\mathrm{n}\gamma ){}_{}{}^{220}{}_{}{}^{}\mathrm{Ra}$ data, shows structure similar to that of ${}_{}{}^{218}{}_{}{}^{}\mathrm{Ra}$, with interleaved states of alternating parities connected by enhanced $B\left(E1\right)$ deexcitations. The $\frac{B\left(E1\right)}{B\left(E2\right)}$ ratios (for moderately high spins) are two to three times smaller than in ${}_{}{}^{218}{}_{}{}^{}\mathrm{Ra}$; we observe a smooth and rapid increase of the $B\left(E1\right)$ values toward shell closures. The systematics of the Ra isotopes are used to examine the alpha cluster model of Iachello-Jackson and the permanent octupole shape model.