Level structure ofRa220

A level scheme for ${}_{}{}^{220}{}_{}{}^{}\mathrm{Ra}$ is presented, established using the ${}_{}{}^{208}{}_{}{}^{}\mathrm{C}$,2n) reaction studied near the Coulomb barrier (60≤E≤68 MeV). Measurements included γ-ray excitation functions, γ-γ coincidences, and γ-ray angular distributions. The dominant features in the spectrum are states of alternating parity connected by fast E1 transitions. Values of B(E1)/B(E2) are obtained for states with J=6–17 ħ. Examination of the systematic behavior of even-even Ra isotopes reveals a sharp change in structure as one proceeds from ${}_{}{}^{214}{}_{}{}^{}\mathrm{Ra}$ to ${}_{}{}^{226}{}_{}{}^{}\mathrm{Ra}$. Results are discussed in terms of alpha-particle clustering (in particular as described by the vibron model) and of a stable octupole deformation; calculations of the energy spectrum based on the vibron model are presented.