Enhanced α decays to negative-parity states in even-even nuclei with octupole deformation

Abstract

The $\ensuremath{\alpha}$ decays of even-even Ra, Th, U, and Pu isotopes to ground and excited states of daughter nuclei with neutron numbers of $N=130--140$ are investigated. These nuclei show some enhanced $\ensuremath{\alpha}$-branching ratios to negative-parity states $({1}^{\ensuremath{-}},$ ${3}^{\ensuremath{-}})$, compared with the decays to positive-parity states $({4}^{+})$ of comparable energy. This enhancement correlates with appearance of static octupole deformation, rather than spherical nuclear shapes or dynamic asymmetric vibrational states. The highly enhanced branching ratios occur for $\ensuremath{\alpha}$ decays to the ${1}^{\ensuremath{-}}$ and ${3}^{\ensuremath{-}}$ states of the Ra isotopes with $N=134, 136, 138$, then to ${1}^{\ensuremath{-}}$ state in Th $(N=134--140)$ and to the ${3}^{\ensuremath{-}}$ state in Rn $(N=132--136)$ isotopes.