Reflection asymmetry in the structure and spectroscopy of²²⁴Ac

Abstract

Minor changes in the assignments of gamma rays following the alpha decay of²²⁸Pa in two previous studies make possible a reinterpretation of²²⁴Ac into two alternative level schemes. The resulting level structures arise from the reflection asymmetric configurations π3/2^±(0.0 −0.3)−ν3/2^±(−0.1 0.6), π5/2^±(0.0 −0.2)±ν3/2^±(−0.1 0.6) and π5/2^±(0.0 −0.2)±ν1/2^±(0.2 −0.1 3) which give rise to eitherK=0^± or 1^±,K=4^±,K=2^± andK=3^± parity doublet bands. The bands with appreciable band structure, namelyK=0^± or 1^± andK=3^±, have average parity doublet splittings of 11.0 and 5.8 keV respectively. These are extremely small values and suggest that²²⁴Ac is the most octupole deformed nucleus studied thus far. A method of calculating the parity doublet splitting in odd-odd nuclei is suggested and tested for²²⁴Ac. It seems to work remarkably well. The systematics of the hindrance factors for the bands with extended band structures confirm their interpretations as band structures. Finally, the two alternative level schemes are analyzed in the framework of the axially-symmetric rigid rotor model including the Coriolis interaction.