Reflection asymmetry in the structure and spectroscopy of 224Ac

Minor changes in the assignments of gamma rays following the alpha decay of 228Pa in two previous studies make possible a reinterpretation of 224Ac 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 either K = 0± or 1±, K = 4±, K = 2± and K = 3± parity doublet bands. The bands with appreciable band structure, namely K = 0± or 1± and K = 3±, have average parity doublet splittings of 11.0 and 5.8 keV, respectively. These are extremely small values and suggest that 224Ac 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 for 224Ac. 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. (author)