Nuclear structure of 231Ac

The low-energy structure of 231Ac has been investigated by means of γ ray spectroscopy following the β− decay of 231Ra. Multipolarities of 28 transitions have been established by measuring conversion electrons with a mini-orange electron spectrometer. The decay scheme of 231Ra → 231Ac has been constructed for the first time. The Advanced Time Delayed βγγ(t) method has been used to measure the half-lives of five levels. The moderately fast B(E1) transition rates derived suggest that the octupole effects, albeit weak, are still present in this exotic nucleus.