Nuclear structure of 231 Ac

The low-energy structure of 231 Ac has been investigated by means of ray spec- troscopy following thedecay of 231 Ra. Multipolarities of 28 transitions have been established by measuring conversion electrons with a mini-orange electron spectrometer. The decay scheme of 231 Ra → 231 Ac has been constructed for the first time. The Advanced Time Delayed �(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.