Nuclear structure of $^{231}$Ra

The study of the upper border of the octupole deformation region near A=225, where the octupole deformation vanishes in the presence of a well developed quadrupole field, is of great relevance in order to understand the interplay of octupole and quadrupole collectivities. Within the IS322 collaboration at CERN we carry out a systematic investigation of the heavy Fr-Th nuclei that presently includes $^{227}$Fr, $^{227, 228, 229}$Ra, $^{229}$Ac and $^{229, 231}$Th. The heaviest Ra isotope we have studied so far and in which the fast timing $\beta\gamma\gamma$(t) method has been applied is $^{231}$Ra. (2 refs).