Prolate-oblate shape transition in heavy neutron-rich nuclei

A large amount of experimental information was obtained on heavy neutron-rich nuclei in the Hf-Hg region during the last decade. In the majority of the cases these nuclei were populated in relativistic energy fragmentation and studied via isomeric and β decays. In addition, deep-inelastic studies gave information to nuclei close to stability. The experimental data were used to establish the sign of quadrupole deformation, prolate or oblate. In the present paper this information is compared with two global theoretical calculations, one which is constrained to axial symmetry and one which considers triaxiality. The prolate-oblate transitional region was reached for (Z=76) Os and Ir (Z=77), as proved by the observation of oblate isomeric states in 197,198,199Os and 201Ir. For Ta (Z=73) and W (Z=74) isotopes no clear evidence of oblate deformation exists so far, with 192W and 189Ta being the most neutron-rich isotopes with spectroscopic information.