Investigation of nuclear collectivity in the neutron mid-shell nucleus Pb186

For the first time, non-yrast structures of the neutron mid-shell nucleus Pb186 have been identified in an in-beam I -ray spectroscopy measurement using the recoil-decay tagging technique. The yrast band has been tentatively extended up to IÏ€=20+, revealing a similar backbend to that observed in the Pt and Hg isotones. Three new bands and several other transitions have been observed. Calculations carried out in the framework of the interacting boson model together with mean-field studies using the generator coordinate method provide arguments for the association of one of the new bands with an oblate shape. The present data also show evidence for octupole and I -vibrational bands. © 2007 The American Physical Society.