Low- Z boundary of the N=88 -90 shape phase transition: Ce 148 near the critical point

Abstract

Excited states of the neutron-rich nucleus Ce148 have been populated by neutron-induced fission of a U235 target. Its electromagnetic decays were studied by means of γ-ray coincidence spectroscopy with fast-timing capabilities. Lifetimes of the 21+ and 41+ states of Ce148 were obtained and their E2 decay rates deduced. The B4/2=B(E2;41+→21+)/B(E2;21+→01+) ratio indicates that Ce148 is a transitional nucleus while the N=88/90 shape phase transition evolves into a gradual change of nuclear deformation for proton numbers Z<60.