Lifetimes of the 2$^+_1$ and the 4$^+_1$ States of $^{148}$Ce and its B$_{4/2}$ Ratio from EXILL&FATIMA Experiment

Abstract

International audienceThe even-even N=90 isotones with Z=60-66, present an interesting phase transition. This phasetransition in nuclei is characterized by a sudden change of the shape of the nucleus [1]. 148Ce lies onthe downboundaries of the phase transition region and therefore further elucidate the underlyingmechanisms that lend the shape phase transition behavior. 235U and 241Pu fission fragments were measured by a mixed spectrometer consisting of highresolution Ge and fast LaBr3(Ce)-scintillator detectors at the high-flux reactor of the ILL. Prompt γ-ray cascades from the nuclei of interest are selected via Ge-Ge-LaBr3-LaBr3 coincidences. The goodenergy resolution of the Ge allows precise gates to be set, selecting the cascade, hence, the nucleusof interest. The excellent timing performance of the LaBr3 detectors in combination with theGeneral Centroid Difference method [2] allows the measurement of lifetimes in the ps range inpreparation for the FATIMA experiment at FAIR. The first results on neutron-rich 148Ce arepresented