Levels and transitions in142,144Ce populated following the βdecay of142,144La

Abstract

The levels populated in 142,144Ce and the gamma -ray transitions between these levels have been studied by the gamma gamma directional correlation method following the beta decay of 142,144La. The lanthanum activities were produced by the decay of the corresponding caesium fission products. These were selected by the on-line mass separator OSTIS and the measurements were made in an off-line position. Coincidences were recorded in the event-by-event mode by a pair of Ge(Li) detectors and the correlations were measured at six angles. The coincidence data were analysed for a selection of gates to produce extensive decay schemes and transition intensities were also determined. The correlation data provide firm spin assignments to most levels and yielded multipole mixing ratios for many transitions in each isotope. Parity assignments to levels were made on the basis of dominant multipolarities. The experimental results provide extensive data on these transitional nuclei.