Lifetimes in Sn 120, Ba 138 and Ce 140

Abstract

As a sequel to an earlier measurement 1) of an unusually long E2 lifetitime in Ce 140, the mean lives of two states in Sn 120 and Ba 138 have been measured by time-to-pulse-height conversion. The value found for the 2.3 MeV level in Sn 120 is 8.24±0.23 nsec which is in good agreement with two other recent measurements 6,7). For the 1.89 MeV level in Ba 138 the figure obtained is 3.13±0.11 nsec, 8 times longer than the single-particle estimate. The slowness of the transitions in Ce 140 and Ba 138 is accounted for by treating them as quasi-particle transitions and using data from the work of Kisslinger and Sorensen 2) on the theory of pairing correlations. A simple view of these quasi-particle transitions is given in an appendix.