Lifetimes and electromagnetic decay properties of negative-parity states in Sm150,152,154 from (n,n'γ) measurements

The Doppler shifts of γ rays following the decay of the 11- and 31- states in Sm150,152,154 excited by inelastic scattering of 1.3 MeV neutrons from natural Sm2O3 have been measured. With the Winterbon theory to describe the slowing down process of the recoiling atoms in the bulk of the target material, nuclear lifetimes could be extracted from these data. These measured lifetimes are compared to the results of a recent investigation with the gamma-ray induced Doppler (GRID) broadening technique and have been used to clarify problems associated with the incomplete knowledge of the feeding pattern in heavy nuclei inherent in the GRID method. The large E1 transition rates in Sm152 obtained in the previous study are confirmed; the B(E1) systematics has been extended to Sm154 and is interpreted within the framework of the interacting boson model.