Experimental studies of hexadecapole motion in spherical nuclei

Abstract

The 0+ to 41+ hexadecapole transitions in 60Ni and 140Ce have been investigated experimentally by means of alpha -particle scattering as well as by the spectroscopy of the electromagnetic decay of the 41+ states. In the case of 60Ni an upper limit of 1*10-7 was found for the branching of the E4 and E2 cascade decay of the 41+ state by conversion electron spectroscopy. It corresponds to an enhancement factor G4<9.0 spu, while the alpha -particle scattering measurements result in G4=(5.5+or-0.8) spu. In 140Ce the 41+ to 0+ cross-over gamma decay has been observed with an enhancement of G4=(11.8+or-0.7) spu, in very good agreement with the value G4=(13+or-2) spu from the alpha -particle scattering experiments. The evaluation of the alpha -particle scattering cross sections is based on a specific reaction model (folding model). The experimental results from the direct (41+ to 0+) decay are considered to be an empirical test of the model dependence of the procedure for extracting L=4 transition rates from alpha -particle scattering. By comparing similar results, the consistency of the methods applied together with the evidence for and some implications of hexadecapole motion in spherical nuclei are discussed briefly.