In-Beam -Spectroscopy of Low-Spin Mixed-Symmetry States of 138Ce with Gammasphere in Singles-Mode

摘要

Gamma-rays from the nuclide 138Ce have been measured with the Gammasphere-array following Coulomb excitation. Beams of 138Ce ions were focussed on a carbon target at beam energies of 480 and 400 MeV. Gamma-ray yields and relative Coulomb excitation cross sections were measured in singles-mode. M1, E2, and E3 transition matrix elements from low-spin states were measured relative to the known B(E2; 0 2). The 2+ 2 M1 strength distribution from the lowest six 2+ states up to 2.7 MeV enables us to identify the 2 state of 138Ce as the dominant fragment of the one-phonon 2 mixed-symmetry state with F-spin quantum number Fmax – 1. From its mixing with the nearby 2 state an F-spin mixing matrix element of 44 keV can be estimated.