Studies of collective states in <super>160</super>Dy and <super> 188</super>Os nuclei

Abstract

Gamma rays following the decay of 160Tb and 188W were detected in both singles and coincidence in order to establish the energy level scheme of the two medium mass nuclei 160Dy and 1880s.

Two large volume Ge(Li) detectors together with a plastic scintillation counter were incorporated in a Dual Parameter Energy-Time Spectrometer to measure the gamma-gamma coincidence spectra: the half-life of the first excited state of 160Dy was measured. An intrinsic Germanium detector was used to measure low energy transitions. New levels and transitions are proposed, relative intensities, log ft values, multipolarities, spins/parities and transition probabilities are deduced.

The nuclear properties of 160Dy and 188Os are analysed in terms of current nuclear models. The deviations from the predictions of the symmetric rotor model for the states in 160Dy are explained in terms of band-mixing. The Coriolis coupling is applied to the negative states which gives good account to the electric dipole transition probabilities. The possible effect of the recently discovered sub-shell closure at Z = 64 is investigated for 160Dy, a nucleus with proton number (Z=66) exactly midway between the closures at 50 and 82, and the number of neutrons (N=94) above the limit of 90. Energy levels, B(E2) absolute values and ratios are compared with IBM-1 calculations assuming either a single Z = 50-82 shell or a subshell closure at Z = 64. The latter calculation improves agreement with experiment. The O(6) limit description is applied to the 188Os nucleus. Particular attention is made to the 0+ states and M1 transitions, the presence of which form the basic test for an 0(6) type nucleus. The calculations in the context of IBM-1 were undertaken with the aid of the computer codes PHINT and FBEM.