Shell model description of normal parity bands in heavy deformed nuclei.

摘要

The low-energy spectra and electromagnetic transition strengths in 160,162,164Dy, 156,158,160Gd, and 168Er are described in the framework of the pseudo-SU(3) model. The Hamiltonian includes spherical single-particle energies, the Quadrupole-quadrupole interaction, and proton and neutron pairing terms with the strengths of these interaction fixed from systematics. The strengths of an additional four rotor-like terms that are included in the Hamiltonian, which do not mix SU(3) representations and induce only small changes in the spectra, were allowed to vary and a consistent set of these parameters was found. Proton and neutron degrees of freedom are considered explicitly by building the basis states as linear combinations of SU(3) states that are the direct product of SU(3) proton and neutron states with pseudo spin zero.;The results show that the proton and neutron single particle energies introduce strong mixing of the SU(3) representations, but nevertheless the dominance of the quadrupole-quadrupole two-body interaction ensures that the SU(3) band-structure is maintained. By and large, the excitation energy of the excited 0+ states is determined by the strength of the single-particle, quadrupole-quadrupole, pairing and C3 interactions. The interaction strength of the J2 term in the Hamiltonian is responsible for fine tuning of the effective moments of inertia. The KJ interaction fixes the K-bands relative to the ground-state.;The theoretical normal parity states of the low-energy spectra---states in the ground state, first excited K = 2, and K = 0 bands---were all found to lie very close to their experimental counterparts. The results analyzed extend beyond quantities used in the fitting procedure, including intra- and inter-band B(E2) strengths, the M1 strength distribution of the ground state, and band head energies of the first Kpi = 1 + and Kpi = 4+ bands. In all cases the summed strength of the M1 distribution is in good agreement with the experimental numbers. The results also show that by adding one- and two-body pairing interactions to the Hamiltonian the experimentally observed fragmentation of the M1 strength can be reproduced.