Quasi-SU(3) truncation scheme for even-even sd-shell nuclei

The quasi-SU(3) symmetry was uncovered in full pf and sdg shell-model calcu lations for both even-even and odd-even nuclei. It manifests itself through a dominance of single-particle and quadrupole-quadrupole terms in a Hamilt onian used to describe well-deformed nuclei. A practical consequence of the quasi-SU(3) symmetry is an efficient basis truncation scheme. In [C.E. Var gas et al., Phys. Rev. C 58 (1998) 1488] it is shown that when this type of Hamiltonian is diagonalized in an SU(3) basis, only a few irreducible repr esentations (irreps) of SU(3) are needed to describe the yrast band, the le ading S = 0 irrep augmented with the leading S = 1 irreps in the proton and neutron subspaces. In the present article the quasi-SU(3) truncation schem e is used, in conjunction with a "realistic but schematic" Hamiltonian that includes the most important multipole terms, to describe the energy spectr a and B(E2) transition strengths of Ne-20,Ne-22, Mg-24 and Si-28. The effec t of the size of the Hilbert space on both sets of observables is discussed , as well as the structure of the yrast band and the importance of the vari ous terms in the Hamiltonian. The limitations of the model are explicitly d iscussed. (C) 2001 Elsevier Science B.V. All rights reserved.