Quasi-SU(3) truncation scheme for odd–even and odd–odd sd-shell nuclei Original Research Article

The quasi-SU(3) symmetry, as found in shell-model calculations, refers to the dominance of the single-particle plus quadrupole–quadrupole terms in the Hamiltonian used to describe well-deformed nuclei, and to the subspace relevant in its diagonalization. It provides a very efficient basis truncation scheme. It is shown that a small number of SU(3) coupled irreps, those with the largest C2 values within the direct product of the proton and neutron SU(3) irreps with spin 0 and 1 (for even number of particles), and spin 1/2 and 3/2 for (for odd number of nucleons), are enough to describe the low-energy spectra, B(E2) transition strengths and band structure of 21Ne, 23Na and 25Mg odd-mass and 22Na, 24Na, 26Al and 28Al odd–odd nuclei. A simple but realistic Hamiltonian is employed. Results compare favorably both with experimental data and with full shell-model calculations. Limitations and possible improvements of the schematic Hamiltonian are discussed.