Effects of orbital occupancies and spin-orbit partners on 0vββ-decay rates

Neutrinoless double beta (0 nu beta beta) decay of the Ge-76, Se-82, Te-128, Te-130 and Xe-136 nuclei is discussed in terms of the associated nuclear matrix element (NME). The effects of the size of the single-particle model space and the occupancies of individual orbits on the NME are discussed by using the proton-neutron quasiparticle random-phase approximation (pnQRPA) with effective, G-matrix-derived nuclear forces. It is found that only in some cases the orbital occupancies play a decisive role for the size of the NME, whereas the inclusion of all the spin-orbit partners is essential to achieve a NME of reasonable quality. The obtained results are compared with published results of other models. (C) 2010 Elsevier B.V. All rights reserved.