CONTRIBUTIONS OF UNIQUE FIRST-FORBIDDEN TRANSITIONS TO 2-NEUTRINO DOUBLE-BETA-DECAY HALF-LIVES

The two-neutrino double-beta-decay transition of Ge-76 to the ground s tate of Se-76 is calculated using a realistic proton-neutron force and including unique first-forbidden single-beta-decay transitions to vir tual 2(-) intermediate states. The corresponding nuclear matrix elemen ts are computed by using the proton-neutron quasiparticle random-phase approximation (pn-QRPA). From the results of the present study it is concluded that the inclusion of virtual unique first-forbidden transit ions, as possible ''new'' steps contributing to the half-life of the t wo-neutrino double-beta-decay mode, can be disregarded.