Unified description of the 2νββ decay in spherical and deformed nuclei

The Gamow-Teller double-beta decay, with two neutrinos in the final state, is calculated within the QRPA approach. Higher-order corrections to the RPA result are studied within a boson expansion formalism. The specific feature of the present paper is that the single-particle basis is obtained through angular-momentum projection from an orthogonal set of deformed wave functions. The effect of deformation on the Gamow-Teller transition amplitude, as well as on the single β- and β+ strengths distribution is obtained. The Gamow-Teller amplitude is calculated for the transitions 0+i → 0+f and 0+i → 2+f. The method is applied to the 2νββ decay probability 8234Se to 8236Kr. (orig.)