Two neutrino double- β decay in deformed nuclei with an angular momentum projected basis

Four nuclei which are proved to be 2nbb emitters ( 76 Ge, 82 Se, 150 Nd, 238 U), and four suspected, due to the corresponding Q-values, to have this property ( 148 Nd, 154 Sm, 160 Gd, 232 Th), were treated within a protonneutron quasiparticle random phase approximation spnQRPAd with a projected spherical single particle basis. The advantage of the present procedure over the ones using a deformed Woods-Saxon or Nilsson single particle basis is that the actual pnQRPA states have a definite angular momentum while all the others provide states having only K as a good quantum number. The model Hamiltonian involves a mean field term yielding the projected single particle states, a pairing interaction for alike nucleons and a dipole-dipole proton-neutron interaction in both the particle-hole sphd and particle-particle sppd channels. The effect of nuclear deformation on the single beta strength distribution as well as on the double beta Gamow-Teller transition amplitude sMGTd is analyzed. The results are compared with the existent data and with the results from a different approach, in terms of the process half-life T1/2. The case of different deformations for mother and daughter nuclei is also presented.