Two neutrino double-β decay in deformed nuclei with an angular momentum projected basis -: art. no. 064321

Four nuclei which are proved to be 2nubetabeta emitters ( Ge-76, Se-82, Nd-150, U-238), and four suspected, due to the corresponding Q-values, to have this property ( Nd-148, Sm-154, Gd-160, Th-232), were treated within a proton-neutron quasiparticle random phase approximation (pnQRPA) 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 (ph) and particle-particle (pp) channels. The effect of nuclear deformation on the single beta strength distribution as well as on the double beta Gamow-Teller transition amplitude (M-GT) 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 T-1/2. The case of different deformations for mother and daughter nuclei is also presented.