Shell-model calculations of two-neutrino double-β decay rates of 48Ca with the GXPF1A interaction

The two-neutrino double-beta decay matrix elements and half-lives of Ca-48 were calculated within a shell-model approach for transitions to the ground state and to the 2(+) first excited state of Ti-48. We use the full pf model space and the GXPF1A interaction, which was recently proposed to describe the spectroscopic properties of the nuclei in the nuclear mass region A=47-66. Our results are T-1/2(0(+)-> 0(+))=3.3x10(19) yr and T-1/2(0(+)-> 2(+))=8.5x10(23) yr. The result for the decay to the Ti-48 0(+) ground state is in good agreement with experiment. The half-life for the decay to the 2(+) state is two orders of magnitude larger than that obtained previously.