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

The two-neutrino double-β decay matrix elements and half-lives of ⁴⁸Ca were calculated within a shell-model approach for transitions to the ground state and to the 2⁺ first excited state of ⁴⁸Ti. 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⁺)=3.3×10¹⁹ yr and T_1/2(0⁺→2⁺)=8.5×10²³ yr. The result for the decay to the ⁴⁸Ti 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.