Nuclear structure and double beta decay: Two neutrino mode

The decay rate of the 2ν double beta decay is calculated. The effects of pairing, static quadrupole deformation, spin-isospin polarization, and the ${\Delta }_{33}$ isobar admixtures on the nuclear matrix elements are studied and the relation of the 2ν ββ rate and the ${\beta }^{\mathrm{-}}$ and ${\beta }^{+}$ strength is stressed. In agreement with other calculations, we predict a faster decay rate than has been observed experimentally in ${}_{}{}^{82}{}_{}{}^{}\mathrm{Se}$, ${}_{}{}^{130}{}_{}{}^{}\mathrm{Te}$, and ${}_{}{}^{150}{}_{}{}^{}\mathrm{Nd}$.