Nuclear structure calculation of β+β+, β+/EC and EC/EC decay matrix elements

Abstract

Nuclear matrix elements for double positron emisson (β+β+), positron emission/electron capture (β+/ EC) and double electron capture (EC/EC) in the 2 νββ decay mode and for β+β+ and β+/EC decay in the 0 νββ mode are calculated for the experimentally most promising isotopes58Ni,78Kr,96Ru,106Cd,124Xe,130Ba and136Ce within pn-QRPA. We point out that the matrix element for the 2 νβ+/EC decay differs from the 2 νβ+β+ matrix element, an effect not considered previously. For the neutrino accompanied decays our calculation predicts for the β+/EC and the EC/EC mode half lives which are shorter typically by 4-7 orders of magnitude than those for the double positron emission. However, even for the best candidates typical values for 2 νβ+/EC (2 ν EC/EC) are still in the range of ∼1022 ((some) 1021) years. For 0 νββ decay we have calculated all matrix elements relevant for both, the mass mechanism and the right-handed currents for the first time complete. A detailed discussion of the differences between the 0 νβ+β+, the 0 νβ+/EC and 0 νβ-β- decay is given. © 1994 Springer-Verlag.