Double-beta decay to excited 0+ states: Decay of 100Mo

We develop a formalism for describing the 2ν mode of double-beta decay to an excited final state in the quasiparticle random phase approximation (QRPA). With this, we deduce the half-lives for the 100Mo double-beta decays to both the ground and 1130 keV excited 0+ states in 100Ru. We predict the matrix elements of these two transitions to be of a similar magnitude. We also calculate the strengths of the associated single-beta decays from the ground state of the intermediate nucleus, 100Tc, and compare them with experiment. We find that the QRPA cannot simultaneously reproduce all of the experimental quantities, and, in particular, the single-beta transition between the initial and intermediate nuclei is overestimated by the theory. In addition, we demonstrate that the influence of the particle-particle force is an important factor in the calculation of both β- and β+ transition strengths.