Search for β+EC and ECEC processes in 112Sn and β−β− decay of 124Sn to the excited states of 124Te

Limits on β+EC and ECEC processes in 112Sn and on β−β− decay of 124Sn to the excited states of 124Te have been obtained using a 380 cm3 HPGe detector and an external source consisting of natural tin. A limit with 90% C.L. on the 112Sn half-life of 0.92×1020y for the ECEC(0ν) transition to the excited state in 112Cd (1871.0 keV) has been established. This transition is discussed in the context of a possible enhancement of the decay rate by several orders of magnitude given that the ECEC(0ν) process is nearly degenerate with an excited state in the daughter nuclide. Prospects for investigating such a process in future experiments are discussed. The β−β− decay limits for 124Sn to the excited states of 124Te were obtained on the level of (0.8–1.2) × 1021 y at the 90% C.L.