Double-β transformations in isobaric triplets with mass numbers A = 124, 130, and 136

The Q values of double-electron capture in 124 Xe, 130 Ba, and 136 Ce and double-beta decay of 124 Sn and 130 Te have been determined with the Penning-trap mass spectrometer SHIPTRAP with a few hundred eV uncertainty. These nuclides are members of three isobaric triplets with common daughter nuclides. The main goal of this work was to investigate the existence of the resonant enhancement of the neutrinoless double-electron-capture rates in 124 Xe and 130 Ba in order to assess their suitability for the search for neutrinoless double-electron capture. Based on our results, in neither of these cases is the resonance condition fulfilled.