Precise determination of the 136Xe – 136Ba atomic mass difference and related mass differences in Ba and Cd

Abstract

In light of present (EXO) and future (BOREXINO & XMASS) projects searching for evidence of the, as yet, unobserved double-beta decay of 136Xe, an atomic mass difference of 136Xe – 136Ba was determined using the high-precision Manitoba II mass spectrometer at the University of Manitoba. The Q-value for this difference was determined to be 2458.72(56) keV. The double-beta decay mode can be either neutrino (ββ2υ) or neutrinoless (ββ0υ), where the latter would be proof of the Majorana nature of neutrinos. A ββ0υ decay, which violates several principles of the Standard Model of particle physics, would emit only electrons and would provide a defined peak at the Q-value for the decay. This decay would also require the Majorana neutrino to have a non-zero rest mass and be its own antiparticle. Results of mass measurements on mass doublets of 135Ba, 136Ba, 137Ba, and 138Ba will be given. An improved measurement of the 116Cd35Cl - 114Cd37Cl doublet, previously done by Meredith et al. in 1973, will also be given.