Qvalue for the double-βdecay ofXe136

The high-resolution, deflection-type mass spectrometer, Manitoba II, has been used to determine directly the mass difference $^{136}\mathrm{Xe}\ensuremath{-}^{136}\mathrm{Ba}$ to be 2639.6 (0.6) $\ensuremath{\mu}$u, giving ${\mathrm{Q}}_{\ensuremath{\beta}\ensuremath{\beta}}$ $=2458.7$ (0.6) keV.