Experimental Investigation of Double-Beta Decay inSe82

A time projection chamber with a selenium double-beta decay source as the central electrode has yielded a lower limit of 1.0 × ${10}^{20}$ yr at 68% confidence level for the two-neutrino half-life of ${}_{}{}^{82}{}_{}{}^{}\mathrm{Se}$. This limit is consistent with the results of geochemical measurements, and disagrees with the shorter half-life predictions of nuclear theory. For the neutrinoless mode we find a corresponding lower limit of 7 × ${10}^{21}$ yr, also at 68% confidence level.