The energy of a gamma transition in the decay of ${}_{}{}^{83}{}_{}{}^{}\mathrm{Kr}_{}^{\mathrm{m}}{}_{}{}^{}$ has been determined to be 32 147.3(16) eV in a comparison with transitions in ${}_{}{}^{241}{}_{}{}^{}\mathrm{Am}$ decay. This value, substantially more precise than previous ones, leads to a corresponding improvement in precision in the atomic mass difference between ${}_{}{}^3{}_{}{}^{}\mathrm{H}$ and ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ as determined from an experiment on the beta decay of free molecular tritium. The mass difference, 18 589.0(26) eV, is in agreement with some independent determinations but disagrees with others, most notably with some recent ion-cyclotron-resonance data. The latter disagreement calls into question the 17-eV lower limit on the mass of the electron antineutrino claimed by Boris et al.

• Received 19 September 1988

DOI:https://doi.org/10.1103/PhysRevC.39.1503