Limit on the anti nu/sub e/ mass in free molecular tritium beta decay

The question of a nonzero neutrino mass has received considerable attention since the claims of Lyubimov et al in 1980 were published which showed evidence for an electron antineutrino mass between 14 and 46 eV, with a best fit value of 35 eV. However, there are still considerable concerns about possible systematic problems in thier experiment. Many of these concerns revolve around the use of a tritiated valine source, in which the energy given up in final state excitations of the molecule following the veta decay of one of the tritium atoms is comparable to the size of the neutrino mass observed. The effect of these final state effects is difficult to calculate in a molecule as complex as valine. In addition, ionization energy loss and backscattering of the betas in traversing the solid source are appreciable and must be very accurately accounted for. These concerns have led us to carry out an experiment using free molecular tritium as the source material. The final state effects have been accurately calculated for the tritium molecule and the uncertainties in these calculations cannot generate a spurious neutrino mass greater than 1 eV. in addition, the energy loss in the source is small because the source consists of tritium only and there is no backscattering