We have made high statistics measurements of tritium beta decay to set a limit on the mass of the electron antineutrino.The measurements used a windowless gaseous source of molecular tritium and a high resolution toroidal field magnetic spectrometer. We calibrate the system using conversion electrons from the decay of Kr. The best fit value for the neutrino mass squared is significantlynegative. An anomalous structure in the beta decay spectrum in the last 55 eV closest to the end point causes this result.A direct measurement of neutrino mass can be made by studying the beta decay of tritium as a massive electron antineutrino will alter the shape of this lowenergy beta decay spectrum. In 1980 Lubimov and coworkers [1] reported evidence for a 30-eV neutrino mass in their studies of the beta decay of tritium implanted in valine. Subsequent attempts by groups in Tokyo [2] and Zurich [3], who implanted tritium in thin films, found no evidence for this mass. These groups were able to

Excited states in 208 Pb have been studied by measuring ␥ rays in time coincidence with reaction charged particles. 208 Pb states were produced with both the 207 Pb(d, p) 208 Pb and 209 Bi(t,␣) 208 Pb reactions. The energy resolution of the particle spectra of 100 keV allowed a rough determination of level excitation, which then was determined with high resolution from the coincident ␥ decay measured in Ge detectors. Many new ␥ transitions have been found and previously unresolved multiplets of states resolved. The data give spectroscopic factors for neutron transfer and proton pickup. Spins and parities of levels could be deduced from their ␥ decays. A least squares fit of all ␥ energies gave very precise ͑0.1 keV͒ level energies. All states predicted by the shell model below 4.6 MeV are now found and their spins determined unambiguously. ͓S0556-2813͑97͒03009-4͔PACS number͑s͒: 21.60. Cs, 23.20.Lv, 25.45.Hi, 27.80.ϩw II. THE 209 Bi"t,␣␥… 208 Pb EXPERIMENT A. Design of the experiment and proceduresThe 209 Bi(t,␣␥) 208 Pb reaction was used to excite levels in 208 Pb. Due to the huge positive energy balance of this

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