ON MEASURING THE NEUTRON BETA-DECAY LIFETIME USING ULTRACOLD NEUTRONS PRODUCED AND STORED IN A SUPERFLUID-HE-4-FILLED MAGNETIC TRAP

We propose an experimental technique to measure the neutron beta-decay lifetime using ultracold neutrons (UCN) produced and stored in a superfluid-He-4-filled magnetic trap. UCN will be produced by inelastic scattering of cold (8.9 angstrom) neutrons in the He-4. The neutron beta-decay should result in scintillation that can be detected with high efficiency. This direct measure of the UCN number vs. time can be used to determine the beta lifetime. Systematic effects which include leakage of marginally trapped UCN, absorption by impurities (particularly He-3), and inelastic upscattering, are expected to be at the 0.001% level. The expected accuracy based on counting statistics obtainable using existing cold neutron beams is at the 0.004% level.