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We examine the feasibility of using evaporative techniques for isotopic purification of bulk liquid 4He in the ultra‐pure (sub ppb 3He concentration) limit. At temperatures of order several‐tenths of a degree Kelvin the 3He‐impurity diffusion coefficient and equilibrium vapour density are simultaneously large enough that one should be able to extract impurities simply by pumping on a free liquid surface. At somewhat lower temperatures the equilibrium distribution of impurities is dramatically modified by surface (Andreev) states, providing an alternate mechanism for purifying the bulk liquid.

As part of an on‐going program utilizing magnetically trapped ultracold neutrons (UCNs), we are developing a technique that offers the possibility of improving the precision of the neutron lifetime by more than an order of magnitude. The experiment works by loading an Ioffe‐type superconducting magnetic trap with UCNs through inelastic scattering of 0.89 nm neutrons with phonons in superfluid 4He. Trapped neutrons are detected when they decay; charged decay electrons ionize helium atoms in the superfluid resulting in scintillation light that is recorded in real time using photomultiplier tubes. At present, we are installing a larger and deeper superconducting magnetic trap into our apparatus, implementing techniques to reduce background events, and working to increase the neutron decay detection efficiency. We report the status of the construction of the improved apparatus.