Sealed (sup 4)He superfluid-transition fixed-point device

摘要

The superfluid transition in pure (sup 4)He under its saturated vapor pressure provides an ideal fixed-point reference for thermometry near 2 K. In practice, the transition may be located to within a few nanokelvin, and it is virtually immune to drift. Here we first review the properties of (sup 4)He very near the transition which may affect the performance of this fixed-point reference. Then we report on the construction and use of a sealed fixed-point device that requires no external capillaries or valves. It is as easily used in a vacuum cryostat as are superconductive fixed-point devices. Unlike superconductors, it is virtually unaffected by magnetic fields and material purity.