Realization of the ~3He Vapour-Pressure Temperature Scale at NMIJ/AIST

摘要

An apparatus for realizing the ~3He vapour-pressure temperature scale has been constructed at NMIJ/AIST. The apparatus is designed to be operated for a long time by adopting a continuously operating ~3He cryostat. The cryostat has an experimental access port, which is a top-loading type. The diameter of the access port is 50 mm. An insert for ~3He vapour-pressure measurements is placed in the access port. The preliminary measurement results confirm that the cryostat system stabilizes the temperature of a ~3He vapour-pressure cell to better than 50 μK over several hours over the temperatures range of the ~3He vapour-pressure scale. The ~3He vapour pressure is measured with a diaphragm differential pressure gauge, which has a silicon-resonant sensor. The uncertainties of this system are estimated in the case of calibrating a rhodium-iron resistance thermometer measured by an automatic DC bridge.