A Determination of the Thermodynamic Temperature of the Triple Point of Neon

A constant-volume gas thermometer has been used to measure the thermodynamic temperature, and also the second virial coefficient of helium 4, at the triple point of neon (24.5 K). This was carried out by measuring a relative isotherm at 24.5 K referenced to the temperature of the boiling point of hydrogen on the NPL75 temperature scale. The thermodynamic temperature values measured for the triple points of natural neon and neon 20 were (24.557 0 ± 0.001 1 ) K and (24.539 4 ± 0.001 1 ) K respectively. The result for natural neon agrees well with the corresponding temperature value of (24.556 5 ± 0.001 1 ) K inferred from NPL75 and may be related to other laboratory realizations of the neon triple point through the recent international intercomparison of sealed triple-point cells.