Constant-Volume Gas Thermometry Between 4 K and 100 K

Abstract

Gas-thermometer measurements between 4 K and 100 K have been performed at the Kamerlingh Onnes Laboratory as part of the preparatory work in several institutes for a future, revised, International Practical Temperature Scale. Gas-thermometer temperatures are compared, between 13.8 K and 100 K, with platinum resistance thermometers calibrated on IPTS-68 and, between 4.2 K and 27.1 K, with rhodium-iron resistance thermometers calibrated on the National Physical Laboratory (Teddington) Scale of 1975 (NPL-75).Results of the measurements, with NPL-75 at 20.3 K as a reference temperature for the gas thermometer, show agreement with NPL-75 within 0.3 mK over most of the range. Differences from NPL-75 of 0.6 mK were found in the range 10 K to 14 K and around 27 K.Below 50 K, IPTS-68 is shown to be 4 mK to 10 mK higher than thermodynamic temperatures. Between 70 K and 100 K, IPTS-68 is 9 mK lower than thermodynamic temperatures.

Present Estimates of the Differences Between Thermodynamic Temperatures and the ITS-90

“…Two other CVGT experiments in the range (Steur [5], up to 100 K and Kemp [4], up to 287 K), together with the original Astrov [30] CVGT and Quinn and Martin's [24] total radiation thermometry, constituted the main ingredients for the construction of the ITS-90. The principal problem in this temperature range is the disagreement between the gas thermometry work of Astrov and of Kemp, see Fig.…”

“…Therefore, WG4 remains concerned about the effect of the interface between the copper and gold. However, the data sets of NML and KOL [4,5] cannot be excluded from consideration, because no published data are available on the effect of gold-plating on thermal expansion.…”

“…It was agreed to exclude the Quinn and Martin [24] total radiation measurements and the gas thermometry measurements of Guildner and Edsinger [6] from the averaging procedure as explained above, while those of Edsinger and Schooley [7] are retained. The gas thermometry results of Kemp, Steur, and Astrov [4,5,8] are retained for the averaging, but with recalculated uncertainties. The relative radiation thermometry of Fischer and Jung [16] at the Al, Ag, and Au points and of various other sources at the Cu point [23] are included to benefit from their low uncertainties.…”

Review of temperature measurement

“…Examples of the utilization of constant volume gas thermometry are reported by Guildner and Edsinger, 7 by Berry, 9 Kemp et al 10 and in Refs. [13][14][15][16]. It is used to define the ITS-90 between 3 and 24.5561 K. 1 Corrections to account for the behavior of the measuring apparatus include ͑1͒ the dead space in connection tubes; 9 ͑2͒ thermal expansion of the gas bulb; 17,18 ͑3͒ the difference in density of the gas at different levels in the pressure sensing tubes; 9,17 ͑4͒ a thermomolecular pressure correction to account for temperature differences along the pressure sensing tube; 9,19,20 ͑5͒ the absorption of impurities in the gas.…”

The Dutch National Realization of the ITS-90 over the Range 13.8033 K–273.16 K

“…For the case of the hydrogen fixed-point cell, the average value is then corrected for the isotopic composition of the sample. Thermometer 226246, the same used in CCT-K1 [8], carries the NMi VSL gas thermometer scale [9]. Thermometer 229080 carries the NPL-75 gas thermometer scale.…”