The triple-point temperature of neon, T tp−Ne , is known to have dependence on the isotopic composition. Recently, the Technical Annex for the International Temperature Scale of 1990 was updated to specify the method of correction for the isotopic reference ratio of neon. In this study, to confirm this correction in the Technical Annex independently, the effects of the isotopic composition of neon on T tp−Ne for three commercial neon gas sources were studied. For the measurement of the isotopic composition, a gas mass spectrometer was used to compare the sample gases with a reference neon gas whose isotopic composition was known with high precision by a gravimetric method. For the measurement of T tp−Ne , an open-cell type cryostat for the realization of low-temperature fixed points was used. The physical cell and the thermal environment around it remained very similar for all T tp−Ne measurements with the neon gases due to the nature of the open-cell type system. Therefore, the difference in T tp−Ne among different samples could be measured with a relatively low uncertainty, canceling many systematic effects that are common to all measurements. Our result was consistent with the correction in the Technical Annex. Furthermore, because one of the commercial neon gases was the bottle that was used for KRISS measurements in the international comparison CCT-K2, it is now possible to correct the measurement for the reference isotopic ratio and compare it with other measurements for which isotopic composition data are available.

Thin-film platinum resistance thermometers (PRTs) are generally manufactured using the deposition of a thin platinum film on an alumina substrate and a laser-trimming method. Because of the strong adhesion between the platinum thin film and the alumina substrate, the PRTs inevitably have strain over the operating temperature range. This causes anomalies and instabilities in the resistance versus temperature characteristics (R-T ). The most prominent and observable effect of thermally induced strain is the thermal hysteresis in the R-T characteristics. Thermal hysteresis is one of the main uncertainty factors in the calibration of industrial platinum resistance thermometers in laboratories. The thermal hysteresis for 30 thin-film PRTs was measured in the range of 0 • C to 500 • C in 100 • C steps. The thermal hysteresis was measured repeatedly using the same process, and the hysteresis decreased drastically with the repeated measurements. The thermal hysteresis was distributed from 16 mK to 156 mK for all sensors, and the lowest hysteresis was 1 mK to 11 mK in the test temperature range.

As another crucible material for metal-carbon eutectic points, alumina ceramic was used in the first trial to make an Fe-C eutectic point for the calibration of a thermocouple. Its melting and freezing behavior was tested 26 times with a type S thermocouple at various melting offset temperatures, namely, +4 • C, +9 • C, and +19 • C, and at a fixed freezing offset temperature of −11 • C. The melting emf is reproducible independent of the melting offset temperatures, and the standard deviation of the 26 melting temperatures is 0.02 • C without breakage of the cell. The difference of melting emf between alumina Fe-C and graphite Fe-C fixed points is only 25 mK within an uncertainty of 0.39 • C (k = 2). The melting behaviors of an alumina cell are quite similar to a common graphite cell. Thus, alumina can be used as a crucible material in an Fe-C eutectic system without breakage, and it can be used at a higher temperature range. As possible application systems using alumina crucibles, Pd-C and Si-SiC eutectic points are suggested.

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A cryostat for fixed-point calibration of capsule-type SPRTs (standard platinum resistance thermometers) was developed. Using this system, cryogenic fixed points defined on the International Temperature Scale of 1990 (ITS-90) were realized. The cryogenic cells were argon, oxygen, neon, and two equilibrium-hydrogen (e-H 2 ) cells, made by INRiM, Italy. The uncertainty of the realization of each fixed point was estimated to range from 0.53 mK to 0.43 mK (k = 2). The realizations of the triple point of e-H2 using two sealed cells coincided within 0.1 mK. Therefore, we are able to calibrate capsule-type SPRTs down to 24.5561 K within an uncertainty of 1 mK (k = 2) by this system. A closed-cycle helium gas refrigerator was used for the cryostat. Each sealed cell was designed so that it could accommodate three sealed cells in the thermometer wells made within the cell. Therefore, the cryostat was designed to accommodate only one sealed cell at a time. The base temperature of this liquid-free cryostat, when one sealed cell and three capsule-type SPRTs were attached for calibration, was ∼17 K. For the realization of the triple point of e-H 2 , we used liquid helium for additional cooling. Adiabatic melting of the triple point was realized by controlling the inner-most radiation shield at a temperature very close to that of the triple point, and by applying a heat pulse by a heater directly wound to the cell. The amount of the heater power and the waiting time for the thermal equilibrium after each heat pulse were chosen in a way that the adiabatic melting could be finished within ∼6 h for each cell. The triple point of each cryogenic fixed point was deduced from the equilibrium temperatures between the heat pulses and subsequent extrapolation to the liquidus point. For the oxygen cell, temperatures of two solid-solid transitions (α-β and β-γ transitions) were also measured, and the results were consistent with values reported in the literature within the designated uncertainty.