Realization of Low-Temperature Fixed Points of the ITS-90 at NMIJ/AIST |
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Authors: | T Nakano O Tamura H Sakurai |
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Affiliation: | (1) National Metrology Institute of Japan (NMIJ), AIST, Central 3 1-1-1, Umezono, Tsukuba, Ibaraki 305-8563, Japan |
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Abstract: | A new model of sealed cells with three thermometer wells for calibration of capsule-type thermometers at low-temperature fixed
points of the International Temperature Scale of 1990 has been developed at the National Metrology Institute of Japan (NMIJ).
The melting curves of Ar and O2 obtained using the new cells show very flat plateaux and a linear temperature dependence as a function of the inverse liquid
fraction (1/F) over the range 1/F = 1 to 1/F = 20 with a narrow melting curve width of 0.1 mK. The melting curves of Ne obtained with the new cell also show very flat
plateaux and approximately linear temperature dependence versus 1/F and a narrow melting curve width of 0.1 mK, though with a slight concave structure at high 1/F. The melting temperatures with the new cells agree with previous NMIJ sealed cells within 10 μK, which is similar to the reproducibility of the realization of the triple points at NMIJ. The source dependence of the triple-point
temperature of Ne was investigated by filling two of the new cells from different sources of Ne. The difference in the realized
triple point temperatures between the two sources is 0.031 mK, consistent with that estimated from isotope analysis. The uncertainties
in the calibration of standard platinum resistance thermometers at the low-temperature fixed points are summarized. The uncertainty
of the calibration at the triple point of e-H2 has been reduced to about one-third of its value without the correction by making the isotopic correction on the basis of
the technical annex for the ITS-90 in the mise en pratique for the definition of the kelvin. |
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Keywords: | Ar e-H2 ITS-90 Low-temperature fixed points Ne O2 Uncertainty |
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