A determination of the molar gas constant R by acoustic thermometry in helium

We have determined the acoustic and microwave frequencies of a misaligned spherical resonator maintained near the temperature of the triple point of water and filled with helium with carefully characterized molar mass M = (4.002 6032 ± 0.000 0015) g mol-1, with a relative standard uncertainty ur(M) = 0.37×10-6. From these data and traceable thermometry we estimate the speed of sound in our sample of helium at TTPW = 273.16 K and zero pressure to be u0 2 = (945 710.45 ± 0.85) m2 s-2 and correspondingly deduce the value R = (8.314 4743 ± 0.000 0088) J mol-1 K-1 for the molar gas constant. We estimate the value k = R/NA = (1.380 6508 ± 0.000 0015) × 10-23 J K-1 for the Boltzmann constant using the currently accepted value of the Avogadro constant NA. These estimates of R and k, with a relative standard uncertainty of 1.06 × 10-6, are 1.47 parts in 106 above the values recommended by CODATA in 2010

Further confirmation of the value 22T(90)-20T(90) at INRIM

Values are given for the difference 22T-20T of a new sample with a dedicated isotopic and chemical assay. The new value changes the overall average by only 3 microK

Production of a new Tin Cell at INRIM

Over the years some of the INRIM metal fixed-point cells, ≥20 years old, have shown a variable deterioration consisting in the leaking of some of the metal through the walls of the crucible. The variation in the deterioration is assumed to be connected with the frequency with which the cells have been used. New cells are therefore being produced at INRiM as substitutes for the older cells. A description of the new cells and their preparation is given, along with a preliminary comparison between the new cell and the older cell(s)

Reanalysis of Possible effects due to Gold-plating on the Thermal Expansion of Copper on Constant-volume Gas Thermometry at Low Temperatures

Constant-volume gas thermometry below the triple point of water (TPW) with reference to TPW gives temperature values higher than the correct ones when the thermal expansion coefficient of the bulb assumed in the calculation is smaller than the real one. Therefore, in order to attribute this temperature difference to a change in the thermal expansion coefficient of copper due to gold-plating, it is necessary that gold-plating increases the thermal expansion coefficient of copper even though that of gold is smaller than that of copper

Preliminary Measurements of the Xenon Triple Point

Ever since the construction and definition of the highly successful International Temperature Scale of 1990 (ITS-90), one severe deficiency of the scale has been recognized, without a reliable remedy. The problem is the fact that the only then available high-quality fixed point between the argon triple point and the water triple point was the mercury triple point, which unfortunately is situated rather closely to the water triple point, thus having an extremely strong influence on the interpolation function of SPRTs in the Ar−H2O range. Already before 1990, measurements on possible fixed points better placed in this temperature range have been investigated, such as the triple points of krypton and xenon. However, results have been rather elusive, mainly regarding the rather large melting range of their transition. A turning point was the 2005 paper from the National Research Council (NRC, Canada), where it was established that the relatively high content of krypton was the culprit for the large melting range of the xenon transitions published previously. Indeed, measurements on a xenon sample with very low krypton content produced a very high-quality plateau, of the same level as other ITS-90 fixed points. However, no follow-up measurements have been reported, and thus neither have comparison measurements been reported. Shortly, after the appearance of the NRC paper, Istituto Nazionale di Ricerca Metrologica (INRIM, Italy) acquired a batch of the same high-purity xenon as used by NRC with the aim of preparing a few sealed cells with it and trying to reproduce the NRC results. However, with the start of the Neon Project (Euromet Project 770), the realization of these intentions had to be postponed until now. Last December, three cells of different design have been filled with this high-quality xenon and preliminary results of the measurements on the triple point are reported

Some Curious Results with a Gallium Fixed Point Cell

In 2009, most of the gallium fixed-point cells in use in different INRIM laboratories were compared with Italy’s national standard. The comparison has uncovered problems with one of the commercial devices, realizing a temperature about 0.7mK too low which initially was even changing linearly with time. An additional series of measurements was undertaken to find out the reason for this behavior, but not being allowed to open the cell, only a suspicion on the possible cause has remained. A way is suggested that might give users an indication of such misbehavior of their cell. The results underline the importance for those NMIs with only a single cell, for any fixed point, to undertake regular comparisons with another cell as a check on its behavior