Polarizability of Helium, Neon, and Argon: New Perspectives for Gas Metrology

With dielectric-constant gas thermometry, the molar polarizability of helium, neon, and argon has been determined with relative standard uncertainties of about 2 parts per million. A series of isotherms measured with the three noble gases and two different experimental setups led to this unprecedented level of uncertainty. These data are crucial for scientists in the field of gas metrology, working on pressure and temperature standards. Furthermore, with the new benchmark values for neon and argon, theoretical calculations, today about 3 orders of magnitude larger in uncertainty, can be checked and improved.

Figure 1

Upper part above the grey dotted line: Typical measuring data pairs of pressure $p$ and scaled relative capacitance change $\mu$ of high-pressure isotherms for He (black dots), Ne (red dots) and Ar (blue dots) measured with setup $\mathrm{DCGT}k$ [8]. The picture shows a tungsten carbide capacitor. Lower part below the grey dotted line: Typical measuring data pairs of $p$ and $\mu$ of low-pressure isotherms for Ne (red stars) and Ar (blue stars) obtained with setup DCGT2 [4]. The picture shows a copper-beryllium capacitor.

Figure 2

Three plots on the left: Black dots: Relative deviations $\mathrm{\Delta }{A}_{\epsilon }/A_{\epsilon }$ in ppm of the individual results obtained with capacitors TC1, TC2, TC3, C1, and C2, respectively, from the correlated weighted mean of them are shown for He, Ne, and Ar. Dashed red lines: Confidence intervals of the correlated weighted-mean values corresponding to the relative standard uncertainties. Three plots on the right: Relative deviations in ppm of different theoretical and experimental literature results (for more details see text) from the correlated weighted-mean values are shown.