We have measured the refractive index of helium using a quasi-spherical copper microwave resonator at five different temperatures in the interval between the triple point of hydrogen at 13.8K and the triple point of xenon at 161.4K for pressures up to 380 kPa. From these results and additional measurements of the refractive index of neon near 54.4K, 83.8K and 161.4K we determine the differences (T − T ₉₀) between the thermodynamic temperature T and its approximation T ₉₀ by the International Temperature Scale of 1990 (ITS-90). We have estimated the isothermal compressibility of copper and the effective compressibility of our microwave resonator by different methods including resonant ultrasound spectroscopy (RUS) and microwave measurements with helium at 273.16K. We compare the results of these compressibility estimates and discuss the associated uncertainty. From the refractive index measurements, we estimate the second density virial coefficient of helium and neon which are found in good agreement with the ab initio calculations of the same properties.

我们使用准球形铜微波谐振器在 13.8K 的氢三相点和 161.4K 的氙三相点之间的五个不同温度下测量了氦的折射率，压力高达 380 kPa。根据这些结果和对 54.4K、83.8K 和 161.4K 附近氖的折射率的额外测量，我们确定了热力学温度T与其近似值T _{90之间的差异 (} T - T _{90 )} 由 1990 年国际温标 (ITS-90)。我们通过不同的方法估计了铜的等温压缩率和我们的微波谐振器的有效压缩率，包括谐振超声光谱 (RUS) 和在 273.16K 的氦气微波测量。我们比较了这些可压缩性估计的结果并讨论了相关的不确定性。从折射率测量中，我们估计了氦和氖的第二密度维里系数，这与从头计算相同性质的计算结果非常吻合。