Comparison of the National Bureau of Standards and the Helsinki Temperature Scales and its Effect on the Heat Capacity of LiquidHe3below 10 mK

The Helsinki temperature scale, used earlier in measurements of the heat capacity of liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ (1-10 mK), is compared with the National Bureau of Standards (NBS) noise and nuclear-orientation temperature scale. The superfluid transition temperature ($T_c$) of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ at zero pressure and the superconductive transition temperatures of tungsten and beryllium were used as fixed points. $T_c$ on the NBS scale was found to be 1.025 ± 0.02 mK, in close agreement with the Helsinki value 1.04 mK. The results support the Helsinki data on the heat capacity of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$.