Abstract
Primary dielectric constant gas thermometry (DCGT) has been used to establish a quasi-continuous temperature scale in the range 4,2 K to 27,0 K with a measurement uncertainty which increases with rising temperature from 0,6 mK to 1,2 mK (confidence level 95%). (It should be noted that previous papers refer to the 68% level which yields about one half of the uncertainty values.) The large number of experimental data for 4He (about thirty isotherms, more than 200 triplets of pressure, temperature, and dielectric constant) allowed, furthermore, the determination of the temperature dependencies of the second and third virial coefficients, without any constraints. The virial coefficients thus obtained exhibit good agreement with data based primarily on conventional gas thermometry and potential calculations. The established temperature scale is compared with the isotherm and constant volume gas thermometry scale NPL-75. A flat sinusoidal form for the differences between the two scales may be seen, which is in accordance with other published data. However, the differences are well within the thermodynamic uncertainties estimated for the NPL-75 and the DCGT scale. This result supports the theoretical polarizability value with a relative combined uncertainty of 6 × 10-5, i.e. the bounds for the polarizability value of 4He have been decreased by one order of magnitude compared with the available rigorous theoretical bounds.