DETERMINATION OF THERMODYNAMIC TEMPERATURE AND HE-4 VIRIAL-COEFFICIENTS BETWEEN 4,2 K AND 27,0 K BY DIELECTRIC-CONSTANT GAS THERMOMETRY

Primary dielectric constant gas thermometry (DCGT) has been used to es tablish a quasi-continuous temperature scale in the range 4,2 K to 27, 0 K with a measurement uncertainty which increases with rising tempera ture from 0,6 mK to 1,2 mK (confidence level 95 %). (It should be note d that previous papers refer to the 68% level which yields about one h alf of the uncertainty values.) The large number of experimental data for He-4 (about thirty isotherms, more than 200 triplets of pressure, temperature, and dielectric constant) allowed, furthermore, the determ ination of the temperature dependencies of the second and third virial coefficients, without any constraints. The virial coefficients thus o btained exhibit good agreement with data based primarily on convention al gas thermometry and potential calculations. The established tempera ture scale is compared with the isotherm and constant volume gas therm ometry scale NPL-75. A flat sinusoidal form for the differences betwee n the two scales may be seen, which is in accordance with other publis hed data. However, the differences are well within the thermodynamic u ncertainties estimated for the NPL-75 and the DCGT scale. This result supports the theoretical polarizability value with a relative combined uncertainty of 6 x 10(-5), i.e. the bounds for the polarizability val ue of He have been decreased by one order of magnitude compared with t he available rigorous theoretical bounds.