Deviation of Temperature Determined by ITS-90 Temperature Scale from Thermodynamic Temperature Measured by Acoustic Gas Thermometry at 79.0000 K and at 83.8058 K

A difference was determined between temperature defined by International Temperature Scale (ITS-90) and thermodynamic temperature measured by relative acoustic gas thermometry at 79.0000 K and at 83.8058 K. Measurement were carried out using misaligned spherical acoustic resonator filled with helium at different pressures. The isotherms were fitted for four different acoustic modes simultaneously assuming the same thermal accommodation coefficient and third acoustic virial coefficient for all modes. Our measurements yield the following differences between the thermodynamic temperature T and ITS-90 temperature T 90 : T - T 90 = - 4.81 ± 1.02 mK at 83.9058 K and T - T 90 = - 4.47 ± 0.97 mK at 79.0000 K.