Progress in INRiM Experiment for the Determination of the Boltzmann Constant with a Quasi-spherical Resonator

Current progress in the INRiM experiment for the determination of the Boltzmann constant k (B) by means of acoustic thermometry is reported. Particularly, the microwave determination of the volume of a triaxial ellipsoidal resonator with an inner radius of 5 cm which was designed at LNE-CNAM is discussed. For the same cavity, acoustic measurements in helium at T (w) over the extended pressure range between 50 kPa and 1.4 MPa are reported and these results are compared with the predictions of a model which accounts for several perturbing effects. The procedures, methods, and results obtained in the calibration of several capsule-type SPRTs used in the experiment are briefly illustrated, together with the estimate of the temperature uniformity of the experiment