Determination of the Boltzmann constant with cylindrical acoustic gas thermometry: new and final results
Keith A. Gillis, XiaoJuan Feng, Jintao Zhang, H. Lin, James B. Mehl, Michael R. Moldover, K Zhang, Y.N. Duan
We report a new determination of the Boltzmann constant kB using a cylindrical acoustic gas thermometer. We determined the length of the copper cavity from measurements of its microwave resonance frequencies. This contrasts with our previous work (Zhang et al. 2011 Int. J. Thermophys. 32 1297; Lin et al. 2013 Metrologia 50 417, Feng et al. 2015 Metrologia 52 S343) that determined the length of a different cavity using two-color optical interferometry. In this new study, the half-widths of the acoustic resonances are closer to their theoretical values than in our previous work. We follow CODATA's method (Mohr P J and Taylor B N 2000 Rev. Mod. Phys. 72 351) to calculate the weighted mean value of kB that accounts for the correlations among the measured quantities in this work and our 4 previous determinations of kB. The weighted mean B> is 1.3806487×10-23 J K-1 with the relative standard uncertainty of 2.0×10-6. The corresponding gas constant is 8.314461 J K-1 mol-1 with the relative standard uncertainty of 2.0×10-6.