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New measurement of the Boltzmann constant k by acoustic thermometry of helium-4 gas



Laurent Pitre, Fernando Sparasci, Michael R. Moldover, Cecile Guianvarch, Catherine Martin, Martin Himbert, Mark Plimmer, James B. Mehl, Giuliano Albo, Bo Gao, Lara Risegari


The SI unit of temperature will soon be redefined in terms of a fixed value of the Boltzmann constant k derived from an ensemble of measurements worldwide. We report on a new determination of k using acoustic thermometry of helium-4 gas in a 3-litre quasi-sphere. The method is similar to that used in our own experiments on helium and argon with a 0.5-litre resonator. We find for the universal gas constant R = 8.3144597 (49) J·mol-1·K-1. Using the current best available value of the Avogadro constant, we obtain k = 1.38064849 (81) ×10-23 J·K-1 and ur(k) = 0.59x10-6, where the uncertainty is one standard uncertainty corresponding to a 68 % confidence level. This value is in good agreement with those of our earlier measurements and with that of the 2014 CODATA adjustment of the fundamental constants, within the standard uncertainties.


Boltzmann constant, acoustic thermometry, temperature scale, resonator, Gas constant, fundamental constants


Pitre, L. , Sparasci, F. , Moldover, M. , Guianvarch, C. , Martin, C. , Himbert, M. , Plimmer, M. , Mehl, J. , Albo, G. , Gao, B. and Risegari, L. (2017), New measurement of the Boltzmann constant k by acoustic thermometry of helium-4 gas, Metrologia, [online],, (Accessed March 2, 2024)
Created September 10, 2017, Updated October 12, 2021