A determination of the molar gas constant R by acoustic thermometry in helium

We have determined the acoustic and microwave frequencies of a misaligned spherical resonator maintained near the temperature of the triple point of water and filled with helium with carefully characterized molar mass g mol−1, with a relative standard uncertainty . From these data and traceable thermometry we estimate the speed of sound in our sample of helium at K and zero pressure to be m2 s−2 and correspondingly deduce the value J mol−1 K−1 for the molar gas constant. We estimate the value J K−1 for the Boltzmann constant using the currently accepted value of the Avogadro constant NA. These estimates of R and k, with a relative standard uncertainty of 1.06 × 10−6, are 1.47 parts in 106 above the values recommended by CODATA in 2010.