Low-temperature determination of the Boltzmann constant by dielectric-constant gas thermometry

The Boltzmann constant has been determined by performing isotherm measurements around the triple point of neon with dielectric-constant gas thermometry (DCGT). The necessary thermodynamic reference has been established with an uncertainty of about two tenths of a millikelvin, via realizing the International Temperature Scale of 1990, ITS-90, and exploiting the recently published results for the deviation between thermodynamic temperature and the ITS-90. In combination with a detailed treatment of uncertainty estimates and correlations, a value for the Boltzmann constant of k LT = 1.380 657 × 10 −23 J K −1 with a standard uncertainty of 15.9 parts per million (ppm) has been determined. This value deviates from the CODATA value, published in 2008, by only 4.7 ppm and is in very good agreement with the value obtained by DCGT at the triple point of water k TPW = 1.380 654 × 10 −23 J K −1 with an uncertainty of 9.2 ppm. The weighted mean of k LT and k TPW leads to the DCGT estimate for the Boltzmann constant of k = 1.380 655 × 10 −23 J K −1 with an uncertainty of 7.9 ppm.