Re-estimation of argon isotope ratios leading to a revised estimate of the Boltzmann constant

Abstract

In 2013, NPL, SUERC and Cranfield University published an estimate for the Boltzmann constant Subsequently, an extensive investigation by Yang et al [2] revealed that there was likely to have been an error in the estimate of the molar mass of the argon used in the experiment. Responding to [2], de Podesta et al revised their estimate of the molar mass [3]. The shift in the estimated molar mass, and of the estimate of kB, was large: -2.7 parts in 10 6 , nearly four times the original uncertainty estimate. The work described here was undertaken to understand the cause of this shift and our conclusion is that the original samples were probably contaminated with argon from atmospheric air.