Determination of the Boltzmann constant—status and prospects

Abstract

The present definition of the kelvin links the unit of temperature with a material property, namely the triple point temperature of water. It would be more consistent with the current approaches to other base units of the International System of Units to fix the value of the Boltzmann constant k, instead. This would rationalize the definition and make it separate from any technique of realization. Furthermore, it is needed to improve temperature measurement, particularly at temperatures far away from the triple point of water. For this purpose, k must first be determined with appropriately small uncertainty applying different measurement methods. In this paper, the primary-thermometry methods for determining the Boltzmann constant (acoustic gas thermometry, thermal-equation-of-state methods, radiation thermometry and methods based directly on statistics and quantization) and their state-of-the-art level of uncertainty are discussed. Special emphasis is given to the basic physics underlying these methods, the fundamental error sources and the uncertainty, which seems to be attainable on a five-year timescale in view of some new developments and the foreseeable progress. Finally, a possible simple new definition of the kelvin is proposed.

Theory and application of explicitly correlated Gaussians

“…Boltzmann's constant, the definition of the mol, and the universal gas constant are all interrelated through the identity R ¼ k B N A . Further improvement in the precision of experiments measuring either the refractive index or the dielectric constant of helium could lead to a redefinition of these quantities in terms of a standard which is based on the calculated helium polarizability (Stone and Stejskal, 2004;Fellmuth, Gaiser, and Fischer, 2006). Another atomic polarizability calculation with potential practical applications is that for the Be atom.…”

Quantum Virial Coefficients via Path Integral Monte Carlo with Semi-classical Beads

“…4). Calculation of very precise physical properties of helium is of interest in the field of metrology to develop accurate calibration and pressure standards, to accurately compute the Boltzmann constant, and to improve acoustic gas thermometry [9][10][11][12][13][14]. Semi-classical virial coefficients up to fifth order have been computed for helium-4 by Shaul et al [15], and showed that first-principles properties could be evaluated with precision and accuracy that exceeds experiment.…”

Towards a new SI: a review of progress made since 2011

“…The Consultative Committee for Thermometry (CCT) has considered the proposed definition and has emphasized the importance of the numerical value for the Boltzmann constant Methods that can contribute to the determination of the Boltzmann constant [48] could include dielectric gas thermometry, refractive index gas thermometry, Johnson noise thermometry and Doppler broadening thermometry. The most accurate published results to date come from the method of acoustic gas thermometry [49] and are plotted in figure 3.…”