THE IMERAPLUS JOINT RESEARCH PROJECT FOR DETERMINATIONS OF THE BOLTZMANN CONSTANT

Abstract

To provide new determinations of the Boltzmann constant, k, which has been asked for by the International Committee for Weights and Measures concerning preparative steps towards new definitions of the kilogram, the ampere, the kelvin and the mole, an iMERAPlus joint research project has coordinated the European activities in this field. In this major European research project the Boltzmann constant has been determined by various methods to support the new definition of the kelvin. The final results of the project are reviewed in this paper. Determinations of the Boltzmann constant k were achieved within the project by all three methods acoustic gas thermometry, Doppler broadening thermometry, and dielectric constant gas thermometry. All of these results are consistent with the currently accepted value of k. Remarkably, the standard uncertainty associated to the most recent acoustic result by LNE-INM/CNAM is a factor of 1.5 smaller than the best previous determination. These results were exploited by the interdisciplinary Committee on Data for Science and Technology (CODATA) in their recent adjustment of recommended values for fundamental constants. As a result, the CODATA group recommended a new value for k with a relative standard uncertainty about a factor of two smaller than the previous ur of 1.7×10−6