The international Boltzmann project – the contribution of the PTB

To support new determinations of the Boltzmann constant, which have been requested by the International Committee for Weights and Measures (CIPM) and which are necessary for preparative steps towards new definitions of the kilogram, the ampere, the kelvin and the mole, an iMERAPlus joint research project is coordinating the European activities in this field in Spain (CEM), Denmark (DFM), France (LNE-INM/CNAM, University Paris North), Italy (INRiM, Universities of Naples and Milan), United Kingdom (NPL), Germany (PTB) and in the European Institute for Reference Materials and Measurements (IRMM). In this major European research project, the Boltzmann constant will be determined with various methods. The aims and the progress to date of the PTB contribution are reviewed in this article. To cite this article: B. Fellmuth et al., C. R. Physique 10 (2009).