The iMERA/EUROMET Joint Research Project for New Determinations of the Boltzmann Constant

The international Boltzmann project – the contribution of the PTB

“…1 illustrates another important result of the performed DCGT experiments. The agreement between the experimental and theoretical results for the ratio of the polarizabilities of 3 He and 4 He is excellent, see the detailed discussion in [9]. Furthermore, the differences between the results obtained for the virial-coefficients and new theoretical ab initio values are well within the uncertainty estimates [18].…”

“…1. It is noted that the difference between the two evaluations of the new DCGT data for 4 He performed in 2007 [17] and in 2008 [18], respectively, is connected with the special effects below 3.7 K. For the fermionic measuring gas 3 He, no problems were observed. It corroborates also the value for the triple-point temperature of hydrogen of 13.80365(50) K at a deuterium content of 35 µmol/mol that is based on the first DCGT data set [16].…”

“…As one result of a workshop held at PTB in 2006 [2], an iMERAPlus joint research project is now coordinating the European activities to determine the Boltzmann constant in Spain (Centro Español de Metrología, CEM), Denmark (Danish Fundamental Metrology, DFM), France (Institut National de Métrologie, LNE-INM/CNAM, and University Paris North), Italy (Istituto Nazionale di Ricerca Metrologica, INRiM, and Universities of Naples and Milan), United Kingdom (National Physical Laboratory, NPL), Germany (Physikalisch-Technische Bundesanstalt, PTB) and in the European Institute for Reference Materials and Measurements, IRMM [3]. In this major European research project, the partners use different methods to determine the Boltzmann constant aiming at a relative standard uncertainty on the level of a few ppm.…”

“…Dashed line: first DCGT results (DCGT1) published in [16]. Thick dots: new data for 3 He. In the insert, experimental and theoretical results for the ratio of the polarizabilities of 3 He and 4 He are shown together with the combined standard uncertainties.…”