Acoustic Resonator Experiments at the Triple Point of Water: First Results for the Boltzmann Constant and Remaining Challenges

We report on two sets of isothermal acoustic measurements made with argon close to the triple point of water using a 50mm radius, thin-walled, diamond-turned quasisphere. Our two isotherms yielded values for the Boltzmann constant, kB, which differ by 0.9 parts in 106, and have an average value of kB = (1.380 649 6 ± 0.000 004 3)×10-23J · K-1. The relative uncertainty is 3.1 parts in 106, and the average value is 0.58 parts in 106 below the 2006 CODATA value (Mohr et al. Rev Mod Phys 80:633, 2008), and so the values are consistent within their combined (k = 1) uncertainties.JRC.D.3-Knowledge Transfer and Standards for Securit