At the invitation of CAS Key Laboratory of Cryogenics and Center for Public Technical Service, Dr. Pitre from the French Metrology Organization LNE-CNAM visited TIPC and gave a lecture “New measurement of the Boltzmann constant by acoustic thermometry of helium-4 gas at LNE” for academic communication on 14^th June.

Dr. Pitre introduced that the SI unit of temperature will soon be redefined in terms of a fixed value of the Boltzmann constant k derived from an ensemble of measurements worldwide. This lecture described the determination of k from the measurement of the speed of sound in helium in a quasi-spherical resonator at constant temperature near 273.16 K. The speed of sound is extracted from acoustic resonance frequencies extrapolated to an ideal gas behavior. The dimensions of the resonator are determined by microwave resonance frequencies. Key aspects of the experiment have been outlined namely thermometry and pressure measurement, acoustic and microwave resonances and gas handling. Finally the overall uncertainty of 0.6ppm has been presented that is lower than all previously published values.

Dr. Laurent Pitre is a Researcher at the French Metrology Organization LNE-CNAM since 2000. He has continued the development and the fine-tuning of the quasi spherical resonator. Today he leads a team, which uses this resonator for the re-determination of the Boltzmann constant and the thermometry in the range of 4K to 300K.

Dr. Laurent Pitre is giving a lecture