Diameter comparison of a silicon sphere for the international avogadro coordination project

Abstract

In the International Avogadro Coordination (IAC) Project using the X-ray crystal density method, volume measurements of silicon spheres by optical interferometry play a crucial role for the density measurement of the 28Si-enriched crystal. To confirm the reliability of the volume measurement, specified diameters of a silicon sphere were measured independently by optical interferometers at NMIJ (Japan), PTB (Germany) and NMIA (Australia). The sphere was washed before the measurement with the same procedure. The directions of the diameters were identified with reference marks prepared on the surface of the sphere. All of the results agree with each other within their uncertainties. This strongly confirms the reliability of the diameter and volume measurements in the IAC project. Show more