Realization of the kilogram via the Avogadro experiment

Prof. Dr. Frank Härtig, PTB, Braunschweig, Germany

The Avogadro experiment was launched in order to define the mass unit kilogram on an atomic basis. During the last decades, highly sophisticated experiments have been developed among partners of the International Avogadro Coordination (IAC) in order to substitute the probably instable international kilogram prototype by the fundamental Planck constant. One required link between the well-defined and unchangeable number of the Planck constant on the one side and a manageable mass standard on the other side is given by a spherical object. It is made of isotropically enriched monocrystalline silicon. However, many organizational and technical obstacles had to be overcome before finalizing the first 28Si-sphere that fulfills all requirements. Therefore, manufacturing procedures and measurement devices had to be developed which operate at an atomic level and much below. Actual and future activities concentrate on the development of maintenance procedures that enable the worldwide acceptance and dissemination of the SI-unit kilogram via highly robust silicon spheres.