4137 / Mass (Kilogram): Avogadro-Kugel made of Silizium at the PTB in Braunschweig: EUROPA, DEUTSCHLAND, NIEDERSACHSEN, BRAUNSCHWEIG (BRAUNSCHWEIG, GERMANY), 10.05.2007: Avogadro experiment at Physikalisch-Technische Bundesanstalt PTB in Braunschweig, Germany. In an attempt to redefine SI base unit of mass, the kilogram, by tying it to a fundamental constant, the mass of a single atom, metrologist Dr. Arnold Nicolaus and colleagues have designed the Avogadro sphere. The single crystal silicon ball of 1 kg is polished to 50 nm accuracy and measured by laser interferometry in order to determine via the Avogadro constant the number of atoms it consists of. Checking for dust. - Marc Steinmetz / VISUM - Keywords: Germany, Physikalisch, Technische, Bundesanstalt, PTB, science, technology, physics, metrology, base, unit, international, system, of, units, SI, metrical, measure, measurement, standard, accurate, accuracy, lab, experiment, scientist, scientists, people, kilogram, mole, mas