4137 / Time (seconds): Caesium-Atomic clocks at the PTB in Braunschweig: EUROPA, DEUTSCHLAND, NIEDERSACHSEN, BRAUNSCHWEIG (BRAUNSCHWEIG, GERMANY), 18.04.2007: Caesium atomic clocks at Physikalisch-Technische Bundesanstalt PTB in Braunschweig, Germany. Realization of SI base unit of time, the second, as defined by the duration of 9,192,631,770 periods of radiation associated with a specified transition ot the caesium-133 atom. These 3 clocks define UTC (PTB) as basis of legal time in Germany and are part of a worldwide network of atomic clocks in some 50 institutions defining UTC. Copper lining on the walls shields against electromagnetic interference. - 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, time, caesium, cesium, atomic, clock, clocks, frequency, people, copper, lining,