The PTB water calorimeter for the absolute determination of absorbed dose to water in60Co radiation

The quantity to be measured in dosimetry for radiation therapy is the absorbed dose to water, Dw. At the Physikalisch-Technische Bundesanstalt a water calorimeter is established as the primary standard for Dw in 60Co radiation under reference conditions. The water calorimeter is capable of measuring the absorbed dose to water with a combined standard uncertainty of 0.20%. Some aspects of the design and operation of the water calorimeter are discussed. Detailed experimental and theoretical investigations for the different influence quantities affecting the calorimetric results are presented.