WATER CALORIMETRY - THE HEAT DEFECT

Domen developed a sealed water calorimeter at NIST to measure absorbed dose to water from ionizing radiation. This calorimeter exhibited ano malous behavior using water saturated with gas mixtures of H-2 and O-2 . Using computer simulations of the radiolysis of water, we show that the observed behavior can be explained if, in the gas mixtures, the am ount-of-substance of H-2 and of O-2 differed significantly from 50 %. We also report the results of simulations for other dilute aqueous sol utions that are used for water calorimetry-pure water, air-saturated w ater, and H-2-saturated water. The production of H2O2 was measured for these aqueous solutions and compared to simulations. The results indi cate that water saturated with a gas mixture containing an amount-of-s ubstance of H-2 Of 50 % and of O-2 of 50 % is suitable for water calor imetry if the water is stirred and is in contact with a gas space of s imilar volume. H-2-saturated water does not require a gas space but O- 2 contamination must be guarded against. The lack of a scavenger for O H radicals in ''pure'' water means that, depending on the water purity , some ''pure'' water might require a large priming dose to remove rea ctive impurities. The experimental and theoretical problems associated with air-saturated water and O-2-saturated water in water calorimeter s are discussed.