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A Sealed Water Calorimeter for Measuring Absorbed Dose
1National Institute of Standards and Technology, Gaithersburg, MD 20899-0001.
Abstract:
The NIST sealed water calorimeter is intended for direct measurement of absorbed dose to water. This calorimeter was used for a series of approximately 3700 measurements to investigate the so-called heat defect, that is, anomalous endothermic or exothermic effects caused by dissolved gases. The three systems investigated were "high-purity" water saturated with N2, H2, and mixtures of H2/O2. The repeatability of the measurements of absorbed dose rates for the 60Co teletherapy beam was studied with different water fillings and accumulated absorbed dose. Measurements with the H2/O2 system varied with accumulated absorbed dose. Based on the measurements and theoretical considerations, it appears that the H2-saturated system is the best choice for eliminating the heat defect. Measurements with both the N2- and H2-saturated systems are in good agreement with those determined with a graphite and graphite-water calorimeter (for which there is no heat defect).
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