A direct comparison of water calorimetry and Fricke dosimetry

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Abstract
Considerable effort has been devoted to measuring the absorbed dose to water using water calorimetry. Most of these efforts have been hampered by a lack of adequate knowledge of the heat defect of water. The authors argue that there is now sufficient information to establish with considerable confidence the heat defect of high-purity water containing various dissolved gases. For the present work the authors used water saturated with a 50/50 mixture of H2 and O2 gases, for which the heat defect is calculated to be -2.1%. As a test of this assignment, they have compared the absorbed dose to water as measured using water calorimetry with that obtained from Fricke dosimetry. The authors find that for 20 MV X-rays, the dose to water determined by water calorimetry is 1.006+or-0.004 times the dose determined by Fricke dosimetry. Within 0.6(+or-0.4)%, this result supports the calculated heat defect of -2.1% for water saturated with a 50/50 mixture of H2 and O2 gases.