A direct comparison of water calorimetry and Fricke dosimetry

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% and compared the absorbed dose to water as measured using water calorimetry with that obtained from Fricke dosimetry. The water calorimeter consisted of a small sealed vessel containing 100 ml of stirred water saturated with a 50/50 mixture of H2 and O2 gases, irradiated with 20 MV x-rays at a dose rate of about 0.4 Gy s-1. The same vessel was then filled with Fricke dosemeter solution, and irradiated under identical conditions. The Fricke dosimetry was based on the Svensson and Brahme value of εG (3.515 x 10-3 1 cm-1 J-1) and agrees to within 0.2% with the dose to water for 60Co γ-rays obtained via graphite calorimetry. For 20 MV x-rays, the dose to water determined by water calorimetry is 1.006 ± 0.004 times the dose determined by Fricke dosimetry. Within 0.6(±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. (author)