Absorbed dose determination with a water calorimeter in comparison with an ionisation chamber.

The absorbed dose in water has been measured for both photon and electron beams using a water calorimeter. The results were compared with those obtained with a Farmer type ionisation chamber. Doses measured with the water calorimeter for 60Co gamma rays, 10 and 25 MV x-rays, and 16.6 and 22.3 MeV electrons are approximately 4.5 to 5% higher than those derived from ionisation chamber measurements using the formation of ICRU 14 and 21. Based on a new formalism which has been under study, the calorimeter results for gamma and x-rays were found to be approximately 2-4% higher than predictions. For electrons the calorimeter results were approximately 3.5% higher than predictions. The differences found are discussed in terms of the heat defect of water.