An Experimental Method for Measuring the Heat Defect of Water Using Total Absorption of Soft X-Rays

Abstract

The realization of the unit gray of the quantity absorbed dose to water by means of a water calorimeter requires knowledge of the heat defect to water, which is defined as the fraction of the radiation energy absorbed not appearing as heat. For low energy X-rays the heat defect can be determined by a method which uses total absorption of soft X-rays without involving absorbed dose measurements. The method described takes advantage of relative measurements allowing equal amounts of radiation energy to be absorbed in water or in a metal without heat defect. The method is outlined, the experimental set-up is described and the necessary corrections are discussed. Within the limits of uncertainty it is found that the pure water used in this study does not exhibit a heat defect.