Measurement of absorbed dose to water for medium energy x rays

The aim of this thesis is to determine the factors required to convert the air kerma measured using an ionization chamber to absorbed dose to water when irradiated with medium energy x rays. This involved determining the ratio of the mass energy absorption coefficients of water to air and the chamber correction factor (kch) for an NE2561 ionization chamber. The latter can be expressed as the product of the stem correction, the correction for the angular and energy dependence of the chamber, the replacement correction and a correction for the effect of the waterproof sleeve. The chamber correction factor for a NE2561 chamber was determined using two independent methods. First, the absorbed dose to water was compared using an NE2561 chamber with that using an NE2571 chamber. Second, the air kerma in water was measured using the NE2561 chamber and compared with the absorbed dose to water determined using an ice calorimeter. The validity of the absorbed dose to water measured using the ice calorimeter was then checked by comparison with the primary standard graphite calorimeter irradiated with 60Co gamma rays.