Calibration of a 137Cs gamma-ray beam irradiator using large size chambers.

A (137)Cs gamma-ray beam irradiator has been calibrated in terms of air kerma using large size chambers. The available air-kerma rates range between 1.8 microGy/h (0.2 mR/h) and 5.3 mGy/h (0.6R/h). Large-volume chambers were used to characterize the source in terms of the radiation quantity air kerma (and exposure). Two types of chambers with significantly different characteristics and energy responses were used. This work shows that very good agreement can be obtained between the measurements performed with such different types of chambers. An agreement of 0.3% is observed between chambers even for the lowest air-kerma rates measured.