Monte Carlo correction factors for the ARPANSA kilovoltage free-air chambers and the effect of moving the limiting aperture

Abstract

ARPANSA has calculated new Monte Carlo corrections for their low and medium energy x-ray free-air chambers. The new calculations include a diverging beam and details of the limiting aperture. The diverging beam simulations are compared with previous parallel beam simulations. The electron loss, scattering and fluorescence corrections do not change when beam divergence is included, even for the short source–detector distance of 30 cm used in post-2008 low energy calibrations. Transmission and scattering from the aperture are significant for both free-air chambers and dependent on the beam divergence. The constancy of the correction factors with changing air path length was investigated at low energies. In the extreme conditions of 100 kV and a distance of 30 cm the correction factors showed significant deviation.