Effect of pressure, temperature and humidity in air on photon fluence and air kerma values at low photon energies

An investigation into the effect of pressure, temperature and humidity in air on photon fluence at a typical mammography, low bremsstrahlung energy (25 kVp), has been carried out. Pressure values corrected for humidity at varying temperatures were employed to determine the density of moist air. Using the corrected moist air densities, the X-ray photon fluence remaining after air attenuation has been computed assuming an X-ray focal spot-detector distance of 65 cm. Bremsstrahlung spectral distributions and the effects of pressure, temperature and humidity on the photon fluence from molybdenum and tungsten targets are illustrated. Comparative results suggest that such effects could be significant and need to be considered when calculating exposure levels from low-energy photons. The investigation showed that air kerma values from an X-ray spectrum that has significant lower-energy components is likely to be more sensitive to changes in pressure, temperature and humidity than the air kerma from an X-ray spectrum with lower-energy components less pronounced. Non-negligible air kerma values are involved