Food irradiation using bremsstrahlung X-rays

A mathematical model is developed for characterizing the X-ray depth-dose distribution in products of uniform density. Model comparisons with detailed Monte Carlo calculations and experimental data illuminate the importance of various features of the process, including (1) the angular dependence of the radiation, (2) the energy dependence of X-ray absorption coefficients, and (3) in-product scattering. The model results are further used to develop an empirical formula that provides an acceptable fit to the depth-dose profile. The particular functional dependence of the empirical formula is that of decaying exponentials that model the geometric decrease in dose with distance from the converter, as well as the in-product absorption. As a final step, the empirical formula is used to estimate the max:min ratio, the X-ray energy utilization efficiency, and the mass throughput efficiency for the frequently used symmetric, double-sided irradiation configuration. Based on these analyses, maximum mass throughput efficiencies for this configuration, using 5-MeV bremsstrahlung X-rays, are shown to generally lie in the range of 2.5-3.75%, depending on the product density and thickness, and the details of the irradiation geometry. (C) 2003 Elsevier Ltd. All rights reserved.