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Full text (en) Determination of empirical parameters of depth-dose distribution models for cases without any control of the electron beam spectrum
I. O. Girka1, V. T. Lazurik1, Y. V. Rudychev2, O. O. Zolotukhin1,*
1 V. N. Karazin Kharkiv National University, Kharkiv, Ukraine
2 National Science Center “Kharkiv Institute of Physics and Technology”, Kharkiv, Ukraine
*Corresponding author. E-mail address:
oozolotukhin@karazin.ua
Abstract: Two preconditions are crucial for the calculation of depth-dose distributions in existing semi-empirical models. An available detailed information regarding the electron beam spectrum is one precondition. And the dependence of the model's empirical parameters on the energy and incidence angle of the beam on the irradiated object is the other precondition. However, in industrial applications, the electron beam spectrum is typically not controlled during the radiation sterilization process. The present paper addresses and solves the problem of developing a procedure for using existing semi-empirical models to calculate depth-dose distributions if the electron beam spectrum is not controlled. The procedure for determining the empirical parameters of the model is suggested. It is based on the selection of a single irradiation mode from a set of values for electron energies and electron beam incidence angles on the layer that make a significant contribution to the depth-dose distribution. An estimation of the electron energy range in the spectrum is carried out based on an approximation of the spectrum by a triangular distribution with parameters corresponding to standard characteristics of the electron depth-dose distribution. The errors in determining the empirical parameters of the model are evaluated using a set of irradiation modes in the electron energy range from 5 to 10 MeV and electron beam incidence angles on the layer from 0° to 60°. The error of the SEM2U model is determined based on the deviations of the model’s predictions from the results of numerical experiments obtained by simulating depth-dose curves in the layer using the Monte Carlo method. Standard characteristics of the radiation sterilization process are used to estimate errors: values of optimal layer thicknesses, dose uniformity indices, and beam energy utilization coefficients. The method for using semi-empirical models is described for the cases without any control of the electron spectrum. The method consists of processing measurements taken using a dosimetric wedge to obtain the depth-dose curve under normal incidence of the electron beam on the irradiated object (the baseline curve for the models) and selecting a single irradiation mode to determine the empirical parameters of the models. The depth-dose curves in a semi-infinite medium, calculated using the described method, are compared with the results of simulating depth-dose curves using the Monte Carlo method. For these comparisons, an electron beam with a broad Spectrum_8 spectrum is used at various beam incidence angles on the medium. The error of the calculations of depth-dose curves for electron beams with the Spectrum_8 spectrum is evaluated according to the characteristics of the two-sided irradiation process, which is standard in radiation sterilization. The error is estimated based on the deviation of the predictions of the semi-empirical SEM2U model from the results of numerical experiments obtained by simulating depth-dose curves in the layers of optimal thickness using the Monte Carlo method. It is shown that the procedure for determining the empirical parameters of the model, based on the selection of a single irradiation mode, provides sufficient accuracy for the calculations in the SEM2U model for electron beams with a broad spectrum. The possibilities of the proposed method for using semi-empirical models to calculate depth-dose curves when selecting optimal irradiation modes in radiation sterilization in cases without any control of the spectrum are discussed.
Keywords: electron beam dosimetry, sterilization, two-side irradiation, depth-dose curve, selection of optimal modes, semi-empirical model, Monte Carlo method.
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