GEANT4 Modeling of the Bremsstrahlung Converter Optimal Thickness for Studying the Radiation Damage Processes in Organic Dyes Solutions
Authors: Malykhina Tetiana , Kovtun Vladimir , Kasilov Valentin , Gokov Sergey 
Published: August 2022

The study of the processes occurring in a matter when ionizing radiation passes through is important for solving various problems. Examples of such problems are applied and fundamental problems in the field of radiation physics, chemistry, biology, medicine and dosimetry. This work is dedicated to computer modeling of the parameters of a tungsten converter for studying the processes of radiation damage during the interaction of ionizing radiation with solutions of organic dyes. Simulation was carried out in order to determine the optimal thickness of the converter under predetermined experimental conditions. Experimental conditions include: energies and type of primary particles, radiation intensity, target dimensions, relative position of the radiation source and target. Experimental studies of the processes of radiation damage occurring in solutions of organic dyes are planned to be carried out using the linear electron accelerator "LINAC-300" of the National Scientific Center "Kharkov Institute of Physics and Technology". Electrons with 15 MeV energy are chosen as primary particles. The interaction of electrons with the irradiated target substances is planned to be studied in the first series of experiments. Investigations of the interaction of gamma quanta with the target matter will be carried out in the second series of experiments. The tungsten converter is used to generate a flux of bremsstrahlung gamma rays. One modeling problem is determination of the converter thickness at which the flux of bremsstrahlung gamma will be maximal in front of the target. At the same time, the flow of electrons and positrons in front of the target should be as low as possible. Another important task of the work is to identify the possibility of determining the relative amount of radiation damage in the target material by the Geant4-modeling method. Radiation damage of the target substance can occur due to the effect of bremsstrahlung, as well as electrons and positrons. Computational experiments were carried out for various values of the converter thickness – from 0 mm (no converter) to 8 mm with a step of 1 mm. A detailed analysis of the obtained data has been performed. As a result of the data analysis, the optimal value of the tungsten converter thickness was obtained. The bremsstrahlung flux in front of the target is maximum at a converter thickness of 2 mm. But at the same time, the flux of electrons and positrons crossing the boundaries of the target does not significantly affect the target. The computational experiment was carried out by the Monte Carlo method. A computer program in C++ that uses the Geant4 toolkit was developed to perform calculations. The developed program operates in a multithreaded mode. The multithreaded mode is necessary to reduce the computation time when using a large number of primary electrons. The G4EmStandardPhysics_option3 model of the PhysicsList was used in the calculations. The calculations necessary for solving the problem were carried out using the educational computing cluster of the Department of Physics and Technology of V.N. Karazin Kharkiv National University.