Simulation of a High-Energy Electron Beam Transmission Through Titanium and Kapton® Thin Films

Abstract

The results of computer simulation of the high-energy electrons passage through thin layers of titanium (Ti) and polyimide Kaptonâ (C₂₂H₁₀N₂O₅) in the energy range from 3 MeV to 20 MeV are presented. Simulation is carried out using the Geant4 toolkit. The number of primary electrons is 6.24×10⁷ for each series of calculations. The thickness of the titanium foil in the model experiment is 50 µm, the thickness of the Kaptonâ film is 110 µm. The energies of primary electrons are chosen as following: 3 MeV, 5 MeV, 10 MeV, 15 MeV, and 20 MeV. The purpose of the calculations is to reveal the possibility of using the Kaptonâ film in the output devices of linear electron accelerators. It was necessary to calculate the probable values of the energy absorbed in a Kaptonâ film and in a titanium foil for each value of primary electrons energy. Another important characteristic is the divergence radius of the electron beam at a predetermined distance from the film, or the electron scattering angle. As a result of calculations, the energy spectra of bremsstrahlung gamma-quanta, formed during the passage of electrons through the materials of the films, are obtained. The most probable values of the energy absorbed in the titanium foil and in the Kaptonâ film are calculated. The scattering radii of an electron beam for the Kaptonâ film and also for the titanium foil at a distance of 20 centimeters are estimated. These calculations are performed for electron energies of 3 MeV, 5 MeV, 10 MeV, 15 MeV, and 20 MeV. A comparative analysis of the obtained results of computational experiments is carried out. It is shown that the ratio of the total amount of bremsstrahlung gamma quanta in the case of use the Kaptonâ film is approximately 0.56 of the total amount of bremsstrahlung gamma quanta when using the titanium foil. The coefficients of the ratio of the electrons scattering radius most probable value after passing through Kaptonâ to the most probable value of the scattering radius after passing through titanium are from 0.62 at electrons energy of 3 MeV to 0.57 at electrons energy of 20 MeV. The analysis of the calculated data showed that the use of Kaptonâ (C₂₂H₁₀N₂O₅) as a material for the manufacture of output devices for high-energy electron beams is more preferable in comparison to titanium films, since the use of Kaptonâ instead of titanium makes it possible to significantly reduce the background of the generated bremsstrahlung gamma quanta and reduce the scattering radius of the electron beam.