Computer Simulation of the Angular Distribution of Electrons and Bremsstrahlung Photons in Tantalum Converter

Abstract

The present work is dedicated to study of the possibilities of improving the production method of 11 C and 18 F medical isotopes using a linear electron accelerator. Experimental studies of 11 C and 18 F isotopes production by the photonuclear technique were carried out in [1]. Various targets were irradiated by bremsstrahlung photons following by measurements targets' activities. This experimental research has been carried out in the energy range from 10 to 40 MeV. The current work studies an angular distribution of bremsstrahlung photons in order to estimate the possibilities of producing maximum achievable levels of medical isotopes 18 F and 11 С activities. The angular distribution of bremsstrahlung photons is an important property of the irradiation stand which contains an assembly of targets. This important property allows designing necessary changes in the target assembly setup used to produce medical isotopes. The research presented in the current work was done as a computer simulation. The computer software package 'KIPT' was developed in С++ programming language, using the Geant4 toolkit in order to obtain the angular distribution of bremsstrahlung photons. Experimental setup materials as well as structural elements positions were defined in the DetectorConstruction class of our program. The parameters of an electron beam were defined in the PrimaryGeneratorAction class. The electron beam diameter was defined as 8 mm, energy Е е =36.7 MeV, corresponding to the real experiment carried out at the "Accelerator" Science and Research Establishment of Kharkiv Institute of Physics and Technology [1]. Models of physical processes occurring while the electron beam crosses the target assembly were defined in the PhysicsList class. All classes and modules necessary for the analysis of simulation results were included to our program together with visualization modules. Visualization modules use the OpenGL graphics library and the Qt5 software to represent the relative position of experimental setup parts and to visualize particle trajectories. As a result of this work, the angular distributions were obtained for the beam of electrons and bremsstrahlung photons directly before the target. This result will allow target assembly parameter optimization for optimal production of medical isotopes by the photonuclear technique.

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“…The outputs of bremsstrahlung photons and their energy spectra obtained by converting electron beams into bremsstrahlung (via the (e,γ) reaction channel) depend primarily on the initial electron energy, characteristics (material, geometric dimensions) of converters [8][9][10]. The electron spans in the materials from which the converters are made will be greater than the thickness at which the photon outputs have maximum values, i.e., residual electrons will be present in the beams [11].…”