Simulation and optimization of producing medical radioactive nuclide technetium-99m via electron accelerator based on Geant4

Sumitted to PubDB: 2026-05-07

Category: Master Thesis

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Principal Authors Kang Chen
Date 2026-05-07
Belle II Number BELLE2-MTHESIS-2026-026
Abstract Technetium-99m (Tc-99m) is the most widely used radionuclide in the field of nuclear medicine diagnostics, which accounts for over $80\%$ of all nuclear medicine applications worldwide. Currently, the mainstream industrial production method relies on the fission of molybdenum-99 (Mo-99) in nuclear reactors, which then decays into Tc-99m. In China, the production of Tc-99m is entirely dependent on imported Mo-99. Any supply disruptions in the international market could severely impact China's healthcare system. Therefore, the electron accelerator irradiation method has emerged as a promising alternative technology. This thesis uses Geant4 to simulate and optimize the production of Tc-99m via the electron accelerator. This approach involves irradiating a heavy metal conversion target with an electron accelerator, generating bremsstrahlung photons that irradiates an Mo-100 target, inducing photonuclear reaction to produce Mo-99. Mo-99 then decays into Tc-99m, which is chemically separated and extracted for medical use. This project focuses on the first part of the process, using Monte Carlo simulations to model the physical production of Mo-99. Initially, a verification simulation was conducted in Geant4 to ensure that the simulated results accords with theoretical predictions. The results confirmed that both $^{100}Mo(\gamma,n)$ $^{99}Mo$ reaction and the bremsstrahlung effect fit well. Subsequently, a complete simulation system was constructed, where electrons were used to irradiate a tantalum target, with a molybdenum target placed behind it. The electron energy range was set from 8.2 to 50 MeV, with an energy point for each 0.1 MeV to optimize the electron accelerator energy. Firstly, the bremsstrahlung photon spectrum was obtained, showing that photons with energies up to the incident electron energy were produced, with most photons concentrated in the low-energy region. The yield of Mo-99 as a function of electron accelerator energy was also derived. However, this value could not determine the optimal energy, as higher energies naturally increased the yield of photons capable of inducing the photonuclear reaction, but the yield per unit power was limited. Therefore, a relative yield was defined, identifying the optimal energy range to be between 20 and 30 MeV, providing a reference for the design of this production method. Additionally, simulations of byproducts and radiation protection were conducted. The results indicated that excessively high electron accelerator energies would significantly increase the production of unwanted byproducts, Mo-98 and Mo-97, which should be avoided. Furthermore, the process generates MeV-level neutron radiation, which needs appropriate shielding and isolation measures.
Institute Nankai

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