Optimization of target system for the production of ⁹⁹Mo via ¹⁰⁰Mo(γ,n)⁹⁹Mo reaction

With an increase of stopping operation of nuclear reactors worldwide, the supply of medical ⁹⁹Mo becomes difficult and thus many efforts have been made to find an alternative. A process based on an electron linear accelerator (linac) system and a¹⁰⁰Mo target via the ¹⁰⁰Mo (γ,n)⁹⁹Mo reaction receives a lot of attention due to the relatively low level of co-produced impurities. This process has been recently developed at the Institute of Modern Physics (IMP) and the Monte Carlo simulation was used to optimize the target system before operating pilot irradiation experiments. First, tungsten and tantalum, as mostly used converter materials, were tested. The yield of ⁹⁹Mo was evaluated with respect to the converter thickness and the electron beam energy by means of Geant4 simulations. Besides, the specific activity of ⁹⁹Mo produced from one-stage approach (¹⁰⁰Mo target without a converter) and two-stage approach (¹⁰⁰Mo target with a converter) was compared when varying the testing conditions. The two-stage approach was selected for the experiment due to the higher specific activity of produced ⁹⁹Mo at all tested conditions. A target consisting of a 10 mm thickness of the ¹⁰⁰Mo tablets and a 2.4 mm thick Ta converter was irradiated for 40 h (50 MeV with 0.2 μA). The Geant4-calculated specific activity of generated ⁹⁹Mo at the end of bombardment agreed well with the experimental value, which proved high level of accuracy of the Geant4 simulation. In future studies, the Geant4 simulation will be used to optimize the production process when using high power linac system.