Geant4-based optimization of spallation targets for high-intensity neutron production

Spallation reactions are the basis of high-flux neutron source development for accelerator-driven systems (ADS), transmutation of radioactive waste, and radioisotope production. Using detailed simulations based on the Monte Carlo framework of the GEANT4 toolkit and the FTFP_BERT_HP physics model, this work offers a systematic approach to optimize spallation target shape and material. Neutron and photon yields from two different target materials, liquid mercury and natural uranium, irradiated with a 1.4 GeV proton beam are investigated. The geometries of the two cylindrical targets were varied in height from 1 cm to 75 cm while keeping the constant diameter at 34.4 cm. The simulations show that uranium emits about 2.5 times as many neutrons as mercury per incident proton, and these are emitted closest to the proton beam entry points. The locations that produce the maximum number of neutrons are found to be 4 cm from the entry points for uranium (52.65 neutrons per proton) and 2 cm from these points in the mercury target (22.9 neutrons per proton). The work shows that uranium is preferred based on neutron yield maximization while minimizing costs, and that there are unique advantages offered by the mercury target regarding thermal properties in continuous operation modes. The data are verified by comparisons with other models presently used in spallation physics. • Geant4-based optimization of spallation target material and geometry for high-intensity neutron production. • Natural uranium yields about 2.5 times more neutrons per 1.4 GeV proton than liquid mercury, with a maximum at 4 cm from the beam entry. • Neutron production is strongly localized near the beam entrance (4 cm for uranium at 52.65 n/p, 2 cm for mercury at 22.9 n/p), enabling compact target designs. • Uranium is preferred for neutron yield and cost, while mercury offers superior thermal performance for high-power continuous operation.