Characteristics and parameterisation of spallation neutrons

The present study investigates neutron generation by spallation with an emphasis on optimisation and parameterisation of target geometry and examines its implications for accelerator-driven subcritical reactors (ADSRs) and other advanced neutron sources. We investigate neutron yields, energy spectra, and spatial/radial distributions from a cylindrical lead target throughout a broad range of proton energies (100–1400 MeV) using the GEANT4 toolkit. The results were validated against MCNPX predictions, with experimental validation of the integral neutron yield and differential comparison of the axial side leakage and the leakage energy spectra against thick-lead measurements from the Joint Institute for Nuclear Research (JINR) [1]. In order to represent spallation neutron sources, compact parameterisation equations are developed. The findings show that neutron production rises almost linearly with proton energy, with an effective target length of 60 cm and an optimal utilisation efficiency at 1 GeV. In addition to numerical validation, we present a physical interpretation of neutron emission patterns, encompassing energydependent spectrum features and their relevance to minor actinide transmutation. The proposed parameterisations are intended as ready-to-use bare-target source terms for preliminary ADSR neutronics and spallation-target design. The main contribution of this work is methodological: a compact, cross-validated source representation that can support early-stage studies of advanced neutron sources.