Development of an Advanced Computational Framework for Monte Carlo Simulation of Radiation Transport in Complex Nigerian Shielding Geometries

Accurate radiation transport simulation is the foundation of shielding design, dosimetry verification, and radiation safety assessment for nuclear installations, medical facilities, and industrial radiography sites across Nigeria. While established Monte Carlo codes such as MCNP and GEANT4 provide general-purpose frameworks, their application to the specific geometries and material compositions encountered in Nigerian facilities requires substantial model development and validation work. This study develops an advanced computational framework for Monte Carlo simulation of photon, neutron, and electron transport in complex Nigerian shielding geometries, extending the GEANT4 toolkit with custom material definitions, variance reduction techniques, and validation datasets. The framework incorporates locally characterised material cross-sections for laterite-barite composites, locally sourced concrete aggregates, and Nigerian crude oil-based polymer compounds not present in standard GEANT4 material libraries. Validation experiments using Co-60 and Cs-137 sources and laterite-barite shield geometries are conducted at the Centre for Energy Research and Training in Zaria, and simulated dose rates are compared with ionisation chamber measurements. The framework achieves simulation-to-measurement agreement within 5 percent for photon dose rate across all tested shield configurations. It is applied to design optimised shielding configurations for a proposed CT scanner installation at the National Hospital Abuja. Keywords: Monte Carlo simulation, radiation transport, GEANT4, shielding design, Nigeria