A method for simulating real-time neutron populations, materials and geometries using the GEANT4 Monte Carlo toolkit

GEANT4 is a Monte Carlo particle physics toolkit that simulates elementary particles moving through matter [1]. GEANT4 allows a population of neutrons to be tracked in a multiplying medium as the population and the medium evolve. However, the population must be artificially stabilized so that it neither explodes nor vanishes. We present a stabilization method where the simulation is divided into short time intervals and the population is renormalized at the end of each interval. This method was used with a simple sphere of U235 to calculate the effective neutron multiplication factor (keff) from the continuous evolution of the neutron population.