A GEANT4 model is presented for nuclear forensics analysis of nuclear detonation in urban environments utilizing an intense gamma ray and neutron pulse source to simulate post-detonation scenarios. Exterior building dimensions and locations for a small region of downtown Salt Lake City are derived from data in geographic information system (GIS) software to recreate a real-world environment in GEANT4. Common building materials, such as brick and structural steel, are characterized by material composition and defined for building material assignment. Different neutron and gamma ray point sources can be simulated with a user-defined spectral energy distribution, using reference data to approximate the prompt gamma ray and neutron energy distribution after the detonation event. A scoring mesh is implemented across the world environment to examine simulated detection spectra at any location within the simulated environment. By comparing the simulated detection output with observed detection data, the model may be utilized for approximating a spectral energy distribution at the source. Visualizing model outputs also helps to identify regions and locations impacted by radiation from the detonation.
Currently, a model in GEANT4 has been assembled with a user-variable radiation source and scoring mesh for detection. Model outputs include 2D and 3D representations of particle trajectories in the environment and particle density maps from scoring mesh results visualized in Matlab.