Monte Carlo Simulation of a Large NaI Detector Using GEANT4

A Monte Carlo simulation of a high-resolution large-volume NaI detector has been created for the analysis of Compton scattering experiments. This simulation (based on GEANT4) models the components of the detector (a single cylindrical core and four annular quadrants) and its response to a tagged photon beam of variable energy (60-90 MeV), for both in-beam and scattering configurations. The simulation outputs the energy deposited in each component of the NaI to a file for further analysis using the ROOT data analysis package. To more accurately represent the detector lineshape, the output from the simulated in-beam geometry is fitted to experimental in-beam data using a Gaussian smearing function which helps characterize the intrinsic response function of the detector. Once this response function has been determined, the simulation can then be used to model the lineshape for a scattering run from Compton scattering on carbon. With the appropriate lineshape for the scattering geometry and with an analysis of the experimental yields, the differential cross sections for Compton scattering can be extracted from the carbon data taken at MAX-Lab in Lund, Sweden.