Simulation Study on Pinhole Imaging of ²³⁹Pu Using Nuclear Resonance Fluorescence With Laser Compton Scattering Gamma Rays

Nuclear resonance fluorescence (NRF) has significant potential in the identification and measurement of isotopes due to its specificity for different nuclei. This study explored the NRF pinhole imaging method through Monte Carlo simulation in the detection of 239Pu samples. By designing and optimizing parameters of the pinhole imaging system, including the direction of incident photons, geometric aperture, acceptance angle, pinhole thickness, object distance, and magnification factor, a spatial resolution of 1.2 cm with a signal-to-noise ratio (SNR) of 1.63 has been achieved. Monochromatic incident photons were used in the simulation to improve data statistics and reduce computation time. Although there are no suitable monochromatic photon beams, quasi-monochromatic gamma rays generated by laser Compton scattering (LCS) sources would be available for NRF applications. Simulation with a quasi-monochromatic incident photon beam suggested that off-resonance photons contributed little to the final results after energy filtering. Simulation results demonstrate the potential of NRF pinhole imaging to distinguish isotope samples, such as 239Pu, with different concentrations and sizes and obtain direct imaging results without the need for further data processing. However, challenges, such as high-energy noise photons and low count rate of NRF photons, limit the image quality. To compensate these errors and enhance the accuracy of NRF pinhole imaging, imaging correction algorithms can be developed for further improvements.