Application of a Water-Based Liquid Scintillator in Active Interrogation Imaging and Spectroscopy

Fast neutron active interrogation is a well-established and powerful technique for the detection of concealed contraband and special nuclear material. However, active interrogation signatures of contraband and special nuclear material are often relatively weak, requiring the use of long measurement times and high radiation doses from the interrogating source. High rates of active background also limit sensitivity to weak contraband signatures. We are exploring the use of water-based liquid scintillator (WbLS) to enhance the detection of concealed contraband and special nuclear material with a focus on prompt gamma-ray signatures for drug and explosive detection and fast neutron detection for special nuclear material. WbLS allows for combined Cherenkov and scintillation light measurements, which may provide simultaneous gamma-ray spectroscopy and imaging capabilities to reject active background while also providing the pileup resistance and cost effectiveness of an organic scintillator. We present initial simulation results demonstrating the feasibility of WbLS for neutron active interrogation applications. We investigate the separability of scintillation and Cherenkov light in WbLS for different scintillator loadings. We show simulated angular dependence of Cherenkov and scintillation light in WbLS to high energy gamma-rays for angular discrimination of signal from the background. We additionally simulate gamma-ray spectroscopy of major contraband gamma-ray signatures using WbLS scintillation light enhanced by maximum-likelihood estimation maximization based spectral reconstruction.