Enhancing Nuclear Resonance Fluorescence with Coded Aperture for Security Based Imaging

Abstract

Nuclear resonance fluorescence (NRF) is a nuclear phenomenon where the nucleus can be made to emit a spectral pattern that can be used to distinguish the material. This effect is triggered by exposing the material to a continuous spectrum of high-energy photons and then observing the resulting fluorescence spectrum, which varies with material. The photons used in the excitation process occur at energy levels of 2-8 MeV, which are among the most penetrating and can see through several inches of steel. The combination of material specific signatures and high penetration are well matched to applications such as cargo screening for threats and contraband. An imaging system has been proposed based on NRF using straight forward raster scanning of an excitation beam combined with simple collimation of the resulting emissions. While such a system is computationally inexpensive, it results in low inherent signal-to-noise ratio because most emitted photons are discarded, necessitating long scanning times. In this work we propose and explore the use of a coded aperture to increase the signal-to-noise ratio and lower acquisition time of NRF-based imaging.