Proof of concept for illicit material detection via active photon interrogation and photoneutron spectrometry in realistic inspection scenarios

Abstract

This study investigates the application of Active Photon Interrogation coupled to Photoneutron Spectrometry (API-PS) as a novel technique for detecting nitrogen-rich materials, such as explosives and narcotics, in realistic inspection scenarios. API-PS leverages high-energy photons to induce neutron emission from target materials, allowing for element-specific identification based on corresponding unique photoneutron spectra. Through a series of controlled experiments, we assessed API-PS's effectiveness by analysing the photoneutron spectra of melamine—a nitrogen-rich compound often used as a surrogate for illicit materials—embedded in various configurations alongside common items such as clothing, electronics, and scrap metals. Our findings demonstrate that API-PS is capable of distinguishing nitrogen signature even in the presence of significant other photoneutron contributions from higher Z metals, such as copper. In particular, spectral features characteristic of nitrogen remained identifiable, despite interference from other elements like oxygen, underscoring API-PS's potential to reliably identify illicit substances in challenging inspection conditions. The complementary use of dual-energy X-ray imaging enhanced our ability to interpret the API-PS spectra by providing a spatial context for the material arrangement, aiding in the differentiation of target signals. The results of this proof-of-concept study suggest that API-PS could offer substantial benefits for security screening applications, particularly in high-stakes environments such as airports, harbours, and border checkpoints, where accurate detection of hazardous or illicit materials is essential.