Fusion of X-ray Imaging and Photoneutron Induced Gamma Analysis for Contrabands Detection

A 7 MV LINAC based photoneutron interrogating system has been setup to fulfill the demand of contrabands detection in homeland security. Both X-ray imaging and photoneutron induced γ-ray analysis are used to extract the information of inspected materials. 480 CsI detectors of 5 mm (height) x 10 mm (width) x 20 mm (length) are used to form the detector array to measure the attenuation information of penetrating X-rays. 16 NaI(Tl) detectors of 127 mm (height) x 127 mm (diameter) are used to register the photoneutron induced γ-ray spectra of inspected materials. 2-dimensional elemental distributions of H, N, Fe and Cl are extracted by calculating the area of 2.223 MeV, 10.829 MeV, 7.64/9.298 MeV and 1.165/1.951/1.959 MeV γ-ray peaks in the spectra measured by NaI(Tl) arrays respectively. Mixed materials like iron, salt, water, melamine and sugar are scanned to test the contrabands detection capability. The images of X-ray attenuation and 4 elemental 2-dimensional distributions are fused together to separate suspicious materials. Areas with high concentrations of nitrogen and chlorine are easily identified and can indicate the potential existence of illicit substances.