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Mobile High-energy X-ray Radiography for Nondestructive Testing of Cargo Containers

Radiologic evaluation techniques are nondestructive testing (NDT) used to detect the bulk of explosives and contraband materials in large objects. As compared to conventional low-energy (<450 keV) X-ray imaging, high-energy (>1 MeV) digital X-ray radiography is required for the NDT of large containers because of the need for high penetration through thick materials, sensitivity, and the ability to distinguish between low- and high-Z materials. Mobile, high-energy, and highresolution radiologic techniques are useful to detect contraband and threat materials in digital radiographic images of containers with complex packing. This paper presents a mobile, high-energy X-ray radiographic technique for the in-field nondestructive inspection of cargo containers. The developed experimental technique consisted of a betatron as a high-energy (7.5 MeV) X-ray source and a high-resolution (400 μm) matrix detector for the digital X-ray imaging. In order to evaluate the detection efficiency and image quality of the measurement technique, a test specimen was proposed that was made of a 3 mm thick steel container with an inner dimension of 60  30  40 cm3 comprising different low- and high-Z materials. Image quality indicators were used to assess the essential image quality parameters such as image basic spatial resolution, effective attenuation coefficient, and signal-to-noise ratio (SNR). Experimental investigations were performed on a 6.1 m sea freight container with mockup dangerous materials in complex packing. Preliminary experimental results showed that the proposed technique was able to distinguish between liquids and solids, as well as detect contraband materials. Furthermore, a remarkable SNR of ~400 was achieved in the measured digital X-ray images. The influence of temperature on X-ray radiation dose rate at different X-ray energies was also investigated. Finally, important applications of the proposed technique in the context of maritime security are discussed.

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