Abstract: A method of determining an effective atomic number, Zeff, of an object may include obtaining a plurality of radiographic images of the object. Each radiographic image can be obtained using a different independent X-ray energy level. An intensity value for each pixel in a region of interest in each radiographic image can be determined. A plurality of measured ratios, R, can be formed using attenuation coefficients from a pair of different radiographic images. At least one adjusted measured ratio, Rm, can be calculated based on the plurality of measured ratios, R, and at least one corresponding estimation coefficient, ?. Zeff values can be assigned based on a comparison of the at least one adjusted measured ratio, Rm to a material attenuation database.

Abstract: A method for automatically detecting nuclear material using radiographic images of a cargo container includes receiving a plurality of radiographic images of the cargo container and aligning the plurality of images with respect to each other to produce registered images. The method also includes segmenting the registered images using the atomic number and other edge/texture information in order to locate one or more regions of interest within the registered images and estimating atomic number information for each of a predetermined number of portions of the registered images. The method includes assigning a threat level and a confidence value to regions of interest identified as a potential threat and evaluating the regions of interest identified as potential threats using material context information and adjusting, based on the evaluation, the threat level values and confidences of the regions of interest identified as potential threats.