X-ray fluorescence imaging of elements

Abstract

A system for detecting the presence of known materials in a body or container. The system incorporates a gamma or X-ray source for irradiating the body with gamma rays to produce X-ray fluorescence of materials contained therein. A directionally discriminate X-ray detector is positioned to intercept X-rays emitted from the body and is adapted to pass only those X-rays having a predetermined wavelength and incident from a specific direction that are characteristic of a material of interest contained in the body. The detector includes a dislocation free single crystal having substantially parallel input and output surfaces. A second crystal aligned parallel to the first crystal may be disposed at a position offset from the first crystal to receive the X-rays transmitted by the first crystal in order to discriminate between materials fluorescing within the body. In a specific embodiment of the invention, the first detector comprises an elongated crystal which pass X-rays in accordance with the Borrmann effect. A plurality of the crystals are arranged in a linear array and the container is either scanned with the array or the container passed linearly past the array. The detected X-rays are measured in intensity and the data is processed by suitable data processor to generate a video image indicative of the presence and shape of the specific materials for which the system is adapted. In yet another specific embodiment of the invention, a plurality of such arrays can be arranged with the input surfaces of the crystals disposed at different Bragg angles to simultaneously detect the presence of a selected group of materials.