Multi-energy x-ray absorption imaging for detecting foreign objects on a conveyor

Apparatus for detecting materials on a conveyor belt, comprising:

• a conveyor belt conveying product in a conveying direction;
• an x-ray source directing a beam of x-rays having a source intensity distributed across a source spectrum through the thickness of the conveyor belt along an x-ray path;
• a spectroscopic x-ray detector comprising one or more pixels on the opposite side of the conveyor belt from the x-ray source that receive the x-rays that are attenuated as they pass through the conveyor belt, the conveyed product, and any foreign object advancing with the conveyed product on the conveyor belt at discrete pixel positions across the width of the conveyor belt;
• wherein the one or more pixels define a corresponding field of view at each pixel position and determine a received intensity distributed across a received spectrum of the attenuated x-rays in its corresponding field of view at each pixel position;
• a processing system that relates the received spectrum at each pixel position to the source spectrum to determine a measured attenuation of the x-rays and relates the measured attenuation to an x-ray attenuation model that includes attenuation coefficients of a set of preselected constituent materials including materials constituting the product, materials constituting the conveyor belt, and materials constituting foreign objects suspected as possible contaminants to determine the thickness of those materials in the fields of view at each pixel position.