Explosive detection system

This patent describes a method of producing a three dimensional profile of the concentration of a particular element in a particular object. It includes providing a cavity structure for receiving the particular object, providing a source for producing thermal neutrons, directing the thermal neutrons within the cavity structure to the object to interact with the particular element in the object to form gamma rays of a particular energy, providing a plurality of detectors around the periphery of the cavity structure in a common plane with the thermal neutron source in the cavity structure and in a C-shaped ring configuration and in a close loop with the thermal neutron source to detect the concentration of the particular element within the common plane, operating each of the detectors in the plurality of detectors independently of one another; moving the object through the cavity structure in a direction transverse to the common plane to obtain the detection by the detectors of the presence of the particular element in successive planes of the object parallel to the common plane, processing the detections by the detectors of the particular element in the successive planes of the object parallel to the common plane to obtain the three dimensional profile of the concentration of the particular element within the object