h for the system showing the positioning of a pair of thermal neutron sources and sets of inorganic scintillator detectors comprising a C-ring detector array;
FIG. 4 is a block diagram of the system showing the detection of particular gamma rays used in the detection of explosive material, with waveforms (a), (b) and (c) in FIG. 4 being representative of the signals at particular points in the system;
FIG. 5(a), (b) and (c) illustrate typical spatial profiles of nitrogen concentration for explosive and non-explosive materials;
FIG. 6 illustrates a typical thermal neutron activation gamma spectrum, and further illustrates the manner in which background noise form one area of the spectrum is subtracted from another area of the spectrum in order to remove background noise;
FIG. 7 schematically illustrates the neutron detection system of the present invention combined with an X-ray system;
FIG. 8 depicts a three layer back propagation network of a preferred ANS that may be used in analyzing the detector data of the present invention for the purpose of classifying whether the object under investigation carries explosives; and
FIG. 9 is a graph that compares the probability of detection and the probability of false alarms obtained with an explosive detection system using an ANS analysis of the detector data verses an explosive detection system using a more conventional discriminate analysis of the detector data.
The following description is of the best mode presently contemplated of carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles of the invention. The scope of the invention should be determined with reference to the appended claims.
Referring first to FIG. 1, a simplified schematic diagram of a nuclear-based explosive detection system 100 is illustrated. The system includes a radioactive source 102 that emits neutrons 106. The neutron source 102 may include a nozzle 104, or equivalent structure, that thermalizes the neutrons 106 and points them towards the object under examination, such as luggage 108, so as to irradiate or immerse the luggage and its contents with neutrons. Nitrogen contained within an explosive material 110, placed inside of the luggage 108, interacts with the probing neutron radiation and emits prompt gamma rays 112 of a particular energy level. Non-explosive materials within the luggage may have other elements that also interact with the probing neutron radiation, but the gamma rays emitted from such other elements have a different energy than do those from nitrogen. The number and energy of the gamma rays are measured in detector 114, which detector generates an appropriate output signal for each gamma ray of a particular energy that is received. A computer 116 monitors the output of the detector 114 and, after appropriate signal processing, makes a determination as to whether explosive material is present within the luggage. If so, an alarm 118 sounds, or is otherwise generated (e.g., visually) which alarm alerts operating personnel that explosive material 110 may be present within the luggage 108 so that appropriate action may be taken. Such action may include, for example, automatically diverting the suspect luggage away from the other luggage so that an extensive manual or other search of the luggage and its contents can be made.
As shown in FIG. 2A, one type of an explosive detection system 10 in accordance with the present invention includes a loading station 12 (which may consist of a scale to weigh the luggage) and an unloading station 14 (which may consist of a diverter to separate the alarmed luggage from the rest). The loading station leads to a continuous conveyer belt 16 which extends from the loading station 12 to the loading station 16 and has a continuous motion as indicated by the arrows 18. A central shield structure 20 encloses the explosive detection system and with two external wing portions 22 and 24 extending from the central structure 20 to enclose the conveyer belt 16 leadi