then be readily analyzed by the detection system to indicate the possible presence of an explosive threat. A high count rate of detected gamma rays of a particular energy, for example, immediately indicates the presence of a great deal of nitrogen. The ANS can then quickly determine with a high PD whether the presence of the nitrogen indicates the presence of an explosive material, or whether it indicates the presence of some other benign nitrogen-rich material. Advantageously, with the ANS, the system of the present invention is also capable of detecting explosives in unconventional configurations while maintaining the number of false alarms to a relatively low level. The prior art detector systems, in contrast, while providing for the gross detection of explosives, cannot provide for the more sensitive detection of the unconventional explosive configurations concurrent with a relatively low level of false alarms.
A preferred embodiment of the explosive detection system of the present invention includes the use of efficient inorganic scintillators capable of resolving closely spaced high energy gamma ray lines. Specifically, sodium iodide scintillators are used to provide for detection. It is to be appreciated, however, that other inorganic scintillators such as cesium iodide, bismuth germinate and barium fluoride scintillators may also be used. In addition, inorganic solid state detectors such as lithium-drifted germanium, high purity germanium or mercuric iodide may be used.
The inorganic scintillators of the present invention are arranged to form at least one ring of detectors so as to provide for a detection of a plurality of slices or parallel successive planes of the object under inspection as the object is moved continuously through the ring of detectors. In a specific embodiment of the invention, this ring is broken into sets of C-rings; and in order to provide for a better three dimensional representation, two spaced sets of C-ring detectors may be used with the open ends of the C-rings facing each other so as to provide for a detection completely around the object and with the plurality of successive planes building up a three dimensional profile of the object under inspection. These rings need not all be in the same plane, nor must they be shaped similarly.
The detectors included in the detector arrays of the present invention may include one or more neutron detectors. Such neutron detector(s) are typically separate and may be apart from the C-ring array of gamma ray detectors. Each detector is coupled to appropriate processing circuitry. This processing circuitry may include an artificial neural system (ANS). The ANS allows the signals from each detector to be processed in a parallel distributed processing scheme that provides for a very rapid, yet accurate analysis of the complete data set. In effect, the ANS learns and merges features in the detector observations and automatically generates classification criteria. The ANS has the ability to learn patterns and classify objects based on these patterns. This learning ability is advantageously inherent in the ANS and does not require programming or algorithmic development. The ANS needs only examples from which to learn.
The system of the present invention is further capable of scanning a continuous flow of objects, such as luggage and parcels carried on a conveyor belt. In addition, the operation of the system may be fully automatic so that the system does not depend on operator experience or interpretation, thereby providing for the automatic detection of explosives.
It is a feature of the present invention to provide an explosive detection system that can continuously examine objects for explosive materials at an acceptably high throughput rate, e.g., approximately one object every six seconds.
It is another feature of the invention to provide such a detection system that does not damage film or magnetic recording media.
A further feature of the invention is to provide a detection system that exhibits a high PD at an acceptably low PFA, and that provides a