ng neutrons that pass through said object without substantially interacting with atomic nuclei, the detection of said neutrons thereby providing a rough measure of the density distribution of most nuclear species within said object;
(e) generating a three-dimensional elemental density image of said object based upon the density distributions obtained from steps (c) and (d); and
(f) determining whether said three-dimensional elemental density image indicates the presence of explosives within said object.
11. The method of detecting explosives as set forth in claim 10 wherein step (c) includes rejecting background noise in the spectrum of detected gamma rays, said background noise including gamma rays that are emitted from non-explosive elements within said object and its surrounding environment.
12. The method of detecting explosives as set forth in claim 11 wherein said means for rejecting background noise includes measuring background noise at a first region in the spectrum of detected gamma rays and subtracting said background noise from a second region in the spectrum of the detected gamma rays, said second region in the gamma ray spectrum corresponding to gamma rays resulting from neutron interaction with nitrogen nuclei.
13. The method of detecting explosives as set forth in claim 10 further including generating at least one two-dimensional electron density image of said object; and using said electron density image in combination with said three-dimensional elemental density image to help confirm the presence of explosives within said object.
14. The method of detecting explosives as set forth in claim 13 wherein the step of generating at least one two-dimensional electron density image of said object comprises generating two two-dimensional electron density images of said object, a first electron density image lying in a first plane, and a second electron density image lying in a second plane that is orthogonal to said first plane, whereby the combination of said first and second electron density images provides three-dimensional electron density information relative to said object.
15. The method of detecting explosives as set forth in claim 13 wherein step (f) includes using an artificial neural system for processing the information obtained form steps (c) and (d) in a parallel distributed network for the purpose of quickly recognizing a pattern of detected gamma rays and neutrons indicative of an explosive.
This application is a divisional of U.S. application Ser. No. 07/463,036, filed 1/10/90; which is a continuation-in-part of U.S. application Ser. No. 7/367,534, filed 06/16/89, now abandoned; which is a continuation-in-part of U.S. application Ser. No. 7/321,511, filed 03/09/91, now U.S. Pat. No. 5,006,299; which is a continuation-in-part of application
The present invention relates to an explosive detection system used to detect explosives in checked airline baggage. More specifically, the present invention relates to a nuclear-based explosive detection system that accurately discriminates between parcels with and without explosives. The system includes, in addition to a neutron source and an array of gamma ray detectors, at least one neutron detector, means for removing background noise from the ensuing gamma ray spectrum, an X-ray system, and/or an artificial neural system (ANS).
A great need exists for the scanning of luggage, baggage and other parcels for the detection of any explosive material contained or concealed within their confines. For example, a large number of pieces of luggage (estimated at over 2,000,000) are checked and/or carried onto aircraft daily by close to seven hundred and fifty thousand (750,000) passengers within six hundred (600) airports extending across the country. Many more packages move through the mails or are shipped to sensitive buildings. There is a possibility, albeit small, that any one piece of luggage or parcel might contain explosive material. It is, therefore, desirable to protect the public by providing detection systems to scan the luggage and parcels to detect th