ovides 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 the presence of any explosive material.
It thereby follows that any system of checking luggage or parcels must have a very high probability of detection (PD) in order to be effective. Because of the large number of parcels processed, a high throughput is necessary for practicality. In addition, any detection system, because of the large number of scanned items, is bound to occasionally give a false alarm. The probability of these false alarms (PFA) must be minimized in order to provide for an effective explosive detection system. This is because when an alarm occurs it is not known, at that time, whether it is true or false. This means that each time an alarm occurs, a passenger or parcel must be detained for further investigation. If false alarms are significantly high the nuisance level and the delays could be unacceptable to the public. It is, therefore, important that any explosive detection system must have a very high probability of detection (high PD), a high throughput rate, and yet at the same time have a very low probability of false alarms (low PFA). These conflicting criteria have hampered efforts in the past to build a reliable and usable system.
In general, prior art systems have not met the desired characteristics of having a high probability of detection (PD) with a low probability of false alarms (PFA) at acceptable throughput rates. As an example, one such prior art system is shown in U.S. Pat. No. 3,832,545. This patent provides for a system for the detection of nitrogen, which is generally present in the explosive materials to be detected. As described in the referenced patent, a rough two-dimensional profile of the nitrogen content within the object being inspected is provided. This profile is then used in an attempt to determine whether explosive materials are present. Unfortunately, however, because of the types of detectors used by the invention described in the '545 patent (liquid or plastic scintillators), the processing of the detector signals is quite inefficient. Moreover, the two-dimen