Radiant energy – Invisible radiant energy responsive electric signalling – Neutron responsive means
Patent
1994-10-11
1995-12-26
Fields, Carolyn E.
Radiant energy
Invisible radiant energy responsive electric signalling
Neutron responsive means
2503591, 378 53, 378 57, G01N 2306, G01N 2309, G01N 2310
Patent
active
054790239
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a method and device for detecting concealed substances such as explosives or drugs, for example in luggage at an airport.
Explosives are occasionally concealed in luggage and parcels by terrorists for example, and smuggled through airports despite the efforts of customs officers. These devices are often not found because the daily volume of luggage and cargo is such that manually searching every item is simply impractical.
The Lockerbie disaster in 1988 highlighted the danger posed by Semtex, a plastic explosive that is difficult to detect by conventional means, particularly when formed into thin sheets. It is believed that the bomb contained only 1/2 kg of Semtex which was packed into a portable radio.
The U.S. Federal Aviation Administration (FAA) is searching for a means of detecting concealed explosives and has set minimum requirements for such a detection system.
A balance must be struck between the risk of not detecting an explosive and the delay and disruption caused by searching and false alarms since while the detonation of an explosive device in an airport or aircraft is a rare event, delays and disruptions are daily concerns.
BACKGROUND ART
Most explosives are characterized by high nitrogen and oxygen content and low carbon and hydrogen content. They are also usually of high density. Aware of this, the FAA began funding tests of thermal neutron activation (TNA) in 1985. TNA involves the use of a radioactive source such as Californium-252 which emits neutrons. The neutrons are slowed or moderated in materials high in hydrogen such as polyethylene (at which stage the neutrons are "thermalized") and are then absorbed by the object of interest. The absorption leads to the emission of gamma rays which are characteristic of the elements present.
Analysis of these rays provides information as to the nitrogen content of the object bombarded. While explosives characteristically have a high nitrogen content, so do other materials such as certain plastics, silk and nylon which are commonly contained in luggage. Unfortunately TNA screening devices cannot distinguish between explosive materials and these non-explosive materials and so false alarms are often raised which can cause considerable delays. Also, TNA scanning devices require a very intense neutron source and extreme measures are needed to shield airport staff and travellers from the radiation.
The sensitivity of these devices is also less than desirable but improving that would increase the incidence of false alarms. Furthermore, TNA scanning devices are about the size of a small car, can weigh of the order of 10 tonnes and cost about $1 million each. Also, it has been suggested that between 300 and 700 such units would be required to deal with the demands of large international airports in the United States at a cost of $500 million for the machines plus housing and operating costs of at least $92 million a year.
Dual beam X-ray machines are being field tested. They can detect organic materials, such as explosives, with one beam and inorganic materials, such as metals, with the other beam.
Hand-held vapour sniffers are also being tested. These take in air and identify molecules in terms of their vapour pressure, atomic weight and liquid solubility by chromographic means.
Plastic explosives such as Semtex however have a lower vapour pressure than TNT so they can be difficult to detect by such means.
Computerised tomography or CT scanning commonly used in medical diagnosis and research has been applied to the problem by scanning for an object's density, total mass and indicating its atomic number and composition. But as Dr. Grodzin of MIT explained at an international meeting (International Conference on Accelerators in Industry and Research, Denton, Tex., Nov. 5-9, 1990): "More than a dozen nuclear-based techniques have been proposed for rapidly scanning airport luggage to find hidden explosives by measuring their elemental distributions. In most almost every scheme, the technological challenge is the a
REFERENCES:
patent: 3508047 (1970-04-01), Mott et al.
patent: 4884228 (1989-11-01), Stanley et al.
patent: 4884288 (1989-11-01), Sowerby
patent: 4941162 (1990-07-01), Vartsky et al.
patent: 5068883 (1991-11-01), DeHaan et al.
patent: 5278418 (1994-01-01), Broadhurst
Grodzins, L., Applications of Nuclear Techniques, International Conference Proceedings, Heraklio, Crete, Greece, Jun., 1990.
Bartle, C. M., Simultaneous Transmission of Neutrons and Gamma Rays (NEUGAT) to Measure Fat in Meat, Appl. Radiat. Isot. vol. 42, No. 11, pp. 115-556, 1991, Pergamon Press, Great Britain.
Bartle, C. M., Determination of the Moisture Content of Wheat Using the NEUGAT Technique, Nuclear Instruments and Methods in Physics Research A291 (1990) 655-661, North Holland.
Bartle, C. M. et al., Neutron-Gamma Transmission (NEUGAT) Based Composition Measurements Using an Acclerator, Nuclear Instruments and Methods in Physics Research A254 (1987) 219-221, North Holland, Amsterdam.
Fields Carolyn E.
Glick Edward J.
Institute of Geological and Nuclear Sciences, Ltd.
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