X-ray or gamma ray systems or devices – Specific application – Absorption
Patent
1996-07-16
1998-09-08
Porta, David P.
X-ray or gamma ray systems or devices
Specific application
Absorption
378 57, G01V 500
Patent
active
058056602
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a method and an implementing device/equipment for the purpose of detecting one or several objects containing a specific material, said object(s) being hidden from view and illustratively placed in a receptacle or envelope.
In particular the present invention applies to detecting objects enclosed in monitored or inspected luggage in airports or seaports prior to passenger boarding. Even more specifically, the invention applies to detecting detonators/squibs used to trigger the explosion of explosives. The squibs contain very special substances such as lead salts for instance.
Luggage-inspection methods and equipment at airports are known, whereby luggage-contents images are obtained to detect any prohibited or out-of-bounds objects such as weapons and explosives.
The known methods and equipment are based on the following principle: The receptacle, luggage or other is irradiated with an x-ray beam of a given energy spectrum, and thereupon the quantity of x-rays transmitted through the receptacle is measured in order to form a receptacle image. Accordingly a looked-for object is detected by visual recognition of the object shape in the image that was formed in this manner.
In a variation of the prior art, the incident x-ray spectrum is split into two parts, one low-energy part and one part with higher energies in order stress one physical phenomenon over another. Illustratively photo-ionization is predominant at low energies whereas the Compton effect predominates at higher energies. Comparison of the intensities transmitted through the tested object in the two spectrum parts allows separating bodies evincing atomic numbers Z less than or equal to 12 from the other bodies.
The prior art methods incur a number of drawbacks. They provide only little information, insufficient to identify the presence of a particular body.
In this field the invention remedies these drawbacks and proposes a method and equipment to implement said method whereby an object hidden from view and containing a specific material can be detected, and to do so reliably and rapidly, appropriate application being in particular to detecting specific objects containing a given material and placed in luggage when such luggage is being inspected at airports.
For that purpose the method of the invention detecting the presence of at least one specific material contained in an object and evincing a characteristic photo-ionization threshold comprises said photo-ionization threshold, in that furthermore x-rays in terms of energy is determined, and material is searched for on the curve representing the attenuation or transmission in the vicinity of the said photo-ionization threshold energy.
Preferably the material evinces a photo-ionization threshold K between 10 key and 120 key and more particularly this material evinces an atomic number Z higher than 70.
In a preferred mode of implementation, the material is lead or any lead compound (lead salts . . . )
Advantageously the beam comprises at least two substantially contiguous spectral bands present around the threshold K characteristic of the material being looked for.
In an advantageous implementation of the invention, the attenuation function is determined as follows: of the transmission u of a reference thickness of a reference material, each power of u being associated with a coefficient, the expansion powers being equal to a ratio of the previously determined thicknesses of the reference material to the reference thickness. each of the said thicknesses of the reference materials is measured, object is measured, the object is resolved into a sum of the intensities measured in the above step and relative to the particular spectrum, said intensities being associated with the searched-for coefficients, stages A and B.
Moreover the invention relates to equipment with which to implement the above described method.
The invention is elucidated below by a description of an illustrative and non-limiting implementation in relation to the attached drawing.
FIG. 1 is a functiona
REFERENCES:
patent: 4317994 (1982-03-01), Mallozzi et al.
patent: 4839913 (1989-06-01), Annis et al.
patent: 5060249 (1991-10-01), Eisen et al.
patent: 5479023 (1995-12-01), Bartle
Maitrejean Serge
Perion Didier
Sundermann Dietmar
Europ Scan S.A.
Porta David P.
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