X-ray or gamma ray systems or devices – Specific application – Absorption
Reexamination Certificate
1998-11-02
2001-10-09
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Absorption
C378S051000, C378S053000, C378S054000, C378S055000
Reexamination Certificate
active
06301326
ABSTRACT:
FIELD OF INVENTION
This invention relates to a detection system for detecting thin sheets of material, and more particular to a system for detecting sheets of organic material including contraband materials such as drugs and explosives.
BACKGROUND OF INVENTION
There are a number of different techniques for detecting objects in closed containers such as suitcases and boxes carried by airplanes which involve conveying the suitcases past an X-ray scanner. In particular, contraband such as drugs or explosive materials are sought to be detected by discerning their densities and/or atomic number using dual energy approaches. The dual energy atomic number approach relies on the fact that when an X-ray beam strikes material the energy of the beam is diminished either because of absorption (the photoelectric effect &mgr;
pe
) or because of scattering (the Compton scattering effect &mgr;
cs
) and that the probability of the photoelectric effect, &mgr;
pe
, changes markedly with increased energy while the compton scattering, &mgr;
cs
, does not. Since &mgr;
pe
is a function of atomic number/energy and &mgr;
es
is a function of atomic mumber, these expressions can be solved for atomic number by using two different X-ray energy levels, e.g., 40 Kev and 90 Kev. In the case of explosives the materials sought are organic, containing carbon, nitrogen and oxygen, and have an atomic number of around 7. Heavier metals such as iron and chromium often found in luggage have atomic numbers of 28 or higher, and aluminum and chlorine have atomic numbers of around 12. Therefore, there is a comfortable margin for detection of the organic explosives. See “Device and Method for Inspection of Baggage and Other Objects”, Krug et al., U.S. Pat. No. 5,319,547.
Density is also used to detect explosives because they typically have a density of 1.2-1.9 gm/cm
3
for military and 1-1.4 gm/cm
3
for commercial grade explosives which are well separated from the densities of other materials commonly found in luggage. Since a single dimension X-ray system can only produce a two dimensional or areal density, that is, weight per unit area related to the projected area of an object, it is not entirely reliable: the projected density is a composite of all densities in the line of the X-ray beam and one material can mask another. To overcome this and other shortcomings a three-dimensional scanner was developed. See “Three-Dimensional Reconstruction Based on a Limited Number of X-Ray Projections”, Bjorkholm et al., U.S. Pat. No. 5,442,672.
But even this approach is subject to failure when thin sheets of explosive or other contraband are imaged perpendicularly or transversely relative to the sheet. A sheet imaged on edge, i.e., aligned with a scanning beam, is highly contrasted and detectable but when it is crosswise or wholly perpendicular to the scanning beam its thin dimension gives a very low areal density, e.g., less than 1 gm/cm, easily obscured when combined with the other objects in the line of sight. Such sheets of material are most likely to be disposed or secreted in the broad sides of a suitcase, not in the narrower ends or top and bottom, so they are not likely to be seen on edge. The only present technique for detecting these sheets with good reliability are computerized axial tomography systems which are large, complex and expensive.
SUMMARY OF INVENTION
It is therefore an object of this invention to provide an improved detection system which can detect thin sheets of material.
It is a further object of this invention to provide such a detection system which can detect thin sheets of organic material.
It is a further object of this invention to provide such a detection system which can detect thin sheets even when they are aligned in the broad sides of a container or luggage.
It is a further object of this invention to provide such a detection system which is simple and inexpensive and requires no complicated solutions.
The invention results from the realization that a truly effective detection system capable of exposing even a thin sheet of contraband such as explosives or drugs hidden density in a container can be achieved by shifting the X-ray source as it scans so that at at least one point the X-ray beam will align with a contraband sheet in one of its possible orientations in the container producing a high contrast, highly detectable edge-on view.
This invention features a detection system for detecting sheets of material. There are means for moving along a path a container which can harbor a sheet of material and an X-ray scanner having a scanning beam for scanning across the path of the container through a predetermined angle. There are means for shifting the origin of the scanning beam to align during at least a portion of the scan the scanning beam with the sheet for producing a high projected density contrasted with its surroundings.
In a preferred embodiment the X-ray scanner may include an X-ray source and a spaced detector and the means for shifting may include a movable member for supporting the source and the detector. Alternatively, the X-ray scanner may include an X-ray source and a spaced detector and may include the means for shifting may include a movable member for supporting the source. The X-ray scanner may include an X-ray source including a plurality of individual sources and said means for shifting may include means for sequentially enabling the individual sources. The X-ray scanner may include a linear X-ray anode and said means for shifting may include means for sweeping an electron beam across the anode for generating a series of X-ray scanning beams. The X-ray scanner may include a detector for detecting X-ray energy transmitted by the sheet. The X-ray scanner may include means for determining whether the X-ray energy detected from the sheet represents an areal density within a target envelope of areal densities. The X-ray scanner may include a threshold detector for determining whether the areal density representative of the sheet exceeds a predetermined level. The detector may include a dual energy detector for detecting high and low X-ray energies. The means for determining may include a look-up table of stored areal densities within the target envelope. The X-ray scanner may include a storage device for storing areal densities representing a set of scans of the sheet. The X-ray scanner may include an envelope comparator for determining whether the areal density which exceeds the threshold represents an atomic number indicative of a sheet of the particular material sought. The X-ray scanner may include an angular response circuit for determining the angular response of a set of scans. The angular response circuit may include means for determining symmetry in the areal density of scans surrounding a scan which exceeds the threshold level to confirm the presence of a sheet. The angular response circuit may include means for determining the slope of the angular response of the areal densities of a set of scans indicative of the presence of a sheet of material. The X-ray scanner may provide a fan beam of X-ray energy.
REFERENCES:
patent: 4029963 (1977-06-01), Alvarez et al.
patent: 4349740 (1982-09-01), Grassmann et al.
patent: 5237598 (1993-08-01), Albert
patent: 5319547 (1994-06-01), Krug et al.
patent: 5442672 (1995-08-01), Bjorkholm et al.
patent: 5479023 (1995-12-01), Bartle
patent: 5638420 (1997-06-01), Armistead
patent: 5642393 (1997-06-01), Krug et al.
patent: 5818897 (1998-10-01), Gordon
patent: 5838759 (1998-11-01), Armistead
patent: 5970113 (1999-10-01), Crawford et al.
patent: 6026143 (2000-02-01), Simanovsky et al.
patent: 6035014 (2000-03-01), Hiraoglu et al.
patent: 6088423 (2000-07-01), Krug et al.
patent: 6167113 (2000-12-01), Armentrout et al.
Grodzins, L., “Photons in—Photons Out: Non-Destructive Inspection of Containers Using X-Ray and Gamma Ray Techniques”, Proceedings of the 1st International Symposium on Explosive Detection Technology, pp. 201-225, Nov. 1-15, 1991.
Kuauss et al., “Signatures of Explosives by Elemental Composition Analysis”, Proceedings o
Ho Allen C.
Iandiorio & Teska
Kim Robert H.
PerkinElmer Detection Systems, Inc.
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