X-ray or gamma ray systems or devices – Specific application – Absorption
Reexamination Certificate
1998-08-19
2001-02-20
Church, Craig E. (Department: 2876)
X-ray or gamma ray systems or devices
Specific application
Absorption
C378S057000
Reexamination Certificate
active
06192101
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the examination of a container by means of penetrating radiation in order to derive the masses of individual objects contained within the container.
BACKGROUND ART
X-ray radiography applied to the non-invasive inspection of the contents of containers is a mature technology carried out by a wide variety of methods. An early purpose of x-ray radiography was to produce a high resolution projected image for visual inspection of the contents. In the past decade, as the purposes of the inspection have become targeted to finding specific contraband such as drugs and explosives, methods of dual energy and backscatter radiography have been developed to measure the atomic number of the objects, as have tomographic techniques to measure the density of the objects and coherent scattering methods to measure the crystalline properties of objects. None of these advances have measured the masses of the objects inside the containers.
There are many instances where it is important to determine, in a non-invasive way, the mass of an object inside a container. For example, the U.S. Customs needs to verify that a container shipped into this country contains the goods described by the container manifest. Because it is impractical to open and examine even a fraction of the millions of containers that enter the country every year, the U.S. treasury loses considerable revenue from high-duty goods that are declared to be low-duty items. The manifest of a container lists the contents by description and weight. It is one purpose of this invention to provide a on-destructive means of verifying that the weights of the items in the container are those declared on the manifest. The invention for measuring masses can be an integral part of the well-used technique of dual-energy analysis so that both the mass and the atomic number of objects can be measured simultaneously to give additional information to compare with the manifest or to find contraband.
SUMMARY OF THE INVENTION
The present invention may be used advantageously to measure, in a non-invasive manner, the individual masses of objects in containers by means of x-ray radiography, to determine the distribution of masses of objects as a function of their position in the container, to determine the dimensional masses—the so-called DIM weights—of odd shapes, from radiographs taken from at least two angles, and to simultaneously measure the mass and the mean atomic number of objects in containers.
In accordance with one aspect of the present invention, in one embodiment, there is provided an apparatus for measuring the mass of one or more objects disposed within a container. Each object has a characteristic mass attenuation factor to penetrating radiation and the mass attenuation factor, which, in particular applications, may or may not be known, is a function at least of the energy of the penetrating radiation. The apparatus has a source of penetrating radiation for generating a beam incident upon the container at a region of incidence and a scanner for causing the region of incidence to traverse a planar projection of the container. Additionally, the apparatus has at least one detector having an output proportional to the intensity of the penetrating radiation traversing the container at the region of incidence, as well as a controller for determining the mass of the at least one object based on the output of the at least one detector and the characteristic mass attenuation factor of the object or objects.
In accordance with alternate embodiments of the present invention, the detector or detectors may include an energy selection arrangement, and the energy selection arrangement may permit analysis of penetrating radiation having energies dominated by Compton scattering. The energy selection arrangement may also permit analysis of penetrating radiation having energies in excess of 60 keV.
In further alternate embodiments of the present invention, the beam may include a fan beam, and may include a pencil beam. Additionally, there may be provided a fiducial mass for intermittent interposition in the beam for normalizing the output of the detector or detectors, and there may be a modulator for alternating interposition of a fiducial mass in the beam.
In accordance with another aspect of the present invention, there is provided a method for measuring the mass of at least one object having a characteristic mass attenuation factor to penetrating radiation, the mass attenuation factor being a function at least of the energy of the penetrating radiation and the object being disposed within a container. The method consists of the steps of generating a beam of penetrating radiation incident upon the container at a region of incidence, scanning the region of incidence such as to traverse a planar projection of the container, detecting the penetrating radiation traversing the container at the region of incidence, producing a detector output proportional to the intensity of the penetrating radiation traversing the container, and determining the mass of the at least one object based on the detector output and the characteristic mass attenuation factor of the at least one object. In accordance with other embodiments of the invention, the method may also include steps of interposing a fiducial mass alternatingly within the beam of penetrating radiation or of discriminating between detected penetrating radiation of energy greater and less than a predetermined discriminant energy. Additionally, the method may include the step of storing the detector output in at least one memory array to produce at least one image.
Where a fiducial mass is intermittently interposed in the beam of penetrating radiation, the step of storing the detector output may include storing the detector output corresponding to an interposed fiducial mass in a first memory array to produce a first image and storing the detector output corresponding to no interposed fiducial mass in a second memory array to produce a second image. The method may also include determining a characteristic atomic number associated with the object or objects.
In accordance with yet another aspect of the present invention, there is provided a method for measuring the mass of an object or of multiple objects, each object having a characteristic mass attenuation factor to penetrating radiation, the mass attenuation factor being a function at least of the energy of the penetrating radiation, the objects being disposed within a container. This method has the steps of generating a beam of penetrating radiation incident upon the container at a region of incidence, scanning the region of incidence such as to traverse a plurality of projections of the container onto a plurality of planes, detecting the penetrating radiation traversing the container at the region of incidence, producing a detector output proportional to the intensity of the penetrating radiation traversing the container, and determining the dimensional mass of the object or objects based on the detector output and the characteristic mass attenuation factor of the object or objects.
REFERENCES:
patent: 5040199 (1991-08-01), Stein
patent: 5585603 (1996-12-01), Vogeley
American Science & Engineering, Inc.
Bromberg & Sunstein LLP
Church Craig E.
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