Multiple scatter system for threat identification

Details Multiple scatter system for threat identification Multiple scatter system for threat identification

1999-11-24

2001-11-20

Church, Craig E. (Department: 2882)

X-ray or gamma ray systems or devices

Specific application

Diffraction, reflection, or scattering analysis

C378S086000

Reexamination Certificate

active

06320933

ABSTRACT:

TECHNICAL FIELD
The present invention relates to x-ray inspection of containers or of the ground, and, more particularly, to x-ray inspection employing the detection of backscatter radiation by means of multiple backscatter detectors in order to derive information including both density and effective atomic number with respect to sources of scattering.
BACKGROUND OF THE INVENTION
It is desirable to be able to determine the presence of objects, such as contraband, weapons, or explosives, that have been concealed in an enclosure, such as luggage or a shipping container. Conventional x-ray techniques provide measures either of attenuation, in the case of transmission techniques, or of scatter, in the case of scatter techniques.
The measurement of the intensity of x-rays backscattered from an object has been used extensively to give a measure of the effective atomic number of the object. Various methods of identifying a backscatter signal with a position within the illuminated object employ scanned pencil beams of x-rays, as described, for example, in U.S. Pat. Nos. 4,809,312 and 4,825,454 which are hereby incorporated herein by reference. In practice, the backscatter intensity may give only a crude measure of the atomic number of the object since the backscatter intensity is a function of several variables: the effective atomic number of the object; the object's geometry, including its distance from the x-ray source and the detectors; and the presence of material interposed between the object and the x-ray source/detector arrangement. In particular, current backscatter techniques do not provide a measure of the density of the scattering object.
SUMMARY OF THE INVENTION
In accordance with one aspect of the invention, in a preferred embodiment, there is provided an inspection system for analyzing the density of an object which may be concealed within an enveloping surface. The system has a source of penetrating radiation for emitting a beam having a propagation axis, the beam being incident upon the object. The system has a first scatter detector for detecting penetrating radiation scattered at least one time within the object and for generating a first signal, and, additionally, a second scatter detector, having a field of view, for generating a second signal corresponding to penetrating radiation that has been multiply scattered within the object. Furthermore, the system has a controller for determining an effective density of the object on the basis of at least the first and second signals. In accordance with alternate embodiments of the invention, the first scatter detector may be disposed at a first distance measured on an orthogonal to the propagation axis of the beam and the second scatter detector may disposed at a second distance measured on an orthogonal to the propagation axis of the beam, the second distance being greater than the first distance.
The field of view of the second scatter detector may be limited by at least one collimator to radiation that has been multiply scattered within the object, and the second scatter detector may also be limited by spectral sensitivity from detecting penetrating radiation scattered fewer than twice by the object.
In accordance with a further alternate embodiment of the invention, the system may have a third scatter detector for generating a third signal corresponding to penetrating radiation that has been multiply scattered within the object, such that the controller determines an effective density of the object on the basis of the first, second, and third signals. The source of penetrating radiation may be an x-ray source, and, more particularly, a radioactive x-ray source. The system may also have a scanner for moving the propagation axis of the beam of penetrating radiation relative to the object.
In accordance with further aspects of the present invention, in other embodiments, there are provided methods for analyzing an object concealed within the ground or within an enclosure. The methods have the steps of illuminating the ground or the enclosure with a beam of penetrating radiation, generating a first signal corresponding to penetrating radiation scattered at least one time within the object, generating a second signal corresponding to penetrating radiation that has been multiply scattered within the object, and determining an effective density of the object on the basis of at least the first and second signals.


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patent: 5430787 (1995-07-01), Norton
patent: 5763886 (1998-06-01), Schulte
patent: 0 864 884 A2 (1998-04-01), None
patent: WO 98/20366 (1997-07-01), None

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