WO2006011899A1

WO2006011899A1 - Security system for detecting nuclear masses

Info

Publication number: WO2006011899A1
Application number: PCT/US2004/039730
Authority: WO
Inventors: Stanley B. Alterman
Original assignee: L-3 Communications Security and Detection Systems Corporation
Priority date: 2003-11-25
Filing date: 2004-11-26
Publication date: 2006-02-02

Abstract

An inspection system for screening items for nuclear material, such as may be concealed in containerized cargo, suitcases or other containers. The system employs microgravitometers to sense perturbations in the gravitational field such as may be caused by nuclear material. Outputs of the microgravitometers are processed to identify items containing nuclear materials or to select items for further inspection. Processing may include combining the gravity measurements with information obtained with other inspection technologies. The processing may be done manually, such as by presenting an image to a human operator. Processing may be fully automated, such as being performed by a computer, or may be partially automated, such as by presenting a partially processed image to a human operator.

Description

SECURITY SYSTEM FOR DETECTING NUCLEAR MASSES

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Application Serial No. 60/525,090, entitled "Security System that Detects Nuclear Masses," filed on November 25, 2003, which is herein incorporated by reference in its entirety.

BACKGROUND OF INVENTION

1. Field of Invention

This invention relates generally to security and inspection systems and more particularly to security and inspection systems that employ gravity measurements to detect suspicious objects.

2. Discussion of Related Art

Security and inspection systems are widely used to screen items. The purpose of screening is often to detect contraband objects hidden within the items and to block the contraband items from entering a particular location. For example, scanners that detect plastic explosives or conventional explosive materials are widely used at airports to block these contraband items from being taken onto airplanes.

Many inspection technologies are used to screen items. For example, systems using X-ray based imaging are widely used. X-ray imaging systems can be used to observe the outline of objects within an item. Some systems create 2-dimensional images and others, such as those which use computed tomography (CT), create 3- dimensional images. X-ray systems are available that can also determine material properties of objects, such as the atomic number of the material. Examples of such systems are found in US patent 5,319,547 to Krug et al. entitled Device and Method for Inspection of Baggage and Other Objects; and 5,642,393 to Krug et al. entitled Detecting Contraband by Employing Interactive Multiprobe Tomography; 5,917,880 to Bjorkholm entitled X-Ray Inspection Apparatus, all of which are hereby incorporated by reference.

As the severity of threats to national security increases, the nature of objects that must be detected by scanning also increases. The number of places in which scanning must be performed also increases. Thus, there is an ever increasing need for new scanners that can detect more sophisticated threats. Additionally, there is a need for these scanners to be fast, accurate and easy to use so that they can be widely deployed.

One threat of particular concern is that posed by nuclear materials. Such materials have the potential for being incorporated into weapons that could create significant damage.

It would be desirable to have an improved system and method for screening objects that may contain contraband nuclear objects.

SUMMARY OF INVENTION

In one aspect, the invention relates to a method of detecting contraband objects within an item under inspection, the method includes sensing the gravitational force adjacent the item under inspection to obtain information on the gravitational force and making a threat assessment based on the information on the gravitational force.

In another aspect, the invention relates to a security system. The security system includes at least one force sensor having an output with a value representative of the gravitational force sensed. A processor, coupled to the output of the force sensor, has a program adapted to process the output of the force sensor as part of making a threat assessment.

In yet a further aspect, the invention relates to a security system for detecting nuclear contraband in an item under inspection. The system includes an array comprising a plurality of gravitational force sensors, the array having an output reflecting the gravity sensed by each of the plurality of gravitational force sensors. A processor, coupled to the output of the array, has a program adapted to process the output of the array to classify regions in the item under inspection based on the mass concentration of the regions and position of the regions relative to the array.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings:

FIG. 1 is a sketch illustrating a system according to an embodiment of the invention deployed at a border crossing; and

FIG. 2 is a sketch illustrating a system according to an alternative embodiment of the invention deployed at a cargo inspection facility.

DETAILED DESCRIPTION

This invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of "including," "comprising," or "having," "containing," "involving," and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.

FIG. 1 shows a security system 110 that may be used to screen items such as baggage, shipping containers for cargo, trucks, or other containers in which the contents cannot be readily observed. The system may be used to detect nuclear material inside containers. Here the containers are vehicles, such as a truck 112. In the example of FIG. 1, the system is deployed at a checkpoint 150, such as a tollbooth, border crossing, cargo loading facility or other location through which trucks may pass.

System 110 uses microgravitometers, such as 120, to detect nuclear material. In the illustrated embodiment, microgravitometers are positioned in arrays IM₁ and 114₂. The arrays are positioned so that truck 112 will pass near the arrays as the truck goes through the checkpoint 150.

Each microgravitometer produces an output representative of the gravity at the microgravitometer. These outputs can be processed, such as with a computer, to identify suspicious items which may represent nuclear masses. The system operates under the principle that all objects exert gravitational force on other objects. The force is given by a formula called the law of universal gravitation:

where K_ay iκprEsentsthe£-mBofgtavit^between.two cibjects *— ^• meam 'prapcartionalto' m-_j represents the mass of object 1 m₂ represents the mass of object 2 d represents the distance separating line objects¹ centeis

The formula indicates that the amount of gravitational force exerted on one of the objects depends on the mass of the objects and the distance between the objects.

A container, and all objects in it, will create a gravitational force. This gravitational force is small relative to the earth's gravitational field. However, the force produces a small distortion in the gravitational field. Nuclear materials, because they have a high mass concentration, will exert more gravitational force than other less dense objects likely to be in the container. Consequently the presence of nuclear material creates more distortion in the gravitational field near the container - though still small in relation to the earth's gravitational field. A detector near the container that is sensitive to small differential gravitational forces can be used to detect the presence of nuclear material from the differential gravitational forces.

A microgravitometer is a sensor that is sensitive to very small differential gravitational forces. Because materials with higher mass concentrations create more gravitational attraction than less dense materials, the output of the microgravitometer indicates when material with a high mass concentration is close by. Because nuclear material has a high mass concentration, the output of a microgravitometer can be used to indicate when nuclear material is close to the sensor, even when the earth's gravitational attraction is large.

If a container with nuclear material moves past a microgravitometer, the output of the microgravitometer will change as the portion of the container with the nuclear material passes the microgravitometer. A system to detect nuclear material can be formed by analyzing the output of the microgravitometer to detect a pattern indicating a large mass concentration, such as would result from a nuclear material in the container. In one embodiment, this analysis is done automatically by an electronic circuit. For example, such analysis can be performed with a computer programmed to analyze the sensor output and identify regions of dense material in the item under inspection.

In the embodiment of FIG. 1, the microgravitometers such as are deployed in arrays 114i and 114₂ around a portal through which a truck 112 passes. In this case, the "container" being scanned is the truck. Truck 112 has mass regardless of whether it contains any nuclear material. As truck 112 passes the arrays 1 H₁ and 114₂, the outputs of the microgravitometers change. However, the microgravitometers will change more when truck 112 contains nuclear material than if it contains less dense materials. And, those microgravitometers closest to the nuclear material will change the most. As trucks are screened, the output signals from the microgravitometers can be analyzed, for example by comparing them to signals that would result if there were nuclear material in the truck. In this way, the presence of nuclear material can be indicated.

It is not necessary that the screening system predict the presence of nuclear material with 100% certainty. Analysis of the outputs of the microgravitometers can be used to indicate which containers should be examined further. For example, while it may not be possible to thoroughly search every truck passing through a certain checkpoint, a system that indicates which trucks are likely to contain nuclear material would still be a significant advantage because it would allow limited resources to be deployed to search only those containers most likely to contain threat material.

In some situations, it may be desirable for the microgravitometers to be used in connection with other sensor technology to increase the accuracy with which nuclear material is identified. FIG. 2 shows a system 210 in which microgravitometers are used in connection with X-ray imaging technology.

System 210 incorporates an X-ray imaging system that includes an x-ray source 250 and an x-ray detector array 252. Here, a linear array is shown, but any suitable shape may be used for detector array 252. The X-ray source 250 and X-ray detector array 252 combine to form an x-ray scanner that may form an x-ray image of crate 212 as it moves on conveyor 216 past detector array 252.

The X-ray scanner can be of the type described in one of the above referenced patents, such as a multi-energy system, that is capable of measuring an effective atomic number of objects in the item under inspection. The X-ray scanner could be a line scanner that forms a 2-dimensional projection or CT type scanner, with or without multi- energy capabilities.

In FIG. 2, the item under inspection is a packing crate 212. Crate 212 is moved on conveyor 216. Conveyor 216 moves past the X-ray scanner formed by source 250 and detector array 252 and the gravitational scanner formed by microgravitometer array 214. The outputs of both are coupled to a computer, which may be a component of work station 260 or located in any other suitable place. The computer is programmed to combine the information provided by both the X-ray scanner and the microgravitometer array to produce a more reliable indication of nuclear material than either would produce alone.

In the illustrated embodiment, work station 260 contains a computer that combines the information from the X-ray scanner and the microgravitometer array into an image for a human operator 262 to observe. In the example of FIG. 2, the computer creates a display 264 that includes an outline of the item being scanned. In this embodiment, the X-ray imaging system is capable of detecting nuclear materials by measuring the atomic number of the material according to a projection imaging technique described in one of the above referenced patents. The X-ray imaging system may alternatively be a dual energy tomographic system of the type known in the art or hereafter developed. When the output of the X-ray detector indicates the presence of nuclear material, the computer marks the location of the nuclear material within the outline of the container.

However, detecting nuclear material with X-rays alone is not effective when the nuclear material is near shielding 232, such as lead or other material that blocks or reflects X-rays and therefore prevents X-rays from source 250 from reaching detectors 252. In this scenario, microgravitometers, such as 220, can be used to more accurately indicate the presence of nuclear materials. The microgravitometers are arranged in an array 214 that is positioned so that create 212 will pass near it. The computer can be programmed to correlate the information provided by the X-ray scan and the microgravitometer scan, thereby determining whether the areas shielded from X-ray inspection have a high mass concentration and indicating a threat of nuclear materials. The computer is programmed to detect areas in the container where shielding is present. For example, a very low amount of X-rays reaching the X-ray detector array 252 at a certain time indicates shielding in crate 212 along the path between source 250 and detector array 252 at that time. As pictured in FIG.2, shielding 232 may prevent object 230 from appearing in an X-ray image.

In the illustrated embodiment, the X-ray imaging system produces a 2- dimensional projection through the container. With a 2-dimensional projection, the computer can indicate the shielded region as a projection in the plane perpendicular to the X-ray sensor. For the embodiment illustrated in FIG. 2, this plane is relative to the front-back and top-bottom directions. If an X-ray scanner can produce a 3 -dimensional view of objects, the shielded region can be indicated in a 3 -dimensional representation of the item under inspection, such as may be made with computer graphics processing.

In the illustrated embodiment, the correlation between the X-ray sensor outputs and microgravitometer outputs can be performed based on the time at which outputs are measured and position of the microgravitometers within the arrays. For example, the sketch in FIG. 2 shows a region near the lower front corner of crate 212 that is shielded from X-rays by material 232. The computer may be programmed to determine when that region of the container is passing the microgravitometer array 214. The computer can examine the outputs of the microgravitometers produced at that time. If the outputs of the microgravitometers are higher as that region passes, it can be determined that the region contains dense material that may warrant further investigation. Likewise, if the microgravitometers near the lower portion of the array produce larger outputs than the other microgravitometers, the computer can indicate the presence of a high mass concentration indicative of nuclear material.

In some embodiments, the computer is programmed to apply a threshold before indicating the presence of nuclear material. The threshold may be an absolute value or may be a value computed dynamically. An example of a threshold is a predetermined percentage difference between one microgravitometer output and outputs of other microgravitometers in the array . Another example of a threshold is a predetermined percentage difference between outputs of the same microgravitometer at the time when a certain region of the item under inspection is passing array 214 and some other time when a different portion of item under inspection is passing the array 214. A further example of a threshold is a microgravitometer output exceeding a predetermined absolute level. Where absolute levels are used, it may be desirable to calibrate the microgravitometer sensors with a test mass having a mass concentration representative of nuclear material corresponding to a threat.

Where the X-ray imaging system forms a 3 -dimensional image such that the computer can represent in a 3 -dimensional coordinate system where inside the container the shielded region is located, the computer can combine the outputs of different microgravitometer arrays to better correlate the output of the microgravitometers with the outputs of the X-ray sensors. In FIG. 2, microgravitometer sensors encircle the container. By comparing outputs of microgravitometers that have the same height relative to the floor of the container but different positions relative to either side, the computer can determine the relative side-to-side position of a region of high mass concentration.

In one embodiment, regions that are both shielded from X-ray inspection and have a high mass concentration can be indicated with a high confidence to contain threat materials. In the illustrated embodiment, a human operator 262 is presented with a display screen that shows the outline of the container. Within that outline is an indication of an obscured region. The outline of the container may be derived from X- ray image data, from visible image data or in any other suitable way. Within the area representing that obscured region, there is an indication of an object with a high mass concentration. From this display, the operator can see that there is a sufficient risk that the container contains nuclear material to warrant further action. For example, the container may be physically searched or denied passage.

FIG. 2 shows that the computer analyzing the scan data presents display 264 to a human operator 262 for a decision. It is alternatively possible that, without human intervention, the computer could make a determination that there is a threat of nuclear material in a specific container and automatically take an action in response.

In one embodiment, a known microgravitometer can be used.

Microgravitometers are used, for example, in submarine navigation. Microgravitometers in submarines are so sensitive that they can detect changes in the gravitational force caused by variations in the make-up of the earth's surface below the water or even man- made distortions caused by large or heavy objects. A gravitational gradient is sensed, which the submarine navigation system compares to a pre-stored gradient map to find the current location of the submarine.

However, any device now known or hereafter developed that is sensitive to small changes in the gravitational force could be used as a microgravitometer. For example, a microgravitometer could be constructed as a Micro Electro-Mechanical (MEMs) device. MEMs are fabricated using semiconductor processing techniques to form very small structures - such as beams, tuning forks, accelerometers or other shapes sensitive to gravitational change. The small beams deflect differently as the gravitational force changes. By measuring the deflection of the beam, the differential force on the beam could be determined. Deflection of the beam may be measured directly, for example using laser interferometer measurements. Or, the deflection of the beam could be measured indirectly by measuring the stress in the beam, for example.

Any other object or energy impacted by gravity could be used to make a microgravitometer. For example, the properties of a quantum well device under the influence of gravity may serve as the basis for a microgravitometer. Likewise, a microgravitometer could be constructed with a system that measures changes in the axis of rotation of a rotating object or even incremental effects of gravity on laser beams.

Having thus described several aspects of at least one embodiment of this invention, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art.

For example, in the above described systems, an object is moved relative to a microgravitometer sensor. This relative motion allows dense materials to be detected because of changes in the gravitational field near the microgravitometer as the high mass object moves past the sensor. The same effect can be achieved by moving the microgravitometer relative to the object. Alternatively, it is not necessary that relative motion be used to detect a high mass object. The microgravitometers could be calibrated so that outputs above a certain threshold indicate a high mass object in the vicinity of the microgravitometer. Also, relative motion allows a limited number of sensors to scan a large area. Where more sensors can be used, there is less need for relative motion.

In the embodiments illustrated above, differently shaped arrays of microgravitometers are used. The shape of the array is not critical to the invention. It is contemplated that the ideal shape of the array will vary based on the intended application. Further, it is contemplated that there will be some applications in which an array is not required. A system may be built around a single microgravitometer.

As another example, it was described that the X-ray images were used to determine positions of suspicious regions within the container. It is possible that the position of suspicious regions may be detected by measuring x-rays emitted from the object. Or, other scanning techniques may be used, such as those that employ other types of photons or energy, to scan an object. Accordingly, the term X-rays as used herein should be understood to refer to radiation that partially penetrates and partially interacts with items of interest, such that it may be used to obtain information about objects within an item and is not limited to radiation of any specific wavelength.

As yet another example, a transmission X-ray system was used for the X-ray scan. A back scattered X-ray system could be used instead of or in addition to a transmission type X-ray system to more accurately locate areas of shielding.

As a further example, it is possible that motion or position sensors could be incorporated into the system to aid in correlating the output of the X-ray sensor and the microgravitometer sensor.

Also, where it was described that outputs of different microgravitometers in the arrays could be compared, a system could be formed that includes a mechanism to measure the extent of the container to ensure that only outputs of sensors adjacent the container are used in processing. The extent of a container can be measured any way now known in the art or hereafter developed. For example, a "light curtain" is sometimes used to measure the extent of article. Alternatively, ultrasound sensors can be used. As another example, an optical image may be used to identify the extent of the item under inspection.

Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description and drawings are by way of example only.

What is claimed is:

Claims

1. A method of detecting contraband objects within an item under inspection, comprising: a) sensing the gravitational force adjacent the item under inspection to obtain information on the gravitational force; b) making a threat assessment based on the information on the gravitational force.

2. The method of claim 1 wherein making a threat assessment comprises correlating the sensed gravitational force to the density of a region within the item under inspection.

3. The method of claim 1 wherein sensing the gravitational force comprising sensing the gravitational force while moving the item under inspection relative to a gravity sensor.

4. The method of claim 1 : a) additionally comprising scanning the item under inspection with an x-ray imaging system to produce x-ray information about the item under inspection; and b) wherein making a threat assessment comprises correlating the x-ray information with the information on the gravitational force.

5. The method of claim 4 wherein correlating the x-ray information with the information on the gravitational force comprises identifying from the x-ray information a region within the item under inspection that is shielded from x-rays and indicating that region as suspicious when the sensed gravitational force adjacent that region has a value exceeding a threshold.

6. The method of claim 5 wherein the x-ray information includes an x-ray image of the item under inspection and the method additionally comprises displaying the x-ray image of the item under inspection and a threat indication superimposed thereon when the region is indicated as suspicious.

7. The method of claim 5 wherein the x-ray information comprises multi-energy x- ray information and making a threat assessment comprises using the multi-energy information to determine the effective atomic number of a region in the item under inspection that is not shielded from x-rays and indicating a threat when that region has an effective atomic number in a range correlated to the effective atomic number of nuclear material.

8. The method of claim 1 additionally comprising subjecting the item under inspection to further examination selectively in response to the threat assessment.

9. The method of claim 1 wherein: a) sensing the gravitational force comprises making a plurality of measurements with a sensor during a time interval with the sensor having a changing positional relationship with the item under inspection during the time interval; and b) making a threat assessment comprises detecting changes in the sensed gravitational force over time.

10. The method of claim 1 additionally comprising a) moving the item under inspection relative to a gravitational sensor; b) sampling the output of the gravitational sensor at a plurality of times to produce a sampled signal; and c) analyzing the sampled signal to detect a pattern indicating a high mass concentration passing the gravitational sensor.

11. A security system comprising: a) at least one force sensor having an output with a value representative of the gravitational force sensed; b) a processor, coupled to the output of the force sensor, the processor having a program adapted to process the output of the force sensor as part of making a threat assessment.

12. The security system of claim 11 deployed at a border crossing.

13. The security system of claim 11 deployed at an airport.

14. The security system of claim 11 deployed at a cargo terminal.

15. The security system of claim 11 wherein the at least one force sensor comprises an array of force sensors.

16. The security system of claim 11 wherein each gravity sensor comprises a MEMS device.

17. The security system of claim 16 wherein each MEMS device comprises a beam and the output of the force sensor reflects the deflection of the beam.

18. The security system of claim 17 wherein each force sensor additionally comprises a laser interferometer positioned to measure the deflection of the beam.

19. The security system of claim 17 wherein each force sensor additionally comprises a strain sensor positioned to measure strain caused by deflection of the beam.

20. The security system of claim 11 additionally comprising a user interface coupled to the processor, and wherein the program is adapted to control the display to present information relating the threat assessment.

21. The security system of claim 20 additionally comprising a radiation-based imaging system, the radiation based imaging system having an output providing information obtained by the radiation-based imaging system, the output coupled to the processor, and wherein the program is further adapted to derive information by processing the output of the force sensor and to synthesize information obtained by the radiation-based imaging system with information derived by processing the output of the force sensor.

22. A security system for detecting nuclear contraband in an item under inspection, comprising: a) an array comprising a plurality of gravitational force sensors, the array having an output reflecting the gravity sensed by each of the plurality of gravitational force sensors; and b) a processor, coupled to the output of the array, the processor having a program adapted to process the output of the array to classify regions in the item under inspection based on the mass concentration of the regions and position of the regions relative to the array.

23. The security system of claim 22 additionally comprising a display coupled to the processor, and wherein the program is adapted to control the display to present an image reflecting the classification of regions in the item under inspection.

24. The security system of claim 22 wherein the program is adapted to process the output to classify regions of material based on mass concentration and position relative to the array based on the gravity sensed by one or more of the plurality of gravitational force sensors in the array sensing gravity in a magnitude above a threshold.