Method of detecting concealed nuclear materials on a cargo-carrying vehicle

METHOD OF DETECTING CONCEALED NUCLEAR MATERIALS ON A CARGO-CARRYING VEHICLE

BACKGROUND OF THE INVENTION

0003Field of the Invention

0004[0001] This invention relates generally to the detection of concealed nuclear materials. More particularly, this invention relates to a method of detecting concealed nuclear materials on a cargo-carrying vehicle. Description of the Related Art

0005[0002] The detection and interdiction of nuclear materials that might be clandestinely shipped to the United States is an item that is crucial to the interest of the United States government. Accordingly, various methods have been developed to detect nuclear material that might be concealed in shipping containers that have been unloaded from a cargo-carrying vehicle once the cargo-carrying vehicle has reached the United States. For instance, after a shipping container has been unloaded from the cargo-carrying vehicle, the shipping container can be subjected to one or more Portal Monitors. Portal Monitors are comprised of a variety of neutron and gamma-ray radiation detectors that are designed to detect whether a nuclear material is contained in the shipping container. Another method utilized to detect whether nuclear material has been concealed in a shipping container is through the use of X-ray radiography systems. X-ray radiography systems are designed to detect high density or high atomic number objects, which could potentially be nuclear material. Moreover, similar to X-ray systems used at virtually all airports around the world, the X-ray radiography systems used to screen a shipping container allow an individual inspecting the shipping container to detect unusually shaped objects, which could be an indication of concealed nuclear material, within the shipping container. [0003] The drawback to these methods is that the shipping container must be subjected to the screening process at the port of entry. This means that the shipping container, and the vehicle on which it was transported, has reached U.S. soil. Another drawback to these methods is that the amount of time given to screen a shipping container could be on the order of seconds or minutes once the shipping container has been unloaded from the cargo-carrying vehicle since commercial cargo is unloaded and shipped from the receiving site in an expedited manner. Accordingly, there is a need for a method of detecting nuclear material that might be concealed in the cargo of a cargo-carrying vehicle, which is bound for the United States, prior to the cargo being unloaded from the cargo-carrying vehicle.

SUMMARY OF THE INVENTION

0007[0004] This need and others are met by embodiments of this invention, which provide a method for detecting nuclear materials that might be concealed in the cargo of a cargo-carrying vehicle prior to unloading the cargo from the cargo-carrying vehicle.

0008[0005] In accordance with one embodiment of the invention, a method for detecting a fissile material on a cargo-carrying vehicle that includes: deploying a number of dosimeters in a number of locations in the cargo-carrying vehicle; and analyzing an output of the number of dosimeters to determine whether the fissile material is on the cargo-carrying vehicle.

0009[0006] In accordance with yet another embodiment of the invention, a method of detecting a fissile material on a cargo-carrying vehicle that includes: deploying a number of dosimeters in a number of locations in the cargo-carrying vehicle; and electronically monitoring the number of dosimeters to determine whether the fissile material is on the cargo-carrying vehicle.

0010[0007] In accordance with another embodiment of the invention, a cargo-carrying container that includes: a base having a first end, a second end, a first side, and a second side; a first side wall is connected to and extends from said first side of said base; a second side wall is connected to and extends from said second side of said base; a first end wall is connected to and extends from said first end of said base; a door is attached to an end of each of said first and second side walls, each of said doors being adjacent to said second end of said base; a top wall that is substantially parallel to said base is connected to each of said first side wall, said second sidewall, and said first end wall; and a number of dosimeters are disposed on a perimeter of said cargo-carrying container.

0011[0008] One object of this invention is to provide a method for detecting a concealed nuclear material on a cargo-carrying vehicle prior to the cargo-carrying vehicle reaching the United States. [0009] Another object of this invention is to provide a method for detecting concealed nuclear material on a cargo-carrying vehicle prior to cargo-carrying vehicle being unloaded of its cargo.

0012[0010] Another object of this invention is to provide a method of detecting concealed nuclear material on a cargo-carrying vessel, such as a ship, prior to the vessel reaching a port that is located in the United States.

0013[0011] Another object of this invention is to provide a method of determining the location of the concealed nuclear material on the cargo-carrying vehicle once it has been determined that there is nuclear material on the cargo-carrying vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

0015[0012] A full understanding of the disclosed and claimed concept can be gained from the following Description when read in conjunction with the accompanying drawings in which:

0016[0013] FIG. 1 is plan view of a cargo hold in a cargo-carrying vehicle, such as a ship, with a number of dosimeters deployed throughout the cargo hold; [0014] FIG. 2 is a cross-sectional view of a radiation dosimeter that can be utilized in the disclosed invention;

0017[0015] FIG. 3 is a cross-sectional view of an active dosimeter that can be utilized in the disclosed invention; and

0018[0016] FIG. 4 is an isometric view of a cargo-carrying container with dosimeters disposed on a periphery of the cargo-carrying container.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

0020[0017] As used herein, the term "dosimeter" and variations thereof shall broadly refer to devices that have the capability of measuring or detecting radiation, doses of radiation, or radioactive material. It is understood that the term includes neutron dosimeters and gamma-ray dosimeters.

0021[0018] As used herein, the term "vehicle" and variations thereof broadly includes, without limitation, automobiles, locomotives (trains), aircraft, tractor trailers or water faring vessels such as ships or boats.

0022[0019] As used herein, the term "cargo-carrying vehicle" and variations thereof shall broadly refer to a vehicle that is carrying cargo such as shipping containers or shipping boxes. [0020] As used herein, the term "cargo hold" refers broadly to an area where cargo is kept or secured during transport.

0023[0021] As used herein, the term "a number" and variations thereof shall mean a plurality.

0024[0022] As used herein, the term "detection radius^" and variations thereof refers to the dosimeter's effective radius (range) for detecting radiation or material emitting radiation.

0025[0023] As used herein, the term "mechanical fastener" and variations thereof refers to any suitable fastening, connecting or tightening mechanism including, but not limited to, screws, bolts, and the combination of bolts and nuts.

0026[0024] When referring to any numerical range of values, such ranges are understood to include each and every number and/or fraction between the stated range minimum and maximum.

0027[0025] Directional phrases used herein, such as, for example, upper, lower, left, right, vertical, horizontal, top, bottom, above, beneath, clockwise, counterclockwise and derivatives thereof, relate to the orientation of the elements shown in the drawings and are not limiting upon the claims unless expressly recited therein.

0028[0026] As stated above, various methods have been developed to detect nuclear material that might be concealed in shipping containers that have been unloaded from a cargo-carrying vehicle once the cargo-carrying vehicle has reached the United

0029States. Unlike these methods, however, the method disclosed in this invention allows the cargo of a cargo-carrying vehicle to be screened for nuclear material during the voyage to the United States thereby allowing for the determination of whether a nuclear material has been concealed amongst the cargo prior to the cargo being unloaded from the cargo-carrying vehicle.

0030[0027] Referring to FIG. 1, in one embodiment of the invention a number of dosimeters 2, such as neutron dosimeters, are deployed throughout a cargo-carrying vehicle prior to the cargo-carrying vehicle's departure for the United States. In the embodiment depicted in FIG. 1, the dosimeters 2, which have an approximate detection radius 4, are deployed throughout the cargo hold 6 of the cargo-carrying vehicle in a manner that allows the dosimeters 2 to monitor the area in which the cargo 8 is located for concealed nuclear materials by detecting whether radiation, such as neutron radiation, is being emitted from the cargo 8. The dosimeters that are deployed in the cargo-carrying vehicle can be of any type including, but not limited to, neutron dosimeters and gamma-ray detectors. As will be explained in greater detail below, the dosimeters that are used in one embodiment of the invention are Solid State Track Recorder (SSTR) neutron dosimeters. In yet another embodiment of the invention, the dosimeters that are used are active dosimeters that can be monitored electronically. Once the dosimeters have been deployed in the cargo- carrying vehicle, the dosimeters will begin to detect and record whether there are nuclear materials in the cargo. Prior to the cargo-carrying vehicle reaching the United States, the locations of the dosimeters are mapped before they are removed from the cargo-carrying vehicle or the detected counts are transmitted electronically to a remote facility if active dosimeters are used. If the dosimeters are removed from the cargo-carrying vehicle, then the dosimeters are transported to a remote facility that analyzes the dosimeters to determine whether the dosimeters recorded any unusual levels of radiation in the cargo hold or in the cargo. If it is determined that there is nuclear material concealed in the cargo, then location of the concealed nuclear material can be determined by utilizing the dosimeters in a variety of ways. For example, if a dosimeter is located relatively close to a radioactive source, then the dosimeter will record a high radiation reading. In contrast, if a dosimeter is located relatively far from a radioactive source, then the dosimeter will record a low radiation reading. Accordingly, the location of the concealed radioactive material can be determined by analyzing whether one or more dosimeters that are located near a particular shipping container have a high radiation reading. If so, then that particular shipping container is suspect for containing the concealed radioactive materials. Additionally, the approximate location of the concealed nuclear material can be deduced by using the relative readings of the dosimeters. For example, the location of the concealed nuclear material can be triangulated by using the relative readings of the dosimeters.

0031[0028] As stated above, the dosimeters 2 that are deployed in the cargo-carrying vehicle can be Solid State Track Recorder (SSTR) neutron dosimeters 10. Fissle material such as ²³⁹Pu can be detected via the fission neutrons emitted by associated spontaneously fissioning isotopes such as ²³⁸Pu, ²⁴⁰Pu, or ²⁴²Pu. Although ²³⁵U and associated isotopes due not have appreciable spontaneous fission rates, ²³⁵U can be detected via the secondary neutrons emitted following cosmic-ray neutron interactions with ²³⁵U-containing materials. Therefore, SSTR neutron dosimeters or active dosimeters can be used to detect fissile material, such as U-235 or Pu-239, which could be concealed in a shipping container on a cargo-carrying vehicle and subsequently retrieved and used to create a nuclear explosive device. [0029] Referring to FIG. 2, a SSTR neutron dosimeter 10 consists of a thin layer of fissionable material 12 placed in contact with or adjacent to a track recording material 14. When exposed to neutrons 16 from a fission event, energetic fission fragments (fission ions) 18 are produced in the layer of fissionable material 12. One of these fission fragments 18 recoil into the track recording material 14 and produce particle tracks 20 that form a visual output that can be visually observed in the track recording material 14. Because the number of observed particle tracks 20 in the track recording material 14 is a measure of the number of fissions that have occurred over a specified amount of time per unit of area, which is in turn a measure of the number of neutrons which have impinged on the dosimeter over the same time, the neutron fluence through the SSTR neutron dosimeter 10 can be calculated and used to determine whether there is concealed nuclear material on the cargo-carrying vehicle. [0030] In one embodiment of the invention, the SSTR neutron dosimeter 10 has mica as its track recording material 16 that is overlaid with a fissionable material 12 of actinide isotopes, such ²³⁵U, ²³⁸U or ²³⁷Np. When a nuclear fission event occurs, a particle track 20 is produced in the mica due to fission fragments 18 recoiling into the mica. After the SSTR neutron dosimeter has been removed, the mica is chemically etched with hydrofluoric acid using techniques that are well known in the art and analyzed to determine whether a particle track 20, which is enhanced due to the etching process, can be observed on the mica. As stated above, the number of observed tracks provides an indication of the number of neutrons per unit area that have impinged onto the SSTR neutron dosimeter, which constitutes a measure of the neutron fluence through the SSTR neutron dosimeter at the detector location during the period of observation.

0032[0031] Referring to FIG. 3, as stated above the dosimeters that are deployed throughout the cargo-carrying vehicle can be active dosimeters. Unlike the mica containing SSTR neutron dosimeters described in the preceding paragraph, the active dosimeters utilize a semiconductor material 22, comprised of a depleted layer 24 and a conducting substrate 26, as the track recording material 14 in lieu of mica. The semiconductor material 22 can be selected from silicon, germanium, cadmium zinc teluride (CZT), cadmium telluride (CdTe), diamond, or silicon carbide (SiC). Positioned adjacent to the semiconductor material 22 is a fissionable material 12 such as ²³⁵U, ²³⁸U, or ²³⁷Np. When exposed to neutrons 16 from a fission event, energetic fission fragments (fission ions) 18 are produced in the layer of fissionable material 12 and recoil into the semiconductor material 22. The impact of the fission fragments 18 in the semiconductor material 22 creates ionization (an electrical pulse) in the depleted layer 24 of the semiconductor material 22. Similar to the particle tracks 20 that are produced in the track recording material in the SSTR neutron dosimeters, each electrical pulse is a measure of the number of fissions that have occurred over a specified amount of time per unit of area. The electrical pulses that are generated in the semiconductor material 22 can be electronically monitored by an electronic device that can be programmed to monitor not only the total number of electrical pulses detected over a specific amount of time, but also the pulse height distribution. Accordingly, the number of electrical pulses with pulse heights corresponding to fission events can be used to calculate the neutron fluence through the active dosimeter 10 thereby allowing for the determination of whether there is concealed nuclear material on the cargo-carrying vehicle.

0033[0032] In order to facilitate the determination of whether there is concealed nuclear material on the cargo-carrying vehicle prior to the cargo-carrying vehicle reaching its final destination, the electrical pulses that are detected by the electronic device can be transmitted to a remote monitoring location for analysis. The transmission of the detected pulses can either happen "in real time" or the electronic device can be programmed to transmit the detected pulses at specified time intervals. Additionally, the electronic device could also store the detected electrical pulses in the electronic device's memory for later analysis or for analysis en route to the final destination. The methods used to transmit the detected pulses to the remote monitoring location can include, without limitation, satellite transmission, radio frequency transmission, or a ship-to-shore phone line.

0034[0033] In one embodiment of the invention, each active dosimeter has a transmission code that is unique to a particular active dosimeter in order to facilitate locating the concealed nuclear material on the cargo-carrying vehicle. Referring to FlG. 4. the cargo-carrying container 8 can have one or more dosimeters 2 disposed on the periphery of the cargo-carrying container 8 or deployed in the vicinity of the cargo-carrying container. The dosimeters 2 can either be mechanically fastened to the cargo-carrying container 8 using a mechanical fastener or the dosimeters 2 could be manufactured as an integral part of the cargo-carrying container 8. In the embodiment depicted in FIG. 4, the container 8 has a base 28 with a first end 30, a second end 32, a first side 34, and a second side 36. Extending from the first side and second sides 34,36 of the base 28 is a first and second side wall 38,40, respectively. Extending from the first end 30 of the base 28 is a first end wall 42. A door 44 is attached to an end of each of said first and second side walls 38,40. As can be seen from this figure, the doors 42 are positioned substantially adjacent to said second end of the base 32. A top wall 46, which is substantially parallel to the base 28 is connected to each of the first and second side walls 38,40 as well as the first end wall 42.

0035[0034] The accompanying figures and the description above set forth this invention in its preferred embodiments. It is, however, contemplated that persons generally familiar with the detection of nuclear material will be able to apply the novel characteristics of the structures and methods illustrated and described herein in other contexts by modification of certain details. Accordingly, the figures and description are not to be taken as restrictive on the scope of this invention, but are to be understood as broad and general teachings.