Abstract:
A dosimeter is disclosed for use in container including outer walls defining an interior volume, the dosimeter including: a radon detection element adapted to detect a radon level for the interior volume; a neutron detection element adapted detect a neutron level for the interior volume. The dosimeter is adapted to measure the radon level and neutron level for a period of time, compare the measured radon level to a first threshold, compare the measured neutron level to a second threshold, and determine information indicative of the presence or absence of fissile material within the interior volume based on the comparisons.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application Ser. No. 60/899,212, U.S. Provisional Application Ser. No. 60/899,216, and U.S. Provisional Application Ser. No. 60/899,088, each of which were filed Feb. 1, 2007. 
     
    
     BACKGROUND 
       [0002]    This disclosure relates to containers, in particular, to containers for transportation and shipping. 
         [0003]    Based on recent domestic and foreign events, governments and the commercial sector have become concerned with the potential importing and exporting of weapons of mass destruction by terrorists or other similar organizations. By accessing a standard shipping container, a weapon such as a nuclear weapon may be placed in the container and passed undetected through a port or other import/exporting facility. 
         [0004]    In general, approximately sixteen million twenty foot containers are in use throughout the world. Additionally, approximately 40% of the personnel that load and off-load these containers come from nations that are on the terrorist list. Bribery and sabotage are common throughout the shipping industry, including government officials, shipping companies and freight forwarders. Large quantities of contraband material now pass through maritime commerce into many ports in the US. 
         [0005]    Most containers, including, for example, 20 foot and 40 foot dry and hi-cube shipping containers currently entering the US are made of steel. Steel is a difficult medium to scan with X-rays, since considerable energy is required to penetrate a steel wall. Substantially less energy is required to penetrate a wall made of composite material. However, composite material is typically substantially more expensive than steel. It is possible to make a container entirely from composite materials or from composite panels welded to a steel frame. A potential advantage of a composite container is that it can be manufactured so as to embed sensor grids in the composite walls, with the result that it can detect intrusions through its sides as described in U.S. Patent Publication No. 2007/0229285 filed Oct. 4, 2007 and entitled “Secure panel with remotely controlled embedded devices.” However, primarily composite containers are typically substantially more expensive than a steel container. 
         [0006]    Nuclear weapons contain fissile material. A nuclear weapon will emit radon gas and neutrons. Lead shielding will not shield radon gas and is a poor shield for neutrons. Currently available radon shielding involves an elaborate system of rubber and plastic seals. Only the United States Government has developed the technology to effectively shield radon from escaping from a nuclear weapon. It is very unlikely that a foreign adversary could produce a nuclear weapon that was shielded with lead so as to prevent the escape of gamma rays and also shielded so as to prevent the escape of radon gas and neutrons. 
       SUMMARY 
       [0007]    The inventors have realized that a low power, inexpensive scanner may be used to scan composite containers for the presence of nuclear weapons. Such scanners can be used in an efficient triage and scanning system. 
         [0008]    The inventors have also realized that plugs made of material having relatively high transmissivity to a scanning radiation beam (e.g. composite material) may be embedded in the panels of conventional containers made of material having relatively low transmissivity to a scanning radiation beam. The plugs act as windows for a scanning radiation beam (e.g. an X-ray beam), allowing the contents of the container to be scanned using relatively low power scanners. For example, the scanners may produce scanning beams having beam energies sufficient to penetrate through the plugs, but insufficient energy to penetrate the remaining portion of the container panels. 
         [0009]    The inventors have also realized that a dosimeter, e.g. a boron dosimeter, may be placed within the interior volume of a shipping container (e.g. a sealed air-tight steel or composite container). The dosimeter is capable of detecting the radon gas levels and neutron levels in the interior volume of the container over a period of time. Because even shielded fissile material emits radon gas, the dosimeter can reliably detect the presence of such material in the container. Using the techniques described below, the dosimeter can communicate with devices (scanners, remote control units) outside of the container without the need to open or unseal the container. In this fashion, the containers can be efficiently monitored for nuclear devices (e.g. prior to loading on a transport such as a container ship). 
         [0010]    In one aspect, a dosimeter is disclosed for use in a container including outer walls defining an interior volume, the dosimeter including: a radon detection element adapted to detect a radon level for the interior volume; a neutron detection element adapted to detect a neutron level for the interior volume. The dosimeter is adapted to measure the radon level and neutron level for a period of time, compare the measured radon level to a first threshold, compare the measured neutron level to a second threshold, and determine information indicative of the presence or absence of fissile material within the interior volume based on the comparisons. 
         [0011]    In some embodiments, the radon detection element or the neutron detection element include a boron element. 
         [0012]    In some embodiments, the dosimeter is adapted to: measure the change in the radon level for the interior volume during a period of time; compare the measured change in radon level to an expected change in radon level, the expected change being based on the known four day half life of radon, and output an alarm if the measured change in radon level does not substantially match the expected change in radon level. 
         [0013]    In some embodiments, the dosimeter is adapted to determine information indicative of the amount of air circulation in the volume of the container based on the measured change in radon level. 
         [0014]    In some embodiments, the dosimeter is adapted to measure the change in the neutron level for the interior volume during a period of time; and determine information indicative of the presence or absence of fissile material within the interior volume based on the measured change. 
         [0015]    Some embodiments include a beam detection element adapted to detect a radiation beam directed into the interior volume of the container through one or more of the outer walls. In some embodiments, the beam detection element is adapted to demodulate a message modulated onto the detected beam. 
         [0016]    Some embodiments include a transmitter element in communication with the beam detection element, the transmission element adapted to transmit a response message in response to the demodulated message, the response message including information indicative of the presence or absence of fissile material within the interior volume. In some embodiments, the transmitter element includes at least one from the group of: a Bluetooth transmitter, a wireless transmitter, a radio transmitter. In some embodiments, the transmitter is adapted to modulate the response message onto the scan beam. 
         [0017]    In another aspect a system is disclosed including: a container including outer walls defining an interior volume; a dosimeter positioned within the interior volume, the dosimeter including a radon detection element adapted to detect a radon level for the interior volume; a neutron detection element adapted to detect a neutron level for the interior volume; a beam detection element; and a transmitter element. The system also includes a scanner adapted to direct a scan beam into the interior volume of the container through one or more of the outer walls and onto the beam detection element; a receiver positioned in proximity to the scanner; and a remote control unit, the remote control unit being in remote communication with the scanner and the receiver. The dosimeter is adapted to measure the radon level and neutron level for a period of time, compare the measured radon level to a first threshold, compare the measured neutron level to a second threshold, and determine information indicative of the presence or absence of fissile material within the interior volume based on the comparisons. The scanner is adapted to receive a message from the remote control unit and modulate the message onto the beam. The beam detection element is adapted to detect the beam and demodulate the modulated message. The transmitter element is adapted to transmit a response message in response to the demodulated message, the response message including information indicative of the presence or absence of fissile material within the interior volume. The receiver is adapted to receive the response message and send information indicative of the response message to the remote control unit. 
         [0018]    Some embodiments include a crane located in proximity to the scanner and receiver, the crane in remote communication with the remote control unit. The remote control unit is adapted to control the crane to load the container onto a transport based on information indicative of the response message. 
         [0019]    In some embodiments, the scan beam includes an x-ray beam. 
         [0020]    In some embodiments, at least a portion of one of the walls of the container consists of a composite material, and the scanner is adapted to direct a scan beam into the interior volume of the container through the composite material. 
         [0021]    In some embodiments, the transmitter element includes at least one from the group of: a Bluetooth transmitter, a wireless transmitter, a radio transmitter. In some embodiments, the transmitter is adapted to modulate the response message onto the scan beam. 
         [0022]    In another aspect, a method of detecting the presence of fissile material within a container including outer walls defining an interior volume is disclosed. The method includes providing a dosimeter positioned within the interior volume; using the dosimeter, measuring a radon level and a neutron level in the interior volume for a period of time; comparing the measured radon level to a first threshold; comparing the measured neutron level to a second threshold; determining information indicative of the presence or absence of fissile material within the interior volume based on the comparisons; and outputting the information indicative of the presence or absence of fissile material within the interior volume. 
         [0023]    Some embodiments include sealing the interior volume of container to be substantially air-tight. 
         [0024]    Some embodiments include measuring the change in the radon level for the interior volume during a period of time; comparing the measured change in radon level to an expected change in radon level, the expected change being based on the known four day half life of radon; and outputting an alarm if the measured change in radon level does not substantially match the expected change in radon level. 
         [0025]    Some embodiments include determining information indicative of the amount of air circulation in the volume of the container based on the measured change in radon level. 
         [0026]    Some embodiments include measuring the change in the neutron level for the interior volume during a period of time; and determining information indicative of the presence or absence of fissile material within the interior volume based on the measured change. 
         [0027]    Some embodiments include detecting a radiation beam directed into the interior volume of the container through one or more of the outer walls. Some embodiments include demodulating a message modulated onto the detected beam. Some embodiments include transmitting a response message in response to the demodulated message, the response message including information indicative of the presence or absence of fissile material within the interior volume. 
         [0028]    In another aspect, a scanner is disclosed for scanning a container including a plurality of composite panels defining an interior volume. The scanner includes a beam generator adapted to emit a directed radiation scan beam having a beam energy sufficient to penetrate through at least one material of the plurality of composite but insufficient to penetrate through bulk metal material; a scan beam detector adapted to detect the scan beam, and an analyzer. The beam generator is adapted to direct the scan beam along a path into the interior volume of the container through one of the plurality of composite panels, across a portion of the interior volume, out of the interior volume through one of the plurality of composite panels, and onto the scan beam detector. The analyzer is adapted to determine information indicative of the material properties of contents of the interior volume based on the detected beam. 
         [0029]    In some embodiments, the scan beam has a beam energy insufficient to penetrate a 2 inch thickness of solid steel material. 
         [0030]    In some embodiments, the beam generator includes an x-ray source. 
         [0031]    In some embodiments, the x-ray source has an operating voltage of about 200 kV or less. In some embodiments, the x-ray source includes a cobalt-60 x-ray source. 
         [0032]    In some embodiments, the information indicative of the material properties of contents of the interior volume includes information indicative of the presence of metal in the interior volume of the container along the path of the scan beam. 
         [0033]    In some embodiments, the beam generator is adapted to modulate a message onto the scan beam. In some embodiments, the analyzer is adapted to demodulate a message modulated on to the detected scan beam. 
         [0034]    In some embodiments, the beam emitter is adapted to, respectively, for each of multiple points on one or more of the plurality of composite panels, direct a respective scan beam along a respective path along a path into the interior volume of the container through the respective point, across a portion of the interior volume, out of the interior volume through one of the plurality of composite panels, and onto the scan beam detector. The detector is adapted to detect each of the respective scan beams. The analyzer is adapted to, for each of the respective detected scan beams, determine information indicative of the presence or absence of metal in the portion of the interior volume along the respective scan beam path. In some embodiments, the multiple points are arranged in a regular array on one or more of the plurality of panels. In some embodiments, the regular array has an array spacing of about  6  inches or less. In some embodiments, the multiple points are spaced sufficiently closely that the information indicative of the presence of absence of metal in the ports of the interior volume along the scan beam paths includes cumulative information indicative of the presence or absence of metal at any point within the interior volume, the cumulative information having a probability of error of less than 1 in 1 trillion. In some embodiments, the multiple points consist of fewer than about 400 points. 
         [0035]    In some embodiments, the scanner is in communication with a remote control unit. In some embodiments, the scanner is in communication with a remote control unit via the Internet. 
         [0036]    In another aspect, a system is disclosed including a first scanner adapted to produce a relatively low energy directed radiation scan beam; a second scanner adapted to produce a relatively high energy directed radiation scan beam; and a sorting module adapted to direct containers represented to contain substantially no metal material to the first scanner and to direct containers represented to contain metal material to the second scanner. The first scanner is adapted to receive a container represented to contain substantially no metal material from the sorting module, and to scan the container to verify that substantially no metal material is present inside the container. The second scanner is adapted to receive a container represented to contain metal material from the sorting module, and to scan the container to detect the presence of a nuclear device. 
         [0037]    Some embodiments include a third scanner adapted to produce a relatively moderate energy directed radiation scan beam. The sorting module is adapted to direct containers represented to contain metal material having a density above a threshold value to the second scanner, and to direct containers represented to contain metal material consisting only of metal material having a density below the threshold value to the third scanner. The third scanner is adapted to receive a container represented to contain metal material consisting only of metal material having a density below the threshold value from the sorting module, and to scan the container to verify that substantially no material is present inside the container having a density above the threshold value. In some embodiments, the threshold value corresponds to a density less than the density of fissile material. 
         [0038]    In another aspect, a method for scanning a container including a plurality of composite panels defining an interior volume is disclosed. The method includes generating a directed radiation scan beam having a beam energy sufficient to penetrate through at least one of the plurality of composite panels but insufficient to penetrate through bulk metal material, directing the scan beam along a path into the interior volume of the container through one of the plurality of composite panels, across a portion of the interior volume, out of the interior volume through one of the plurality of composite panels, and onto a scan beam detector, detecting the scan beam with the scan beam detector, analyzing the detected beam to determine information indicative of the material properties of contents of the interior volume based on the detected beam; and outputting the information indicative of the material properties of contents of the interior volume. 
         [0039]    In some embodiments, the scan beam includes an x-ray beam. In some embodiments, the scan beam has a beam energy insufficient to penetrate a 2 inch thickness of solid steel material. 
         [0040]    In some embodiments, the information indicative of the material properties of contents of the interior volume includes information indicative of the presence of metal in the interior volume of the container along the path of the scan beam. 
         [0041]    Some embodiments include modulating a message onto the scan beam. Some embodiments include demodulating a message modulated onto the detected scan beam. 
         [0042]    Some embodiments include, respectively, for each of multiple points on one or more of the plurality of composite panels, directing a respective scan beam along a respective path into the interior volume of the container through the respective point, across a respective portion of the interior volume, out of the interior volume through one of the plurality of composite panels, and onto the scan beam detector; detecting each of the respective scan beams, and for each of the respective detected scan beams, determining information indicative of the presence or absence of metal in the portion of the interior volume along the respective scan beam path. 
         [0043]    In another aspect, a method of sorting and scanning multiple containers each including a plurality of composite panels defining an interior volume is disclosed. The method includes providing a first scanner adapted to produce a relatively low energy directed radiation scan beam; providing a second scanner adapted to produce a relatively high energy directed radiation scan beam; directing a container represented to contain substantially no metal material to the first scanner; directing a container represented to contain metal material to the second scanner; receiving the container represented to contain substantially no metal material at the first scanner, and scanning the container to verify that substantially no material is present inside the container, and receiving the container represented to contain metal material from the sorting module, and scanning the container to detect the presence of a nuclear device. 
         [0044]    In another aspect a container is disclosed including: a plurality of panels that define the volume of the container, the panels including a material having relatively low transmissivity to radiation; and at least one plug embedded in at least one of the panels, the plug consisting of a material having relatively high transmissivity to radiation. In some embodiments, the material having relatively low transmissivity to radiation includes a metal and the material having relatively high transmissivity to radiation includes a composite material. In some embodiments, at least one plug consists of a material having a relatively high transmissivity of x-ray radiation and the panels include a material having a relatively high transmissivity of x-ray radiation. 
         [0045]    In some embodiments, at least one plug includes: a first plug embedded in a first panel of the plurality of panels; and a second plug embedded in a second panel of the plurality of panels. The first and second plug are aligned opposing each other such that a beam of radiation directed into the volume of the container through the first plug will exit the volume of the container through the second plug. 
         [0046]    In some embodiments, at least one plug includes: a first plug embedded in a first panel of the plurality of panels and a plurality of plugs embedded in a second panel of the plurality of panels. The first plug includes a lens element or scattering element adapted to receive a beam of radiation directed into the volume of the container through the first plug and direct portions of the beam to exit the volume of the container through each of the plurality of plugs embedded in the second panel. 
         [0047]    In some embodiments, at least one plug includes: a first plurality of plugs embedded in a first panel of the plurality of panels; and a second plurality of plugs embedded in a second panel of the plurality of panels. Each plug of the first plurality of plugs is aligned opposing at least one respective plug of the second plurality of plugs such that a beam of radiation directed into the volume of the container through the plug of the first plurality of plugs will exit the volume of the container through at least one respective plug of the second plurality of plugs. 
         [0048]    The first plurality of plugs and second plurality of plugs are arranged such that substantially all of the volume can be accessed by scanning beams of radiation which are directed into the volume through a plug from the first plurality of plugs, pass through a portion of the volume, and exit the volume through a plug from the second plurality of plugs. 
         [0049]    Some embodiments include a fabric liner disposed adjacent the plurality of panels to enclose a portion of the volume of the container. The fabric liner includes one or more sensor elements adapted to detect an intrusion into the enclosed portion. One or more of the sensor elements is in communication with at least one plug. In some embodiments, one or more sensor elements include at least one of: an electrical grid, and an optical grid. In some embodiments the fabric liner is adapted to: receive a message modulated on a radiation beam directed through at least one plug and; transmit a response indicating the presence or absence of an intrusion into the enclosed portion. 
         [0050]    In some embodiments, the fabric liner contains one or more storage modules adapted to store electronic identification information. The fabric liner is adapted to: receive a message modulated on a radiation beam directed through at least one plug and; transmit a response based on the stored identification information. 
         [0051]    In some embodiments, the container includes: a dosimeter positioned within the volume of the container and adapted to detect the presence of fissile material within the volume of the container; a communication module positioned within the volume of the container and in communication with the dosimeter. The communication module is adapted to: receive a message modulated on a radiation beam directed through at least one plug and transmit a response indicating the presence or absence of an intrusion into the enclosed portion. In some embodiments, the communication module includes at least one of the group of: a Bluetooth transmitter, a wireless transmitter, a radio transmitter. 
         [0052]    In another aspect, a system is disclosed including: a container which includes a plurality of panels that define the volume of the container, the panels including a material having relatively low transmissivity to radiation; at least one plug embedded in at least one of the panels, the plug consisting of a material having relatively high transmissivity to radiation. The system also includes a scanner including: a beam generator adapted to emit a radiation beam having a beam energy sufficient to penetrate at least one plug consisting of a material having relatively high transmissivity to radiation and insufficient to penetrate portions of the plurality of panels including the material having relatively low transmissivity to radiation. 
         [0053]    In some embodiments, at least one plug includes a first plug embedded in a first panel of the plurality of panels and a second plug embedded in a second panel of the plurality of panels. The first and second plugs are aligned opposing each other. The beam generator is configured to direct the radiation beam into the volume of the container through the first plug, across a portion of the volume of the container, and out of the volume of the container through the second plug. The scanner includes a detector adapted to detect the radiation beam exiting out of the volume of the container through the second plug. 
         [0054]    In some embodiments, the volume of the container contains cargo material, and the scanner is adapted to determine information indicative of the material properties of the cargo material based on the detected radiation beam. In some embodiments, the information indicative of the material properties of the cargo material includes information indicative of the presence of at least one of the group of: metal, fissile material, electronic components. 
         [0055]    In some embodiments, at least one plug includes a first plurality of plugs embedded in a first panel of the plurality of panels and a second plurality of plugs embedded in a second panel of the plurality of panels, where each plug of the first plurality of plugs is aligned opposing at least one plug of the second plurality of plugs. The scanner includes a plurality of beam generators, each beam generator configured, respectively, to emit a radiation beam having a beam energy sufficient to penetrate the at least one plug consisting of a material having relatively high transmissivity to radiation and insufficient to penetrate portions of the plurality of panels including the material having relatively low transmissivity to radiation; and direct the beam into the volume of the container through a respective one of the first plurality of plugs, across a portion of the volume of the container, and out of the volume of the container through a respective one of the second plurality of plugs. 
         [0056]    Some embodiments include a remote control unit in remote communication with the scanner and with a receiver unit located in proximity to the scanner, and a communication module located within the volume of the container. The scanner unit is adapted to modulate a message received from the remote control unit onto at least one beam, and to direct the modulated beam into the volume of the container through the at least one plug. The communication module is adapted to receive the modulated beam, demodulate the message from the beam, and transmit a response signal based on the demodulated message. The receiver unit receives the response signal and transmits information indicative of the response signal to the remote control unit. 
         [0057]    Some embodiments include a dosimeter (e.g. a radon dosimeter) located within the volume of the container and adapted to detect the presence of fissile material within the volume of the container. The communication module is in communication with the dosimeter, and the response signal includes information indicative of the presence of fissile material within the volume of the container. 
         [0058]    In yet another aspect, a method is disclosed including: providing a container including: a plurality of panels that define the volume of the container, the panels including a material having relatively low transmissivity to radiation; and at least one plug embedded in at least one of the panels, the plug consisting of a material having relatively high transmissivity to radiation; generating a radiation beam having a beam energy sufficient to penetrate at least one plug consisting of a material having relatively high transmissivity to radiation and insufficient to penetrate portions of the plurality of panels including the material having relatively low transmissivity to radiation; and directing the beam into the volume of the container through at least one plug. 
         [0059]    In some embodiments, at least one plug includes a first plug embedded in a first panel of the plurality of panels and a second plug embedded in a second panel of the plurality of panels, and where the first and second plug are aligned opposing each other. The method includes directing the radiation beam into the volume of the container through the first plug, across a portion of the volume of the container, and out of the volume of the container through the second plug, and detecting the radiation beam exiting out of the volume of the container through the second plug. 
         [0060]    In some embodiments, the volume of the container contains cargo material. The method includes determining information indicative of the material properties of the cargo material based on the detected radiation beam, and outputting the information. 
         [0061]    Various embodiments may include any of the above described features, alone or in any combination. These and other features will be more fully appreciated with reference to the following detailed description which is to be read in conjunction with the attached drawings. 
         [0062]    It is to be understood that, as used herein, the term “detecting a beam” and related terms refer to detecting any property of a beam of radiation (e.g. an x-ray beam) including, but not limited to: intensity, fluence, cross section, wavelength, pulse duration, etc. Further detecting a beam may include detecting the interruption or blocking of a beam. (e.g. when an x-ray beam is blocked by metallic material positioned between the beam source and the detector). 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0063]    The foregoing and other objects of this disclosure, the various features thereof, may be more fully understood from the following description, when read together with the accompanying drawings in which: 
           [0064]      FIG. 1  shows a perspective view of a container and a scanning system; 
           [0065]      FIG. 2  illustrates a scanning pattern on a container panel; 
           [0066]      FIG. 3  illustrates a triage and scanning system; 
           [0067]      FIG. 4  is a block diagram showing a dosimeter installed in a container; 
           [0068]      FIG. 5  illustrates a scanning system for use with a dosimeter installed in a container; 
           [0069]      FIG. 6  a perspective view of a dosimeter installed in a container and a scanning system; 
           [0070]      FIG. 7  shows a perspective view of a container with composite plugs and a scanning system; 
           [0071]      FIG. 8  shows a perspective view of a container with composite plugs and a scanning system; 
           [0072]      FIG. 9  is a block diagram of a remotely controlled scanning system and container with composite plug; and 
           [0073]      FIG. 10  shows a top down view of a container with composite plugs and a fabric liner containing intrusion detection grids; 
       
    
    
     DETAILED DESCRIPTION 
       [0074]    Composite Container Scanner and Triage System 
         [0075]    Referring to  FIG. 1 , container  100  is constructed from composite panels  102  enclosing an interior volume. Scanner  106  includes directed radiation beam emitter source  108  which produces scan beam  110 . Scan beam  110  is directed along a path which travels through a side panel  102  of container  100  into the interior volume, across a portion of the interior volume, out of opposing side panel  102 , and onto detector  112 . Scanner  106  includes directed x-ray beam emitters  108 . A detector signal from detector  112  is transmitted to a remote control unit (not shown), and analyzed to determine the material properties of cargo (not shown) loaded in the interior volume of container  100 . For example, the detector signals can be analyzed to determine the presence of metals, fissile material, medium density material (e.g. electronic components), etc. In some embodiments detector  110  may be in communication with a local analyzer, such as a personal computer or laptop. 
         [0076]    In the illustrated embodiment, where container  100  is a rectangular parallelpiped, scan beams  110  and their respective emittiters  108  and detectors  112  are along axes parallel to one of the sidewalls of container  100 . In some embodiments, beams  110  and their respective emittiters  108  and detectors  112  may be angularly offset with respect to the container sidewall. 
         [0077]    Because panels  102  are made of composite material having relatively high transmissivity (e.g. in comparison to metal, such as steel), scan beam  110  need not be a high energy beam. Accordingly emitter  108  may be an inexpensive, relatively low power beam emitter. For example, emitter  108  may have sufficient power to penetrate composite panels  102  and low density, non-metal cargo loaded into the interior volume of container  100 , but insufficient power to penetrate dense, bulk metal (e.g. steel, lead, fissile material) etc. In such a case, an interruption of scan beam  110  measured by detector  112  would indicate the presence of dense metal material in the interior volume. 
         [0078]    In various embodiments, emitter  108  may be low-voltage x-ray source (e.g. a 200 kV or less x-ray source) or a cobalt-60 x-ray source. A scanner including such a source could be manufactured at a cost of about $10,000 or less. In contrast, to generate a scan beam with sufficient energy to penetrate a steel container would require a high voltage x-ray source operating at 3000 kV or more. 
         [0079]    Container  100  can be moved relative to scanner  108  and detector  112  (e.g. by driving a truck hauling the container past scanner  106 ) to allow scan beam  110  to be directed through additional points on side panel  102  such that additional portions of the interior volume are scanned. Alternatively, scanner  108  and detector  112  may be moved relative to container  100  to scan different portions of the interior volume. For example, referring to  FIG. 2 , a scan could sample data points for scan beams directed through points  150  on side panel  102  located every six inches vertically and horizontally. For example, for a 20 foot by 5 foot panel a total of (40*10)=400 data points might be sampled, with each data point indicating the presence or absence of metal along the scan beam passing through a given point. The results of this scan may be analyzed and compared to a threshold to determine the presence of, for example, a nuclear device. For example, if less than 30 of the 400 data points in the example above showed the presence of metal, it may be determined that the container does not contain a nuclear weapon with a probability of error of 1 part in 1 trillion. The 400 point data sample will be compressible into a computer file size of 40 bytes, allowing easy storage or transmission to, for example, a remote monitoring or control unit. 
         [0080]    In some embodiments, scanner  106  may contain multiple emitters:  108  which may produce multiple scan beams  110  simultaneously or sequentially. As described in greater detail below, in some embodiments only select portions of one or more of panels  102  of container  100  consist of composites with the remainder being made up of metal (e.g. steel). The composite portions allow scan beam  110  to access the interior volume of the container. 
         [0081]    As will be discussed in greater detail below, in some embodiments it is possible to place a detector inside a shipping container  100  that could detect a scan beam  110 . With an appropriate detector, messages could be modulated over the scan beam and demodulated by the detector, so that the scanner could communicate with the detector inside the container. Such communication capability could be useful for a remote monitor to communicate (e.g. using wireless, radio, or Bluetooth links) with a sensor or identification elements inside the container and also to communicate with the same container over the scan beam. This would allow remote assurance that the container in front of the scanner was the same container that was in communication with the remote monitor. 
         [0082]    Approximately 66% of container traffic inbound to the West Coast of the US is volume limited. Of this traffic, half contains no metal (i.e. clothing and shoes), a quarter contains electronic parts and games, and the remainder contains other goods such that a full 20 ft. container weighs less than the maximum weight of 67,200 lbs. A scanner slightly more powerful than the type of scanner discussed above could be built that would penetrate a cargo consisting of light electronic goods but would be blocked by dense metal. A nuclear weapon will contain dense metal, even if not shielded with lead. If shielded with lead, it will be even denser. Consequently, 33% of the inbound West Coast Cargo traffic could be scanned with an inexpensive scanner and declared not to contain metal, provided the cargo were transported in a composite container. On the assumption that if a container does not contain metal, it does not contain a nuclear weapon, 33% of the inbound container traffic to the West Coast can be inexpensively scanned and declared safe. 
         [0083]    In the following, an exemplary scanning and triage system is disclosed for efficiently scanning multiple at least partially composite containers for the presence of a hidden nuclear device. 
         [0084]    Referring to  FIG. 3 , system  500  includes one or more low power scanners  502  having a scan beam with insufficient energy to penetrate dense metals or medium density partially metallic material (e.g. electronic components). The system also includes one or more medium power scanners  504  having a scan beam with insufficient energy to penetrate dense metals but sufficient energy to penetrate medium density partially metallic material (e.g. electronic components). The system also includes one or more high power scanners  506  having a scan beam with sufficient energy to penetrate dense metals. 
         [0085]    Any of scanners  502 ,  504 ,  506  could be coupled with a data collection program on a lap top or remote monitoring unit which analyzes scan data using one or more of the techniques described above to determine information about the content of the containers. 
         [0086]    Containers  508  that are represented as containing non-metallic low density material such as clothing are directed to low power scanners  502 . Containers  508  which pass this scan (i.e. if no metal is detected in the container) are declared not to contain a nuclear weapon. These containers would not have to be scanned by a more powerful and more expensive scanner. Approximately one third of in-bound container traffic in the U.S. is of this type. This will save money in scanning equipment and delay. 
         [0087]    Containers  510  that are represented as containing electronic components or other medium density cargo are directed to the medium power scanners  506  suitable for this type of cargo. Containers  510  which pass this scan (i.e. if no metal having a density greater than that typical of medium density cargo is detected) are declared not to contain a nuclear weapon. These containers would not have to be scanned by a more powerful and more expensive scanner. Approximately one third of in-bound container traffic is medium density. This will save money in scanning equipment and dock delay. 
         [0088]    Containers  512  that are represented as containing high density metallic material are directed to high power scanners  512 . These scanners can scan the containers for nuclear weapons using, for example, high energy x-ray scanning techniques known in the art. Containers  512  which pass this scan (i.e. if no metal having a density greater than that typical of medium density cargo is detected) are declared not to contain a nuclear weapon. 
         [0089]    In some embodiments, containers  508 ,  510 ,  512 , are secured so that after scanning the container, a breach through any of its six sides will be detected (e.g. using a sensor grid embedded in the composite panels of the containers of the type described in U.S. Patent Publication No. 20070229285 filed Oct. 4, 2007 and entitled “Secure panel with remotely controlled embedded devices”). In such a case, it would be feasible to scan containers at some distance from a dock where the containers are loaded onto a ship bound for the United States. As shown in  FIG. 3 , because containers  508 ,  510 , and  512  can be scanned some distance from the dock, it is feasible to provide numerous scanning lanes for container scanning. In typical settings, a great number of such lanes might not be feasible at dockside, where space is limited. Because the need for expensive high power scanners  506  is limited, numerous scanning lanes having low and medium power scanners  502 ,  504  may be provided at a relatively low cost. 
         [0090]    Further, as described above, analysis of the presence or absence of dense metal is very simple and requires very little data and very little data analysis. Consequently, low and medium power scanners  502 ,  504  (and, in some embodiments, even high power scanners  506 ) may be automated and/or remotely managed. For example, scanners  502 ,  504 , and  506  may be automated using a system analogous to the familiar toll booth automation systems used on highways. Automated scanning reduces or eliminates the need for on-site operators. This will reduce costs and security risks. For example, it will not be necessary to place trust in an on-site operator. This will be a significant advantage in the maritime shipping environment, which is, unfortunately notoriously corrupt in certain venues. 
         [0091]    Dosimeter 
         [0092]    Referring to  FIG. 4 , dosimeter  1100  is positioned inside of container  1102 . Container  1102  has exterior walls  1104  defining an interior volume  1106 . Exterior walls  1104  may be metal (e.g. steel), composite, or some combination thereof (e.g. composite panels on a steel frame or steel panels with embedded composite plugs). Interior volume  1106  may be sealed air-tight, such that air does not circulate between the exterior environment and the interior volume. 
         [0093]    Dosimeter  1100  includes a boron element  1108  capable of measuring the level of radon gas and the neutron level within interior volume  1106 . For example, dosimeter  1100  may be a commercial off-the-shelf radon detector. In some embodiments, such an off-the-shelf detector may be made more sensitive by modifying boron element  1108 , using techniques known in the art. 
         [0094]    As noted above, detection of radon and neutrons is a good indicator of fissile material. Substances that do not contain fissile material will typically not produce radon and neutrons. 
         [0095]    When interior volume  1106  of container  1102  is sealed such that the air volume does not circulate, if dosimeter senses less than a threshold number of neutrons and a threshold radon level over a period of time, the probability that the container contains a nuclear weapon approaches zero. The threshold levels and time periods can be easily determined based on measured background neutron and radon levels for a given container type and/or known neutron and radon emission rates for fissile material. 
         [0096]    In some embodiments, dosimeter  1100  can communicate with devices external to container  1102 . For example, referring to  FIG. 5 , remote controller  1200  is in communication (e.g. over an Internet connection) with scanner  1202  and receiver unit  1204  (e.g. a computer) located in proximity to scanner  1202 . Scanner  1202  includes beam emitter  1206  which directs a radiation beam  1208  (e.g. an x-ray beam) through panel  1104  onto beam detector element  1210 , which is in communication with dosimeter  1100 . Scanner  1202  receives a message from remote control unit  1200  and operates to modulate the message onto beam  1208  emitted. Detector  1210  detects beam  1110  and demodulates the message. In response to the message, dosimeter  1100  outputs information indicating whether fissile material has been detected inside container  1102 . This information is sent to transmitter  1212  which transmits a response message based on the demodulated message and the information output by dosimeter  1100 . The response signal may be sent using a non-directed signal, for example using a radio broadcast or other wireless transmission. As shown, the response message is transmitted over an antenna to a Bluetooth receiver in receiver unit  1204 . Receiver unit  1204  then passes the message to remote control unit  1200 , thereby providing remote monitoring of container  1102  for fissile material. In some embodiments, beam  1208  is directed into interior volume  1106  through a portion of panels  1104  composed of a material having relatively high transmissivity to the radiation beam (e.g. a composite material). This allows emitter  1206  to be a relatively low powered source, e.g. a low voltage (200 kV or less) x-ray source or a cobalt-60 x-ray source. 
         [0097]    Note that the above described arrangement provides a closed loop so that a remote monitor can be assured of the position of a particular container while communicating with it. The scan beam  1208  is a directed beam, which can be used to assure that the container is located in a particular place, whereas the communication link between transmitter  1212  and receiver  1204 , e.g. using Bluetooth, is a non-directed wave that will only locate a container within the Bluetooth range. 
         [0098]    This capability of using a communication path consisting of both a directed beam and a non-directed Bluetooth wave would allow a remote monitor to assure that the container with which it was communicating was the container actually being scanned. The ability to assure that a particular container is in front of the scanner is important to avoid various ploys that might be attempted by a clever adversary to avoid the container scanning process. In some embodiments, scanner  1202  and receiver  1204  may be positioned on or in proximity to loading crane  1130 . This allows for a positive identification of container  1102  and a determination that it does not contain a nuclear device immediately prior to loading onto a transport (e.g. a maritime container ship, train, truck, etc.). Of course, identification and determination may additionally or alternatively be made during or after loading and/or before during or after off-loading. 
         [0099]    Referring to  FIG. 6 , in some embodiments, scanner  1202  emits scan beam  1208  from emitter  1206  which is directed along a path which enters container  1102  through a first panel  1104 A, passes through dosimeter  1100 , exits container  1102  through a second panel  1104 B and is detected by detector  1300 . As described above, a query message (e.g. from a remote control unit) is modulated onto beam  1208 . Beam  1208  is detected by dosimeter  1100  (e.g. either directly using boron element  1108 , or using a separate detector unit), and the message demodulated. In response to the demodulated query, dosimeter  1100  outputs information indicating whether fissile material has been detected inside container  1102 . This information is included in a response message modulated onto beam  1208  by a modulator integral with or in communication with dosimeter  1100 . Detector  1300  detects beam  1208  after it exits container  1100 , and demodulates the response message. Detector  1300  may communicate the response message to a remote controller (not shown), e.g., using an Internet link. 
         [0100]    Composite Plugs 
         [0101]    Referring to  FIG. 7 , container  100  is constructed from steel panels  102 ,  102 A,  102 B enclosing an interior volume. Plugs  104  of composite material are embedded in side panels  102 A and  102 B. The composite plugs  104  have relatively high transmissivity to x-ray radiation while steel panels  102 ,  102 A,  102 B have relatively low transmissivity. Accordingly, composite plugs  104  act as x-ray “windows” into the interior volume of container  100 . 
         [0102]    In the illustrated embodiment, where container  100  is a rectangular parallelpiped, scan beams  110  and their respective emitters  108  and detectors  112  are along axes parallel to one of the sidewalls of container  100 . In some embodiments, beams  110  and their respective emitters  108  and detectors  112  may be angularly offset with respect to the container sidewall. 
         [0103]    Each plug  104  in side panel  102 A is located directly opposite to a plug  104  in side panel  102 B. Scanner  106  includes directed x-ray beam emitters  108 . The emitters  108  each direct scan beams  110  through one plug  104  in sidewall  102 A, then through the interior volume of container  100 , then through another plug  104  on the opposite sidewall  102 B and on to a detector  112  outside on the other side of the container. The detector signals are transmitted to a remote control unit (not shown), and analyzed to determine the material properties of cargo (not shown) loaded in the interior volume of container  100 . For example, the detector signals can be analyzed to determine the presence of metals, fissile material, medium density material (e.g. electronic components), etc. Because scan beams  110  need not penetrate the steel portions of side panels  102 A,  102 B, emitters  108  may be inexpensive, relatively low power beam emitters. For example, in various embodiments, emitters  108  may be low-voltage x-ray source (e.g. a 200 kV x-ray source) or a cobalt-60 x-ray source. 
         [0104]    Container  100  can be moved relative to scanner  106  and detectors  112  (e.g. by driving a truck hauling the container past scanner  106 ) to allow scan beams  110  to be directed through additional pairs of plugs to allow other areas of the interior volume to be scanned. Alternatively, scanner  108  and detector  112  may be moved along the length of the container to access different pairs of plugs  104 . In some embodiments, container  10  and scanner  108  and detectors  110  remain stationary during each scan event. For some applications, e.g. for detecting the presence of nuclear weapons, a sufficient quantity of plugs  104  are provided such that that no matter where the weapon was located within the interior, it could be detected by the scan. 
         [0105]    Composite plugs  104  may be inserted into panels  102 A,  102 B by an operation after the steel panel is stamped, or the operation could be integrated into the stamping operation. 
         [0106]    In some embodiments, composite plugs  104  have considerable structural strength so that insertion of a plug would not degrade the structural strength of the steel container. 
         [0107]    In some embodiments, plugs  104  could be retrofitted to an existing steel container  100  at a modest cost so as to overcome the significant cost disadvantage of all-composite containers. 
         [0108]    Referring to  FIG. 8 , in some embodiments, one or more of the composite plugs  104  located in side panel  102 A contain a lens or scattering element that directs or scatter the incoming beam  110  to form beams  110 A,  110 B, and  110 C, which travel along different paths through the interior volume of container  100 . Each of beams  110 A,  110 B, and  110 C exit the container through a different composite plug  104  in side panel  102 B and is detected by a detector  112 . Thus, a given input beam  110  generates beams  110 A,  110 B, and  110 C which would be detectable by the detector  112  immediately opposite and by detectors  112  the left and right (and/or above and below depending on the type of lens or scattering element). Accordingly, each scanning beam emitted from scanner  108  is able to scan a larger portion of the interior volume of container  100  than in the configuration shown in  FIG. 7 . 
         [0109]    In some embodiments, several inexpensive beam emitters  108  might be arrayed vertically. Opposite these beams, several detectors  112  would be arrayed both horizontally and vertically. In some embodiments beam sources  108  are pulsed sequentially so that the detected pulse could be measured separately for each beam pulse. In some such embodiments, it might be necessary to stop container  100  and scan it while it was stationary rather than driving the container through a scanner. In some embodiments, indicial markers or position detectors may be used to ensure proper alignment of plugs  104  and scanner  106 . 
         [0110]    Referring to  FIG. 9 , remote controller  300  is in communication (e.g. over an 
         [0111]    Internet connection) with scanner  106  and computer  302  located in proximity to scanner  106 . Scanner  106  operates to modulate a message on beam  110  emitted by emitter  108 . Beam  110  is directed through composite plug  104  into the interior volume of container  100 . Detector/demodulator  304  positioned within container  100  detects beam  110  and demodulates the message. Transmitter  306  transmits a response message based on the demodulate message, e.g. over an antenna to a Bluetooth receiver in computer  302 . In some embodiments, other types of transmission can be used including radio, wireless, etc. The above described arrangement provides a round trip loop so that a remote monitor could be assured of the position of a particular container while communicating with it. 
         [0112]    In some embodiments, a dosimeter  308  is located inside the container. Dosimeter  308  detects the presence of even shielded fissile material. Dosimeter  308  is in communication with detector/demodulator  304  and transmitter  306 . A query message is sent from remote monitor  300  via modulated beam  110  through plug  104  to detector/demodulator  304 . In response to this massage, information indicating the presence or absence of fissile material is sent from dosimeter  308  via transmitter  306  to computer  302  and on to remote monitor  300 . In some such embodiments, a single composite plug could be inserted into the container allowing communication with dosimeter  308  and reducing or eliminating the need to actually scan for metal. 
         [0113]    Referring to  FIG. 10 , wall fabric liner  400  is installed inside container  100  to enclose substantially all of the interior volume of the container. Wall fabric  400  contains grids (e.g. electrical or optical grids) that produce an alarm if an intrusion is sensed (e.g. in response to a breach in a portion in one of the grids). For example, fabric liner  200  may include dispersed, interconnected electronic components integrally attached to the liner. Each electronic component of the plurality of components may be in communication with a remotely accessible interface and includes a memory for storing a respective sub-division of at least one numeric value. The numeric values can be inserted, altered, or deleted remotely through the remotely accessible interface. Upon detection of an attempted breach of or tamper with fiber liner  400  one or more of the stored sub-divisions are selectively destroyed. Detection of an attempted breach or tamper is remotely observable upon inspection of a previously stored numeric value, subsequently altered in response to detection of a breach of the secured asset. 
         [0114]    Fabric liner  400  has tabs  402  that stick to the panels  102 ,  102 A,  102 B for easy installation. In some embodiments, the fabric used along the floor of the container has increased durability, since, in typical applications, fork lifts would need to be driven over it. 
         [0115]    Composite plugs  104  contain connections for insertion of leads  404  from the fabric. In some embodiments, these plugs  104  having connections may be installed at or near the corners of the sidewalls of container  100 . 
         [0116]    When the fabric liner  400  is installed and the connections were made with plugs  104 , a scanner could be used to query fabric liner  400  (e.g. using a closed loop modulation/demodulation/response scheme of the type described above) to assure that the system was functioning properly. As described above, fabric liner  400  could contain unique embedded identification information so that by scanning through the plugs  104  to communicate with fabric liner  400 , a remote monitor could assure that the plugs were connecting to one another through the fabric rather than through some wiring device that avoided the fabric liner  400 . Such a configuration allows an inexpensive intrusion detection system to be installed in steel container  100  and permits a remote check-out that the system was providing the required coverage. 
         [0117]    In some embodiments, fabric liner  400  is manufactured as an integrated electrical unit so that a reduced number of wiring connections would need to be made upon installation. In some embodiments, the fabric liner  400  is capable of being checked out before installation, so that the time spent installing a defective fabric can be avoided. 
         [0118]    One or more or any part thereof of the control, sensing, detection, scanning or other techniques described above can be implemented in computer hardware or software, or a combination of both. The methods can be implemented in computer programs using standard programming techniques following the method and figures described herein. Program code is applied to input data to perform the functions described herein and generate output information. The output information is applied to one or more output devices such as a display monitor. Each program may be implemented in a high level procedural or object oriented programming language to communicate with a computer system. However, the programs can be implemented in assembly or machine language, if desired. In any case, the language can be a compiled or interpreted language. Moreover, the program can run on dedicated integrated circuits preprogrammed for that purpose. 
         [0119]    Each such computer program is preferably stored on a storage medium or device (e.g., ROM or magnetic diskette) readable by a general or special purpose programmable computer, for configuring and operating the computer when the storage media or device is read by the computer to perform the procedures described herein. The computer program can also reside in cache or main memory during program execution. The technique can also be implemented as a computer-readable storage medium, configured with a computer program, where the storage medium so configured causes a computer to operate in a specific and predefined manner to perform the functions described herein. 
         [0120]    Although in the examples described above container  100  was composed of rectangular panels (e.g. corrugated metal panels), it is to be understood that in various embodiments one or more of the panels may be curved and/or have any suitable shape. For example, a tank type container may be made up of a cylindrical panel and two circular end cap panels. Similarly, plugs  104  may be of any suitable shape including, for example square, rectangular, circular, oval, polygonal, etc. The plugs may be arranged in any suitable pattern on any number of the panels. 
         [0121]    The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.