Abstract:
A radioactive material detection system includes a plurality of radioactive material detection apparatuses and a master unit/master module. Each apparatus is disposed in or on a cargo receptacle and each apparatus has a wireless transmitter, a radiation sensor and a detection controller. The master unit/master module has a receiver configured to receive the wirelessly transmitted information from each of the wireless transmitters and a master controller. The system detects fissile or nuclear material that emits radiation by (i) calculating and storing at the master unit/master module an initial average measured radiation level at each radioactive material detection apparatus location throughout the entire array of radioactive material detection apparatuses and (ii) comparing the current measured radiation at each radioactive material detection apparatus location to the initial radiation level at each location in order to identify an anomaly amongst the plurality of cargo receptacles.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation of copending application Ser. No. 10/458,923 filed Jun. 10, 2003 entitled “Method And Apparatus For Detection Of Radioactive Material.” 
         [0002]     This application claims the benefit of U.S. Provisional Patent Applications Nos. 60/460,202 filed on Apr. 3, 2003; 60/456,754 filed on Mar. 21, 2003; 60/445,408 filed Feb. 6, 2003; 60/407,148 filed Aug. 28, 2002; and 60/388,512 filed Jun. 12, 2002, all entitled “Method and Apparatus for Detection of Radioactive Material”. 
     
    
     BACKGROUND OF THE INVENTION  
       [0003]     The present invention relates generally to a method and apparatus for the detection of radioactive material and, more particularly, to a method and apparatus for detecting the presence of radioactive material within a vessel or container during shipment from one location to another.  
         [0004]     There is a growing concern that terrorists or others may at some time in the near future attempt to import into the United States or some other country radioactive or nuclear material which may then be used for the construction of a nuclear weapon for carrying out terrorist objectives. One way of shipping such radioactive or nuclear material is to hide the material among or within seemingly innocuous cargo. For example, such nuclear material could be placed within a standard, sealed cargo container of the type typically employed for shipping cargo by sea, rail, air or by truck. The nuclear material could be positioned within such a sealed cargo container along with other innocuous goods with the container being positioned, for example, within the hold of a large container ship which may be transporting a thousand or more such containers from one location to another. Typically, existing cargo inspection systems are employed either at the port of debarkation or the port of entry for such container ships. Because of the large number of containers which are typically transported by a single large container ship, it is difficult, if not impossible, using the presently available inspection equipment and personnel to thoroughly check each and every container for the presence of any type of contraband, including radioactive or nuclear material. To beef up the inspection equipment and personnel at ports of entry to facilitate a more thorough or detailed inspection of each container is not practical because of the time involved in inspecting each such container and the unacceptable delays in the transport of the containers, as well as potential huge back ups in the loading and unloading of the container ships.  
         [0005]     The present invention overcomes the problems associated with the existing container inspection systems by providing a method and apparatus for the detection of radioactive or nuclear material within a sealed container while the container is in transit from one location to another. In this manner, it is possible to identify potential threats while in transit to permit appropriate action to be taken long before the radioactive or nuclear material enters the territorial limits of a country.  
       BRIEF SUMMARY OF THE INVENTION  
       [0006]     Briefly stated, the present invention comprises a radioactive material detection system that includes a plurality of radioactive material detection apparatuses and a master unit/master module. Each apparatus is disposed in or on a cargo receptacle and each apparatus has a wireless transmitter, a radiation sensor and a detection controller configured to receive a sensor output from the radiation sensor and to send the signal to the wireless transmitter for transmission. The master unit/master module has a receiver configured to receive the wirelessly transmitted information from each of the wireless transmitters and a master controller coupled to the receiver. The system is configured to detect fissile or nuclear material that emits radiation by (i) calculating and storing at the master unit/master module an initial average measured radiation level at each radioactive material detection apparatus location throughout the entire array of radioactive material detection apparatuses and (ii) comparing the current measured radiation at each radioactive material detection apparatus location to the initial average measured radiation level at each location in order to identify an anomaly amongst the plurality of cargo receptacles.  
         [0007]     The present invention also comprises a radioactive material detection apparatus including a transmitter, a radiation sensor and a controller. The transmitter is capable of transmitting information in correspondence with a signal. The radiation sensor has a sensor output and is configured to detect radiation over a predetermined period of time. The controller is configured to receive the sensor output from the radiation sensor and to send the signal to the transmitter for transmission.  
         [0008]     The present invention also comprises a portable radioactive material detection apparatus for detecting radiation during shipping. The portable apparatus also includes a transmitter, a radiation sensor and a controller. The transmitter is capable of transmitting information in correspondence with a signal. The radiation sensor has a sensor output and is configured to detect radiation over a predetermined period of time. The controller is configured to receive the sensor output from the radiation sensor and to send the signal to the transmitter for transmission.  
         [0009]     In another aspect, the present invention comprises a radioactive material detection system. The system includes a plurality of radioactive material detection apparatuses and a master unit/master module. Each apparatus includes a transmitter, a radiation sensor, a detection controller and an identification tag. Each transmitter is capable of transmitting information in correspondence with a signal. Each radiation sensor has a sensor output which is configured to detect radiation over a predetermined period of time. Each detection controller is configured to receive the sensor output from the radiation sensor and to send its respective signal to its respective transmitter for transmission. Each identification tag is electrically coupled to one of the controller and the transmitter and is configured to provide identification data or location data to the information being transmitted by the transmitter. The master unit/master module includes a receiver, an indication output and a master controller. The receiver is configured to receive the transmitted information from each of the transmitters of the radioactive material detection apparatuses. The master controller is coupled to the receiver and is configured to drive the indication output based upon a status of the information received.  
         [0010]     In another aspect, the present invention comprises a method of detecting radioactive material within an object to be tested using a radioactive material detection apparatus. The apparatus has a transmitter, a detection controller and a radiation sensor configured to detect radiation over a predetermined period of time. The method includes the steps of: mounting the radioactive material detection apparatus to the object to be tested; sensing at least one of gamma radiation and neutrons over the predetermined period of time; and transmitting a signal when a predetermined amount of radiation is detected.  
         [0011]     In yet another aspect, the present invention comprises a method of detecting radioactive material within a plurality of objects to be tested using a master unit/master module and a plurality of radioactive material detection apparatuses. Each apparatus has a transmitter, a detection controller and a radiation sensor configured to detect radiation over a predetermined period of time. The method includes the steps of: mounting the plurality of radioactive material detection apparatuses to the plurality of objects to be tested; sensing at least one of gamma radiation and neutrons at each radioactive material detection apparatus and transmitting the initially sensed signal to the master unit/master module; establishing a background radiation space for the plurality of objects to be tested based upon the initially sensed signals; storing the background radiation space in the master unit/master module or a control center; sensing at least one of gamma radiation and neutrons over the predetermined period of time at each radioactive material detection apparatus and transmitting the currently sensed signal to the master unit/master module; establishing a current radiation space for the plurality of objects to be tested based upon the currently sensed signals; and comparing the current radiation space as currently sensed by the radioactive material detection apparatuses to the background radiation space as initially sensed by the radioactive material detection apparatuses in order to identify an anomaly amongst the plurality of objects to be tested. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0012]     The following detailed description of preferred embodiments of the invention will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.  
         [0013]     In the drawings:  
         [0014]      FIG. 1  is a functional block diagram of radioactive material detection system having a plurality of radioactive material detection apparatuses arranged on a plurality of objects to be tested which are arranged in a three-dimensional matrix;  
         [0015]      FIG. 2  is a schematic functional block diagram of a radioactive material detection apparatus in accordance with a preferred embodiment of the present invention; and  
         [0016]      FIG. 3  is a schematic functional block diagram of a master unit/master module or receiver station in accordance with a preferred embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]     Referring to the drawings, wherein the same reference numerals are employed for indicating like elements throughout the several figures, there is shown in  FIGS. 1-3 , a schematic representation of a radioactive material detection system  10  in accordance with the present invention. The radioactive material detection system  10  ( FIG. 1 ) includes a plurality of radioactive material detection apparatuses  20  ( FIG. 2 ) and a master unit/master module  40  ( FIG. 3 ). Each radioactive material detection apparatus  20  includes a transmitter  26 , a radiation detector or sensor  24 , a detection controller  30  and an identification tag or ID tagger  28 . Each transmitter  26  is capable of transmitting information in correspondence with a signal. Preferably, the transmitter  26  transmits information using radio frequency, infrared, light waves, microwaves, electrical voltage, electrical current and the like. Each radiation sensor  24  has a sensor output and is configured to detect radiation over a predetermined period of time. Preferably, the radiation sensor  24  is configured to vary the sensor output in proportion to an amount of radiation detected. The amount of radiation detected may be an amount of intensity or a cumulative value as sensed over a predetermined period of time. Each detection controller  30  is configured to receive the output from its associated radiation sensor  24  and to send its respective output signal to its respective transmitter  26  for transmission. Each identification tag  28  is electrically coupled to at least one of the controller  30  and the transmitter  26  and is configured to provide identification data and/or location data to the information being transmitted by the transmitter  26 . The identification data may include a unique identifier for an object to be tested  12 , and may additionally include information about the contents, ownership, source and/or destination of the object to be tested  12 . Preferably, the radiation sensor  24  varies the sensor output in proportion to an amount of radiation detected.  
         [0018]     The master unit/master module  40  includes a receiver  42 , an indication output such as transmitter  48  of the master control unit  40  and a master controller or information processing system  46 . The receiver  42  is configured to receive the transmitted information from each of the transmitters  26  of the radioactive material detection apparatuses  20 . The master controller  46  is coupled to the receiver  42  and is configured to drive an indication output or transmitter  48  based upon a status of the information received. The indication output  48  may be connected to a remote or local indicator light, annunciator panel, display device, sound generating device (i.e., a horn or a buzzer), and the like. Alternatively, the indicator output  48  may be a transmitter connected to a remote communication system such as a cellular system, a telephonic system, a wired computer network, a satellite system, a radio system and the like.  
         [0019]     Preferably, a plurality of subsets of the plurality of radioactive material detection apparatuses  20  are arranged on a plurality of objects to be tested  12 , as depicted in  FIG. 1 , and the plurality of objects to be tested  12  are arranged such that subsets of the plurality of radioactive material detection apparatuses  20  arranged on adjacent objects to be tested  12  are capable of detecting at least a portion of other adjacent objects to be tested  12  nearest thereto. For example, a first subset of the plurality of radioactive material detection apparatuses  20  may be arranged on a first object to be tested  12  and a second subset of the plurality of radioactive material detection apparatuses  20  may be arranged on a second object to be tested  12 . The first and second objects to be tested  12  are arranged such that the first subset of the plurality of radioactive material detection apparatuses  20  is capable of detecting at least a portion of the second object to be tested  12  and vice versa. Preferably, at least three of the plurality of radioactive material detection apparatuses  20  are arranged on each object to be tested  12  and are oriented on the object to be tested  12  in a manner that minimizes the distance from any point within the object to be tested  12  to one of the three radioactive material detection apparatuses  20 . It is contemplated that a plurality of radioactive material detection systems  10  can be inter-connected by a supervisory monitoring or control station for monitoring a plurality of floors, areas, buildings, holds and the like.  
         [0020]     In one possible implementation,  FIG. 1  may be a schematic representation of the hold of a typical container ship  10  of a type well known to those of ordinary skill in the art. The container ship  10  is employed for receiving within its hold and, in some cases upon its deck, a plurality of box-like containers or other objects to be tested  12  generally of a predetermined size of approximately 10 feet by 10 feet by 40 feet. The containers  12  are preloaded with goods to be shipped from one location to another before being loaded onto the container ship  10 . Typically, the containers  12  preloaded with the goods to be shipped are sealed before being placed on the container ship  10 . The hold of the container ship  10  is sized for receiving a plurality of such containers  12  in a side by side, end to end relationship with other containers  12  being stacked one on top of another to effectively establish a three dimensional container matrix  14  to take advantage of the available space of the container ship  10  for maximum shipping efficiency. The containers  12  are typically made of steel or some other rigid, high strength material in order to provide adequate support for the overlying containers  12  and to adequately protect the goods being shipped within each container  12  from damage which may occur during shipment and the loading/unloading of the containers  12 . A typical large container ship  10  may receive one thousand or more containers  12  for shipping from one location to another. As mentioned above, because of the size of the containers  12  and the number of containers on each container ship  10 , it is difficult if not impossible to adequately inspect each and every container for contraband, including radioactive material, at the time the containers  12  are being unloaded from the container ship  10  for further transport.  
         [0021]     The present invention provides a method and system for detecting the presence of radioactive or nuclear material within such containers  12  on a container ship  10  (or in some other mode of transport) as the ship is transporting the containers  12  from one location to another. Typically, the ocean transit time of a container ship  10  is at least several days and could be as many as 10 or more days from the time a loaded container ship  10  leaves a port at a first location until the time that the container ship  10  enters a port at a second location. For shipments between Western Europe and the United States, a typical transit time is in the range of 9 to 11 days for an east coast U.S. port. The present invention takes advantage of the relatively long transit time to facilitate an orderly, thorough detection of the presence of radioactive or nuclear material within a container  12  without creating any unacceptable delays or port congestion either at the departure or arrival port of the container ship  10 . In this manner, appropriate action may be taken while the ship  10  is still out to sea, long before approaching or entering a port. In addition, because the presence of nuclear or radioactive material can be detected while the ship  10  is at sea, the ship  10  can be held outside of a port to prevent entry of the material into a country or may be diverted to a safe harbor for further inspection.  
         [0022]      FIG. 2  is a functional schematic block diagram of the sensor apparatus  20  in accordance with a preferred embodiment of the present invention. The sensor apparatus  20  is contained within a housing  22  which is preferably sealed and is made of a generally rigid high strength material such as a polymeric material. Preferably, the sensor housing  22  is tamper resistant and includes a mechanism for identifying by a quick, visual or other inspection whether the housing  22  has been opened or otherwise tampered with and or an internal electronic means to detect tampering. The housing  22  is adapted to be secured to the inside or outside of a container  12  at a predetermined location. Various techniques and methods well known to those of ordinary skill in the art may be employed for securing the housing  22  to the container  12  including the use of one or more mechanical fasteners such as screws, bolts, clamps, etc., the use of an adhesive or epoxy adhesive, suction cups, a magnetic attachment device or any other suitable attachment device or technique. Preferably, the housing  22  is adapted to be temporarily secured to an interior or exterior surface of the container  12 . Thus, the radioactive material detection apparatus  20  may be a portable unit. However, it is within the scope and spirit of the present invention that the housing  22  be permanently secured to a container  12 . Preferably, the location on the container  12  where the housing  22  is secured will be such that the housing  22  will not affect the loading or unloading of the container  12  or the stacking of the containers  12  in the three dimensional matrix  14 . Preferably, the housing  22  is relatively small as compared to the container  12  or other object to be tested.  
         [0023]     Referring again to  FIG. 2 , the housing  22  contains the components necessary for passive detection of the presence of radioactive material over the time period during which the container ship  10  moves from one port to another. In the present embodiment, the housing  22  includes a gamma radiation detection sensing component or sensor  24 , a transmitter  26 , an identification component or ID tagger  28 , a controller  30 , a location component or tagger  32  and a power source  34  for providing operating power to the other components as needed. Preferably, the gamma radiation sensor component  24  is a self-contained passive device capable of sensing the presence of gamma radiation emitted from radioactive material which may be present within or near the container  12  to which the sensor apparatus  20  is attached. The gamma radiation sensing component  24  is preferably of a type which is generally well known to those of ordinary skill in the art and is available from several sources. The gamma radiation sensing component  24  provides an electrical output signal which is proportional to the sensed gamma radiation. The output from the gamma radiation sensing component  24  is supplied as an input to the transmitter  26 . The output of the radiation sensor  24  may also be accumulated over a predetermined or commanded intervals of time prior to transmission to transmitter  26 . Suitable signal conditioning components (not shown) may be interposed between the gamma radiation sensing component  24  and the transmitter  26 .  
         [0024]     The purpose of the gamma radiation sensing component  24  is to maximize sensitivity and thus the detection of counterband radioactive or nuclear material (fissile material). However, sensitive gamma ray detectors may also be sensitive to particular radioactive isotopes occurring naturally as trace elements within certain commercially acceptable materials. Potassium  40  which occurs in potassium based fertilizer as well as the decay products of trace radioactivity in clay are examples of commercially acceptable materials which may be detected by the gamma radiation sensing component  24 . Man-made radioactive materials intended for use in medical or industrial applications which may also be legally shipped in cargo containers could also be detected. Thus, the detection by the gamma radiation sensing component  24  of the present system could constitute false detection of apparently clandestine fissile material.  
         [0025]     One way to minimize the occurrence of such false positive detections is by using a separate detector which is sensitive to neutrons, along with the gamma radiation sensing component  24 . The vast majority of naturally occurring radioactive elements and of man-made radioactive isotopes do not emit neutrons whereas fissile materials do emit neutrons. In this manner, simultaneous monitoring using the gamma radiation sensing component  24  along with a neutron monitoring component permits differentiation between the fissile materials and other radioactive sources.  
         [0026]     Another way of identifying potential false positive detections by the gamma radiation sensing component  24  is by also detecting gamma-ray spectral characteristics. Each radioactive isotope emits gamma rays having an identifiable characteristic energy spectrum. By detecting the gamma ray spectrum, the specific source material can be easily identified. Detection can be registered as a spectral continuum or more simply in properly chosen discreet energy bins. Detectors and associated electronics that register radiation in specific energy windows are commercially available. For example, potassium  40  with an energy peak of 1.466 MEV can be readily distinguished from other isotopes and particularly from fissile materials having different energy peaks. Other naturally occurring and man-made isotopes can be distinguished in the same manner. The presence of heavy shielding (e.g., “high Z material”) between the radiation source and the detector can potentially degrade and smear the characteristic spectral lines and thus lessen the usefulness of spectral identification. However, commercially acceptable, legitimately shipped naturally occurring materials, such as potassium, are likely to be uniformly distributed in the cargo containers and not deliberately shielded. Hence, some of the radiation will still reach the detector unobstructed and will thus provide a means of detecting the associated energy spectrum and identifying signature. Man-made radiation sources also have characteristic radiation signatures and ideally will be declared on the shipping manifest to facilitate the occurrence of false positive detections.  
         [0027]     Although the sensing component  24  employed in connection with the present invention is extremely sensitive, in part due to the long detection times and highly sensitive detector structure, massive deliberate shielding of the interior of all or part of a container  12  remains a potential concern. For such shielding to be most effective, it must contain both gamma and neutron attenuating components. Gamma attenuating materials must be very dense and of a high atomic number, such as lead or a similar dense material. On the other hand, neutron attenuating materials must be of a low atomic weight but of a large volume. The conflicting shielding requirements between gamma radiation and neutrons are impractical in terms of both the container weight and volume constraints. To meet the weight constraints, the high density shielding required for gamma radiation must be concentrated right around the fissile material. This results in a disproportionately high weight to moment of inertia ratio for the container  12 . As a result, massive shielding within a container  12  can be detected by measuring the weight to moment of inertia ratio of the container  12 . Any container  12  having an unusually high weight to moment of inertia ratio is likely to have deliberate shielding and can be identified for further analysis. Thus, when the measured moment of inertia varies by a predetermined deviation amount, the detection controller  30  or the master unit/master module  46  may determine that heavy shielding is being used within a particular object to be tested  12 . To preclude degradation of the sensitivity of the gamma radiation sensing component  24  due to massive shielding, the present invention includes equipment (not shown) for measuring the mass and at least one but preferably three moments of inertia of each cargo container  12  at the port of embarkation, prior to loading the container  12  onto the container ship. Thus, measurement of a threshold mass/moment of inertia concentration can be considered to be a probable detection of a false negative condition.  
         [0028]     Alternatively, a rotational inertia test may be performed on each container  12  being shipped. The rotational inertia test comprises simply raising one or more edges of the container  12  and measuring the movement and/or acceleration for a given lifting force. The test may be performed along one or more axes. The density of any shielding material may be determined using a simple algorithm along with the measured test data and the total weight of the container  12 . The calculation provides an indication of how concentrated the total weight of the container  12  may be—a concentrated weight may be high density shielding (i.e., “high Z material” or the like). Thus, when the measured rotational inertia varies by a predetermined deviation amount, the detection controller  30  or the master unit/master module  46  may determine that heavy shielding is being used within a particular object to be tested  12 . This technique may be used to test for false negation in detection systems used for ship borne containers, trucks, cares, airline cargo containers and in almost any other shipping environments or non-shipping environment in which details of the contained material may be obscured from observation or might not otherwise be available.  
         [0029]     Performance of the present invention can be further enhanced by utilizing information from the shipping manifest and from other sources relating to the type of contents, the shipper, the destination, prior history of the cargo, etc. in combination with the gamma radiation sensing component  24  and related components. One example of the use of such information relates to the manifest of man-made radioactive sources or a threshold concentration of high density as discussed above. The combination of data from the present invention along with information from other sources improves the probability of the detection of fissile material and minimizes the probability of false positives or false negatives. Thus, the present invention includes provisions for merging data from various sources to improve true positive detection and to minimize false positives or false negatives.  
         [0030]     A neutron detector or any other suitable sensor could be employed instead of or in addition to the gamma radiation sensing component  24 . If a neutron detector is used in conjunction with the gamma radiation sensing component  24  both types of emissions would be measured with the measured information being provided on separate channels or multiplexed over a single channel. In addition, the gamma radiation sensing component  24 , neutron detector and/or other sensor would have self diagnostics to periodically confirm proper functionality and to provide an indication of any potential tampering and/or damage. The lack of an appropriate output signal from a gamma radiation sensing component  24 , neutron detector or other sensor would suggest that the associated container  12  could be suspect.  
         [0031]     The transmitter  26  is adapted to receive the output signal from the gamma and/or neutron radiation sensing component  24  and to transmit the signal in a manner well known to those of ordinary skill in the art. Preferably, the transmitter  26  is of the radio frequency type. However, it will be appreciated by those of ordinary skill in the art that the transmitter  26  may be of some other type such as an infrared or acoustic transmitter. Alternatively, the transmitter  26  may be of a type used in connection with satellite transmissions and/or a type used with cellular telephones. Alternatively, the transmitter  26  may use a spread spectrum or other efficient commercial communications method to facilitate transmission to and/or from a plurality of transmitters  26  arranged in an array, a matrix, a cluster and the like. Alternatively, the transmitter  26  may be a part of a transceiver, with the capability of sending as well as receiving signals. Any received signals would be routed to the controller  30  for execution of the received commands. The precise type of transmitter  26  employed should not be considered to be a limitation on the present invention. Preferably, the transmitter  26  includes a built in antenna or other transmitting element. Alternatively, a separate antenna (not shown) may be employed.  
         [0032]     The identification component or ID tagger  28  is also connected to the transmitter  26  for the purpose of transmitting identification information. Preferably, each sensor apparatus  20  can be uniquely identified utilizing the identification component  28  in combination with the transmitter  26 . The identification component  28  may use any of a variety of techniques including the use of a particular transmitter frequency, the use of digital identification techniques or the like. Accordingly, the particular techniques or technology used by the identification component  28  should not be considered to be a limitation on the present invention.  
         [0033]     A location component or location tagger  32  is also included to permit identification of the physical location of the sensor  20 . Again, any standard technique or device known to those skilled in the art may be employed for performing the functions of the location component  32 . Location information from the location component  32  is also transmitted by the transmitter  26 . Alternatively, the location information may be input to the receiver station ( FIG. 3 ) by bar coding or other means as would be recognized by one skilled in the art.  
         [0034]     The controller  30  is employed for controlling the operation of the gamma radiation sensing component  24 , the transmitter  26 , the identification component  28  and the location component  32 . The controller  30  may be a microprocessor, ASIC, or any other suitable known controlling device which has been programmed with software or firmware for providing the necessary control signals to the other components within the sensor apparatus  20 . For example, in one embodiment, the controller  30  may control the timing of the transmission by the transmitter  26  of the identification information and/or the information received from the gamma radiation sensing component  24 . Moreover, the controller  30  may control the operation of the other components to minimize battery life. Other control schemes or techniques will be apparent to those of ordinary skill in the art.  
         [0035]     The power source  34  is preferably a self contained, battery which contains sufficient energy to power the other components within the sensor apparatus  20  for at least the transit time of the container ship  10 . Preferably, the battery is of the rechargeable type. However, non-rechargeable batteries may alternatively be employed. The power source  34  also includes the necessary protection circuitry for the battery including a voltage regulator, short circuit protection, etc., as well as the necessary circuitry for recharging the battery. Although in the presently preferred embodiment a battery is employed as the primary power source, it will be appreciated by those of ordinary skill in the art that other power sources may be employed such as solar cells or the like. It will also be appreciated by those of ordinary skill in the art that external power may be supplied to the sensor apparatus  20  on a periodic basis to permit a form of “burst” transmission of the data obtained by the gamma radiation sensing component  24 . Accordingly, it will be appreciated by those of ordinary skill in the art that any suitable power source may alternatively be employed.  
         [0036]     As previously stated, the housing  22  containing the various components of the sensor apparatus  20  is adapted to be secured to a container  12 .  FIG. 1  illustrates a container in which three separate sensor apparatuses  20  are secured at three spaced locations on different sides of the container  12 . In particular, a first sensor apparatus  20  is secured to a first side panel of the container approximately one third of the distance from a first end, a second sensor apparatus is secured to an end panel of the container  12  and a third sensor apparatus  20  is secured to a top panel of the container  12  approximately one third of the distance from the second end of the container  12 . Alternatively, the first and third sensor apparatuses  20  can be affixed on the same side of the container. By positioning the three sensor apparatuses  20  in this manner, complete coverage of the interior of the container  12  and the surrounding vicinity may be obtained. It will be appreciated by those skilled in the art that a lesser or greater number of sensor apparatuses  20  may be used for a container  12 , for example, one for each container  12 . Additionally, a single sensor apparatus  20  may be used for detecting the presence of nuclear material in two or more containers.  
         [0037]     As discussed above, the primary concept of the present invention involves detecting the presence of radioactive or nuclear material within a container  12  during transit to take advantage of a longer detection time and to prevent entry of any nuclear or radioactive material into a country or port. To achieve this result, a receiver station  40  is provided. The receiver station  40  is preferably located on the container ship  10 . However, it will be appreciated by those of ordinary skill in the art that the receiver station  40  may be at some other location, such as a land-based location, if desired. All that is necessary is that the receiver station  40  have the ability to receive signals from the transmitter  26  of each sensor apparatus  20  within a container ship  10  either directly or indirectly such as through a satellite link or the like.  
         [0038]     As best shown in  FIG. 3 , the receiver station  40  includes a receiver  42 , a decoder  44  and an information processing system  46 . The receiver  40  is preferably of the same type as the transmitter  26  so that the receiver  40  is capable of receiving signals transmitted by the transmitter  26  of each sensor apparatus  20 . Preferably, the receiver  42  includes a built in antenna or, alternatively, a separate antenna (not shown) may be provided. The receiver  42  receives and demodulates signals received from the transmitter  26  for each of the sensor apparatuses  20 . However, special purpose processors may be used as well. The demodulated signals are then fed to a decoder  44  which is also of a type known to those of ordinary skill in the art. The decoder  44  effectively decodes the received signals and converts them to a digital format, sending them to the information processing system  46 . In the present embodiment, the information processing system is a personal computer which includes suitable software to permit analysis of the information signals received from each of the sensor apparatuses  20 . Preferably the information processing system  46  includes a database which is keyed to each individual sensor apparatus  20  utilizing the identification information provided by the identification component  28  of each sensor. The received information creates a background radiation space. Preferably, the information system  46  receives and stores in the database the information obtained from the gamma and neutron radiation sensing component  24  of each sensor apparatus  20 . Alternatively, a command center receives and stores a database of the information obtained from each sensor apparatus  20  and/or for each information system  46 . The received information from each sensor apparatus  20  permits the information system  46 , over time, to make adjustments for background or cosmic radiation to facilitate the identification of anomalies or unusual data which is likely to indicate the presence of radioactive material. Software available within the information processing system  46  analyzes the received information from each gamma and neutron radiation sensing component  24 , over time, for the purpose of determining background radiation and any such anomalies which could indicate the presence of radioactive or nuclear material. Typically, the entire set of sensor apparatuses  20  will measure the sum of any signal due to radioactive cargo and the background radiation at each sensor location. The background radiation level can be determined to high accuracy at each sensor location by fitting smooth curves to the radiation curve measured throughout the matrix of containers or objects to be tested and the associated sensor apparatuses  20  attached thereto which thereby creates the aforementioned background radiation space. Deviation in radiation count at any detector or sensor apparatus  20  over the smoothed background radiation level for that position are indications of local radioactivity. If the presence of radioactive or nuclear material is detected, the information processing system  46  transmits an alarm signal either to personnel on board the container ship  10  or to a central facility utilizing an indication output or transmitter  48 . The indication output  48  may be a cellular phone, satellite radio, Internet connection, or any other suitable device which may employed for transmitting the alarm signal to the desired location. The information processing system  46  also includes software which uses information from the location component  32  to identify the particular location on the container ship  10  where a sensor apparatus  20  detects the presence of radioactive material using the three dimensional container matrix  14 . In this manner, identification of a particular container  12  which may contain radioactive material is facilitated. Transmitter  48  may also have the capability of transmitting command signals to component  26  attached to container  20 , if the embodiment of component  26  is a transceiver. Thus, the master unit/master module  40  may be a monitoring device or a controlling device.  
         [0039]     It will be appreciated by those of ordinary skill in the art that while a particular preferred embodiment of a system for detecting the presence of radioactive material within a ship board container  12  has been described, the basic concepts of the present invention are applicable in other environments. For example, the same basic techniques and technology may be employed in sensing the presence of radioactive or nuclear material in containers  12  being shipped by other methods such as by rail, air, truck, etc. Further, the same techniques could alternatively be employed for detecting the presence of radioactive or nuclear material in a non-container environment such as non-container, bulk shipments, by merely placing sensor apparatuses  20  at various locations within, for example, the hold of a ship where bulk shipments are stored for transit. Thus, it will be appreciated by those of ordinary skill in the art that the basic concept of the invention is to make maximum use of the transit time for the purpose of detecting the presence of radioactive material and thereby eliminate or at least minimize the need to check individual containers or bulk shipments upon arrival at a port or other location. The preferred invention may also be utilized for non-modularized bulk shipments, for example on a ship, by regular loading and spacing of detector apparatuses  20  to that have larger area of detection and thus greater range of detection. If the arrays have directionality as well, locating the specific point within a larger space can be accomplished via triangulation. Location determination within a ship greatly facilitates intervention. Each module would still be linked to a central relay point as before. The larger arrays would compensate for lessened regularity of the array positioning and will use the transit time for most efficient detection a substantial improvement of detection accuracy and provide for intervention by the inspection authority during transit when flexibility of response is possible.  
         [0040]     The whole system transmission can be made more secure by proper encoding of all communications to and from the detection apparatuses  20  and the receiver station  40  as would be known to one skilled in the art.  
         [0041]     Each sensor or detector  24  can be calibrated during production for a particular energy spectrum response as compared to an isotopic element calibration standard. The calibration standard may also be attached or disposed on or near each sensor or detector  24  to serve as a continuous reference for comparison during measurement. Further, the sensors or detectors  24  may also be configured for field calibration or standardization as would be known in the art. Furthermore, each sensor or detector  24  can be operated with an automatic temperature calibration or compensation feature to facilitate consistent performance across a wide range of temperatures.  
         [0042]     The radioactive material detection system  10  described herein may be used in conjunction with, or integrated with other cargo security systems, such as chemical and biological detectors, tamper-proof security systems and information systems that may be used in cargo inspection systems. The radioactive material detection system  10  as described above can also incorporate human sensor technology. For example, an acoustic sensor or microphone, an odor sensor, a motion sensor or any other type of sensor which may detect the presence of humans could be included either within the sensor housing  22  or within a separate housing. Such a sensor could function continuously or could be activated by the controller  30  or by the receiver station  40  to confirm the presence of a human stowaway or “minder” within a container  12 . The detection of the presence of a human within a container  12  together with the detection of radioactive material in the container  12  provides additional confirmation of the successful use of the radioactive material detection system  10 . Thus, it is contemplated that the present invention can be used in combination with a live being detector configured to detect the presence of a live being within an object to be tested  12 , like a container  12  described above.  
         [0043]     Successful detection of fissile or “dirty” nuclear waste material is a function of a number of variables: fissile strength, shielding of target, attenuation of target by surrounding material, area of detection devise, and time available for detection. The latter variable, the time of detection, will overcome all other variables in successful detection.  
         [0044]     The sensor apparatus  20  could also be used with a GPS system for identifying the location of a container  12 , truck, or other object to be tested, etc. to which the sensor apparatus  20  may be secured. In addition, the sensor apparatus  20  may be used to indicate that the seal of a container has been breached.  
         [0045]     When the present invention is implemented as a communication-linked system  10 , the system  10  can also be used to perform other vital and non-vital functions such as commercial GPS locating, protection against clandestine opening of the transportation unit and simple logistical information polling. The linked data can be compared to a database of manifest shipping information to identify the parties involved in the shipment of the target shipment, thus proving for rapid investigation even during transit and to resolve a target identification of legitimate cargo.  
         [0046]     It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.