Abstract:
A method and apparatus for the detection of radioactive material in an area is disclosed. The apparatus comprises a transmitter operatively arranged to transmit electromagnetic radiation, a receiver operatively arranged to measure an intensity of the electromagnetic radiation, and processing means operatively arranged to determine the presence of radioactive material based on the intensity measurement. Two receiver configurations are possible. In the first, the receiver measures the intensity of the electromagnetic radiation reflected by ion tracks in the air proximate to the area scanned for radioactive material. Alternatively, the receiver measures the intensity of the electromagnetic radiation transmitted by the air proximate to the area scanned for radioactive material.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to the detection of radioactive materials. More specifically it relates to a method and apparatus for the detection of radioactive materials using electromagnetic radiation. Even more specifically, the present invention relates to a method and apparatus for the detection of radioactive material by detecting the reflection of electromagnetic radiation from ion tracks created by alpha, beta, and gamma radiation.  
         BACKGROUND OF THE INVENTION  
         [0002]    It is well known that emissions from radioactive materials, alpha and beta particles and gamma rays, are extremely dangerous to both plants and animals. Various means to detect the presence of radioactive materials have been developed. One of the most common and well-known radiation measuring apparatuses is the Geiger counter. The Geiger counter detects the ionization that occurs in the atmosphere due to the presence of alpha and beta particles and gamma rays. A Geiger counter typically comprises a tube enclosing a cylinder cathode surrounding a rod-like anode. The cathode and anode are connected through an end wall of the tube to a source of electrical voltage. The tube is filled with a gas, usually a mixture of an inert gas, such as argon or neon, and a halogen, such as chlorine or bromine, at a low pressure, e.g., a few centimeters of mercury. A high voltage, e.g. 550 volts, is set up between the cylinder and the anode. This voltage is just a little less than that needed to create an electrical discharge between the two electrodes.  
           [0003]    When a charged particle of sufficient energy enters the tube, it knocks electrons out of the atoms of the gas. These electrons, being negatively charged, are attracted towards the anode, and the atoms from which the electrons originated (which become positively charged ions) are attracted by the cathode. The high voltage established between the anode and cathode creates a high voltage gradient that accelerates the liberated electrons sufficiently to knock further electrons out of atoms, which in turn are accelerated by the high voltage gradient to knock still further electrons out of other atoms, creating an “avalanche” of electrons. As the avalanche of electrons continues, the positive ions are also accelerated towards the cathode wall. These positive ions strike the cathode wall with sufficient energy to release still additional electrons. All of these electrons descend on the anode wire and are detected as a pulse of electric current. The occurrence of this pulse thus indicates that a charged particle has passed through the tube. The electrical pulses can then be amplified and counted, using appropriate electronic counting circuitry, and/or converted to audible sound, to provide a user of the Geiger counter a quantitative and/or qualitative measure of the number of charged particles encountered by the Geiger counter.  
           [0004]    An underlying problem with Geiger counters, and other radiation detecting apparatuses, is that they must be within the vicinity of the radioactive material to detect it. This means that they need to be carried to the area to be evaluated, exposing human personnel to the radiation. Even if carried by a remotely operated vehicle, the vehicle may be exposed to radioactive material and need to be cleaned before human personnel can safely come in contact with it.  
           [0005]    Clearly, then, there is a longfelt need for a radioactive material detection apparatus that can detect the presence of radioactive materials from a distance, to prevent potential exposure of the apparatus and the user to radioactive material.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention broadly comprises a method and apparatus for the detection of radioactive material in an area. The apparatus comprises a transmitter operatively arranged to transmit electromagnetic radiation, a receiver operatively arranged to measure an intensity of the electromagnetic radiation, and processing means operatively arranged to determine the presence of radioactive material based on the intensity measurement.  
           [0007]    A general object of the present invention is to provide a method and apparatus to remotely detect radioactive material.  
           [0008]    Another object of the present invention is to provide a method and apparatus to detect ion tracks in the atmosphere.  
           [0009]    These and other objects, features and advantages of the present invention will become readily apparent to those having ordinary skill in the art upon a reading of the following detailed description of the invention in view of the drawings and claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The nature and mode of operation of the present invention will now be more fully described in the following detailed description of the invention taken with the accompanying drawing figures, in which:  
         [0011]    [0011]FIG. 1 is a view of a Geiger counter being used to test a substance for radioactive material;  
         [0012]    [0012]FIG. 2 is a view of an embodiment of the present invention testing an object emitting alpha radiation;  
         [0013]    [0013]FIG. 3 is a view of an embodiment of the present invention testing an object emitting beta and/or gamma radiation;  
         [0014]    [0014]FIG. 4 is a schematic of a typical embodiment of the present invention;  
         [0015]    [0015]FIG. 5 is a schematic of an embodiment of the present invention that measures the amount of radio frequency radiation reflected by ionization trails.  
         [0016]    [0016]FIG. 6 is a schematic of an embodiment of the present invention that measures the amount of radio frequency radiation attenuated by ionization trails. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]    It should be appreciated that, in the detailed description of the invention which follows, like reference numbers on different drawing views are intended to identify identical structural elements of the invention in the respective views.  
         [0018]    As is known in the art, alpha, beta, and gamma radiation ionize molecules in the air as they traverse the air, creating tracks of ionized molecules. Alpha particles produce ion tracks that are approximately 1-10 cm. Gamma rays do not directly ionize air molecules. Instead gamma particles produce beta particles that ionize the surrounding air. Thus, both gamma and beta radiation will produce similar ion tracks, which are relatively longer, on the order of 10-100 cm. Ion tracks created by either alpha or beta particles last approximately 1 ms.  
         [0019]    [0019]FIG. 1 shows a person using Geiger counter  10  to determine if object  11  is emitting radiation. As discussed above, tube  15  detects ion tracks created in the presence of radioactive material. Unit  12  provides electrical power to the tube for maintaining a voltage between the anode and the cathode. As described above, the user must be proximate the object  11  to determine if it contains radioactive material, which exposes the user to the potential radiation hazard.  
         [0020]    [0020]FIG. 2 shows a person using an embodiment of the present invention to determine if object  24  contains radioactive material emitting alpha particles. Apparatus  20  emits radio frequency waves  22  in the direction of object  24 . If object  24  contains radioactive material emitting alpha particles, then relatively short ion tracks  21  will be created in the air surrounding object  24 . If the wavelength of waves  22  is comparable to the length of tracks  21 , then tracks  21  will act as antennae in a similar manner to chaff. By emitting waves  22  at frequencies in the range of approximately 3 to 30 GHz, waves  22  will be reflected by tracks  21 . By detecting the level of the reflected radiation, the amount of ionization in the air can be determined, and the presence of radioactive material emitting alpha particles in object  24  can be confirmed.  
         [0021]    [0021]FIG. 3 depicts longer tracks  31  being created in the atmosphere proximate object  34 , such as those created by the presence of beta particles in the atmosphere. Apparatus  20  emits radio frequency waves  32  to determine the presence of radioactive materials in object  34 . Emitting radio frequency radiation having a frequency of approximately 300 MHz to 3 GHz enables apparatus  20  to detect beta and gamma radiation. In a preferred embodiment, the frequency is varied within the range of 300 MHz to 30 GHz to determine if any alpha, beta, or gamma particles are being emitted by an object being tested. However, it should be readily apparent to one skilled in the art that radio waves having frequencies outside the range of 300 MHz to 30 GHz can be used to detect ion tracks, and these modifications are within the spirit and scope of the invention as claimed.  
         [0022]    As stated above, the ion tracks last on the order of 1 ms. To separate the return from different tracks, a preferred embodiment of the present invention maintains a spacing of 1 ms between each transmitted pulse. In a preferred embodiment, the pulse length is 10% of the range of the object being tested. Thus, testing objects at 3000 m would result in a pulse length of 1 μm. Including a 1 ms pause between pulses results in a pulse rate frequency of 1/(0.001001 seconds) or 999 Hz. Since the distance at which objects are to be tested ranges from 10 m to 10 km, pulse lengths range from 33 ns to 33 μs. Thus pulse repetition frequencies range from approximately 968 Hz to 1 kHz, in a preferred embodiment. However, it should be readily apparent to one skilled in the art that other pulse lengths and rates could be used to detect ion trails, and these modifications are within the spirit and scope of the invention as claimed.  
         [0023]    [0023]FIG. 4 shows a schematic of a typical pulse-doppler radar system  100  that can be used to practice the present invention. Apparatus  100  comprises planar array antenna  108 , which is operatively arranged to both send and receive radio frequency radiation. Exciter  102  produces a signal at the desired transmission frequency and phase for the transmitter, and a reference signal used by the receiver. Transmitter  104  amplifies the signal it receives from the exciter to generate radio frequency pulses. Transmitter  104  is typically a traveling wave tube, well known in the art. Duplexer  106  allows transmission waves to travel from the transmitter to the antenna and received waves to travel from the antenna to the receiver protection device  110 , but attenuates all other signals. Antenna  108  directs the radio frequency wave in a desired direction and receives electromagnetic radiation from that direction. Radio frequency waves incident on antenna  108  pass through receiver protection device  110  to receiver  112  as long as the waves have a power level below a predetermined threshold. Device  110  attenuates signals above the predetermined threshold to prevent receiver  112  from being exposed to signals that would damage the receiver circuits. The receiver mixes the return with the reference signal from the exciter to produce video frequency signals. The video signals are sent to signal processor  114 . Signal processor  114  analyzes the video signals and determines if any targets have been detected. The targets are shown on display  116 . A user viewing the display can determine, based on the returns displayed, if there is any radioactive material in the object being tested. Controls  120  send commands to the antenna. These commands can be user generated or a predetermined search pattern. Radar data processor  118  modifies these commands if the radar system is moving relative to the ground. The modified commands are sent to drive  122  that adjusts the orientation of the antenna. It should be readily apparent to one skilled in the art that other components known in the art can be used to implement the present invention, and these modifications are within the spirit and scope of the invention as claimed. It should also be readily apparent to one skilled in the art that the present apparatus can activate an audible and/or visible alarm when a predetermined level of return is received, rather than requiring a user to watch a display to determine the presence of radioactive material. These modifications are also within the spirit and scope of the invention as claimed.  
         [0024]    [0024]FIG. 5 shows an embodiment of the present invention  70  comprising radio frequency antenna  71 . The antenna shown in FIG. 4 is operatively arranged to both send and receive radio frequency radiation  72 , as shown by the arrows. The radiation  72  is reflected by ion tracks  73  created by radioactive particles emitted by object  74 . Unit  75  comprises the rest of the apparatus, an example being shown in FIG. 4. Apparatus  70  determines the level of radio frequency radiation reflected by ion tracks  73 , and determines the presence of radioactive material from this measurement.  
         [0025]    [0025]FIG. 6 shows an alternative embodiment of the present invention. Apparatus  80  comprises antenna  71  operatively arranged to emit radio frequency waves  72 . Receiver  82  is operatively arranged to receive waves  72  that are transmitted through the air proximate object  74 . Line  81  connects receiver  82  with unit  75 , which comprises the rest of the apparatus. Thus, if object  74  comprises radioactive matter, ion tracks  73  will reflect some of waves  72 . Receiver  82  will thus detect attenuation in the radio frequency wave emitted by transmitter  71 . By measuring the level of attenuation, the presence of radioactive matter in object  74  can be determined. It should be readily apparent to one skilled in the art that these and other configurations may be used to determine the level of radio frequency radiation scattered or transmitted by a volume, and these modifications are intended to be within the spirit and scope of the invention as claimed.  
         [0026]    Additionally, individual tracks may be detected if the radar energy is intense enough. This will occur if the electric field produced by the radar is strong enough to produce secondary ionization and thus amplify the ionization due to the radioactivity. Thus, the present invention determines the presence of radioactive material by detecting individual ion tracks, measuring the amount of radiation scattered by ion tracks, or measuring the amount of attenuation by ion tracks of a signal transmitted through a volume of air near an object. Based on the strength of the scattering return or attenuation, the present invention can also determine the strength of the radioactive material present.  
         [0027]    It should be readily apparent to one skilled in the art that the above-described invention may be used as a stationary unit, in which case the frequency of the waves reflected or transmitted should be approximately the same as the transmitted wave. The present invention may also be used while being moved, in which case the reflected or transmitted wave received by the receiver may be doppler shifted from the transmitted wave. In this case, the apparatus is operatively arranged to account for any doppler shifts due to the movement of the transmitter and/or receiver. The present invention practiced with a moving or stationary transmitter, receiver, or transceiver is intended to be within the spirit and scope of the invention as claimed.  
         [0028]    Thus, it is seen that the objects of the present invention are efficiently obtained, although modifications and changes to the invention should be readily apparent to those having ordinary skill in the art, and these modifications are intended to be within the spirit and scope of the invention as claimed.