Abstract:
The invention is a digital radiation detector utilizing the stable timing functions of a microcontroller or plurality of microcontrolling devices to perform three independent functions. A first timer generates a continuous square wave output that is fed through a class B amplifier to yield a stable, drift-free power supply for a connected radiation sensor. A second timer is used as an event counter for counting the processed pulses coming from the radiation sensor. A third timer acts as a real time clock generating a one-second interrupt for quantifying the number of counts per second. The number of counts per second can be communicated as raw data through a communication interface or presented as a number of audible or visual displays.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to devices used to detect radiation. Specifically, the invention concerns apparatus and circuits that are used to detect and measure the radiation released from a radiological device, a so called dirty bomb, or associated with radioactive fallout following a nuclear or thermonuclear detonation.  
         [0003]     2. Description of the Prior Art  
         [0004]     Terrorist threats to the safety and stability of civilized countries have become an unfortunate reality of the modern era. The devastating attack upon the world trade towers in New York City clearly demonstrated that the nature of terrorist attacks has shifted in recent years. Formerly, modestly organized insurgent groups limited their attacks to small-scale targets, typically motivated by political interest, religious extremism, or the desire to release their captured cohorts. Today&#39;s terrorists are highly organized, well financed, multi-national organizations bent on the broad destruction of capital assets and the senseless mass killing of innocent noncombatants.  
         [0005]     Modern terrorists have enbarked on a campaign to obtain and use weapons of mass destruction, or WMDs. One such WMD is the radiological device or ‘dirty bomb’. A dirty bomb consists of radiological material, such as low-grade uranium, and a disbursement means for distributing the radiological material over a large area, thereby indiscriminately exposing a population and inducing radiation sickness. In a typical dirty bomb, minimally processed uranium is packed around a core of conventional high explosive. Once the high explosive is detonated, a cloud of finely particulate radiological material is distributed over a moderately large area. Alternatively, the disbursement means may be a low-flying aircraft distributing fine particulates of radiological material.  
         [0006]     A second WMD of concern is the nuclear or thermonuclear bomb. During a nuclear bomb detonation, nuclear fission is induced in highly processed uranium and/or plutonium. During a thermonuclear bomb detonation, nuclear fission is itself employed as a primer for the thermonuclear fusion of hydrogen isotopes such as deuterium or tritium. During both nuclear and thermonuclear detonations, enormous amounts of energy are released in the form of a destructive shock wave and fireball. Radiological material is ejected over a broad area as nuclear fallout causing radiation sickness long after the initial destruction. However, while nuclear and thermonuclear devices combine radiation poisoning with immediate, large-scale capital destruction, they are extremely complex devices requiring highly processed material, such as plutonium-238, and considerable technical expertise to construct.  
         [0007]     Of the two WMDs identified above, the dirty bomb is considered the greatest potential threat due to the relative ease with which low-grade radiological material can be obtained and the low-technology associated with its disbursement means. Dirty bombs have the desired effect of creating terror to the public at large as well as incurring tremendous cost and clean up effort to make an affected area safe again as defined by government agencies such as the United States Environmental Protection Agency.  
         [0008]     Accurate means for both detecting and quantifying the presence of radiological material are not known in general practice. Prior art detectors are analog devices based on Geiger counter techniques. Such Geiger counters are notoriously imprecise due to thermal drift instability in the circuit design. What is needed is a more precise, digital counter capable of accurately defining the normal background level at the installation and an elevated level due to the introduction of radioactive material. For a digital counter to work properly, a novel stable power supply is required since any drift in voltage may cause false alarms.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention is a novel, digital radiation detector utilizing the stable timing functions of a microcontroller or plurality of microcontrolling devices to perform three independent functions. A first timer generates a continuous square wave output that is fed through a class B amplifier to yield a stable, drift-free power supply for a connected radiation sensor. A second timer is used as an event counter for counting the processed pulses coming from the radiation sensor. A third timer acts as a real time clock generating a one-second interrupt for quantifying the number of counts per second. The number of counts per second can be communicated as raw data through a communication interface or presented as a number of audible and/or visual displays. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  shows a functional block diagram of the present invention.  
         [0011]      FIG. 2  is a schematic diagram of the timing/controller elements of the present invention.  
         [0012]      FIG. 3  is a schematic diagram of the stable power supply elements of the present invention.  
         [0013]      FIG. 4  is a schematic diagram of the pulse conditioning circuit of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]     With reference to  FIGS. 1-4 , microcontroller U 1  comprises a plurality of timers each with different functions. Microcontroller U 1  uses an external crystal X 1  to produce the master clocks for these timers. From this, the clock signal of first timer  1  is divided down to produce an initial square wave  2  with a frequency of less than 9 kHz, and most preferably with a frequency in the range of 1.5 kHz and 1.75 kHz, in order to reduce potential electromagnetic interference with other nearby devices not associated with the detector. Initial square wave  2  is fed to power supply  13  wherein initial square wave  2  is buffered and inverted by inverter/buffer U 2  to produce first square wave  3  and second square wave  4  that are 180 degrees out of phase from each other. Each of first square wave  3  and second square wave  4  then feeds to an appropriate transistor Q 1  and Q 2  configured as a Class B amplifier  5  driving push/pull transformer T 1 .  
         [0015]     A Class B amplifier is preferable to other amplifier types for this application due to the stability of the output and the lack of thermal drift. Class A amplifiers require excessive power to produce the same level of drive. A self-oscillating Colpitts oscillator experiences thermal drift with aging and produces a wave of varying amplitude which is unacceptable in a sensitive radiation detector.  
         [0016]     The output of transformer T 1  is a sine wave  7  of a much higher voltage which is fed through a Walton Cockroft multiplier  6  made up of diodes D 1  through D 6  and capacitors C 2  through C 7  of which C 7  acts as a final filter capacitor. This produces a high voltage direct current (DC) which is required by radiation sensor  8 .  
         [0017]     Radiation sensor  8  may consist of a Geiger-Muller tube, a photomultiplier tube with a scintillation crystal, or other radiation-sensing elements known in the art of radiation detection. All radiation sensors known in the art require the stable high voltage fed by first timer  1 .  
         [0018]     Radiation sensor  8  produces an electrical signal pulse  9  when struck by a nuclide that has been emitted from a radioactive material. In the case where radiation sensor  8  consists of a Geiger-Muller tube, pulse  9  is output from the cathode of the tube. In the case where radiation sensor  8  consists of a photomultiplier tube with a scintillation crystal, pulse  9  is output from the anode of the tube. The present invention works equally well with pulses output from these or other devices known in the art.  
         [0019]     Signal conditioner  10  attenuates the amplitude of raw pulse  9  and squares off the ascending and descending voltage of raw pulse  9  to produce a clean voltage change that is identifiable by microcontroller U 1  as a countable radiological event. Raw pulse  9  enters signal conditioner  10  via resistor R 5  where it is divided down by resistor R 6  and clamped by diode CR 3 . The junction of diode CR 3 , resistor R 5 , and resistor R 6  is fed to the base of NPN transistor Q 3  which has a pull-up resistor R 4  from its collector. The collector of transistor Q 3  and the junction of resistor R 4  is fed as conditioned pulse  18  to the Schmidt trigger input RA 4  of microcontroller U 1  which clocks the input to second timer  11 . Second timer  11  acts as an event counter and is incremented upon every conditioned pulse  18 .  
         [0020]     Third timer  12  receives its clock signal from external crystal X 1 . This clock signal is divided down within third timer  12  to produce a software interrupt at predetermined, convenient intervals. Typically the time interval between interrupts is one-second, although other values such as ten seconds, one minute, or one hour may be equally employed. Alternatively, by using an external real time clock (not shown), it is possible to generate an equivalent hardware interrupt without using microcontroller U 1 . The hardware or software interrupt, when serviced, will read the value of the software register located in second timer  11  and subsequently reset the register in second timer  11  to zero. This register value correlates to the number of pulse counts per time interval, and hence, the number of events per time interval. Counts per second is typically the value of interest.  
         [0021]     First timer  1 , second timer  11 , and third timer  12  may be efficiently run using a single microcontroller. Suitable types include, for example, the Microchip™ PIC 16C or 18F series. However, it may also be advantageous to use a plurality of microcontrollers to perform these functions in parallel. In one such embodiment, multiple, remotely-located radiation sensors  8  might each include its own first timer  1  and associated power supply circuitry  13  while second timer  11  and third timer  12  might reside together in a single master microcontroller, which is in turn connected to all remotely-located radiation sensors  8 . In order to function properly, first timer  1 , power supply  13 , radiation sensor(s)  8 , signal conditioner  10 , and second timer  11  must be capable of passing a signal between each other either through hard or wireless interfaces.  
         [0022]     The number of counts per time interval  17  is provided as an output from microcontroller U 1 . Counts per time interval  17  may be outputted as raw data through one or more communication interface  15 . The raw data may require additional processing by processor  14 . Processor  14  function may be performed within microcontroller U 1  or by a separate stand-alone component. Communication interface  15  may comprise RS-232, RS-485, universal serial bus (USB), 10/100 Mbps Ethernet, radio frequency (RF), IEEE 802.11 wireless fidelity network (WiFi), infra-red data (IRD), Inter-Integrated Circuit-bus (I 2 C-bus), IEEE 1394 (Firewire) or other interfaces common in the art of electronic data communication.  
         [0023]     Alternatively, the number of counts per time interval  17  may be further processed by processor  14  and presented through one or more audio/visual display  16 . Again, processor  14  function may be performed within microcontroller U 1  or by a separate stand-alone component. In a first embodiment, the number of counts per time interval  17  may be processed to illuminate a series of colored light emitting diodes (LED) depending upon predetermined threshold values. The colors green, blue, yellow, amber, and red are commonly used to represent ascending threat levels based on such predetermined threshold values. In a second embodiment, the number of counts per time interval  17 , using the same microprocessor U 1  or another microprocessor, may be processed using a predetermined threshold value to trigger a piezo-electric buzzer, another audible device such as a siren, or a visual device such as a strobing light. In a third embodiment, the number of counts per time interval  17  may be converted using the same microprocessor U 1  or another microprocessor for output to a seven-segment LED display. In a fourth embodiment, the number of counts per time interval  17  may be processed using the same microprocessor U 1  or another microprocessor for alphanumeric or graphical output to a liquid crystal display (LCD). In a fifth embodiment, the number of counts per time interval  17  may be integrated with the output from a video camera such that the number of counts per second is superimposed on the video signal using on-screen display (OSD).  
         [0024]     While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.