EP2401636A2 - Système et procédé d'amélioration de la détection de rayons gamma/neutrons - Google Patents

Système et procédé d'amélioration de la détection de rayons gamma/neutrons

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Publication number
EP2401636A2
EP2401636A2 EP10746841A EP10746841A EP2401636A2 EP 2401636 A2 EP2401636 A2 EP 2401636A2 EP 10746841 A EP10746841 A EP 10746841A EP 10746841 A EP10746841 A EP 10746841A EP 2401636 A2 EP2401636 A2 EP 2401636A2
Authority
EP
European Patent Office
Prior art keywords
neutron
detector
gamma
sensor
high speed
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP10746841A
Other languages
German (de)
English (en)
Inventor
David L. Frank
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Innovative American Technology Inc
Original Assignee
Innovative American Technology Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US12/483,066 external-priority patent/US20120175525A1/en
Application filed by Innovative American Technology Inc filed Critical Innovative American Technology Inc
Publication of EP2401636A2 publication Critical patent/EP2401636A2/fr
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
    • G01T1/16—Measuring radiation intensity
    • G01T1/20—Measuring radiation intensity with scintillation detectors
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T3/00—Measuring neutron radiation
    • G01T3/06—Measuring neutron radiation with scintillation detectors

Definitions

  • the present invention generally relates to the field of gamma and neutron detection, and more particularly relates to gamma and neutron detectors deployed in passive or active detection of special nuclear materials
  • a system for detecting at least one of nuclear and fissile materials includes a plurality of high speed scintillator detectors Each high speed scintillator detector in the plurality of high speed scintillator detectors includes a pre-amp circuit adapted to eliminate pulse stretching (distortion) and at least one of pulse stacking and pulse loses
  • An isotope database includes a plurality of spectral images Each spectral image in the plurality of spectral images corresponds to a different known isotope
  • An information processing system is communicatively coupled to the plurality of high speed scintillator detectors and the isotope database The information processing system is adapted to compare spectral data received from each of the plurality of high speed scintillator detectors to one or more of the spectral images in the isotope database and identify one or more isotopes present in an object or container being monitored
  • a high speed scintillator is disclosed The high speed scintillator includes at
  • a passive high performance neutron and gamma scintillation detection system for the detection and identification of shielded special nuclear mate ⁇ al.
  • the system comp ⁇ ses at least one neutron detector and at least one gamma detector
  • Each of the at least one neutron detector and the at least one gamma detector comp ⁇ ses a pre-amp circuit configured to eliminate pulse stretching (distortion) and at least one of pulse stacking and pulse losses
  • An isotope database comp ⁇ ses a plurality of spectral images, wherein each spectral image in the plurality of spectral images corresponds to a different known isotope
  • An information processing system is communicatively coupled to the plurality of high speed scintillator detectors and the isotope database The information processing system is adapted to compare spectral data received from each of the plurality of high speed scintillator detectors to one or more of the spectral images in the isotope database and identify one or more isotopes present in an object being monitored.
  • the speed of the detector preserves the original pulse shape, without distortion, enabling more efficient gamma and neutron differentiation and discrimination in the detector This allows for highly efficient neutron detectors that can be coupled with advanced background subtraction techniques to allow for neutron detections with only three to four counts above background neutrons
  • the neutron background can be reduced using the high performance electronics discussed below that eliminate false positive within the neutron detector from gamma energy
  • Additional embodiments of the high speed gamma and/or neutron detector attach a temperature sensor onto the crystal to define the specific operating temperature of the high speed detector
  • the operating temperature of the high speed scintillation detector can be used as a reference for calibration of the high speed scintillation detector
  • Advanced moderator mate ⁇ als and moderator designs for thermal neutron detectors can be applied to increase detection performance
  • FIG l is a block diagram illustrating an example of a system according to one embodiment of the present invention
  • FIG 2 is block diagram of a gamma and neutron detector according to one embodiment of the present invention
  • FIG 3 is a schematic illustrating a neutron detector and its supporting components according to one embodiment of the present invention
  • FIG 4 is a circuit diagram for a pre-amp according to one embodiment of the present invention
  • FIG 5 is top-planar view of a neutron detector according to one embodiment of the present invention
  • FIG 6 is a graph illustrating a neutron pulse generated from a neutron detector according to one embodiment of the present invention
  • FIG 7 is a graph illustrating a gamma pulse generated from a neutron detector according to one embodiment of the present invention
  • FIG 8 is a block diagram illustrating a detailed view of an information processing system according to one embodiment of the present invention
  • FIG 1 is a block diagram illustrating one example of a gamma/neutron detector system 100 according to one embodiment of the present invention
  • a data collection system 102 is communicatively coupled via cabling, wireless communication link, and/or other communication links 104 with one or more high speed sensor interface units (SIU)
  • SIU high speed sensor interface units
  • the high speed sensor interface units 106, 108, 110 each support one or more high speed scintillation (or scintillator) detectors, which in one embodiment comp ⁇ se a neutron detector 112, a neutron detector with gamma scintillation material 114, and a gamma detector 116
  • Each of the one or more SIUs 106, 108, 110 performs analog to digital conversion of the signals received from the high speed scintillation detectors 112, 114, 116
  • An SIU 106, 108, 110 performs digital pulse discrimination based on one or more of the following pulse height, pulse rise-time, pulse fall-time, pulse-width, pulse peak, and pulse pile-up filter
  • the data collection system 110 includes an information processing system (not shown) comp ⁇ sing data communication interfaces (not shown) for interfacing with each of the one or more SIUs 124
  • the data collection system 110 is also communicatively coupled to a data storage unit 103 for sto ⁇ ng the data received from the SIUs 106, 108, 110
  • the data communication interfaces collect signals from each of the one or more high speed scintillation detectors such as the neutron pulse device(s) 112, 114 and the gamma detector 116
  • the collected signals represent detailed spectral data from each sensor device 112, 114, 116 that has detected radiation
  • the SIU(s) 124 can discriminate between gamma pulses and neutron pulses in a neutron detector 112 The gamma pulses can be counted or discarded
  • the SIU(s) 106, 108, 110 can discriminate between gamma pulses and neutron pulses in a neutron detector with gamma scin
  • the data collection system 102 in one embodiment, is modular in design and can be used specifically for radiation detection and identification, or for data collection for explosives and special materials detection and identification
  • the data collection system 102 is communicatively coupled with a local controller and monitor system 118
  • the local system 118 comp ⁇ ses an information processing system (not shown) that includes a computer system(s), memory, storage, and a user interface 120 such a display on a monitor and/or a keyboard, and/or other user input/output devices
  • the local system 118 also includes a multi-channel analyzer 122 and a spectral analyzer 124
  • the multi-channel analyzer (MCA) 122 can be deployed in the one or more SIUs 106, 108, 110 or as a separate unit 122 and comp ⁇ ses a device (not shown) composed of many single channel analyzers (SCA)
  • SCA single channel analyzer
  • a scintillation calibration system 126 uses temperature references from a scintillation crystal to operate calibration measures for each of the one or more high speed scintillation detectors 112, 114, 116
  • These calibration measures can be adjustments to the voltage supplied to the high speed scintillation detector, adjustments to the high speed scintillation detector analog interface, and or software adjustments to the spectral data from the high speed scintillation detector 112, 114, 116
  • high speed scintillator detector 112, 114, 116 can utilize a temperature sensor in contact with the scintillation crystal and/or both in the photosensor of the detector to determine the specific operating temperature of the crystal The specific operating temperature can be used as a reference to calibrate the high speed scintillation detector
  • the detector crystal and the photosensor both may have impacts on detector signal calibration from changing temperatures
  • a temperature chamber can be used to track the calibration changes of an individual detector, photosensor or mated pair across a range of temperatures The calibration characteristics are then mapped and used as a reference against
  • Histograms representing spectral images 128 are used by the spectral analysis system 124 to identify fissile materials or isotopes that are present in an area and/or object being monitored
  • One of the functions performed by the local controller 118 is spectral analysis, via the spectral analyzer 124, to identify the one or more isotopes, explosives, or special materials contained in a container under examination
  • background radiation is gathered to enable background radiation subtraction
  • Background neutron activity is also gathered to enable background neutron subtraction This can be performed using static background acquisition techniques and dynamic background acquisition techniques Background subtraction is performed because there are gamma and neutron energies all around These normally occurring gamma and neutrons can interfere with the detection of the presence of (and identifying) isotopes and nuclear mate ⁇ als
  • the spectral analyzer 124 compares one or more spectral images of the radiation present to known isotopes that are represented by one or more spectral images 128 stored in the isotope database 130. By capturing multiple variations of spectral data for each isotope there are numerous images that can be compared to one or more spectral images of the radiation present.
  • the isotope database 130 holds the one or more spectral images 128 of each isotope to be identified. These multiple spectral images represent various levels of acquisition of spectral radiation data so isotopes can be compared and identified using various amounts of spectral data available from the one or more sensors.
  • the spectral analysis system 124 compares the acquired radiation data from the sensor to one or more spectral images for each isotope to be identified. This significantly enhances the reliability and efficiency of matching acquired spectral image data from the sensor to spectral image data of each possible isotope to be identified.
  • the local controller 118 can compare the isotope mix against possible materials, goods, and/or products that may be present in the container under examination.
  • a manifest database 132 includes a detailed description (e.g., manifests 134) of the contents of a container that is to be examined.
  • the manifest 134 can be referred to by the local controller 118 to determine whether the possible materials, goods, and/or products, contained in the container match the expected authorized materials, goods, and/or products, described in the manifest for the particular container under examination. This matching process, according to one embodiment of the present invention, is significantly more efficient and reliable than any container contents monitoring process in the past.
  • the spectral analysis system 124 includes an information processing system (not shown) and software that analyzes the data collected and identifies the isotopes that are present.
  • the spectral analysis software is able to utilize more than one method to provide multi-confirmation of the isotopes identified. Should more than one isotope be present, the system 124 identifies the ratio of each isotope present.
  • methods that can be used for spectral analysis for fissile material detection and isotope identification.
  • the data collection system 102 can also be communicatively coupled with a remote control and monitoring system 136 via at least one network 138.
  • the remote system 136 comprises at least one information processing system (not shown) that has a computer, memory, storage, and a user interface 140 such as a display on a monitor and a keyboard, or other user input/output device.
  • the networks 104, 138 can be the same networks, comprise any number of local area networks and/or wide area networks.
  • the networks 104, 138 can include wired and/or wireless communication networks.
  • the user interface 140 allows remotely located service or supervisory personnel to operate the local system 118; to monitor the status of shipping container verification by the collection of sensor units 106, 108, 110 deployed on the frame structure; and perform the operations/functions discussed above from a remote location.
  • the neutron detector such as the neutron detector 112 or 114 of FIG. 1.
  • the neutron detector of various embodiments of the present invention provides high levels of efficiency with near zero gamma cross talk.
  • the neutron detector is a high efficiency neutron detector that uses a scintillator medium coupled with fiber optic light guides with high speed analog to digital conversion and digital electronics providing digital pulse shape discrimination for near zero gamma cross talk.
  • the neutron detector of various embodiments of the present invention is important to a wide va ⁇ ety of applications such as portal detectors, e g , devices in which a person or object is passed through for neutron and gamma detection, fissile mate ⁇ al location devices, neutron based imaging systems, hand held, mobile and fixed deployments for neutron detectors
  • the neutron detector in various embodiments of the present invention can utilize the Systems Integration Module for CBRNE sensors discussed in the commonly owned U S Patent No 7,269,527, which is incorporated by reference herein in its entirety
  • FIG 2 is a block diagram illustrating a more detailed view of a neutron detector 200 according to one embodiment of the present
  • the neutron detector 200 in this example, comprises a neutron moderator mate ⁇ al 202 such as polyethylene
  • the neutron detector 200 also comprises scintillation mate ⁇ al that can comp ⁇ se, in this example, Li ⁇ ZnSAg mate ⁇ al, Li3PO4 mate ⁇ al, or a mate ⁇ al including 6Li or 6LiF, or any similar substance
  • 6LiF material is mixed in a hydrogenous binder medium with a scintillation (or scintillator) mate ⁇ al 204 and has a thickness of about (but not limited to) 0 1 mm to about 0 5 mm
  • the scintillator mate ⁇ al 204 in one embodiment, can comp ⁇ se one or more mate ⁇ als such as (but not limited to) ZnS, ZnS(Ag), or NaI(Tl)
  • mate ⁇ als such
  • the moderator mate ⁇ al 202 acts as a protective layer that does not allow light into the detector 200 Alternatively, a separate light shield can be applied to the outer shell of the detector layers to eliminate outside light interference Also, the moderator material 202 can comp ⁇ se interposing plastic layers that act as wavelength shifters According to one embodiment, at least one plastic layer is adjacent to (and optionally contacting) at least one light transmissive medium and/or light guide medium
  • the at least one light transmissive medium and/or light guide medium at the at least one scintillator layer is substantially surrounded by plastic that acts as a wavelength shifter That is, the plastic layers (and/or optionally plastic substantially surrounding the light guide medium at the at least one scintillator layer) act(s) as wavelength shifter(s) that receive light photons emitted from the at least one scintillator layer (from neutron particles interacting with the at least one scintillator layer) and couple these photons into the at least one light transmissive medium and/or light guide medium
  • the at least one light guide medium at the at least one scintillator layer comprises fiber optic media that acts as a wavelength shifter (e g , wave shifting fiber) This provides a more efficient means of collecting light out the end of the at least one light guide medium, such as when the light enters from substantially normal incidence from the outside of the at least one light guide medium
  • An example of a moderator mate ⁇ al that can be used with va ⁇ ous embodiments of the present invention comprises dense polyethylene
  • the optimum moderator configuration in one embodiment, is estimated at approximately 2 inches of dense polyethylene Moderator of at least 0 25 inches up to 3 0 inches deep can be used effectively in various embodiments of the present invention
  • the moderator mate ⁇ al 202 thermahzes the fast neutrons before they enter the detector 200 This thermalization of the fast neutrons allows the thermal neutron detector to perform at an optimum efficiency
  • Thermal neutron sensitive scintillator mate ⁇ al that is useful in the fabrication of a neutron detector such as the detector 200 of FIG 2 includes, but is not limited to 6Li-ZnS, lOBN, and other thin layers of mate ⁇ als that release high energy He or H particles in neutron capture reactions
  • Such mate ⁇ als can be 6Li- or lOB-en ⁇ ched ZnS, lOBN, or other phosphors that contain Li or B as an additive Examples of
  • the neutron detector 200 comprises a light guide medium 206 such as one or more optical fibers that are coupled to a photosensor 208
  • the photosensor 508 comprises at least one of a photomultipher tube, an avalanche photo diode, a phototransistor, and a solid-state photomultiplier
  • a layer of photo detecting elements in the SSPM is located adjacent to, and optionally abutting, the scintillation mate ⁇ al
  • the array of photo detecting elements directly detect the light photons emitted from the scintillation mate ⁇ al without using wave guide fibers in the detector (scintillation mate ⁇ al) to pick up and deliver light photons to the photosensor. This simplifies a detector manufacturing process and reduces the overall manufacturing cost of the detector system.
  • the 6Li or 6LiF and scintillator material 204 is optically coupled to the light guide medium 206.
  • the light guide medium 206 includes a tapered portion that extends from one or both ends of the scintillation layer 204 to guide the light to a narrowed section. This narrowed section is optically coupled to the photosensor 208 at the tapered portion.
  • the photosensor such as the photomultiplier tube, is tuned to operate close to the light frequency of the light photons generated from the scintillation material and carried by the light guide medium.
  • the scintillation material 204 is excited by an incident neutron 210 that is slowed (thermalized) by the moderator material 202.
  • the scintillation material reacts 204 with the thermalized neutron particle by emitting an alpha particle 212 and a triton particle 214 into the neighboring scintillation material 204, which can be, in this example, a phosphor material.
  • the scintillation material 204 is energized by this interaction and releases the energy as photons (light) 216.
  • the photons 216 travel into the light carrying medium 206 and are guided to the ends of the medium 206 and exit into the photosensor 208.
  • the light guide medium 206 is a wavelength shifter.
  • the wavelength shifter shifts blue or UV light to a wavelength that matches the sensitivity of a photosensor 208, avalanche sensor, or diode sensor. It should be noted that a gamma particle 218 can also hit the scintillation material 204, which creates photons 216 that are received by the photosensor
  • the neutron detector 200 provides significant improvements in form and function over a helium-3 neutron detector.
  • the neutron detector 200 is able to be shaped into a desired form.
  • the scintillator layer(s) and moderator material can be curved and configured for up to a 360 degree effective detection angle of incidence.
  • the at least one scintillator layer and moderator material can be flat and designed as a detector panel.
  • the neutron detector 200 comprises a uniform efficiency across the detector area.
  • the neutron detector 200 can comprise multiple layers to create an efficiency that is substantially close to 100%.
  • FIG. 3 is a schematic that illustrates various components that are used to support a neutron detector such as the neutron detectors 112, 114 shown in FIG. 1.
  • the various electrical components shown in FIG. 3 provide a signal sampling rate of 50 million samples per second or faster.
  • FIG. 3 shows a neutron detector 302 electrically coupled to a high voltage board 304, which provides power to the neutron detector 302.
  • the neutron detector 302 generates analog signals that are received by a pre-amp component 306, which is also electrically coupled to the high voltage board 304.
  • the pre-amp 306, in one embodiment, drives the detector signal processing rate close to the decay time of the scintillator material in the detector 302.
  • the SIU 308 is electrically coupled to the pre-amp 306, high voltage board 304, and a gamma detector 310 (in this embodiment).
  • the analog signals from the neutron detector 302 are processed by the pre-amp 306 and sent to the SIU unit 308.
  • the SIU 308 performs an analog-to-digital conversion process on the neutron detector signals received from the pre-amp 306 and also performs additional processing, which has been discussed above.
  • FIG. 4 shows a more detailed schematic of the pre-amp component 306.
  • the pre-amp component 306 shown in FIGs. 3 and 4 is enhanced to reduce the pulse stretching and distortion typically occurring with commercial preamps.
  • FIGs. 3 and 4 removes any decay time constant introduced by capacitive and or inductive effects on the amplifier circuit.
  • the impedance in one embodiment, is lowered on the input of the preamp that is attached to the output of a photomultiplier tube 510, 512, 514, 516 (FIG. 5) to maintain the integrity of the pulse shape and with the preamp output signal gain raised to strengthen the signal.
  • the pre-amp circuit 306 of FIG. 4 includes a first node 402 comprising a header block 404 that is electrically coupled to the output 406 of the neutron detector photomultiplier 510 as shown in FIG. 4.
  • a first output 408 of the header block 404 is electrically coupled to ground, while a second output 410 of the header block 404 is electrically coupled a second node 412 and a third node 414.
  • the second output 410 of the header block 404 is electrically coupled to an output 416 of a first diode 418 in the second node 412 and an input 420 of a second diode 422.
  • the input 424 of the first diode 418 is electrically coupled to a voltage source 426.
  • the output of the first diode is electrically coupled to the input of the second diode.
  • the output 440 of the second diode 422 is electrically coupled to a second voltage source 442.
  • the third node 414 comprises a capacitor 444 electrically coupled to ground and a resistor 436 that is also electrically coupled to ground.
  • the capacitor 444 and the resistor 436 are electrically coupled to the second output 410 of the header block 406 and to a first input 438 of an amplifier 440.
  • a second input 442 of the amplifier 440 is electrically coupled to a resistor 444 to ground.
  • the amplifier 440 is also electrically coupled to a power source as well.
  • a fourth node 446 is electrically coupled to the second input 442 of the amplifier in the third node 414.
  • the fourth node 446 includes a capacitor 448 and a resistor 450 electrically coupled in parallel, where each of the capacitor 448 and resistor 450 is electrically coupled to the second input 442 of the amplifier 440 in the third node 414 and the output 452 of the amplifier 440 in the third node 414.
  • the output 452 of the amplifier 440 in the third node 414 is electrically coupled to a fifth node 454 comprising another amplifier 456.
  • the output 452 of the amplifier 440 of the third node 414 is electrically coupled to a first input 458 of the amplifier 456 in the fifth node 454.
  • a second output 460 of the amplifier 456 in the fifth node 454 is electrically coupled to the output 62 of the amplifier 456.
  • the output 462 of the amplifier 456 is electrically coupled to a sixth node 464.
  • the output 462 of the amplifier 456 in the fifth node 454 is electrically coupled to a resistor 466 in the sixth node 464, which is electrically coupled to a first input 468 of another header block 470.
  • a second input 472 of the header block 470 is electrically coupled to ground.
  • An output 474 of the header block 470 is electrically coupled to an analog-to-digital converter such as an SIU discussed above.
  • the pre-amp circuit 306 of FIG. 4 also includes a seventh node 476 comprising a header block 478.
  • a first 480 and third 484 output of the third header block 478 is electrically coupled to a respective voltage source.
  • a second output 482 is electrically coupled to ground.
  • the first output 480 is electrically coupled to a first 486 and second 488 capacitor, which are electrically coupled to the second output 482.
  • the third output 484 is electrically coupled to a third 490 and a fourth 492 capacitor, that are electrically coupled to the second output 482 as well.
  • FIG. 5 shows a top planar cross-sectional view of a neutron detector component 500 that can be implemented in the system of FIG. 1.
  • FIG. 5 shows a housing 502 comprising one or more thermal neutron detectors 504, 506.
  • the thermal neutron detector 504, 506, in this embodiment, is wrapped in a moderator material 508.
  • Photomultiplier tubes 510, 512, 514, 516 are situated on the outer ends of the thermal neutron detectors 504, 506.
  • Each of the photomultiplier tubes 510, 512, 515, 516 is coupled to a preamp 518, 520, 542, 544.
  • Each preamp 518, 520, 522, 524 is electrically coupled to a sensor interface unit 556, 528.
  • Each preamp 518 can be electrically coupled to its own SIU 526, 528 or to an SIU 526, 528 that is common to another preamp 520, as shown in FIG. 5.
  • the thermal neutron detector 504, 506 is wrapped in a moderator material 508 comprising moderator efficiencies that present a greater number of thermalized neutrons to the detector 504, 506 as compared to conventional neutron detectors.
  • a neutron moderator is a medium that reduces the speed of fast neutrons, thereby turning fast neutrons into thermal neutrons that are capable of sustaining a nuclear chain reaction involving, for example, uranium-235.
  • Commonly used moderators include regular (light) water (currently used in about 75% of the world's nuclear reactors), solid graphite (currently used in about 20% of nuclear reactors), and heavy water (currently used in about 5% of reactors).
  • Beryllium has also been used in some experimental types, and hydrocarbons have been suggested as another possibility.
  • the following is a non-exhaustive list of moderator materials that are applicable to one or more embodiments of the present invention.
  • Hydrogen as in ordinary water (“light water”), in light water reactors.
  • the reactors require enriched uranium to operate
  • uranium hydride— UH 3 metallic uranium and hydrogen
  • Hydrogen is also used in the form of cryogenic liquid methane and sometimes liquid hydrogen as a cold neutron source in some research reactors yielding a Maxwell-Boltzmann distribution for the neutrons whose maximum is shifted to much lower energies Deute ⁇ um, in the form of heavy water, in heavy water reactors, e g CANDU Reactors moderated with heavy water can use unen ⁇ ched natural uranium Carbon, in the form of reactor-grade graphite or pyrolytic carbon, used in e g RBMK and pebble-bed reactors, or in compounds, e g carbon dioxide Lower-temperature reactors are susceptible to buildup of Wigner energy in the material Like deuterium-moderated reactors, some of these reactors can use unen ⁇ ched natural
  • one or more embodiments of the present invention can be utilized as a passive neutron detection system for shielded nuclear mate ⁇ als such as highly en ⁇ ched uranium
  • the neutron detector discussed above provides strong detection capabilities for shielded nuclear material Additional detector configurations may be added to increase the shielded nuclear mate ⁇ als detection capability
  • the thermal neutron detector system may also add one or more fast neutron detectors designed as a high performance detector with modified preamp and connection to the sensor interface unit for high speed digital data analysis
  • the sandwich neutron detector design discussed above can be used to increase the detection capability of shielded nuclear mate ⁇ als
  • a more efficient moderator material may be developed to increase the number of fast neutrons that are thermahzed and presented to the neutron detector
  • the neutron detector of the various embodiments of the present invention can use moderator mate ⁇ als for a portion of the detector surface area to enable detection of thermal neutrons and to convert fast neutrons to thermal neutrons
  • the pre-amp circuit is configured to operate substantially close to a decay time of the scintillator layer when interacting with neutrons, and without adding further extension (distortion) to the electrical signal output from the pre-amp.
  • the pre-amp 306 removes decay time constant that may be introduced by capacitive and or inductive effects on the amplifier circuit. For example, the impedance can be lowered on the input of the pre-amp attached to the output from the photomultiplier tube to maintain the integrity of the pulse shape, and optionally with the pre-amp output gain raised to strengthen the output signal.
  • the neutron detector 200 improves the gamma discrimination by utilizing the preamp 306 to keep the pulse as close as possible to its original duration and shape with a pulse duration of approximately 250 nanoseconds (in one embodiment). This improves linearity and increases the ability to process more counts per second, especially in a random burst where multiple gamma and/or neutron pulse events may be blurred into one pulse.
  • the programmable gain and offset of the SIU 106, 108, 110 analog front end presents the pulse signal to a 50MHz high speed/high resolution digitizer which feeds the Field programmable Gate Array (FPGA) that includes proprietary hardware real-time Pulse DSP programmable filters from Innovative American Technology (IAT), Inc.
  • FPGA Field programmable Gate Array
  • the high speed analog-to-digital conversion circuit (within the SIUs) can plot the fastest pulse with approximately 15 points of high resolution data.
  • These programmable filters are used in the second stage of signal processing to eliminate noise and most gamma pulses via a LLD (low level discriminator) or noise canceller as well as employing a pulse rise time filter. Pulses must meet a minimum rise time to be considered for analysis.
  • the next stage of signal processing occurs at a pulse width filter, which measures the duration of the pulse at a point where the shape widens when the pulse originates from a neutron reaction. Gamma pulses have a clean and rapid decay, whereas neutron interaction with the detector produces an extended fall time.
  • the result of the above signal processing is that the speed of the SIU 106, 108, 110 system hardware and embedded processor clearly differentiates between a neutron pulse and a gamma pulse. This enables the neutron detector system 100 to eliminate nearly 100% of the gamma pulses received by the neutron detector without impacting the neutron detector efficiencies. Subsequent testing at various laboratories supported zero gamma detection (zero gamma cross-talk) under high gamma count rates and high gamma energy levels.
  • the neutron detector 200 was deployed using the IAT detection, background subtraction and spectral analysis system software operating at 4.2649 sigma which translates to a false positive rate of 1/100,000 (one in one hundred thousand) or an accuracy rate of 99.999%.
  • FIGs. 6 and 7 show a neutron pulse and a separate gamma pulse, respectively, generated from the neutron detector 200 and digitally converted for processing.
  • the neutron pulse in FIG. 6 represents a pure pulse without distortion, meets the pulse height 602 requirements, is above the noise threshold filter 604, meets the pulse rise-time requirements 604, and has a much wider base than the example gamma pulse in FIG. 7, accordingly identifying the pulse as a neutron pulse.
  • the neutron detector 200 provides various improvements over conventional helium-e type detectors.
  • the pulse height allows the detector system 100 to provide better discrimination against lower energy gamma.
  • the Li + n reaction in the neutron detector 200 produces 4.78 Mev pulse.
  • the He3 +n reaction only produces 0.764 Mev pulse.
  • the neutron detector 200 is thin so a very small fraction of the gamma energy is absorbed making very small gamma pulses. Pile up of pulses can produce a larger apparent pulse. However this is avoided with the fast electronics.
  • the walls of the He3 detectors capture some energy, which broadens the pulse. Thus, such implementation typically uses large size tubes. With a broad neutron pulse fast electronics cannot be used to discriminate against gamma pulses during pile up without cutting out some of the neutron pulse energy.
  • the neutron pulse width is narrower in the neutron detector 200 than in He3 detectors. This makes the use of fast electronics more beneficial.
  • thermal neutron efficiency He3 is very efficient 90% at 0.025 eV neutrons. However He3 efficiency drops off rapidly to 4% for 100ev neutrons. Because He3 is a gas a large volume detector is needed to get this efficiency. He3 efficiency coupled with a moderator assembly is estimated at between 30% down to 1% across the energy range and depends on He3 volume.
  • the neutron detector 200 is a solid material, and smaller volumes can be used. Multiple layers of the neutron detector 200 raise the overall detector system efficiency. In one embodiment of the present invention, a four layer configuration of the neutron detector 200 was constructed that reached efficiencies of close to
  • the neutron detector 200 efficiency coupled with the moderator assembly is estimated at 30% across the energy range.
  • the neutron detector 200 is advantageous over conventional helium-3 neutron detectors for the following reasons.
  • the neutron detector can be shaped into any desired form.
  • the neutron detector comprises uniform efficiency across the detector area. Also, multiple layers of the detector can create an efficiency which is close to 100%. Detection Of Shielded HEU (Passively)
  • the neutron detector 200 in one embodiment, is an effective passive detector of specialized nuclear materials. The most difficult to detect is typically highly enriched uranium (HEU). More difficult is shielded highly enriched uranium.
  • HEU detection capabilities were analyzed and the conclusions are discussed below.
  • the useful radioactive emissions for passively detecting shielded HEU are neutron and gamma rays at IMeV from decay of U-238. The neutrons offer the best detection option.
  • the gamma rays with energy below 200 KeV are practical for detecting only unshielded HEU since these are too easily attenuated with shielding.
  • the most effective detection solutions will place detectors with the largest possible area and most energy-specificity within five meters and for as long a time as possible since: (a.) at distances of 10 meters or more, the solid angle subtended by the detector (-detector area/distance2) from a 50kg HEU source is likely to reduce the signal as much as any reasonable size shielding, and (b) with sufficient time for the detector to detect neutron counts and photon counts within a narrow enough photon energy range, even signals below the background can be detected.
  • the HEU core is shielded externally by lead.
  • the linear attenuation coefficient defined as the probability per unit distance that a gamma ray is scattered by a material, is a function of both the material and the energy of the gamma ray. Steel and concrete have linear attenuation coefficients at 1 MeV that are not all that different from lead, so the conclusions will be roughly similar even with other typical shielding materials.
  • the mass of HEU itself acts to shield gamma rays (self-shielding). The number of neutrons and gamma rays that reach the detector is limited by the solid angle subtended by the detector from the source.
  • detection involves reading enough counts of neutrons and gamma rays to be able to ascertain a significant deviation from the background and the detector only detects a fraction of those neutron and gamma rays that are emitted due to detection inefficiencies.
  • link budget is explained below.
  • Nuclear theory is used to estimate the maximum distance possible for passive detection of a lead-shielded HEU spherical core using both U-238 and U-232 signals. The distance compared against variables of interest including detector area, detection time, shield thickness, and mass of the HEU core. Detection distance depends on amount of HEU and its surface area, shielding, detector area, distance, and time available to detect the emissions. Maximum detection distance is dependent on these factors.
  • the neutron emissions and the neutron detector 200 are used, in this example, to enable neutron detection to four counts above background noise levels.
  • the low number neutron counts and the low number 1 MeV gamma counts are used to identify the source as a high probability of shielded HEU.
  • U-235. and U-234 are used, in this example, to enable neutron detection to four counts above background noise levels.
  • the low number neutron counts and the low number 1 MeV gamma counts are used to identify the source as a high probability of shielded HEU.
  • the neutron "link budget” is not easily amenable to analytical approximation as it is for gammas.
  • WgU weapons grade Uranium
  • WgU weapons grade Uranium
  • Uranium consists of multiple isotopes.
  • highly enriched Uranium HEU
  • HEU highly enriched Uranium
  • weapons grade Uranium contains over 90%14 U-235.
  • Radioactive decay of U-235 results in gamma rays at 185 KeV, but shielding too easily attenuates these and so they are not useful for detecting shielded HEU.
  • HEU also contains the isotope U-238 — the more highly enriched, the less the percentage of U-238.
  • a conservative assumption for detection using U-238 emissions is that HEU or weapons grade Uranium contains at least 5% U-238 by weight.
  • U-232 may also be present in trace quantities (parts per trillion).
  • U-238 emits 81 gammas per second per gram at 1.001MeV. This number can also be derived using first principles and nuclear data, but results in only a slightly higher value based on data from U-232' s decay chain produces even more penetrating gamma rays than U-238.
  • the most important gamma emitter in the U-232 decay chain is Tl-208, which emits a 2.6 MeV gamma ray when it decays. These gamma rays can be effectively used to detect the presence of HEU if U-232 is known to be a contaminant, even to the effect of a few hundred parts per trillion.
  • Embodiments of the present invention can similarly arrive at the rates for U-232, the most penetrating of which has emissions at 2.614MeV at a rate of 2.68 x 1011 gammas per gram per second.
  • the system 100 was able to detect and identify special nuclear materials such as highly enriched uranium and shielded highly enriched uranium at quantities below 24 kilograms through a combination of neutron and gamma detections.
  • the passive scintillation detector system discussed above can be configured to detect and identify shielded highly enriched uranium based on low neutron counts coupled with low IMeV gamma counts.
  • the system detects and identifies highly enriched uranium based on low level neutron counts coupled with low gamma counts at 1 MeV or greater energies coupled with gamma ray energy associated with HUE that are below 200 KeV.
  • the passive scintillation detector system discussed above can also be configured as a horizontal portal, a truck or bomb cart chassis, a spreader bar of a gantry crane, a straddle carrier, a rubber tired gantry crane, a rail mounted gantry crane, container movement equipment, a truck, a car, a boat, a helicopter, a plane or any other obvious position for the inspection and verification of persons, vehicles, or cargo .
  • the system can be configured for military operations or military vehicles, and for personal detector systems.
  • the system can also be configured for surveillance and detection in protection of metropolitan areas, buildings, military operations, c ⁇ tical infrastructure such as airports, train stations, subway systems or deployed on a mobile platform such as a boat, a vehicle, a plane, an unmanned vehicle or a remote control vehicle
  • FIG 8 is a block diagram illustrating a more detailed view of an information processing system 800 according to one embodiment of the present invention
  • the information processing system 800 is based upon a suitably configured processing system adapted to be implemented in the neutron detection system 100 of FIG 1 Any suitably configured processing system is similarly able to be used as the information processing system 800 by embodiments of the present invention such as an information processing system residing in the computing environment of FIG 1, a personal computer, workstation, or the like
  • the information processing system 800 includes a computer 802
  • the computer 802 has a processor(s) 804 that is connected to a main memory 806, mass storage interface 808, terminal interface 810, and network adapter hardware 812 A system bus
  • the mass storage interface 808 is used to connect mass storage devices, such as data storage device 816, to the information processing system 800
  • mass storage devices such as data storage device 816
  • data storage device 816 One specific type of data storage device is an optical d ⁇ ve such as a CD/DVD d ⁇ ve, which may be used to store data to and read data from a computer readable medium or storage product such as (but not limited to) a CD/DVD 818
  • Another type of data storage device is a data storage device configured to support, for example, NTFS type file system operations
  • the information processing system 800 utilizes conventional virtual addressing mechanisms to allow programs to behave as if they have access to a large, single storage entity, referred to herein as a computer system memory, instead of access to multiple, smaller storage entities such as the main memory 806 and data storage device 816
  • a computer system memory is used herein to gene ⁇ cally refer to the entire virtual memory of the information processing system 800
  • Embodiments of the present invention further incorporate interfaces that each includes separate, fully programmed microprocessors that are used to off-load processing from the CPU 804
  • Terminal interface 810 is used to directly connect one or more terminals 820 to computer 802 to provide a user interface to the computer 802
  • These terminals 820 which are able to be non-intelligent or fully programmable workstations, are used to allow system administrators and users to communicate with the information processing system 800
  • the terminal 820 is also able to consist of user interface and pe ⁇ pheral devices that are connected to computer 802 and controlled by terminal interface hardware included in the terminal I/F 810 that includes video adapters and interfaces for keyboards, pointing devices, and the like
  • An operating system (not shown) included in the main memory is a suitable multitasking operating system such as the Linux, UNIX, Windows XP, and Windows Server 2003 operating system Va ⁇ ous embodiments of the present invention are able to use any other suitable operating system
  • Some embodiments of the present invention utilize architectures, such as an object o ⁇ ented framework mechanism, that allows instructions of the components of operating system (not shown) to be executed on any processor located within the information processing system 800
  • the network adapter hardware 812 is used to provide an interface to a network 822
  • Embodiments of the present invention are able to be adapted to work with any data communications connections including present day analog and/or digital techniques or via a future networking mechanism
  • va ⁇ ous embodiments of the present invention are desc ⁇ bed in the context of a fully functional computer system, those skilled in the art will appreciate that embodiments are capable of being dist ⁇ ubbed as a program product via CD or DVD, e g CD 818, CD ROM, or other form of computer readable storage media, or via any type of electronic transmission mechanism
  • Non-Limiting Examples are capable of being dist ⁇ ubbed as a program product via CD or DVD, e g CD 818, CD ROM, or other form of computer readable storage media, or via any type of electronic transmission mechanism
  • the present invention can be realized in hardware, software, or a combination of hardware and software
  • a system according to one embodiment of the present invention can be realized in a centralized fashion in one computer system or in a distributed fashion where different elements are spread across several interconnected computer systems Any kind of computer system - or other apparatus adapted for carrying out the methods described herein - is suited
  • a typical combination of hardware and software could be a general purpose computer system with a computer program that, when being loaded and executed, controls the computer system such that it carries out the methods desc ⁇ bed herein
  • routines executed to implement the embodiments of the present invention may be referred to herein as a "program"
  • the computer program typically is comprised of a multitude of instructions that will be translated by the native computer into a machine-readable format and hence executable instructions
  • programs are comp ⁇ sed of va ⁇ ables and data structures that either reside locally to the program or are found in memory or on storage devices
  • various programs described herein may be identified based upon the application for which they are implemented in a specific embodiment of the invention.
  • any particular program nomenclature that follows is used merely for convenience, and thus the invention should not be limited to use solely in any specific application identified and/or implied by such nomenclature

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Abstract

La présente invention concerne un système qui détecte des matériaux nucléaires et/ou des matériaux fissiles. Le système comprend une pluralité de détecteurs à scintillation haute vitesse. Chaque détecteur à scintillation haute vitesse de la pluralité de détecteurs à scintillation haute vitesse comprend au moins un capteur optique et un circuit préamplificateur conçu pour éliminer l'étalement et la distorsion d'impulsions lumineuses détectées, émises par le matériau de scintillation lors d'une interaction avec des particules neutroniques et/ou des particules γ. Une base de données d'isotopes comprend une pluralité d'images spectrales correspondant à différents isotopes connus. Un système de traitement d'informations est conçu pour comparer les données spectrales reçues de chaque détecteur à scintillation haute vitesse avec une ou plusieurs images spectrales et pour identifier un ou plusieurs isotopes se trouvant dans un objet ou un contenant à surveiller.
EP10746841A 2009-02-25 2010-02-25 Système et procédé d'amélioration de la détection de rayons gamma/neutrons Withdrawn EP2401636A2 (fr)

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US20849209P 2009-02-25 2009-02-25
US20919409P 2009-03-04 2009-03-04
US21007509P 2009-03-13 2009-03-13
US21012209P 2009-03-13 2009-03-13
US21023409P 2009-03-16 2009-03-16
US21023809P 2009-03-16 2009-03-16
US21162909P 2009-04-01 2009-04-01
US12/483,066 US20120175525A1 (en) 2007-01-17 2009-06-11 High performance neutron detector with near zero gamma cross talk
US21911109P 2009-06-22 2009-06-22
US23180509P 2009-08-06 2009-08-06
US23881909P 2009-09-01 2009-09-01
US24629909P 2009-09-28 2009-09-28
US24940809P 2009-10-07 2009-10-07
US25796809P 2009-11-04 2009-11-04
US25796409P 2009-11-04 2009-11-04
US28916309P 2009-12-22 2009-12-22
US29399310P 2010-01-11 2010-01-11
US29397410P 2010-01-11 2010-01-11
PCT/US2010/025429 WO2010099331A2 (fr) 2009-02-25 2010-02-25 Système et procédé d'amélioration de la détection de rayons gamma/neutrons

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WO2010099334A2 (fr) 2010-09-02
WO2010141125A3 (fr) 2011-03-24
WO2010099334A3 (fr) 2011-01-06
WO2010099331A2 (fr) 2010-09-02

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