EP2054704A2 - System and method for resolving gamma-ray spectra - Google Patents
System and method for resolving gamma-ray spectraInfo
- Publication number
- EP2054704A2 EP2054704A2 EP07868260A EP07868260A EP2054704A2 EP 2054704 A2 EP2054704 A2 EP 2054704A2 EP 07868260 A EP07868260 A EP 07868260A EP 07868260 A EP07868260 A EP 07868260A EP 2054704 A2 EP2054704 A2 EP 2054704A2
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- EP
- European Patent Office
- Prior art keywords
- radionuclide
- present
- algorithm
- radionuclides
- gamma
- 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.)
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Classifications
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- 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
- G01T1/17—Circuit arrangements not adapted to a particular type of detector
Definitions
- the present invention is directed to the detection and identification of radionuclides, and, more specifically, to a system, method and apparatus for the detection and identification of radionuclides via spectral analysis.
- a gamma ray is a high-energy electromagnetic emission by certain radionuclides when the state of those certain radionuclei transitions from a higher to a lower energy state.
- Gamma rays have high energy and a short wave length, with energies above 1 million eV and wavelengths less than 0.001 nanometers. All gamma rays emitted from a given isotope have the same energy, which has historically enabled scientists to identify which gamma emitters are present in an unknown sample.
- Gamma rays may cause direct ionization in that these particles or rays transfer at least a portion of the energy thereof upon interaction with matter. This transfer generally occurs by imparting energy to electrons of atoms that have been interacted with. Generally speaking, these ions may be measured by using measuring devices, such as a Geiger counter, for example.
- beta and alpha particles each have mass and charge, and are natural products of the decay of, for example, uranium, radium, polonium, and many other elements, gamma and x-rays have no mass and no electrical charge. Each is thus pure electromagnetic energy.
- gamma and x-rays can easily travel several meters through the air and penetrate several centimeters of human tissue. Some emissions have enough energy to pass through the body, exposing all the organs to radiation. Gamma emitting radionuclides do not have to enter the body to be a hazard, as direct external and internal exposure to gamma rays or X-rays are of concern.
- a large portion of received gamma radiation largely passes through the body without interacting with tissue, as the body is mostly empty space at the atomic level, and gamma rays are atomically small in size.
- alpha and beta particles inside the body lose all their energy by colliding with tissue and causing damage.
- X-rays may act in a manner similar to alpha and beta particles, but with slightly lower energy.
- Gamma rays do not directly ionize atoms in tissue. Instead, they transfer energy to atomic particles such as electrons (which are essentially the same as beta particles). These energized particles then interact with human tissue to form ions, in the same way radionuclide-emitted alpha and beta particles would. However, because gamma rays have more penetrating energy than alpha and beta particles, the indirect ionizations they cause generally occur further away from the emission source, and consequently, deeper into human tissue.
- Sources of gamma rays typically include radioactive elements such as Thulium 170, Iridium 192, Cesium 137, and Cobalt 60, while sources of x-rays typically include x-ray tubes within the controlled environment of a medical office.
- radioactive materials While there are many beneficial uses for radioactive materials in the fields of science and medicine, these materials may be highly threatening to society. It goes without saying, radiation poisoning may be a tactic of terrorist groups and other radical factions with the intent to bring harm or even death to others. For example, the use of "dirty bombs", which add radioactive materials to common explosives, has been well documented. Other possibilities, such as the contamination of food stocks or water sources with radioactive materials, have also been speculated.
- risk priority matrices set forth by the U.S. government include Cs 137 and Co 60, because of the large quantities of these isotopes that exist and, in the case of Cs 137, the ease of dispersal.
- Sr 90, Pu 238, Am 241 and Lr 192 are also included in the matrix of potential threats, hi addition, spent fuel is generally included in potential threat matrices, and needless to say there are very significant quantities of spent fuel available.
- a system for identifying radionuclide emissions includes at least one processor for processing output signals from a radionuclide detecting device, at least one training algorithm run by the at least one processor for analyzing data derived from at least one set of known sample data from the output signals, at least one classification algorithm derived from the training algorithm for classifying unknown sample data, wherein the at least one training algorithm analyzes the at least one sample data set to derive at least one rule used by said classification algorithm for identifying at least one radionuclide emission detected by the detecting device.
- FIG. 1 illustrates a block diagram of the system according to an aspect of the present invention
- FIG. 2 illustrates a block diagram of a neutron detector according to the present invention
- FIG. 3 illustrates a block diagram of an x-ray detector according to an aspect of the present invention
- FIG. 4 illustrates a block diagram of a gamma ray detector according to an aspect of the present invention
- FIG. 5 A illustrates a set of sample data as may be detected by the gamma ray channel according to an aspect of the present invention
- FIG. 5B illustrates a set of sample data as may be detected by the gamma ray channel according to an aspect of the present invention
- FIG. 5C illustrates a set of sample data as may be detected by the gamma ray channel according to an aspect of the present invention
- FIG. 6 illustrates a configuration according to an aspect of the present invention
- FIG. 7 illustrates a neural networking configuration of the software according to an aspect of the present invention
- FIG. 8 shows a screen shot of the main system screen according to an aspect of the present invention.
- FIG. 9 shows a screen shot of the alert for Cs 137 according to an aspect of the present invention.
- FIG. 10 shows a screen shot of the alert for Am241 according to an aspect of the present invention
- FIG. 11 shows a screen shot of the alert for Co60 according to an aspect of the present invention
- FIG. 12 illustrates a housing according to an aspect of the present invention
- FIG. 13 is a flow diagram of a method of detecting radionuclides according to an aspect of the present invention.
- FIG 14 is a graph of generated test spectra for Ba-133.
- FIG 15 is a graph of generated test spectra for 1-131;
- FIG 16 is a graph of generated test spectra for Ba-133 and 1-131;
- FIG 17 is a graph of generated test spectra for Pu-238
- FIG 18 is another graph of generated test spectra for 1-131 ;
- FIG 19 is a graph of generated test spectra for Pu-238 embedded in 1-131.
- FIG 20 is a graph of generated test spectra for Pu-238 embedded in 1-131 and Ba-
- the present invention is directed to a system and method for identifying radionuclides from spectra data in radionuclide detectors.
- the invention may include a device and system suitable for recognizing unique radiant energy emission levels or patterns for a radionuclide, for one or more selected from a selected set of radionuclides, or for an unknown sample.
- the device and system may allow for detection of radionuclides having minimal and trace emission levels.
- the invention may include communicating not only the presence, but also the identity, of a radionuclide in a sample volume to appropriate personnel at a local or remote location.
- the invention may include a plurality of methods for accomplishing these detections, identifications, and communications of the device and system, as further described below.
- the present invention may detect trace, as well as high level, emissions, at low to very high rates or frequencies. This may allow the device to be installed in virtually any location, especially those locations or facilities where there is a high volume of public traffic, which traffic may be traveling at virtually any rate of speed, or any other locations at or through which there may be a heightened likelihood of the transport of hidden radionuclides.
- these locations may include highways, train stations, airports, shipyards, metropolitan mass transit systems, governmental and commercial buildings, truck terminals, railroad freight handling facilities, and the like.
- the present invention may include an alerting function or similar notification of a positive detection of a suspect radionuclide, and an identification of a suspect radionuclide.
- the suspect radionuclide to be detected may be from a predetermined sample.
- These capabilities permit assessing the presence of radionuclides from a local or a remote location in real time.
- the present invention may be installed at a shipping terminal in such a way that shipping containers may pass directly before, or under, one or more detector modules as the containers are offloaded from a vessel. If no emissions are detected, the shipyard tasks carry on without interruption.
- an electronic warning system such as a warning light, sound, and/or triggering of a portable alarm device carried by a security officer may be activated as the detection occurs, and this warning system may, dependently upon the type of radionuclide emission detected, identify the radionuclide and even the amount of the radionuclide detected, thereby allowing appropriate personnel to evaluate the situation.
- the present invention may be used to scan vehicles, cargo containers, and other potential mobile targets, as well as stationary targets, and may provide substantially real-time detections and identifications of gamma emission, and real-time detections of the presence of x-ray or neutrons emissions. Further, because of the identifying nature, rather than solely a detecting nature, of the present invention, benign signatures, such as medical and industrial nuclear signatures, may be separated from suspect signatures as desired, thereby eliminating "false positive" readings that have historically been detrimental to radionuclide alert systems.
- the present invention is directed to a device, system, and method for detection of gamma, x-ray, and neutron emissions, and software for controlling and enhancing the detection and identification of such emissions.
- the device and system may include low level detection and integration in a small package. Additionally, while the discussion of the present invention includes elements that may be proximately located to the source of the signals, portions of the device may be located centrally or remotely.
- the present invention may detect radiation generally, and may detect all or some of the three types of emission discussed herein. According to an aspect of the present invention, the device may be passive.
- the present invention may also detect the presence of at least trace amounts of emissions at high rates, or across short accumulation times, permitting use in sensitive and fast moving environments.
- the present invention may be positioned over a bridge, such that detection of vehicles passing over the bridge may be made.
- the device may recognize that two emissions sources are present, and not simply one. This high rate of detection is critical in the above scenario, as the first vehicle could be transporting radionuclides commonly used for medical purposes, while the second vehicle could be carrying radionuclides for terrorist activities.
- the detector may recognize that two sources of emissions exist and not one.
- the detection and identification of radionuclides at high rates and high sensitivity levels allows for communication of a positive determination of the correct number of emissions sources to appropriate authorities.
- the use of multiple detector/identifiers in accordance with the present invention may allow for an assessment of distances or amounts of a radionuclide(s) detected and identified, even in high rate or high frequency applications.
- system 100 may include a first detection channel 110, a second detection channel 120, a third detection channel 130 and processing 140 coupled to each of the channels for interpreting and analyzing the data from each channel.
- Each channel may be designed to detect signals of interest, commonly referred to throughout this discussion as "emissions", such as gamma rays, x-rays and neutrons, for example.
- emissions such as gamma rays, x-rays and neutrons
- Other types of channels or combinations of channels may be utilized to detect additional emissions (such as alpha and beta particles), and the number of channels may be greater than or less than three.
- three channels will be discussed with regard to detection of gamma rays, x-rays and neutrons, by way of non-limiting example only.
- first detection channel 110 may be designed to detect the presence of neutron radiation.
- Neutron radiation consists of free neutrons. As may be known to those possessing an ordinary skill in the pertinent arts, neutrons may be emitted during nuclear fission, nuclear fusion or from certain other reactions, such as when a beryllium nucleus absorbs an alpha particle and emits a neutron, for example.
- Neutron radiation is a form of ionizing radiation that is more penetrating than alpha, beta or gamma radiation. In health physics it is considered a fourth radiation hazard alongside these other types of radiation.
- neutron radiation Another, sometimes more severe, hazard of neutron radiation is its ability to induce radioactivity in most substances it encounters, including body tissues and instruments.
- This induced radiation may occur through the capture of neutrons by atomic nuclei. This process may typically account for much of the radioactive material released by the detonation of a nuclear weapon. This process may also present a problem in nuclear fission and nuclear fusion installations, as it may gradually render the equipment radioactive.
- the neutrons in reactors are generally categorized as slow (thermal) neutrons or fast neutrons, depending on their energy. Thermal neutrons are easily captured by atomic nuclei and are the primary means by which elements undergo atomic transmutation. Fast neutrons are produced by fission and fusion reactions, and have a much higher kinetic energy.
- a neutron detector may be utilized to detect neutron radiation.
- neutron detector 200 may include a confined element 210, wherein the confined element is suitable for reacting with neutrons, and a converter 220.
- Confined element 210 may take the form of a pressurized tube or rod of a gas, such as He3 or BF3, for example.
- Confined element 210 may be confined at an elevated pressure in the range of 5-60 arm in order to increase the resulting signal level of an incident neutron. More specifically, a pressure range from 35-45 atm may be used. Yet more specifically, a pressure level of 40 atm may be utilized. Increased pressures may provide increased signal strength resulting from the detector in response to incident neutrons. Increased pressures may also increase the background level, so a balance between background detection sensitivity may be performed.
- a gas may be used since the ionized particles of a gas travel more freely than those of a liquid or a solid.
- gases used in detectors include argon and helium, although boron-triflouride may be utilized.
- a central electrode, or anode may collect negative charges within the detector.
- the anode may be insulated from the chamber walls of the detector and the cathode of the detector, which cathode collects positive charges.
- a voltage may be applied to the anode and the chamber walls.
- a resistor may be shunted by a parallel capacitor, so that the anode is at a positive voltage with respect to the detector wall. Thereby, as a charged particle passes through the gas-filled chamber, the charged particle may ionize some of the gas along its path of travel.
- the positive anode may attract the electrons, or negative particles.
- the detector wall, or cathode may attract the positive charges. Collecting these charges may reduce the voltage across the capacitor, which may cause an electrical pulse across the resistor that may be recorded by an electronic circuit.
- the voltage applied to the anode and cathode may directly determine the electric field and its strength.
- Converter 220 may be utilized to detect the presence of a photon or electron.
- Converter 220 may take the form of a conventional detector used for detecting incident photons or electrons and converting detected particles into commensurate electrical signals. For example, if a photon is produced by the interaction of the incident neutron and confined elements 210, converter 220 may be utilized to detect the presence of the produced photon.
- Converter 220 may convert the produced photon or electron into an electrical signal.
- the electrical signal may be filtered and amplified as would be evident to those possessing an ordinary skill in the pertinent arts.
- the electrical signal may be read into a processor, such as a computer, such as by utilizing a channel on a multi-channel analyzer.
- second detection channel 120 may be designed to detect the presence of x-ray radiation.
- Detector 300 may include a converter 310.
- Converter 310 may take the form of a detector suitable for detecting x-rays by converting x-rays into an electrical signal.
- the electrical signal may be read into a processor, such as a computer, utilizing a channel on a multi-channel analyzer.
- converter 310 may take the form of a CdTe detector.
- Bremsstrahlung or braking radiation
- a charged particle such as an electron, proton, alpha or beta particle
- another charged particle such as an atomic nucleus.
- Inner bremsstrahlung occurs, infrequently, from the radiation emission during beta decay, resulting in the emission of a photon of energy less than or equal to the maximum energy available in the nuclear transition.
- Inner bremsstrahlung may be caused by the abrupt change in the electric field in the region of the nucleus of the atom undergoing decay, in a manner similar to that which causes outer bremsstrahlung.
- the photon's energy comes from the electron/neutron pair, with the spectrum of the bremsstrahlung decreasing continuously with increasing energy of the beta particle.
- the energy conies at the expense of the neutrino and the spectrum is greatest at about one third of the normal neutrino energy, reaching zero at zero energy and at normal neutrino energy.
- Bremsstrahlung is thus a type of secondary radiation that it is produced as a reaction in shielding material caused by the primary radiation.
- the bremsstrahlung produced by some sources of radiation interacting with some types of radiation shielding may be more harmful than the original beta particles would have been.
- Detector 300 may be suitable for detecting radioactive material that is shielded within a metal.
- an alpha particle incident on a metal may produce an x- ray.
- Elements hidden within protective metal shields may emit alpha particles that impinge on the metal shield.
- the present device may detect this type of x-ray emission and by so doing detects the presence of elements producing alpha (or beta) particles.
- shielded elements which may produce such x-ray emission may include those with a long half-life.
- third detection channel 130 may be designed to detect the presence of and identify gamma radiation.
- detector 400 may include a gamma ray sensor 410 and a converter 420.
- Gamma ray sensor 410 may take the form of a suitable device capable of converting incident gamma rays into a form capable of conversion into electrical signals.
- sensor 410 may take the form of a crystal, such as NaI or Ge(Li), for example. In such a configuration, gamma rays may interact with a NaI crystal sensor 410.
- the detection efficiency of NaI crystals may improve with increasing crystal volume and the energy resolution may be dependent on the crystal growth conditions. Higher energy resolution is essential in radioactive counting situations where a large number of lines are present in a gamma ray spectrum.
- a NaI crystal may output photons proportional to the gamma ray energy incident thereon.
- the height of the electronic pulse produced in a Ge(Li) detector also may be proportional to gamma ray energy.
- NaI and Ge(Li) detector systems may be used to determine the energies of gamma rays from other radioactive sources.
- Converter 420 may be used to convert the output photons into electrical signals.
- Converter 420 may take the form of a photomultiplier tube, for example.
- Other sensors 410 may be used within the detector of the present invention, and such other sensors may require use of alternative converters 420. Functionally, the combination of sensor 410 and converter 420 may convert incident gamma rays into a usable electrical signal that may be proportional to the energy of the incident gamma ray.
- An electrical signal produced by the detector of the present invention may be filtered and amplified as would be evident to those possessing an ordinary skill in the pertinent arts.
- the electrical signal may be read into a processor, such as a computer, utilizing one or more channels on a multi-channel analyzer. It may be advantageous to use a common filtration and amplification system so that multiple channels may be calibrated in common.
- the number of channels used on the multi-channel analyzer may factor into the resolution of detector 400. For example, as is known to those possessing an ordinary skill in the pertinent arts, quantization effects may result in sampling data and sampling at lower than the nyquist frequency will produce data that may not be resolved into the component energies as necessary.
- a multi-channel analyzer may have a few channels, or up to thousands of channels.
- a 16K multi-channel analyzer may be used, providing approximately 16K channels for the gamma detector and at least one channel for each of the neutron and x-ray detectors.
- FIGS. 5A-C there are shown a spectra and baseline as may be detected by the gamma ray channel according to an aspect of the present invention.
- a given gamma emitting material releases a constant amount of energy.
- Cs 137 may produce channel peaks at approximately 81, 161, and 481 channels, by way of non- limiting example only.
- Each gamma source similarly having a unique signature, may allow for the corresponding identification of sources.
- the present gamma detection function may also be designed to enhance low level measurements.
- low level detection may occur at the level of approximately 10 .mu.Rem/hr for a 1 second integration time.
- This low level detection may be in the range 5-15 .mu.Rem/hr for a 1 second integration time - with background in approximately the 4 .mu.Rem/hr for a 1 second integration time range.
- Enhancement of the crystal, including size optimization, may increase the low level sensitivity to gamma detection.
- the configuration of the present invention provides for rapid identification of emissions and is linked to software.
- FIG. 6 there is shown a configuration according to an aspect of the present invention.
- a computer acquires data from the multichannel analyzer as discussed hereinabove.
- the raw data is transmitted to a processor.
- an additional set of data from a photoelectric detector may be logged.
- the photoelectric detector identifies to the system when an object is present. This detector continuously sends an on/off value to the processor depending on the target presence. For example, if vehicles are to be monitored at a toll booth, the photoelectric detector may monitor the presence of a vehicle to be monitored. This may provide the system with information to determine which vehicle contains the emission of interest. Further, the system may be designed to record and analyze data when the photoelectric detector is triggered, thereby providing data only when a target is positioned as desired.
- the present software may take the form of advanced neural networking.
- Such a configuration may input the data from the multi channel analyzer (MCA) into the software system.
- MCA multi channel analyzer
- input neurons read a designated portion of the input MCA data. Because of the quantization effect which may occur, the greater the number of input neurons, the higher the resolution and accuracy that may be achieved, but greater processing is required. If an input neuron detects a peak, it fires. A second stage of neurons, often called hidden neurons, may process the data from the input neurons (including whether the input neurons fired or not).
- Output neurons may be linked to the second stage of neurons, and may represent particular elements that may be detected.
- the output neurons may fire when the second stage of neurons detect the presence of a given element associated with a particular output neuron. For example, if the second stage neurons determine the presence of cobalt 90, the output neuron associated with cobalt 90 may fire because the output neuron corresponding to cobalt 90 has exceeded its threshold condition.
- a single output neuron may fire, namely the output neuron corresponding to the identity of the isotope detected.
- the software may learn or adapt to conditions, such as weather, temperature, and solar.
- the software may be able to detect an isotope even in the presence of systematic shifts in the data detection. Knowing that an isotope may have a signature that has a ratio between channels of 2:1 for example, wherein the channels are 200 channels apart, may allow the software to shift the incoming data when comparing to the known parameters. Software in this configuration provides greater matching abilities and may reduce the number of false positives or false negatives.
- Additional software configurations may be implemented, including plotting the counts per channel on the MCA and comparing to known isotope curves to provide the identity of the isotope, or to provide a match to a preselected library of isotopes.
- the software may be varied accordingly, to be as sensitive or as insensitive as necessary, based on the radiation type or types to be searched for, and the distance between the potential radiation source and the detectors.
- radionuclides There are literally thousands of radionuclides presently known to exist.
- the present invention may include reference spectra of all such known radionuclides, or any subset of radionuclides as determined by a user.
- a consequence of having a large number of reference waveforms in a library resident in a storage device employed in the apparatus and methods of the invention, however, is to increase the analysis time required to make a decision.
- not all radionuclides are currently considered to be relevant or threatening.
- certain nonlimiting embodiments of the present invention may restrict the identities of relevant and/or threatening radionuclides to a relatively smaller subset.
- the positrons slow rapidly in the radioactive source material and disappear in the annihilation process, producing two characteristic 0.511 MeV annihilation gamma rays.
- an atomic electron may be captured by the Na 22 nucleus in the reaction, and a monoenergetic neutrino may be emitted.
- the electron capture process populates only the first excited state of Na 22 at 1.275 MeV and therefore characteristic 1.275 MeV gamma rays result.
- Annihilation gamma rays at 0.511 MeV are not produced in electron capture because positrons are not created.
- FIGS. 8-11 there are shown screen shots associated with the software of the present invention.
- a start-up and all systems go screen is shown. This screen enables a operator to determine if the system is working and, if so, if the present invention is functioning properly.
- FIGS. 9-11 show alert pages for various emission.
- a screen shot associated with a Cs 137 detection In addition to informing the user of a positive detection, the threat level is provided (which is high for Cs 137), and the half-life of the detected isotope may be provided (which is 30 years for Cs 137). Also provided is a timestamp of the alert time and date.
- FIG. 10 there is shown a screen shot of a detected Am 241 alert page.
- the threat level for Am 241 is defined as medium, and the page conveys that Am 241 has a 432.7 year half-life. Further, the alert is time stamped for ease of reference.
- FIG. 11 there is shown an alert page for the alert of Co 60. Co 60 has a high threat level and a half-life of 5.3 years. Again the time and date stamp is provided. Additional information may be provided and the present screen shots show the features of an exemplary embodiment of the present system.
- screen shots such as, in embodiments wherein one or more detectors are used, or wherein one or more detectors are given certain fields of view or certain assigned angles of a field of view, providing using the screen shots information on distances of radionuclides from the one or more detectors, and amounts of radionuclides within the view field of the one or more detectors.
- FIG. 12 there is shown a housing according to an aspect of the present invention.
- the present invention may be designed in a relatively small and light configuration. While many other housing and storage mechanisms may be employed, this exemplary housing is illustrated solely for the purpose of demonstrating the size and weight benefits of the system of the present invention.
- the housing may be made from a suitable material or materials.
- a PVC enclosure may be utilized. Such a configuration may include an internal metal shield to prevent or limit electrical and environmental disturbances. Aluminum enclosures may also be utilized. Such a configuration may also include an internal metal shield. Kevlar or other protective elements may also be used.
- Kevlar may be utilized to provide high strength protection in a light weight configuration.
- the enclosure of the present invention may be designed to withstand full immersion in water. This may be accomplished by using o-ring designs, for example. Additionally, a weather-proof design may be beneficial to provide independence or minimize reaction to the surrounding environment.
- the present invention may be designed to work over a substantial temperature range. For example, according to an aspect of the present invention, the system described herein may be designed to operate from -25 to +55 degrees C.
- FIG. 12 An advantage of the self-contained detecting portion of the present invention is that it may be installed with ease in any location whereat its use is desired or recommended.
- a housing incorporating a detector is shown in FIG. 12.
- the housing may have a diameter of approximately 4.5 inches and a length of approximately 17 inches.
- the housing may contain system 100 including first detection channel 110, second detection channel 120 and third detection channel 130.
- Processing 140 may be contained within, or coupled but not contained within, the housing as determined by size and weight requirements, and this processing may be for one or more of the channels for interpreting and analyzing the data from that one or more channel.
- the housing as shown, and similar embodiments of a housing may accommodate at least three detectors; nonlimiting examples of which may include a NaI detector, a cadmium-zinc- telluride detector, and a neutron detector based either on BF3 or He3 as the active element.
- a cable may exit the housing shown in FIG. 12 and electrically connect to a processor suitable for performing the processing function described hereinabove.
- a wireless connection may be employed between the detector and the processing, and/or between the processing and one or more monitoring locations.
- a wired or wireless connection may allow for a monitoring of multiple sites having a detector and processing from a single monitoring location.
- Method 1300 may include sensing a target using one or more suitable detectors. Method 1300 may also include processing the signal resulting from the detection of the target in order to detect the presence of or identify the type of radionuclides present. Method 1300 may also include an alert responsive to the detected or identified radionuclides in the present target.
- NaI Scintillation Hardware in the detection of radionuclides.
- NaI crystals may be robust, highly sensitive, and available for relatively low costs.
- no refrigeration of the scintillating material may be necessary, as is typically the case for semiconductor (Germanium-based) detectors. Therefore, highly sensitive NaI detectors robust to a wide range of real world environmental operating conditions may be fabricated within relatively lower budgets.
- Such application of computer algorithms to automated radionuclide identification is a unique and innovative shift in the perception of the task of spectroscopy.
- the characteristic signal produced by a certain scintillating detection apparatus in the presence of a specific radionuclide, including noise and scattering may specify an overall spectrum pattern that may be unique in its own right.
- This recasting of the problem may highlight the role that artificial intelligence (AI) algorithms or systems may play in its resolution.
- AI artificial intelligence
- an artificial intelligence system may provide hyper accurate pattern recognition of spectral data.
- Artificial intelligence codes may include two distinct algorithms or sets of algorithms, such as "training” algorithms and “classification” algorithm, for example.
- the training algorithm may be fed with a large number of multi dimensional data samples, such as gamma ray spectra, for example, which may have been pre labeled with the desired binary classification. Such labeling may signify whether a specific radionuclide in the detection library is present or absent.
- radionuclide identification system and method may include the following steps. First, one binary classifier may be trained for each radionuclide in a desired library, using a set of sample spectra that may be labeled with the presence or absence of that radionuclide's signature. Such sample spectra sets may preferrably be large, but there need not be any requirement for a predetermined minimum number of such samples.
- spectra may represent a sufficient array of signal strengths, background noise levels, and/or combinations of the presence and absence of other radionuclides.
- the efficiency of the classification algorithm may be such that a single spectrum may be tested using computing hardware against a large library of radionuclides in a fraction of a second. In this way the presence or absence of any combination of library resident radionuclides in the spectral record, whether embedded or not, may be determined.
- artificial intelligence based systems may be capable of analyzing the data with sufficient acuity as to render the increased resolution of germanium detectors unnecessary for many applications.
- artificial intelligence based systems may be fully capable of dealing with the problem in which a particular radionuclide's peaks may be masked by peaks of other nuclides in the same energy range. For example, in what would be a very difficult judgment call for the human eye or its software corollary, the present invention may automatically select and weigh the most significant global features of the spectra to enable accurate identification of all library-present radionuclides.
- Support-vector machine training systems may comprise a geometric framework, in that they may define a way to partition the high dimensional space of training samples using a hyperplane that may provide the widest 'margin' between positive and negative samples. By doing so, SVM training systems effectively search for the features of the input space that differentiate the positive from negative examples by the widest margin, thereby discovering the important or essential dimensions that differentiate the two categories of samples.
- the SVM training procedure for a particular radionuclide may examine a set of points occupying 1024 dimensional space, each point consisting of one spectrum in the training set. This procedure may converge to a hyperplane that optimally "slices" the 1024-dimensional space of spectra into two halves with all positive samples on one side and all negative examples on the other. Further to this, in the more difficult case where a perfect separation may not be possible, the training system may work to minimize the weighted error of samples that are placed on the side of the hyperplane opposite to their true classification. [0085] After training is completed, any future spectra may be classified in real time by operation of determining on which side of the trained hyperplane the spectra may fall.
- the training system may find precisely those spectral features that indicate the presence of the designated library-resident radionuclide and, on the negative side, may leam to screen out any 'deceptive' features that may be found in other radionuclides, such as radionuclides with peaks in the same region, for example.
- Features not noticeable to the human eye or its peak-fitting software corollary, such as a series of small variations in relative peak strengths, may thus become obvious to the trained SVM system.
- the support- vector training system may be capable of finding and identifying features in its representation that separate them by a great distance, which may result in more accurate and empirically verifiable identification.
- the isotopes Barium- 133 and Iodine- 131 may provide an example of two common radionuclides that have energy peaks near each other in the gamma ray spectrum, with peaks at energies 302.8 and 284.3 keV, respectively.
- the average peak width for these elements using a NaI crystal is approximately 40 keV.
- the spatial distance between these two peaks is small enough that they may not be distinguishable to peak fitting algorithms or to the unaided human eye.
- Ba-133 and 1-131 are both present, only one distinct peak may be visible in the gamma-ray spectrum.
- the SVM system may correctly identify the radionuclides in both cases.
- the SVM algorithms may first normalize the data that they process, therefore may discriminate using relative peak heights and do not depend upon absolute intensity. Through the SVM training procedure, the code has automatically "learned" to search for the subtler features that differentiate the spectra of the two radionuclides.
- a spectrum was constructed that contained the signatures Ba- 133 and 1-131, present at similar levels of strength.
- both radionuclides are successfully found using the artificial intelligence based system, though to the human eye it is extremely difficult to tell which of the two elements are actually present.
- the classifiers for Ba-133 and 1-131 were not trained on any spectra containing a combination of radionuclides. Nevertheless, the system learned the features that distinguish Ba-133 and 1-131 to a level that both classifiers may consistently recognize their respective element's signature within the combination spectrum.
- a radionuclide of low intensity has its spectrum peaks almost entirely "buried" by the presence of other radionuclides. This could happen if it were attempted to disguise the presence of a radionuclide classified as a threat material by the presence of non threat radionuclides.
- additional spectra were generated containing Plutonium-238 (Pu-238) in addition to the Ba-133 and 1-131 used above.
- Pu-238 will characteristically produce a gamma ray spectrum with much smaller peaks than either of the other two radionuclides. In the combination of these elements, the distinguishing features of the Pu-238 spectra are virtually invisible to the human eye or conventional peak-fitting algorithms.
- the artificial intelligence based system of the present invention was able to correctly identify the presence of any combination of all three radionuclides in real-time, as shown in Figures 17-20.
- Plutonium-238 spectra was identified; in Figure 18, Iodine-131 spectra was identified; in Figure 19, Plutonium-238 was detected embedded in Iodine- 131; and in Figure 20, Plutonium-238 was found embedded in Iodine-131 and Ba-133.
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US20050205799A1 (en) * | 2003-12-18 | 2005-09-22 | Charles Gentile | Radionuclide detector and software for controlling same |
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