Note: Descriptions are shown in the official language in which they were submitted.
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SYSTEM AND METHOD FOR RESOLVING GAMMA-RAY SPECTRA
Government Interests
[001] The inventions described herein have been developed for, pursuant to, or
with the
assistance of, the United States government. These inventions may be
manufactured, used and licensed by or for the United States government for
United States government purposes.
Field of the Invention
[002] 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.
Backeround
[003] 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.
[004] Gamma rays, as well as protons, alpha particles, beta particles and x-
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
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speaking, these ions may be measured by using measuring devices, such as a
Geiger counter, for example.
[005] While 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.
[006] Most 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.
[007] 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. By contrast, 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.
[008] 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
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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.
[009] 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.
[0010] The U.S. government does not take these sorts of potential threats
lightly. For
example, 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 Ir 192 are
also
included in the matrix of potential threats. In addition, spent fuel is
generally
included in potential threat matrices, and needless to say there are very
significant
quantities of spent fuel available.
[0011] Because nuclear devices or threats such as those described above may be
assembled or deployed at any location, it would be advantageous for
authorities
to have the capability of sensing radionuclides at widely dispersed locations.
By
way of nonlimiting examples, such locations may include automotive highways,
bridges, airports, train stations, municipal mass transit systems,
governmental
buildings, freight handling facilities, and the like. Automating the screening
or
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sensing at such sites may enable the screening at those sites to be free of
human
intervention wben no radionuclides are detected, and yet may readily enable
the
alerting of appropriate authorities upon a positive detection and/or
identification
of a specific radionuclide deemed to be a threat.
[0012] To date, there are several types of decectors, each having varying
degrees of
resolution and performance. For example, the differences in performance
characteristics of sodium iodide (Nal) versus Germanium for gamma ray
spectroscopy have been well characterized. However, the increased resolution
of
germanium detectors, obvious upon visual inspection of the spectra, can be
illusive when evaluating the advantages for systems that might automatically
identify radionuclides within spectra. Many gamma spectroscopy based sensors
have and will be deployed as standalone, automated surveillance/detection
systems, a reality that places the performance and reliability of automatic
radionuclide identification systems at central and increasing importance.
[0013] Traditional automated, peak-fitting algorithms for identifying
radionuclides in
gamma-ray spectra may work in a very similar manner to that of the human eye
in determining specific radionuclides. When employing these conventional
tools,
nuclear spectroscopy data derived from scintillators may often prove to be
indeterminate as to the identification of originating specie. The problem of
identifying embedded spectra, while difficult for the unaided eye and
corollary
conventional algorithms, is subject to acceptable resolution when it is
addressed
with more sophisticated algorithm based systems.
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[0014] Thus, there remains a need for automated systems and methods to detect
and
identify any of a wide range of radionuclides from complex or "noisy" spectral
data in a cost-effective manner.
Summary of the Invention
[0015] A system for identifying radionuclide emissions is described. The
system
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.
Description of the Drawings
[0016] Understanding of the present invention will be facilitated by
consideration of the
following detailed description of the embodiments of the present invention
taken
in conjunction with the accompanying drawings, in which like numerals refer to
like parts and in which:
[0017I FIG. I illustrates a block diagram of the system according to an aspect
of the
presentinvention;
[0018] FIG. 2 illustrates a block diagram of a neutron detector according to
the present
invention;
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[0019] FIG. 3 illustrates a block diagram of an x-ray detector according to an
aspect of
the present invention;
[0020] FIG. 4 illustrates a block diagram of a gamma ray detector according to
an aspect
of the present invention;
[0021] FIG. 5A illustrates a set of sample data as may be detected by the
gamma ray
channel according to an aspect of the present invention;
[0022] 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;
[0023] 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;
[0024] FIG. 6 illustrates a configuration according to an aspect of the
present invention;
[0025] FIG. 7 illustrates a neural networking configuration of the software
according to
an aspect of the present invention;
[0026] FIG. 8 shows a screen shot of the main system screen according to an
aspect of
the present invention;
[0027] FIG. 9 shows a screen shot of the alert for Cs137 according to an
aspect of the
present invention;
[0028] FIG. 10 shows a screen shot of the alert for Am241 according to an
aspect of the
present invention;
[0029] FIG. 11 shows a screen shot of the alert for Co60 according to an
aspect of the
present invention;
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[0030] FIG. 12 illustrates a housing according to an aspect of the present
invention;
[0031] FIG. 13 is a flow diagram of a method of detecting radionuclides
according to an
aspect of the present invention.
[0032] FIG 14 is a graph of generated test spectra for Ba-133;
[0033] FIG 15 is a graph of generated test spectra for I-131;
[0034] FIG 16 is a graph of generated test spectra for Ba-133 and I-131;
[0035] FIG 17 is a graph of generated test spectra for Pu-238;
[0036] FIG 18 is another graph of generated test spectra for I-131;
[0037] FIG 19 is a graph of generated test spectra for Pu-238 embedded in I-
131; and
[0038] FIG 20 is a graph of generated test spectra for Pu-238 embedded in 1-
131 and Ba-
133.
Detailed Description of the Preferred Embodiments
[0039] It is to be understood that the figures and descriptions of the present
invention
have been simplified to illustrate elements that are relevant for a clear
understanding of the present invention, while eliminating, for the purpose of
clarity, many other elements found in typical detection components and methods
of manufacturing and using the same. Those of ordinary skill in the art will
recognize that other elements and/or steps are desirable and/or required in
implementing the present invention. However, because such elements and steps
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are well known in the art, and because they do not facilitate a better
understanding of the present invention, a discussion of such elements and
steps is
not provided herein. The disclosure herein is directed to all such variations
and
modifications to such elements and methods known to those skilled in the art.
[0040] 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. According to an
aspect
of the present invention, the device and system may allow for detection of
radionuclides having minimal and trace emission levels. According to an aspect
of the present invention, 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.
[0041] 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 locatzons at or through which there may be a heightened
likelihood of the transport of hidden radionuclides. By way of nonlianiting
example, these locations may include highways, train stations, airports,
shipyards,
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metropolitan mass transit systems, governmental and commercial buildings,
truck
terminals, railroad freight handling facilities, and the like.
[0042] 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. For example, 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. However, if
emissions
from a radionuclide are detected, 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.
[0043] 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
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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.
[00441 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. For example, the present invention may
be positioned over a bridge, such that detection of vehicles passing over the
bridge may be made. In the event two fast moving vehicles are transporting
radionuclides in succession, 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. Using again the example of two vehicles crossing a
bridge,
when the first vehicle contains a very high level of emissions, and the second
vehicle contains a trace level of emissions, the detector may recognize that
two
sources of emissions exist and not one. Thus, the detection and identification
of
radionuclides at high rates and high sensitivity levels allows for
communication
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of a positive determination of the correct number of emissions sources to
appropriate authorities. Further, 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.
[0045] Referring now to FIG. 1, there is shown a block diagram of the system
according
to an aspect of the present invention. As may be seen in FIG. 1, 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.
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. For the sake of the present
discussion of exemplary embodiment(s), three channels will be discussed with
regard to detection of gamma rays, x-rays and neutrons, by way of non-limiting
example only.
[0046] According to an aspect of the present invention, 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.
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[0047] 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. 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.
[0048] According to an aspect of the present invention, a neutron detector may
be
utilized to detect neutron radiation. Referring now also to FIG. 2, there is
shown
block diagram of a neutron detector 200 according to the present invention. As
may be seen in FIG. 2, 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 atm in order to increase
the
resulting signal level of an incident neutron. More specifically, a pressure
range
from 35-45 atm nnay be used. Yet more specifically, a pressure level of 40 atm
may be utilized. Increased pressures may provide increased signal strength
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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.
[0049] While a liquid or a solid may also be used within the confined element,
a gas may
be used since the ionized particles of a gas travel more freely than those of
a
liquid or a solid. Typical gases used in detectors include argon and helium,
although boron-triflouride may be utilized.
[0050] 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.
[0051] After a neutron interacts with element 210, a conversion in the neutron
energy
occurs and a photon or electron may be produced. 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
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converting detected particles into commensurate electricat 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.
[0052] According to an aspect of the present invention, second detection
channel 120
may be designed to detect the presence of x-ray radiation. Referring also now
to
FIG. 3, there is shown a block diagram of the x-ray detector 300 designed for
detection of x-ray radiation according to an aspect of the present invention.
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 electricat signal may be read into a processor, such as a computer,
utilizing a
channel on a multi-channel analyzer. By way of a nonlimiting example,
converter
310 may take the form of a CdTe detector.
[0053] In addition to detecting produced x-rays, detection of x-rays may be
increasingly
useful because of the bremsstrahlung, or secondary, x-ray affect.
Bremsstrahlung,
or braking radiation, is electromagnetic radiation with a continuous spectrum
produced by the acceleration of a charged particle, such as an electron,
proton,
alpha or beta particle, when deflected by another charged particle, such as an
atomic nucleus. Two classes of bremsstrahlung radiation exist. Outer
bremsstrahlung radiation occurs where the energy loss by radiation greatly
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exceeds that by ionization as a stopping mechanism in matter, such as for
electrons with energies above 50 MeV. 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 etectric field in the region of the nucleus of the atom undergoing decay,
in a
manner similar to that which causes outer bremsstrahlung. In electron and
positron emission, 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. In electron capture, the energy comes 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.
[0054] Bremsstrahlung is thus a type of secondary radiation that it is
produced as a
reaction in shielding material caused by the primary radiation. In some cases
the
bremsstrahlung produced by some sources of radiation interacting with some
types of radiation shielding may be more harmful than the originaI beta
particles
would have been.
[0055] Detector 300 may be suitable for detecting radioactive material that is
shielded
within a metal. For example, as may be known to those possessing an ordinary
skill in the pertinent arts, 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
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beta) particles. In particular, shielded elements which may produce such x-ray
emission may include those with a long half-life.
[0056] According to an aspect of the present invention, third detection
channel 130 rnay
be designed to detect the presence of and identify gamma radiation. Referring
now also to FIG. 4, there is shown a block diagram of detector 400. As may be
seen in FIG. 4, 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. For example, sensor 410 may take the form of a crystal, such as Nal
or
Ge(Li), for example. In such a configuration, gamma rays may interact with a
NaI
crystal sensor 410.
[0057] 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 gamtna ray spectrum.
[0058] A Nal 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.
[00591 With appropriate calibration, Nal and Ge(Li) detector systems may be
used to
determine the energies of gamma rays from other radioactive sources.
[0060] 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.
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[0061] Other sensors 410 may be used within the detector of the present
invention, and
such other sensors may require use of altemative 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.
[0062] 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.
[0063] A multi-channel analyzer, as would be evident to those possessing an
ordinary
skill in the pertinent arts, may have a few channels, or up to thousands of
channels. For the sake of discussion 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.
[0064] Referring now to 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. As may be seen in FIGS. 5A-C, a given gamma emitting material
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releases a constant amount of energy. Thus, for example, 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.
[0065] The present gamma detection function may also be designed to enhance
low level
measurements. In particular, low level detection may occur at the level of
approximately 10 mu.Rernlhr for a 1 second integration time. This low level
detection may be in the range 5-15 µRem/hr for a 1 second integration time -
with background in approximately the 4µRem/hr for a 1 second integration
time range. Enhancement of the crystal, including size optimization, may
increase
the low level sensitivity to gamma detection.
[0066] The configuration of the present invention provides for rapid
identification of
emissions and is linked to software. Referring now to FIG. 6, there is shown a
configuration according to an aspect of the present invention. As may be seen
in
FIG. 6, a computer acquires data from the multichannel analyzer as discussed
hereinabove. The raw data is transmitted to a processor. In addition to the
raw
data, 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
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and analyze data when the photoelectric detector is triggered, thereby
providing
data only when a target is positioned as desired.
[00671 Referring now to FIG. 7, there is shown a neural networking
configuration of the
software according to an aspect of the present invention. According to an
aspect
of the present invention, 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. As shown in the configuration
of FIG. 7, 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). This
processing
may result in determining if the peaks detected by the input neurons represent
a
threat. 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. Ultimately, in the presence of a single
isotope, a
single output neuron may fire, namely the output neuron corresponding to the
identity of the isotope detected. In such a configuration, the software may
learn or
adapt to conditions, such as weather, temperature, and solar. Further, the
software
may be able to detect an isotope even in the presence of systematic shifts in
the
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data detection. Knowing that an isotope may have a signature that has a ratio
between channels of 2:1 for exampte, 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.
[0068] 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.
[0069] Further, 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.
[0070] 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. In addition, not all
radionuclides
are currently considered to be relevant or threatening. In the interests of
providing
a device that may be implemented in the field, certain nonlimiting embodiments
of the present invention may restrict the identities of relevant and/or
threatening
radionuclides to a relatively smaller subset.
[0071] Many radionuclides can be identified by examining the characteristic
gamma rays
emitted in the decay of the radioactive parent nucleus. For exampte, two
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characteristic gamma rays occur in the decay of the radionuclide Na 22. The Na
22 decay occurs by one of two independent mechanisms. In each of the two beta
decay branches, a positron and a neutrino are emitted, and the net nuclear
charge
changes from Z=1J. to Z=10. In one decay branch, the Na 22 ground state is
stable; however, the first excited state of Na 22 at about 1.275 MeV decays
with a
lifetime of 3.7 ps in the gamma decay process, which gives rise to a
characteristic
gamma ray with energy of about 1.275 MeV. The positrons slow rapidly in the
radioactive source material and disappear in the annihilation process,
producing
two characteristic 0.511 MeV annihilation gamma rays. In the other decay
branch,
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.
[0072] For example, for Co 60 spectra, two main gamma ray peaks above I MeV
are
evident. In analyzing the spectra, a centroid of the energies peaks including
the
associated uncertainties may be apparent. Comparison of the data with known
energy level diagrams, as would be evident to those possessing an ordinary
skill
in the pertinent arts, may thus be performed. A source may be identified by
comparing the centroids of the energy peaks with a chart of the nuclides
and/or a
table of isotopes.
[0073] Referring now to FIGS. 8-11, there are shown screen shots associated
with the
software of the present invention. As may be seen in FIG. 8, a start-up and
all
systems go screen is shown. This screen enables a operator to determine if the
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system is working and, if so, if the present invention is functioning
properly.
FIGS. 9-11 show alert pages for various emission. For example, in FIG. 9,
there
is shown 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.
Similarly, as may be seen in 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. As may be seen in 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. Other features may be provided via 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.
[0074] Referring now to FIG. 12, there is shown a housing according to an
aspect of the
present invention. As may be seen in FIG. 12, 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
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materials. According to an aspect of the present invention, 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. As is known to those
possessing an ordinary skill in the pertinent arts, products such as 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.
[0075] 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. By way of a nonlimiting example, 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
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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. Similarly, in environments allowing for such a
connection,
a wireless connection may be employed between the detector and the processing,
and/or between the processing and one or more monitoring locations. For
example, a wired or wireless connection may allow for a monitoring of multiple
sites having a detector and processing from a single monitoring location.
[0076] Referring now to FIG. 13, there is shown a method of detecting
radionuclides
according to an aspect of the present invention, such as in accordance with
the
exemplary embodiments of FIGS. 1 through 12 hereinabove. 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.
[0077] According to yet another aspect of the present invention, the
incorporation of
sophisticated algorithms may bring to fruition the true potential for hyper-
accurate, cost-effective NaI-based nuclear detection technologies. There are
several advantages in using NaI Scintillation Hardware in the detection of
radionuclides. For example, as compared to other detection technologies, Nal
crystals may be robust, highly sensitive, and available for relatively low
costs.
Additionally, no refrigeration of the scintillating material may be necessary,
as is
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typically the case for semiconductor (Gerinanium-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.
[0078] Such application of computer algorithms to automated radionuclide
identification
is a unique and innovative shift in the perception of the task of
spectroscopy. For
example, instead of inerely identifying an idealized set of isolated peaks in
the
gamma ray spectrum of a specific radionuclide, 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 (Al) algorithms or systems may
play
in its resolution. As used herein, an artificial intelligence system may
provide
hyper accurate pattern recognition of spectral data.
[0079] 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.
[0080] The training algorithm may then analyze this data to "learn" the most
efficient
and reliable rule for distinguishing positive from negative examples. The
output
of the training algorithm may be a classification algorithm that may further
be
used to classify input samples, or spectra, in real-time.
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[0081] According to an aspect of the present invention, 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.
These spectra may represent a sufficient array of signal strengths, background
noise levels, and/or combinations of the presence and absence of other
radionuclides. After a classifier is trained for each of the library elements,
real
time identification of each spectrum from a gamma sensor may be obtained by
evaluating the classifier for each radionuclide in the library.
[0082] 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.
[0083] This novel approach may capitalize on the fact that artificial
intelligence based
systems do not `see' spectral data in the same way as does the human eye, or
its
corollary conventional peak-fitting algorithms. As described herein,
artificial
intelligence systems may be capable of analyzing the data with sufficient
acuity
as to render the increased resolution of germanium detectors unnecessary for
many applications. Additionally, artificial intelligence based systems, may be
fully capable of dealing with the problem in which a particular radionuciide's
peaks may be masked by peaks of other nuclides in the same energy range. For
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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.
[0084] The nature of the feature selection and weighting done within the
context of the
artifical intelligence based system may be further illustrated by considering
exemplary artificial intelligence frameworlcs, such as Support Vector Machines
(SVMs). 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. For
example, if a gamma ray spectrum consists of 1024 integer data points
corresponding to energy levels, 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.
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[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.
[0086] In this way, 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 learn 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. Even in the case when the spectra
of two distinct radionuclides have a peak in the same energy band, 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.
[0087] The inherent capability of artifical intelligence based systems of the
present
invention may be further enhanced by normalization techniques, as well as by
projecting the data into a higher dimensional feature space that accentuates
the
desired distinguishing features. Furthermore, the system may include
traditional
peak-fitting algorithms, which may be run in parallel. Heuristic decision
logic
may be employed to compare the results of the multiple and/or independent
algorithms, which may produce an ever higher level of classification accuracy.
[0088] The capabilities of artificial intelligence based systems to identify
radionuclides
with overlapping or hidden peaks, may be further illustrated based on the
following set of examples.
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[0089] According to an exemplary embodiment of the present invention, 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.
Furthermore, when Ba-133 and 1-131 are both present, only one distinct peak
may be visible in the gamma-ray spectrum.
[0090] However, there are more significant differences between the spectra of
Ba-133
and 1-131 in the lower energy channels, especially below 152 keV. In order to
more stringently test the capabilities of the artificial intelligence based
system, as
well as to more closely model the real world situation of greater background
noise in the lower channels, the spectra used in the provided examples was
"thresholded" such that no energies below 152 keV were considered. Such
thresholding effectively eliminated these other distinguishing features and
made
the analysis in the provided examples considerably more difficult.
[0091] However, these spectra were analyzed with the SVM artificial
intelligence based
system and found them able to automatically compensate for the above
mentioned similarities, and further produced a highly efficient procedure to
distinguish between Ba-133 and 1-131. In this case, two SVM classifiers were
trained separately, one for Ba-133 and one for 1-131, using training data sets
consisting of spectra synthesized for each of the two radionuclides at various
intensity levels, using the characteristics of a Nal detector. Then, for
testing
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purposes, additional spectra were generated for each element at different
intensities than the training spectra.
[0092] As shown in Figures 14 and 15, graphs of two independently generated
test
spectra for Ba-133 and 1-131 have been depicted, with the results of both the
peak
fitting and artificial intelligence based system labeled on the graph.
[0093] The result of the artificial intelligence based system is displayed in
the text below
the graph. The peak fitting result is shown by the vertical line through the
center
of the peak with the label at the top. Even though the actual element present
is I-
131, the peak fitting algorithm has here been instructed to locate Ba-133 in
this
energy band, and has no means to avoid a false identification.
[0094] Conversely, the SVM system may correctly identify the radionuclides in
both
cases. Note that 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.
[0095] In another example, a spectrum was constructed that contained the
signatures Ba-
133 and I-131, present at similar levels of strength. As shown in Figure 16,
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. Here the classifiers for Ba-133 and 1-131 were not
trained
on any spectra containing a combination of radionuclides. Nevertheless, the
systezx- learned the features that distinguish Ba-133 and 1-131 to a level
that both
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classifiers may consistently recognize their respective element's signature
within
the combination spectrum.
[0096] In yet another example, 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. For this
experiment, 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. However, 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. In
Figure 17, 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.
[0097] Those of ordinary skill in the art will recognize that many
modifications and
variations of the present invention may be implemented without departing from
the spirit or scope of the invention. Thus, it is intended that the present
invention
cover the modification and variations of this invention provided they come
within
the scope of the appended claims and their equivalents.
31
