Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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RADIONUCLIDE DETECTOR AND SOFTWARE FOR CONTROLLING
SAME
Priorit
[1] This application claims the benefit of United States Provisional
Application Serial No. 60/530,539, entitled "Miniature Integrated
Nuclear Detection System with Improved Detection Capability",
filed December 18, 2003. This application incorporates United
States Provisional Application Serial No. 60/530,539, entitled
"Miniature Integrated Nuclear Detection System with Improved
Detection Capability", as if set forth in their entirety herein.
Government Funding
[2] 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
[3] The present invention is directed to the detection of radionuclides,
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and, more specifically, to a system, method and apparatus for the
detection and identification of radionuclides, and to a software
controller for a system, method and apparatus for the detection and
identification of radionuclides.
Background of the Invention
[4] ~ Radiation is a term used to describe the process of emitting radiant
energy, such as in the form of particles or electromagnetic rays,
due to nuclear decay. While there are many different types of
radiation, there are five which are dealt with most frequently.
These five types of frequently encountered radiation emissions
include alpha particles, beta particles, gamma rays, x-rays and
neutrons.
(5] An alpha particle is a positively charged particle made up of two
neutrons and two protons, and is emitted by certain types of
radioactive nuclei. The flow of alpha particles along a given path
can be stopped by thin layers of light materials, such as a sheet of
paper, and thus alpha particles pose no direct or external radiation
threat; however, they can pose a serious health threat if ingested
or inhaled.
[6] A beta particle is an electron or positron emitted by certain types of
radioactive nuclei. While the flow of beta particles can be stopped
by aluminum, beta particles pose a serious direct or external
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radiation threat and can be lethal depending on the amount, or
dose, received. Beta particles, like alpha particles, pose a serious
internal radiation threat if inhaled or ingested.
[7] 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. These 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.
(8] X-rays are high-energy electromagnetic emissions from atoms
caused when electrons within those atoms fall from a higher
energy shell to a lower energy shell. These x-rays, like gamma
rays, have high energy and short wavelengths, with energies
between 1 thousand and 1 million eV and wavelengths between
0.001 and 1 nanometer. X-ray radiation is between ultraviolet and
gamma-radiation in the electromagnetic spectrum.
(9) A neutron is a particle that is found in the nucleus, or center, of an
atom. A neutron has a mass approximately equal to that of a
proton (about 1 amu, which is roughly 1.6X10-27kg) but, unlike a
proton, a neutron does not carry a charge.
[10] Protons, alpha particles, beta particles, gamma rays and x-rays
may cause' direct ionization in that these particles or rays transfer
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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.
[lI] 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, however,
have no mass and no electrical charge. Each is thus pure
electromagnetic energy.
[12] 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.
[13] 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.
(14) Gamma rays do not directly ionize atoms in tissue. Instead, they
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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.
[16] Neutrons, which are non-charged particles, interact differently.
Neutrons interact by colliding with atoms. Neutrons transfer energy
during these collisions, in a manner that is similar, conceptually, to
the collision of billiard balls. These collisions may be 0-100 percent
energy transfers, depending on the speed, angle, and size of the
components, according to the laws of physics as would be
understood by one of skill in the art.
[17] A more efficient energy transfer may occur between a neutron and
a target of the same size. Because of the comparable size of
protons, protons often become good targets for energy transfer
from a neutron collision. Protons, like the nucleus of a hydrogen
atom, when struck by a neutron, may absorb energy and move.
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Thereby, instead of having a non-charged particle moving through
a material, a charged particle is moving, which may give up energy
through ionization, as discussed hereinabove. As the neutrons
slow, they may be absorbed by atoms. This is one way in which a
material may become radioactive, although the absorption of
neutrons does not always lead to a radioactive atom.
[i8] Sources of neutrons include nuclear reactors, making neutrons by
fission and decay of fission products, spent fuel, combining alpha-
emitting isotopes like polonium or radiation with beryllium, the
transuranium element Cf 252 (which undergoes spontaneous
fission), accelerators by photon-neutron production, or smashing a
deuterium atom into tritium, thereby producing fusion and neutrons.
[19] 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.
(20] 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
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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.
[21] 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 sensing at such sites may enable the
screening at those sites to be free of human intervention when 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.
[22] Thus, there remains a need for automated systems and methods to
detect and identify any of a wide range of radionuclides. There is
further a need for such systems and methods to operate rapidly,
automatically and independently of human intervention. There
remains a need for detection and identification systems and
methods capable of operating at high volume, and with high
throughput. There furthermore remains a need for systems and
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methods to detect and identify particular radionuclides from among
a set of candidate radionuclides that may be deployed in a variety
of environments.
Summary of the Invention
[23] A detector, system and method for detecting the presence of
suspect radionuclides in a target is disclosed. The detector
includes a first detection channel for a first detecting neutron
emissions in the target and for providing a first output in
accordance with the first detecting, a second detection channel for
a second detecting x-ray emissions in the target and for providing a
second output in accordance with the second detecting, a third
detection channel for a third detecting and an identifying of gamma
emissions in the target and for providing a third output in
accordance with the third detecting and identifying, a signal
manipulation electrically coupled to each of the first, second, and
third detection channels, the signal manipulation for receiving the
first, second and third outputs and for processing those outputs,
and at least one processor electrically coupled to the signs)
manipulation. The processor determines if the suspect
radionuclide is present in the target and provides an alert when the
suspect radionuclide is present in the target. A method of
detecting the presence of radionuclides in a target is also
disclosed. The method includes sensing the target using at least
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one detector, wherein the at least one detector outputs a signal
commensurate with a presence of the radionuclides in the target,
processing the signal in order to identify a type of the radionuclide,
and alerting responsively to the identified radionuclide. Thus, the
present invention provides automated systems and methods to
detect and identify any of a wide range of radionuclides.
Brief Description of the Figures
[24] 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:
[25] Figure 1 illustrates a block diagram of the system according to an
aspect of the present invention;
[26] Figure 2 illustrates a block diagram of a neutron detector according
to the present invention;
[27] Figure 3 illustrates a block diagram of an x-ray detector according
to an aspect of the present invention;
[28] Figure 4 illustrates a block diagram of a gamma ray detector
according to an aspect of the present invention;
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[29] Figure 5A illustrates a set of sample data as may be detected by
the gamma ray channel according to an aspect of the present
invention;
[30] Figure 5B illustrates a set of sample data as may be detected by
the gamma ray channel according to an aspect of the present
invention;
[31] Figure 5C illustrates a set of sample data as may be detected by
r
the gamma ray channel according to an aspect of the present
invention;
[32] Figure 6 illustrates a configuration according to an aspect of the
present invention;
(33] Figure 7 illustrates a neural networking configuration of the
software according to an aspect of the present invention;
(34] Figure 8 shows a screen shot of the main system screen according
to an aspect of the present invention;
[35] Figure 9 shows a screen shot of the alert for Cs137 according to an
aspect of the present invention;
(36] Figure 10 shows a screen shot of the alert for Am241 according to
an aspect of the present invention;
[37] Figure 11 shows a screen shot of the alert for Co60 according to
an aspect of the present invention;
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(38] Figure 12 illustrates a housing according to an aspect of the
present invention; and,
[39) Figure 13 is a flow diagram of a method of detecting radionuclides
according to an aspect of the present invention.
Detailed Description of the Preferred Embodiments
[40] 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 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.
(41] The present invention is directed to an apparatus, system and
method for detection of neutron and x-ray emissions, and an
identification of gamma emissions. One aspect of the invention
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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.
[42] 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. By way of
nonlimiting example, 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.
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[43) 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, andlor 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.
[44) 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
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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.
[45] 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
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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 of a positive
determination of the correct number of emissions sources to
appropriate authorities. Further, the use of multiple
detectoNidentifiers 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.
[46] Referring now to Figure 1, there is shown a block diagram of the
system according to an aspect of the present invention. As may be
seen in Figure 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
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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.
[47] 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.
[48] 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
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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.
(49] According to an aspect of the present invention, a neutron detector
may be utilized to detect neutron radiation. Referring now also to
Figure 2, there is shown block diagram of a neutron detector 200
according to the present invention. As may be seen in Figure 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 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.
[50] 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
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used in detectors include argon and helium, although boron-
triflouride may be utilized.
[51] 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.
[52] 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
converting detected particles into commensurate electrical signals.
For example, if a photon is produced by the interaction of the
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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.
[53] 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 Figure 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 electrical 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.
[54] 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,
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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 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 rhaximum 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. 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.
(55] 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 original beta particles
would have been.
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[56) 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 beta) particles. In particular, shielded
elements which may produce such x-ray emission may include
those with a long half life.
[57] According to an aspect of the present invention, third detection
channel 130 may be designed to detect the presence of and
identify gamma radiation. Referring now also to Figure 4, there is
shown a block diagram of detector 400. As may be seen in Figure
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 Nal crystal sensor 410.
[58] The detection efficiency of Nal crystals may improve with
increasing crystal volume and the energy resolution may be
dependent on the crystal growth conditions. Higher energy
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resolution is essential in radioactive counting situations where a
large number of lines are present in a gamma ray spectrum.
[59] 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. With appropriate calibration, Nal and Ge(Li) detector
systems may be used to determine the energies of gamma rays
from other radioactive sources.
[60] 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.
[61] 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.
[62] 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.
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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.
[63] 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.
(64] Referring now to Figures 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 Figures
5A - C, a given gamma emitting material 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.
[65] 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 NRem/hr for a 1 second
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integration time. This low level detection may be in the range 5 -
15 NRem/hr for a 1 second integration time - with background in
approximately the 4 NRem/hr for a 1 second integration time range.
Enhancement of the crystal, including size optimization, may
increase the low level sensitivity to gamma detection.
[66] The configuration of the present invention provides for rapid
identification of emissions and is linked to software. Referring now
to Figure 6, there is shown a configuration according to an aspect
of the present invention. As may be seen in Figure 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 and
analyze data when the photoelectric detector is triggered, thereby
providing data only when a target is positioned as desired.
[67] Referring now to Figure 7, there is shown a neural networking
configuration of the software according to an aspect of the present
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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 Figure 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 1'tre,
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.
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Further, 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.
[68] 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.
(69] 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.
[70] 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
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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.
[71] Many radionuclides can be identified by examining the
characteristic gamma rays emitted in the decay of the radioactive
parent nucleus. For example, two 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 = 11 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.
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[72] For example, for Co 60 spectra, two main gamma ray peaks above
1 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.
[73) Referring now to Figures 8 - 11, there are shown screen shots
associated with the software of the present invention. As may be
seen in Figure 8, 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.
Figures 9 - 11 show alert pages for various emission. For
example, in Figure 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 Figure 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 Figure 11, there
is shown an alert page for the alert of Co 60. Co 60 has a high
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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.
[74] Referring now to Figure 12, there is shown a housing according to
an aspect of the present invention. As may be seen in Figure 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 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
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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.
[75] 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
Figure 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 Nal detector, a cadmium-zinc-telluride
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detector, and a neutron detector based either on BF3 or He3 as the
active element. A cable may exit the housing shown in Figure 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.
[76] Referring now to Figure 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 Figures 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.
[77] 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
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modification and variations of this invention provided they come
within the scope of the appended claims and their equivalents.
