U.S. patent application number 13/361060 was filed with the patent office on 2012-05-17 for identifying fissionable material.
This patent application is currently assigned to L-3 Communications Security and Detection Systems, Inc.. Invention is credited to David Perticone, Vitaliy Ziskin.
Application Number | 20120119103 13/361060 |
Document ID | / |
Family ID | 41199484 |
Filed Date | 2012-05-17 |
United States Patent
Application |
20120119103 |
Kind Code |
A1 |
Perticone; David ; et
al. |
May 17, 2012 |
IDENTIFYING FISSIONABLE MATERIAL
Abstract
Fissionable materials are distinguished from other
high-effective atomic number materials by producing dual-energy
x-ray radiation sufficient to cause fission in fissionable
materials and directing the dual-energy x-ray radiation sufficient
to cause fission in fissionable materials towards a physical
region. X-ray radiation and a product of fission from the physical
region are sensed. An absorption of the dual-energy x-ray radiation
by the physical region is determined based on the sensed x-ray
radiation, and whether the physical region includes fissionable
material is determined based on the presence of a product of
fission.
Inventors: |
Perticone; David;
(Winchester, MA) ; Ziskin; Vitaliy; (Brighton,
MA) |
Assignee: |
L-3 Communications Security and
Detection Systems, Inc.
Woburn
MA
|
Family ID: |
41199484 |
Appl. No.: |
13/361060 |
Filed: |
January 30, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12426179 |
Apr 17, 2009 |
8106365 |
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13361060 |
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61045997 |
Apr 18, 2008 |
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61052072 |
May 9, 2008 |
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Current U.S.
Class: |
250/395 |
Current CPC
Class: |
H05H 6/00 20130101; H05H
3/06 20130101; G01V 5/0091 20130101 |
Class at
Publication: |
250/395 |
International
Class: |
G01T 1/16 20060101
G01T001/16 |
Claims
1. A method comprising: directing a first type of radiation towards
a physical region, the first type of radiation having a first
energy; directing a second type of radiation towards the physical
region, the second type of radiation having a second energy that is
higher than the first energy; determining an absorption
characteristic of the physical region based on an absorption of the
first type of radiation and the second type of radiation by the
physical region; determining, from the absorption characteristic,
that the physical region is a region of interest; determining a
characteristic of the region of interest; modifying a third type of
radiation based on the characteristic; and scanning the region of
interest with the modified third type of radiation.
2. The method of claim 1, wherein determining a characteristic of
the region of interest comprises determining a characteristic of a
background of the physical region.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. patent
application Ser. No. 12/426,179, titled IDENTIFYING FISSIONABLE
MATERIAL and filed on Apr. 17, 2009, now allowed, which claims
priority from U.S. Provisional Application Ser. No. 61/045,997,
titled IDENTIFYING NUCLEAR MATERIAL and filed on Apr. 18, 2008, and
U.S. Provisional Application Ser. No. 61/052,072, titled IMAGING
SYSTEM and filed on May 9, 2008, all of which are herein
incorporated by reference in their entirety.
TECHNICAL FIELD
[0002] This disclosure relates to identifying fissionable
material.
BACKGROUND
[0003] Characteristics of a material may be determined based on the
interaction of the material with radiation and neutral
particles.
SUMMARY
[0004] In one general aspect, a system for detecting the presence
of fissionable material includes a source of radiation that is
switchable between a screening mode and a verification mode. The
source of radiation is configured to produce, in the screening
mode, a first type of radiation having a first energy and a second
type of radiation having a second energy, the second energy being
higher than the first energy, and to direct the first type of
radiation and the second type radiation toward a physical region.
In the verification mode, the system is configured to produce a
third type of radiation, and to direct the third type of radiation
toward the physical region, the third type of radiation being
sufficient to induce fission in a fissionable material.
[0005] The system also includes a sensor system that is configured
to sense radiation having the first energy and the second energy
from the physical region, and a sensor configured to sense a
fission product. The system also includes a processor coupled to a
computer-readable storage medium storing instructions that, when
executed, capture data from the sensor configured to sense
radiation having the first energy and the second energy, determine,
for the physical region represented by the captured data, an
absorption of the first type of radiation and the second type of
radiation, determine whether the physical region is a region of
interest based on the absorption, and cause the source of radiation
to switch from the screening mode to the verification mode when the
physical region is a region of interest.
[0006] Implementations may include one or more of the following
features. The first type of radiation may be x-ray radiation, and
the second type of radiation may be x-ray radiation. To determine
whether the physical region is a region of interest based on the
absorption, the processor may be operable to determine an effective
atomic number of the physical region. The third type of radiation
may be x-ray radiation having an energy that is lower than the
energy of the first energy. The first type of x-ray radiation may
have an energy spectrum with a maximum energy of 6 MeV, the second
type of x-ray radiation may have an energy spectrum with a maximum
energy of 9 MeV, and the third type of x-ray radiation may have an
energy spectrum with a maximum energy of 10 MeV. The first type of
radiation, the second type of radiation, and the third type of
radiation may be the same type of radiation. The first type of
radiation, the second type of radiation, and the third type of
radiation may be different types of radiation.
[0007] The system also may include a track configured to support
the source, and enable the source to move along the track with
respect to the physical region. The source and the sensor system
may move concurrently with respect to the physical region. The
physical region may a region within a larger region, the source may
moves with respect to the larger region during the screening mode,
and the physical region may be determined to be a region of
interest. The source may be moved to the physical region during the
verification mode.
[0008] The system also may include a photo-neutron conversion
target configured to produce, in response to interaction with the
third type of radiation, a neutron of sufficient energy to cause
fission in a fissionable material. The photo-neutron conversion
target may be made of beryllium, deuterium, or lithium. The
conversion target may be between the source and the physical
region. The conversion target may be coupled to the source. The
source of radiation may include a first source of radiation and a
second source of radiation that is separate from the first source
of radiation. The first source of radiation may produce the first
type of radiation and the second type of radiation in the screening
mode, and the second source of radiation may produce the third type
of radiation in the verification mode.
[0009] The first type of radiation, the second type of radiation,
and the third type of radiation may be produced by a single source
of radiation that is configured to operate in multiple modes,
including the screening mode and the verification mode.
[0010] In another general aspect, the presence of fissionable
material may be detected. A first type of radiation may be
directed, from an imaging system in a screening mode, towards a
physical region. The first type of radiation has a first energy. A
second type of radiation may be directed, from the imaging system
in the screening mode, towards the physical region. The second type
of radiation has a second energy that is higher than the first
energy. An absorption characteristic of the physical region may be
determined based on an absorption of the first type of radiation
and the second type of radiation by the physical region. Whether
the physical region is a region of interest is determined from the
absorption characteristic. The imaging system switches from the
screening mode to a verification mode in response to determining
that the physical region is a region of interest. In the
verification mode, a third type of radiation is directed toward the
physical region. The third type of radiation is sufficient to
induce fission in a fissionable material. Whether a fissionable
material is present in the physical region is determined based on
an interaction between the third radiation and the physical
region.
[0011] Implementations may include one or more of the following
features. The first type of radiation may be x-ray radiation, the
second type of radiation may be x-ray radiation, and the third type
of radiation may be a photon or a neutron. Radiation from a fission
product emitted from the physical region may be detected after the
source of the third type of radiation is turned off. The absorption
characteristic may be an effective atomic number. The physical
region may be a region of interest. The imaging system may be moved
during the screening mode, and the imaging system may be moved to
the physical region at the beginning of the verification mode.
Fissionable material may be identified.
[0012] In another general aspect, an imaging system for
discriminating fissionable materials from other high-effective
atomic number materials includes a source configured to produce
dual-energy x-ray radiation sufficient to cause fission in
fissionable materials, and to direct the dual-energy x-ray
radiation sufficient to cause fission in fissionable materials
towards a physical region. The system also includes a sensor
configured to sense x-ray radiation and a product of fission from
the physical region, and a processor operable to determine an
absorption of the dual-energy x-ray radiation by the physical
region based on the sensed x-ray radiation, and to determine
whether the physical region includes fissionable material based on
the presence of a product of fission.
[0013] Implementations of any of the techniques described above may
include a method, a process, a system, a device, an apparatus, or
instructions stored on a computer-readable medium. The details of
one or more implementations are set forth in the accompanying
drawings and the description below. Other features will be apparent
from the description and drawings, and from the claims.
DESCRIPTION OF THE DRAWINGS
[0014] FIGS. 1A-1C, 2, 5, and 6 are plan views of example systems
for identifying fissionable materials.
[0015] FIG. 3 shows an example process for identifying fissionable
materials.
[0016] FIG. 4 is a block diagram of an example system for
identifying fissionable materials.
DETAILED DESCRIPTION
[0017] Techniques are described for discriminating fissionable
materials from materials that, because they have a relatively high
effective atomic number, are of interest but are not fissionable.
Many fissionable materials may be weaponizable (e.g., made into a
weapon) or pose other types of hazards not necessarily posed by
materials having a high effective atomic number. Using a
dual-energy x-ray imaging system, a portion of a physical region is
determined to be a region of interest if the portion is associated
with a high effective atomic number. The region of interest is
further examined to determine whether the region of interest
includes a fissionable material by exposing the region of interest
to a type of radiation that is sufficient to induce fission in a
fissionable material. The type of radiation is associated with a
particular type of particle (e.g., a neutron or a photon) and an
energy spectrum that has a maximum energy. The type of radiation
that the region of interest is exposed to may be, for example, a
neutron or a photon that has an energy sufficient to cause fission
in fissionable materials. In some examples, the type of radiation
that is sufficient to induce fission may be x-ray radiation that is
produced by the dual-energy x-ray imaging system.
[0018] The techniques discussed below may be used, for example, to
screen large cargos and/or cargo containers at a seaport, a boarder
checkpoint, a rail yard, and/or an airport or to screen smaller
cargos that are hand-portable by passengers at a rail station,
airport, seaport, and/or bus depot. Thus, the physical region may
be all or a portion of such a container or cargo.
[0019] In particular, a dual-energy detection system and delayed
gamma/neutron nuclear detection techniques are used to identify
fissionable material, including, for example, shielded nuclear
material. The absorption of x-ray radiation by a material may be
used to determine an effective atomic number of the material.
High-Z materials (e.g., materials that have a relatively high
effective atomic number) are typically materials of interest
because high-Z materials (such as lead) may be used to shield
hazardous nuclear material or the materials themselves (such as
uranium) may be weaponizable. Systems that determine regions of
interest based on effective atomic number may produce an alarm
and/or an representation of a location of a region of interest when
a material having an effective atomic number over a pre-determined
threshold is detected. However, in applications that look for
fissionable materials, alarms generated for materials that have a
high-Z but are not fissionable should be distinguished from alarms
generated for materials that are fissionable in order to more
accurately and quickly identify fissionable materials.
[0020] The techniques discussed below may be used to discriminate
between fissionable materials, some of which may be used to make
weapons or other hazardous products, and non-fissionable materials
that have a high effective atomic number.
[0021] FIGS. 1A-1C illustrate a plan view of an example system 100
for discriminating fissionable materials from non-fissionable
materials that have a relatively high effective atomic number. In
the example of FIG. 1A, the system 100 is operating in a screening
mode at a time "t1" and, in FIGS. 1B and 1C, the system 100 is
operating in a verification mode at times "t2" and "t3." As
discussed in more detail below, in the screening mode, the system
100 determines whether a physical region 105 includes a region of
interest by scanning the physical region 105, or a portion of the
physical region 105, with dual-energy x-ray radiation from a source
110 to determine whether the physical region 105, or the portion of
the physical region 105, includes a region that has a high
effective atomic number (e.g., a region having a Z of seventy-two
or greater).
[0022] In the verification mode, the system 100 scans one or more
regions of interest identified in the screening mode with a type of
radiation that causes fission in fissionable materials. For
example, the type of radiation may be a beam of neutral particles
sufficient to first cause fission and then the production of
delayed fission product radiation in a fissionable material. The
type of radiation may be the same as the energy used in the
scanning mode. The system 100 determines whether the regions of
interest include a fissionable material.
[0023] As discussed in greater detail with respect to FIG. 2, the
effective atomic number of materials in the physical region 105 may
be determined based on the absorption of the x-ray radiation by the
materials. A portion of the physical region 105 may be identified
as a region of interest if the portion is associated with a
relatively high effective atomic number (Z). For example, materials
having a high effective atomic number (e.g., materials having a "Z"
of 72 or above), such as lead and uranium, tend to be materials of
interest because such materials may be used for shielding of
hazardous materials or may themselves pose a threat.
[0024] However, a high effective atomic number does not
definitively indicate whether the material is a fissionable
material that may be used to make a weapon or otherwise pose a
significant threat. For example, both lead and uranium have high
effective atomic numbers (Z=82 and Z=92, respectively). However,
lead is not weaponizable, whereas some forms of uranium are
weaponizable. Thus, by performing a second scan of the identified
region of interest with radiation capable of inducing fission in
fissionable materials, the presence of fissionable material in the
region of interest may be determined. For example, after the region
of interest is identified in the screening mode, a type of
radiation sufficient to cause fission in fissionable materials may
be directed toward the region of interest. For example, the type of
radiation may be neutrons that are produced using a photo-neutron
conversion target. In this example, interactions between the
incident neutrons and materials in the region of interest causes
fission and the production of delayed fission products if
fissionable materials are present in the region of interest. In
another example, the type of radiation may be the same as that used
during the screening mode. In these examples, one of the two x-ray
beams generated by the dual-energy x-ray system may be switched to
a higher energy level (such as 10 MeV) and directed toward the
region of interest.
[0025] Fission is an exothermic reaction in which the nucleus of an
atom splits into smaller parts. Fission may release energy as both
electromagnetic radiation in the form of gamma rays and as kinetic
energy in the form of free neutrons that are released from the
fission reaction. Detection of delayed fission products (e.g.,
gamma rays and/or neutrons) from the region of interest indicates
the presence of a fissionable material. The delayed fission
products may be fission products that are emitted from the region
of interest after the incident neutral particles provided by the
source have been extinguished. Accordingly, fissionable materials
may be distinguished from among other materials in the physical
region that have a high effective atomic number. In some
implementations, the region of interest also may be exposed to
neutrons of different energies, a "slow" neutron that only induces
fission in weaponizable materials and a "fast" neutron that induces
fission in all, or almost all, fissionable materials. In these
implementations, the fissionable materials in the region of
interest may be further separated into weaponizable materials and
non-weaponizable materials. The weaponizable material may be a
special nuclear material (SNM).
[0026] In the example shown in FIGS. 1A-1C, the physical region
includes objects 106, 107, and 108. The object 106 is an innocuous
object that does not have a high effective atomic number and is not
fissionable. The object 106 may be, for example, a cardboard box
full of foam peanuts that protect a set of glassware. The object
107 is uranium and the object 108 is lead. Thus, the objects 107
and 108 have high effective atomic numbers, and the system 100
identifies a region 103 in the vicinity of the object 107 and a
region 104 in the vicinity of the object 108 as regions of interest
during the screening mode. However, during the verification mode,
only the uranium object 107 is identified as a fissionable
material.
[0027] The system 100 includes a source 110 and a sensor 120. The
source 110 is switchable between the screening mode and the
verification mode. During the screening mode, the source 110 emits
x-ray radiation at two different energies. The two different
energies used in the screening mode may be x-rays having an energy
spectrum with a maximum energy of between, for example, four
Mega-electron volts (MeV) and ten MeV. In other examples, and in
the verification mode, the source may produce radiation having an
energy spectrum with a maximum energy above 10 MeV and/or below 4
MeV. The x-ray radiation at the two different energies may be
referred to as a dual-energy x-ray 115. The source 110 may include
two x-ray sources, each of which produce radiation at a fixed
energy level, or the source 110 may include one x-ray source that
operates at one of a few selectable energies.
[0028] The sensor 120 is a sensor that is sensitive to x-ray
radiation (e.g., the sensor 120 produces an electrical or light
signal to indicate detection of x-ray radiation) and to products of
fission. In some implementations, the sensor 120 includes more than
one detector and/or sensor. The sensor 120 may be considered to be
a sensor system that includes detectors that are sensitive to x-ray
radiation and detectors that are sensitive to fission products.
[0029] In the screening mode, the source 110 directs the
dual-energy x-ray 115 toward to the physical region 105, the
dual-energy x-ray 115 passes through the physical region 105 while
being attenuated by materials within the physical region 105, and
exits the physical region 105 toward the sensor 120. If the
physical region 105 is partially or completely enclosed by a
container (not shown), the dual-energy x-ray 115 has sufficient
energy to penetrate the container and enter the space within the
container. The sensor 120 detects the attenuated dual-energy x-ray
radiation and creates two images of the physical region 105 based
on the attenuated dual-energy x-ray radiation. One of the images is
an image that represents the absorption of x-ray radiation at the
first energy level by the physical region 105, and the second image
represents the absorption of x-ray radiation at the second energy
level by the physical region 105. The absorption characteristics of
the physical region 105, such as the effective atomic number of the
region 105, may be determined from the sensed attenuated x-ray
radiation. The uranium object 107 and the lead object 108 are
identified as being or including materials of a high effective
atomic number and are respectively flagged as the regions of
interest 103 and 104.
[0030] Referring to FIG. 1A, the source 110 and the sensor 120 move
with respect to the physical region 105 in a direction "d," which
allows the entire physical region 105 to be imaged during the
screening mode. In other implementations, the source 110 and the
sensor 120 may be fixed and the physical region 105 may move with
respect to the source 110 and the sensor 120. A portion of the
physical region 105, rather than the entire physical region 105,
may be imaged in the screening mode.
[0031] The source 110 also emits radiation sufficient to cause
fission in fissionable materials, and the fission produces fission
products (e.g., free neutrons and/or gamma rays). In the screening
mode, the regions of interest 103 and 104, which respectively
include the object 107 and the object 108, were identified. Upon
receiving an indication that a region of interest is present, the
source 110 switches from the screening mode to the verification
mode and the source 110 moves to the a location corresponding to
the region of interest that was identified in the screening mode.
The source 110 and the sensor 120 may move concurrently and in
tandem together. In some implementations, the physical region 105
moves such that an identified region of interest is positioned in
front of the source 110.
[0032] Referring to FIG. 1B, in the verification mode, the source
110 emits radiation 125 toward the region of interest 103, which
includes the uranium object 107. The radiation 125 is a type of
radiation that is sufficient to cause fission in fissionable
materials. The type of radiation 125 is defined by a particle type
and an energy spectrum. For example, the radiation 125 may be a
beam of neutral particles (e.g., a beam of neutrons or photons)
that have an energy sufficient to cause fission in fissionable
materials. As discussed in more detail with respect to FIGS. 2 and
6, in examples in which the radiation is a beam of neutrons, the
radiation 125 may be created by switching the energy level of one
of the x-rays to a lower energy level and causing the emitted x-ray
to interact with a photo-neutron conversion target (not shown). The
photo-neutron conversion target emits neutrons in response to being
struck by photons having sufficient energy to eject a neutron from
a nucleus of the material that makes up the photo-conversion
target. The photo-neutron conversion target also may be referred to
as the conversion target. The photons that strike the conversion
target are produced by striking a bremsstrahlung target with a beam
of electrons. The generated photons then strike the conversion
target. Because the eventual conversion to neutrons involves the
used of both the tungsten target and the photo-neutron conversion
target, the conversion target also may be considered a secondary
target, and the bremsstrahlung target may be considered a primary
target. In some implementations, the energy from the source 110 may
be increased to ten MeV or greater to create the radiation 125
without the use of a conversion target.
[0033] At the time "t2," the radiation 125 travels into the
physical region 105 and strikes the object 107. Because uranium is
a fissionable material, fission begins and fission products 130, in
addition to neutrons that may be present in the radiation 125, are
released from the physical region 125 and sensed by the sensor 120.
The fission reaction causes prompt fission products and delayed
fission products. The delayed fission products may be daughter
neutrons that are released from the fission reaction with the
uranium object 107, and the delayed fission products may be present
even after the radiation 125 is extinguished (e.g., after the
source 110 is turned off or directed away from the physical region
105). For example, the delayed fission products may be present 10
milliseconds (ms) after the radiation 125 is extinguished. The
presence of the delayed fission products indicates that, in
addition to being a high-Z material, the object 107 is also a
fissionable material. In some implementations, the prompt fission
products also may be detected.
[0034] Referring to FIG. 1C, at a time "t3," the source 110 is
still operating in the verification mode, and the source 110 and
the detector 120 move to a location corresponding to the region of
interest 104. The region of interest 104 includes the lead object
108. The source 110 emits the radiation 125 toward the region of
interest 104. In contrast to the uranium object 107, the lead
object 108 is not a fissionable material, and, thus, fission
products are not created from the interaction between the radiation
125 and the lead object 108. Although, in examples where the
radiation 125 is a type of radiation having neutron particles, the
sensor 120 may detect the presence of neutrons while the radiation
125 illuminates the region of interest 104, no delayed fission
products are detected at the sensor 120. Accordingly, the lead
object 108 is not identified as a fissionable material.
[0035] Thus, the system 100 may be used to distinguish between
high-Z materials that are fissionable and those that are
non-fissionable.
[0036] In the example shown in FIGS. 1A-1C, the physical region 105
is scanned in the screening mode and regions of interest 103 and
104 are identified. The regions of interest 103 and 104 are scanned
again in the verification mode, which occurs after the scanning of
the physical region 105. However, in other examples, the
verification of each region of interest may occur immediately, or
soon after, the region of interest is identified. Thus, in some
implementations, the sensor 110 may switch from the screening mode
to the verification mode before the entire physical region 105 is
screened. Additionally, the sensor 110 may switch from the
verification mode back to the screening mode.
[0037] FIG. 2 illustrates a plan view of an example system 200 in
which two separate imaging systems 210 and 220 generate and detect
x-rays 270 and 275 that have two different energies. The two
different energies may be, for example two energies between 4 MeV
and 10 MeV. The example system 200 may be referred to as a dual
energy system and represents only an example configuration of a
dual energy system. The example system 200 also includes a
post-screener linac that may be used to expose regions of interest
identified by the dual-energy system to radiation sufficient to
cause fission in fissionable materials. In the example shown in
FIG. 2, the post-screener linac is part of the dual-energy system.
In particular, either or both the sources 212 and 224 includes a
source that has an adjustable energy level, and the source may be
set to emit an energy that is sufficient to cause fission in
fissionable materials. In some implementations, the post-screener
linac may be a separate from the imaging systems 210 and 220.
[0038] Referring to FIG. 2, the x-rays 270 and 275 interact with
objects 230A-230D after passing through a surface of a container
240 in which the objects 230-230D are located. X-ray radiation that
is not absorbed by the objects 230A-230D or the container 240 are
sensed by detectors 212 and 222. Detection of the x-ray radiation
that is not absorbed by the objects 230A-230D allows determination
of characteristics of the materials that make up the objects
230A-230D. For example, and as described below, a characteristic
related to the effective atomic number of the materials that make
up the objects 230A-230D may be determined based on the absorption
of x-ray radiation by the materials. The effective atomic number
may be used to determine whether the objects 230A-230D may include
contraband or hazardous items, such as nuclear material. For
example, items having a relatively high effective atomic number
(e.g., a Z of 72 or greater), may be an item of interest.
[0039] An alarm, alert, or other indicator may be provided in
response to a determination that the objects 230A-230D include a
high-Z material. The indicator includes a location corresponding to
the material such that the post-screener linac may be moved to the
region of interest (or the container 240 moved relative to the
dual-energy system) to scan the region of interest and determine
whether the region of interest includes fissionable materials.
[0040] In the example shown, the container 240 is a truck. However,
the container 240 may be any type of vessel. In some cases, the
container 240 is a large container used in the transportation
system, such as, for example, a shipping container, a rail car, or
an automobile. In other examples, the container 240 also may be a
smaller container, such as a suitcase, a package, a trunk or even a
smaller item.
[0041] The imaging systems 210 and 220 each include a source that
generates X-rays having a particular energy and a detector that
senses X-rays having that particular energy level. In particular,
the imaging system 210 includes a detector 212 and a source 214,
and the imaging system 220 includes a detector 222 and a source
224. The sources 214 and 224 may be, for example, Varian Linatron
M9 X-ray.RTM. sources available from Varian Medical Systems of Las
Vegas, Nev. The sources 214 and 224 may operate at either a fixed
energy level or at one of a few, selectable energy levels. In the
example shown in FIG. 2, the imaging systems 210 and 220 are
mounted on a gantry and the imaging systems 210 and 220 move
concurrently along rails 250 and 260. The imaging systems 210 and
220 scan the container with x-rays 270 and 275 as the imaging
systems 210 and 220 move along the rails 250 and 260 in a direction
280. In the example shown, the imaging systems 210 and 220 are
physically connected such that they move in tandem. However, in
some implementations the imaging systems 210 and 220 may move
independently of each other. In these implementations, the imaging
systems 210 and 220 may be configured to be connected to each other
and disconnected from each other as required. The detectors 212 and
222 sense radiation that is not absorbed by the objects 230A-230D
such that images of the objects 230A-230D may be created.
[0042] X-rays 270 generated by the source 214 pass through the
container 240 and interact with the objects 230A-230D. X-rays that
are not absorbed by the objects 230A-230D reach the detector 212.
Similarly, x-rays 275 generated by the source 224 that are not
absorbed by the objects 230A-230D reach the detector 222. In
general, the efficiency of a material in absorbing X-ray radiation
provides an indication of the effective atomic number ("Z") of the
material. Thus, the amount of X-ray radiation reaching the
detectors 212 and 222 provides an indication of how the materials
that make up the objects 230A-230D absorb radiation, which also
provides an indication of the effective atomic number of the
materials.
[0043] The rate at which materials absorb x-rays depends on the
energy and the material. Thus, by comparing the amount of
absorption by a material exposed to a lower-energy x-ray to the
amount of absorption by the material when the material is exposed
to a higher-energy x-ray, an indication of the effective atomic
number of the material may be determined. If one material is
present, the effective atomic number of the material may be
determined from the comparison. When more than one material is
present, various processing techniques may be applied to determine
the effective atomic number of a particular material. Also, when
more than one material is present, the average effective atomic
number of the materials present may be determined from the
comparison. At both lower energies and higher energies, high-Z
materials, such as lead, are more attenuating (e.g., absorb more
x-rays) than low-Z materials, such as concrete and organic goods.
At lower energies, the increased absorption is due to the Compton
effect. At higher energies, the increased absorption is due to
pair-production.
[0044] Thus, images of the low-Z material formed from the radiation
detected as a result of exposure of the low-Z material to the
higher-energy x-ray are distinguishable from images formed from the
radiation detected as a result of exposure of the low-Z material to
the lower-energy x-ray. In particular, the images of the low-Z
material formed from exposure to the higher-energy x-ray may appear
lighter as a result in a change in the amount of signal that passes
through the material (e.g., the images formed from exposure to the
higher-energy x-rays have a lower relative intensity as compared to
the images formed from exposure to the lower-energy x-rays).
[0045] The relative change in intensity of the signal is dependent
on material and the energies used. For example, low-Z and high-Z
materials both absorb the lower-energy x-ray; however, only high-Z
materials absorb the higher-energy x-ray. Thus, the images of the
low-Z materials and the high-Z materials formed from exposure to
the lower-energy x-ray are similar, but the images formed from
exposure to the higher-energy x-ray are not (the high-Z material
appears dark while the low-Z material appears lighter).
Accordingly, comparison of an image of an object formed from
interaction between a lower-energy x-ray and the object with an
image of the object formed from the interaction between a
higher-energy x-ray allows a determination of whether the material
that compose the object is a high-Z material. In this example, the
higher-energy x-ray may have a peak energy of 9 MeV, and the
lower-energy x-ray may have a peak energy of 6 MeV.
[0046] The system 200 may be used to perform such a comparison. For
example, the source 214 may generate a lower-energy x-ray that
interacts with the objects 230A-230D. The radiation from the source
214 that is not absorbed by the objects 230A-230D is sensed by the
detector 212. An image of the lower-energy x-ray interaction may be
formed based on the sensed radiation. Similarly, the source 224 may
generate a higher-energy x-ray that interacts with the objects
230A-230D. The radiation from the source 224 that is not absorbed
by the objects 230A-230D is sensed by the detector 222. An image of
the higher-energy x-ray interaction may be formed from the sensed
radiation. The image of the lower-energy x-ray interaction and the
image of the higher-energy x-ray interaction are aligned (or
registered with each other) such that the corresponding portions of
the objects 230A-230D in the images may be compared. More
particularly, these images are aligned to account for the
displacement of the imaging systems 210 and 220 along the direction
280 and are compared to determine if high-Z materials are present
in the image.
[0047] Because the imaging systems 210 and 220 are distinct imaging
systems, the detectors 212 and 222 may be individually optimized
for the sources 214 and 224, respectively. For example, use of the
separate imaging systems 210 and 220 allows the detector 222, which
is associated with the lower-energy source 224 in this example, to
be larger than the detector 212. Because the photons in the
lower-energy x-ray are less energetic than the photons in the
higher-energy x-ray, the lower-energy beam is less penetrating.
Thus, having the detector 222 be larger than the detector 212 may
increase the number of lower-energy photons that are detected by
the detector 222. Increasing the number of lower-energy photons may
improve the image formed from the interaction with the lower-energy
x-ray, which also may improve the comparison of the lower-energy
image and the higher-energy image.
[0048] Moreover, the use of the imaging systems 210 and 220 also
may allow the sources 214 and 224 to be individually optimized to
generate x-rays having a particular peak energy. The peak energy
may be considered the maximum energy. For example, the sources 214
and 224 may be separately filtered to more precisely achieve
generation of a particular energy, or band of energies, or to
remove certain energies from the generated x-ray radiation. Such
filtering may improve the quality of both the lower-energy image
and the higher-energy image, which may improve the results of the
comparison. Additionally, because the imaging systems 210 and 220
each have a source that generates x-rays, the overall number of
photons available to interact with the objects 230A-230D is
increased as compared to a system that has one x-ray source. Thus,
using the sources 212 and 222 may improve the images generated by
the imaging systems 210 and 220 by increasing the signal received
by the detectors 212 and 222.
[0049] Thus, the dual-energy system discussed above, which may be
referred to as a pre-screening linac is used to identify regions of
high-Z materials, and these regions may be referred to as regions
of interest. In some implementations, a dual energy system at the
MeV level (such as the dual-energy system discussed above) and a
post-screener linac may be used to determined whether the regions
of high Z material(s), which may be referred to as region(s) of
interest, also include fissionable materials.
[0050] Once a region of interest is identified, the energy of the
pre-screener linac is changed to 10 MeV, the linac is moved to the
region of interest, the region of interest is exposed to the 10 MeV
beam, and specific material in the region of interest (or object or
cargo) is identified by counting gammas and neutrons some time
after the post-screener linac pulse has ended. Presence of a
delayed neutron/gamma signal indicates a material of interest,
which may be, for example, a nuclear material. Stated differently,
shielded nuclear material detection may be based on detected
delayed neutron/gamma signals from the region of interest (or
object or cargo) that is consistent with photon or neutron induced
fission. For example, photon detection for above 3 MeV and below 1
MeV neutrons may be made with high specificity. These techniques
may help detect special nuclear material at the Z and isotopic
level.
[0051] In one example implementation, the dual energy system 200 of
FIG. 2 with additional neutron/photon detectors and electronics may
be used. In other implementations, the dual-energy system may use
one of the sources 214 or 224 to generate high-energy photons from,
for example, a pulsed laser integrated with one the sources 214 or
224. In other implementations, the energy of one of the sources 214
or 224 may be changed and the radiation produces by the source may
interact with a photo-neutron conversion target such as deuterium,
beryllium, or lithium. The photo-neutron conversion target creates
neutrons from photo-neutron production. In particular, an electron
beam strikes a tungsten target to produce photons. The photons
interact with the conversion target and, if the photons have
sufficient energy, the interactions between the photons and the
conversion target produces neutrons by ejecting a neutron from the
nucleus of an atom of the material from which the target is
made.
[0052] In some implementations, the type of radiation sufficient to
cause fission may be considered a neutron or photon probes, and the
probe may be based on the background Z determined. Neutron or
photon probes may work best in different backgrounds. In some
implementations, the predetermination of a region of high Z
material may reduce the dose of neutron or photon probe needed.
Some implementations may uniquely identify 100 cm.sup.3 of highly
enriched uranium (HEU) and weapons-grade plutonium (WGPu), with or
without shielding. In another example, some implementations may
distinguish uranium-235 (U.sup.235) from uranium-238 (U.sup.238),
which may require measurement beyond Z or fission. Some
implementations may be configured to detect an enhanced fission
rate or to detect relatively low energy neutron fission (e.g.,
fission that occurs as a result of radiation by a 1 MeV neutron).
In these implementations, a "fast" neutron (e.g., a neutron having
an energy greater than about 1.5 MeV) and a "slow" neutron (e.g., a
neutron having an energy less than 1.5 MeV) are both directed
toward the region of interest. The "slow" neutron causes fission in
weaponizable materials (which may be special nuclear materials) but
not in other fissionable materials. Thus, use of both the "slow"
and "fast" neutrons may allow special nuclear materials to be
distinguished from other fissionable materials. As discussed in
more detail below with respect to FIG. 6, in implementations that
use two separate sources (such as the sources 214 and 224), the
radiation from the two sources may be used to interact with two
separate targets made from different materials to produce neutrons
of different energies (e.g., a "slow" neutron and a "fast"
neutron).
[0053] FIG. 3 presents an example process 300 that may be
implemented by a dual energy detection system that uses delayed
gamma/neutron nuclear detection techniques. The process 300 may be
performed using a system such as the system 100 or the system 200
discussed above with respect to FIGS. 1A-1C and 2.
[0054] A physical region (such as the physical region 105 or the
truck 240) is scanned with a dual-energy source (310). The physical
region may be scanned with x-ray radiation of two different energy
levels during a screening mode. For example, the physical region
may be scanned with two sources (such as the sources 214 and 224
discussed above with respect to FIG. 2) that are mounted on a
gantry and that move concurrently with each other and with respect
to the physical region such that the physical region is irradiated
with radiation from the first source and then with radiation from
the second source. In some implementations, the physical region
moves with respect to the sources. The x-rays of both energy levels
travel through the physical region and are attenuated. The
attenuated x-rays are sensed with sensors (such as the sensors 212
and 222), and the sensed radiation is used to produce images of the
absorption of the lower energy x-ray radiation and the higher
energy x-ray radiation by the physical region. The images are
compared as discussed above to determine an estimation of the
effective atomic number of various portions of the physical
region.
[0055] Based on the estimated effective atomic number, it is
determined whether a high-Z material is present in the physical
region (320). A portion of the physical region having an estimated
effective atomic number of seventy-two or more may be determined to
include a high-Z material. Materials having a relatively high
effective atomic number may be of interest because such materials
may be used as shields for nuclear materials or such materials may
be nuclear materials. To determine whether a high-Z material is
present in the physical region, the estimated Z may be compared to
a pre-determined threshold value. The pre-determined threshold
value may be stored in an electronic storage, and the
pre-determined threshold value may be adjustable by an operator of
the system.
[0056] If high-Z regions are present, the regions of high-Z are
considered to be regions of interest, and the location of the
high-Z regions of interest is determined based on the images
produced by the detectors. If the physical region does not include
any portions that have a high-Z, an "all-clear" indicator is
presented (325). The "all-clear" indicator may be, for example, an
alarm, message, or signal that indicates that the physical region
does not include a high-Z material. Once the "all-clear" indicator
is produced, the another physical region may be screened.
[0057] If high-Z portions are present, the source (such as the
source 110 or one or more of the sources 214 and 224) are moved, in
a verification mode, to a location that corresponds to a location
of a region of interest (330). In some implementations, the
physical region is moved with respect to the source such that the
region of interest is positioned to receive radiation from the
source. In some implementations, a source that is separate from the
source that produces the dual-energy x-rays is moved to the
location corresponding to the region of interest.
[0058] The region of interest is scanned using a technique that is
based on characteristics of the background of the physical region
(340). The region of interest is exposed to neutral particles
(e.g., photons or neutrons) of sufficient energy to cause fission
in fissionable materials. Scanning the region of interest with
neutral particles and then detecting for the presence of delayed
fission products allows high-Z materials that are also fissionable
materials to be separated from high-Z materials that are not
fissionable. The characteristics of the background may indicate the
type of photon or neutron probes to use to probe the region of
interest for the presence of fissionable materials. For example, if
the region of interest has a relatively high effective atomic
number, a lower-dose (e.g., lower energy) photon or neutron
radiation may be used to cause fission as compared to the photon or
neutron radiation energy needed to cause fission in a material
having a lower effective atomic number.
[0059] In some implementations, the neutral particles used to probe
the region of interest for fissionable materials is produced by
switching the source from the higher-energy level used in the
dual-energy scan to a mode in which the source produces a 10 MeV
beam of radiation (e.g., a beam of radiation having an energy
spectrum with a maximum energy of 10 MeV), and the 10 MeV beam of
radiation is directed toward the region of interest. In some
implementations, the source includes two separate sources of x-ray
radiation (such as the sources 214 and 224), and each of the
sources is switched to a different energy level (e.g., switched to
produce energy having a different energy spectrum and a different
maximum energy). For example, in the screening mode, the source 214
may produce x-ray radiation of 6 MeV and the source 224 may produce
radiation of 9 MeV. In the verification mode, the source 214 may be
switched to produce 4 MeV radiation, and the source 224 may be
switched to produce 9 MeV radiation. The radiation from the source
214 may be directed toward a conversion target that produces
neutrons in response to being struck by photons having energy
sufficient to eject a neutron from a nucleus of an atom of the
material from which the conversion target is made. Thus, in this
example, the neutral particles used to probe the region of interest
for the presence of fissionable materials are the neutrons produced
by the interaction between the 4 MeV radiation and the conversion
target. The conversion target may be, for example, beryllium,
lithium, or deuterium.
[0060] The presence of delayed fission products is determined
(350). The presence of delayed fission products (e.g., gamma rays
or neutrons emitted from the region of interest after the probe
that exposes the region of interest to neutral particles is
removed) indicates that the region of interest includes a
fissionable material. The delayed fission products may be, for
example, daughter neutrons that are produced as the nuclei of
fissionable materials in the region of interest split apart. These
daughter neutrons are detected (at a detector such as the sensor
120) at a time after the incident neutral particles are removed and
the daughter neutrons indicate the presence of a fissionable
material. If no delayed fission products are detected, the
"all-clear" indicator is presented (325). If delayed fission
products are detector, fissionable material is present (360) and an
alarm is produced (370). The alarm may be, for example, a sound, a
message displayed to an operator of the system, a visual but
non-audio warning, or an automated alert (such as an e-mail or text
message sent to an operator of the system or to an automated
process).
[0061] FIG. 4 shows a block diagram of a system 400 used to
identify fissionable materials. The system 400 includes a source
system 410 and sensor system 450. Together, the source system 410
and the sensor system 450 determine whether a physical region 405
includes materials having a high effective atomic number and
determine whether any such materials are fissionable materials. The
source system 410 includes a dual-energy x-ray source 415 that
produces a lower-energy x-ray (e.g., an x-ray of 6 MeV) and a
higher-energy x-ray (e.g., an x-ray of 9 MeV) in order to determine
an effective atomic number of a physical region 405. The source
system 410 may include a photo-neutron conversion target 420 made
of a material that produces neutrons in response to being struck
with photons. The photo-neutron conversion target 420 may be made
from beryllium, lithium, or deuterium.
[0062] The source system 410 also may include a switch 425 that
switches the source system 410 from a screening mode in which the
source system 410 produces dual-energy x-ray radiation to a
verification mode in which the source system 410 produces a type of
radiation that is sufficient to cause fission in fissionable
materials. The type of radiation may be the same type of radiation
as radiation produced by the dual-energy x-ray system. The switch
425 may be activated upon receipt of a location, or other
indication, of a region of interest identified in the screening
mode. The verification mode is used to determine whether the region
of interest includes fissionable materials.
[0063] The source system 410 also includes a processor 430, an
electronic storage 435, source electronics 440, and an input/output
module 445. The electronic storage 435 stores instructions, that
when executed, cause the switch 425 to transition the source system
410 from the screening mode to the verification mode in response to
receiving an indication of the presence of one or more regions of
interest from the sensor system 450, from the electronic storage
435, or from an operator of the system 400. The processor also may
cause the source system 410 to switch from the verification mode to
the screening mode.
[0064] The electronic storage 435 is an electronic memory module,
and the electronic storage 435 may be a non-volatile or persistent
memory. The processor 430 may be a processor suitable for the
execution of a computer program such as a general or special
purpose microprocessor, and any one or more processors of any kind
of digital computer. Generally, a processor receives instructions
and data from a read-only memory or a random access memory or both.
The processor 430 receives instruction and data from the components
of the source system 410 and/or the sensor system 450, such as, for
example, a location and/or other indication of the presence of a
region of interest that causes the source system 410 to switch from
the screening mode to the verification mode. In some
implementations, the source system 410 includes more than one
processor.
[0065] The input/output module 445 may be any device able to
transmit data to, and receive data from, the source system 410. For
example, the input/output device 445 may be a mouse, a touch
screen, a stylus, a keyboard, or any other device that enables a
user to interact with the source system 410. In some
implementations, the input/output device 445 may be configured to
receive an input from an automated process or a machine and/or
configured to provide an output to an automated process or a
machine.
[0066] The system 400 also includes the sensor system 450. The
sensor system 450 senses attenuated dual-energy x-ray radiation and
fission products that emanates from the physical region 405 due to
the irradiation of the physical region 405 by the source system
410.
[0067] The sensor system 450 includes a dual-energy sensor 455, a
fission product sensor 460, an absorption analyzer 465, a materials
identifier 470, a processor 475, an electronic storage 480, and an
input/output module 485. The dual-energy sensor 455 includes a
sensor that is sensitive to the energy spectra present in the x-ray
radiation produced by the dual-energy source 415. The dual-energy
sensor 455 may be a scintillator that senses x-ray radiation
emitted from the physical region 405 and produces a visible light
signal in response. The intensity of the visible light signal is
proportional to the intensity of the sensed x-ray radiation. The
dual-energy sensor 455 also includes a photodetector, or other
detector that is sensitive to visible light, that senses the
visible light signal from the scintillator and produces an
electrical signal in response. The current of the electrical signal
is proportional to the intensity of the detected visible light,
thus, the value of the electrical signal provides an indication of
the intensity of the detected x-ray radiation. The electrical
signal may be digitized by an analog-to-digital converter, and the
digitized signal may be used to generate an image of the physical
region 405 that represents the attenuation of the x-ray radiation
by the physical region 405. Two such images may be generated, one
representing the attenuation of the lower-energy x-ray from the
dual-energy source 415 and the other representing the attenuation
of the higher-energy x-ray from the dual-energy source 415. These
images may be used to determine the effective atomic number of
various portions of the physical region 405.
[0068] The sensor system 460 also includes a fission product sensor
460 that is sensitive to fission products emitted from the physical
region 405 in response to being irradiated with neutral particles
from the neutral particle source 420. The fission product sensor
460 may be an array of scintillators that detect freed neutrons
and/or gamma rays. For example, the fission product sensor 460 may
be liquid or plastic scintillators and/or germanium (Ge) or
high-performance germanium (HPGe) detectors.
[0069] The sensor system 450 also includes the absorption analyzer
465 that determines absorption characteristics of the region of
interest based on the radiation sensed by the dual-energy sensor
455. The absorption analyzer 465 determines the effective atomic
number of various portions of the physical region 405, compares the
effective atomic number to a pre-set threshold value to determine
whether any of the various portions are regions of interest, and
identifies locations corresponding to any regions of interest. The
materials identifier 470 determines whether a fissionable material
is present based on data from the fission product sensor 460.
[0070] The sensor system 450 also includes a processor 475, an
electronic storage 480, and an input/output module 485. The
electronic storage 480 stores instructions, that when executed,
cause the processor 475 to determine absorption characteristics
(such as effective atomic number) of the physical region 405 that
is scanned by the dual-energy x-rays produced by the dual-energy
source 415 and imaged by detecting attenuated x-ray radiation at
the sensor system 450. The electronic storage 480 may store a
pre-determined threshold value for an effective atomic number above
which a region is considered a region of interest. The electronic
storage 435 also includes instructions that, when executed, cause
the processor 475 and the materials identifier 470 to determine
whether fissionable materials are present in the physical region
405. The electronic storage 435 also includes instructions, that
when executed, cause the processor 475 to determine a location
corresponding to an identified region of interest and to provide
the location to the source system 410.
[0071] The electronic storage 480 is an electronic memory module,
and the electronic storage 480 may be a non-volatile or persistent
memory. The processor 475 may be a processor suitable for the
execution of a computer program such as a general or special
purpose microprocessor, and any one or more processors of any kind
of digital computer. Generally, a processor receives instructions
and data from a read-only memory or a random access memory or both.
In some implementations, the sensor system 450 includes more than
one processor.
[0072] The input/output module 485 may be any device able to
transmit data to, and receive data from, the sensor system 450. For
example, the input/output module 485 may be a mouse, a touch
screen, a stylus, a keyboard, or any other device that enables a
user to interact with the sensor system 450. In some
implementations, the input/output module 485 may be configured to
receive an input from an automated process or a machine and/or
configured to provide an output to an automated process or a
machine.
[0073] Referring to FIG. 5, a plan view of another example system
500 for discriminating fissionable materials from non-fissionable
materials that have a relatively high effective atomic number. Like
the system 100 discussed above with respect to FIGS. 1A-1C, the
system 500 may operate in a screening mode and a verification mode.
In the screening mode, the source 110 emits dual-energy x-ray
radiation, and in the verification mode, the source 110 emits
neutral particles having energy sufficient to cause fission in
fissionable materials.
[0074] The system 500 includes a sensor system 510 having multiple
detectors 511, 512, 513, and 514 that are placed along the physical
region 105 to capture and sense the fission product 130 emitted
from the region of interest 103 during the verification mode.
Because fission products may be emitted equally in all directions
(e.g., fission products are isotropically radiated), the sensor
system 510 may be able to collect more fission products and produce
a higher signal-to-noise ratio, thus improving the accuracy of the
system 500 in detecting fissionable materials.
[0075] A plan view of the system is shown in FIG. 5, which
illustrates that the detectors 511, 512, 513, and 514 are placed
equidistant from the physical region 105, the sensor system 510
also may include additional detectors (not shown) that are
vertically above or below the detectors 511, 512, 513, and 514 and
are equidistant from the physical region 105. Additionally, the
sensor system 510 may include more or fewer detectors. In some
implementations, the detectors included in the sensor system 510
may be arranged such that they are not equally spaced with respect
to each other and/or the detectors included in the sensor system
510 may not be equidistant to the physical region 105.
[0076] Referring to FIG. 6, a plan view of another example system
600 for discriminating fissionable materials from non-fissionable
materials that have a relatively high effective atomic number. The
system 600 also may be used to determine whether a fissionable
material is also a weaponizable material.
[0077] Like the system 100 discussed above with respect to FIGS.
1A-1C, the system 600 may operate in a screening mode and a
verification mode. In the screening mode, the source 610 emits
dual-energy x-ray radiation, and in the verification mode, the
source 610 emits neutral particles having energy sufficient to
cause fission in fissionable materials. The source 610 includes
sources 615 and 620, each of which produce x-ray radiation. The
source 615 produces lower-energy x-ray radiation, and the source
620 produces higher-energy x-ray radiation. For example, in the
screening mode, the source 615 may produce x-ray radiation having
an energy of 6 MeV, and in the verification mode, the source 615
may produce x-ray radiation having an energy of 4 MeV. In the
screening mode, the source 620 may produce x-ray radiation having
an energy of 9 MeV, and in the verification mode, the source 620
may produce x-ray radiation having an energy of 10 MeV.
[0078] In the verification mode, the radiation emitted from the
sources 615 and 620 interacts with photo-neutron conversion targets
625 and 630, respectively. The conversion targets 625 may be made
of different materials. For example, the conversion target 625 may
be made of beryllium and the conversion target 630 may be made of
deuterium. The interactions between the radiation from the sources
615 and 620 and the conversion targets 625 and 630 result in the
production of neutrons 635 and 640. The neutron 635 may be a "slow"
neutron having an energy of less than 1 MeV, and the neutron 640
may be a "fast" neutron having an energy greater than 2 MeV. The
"slow" neutron 635 causes fission only in certain fissionable
materials, such as special nuclear materials and other weaponizable
materials. In contrast, the "fast" neutron 640 may cause fission in
almost all fissionable materials. Thus, by irradiating the region
of interest 103 (which was identified as including a fissionable
material) with both the "fast" neutron 640 and the "slow" neutron
635, the region of interest 103 may be examined to determine
whether the region of interest 103 includes weaponizable materials.
As shown in the example, the region of interest 103 emits fission
product 650 in response to being irradiated with the "slow" neutron
635. Thus, the region of interest includes a special nuclear
material or another type of weaponizable material.
[0079] In some implementations, the techniques discussed above may
provide advantages including, for example, increased throughput of
cargo and automatic detection of nuclear material. For example,
because a dual-energy x-ray system is used to first identify
regions of interest based on effective atomic number, only portions
of the physical region under examination are further probed with
neutral particles to determine the presence of fissionable
materials.
[0080] A number of implementations have been described.
Nonetheless, it is understood that other implementations are within
the scope of the claims.
* * * * *