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Copyright 2004 Questions or Comments: webmaster@williamson-labs.com. |
WMD Hunting Technology-
Example: Utilizing Very Large
MultiSensor Arrays in Mobile
Detection Systems while Hitchhiking
on Tractor Trailers Rigs
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- Cutting Edge --
| The Technology of Nuclear Radiation Detection
has come a long way; from the humble Geiger Counter to the, Scintillation
Counter, to the powerful Compton Camera, and beyond. That distance is an
amazing History of innovation and of cross discipline cooperation. Astronomers
looking for a way to better "See" X-Ray, Gamma Ray sources in the Universe
have lead the way in Passave Detection. |
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-Survey of
Nuclear Detectors
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-Compton
Camera-
The Technology used by Astronomers to seek out Gamma Ray sources
in the Cosmos; holds great promise in finding Clandestine Nuclear Sources.
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Factors influencing Detection
of Nuclear Materials
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| Detecting clandestine nuclear materials is sometimes not unlike prospecting
for Uranium deposits in the western desert. In both cases there are several
factors which greatly influence detection:
1)_ Intensity of the radioactive source.
2)_ The Distance between the source and detector reduces radiation
intensity--in air--according to the Inverse Square Law, i.e., the
amount of radiation at a given distance from the source is inversely proportional
to the square of that distance, e.g., if the exposure rate at 1 meter equals
100 mR/hr then the exposure rate at 2 meters will be 25 mR/hr. see fig
3)_ Shielding of radiation due to the Mass of intervening objects.
The amount and type of shielding material, e.g., to attenuate the radiation
by half requires: Lead = 0.49", Steel = 0.87", Concrete = 5.0".
4)_ Background radiation (background count) is caused by cosmic
rays, naturally occurring radiation from the soil, radon, plants, nuclear
fallout, etc. Background radiation can easily obscure target materials;
it is a matter of Signal to Noise Ratio (SNR).
5)_ Detector types, and their dimensions. Like a lens gathering
light, the larger the detector surface area, the "Faster" the exposure.
6)_ Exposure Time, the longer the detector is exposed to the
radiation source, the more events (counts) are registered, the better the
sensitivity to weak sources, and the greater the spectral accuracy. If
there is relative movement between the two, the measurement accuracy will
degrade.
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.Features
that can Improve Detection
1)_ Selectivity
2)_ Directivity 3)_ Radiography
1)_ Selectivity
(DSP)
Spectral Separation and Identification of radiation sources.
A verity of Detectors respond uniquely to radiation from specific isotopes.
Selecting out the undesired components can improve SNR greatly. Spectral
Separation and Identification of radiation sources. A verity
of Detectors respond uniquely to radiation from specific isotopes. Selecting
out the undesired components can improve SNR greatly. This uniqueness is
manifested by different pulse heights according to the energy (expressed
in Electron Volts, eV) of the event. In addition some detectors also respond
with varing decay times for different isotopes.
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Pulse Height
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Pulse Fall Time
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Isotope Spectra derived from Pulse Height Count Histogram
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Example of Nuclide Spectrum Analyzer Computer Display
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2)_ Directivity
(Imaging)
Directivity (spatial coherence) is not an inherent trait of most detectors.
Normally, to achieve Directivity shielding is usually employed. Unlike
non-ionizing radiation, ionizing radiation—X rays, Gamma Rays, Cosmic Rays,
etc.—are not easily reflected or focused by conventional means; however,
they can be using "grazing."
a. Shielding If the detector is surrounded by mass—lead,
steel, concrete, dirt, etc.—the amount of radiation reaching the detector
is reduced depending on that mass, e.g., reduction to half power would
require: Lead = 0.49", Steel = 0.87", Concrete = 5.0". If an opening is
left in the shielding, radiation entering that opening will be unattenuated—hence
Directivity.
1. Collimation
Oftentimes it is desirable to see the radiation source in 2 dimensions,
X, Y.
By arraying multiple individual detectors, each possessing some degree
of Directivity, one can have a ‘pixelated’ image of the incident radiation
source.
Scintillation Counters in an Array
b. Analysis of Scattering The mechanism behind radiation
detection is the interaction between the incident radiation (photons) and
the atoms of the detection medium, e.g., in the case of the Geiger counter,
Argon gas, or Nal (TI) crystal in the Scintillation counter.
When struck by the radiation photon, the atom first absorbs that energy
and then releases it in the form of new photons or particles. This scattering
can fall into one or all of three categories: Photoelectric Effect, Compton
Effect, or Pair Production.
In the case of Compton Scattering (Compton Effect), there is
a release of a free electron from the struck atom, and the original photon
(sans some energy); both diverge at angles from the original path of the
incident photon (before the collision).
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| Therefore: by detecting the paths of these scattered particles,
and tracing backwards the direction of the origin of the radiation can
be deduced. see below |
Plotting Backwards to the Source
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3)_
Radiography
There are three basic ways to detect fissile material:
"Passive"
detection of the radiation emitted by its radioactive
decay.
"Active" detection
involves two modalities:
Radiography
"X-raying" an object using Gamma Rays to detect dense and absorptive
materials typical of Fission weapons.
Transmission is the
classic medical X-Ray
Backscatter is a
new approach that yields significantly improved resolution by focusing
a narrow beam and detecting the intensities of the reflected or backscattered
radiation. |
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Radiography
using Transmission or Backscatter or Both
X-ray Technologies
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Backscatter and Transmission X-Ray
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Missile in container as seen by Radiography only
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Neutron Activation Analysis (NAA)
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Neutron Inducing Fission: releasing Gamma Ray Photon and Beta
Particle. |
Induced Fission (Neutron
Activation Analysis)
Bombarding an object with high-energy Neutrons and detecting the particles
emitted by the resulting Induced Fission.
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Nuclear warhead using Radiography and NAA
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Notes: [2] Focusing of Gamma Rays,
etc., is possible using "Grazing." more
info |
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Inverse Square Law-
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of the Inverse Square Law, which states that the amount of radiation at
a given distance from a source is inversely proportional to the square
of that distance. |
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-HPGe
Radiation Detector/Spectrometer-
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HPGe Radiation Detector/Spectrometer
(High-Purity Germanium)
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Mechanical Cryogenic Cooler
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HPGe detector cooled mechanical cooler
20x Resolution Improvement over NaI(T1)
www.ortec-online.com/pdf/detex.pdf-
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Neutron Detection
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BF-3, He-3 Gas Neutron Detectors
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-Very
Large Nuclear Detector Arrays-
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Large Airborne Detector Array
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Road Side Detector Array
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.Large
Area Scintillation Counter
Large Area (~ 22" X 26" X 1.5") Plastic (Organic) Scintillator surrounded
by Photomultiplier tubes
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| Radiation Detection has come long way. There
are new detection technologies, as well as improvements in old technology.
Todays detectors not only detect radiation but can identify the different
types and amounts of radioactive sources. They can also seperate background
radiation, such as cosmic rays, from radiation sources of interest. |
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- Basics --
| Ionizing Radiation Detection is dependent on
collisions of Incident Radiation with molecules or atoms of the detector
medium. These collisions cause conversion of Incident Radiation (Photon
particles) to Free Electrons (in the case of the Geiger Counter) and Light
Photons (in the case of the Scintillation Counter). |
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-Geiger
Counter-
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Geiger Counter-
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Geiger Mueller Tube-
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| Incident radiation collides with molecules of Argon gas
within GM tube releasing Free Electrons which causes Electron Avalanche,
thus generating pulses to be counted. . |
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-Scintillation
Counter-
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Scintillation Counter Operation-
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| Incident radiation collides with molecules of the Scintillator
Material releasing Light Photons which are picked up by the system's Photomultiplier
Tube, thus generating pulses of varing Heights and Shape that are counted
and analyzed for Spectrial information on
the Radiation Source. |
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-Experimental-
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Induced Fission Detection
by Naturally Occurring Cosmic Ray Products
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-Active
Interrogation using Muon induced Fission
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Cosmic Ray Conversions-
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| Cosmic rays are mostly protons from outer space
that have kinetic energies as high as that of an apple falling a few meters
in Earth's gravitational field. When a cosmic-ray proton strikes an air
molecule—typically at an altitude of about 15 kilometers—the result is
a shower of energetic particles and radiation. Because the muons produced
move at close to the speed of light, their short lifetimes (2.1 microseconds)
are extended by the time dilation effect of special relativity, which allows
most of them to reach Earth's surface without decaying. |
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Keywords:
CBR, Nuclear, Uranium, Plutonium, Compton Effect, Compton
Imager, WMD, Clandestine Weapon, Gamma Camera, Scintillation Counter, Geiger
Counter, Radiological Survey, HPGe, Scintillator, Nal (TI), Pulse Height
Spectrum, Isotope, Nuclide, Alpha, Beta, Gamma Ray, Neutron, Photon, Electron,
Proton, positron, MeV, Inverse Square Law, Fleet Vehicles, Trucking &
Courier Services, Motor Carrier, Tractor Trailer, Semi Trailer, Trailer
Truck, Freight Motor Carrier, Rail, Container Car, Container, highway surveilance,
homeland security, neutron detector, nuclear materials |
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© Copyright 2004 Questions
or Comments:webmaster@williamson-labs.com.
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| In the absence of
shielding, "ordinary" nuclear weapons-those containing kilogram quantities
of ordinary weapon-grade (6 percent plutonium-240) plutonium or uranium-
238-can be detected by neutron or gamma counters at a distance of tens
of meters. Objects such as missile canisters can be radiographed with high-energy
x-rays to reveal the presence of the dense fissile core of any type of
nuclear warhead, or the radiation shielding that might conceal a warhead.
If subjected to neutron irradiation, the fissile core of any type of unshielded
warhead can also be detected by the emission of prompt or delayed-fission
neutrons at a distance on the order of 10 meters.
* RTD®
technology can detect both neutrons (nuclear WMD) and gamma rays (dirty
bombs) during routine X-ray inspections, allowing additional functionality
without impacting throughput or the flow of commerce. Competitive systems
cannot provide simultaneous inspection.
* RTD alerts
operators to the presence and approximate location of a radioactive threat
through a visual pop-up display and the sounding of an audible alarm.
* AS&E systems
employ multiple technologies simultaneously for the best detection results.
Z Backscatter images reveal the explosives that would accompany a dirty
bomb, while Transmission X-rays would expose dense shielding surrounding
a nuclear threat.
For added security, AS&E's Radioactive
Threat Detection (RTD) technology is an option on selected AS&E detection
systems. RTD technology is capable of detecting both neutrons (characteristic
of fissionable materials) and gamma rays (characteristic of dirty bombs)
during the X-ray inspection process. Gradient color bars, displayed with
the scanned images, show the approximate location of the radioactive object,
and on-screen and audible alerts signal the operator that radiation has
been detected.
Radiography
The examination of the structure
of materials by nondestructive methods, utilizing sealed sources of byproduct
materials. Radiations can be used to produce images of an object either
by measuring their transmission through or their interaction with the object.
Medical x-rays and x-ray baggage inspection are examples of transmission
measurements. A neutron baggage inspection system images an object by measuring
the spatial distribution of capture gamma rays produced by the reaction
of neutrons with nitrogen in the object. Autoradiography describes the
process of imaging an object using radiations produced by the radioactive
decay of nuclides in the object. The radionuclides can be the result of
radionuclide tagging, contamination by some source, or they can be produced
by irradiating the object with neutrons or other radiations. |
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