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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
had come a long way; from the humble Geiger Counter to the, Scintillation
Counter, to the powerful Compton Camera. 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. |
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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 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 function,
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 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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| Attributes that can Improve Detection
1)_ Selectivity
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 ftom Pulse Height Count Histogram
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2)_ Directivity (Imaging)
Directivity 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 amenable to being reflected or focused[2];
it can, however, be attenuated.
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—in the case of the Geiger counter, Argon
gas, or the Nal (TI) crystal in the Scintillation counter.
When struck by the radiation photon, the atom first absorbs that energy
and then releases it 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 Effect (Compton Scattering), there is a release
of an 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,
one can deduce the direction of the origin of the radiation. |
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Notes: [2] Focusing of Gamma Rays, etc., is possable
using "Grazing." more info |
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Inverse Square Law-
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| The radiation field decreases with distance from the source as a function
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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Nuclide Spectrum
Derived from Pulse Height and/or Pulse Shape Discrimination
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Example of Nuclide Spectrum Analyzer Computer Display
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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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-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.
Bismuth Germanate Oxide (BGO) crystals |
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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 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 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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Introduction
The Detection of Radioactive materials present many challenges.
One of America's first lines of defense against nuclear terrorism is
the Nuclear Emergency Search Team (NEST). NEST consist of a force of 1,000
civilians, most of whom come from the nuclear-weapons industry. Aware of
what such weapons can do, they have been selected to find and deactivate
nuclear bombs and materials in the hands of terrorists.
These weapons could be anywhere; from a shipping container to someone's
basement. For a discussion of various Terror
Scenarios----
Proposed: A method for discovering Clandestine Weapons
of Mass Destruction (CWMD) by hitchhiking sensors on existing Fleet Vehicles.
This system would utilize long haul Semi-Trailers, Container Rail cars,
and/or any ubiquitous, high mileage fleet vehicles such as commercial taxicabs,
police cars, mail trucks, etc.
Such vehicles would be equipped with an array of sensors for the detection
of chemical, biological, and radiological weapons or materials.
Information gathered, along with GPS location data, is transmitted in
real, or near real-time, via cellular radio or satellite, to a central
authority for rapid analysis.
The unique feature of such a system is the random nature of its coverage
and the high mileage covered in a relativity short time, as well as the
diversity of sensing vehicles; all for "free."
Statistically, there are two components of this type of random search:
temporal and spatial sampling. In the case of taxis and police cars, both
dimensions are at play; where as, mail trucks would be only temporal--same
routes, at regularly scheduled sampling times.
Factors influencing Detection of Nuclear Radiation
Detecting clandestine nuclear materials is not unlike prospecting for
Uranium deposits in the western desert. In both cases there are several
factors which influence detection:
1)_ Intensity of the radioactive source.
2)_ Attenuation of radiation due to Shielding. 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".
3)_ Detector types, and their dimensions.
4)_ Background radiation (background count). Background (natural
radiation) radiation is caused by cosmic rays, naturally occurring radiation
from soil, plants, nuclear fallout, etc. It is a matter of Signal to Noise
(SNR).
5)_ The Distance between the source and detector reduces radiation
intensity--in air--according to the Inverse Square Law function, i.e.,
the amount of radiation at agiven 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
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Excerpt from: "Elite
U.S. team works to keep nuclear bombs from terrorists"
"...The ease of detection depends greatly on the nuclear material used.
Some will emit alpha radiation, which can be shielded by a single sheet
of paper. Most beta rays won't make it through wood or dry wall. It's the
neutrons and gamma rays, which can shoot out hundreds of yards, that offer
the best bet for detection while driving up a city street or walking through
a convention center, hotel or office building or flying low over a community.
False alarms abound. The granite used in the Capitol and many federal
buildings as well as orange Fiesta Ware dinner plates contain enough radioactivity
to set off detectors. But new sensing equipment and techniques are being
developed for the team members, and many new people are being rushed through
training to help.
Curtis said the teams are highly experienced "and there is a high degree
of confidence that if they locate the device, they can disarm it."
Blair said that locating a device is the problem.
"The ability to find a smuggled nuclear weapon is going to be between
difficult and impossible unless there is good intelligence to give these
teams a clue. If you've got intelligence and can pin the device down to
a certain neighborhood or area, bring in NEST and their gadgets, and they'll
find it." |
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| Due to the probabilistic nature of Nuclear Event
counting, detector sensitivity is directly related to Count Collection
Time. The longer the unit time of counting, the more accurate the
measurement.
For a vehicle speeding down a highway, the greater that speed the less
the sensitivity to weak radioactive sources. In an ideal world, driving
slowly on the highway would help to overcome this effect.
Not being an ideal world, one way to compensate for this effect is to
cause each detector array panel to effectively remain stationary during
the transit of the trailer. This can be accomplished by scanning the contiguous
set of panels such that adjacent panels replace the panel moving out of
view. All this happens at a rate determined by the vehicle speed.
See animation below.
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| 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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LINKS:
----Glossary
----Isotopes
----Depleted
Plutonium and depleted Uranium
----Nuclear
Materials Management & Safeguards System (NMMSS)
----Nuclear
Primer
----GammaCamTM
Radiation Imaging System
----Technical
Aspects of Nuclear Proliferation .pdf ~2MB
----Weapons
Primer
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----"Suitcase
Nukes:" Permanently Lost Luggage 2/13/2004
--------"Suitcase
Nukes": A Reassessment 9/23/2002
----Chemical
& Biological Weapons Resource Page
----Pattern
Recognition and Intelligent Sensor Machines Laboratory
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----Preparedness
for CBR Attack
----Chemical/Biological/Radiological
Incident Handbook
----http://www.radrisk.com/detectors.htm#survey
----Cardinal
Surveys Company
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Terms:
----CBR
Chemical, Biological, Radiological
----NBC
Nuclear, Biological, Chemical
----WMD
Weapons of Mass Distruction
----W
----W
----W
----W |
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Appendix
Detection Distances |
Inverse Square Law:
Inverse Square Law: The radiation field decreases with distance from
the source. When considering a point source in air, the decrease
will follow 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 the distance.
I/i = d2/D2
or
I x D2 = i x d2
(Where I = intensity at a distance (D) from a point source, and i =
intensity at a distance (d) from the same source).
Example: If the exposure rate at 1 meter equals 100 mR/hr then the
exposure rate at 2 meters equals 25 mR/hr.
Exposure Rates VS. Distance - 100 mci Sources
| Radioactive Isotope |
mR/hr @ 3' |
mR/hr @ 6' |
mR/hr @ 9' |
| 192Ir |
61 |
15.25 |
6.8 |
| 131I |
25 |
6.25 |
2.8 |
see fig
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Half-value Layer:
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The half-value layer is the thickness of a substance which reduces the
intensity of a beam of radiation to one-half of its initial value. The
half-value layer is a function of the energy of the gamma and the composition
of the shield or absorber. Examples:
Half-Value Layers
| Radioactive Material |
-Half-Life |
--Lead-- |
--Steel-- |
Concrete |
| Radionuclide |
60Co |
5.27 years |
0.49" |
0.87" |
5.0" |
| Radionuclide |
137Cs |
30.07 y |
0.25" |
0.68" |
2.1" |
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192Ir |
73.831 d |
0.19" |
0.50" |
1.9" |
| Radioiodine |
131I |
8 days |
0.14" |
0.37" |
1.4" |
60Co Cobalt radionuclide halflife 5.27 years.
137Cs Cesium radionuclide
192Ir Iridium
131I Iodine Radioiodine 131I has a half life of 8 days |
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Activity [Curie]:
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The activity of a radioactive substance is often designated by the Curie
[Ci]. The Curie is not a measure of dose; it merely states the amount of
a radioactive disintegrations per unit time. The Curie is a unit of measurement
defined as the activity of a radioactive substance disintegrating
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at a rate of: 3.7 x 1010 disintegrations per second.
Activity Units
| Name |
Definition |
Abreviation |
| Millicurie |
1/1,000 Ci |
[mCi] |
| Microcurie |
1/1,000,000 Ci |
[uCi] |
| Nanocurie |
1/1,000,000,000 Ci |
[nCi] |
| Picocurie |
1/1,000,000,000,000 Ci |
[pCi] |
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Curie:
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Units of measurement. One curie is that quantity of a radioactive nuclide
disintegrating at the rate of 3.700 x 1010 atoms per second.
Units Of Activity
| Units |
Disintegrations / Second |
| microcurie |
3.7 x 104 |
| millicurie |
3.7 x 107 |
| picocurie |
3.7 x 10-2 |
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| Energies in Electron Volts
Room temperature thermal energy of a molecule..................................0.04
eV
Visible light photons....................................................................................1.5-3.5
eV
Energy for the dissociation of an NaCl molecule into Na+ and Cl- ions:.............................................................................................4.2
eV
Ionization energy of atomic hydrogen ........................................................13.6
eV
Approximate energy of an electron striking a color television screen...................................................................................20,000
eV
High energy diagnostic medical x-ray photons...............................200,000
eV (=0.2 MeV)
Typical energies from nuclear decay:
(1) gamma..................................................................................................0-3
MeV
(2) beta.......................................................................................................0-3
MeV
(3) alpha....................................................................................................2-10
MeV
Cosmic ray energies ........................................................................1
MeV - 1000 TeV |
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Abstract
This Web Page will describe a novel approach to "WMD Hunting," by hitching
a ride on various Fleet Vehicles, such as, long haul Tractor Trailers,
Rail Borne Container Cars, Taxicabs, Mail Trucks, Police Cars, etc.
Although this approach is also applicable to Chemical and Biological WMD
detection, this paper/page will focus mainly on Clandestine Radiological
Weapons and Materials.
We will emphasize the need for such systems to use the most effective
Detection System available at the time, with quick upgrade always close
on the heels of new and more efficient discoveries.
Lastly, we will review the fundamentals of radiological detection;
the obstacles to be overcome, and existing and future detection technology.
Also a typical survey instrumentation platform, including detectors, data
gathering, storage and transmission, local and centralized realtime/near
realtime analysis will be covered." |
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© Copyright 2004 Questions
or Comments: webmaster@williamson-labs.com.
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