Nuclear Weapons of Mass Destruction NWMD
The primary objective of any radiation measurement regimen would
be to scan the most territory in the shortest period of time for the least
cost. Detection at a distance remains the primary problem. How does one detect
a radioactive object and distinguish it from the naturally occurring background
radiation (NORM)? Sources such as the naturally occurring minerals consisting
primarily of uranium and thorium and their decay isotopes in rock and soil
along with cosmic rays from outer space contribute approximately 10 to 25
microrad per hour. Any measurements must compete against this "background
A man made, compact "point" source of intense radiation radiates in
all directions. The strength of the radiation will decrease with the "inverse
square" of the distance from the source. If you double the distance between
the detector and the point source, the radiation level drops to one fourth.
Triple the distance and the field strength is now one ninth. In addition,
radiation is adsorbed to varying degrees by any intervening matter, including
air. Alpha particles are stopped by a few centimeters (less than 2 inches)
of air or a sheet of paper. The alpha particle could not be detected at
any realistic distance. The beta particle would travel a greater distance
but the majority of these high-speed electrons are captured in a thin sheet
of lead or a thicker sheet of aluminum shielding. This leaves the detection
of gamma rays (high energy "x-rays") to be the primary means of detecting
radioactive materials. Thermal neutrons emitted by weapons grade material
can be detected provided that neutron shielding is absent.
Three primary portable tools exist to detect gamma rays. The most expensive
and sensitive detectors use a sensitive crystalline semiconducting material
that will directly adsorb the gamma energy and convert it into free electrons
which are captured and measured. These crystals are also very sensitive
to background gamma radiation. Of equal or greater sensitivity, the scintillation
counter relies upon an optically clear crystal coupled to a photomultiplier
tube. The scintillation crystal give a weak burst of light (scintillates)
with each gamma detected and the light enters the photomultiplier tube
where it is converted to electrons which are amplified billions of times.
This forms an electrical pulse which is proportional to the gamma ray energy.
Most radioactive elements emit one or more characteristic gamma rays at
known energy levels. If enough gamma rays are captured, the radioactive
elements can be identified.
The third and least expensive method uses the gas-filled Geiger-Muller
tube to primarily detect gamma rays. A few percent of the gamma rays that
cross through the volume of gas within this Geiger tube are converted
into a pulse of electrons for each detected gamma ray. A Geiger
tube about the size of lipstick container will detect approximately one
gamma ray each minute in a radiation field of a microrad per hour. This
results in 10 to 25 counts per minute in a 10 to 25 microrad/hour NORM
field with the Geiger tube used in the RadScanner Model 500VBR.
No matter which detection method is used, at a certain distance, it
becomes unlikely that a "point source" can be distinguished from the background
radiation. If directional shielding is used around the detector with an
opening pointed toward the suspected source, some relief from detecting
gamma radiation of cosmic or terrestrial origin may be had at the expense
of needing to always keep moving the detector to scan new territory. Alternatively,
at checkpoints, such as entryways to ports, bridges and tunnels, an array
of directionally shielded detectors can be pointed at railcars or truck
containers and scanned for "hotspots".
The detection of neutrons with specialized equipment would require
a better knowledge of the possible sources of neutrons from within a "suitcase
bomb". Since neutrons are used to start the chain reaction, the number
emitted would have to be under some threshold to prevent detonation. This
will not be covered in this review. Since uranium and thorium atoms emit
neutrons upon decay there is always some small background neutron flux. Certain
shielding materials will absorb neutrons and prevent their detection.
The primary task of detecting a point source of nuclear radiation should
be divided into at least three categories.
First, consider the "suitcase bomb" that most probably will be the
size of a heavy footlocker or larger and should not emit much radiation
with heavy shielding. The thick shielding would make the weapon opaque to
x-ray imaging. Suspicion should be aroused upon finding a heavily shielded
container the size of a foot locker or 55 gallon drum that cannot be easily
moved because of the weight of the shielding and that does not allow an
x-ray photograph to be taken.
The second scenario involve the so-called "dirty bomb", a conventional
explosive wrapped with intense radioactive isotopes, like those encapsulated
powders used in medical or industrial applications. Strict inventory and
security of all known hospital and industrial sources must be maintained
to protect against inadvertent or intentional spread of highly radioactive
dust. The capsule of highly radioactive material is always stored in thick
metallic lead shields to protect hospital and industrial workers. The
capsule is easily detected without the shielding.
The third concern would be distinguishing "false positive" responses
to medical tests using trace amounts of radioactive compounds routinely
used for cardiac stress tests and thyroid scans and treatment.
Hand held, pocket sized, Geiger counters like the Model 500VBR RadScanner
from PROGRESSIVE SYSTEMS COMPANY of Houston, Texas (www.antirad.com) are capable
of detecting those persons undergoing medical tests with short-lived,
radioactive trace elements. The detection range is 2 to 3 meters (6 to
12 feet) dependant upon the radioactive isotope used and the elapsed time
since administration. Most of these medical tracers have half-lives of
hours or days, but emit intense fields 1000 to 2000 times the normal background
radiation levels directly after administration.
As an example: "In one case last spring, a man being treated for an
overactive thyroid gland was stopped at Pennsylvania Station. In another
case, a woman who had undergone a diagnostic heart study was stopped while
trying to drive out of Manhattan through a tunnel. In both cases, the people
involved had been treated with radioactive materials. And in both cases,
doctors said, they were stopped by law enforcement officers armed with radiation
detectors used to track possible terrorists."-- "High Security Trips Up
Some Irradiated Patients, Doctors Say" By AL BAKER, NYTimes December 4,
In those war zones where depleted uranium (DU) shells have been deployed,
large areas have higher than normal background radiation. Shell fragments
have a count rate 1000 to 2000 times the background rate. DU is approximately
75% as radioactive as naturally occurring uranium metal. These tank-busting
weapons have been used extensively in the last two Gulf Wars, in the former
Yugoslavia and on practice and test ranges. Each of these rounds bursts
into flame upon impact forming clouds of uranium oxide dust that settles
over the surrounding.
Domestic and overseas areas where uranium is mined and ore processing
sites will give high readings because of spills and leaks.
Some areas have naturally occurring high levels of dissolved radium
salts in well water. Gases purged from these wells, primarily radon, will
give false positive readings.
In spite of the occurrence of false positive responses, a detection
methodology can be structured for any situation.
Equipping and training a large number of first responders with a small,
rugged and low cost Geiger counters like the Model 500VBR would quickly
identify hotspots and allow the greatest area to be covered. Contaminated
areas can be taped off to prevent personnel from tracking radioactive debris
over a larger area. Decontamination stations can be placed at checkpoints
for emergency responders and victims.
PROGRESSIVE SYSTEMS COMPANY 1620 West Main Street Houston,
Tel: 713 523 0515
EMAIL US at
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