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Cosmic particles find potential role in homeland security

LOS ALAMOS, N.M., March 20, 2003 -- Fragments of cosmic rays could
someday lead to the detection of smuggled nuclear materials,
according to researchers at Los Alamos National Laboratory. 

In a paper appearing today in Nature magazine, (vol. 422, p. 277), a
team of Los Alamos National Laboratory astrophysicists and physicists
notes that in both laboratory experiments and corresponding computer
simulations, dense materials such as uranium can be detected and
imaged by tracking the paths of muons as they pass through the target
materials. 

Unlike X-ray imaging, which depends upon small doses of artificial
radiation to create images of dense objects such as bones or smuggled
metal objects, muon radiography needs no additional radiation. Muons,
are created naturally when cosmic rays from space interact with the
Earth's atmosphere, and pass through the Earth's surface at a rate of
approximately 10,000 particles per square meter per minute. Using
these common, naturally occurring particles for imagery came
naturally to the science team, according to one member.

"There's a lot of work between an idea and any successes. Most ideas
don't pan out, but this one did,” said William Priedhorsky, a
high-energy astrophysicist on the project. "New ideas for sensors and
processing that come from fundamental science are essential for us to
carry out our national security mission."

Placing an array of simple sensors above and below a target, the team
developed a computer algorithm to detect variations in the muons'
paths before and after striking a heavy metal target. The change in
direction by the muons was the key to the detection technology,
permitting the scientists to build three-dimensional images of the
target objects. 

"It worked incredibly well, we were really surprised," said
Priedhorsky, chief scientist of the Laboratory's Nonproliferation and
International Security Division. "We knew that back in the 1970s
physicist Louis Alvarez had created images using muon absorption to
map the interior of the Second Pyramid at Giza, but no one had
explored the scattering data to see if it was useful," Priedhorsky
said. "We found that we could detect a 1-liter block of uranium in
the equivalent of a truckload of sheep, for example, and the greater
the efforts at shielding the material, the more obvious it becomes
with the muon technology."

A drawback to the infant homeland security project would be the time
required for an image, since detection is based on a minimal number
of muons impacting the target object, and they fall from space at a
rate that cannot be changed. A 1-minute shower of particles would be
required to reasonably scan a suspected smuggler's vehicle, for
example, according to lead author Konstantin Borozdin. But given that
the particles are free, available worldwide, and that they provide
consistent imaging of any high-atomic-number substance, the concept
offers a promising addition to conventional X-ray, gamma and
neutron-detection systems.

The team developing this technology comes from both the Laboratory's
Physics and Nonproliferation and International Security divisions,
and includes Konstantin N. Borozdin , Gary E. Hogan, Christopher
Morris, William C. Priedhorsky, Alexander Saunders, Larry J. Schultz
and Margaret E. Teasdale (now a student at the University of Hawaii). 

Los Alamos National Laboratory is operated by the University of
California for the National Nuclear Security Administration (NNSA) of
the U.S. Department of Energy and works in partnership with NNSA's
Sandia and Lawrence Livermore national laboratories to support NNSA
in its mission.

Los Alamos enhances global security by ensuring the safety and
reliability of the U.S. nuclear stockpile, developing technologies to
reduce threats from weapons of mass destruction, and solving problems
related to energy, environment, infrastructure, health and national
security concerns.
 
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