Quickly and Accurately
Researchers pursue the goal of a portable detector that instantly identifies a package's radioactive contents.
Hand-held radiation detectors and radiation monitors can
sense radioactivity in abandoned packages. Today's security
challenges, however, require a portable detector that instantly
reveals the precise nature of an unidentified package's radioactive
contents.
Such a detector can be built if a material can be identified
that captures radiation efficiently and provides highly detailed
information about an isotopic source. ORNL researchers are working on this goal.
"The federal government wants radiation detectors that are
smaller, simpler, faster, more sensitive, higher resolution, and
less expensive than today's instruments," says Lynn Boatner,
ORNL researchers developed silicone rubber bonded with boron compounds that emits blue light in the presence of neutrons.
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a materials physicist in ORNL's Condensed Matter Sciences
Division who directs the new Center for Radiation Detection
Materials and Systems at ORNL. "We are investigating various
new materials and systems for detecting radiation and for
tracking sensitive items for the Department of Energy's Nuclear
Nonproliferation Office, the Department of Homeland Security,
and other government agencies."
ORNL researchers are fabricating and characterizing the
radiation response of detectors made of innovative "scintillators,"
including crystalline materials and glasses with high density
that give off photons of light when exposed to radiation.
"These materials show the potential for detecting radiation
with great efficiency and yielding an ultrafast response on
the order of tens of nanoseconds or less," says Boatner, who
is an ORNL corporate fellow. "Some of these materials have a
relatively high energy resolution, suggesting they could enable
a detector to distinguish among radiation emissions from different
radioisotopes."
The best of these materials may be strong candidates
for portable radiation detectors at airports, train stations, and
ports. Other materials might be practical for large-area portal
monitors that screen truck containers at weigh-and-inspection
stations for radioactive cargo. The goal is to distinguish between
benign radioactive products found in normal commerce—such
as medical radioisotopes, smoke detectors, ceramic pots,
and kitty litter—and potentially dangerous nuclear materials
(cesium, strontium, uranium, and plutonium) that could be
intended for a terrorist bomb.
Boatner and colleagues John Neal, Joanne Ramey, and
Jim Kolopus are striving to develop a powerful, versatile, alternative
method for producing large, transparent inorganic
scintillators without the need to grow large single crystals, a
task that is often time consuming and difficult to accomplish.
They have recently synthesized zinc oxide nanoparticles doped
with gallium using urea precipitation methods and were able
to produce translucent ZnO ceramics by techniques based on
hot pressing.
Sheng Dai of ORNL's Chemical Sciences Division is investigating
nanocrystalline and glass scintillators formed by
sol-gel processes. Dai and Zane Bell of ORNL's Nuclear Science
and Technology Division have been fabricating and characterizing
neutron scintillators that are high in lithium or boron.
Bell has been investigating new types of mercury-containing
scintillators.
Bell has led the development of a new radiation detector
material and detector prototype, both of which have been
licensed to NucSafe, an Oak Ridge manufacturer of radiation
detectors. Bell's research team developed a silicone rubber
laced with boron that emits a blue-green light in the presence
of alpha, beta, gamma, and neutron radiation. Having an 18%
boron content makes the silicone rubber material an excellent
detector of neutrons that indicate the presence of uranium
and plutonium. Researchers believe the silicone rubber could
be incorporated into another invention, the HotSpotter, an
inexpensive, handheld gamma-ray spectrometer.
The heart of the HotSpotter is a scintillator made of
cadmium tungstate, whose extremely high density increases
the probability that gamma rays will interact with the crystal's
light-emitting molecules. The HotSpotter software analyzes the
gamma-ray spectrum to identify the radioisotope present.
Other ORNL work in the new center includes research on
cerium-doped, rare-earth double phosphates for radiation detectors,
as well as related research on new phosphor materials for
possible use in tagging, tracking, and locating sensitive items.
The collective goal for all of these projects is the ability
to prevent an increasing array of dangerous materials from
reaching the hands of America's adversaries.
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