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 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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