Thursday, February 1, 2001
Using either x-ray or neutrons in radiographic procedures,
conventional material analysis methods detect absorption of radiation as it
passes through the materials. However, if two of the materials have similar
absorption characteristics, then radiographs show very little.
Researchers at the National Institute of Standards and Technology
(NIST) believe they have a better way of examining materials with similar
absorption rates. It works a little like the way light diffracts when passing
through a glass of water.
Using low levels of radiation, the phase of the wave shifts at the
boundary between the two materials with different densities. "Phase-sensitive
imaging" yields images with greater detail, especially at the boundaries and
edges, according to Muhammad Arif, a physicist at NIST. "With most radiography,
a lack of absorption translates into a lack of sensitivity needed when detecting
small cracks," says Arif. "Phase-sensitive imaging shows these small cracks," he
says.
Potential applications for the technology include checking for
cracks and defects in precision welding, turbine blades, fuel cells, and
pressure vessels in nuclear reactors, according to Arif. For more information,
call him at (301) 975-6303 or e-mail muhammad.arif@nist.gov.
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