With a half-life of 29 years, strontium-90 loses its radioactivity slowly. It is also highly toxic because of its ability to mimic calcium in the body, becoming part of the bone marrow tissue and damaging blood-producing cells. Uranium-238 is a heavy metal that is chemically toxic in certain doses. It is also a long-lived alpha and gamma particle emitter with isotopes of concern.
If strontium-90 or uranium-238 is present in soil, either will produce highly energized beta particles. BetaScint detects these particles through its "smart" plastic fibers that have been coated with a fluorescent material. The fibers light up, or scintillate, when the beta particles come in contact with them. A multi-layer fiber configuration enables BetaScint to discriminate against background interferences, such as low-energy beta particles, gamma rays, and cosmic ray-generated particles, which have different penetrating powers.
"We look at the intensity of light to quantify the activity level of strontium-90 and uranium-238," explained Schilk, Pacific Northwest National Laboratory principal investigator. "This light is then translated into an electrical current and transferred to an internal computer that generates the results."
Although strontium-90 and uranium-238 produce energetic betas that are indistinguishable from one another, the two elements are rarely found in the same location; the former is a fission product and the latter a raw material. "In a case where the two are found together, such as in regions contaminated as a result of the Chernobyl catas-trophe, ancillary analytical techniques can be used to help distinguish the two radionuclides," Schilk said.
