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Record-breaking Detector May Aid Nuclear Inspections

For Immediate Release: March 16, 2006

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Contact: Laura Ost

Scientists at the National Institute of Standards and Technology (NIST) have designed and demonstrated the world’s most accurate gamma ray detector, which eventually is expected to be useful in verifying inventories of nuclear materials and detecting radioactive contamination in the environment.

silicon chip

Silicon chip built by NIST researchers with 16 tiny gamma ray detectors that may help nuclear inspectors improve analysis of plutonium and other radioactive materials. Each detector is one millimeter square.

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Image credit: NIST

The tiny prototype detector, described March 14 at the American Physical Society national meeting in Baltimore, can pinpoint gamma ray emission signatures of specific atoms with 10 times the precision of the best conventional sensors used to examine stockpiles of nuclear materials. The NIST tests, performed with different forms of plutonium at Los Alamos National Laboratory,* also show the prototype greatly clarifies the complex X-ray and gamma-ray emissions profile of plutonium.

Emissions from radioactive materials such as uranium or plutonium provide unique signatures that, if accurately measured, can indicate the age and enrichment of the material and sometimes its intended purpose or origin.

Gamma Ray Peaks

The data plots above show detection of gamma rays with specific energies. Arrows point to energies identified with the new detector that are difficult to detect in the red plot made with a conventional detector.

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Image credit: NIST, National Nuclear Security Agency, Los Alamos National Laboratory

The 1-square-millimeter (mm) prototype collects only a small amount of radiation, but NIST and Los Alamos researchers are collaborating to make a 100-sensor array that could be deployed in the field, perhaps mounted on a cart or in a vehicle.

“The system isn't planned as a primary detection tool,” says NIST physicist Joel Ullom. “Rather, it is intended for detailed analysis of material flagged by other detectors that have larger collection areas but less measurement accuracy.” An array could be used by inspectors to determine, for example, whether plutonium is of a dangerous variety, whether nuclear fuel was made for energy reactors or weapons, or whether what appears to be radium found naturally in the environment is actually explosive uranium.

For further information, see www.nist.gov/public_affairs/releases/gammaraydetector.htm.

* J.N. Ullom, B.L. Zink, J.A. Beall, W.B. Doriese, W.D. Duncan, L. Ferreira, G.C. Hilton, K.D. Irwin, C.D. Reintsema, L.R. Vale, M.W. Rabin, A. Hoover, C.R. Rudy, M.K. Smith, D.M. Tournear, and D.T. Vo. 2005. Development of large arrays of microcalorimeters for precision gamma-ray spectroscopy. Published in The Conference Record of the IEEE Nuclear Science Symposium, Puerto Rico, Oct. 23-29, 2005.