Portable radiation detectors generally perform well enough to meet new consensus standards but provide inaccurate readings for certain types of radiation, according to recent tests by the National Institute of Standards and Technology (NIST).
The results, reported in the May issue of the journal Health Physics,* are based on NIST tests of 31 commercial detectors, including hand-held survey meters; electronic personal alarming detectors (similar to pagers); and radionuclide identifiers (specialized devices that can identify specific radioactive materials). A number of federal, state and local agencies are using such instruments as part of homeland security-related efforts to detect and identify radioactive materials.
Researchers compared the devices' exposure rate readings to NIST measurements for different energy and intensity levels produced by NIST's calibrated gamma ray and X-ray beam lines. The responses of the majority of the detectors agreed with NIST-measured values, within acceptable uncertainties, for tests with gamma rays. This performance meets requirements established by new American National Standards Institute (ANSI) standards, adopted by the Department of Homeland Security (DHS) in 2004. However, there was a large discrepancy between most detectors' readings and the NIST values for the lowest-energy X-rays. For instance, readings by 14 detectors were roughly 40 to 100 percent below the NIST value. The deviations were much larger than those stated in manufacturers' specifications.
The tests are intended to help first responders and government agencies make better use of existing equipment and acquire the right equipment for emergency response, and to encourage manufacturers to better design and characterize their instruments. The tests were performed as part of the NIST program to support the development of the new ANSI standards (see www.nist.gov/public_affairs/factsheet/radiation_detector_standards.htm)
as well as to support the NIST Office of Law Enforcement Standards and DHS in testing detectors for their use by first responders.
*L. Pibida, R. Minniti, M. O'Brien, and M. Unterweger. Test of Radiation Detectors used in Homeland Security Applications. Health Physics. May. Vol. 88, Number 5. Posted online April 13, 2005.
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