Finding Dirty Bombs And Other Radiation Threats

With partial funding from the Department of Homeland Security (DHS) and NIST's Office of Law Enforcement Standards, NIST researchers are investigating a wide variety of detection devices, ranging from 3-meter-high portal towers that scan truck trailers while they move through checkpoints to small, pager-size monitors that serve as personal dosimeters. Many of these devices originally were designed for monitoring workers in factories and laboratories. The new standards under development will ensure that the devices work as intended under the new conditions now encountered in homeland security related tasks.

For example, some devices work differently in the rain or high humidity conditions, as well as in wide temperature ranges. So far, the NIST researchers also have found that the calibration of some detectors depends a lot on the exposure rate and energy of the radiation detected. The accuracy rates for 19 different hand-held detectors ranged within plus or minus 5 percent of the actual radiation value to plus or minus 40 percent depending on whether they were measuring high, medium or low energy radiation sources.