Radiation detectors fall short of standards.

Most portable radiation detectors perform well enough to meet new federal standards, but others provide inaccurate readings for some types of radiation, according to recent government tests.

The National Institute of Standards and Technology evaluated 31 commercially available detectors used by first responders and security personnel to test for radioactivity. Those threats have different signatures, and therefore require detectors that are flexible.

"If you have a wide energy range, you are able to determine exposure more accurately for a wide range of radioactive materials," Leticia Pibida, a physicist at NIST who authored the report, told National Defense.

The experiment used carefully calibrated NIST machines to calculate the value of radioactive material, and then compared results from the commercial machines to see how closely the data meshed.

Researchers compared the devices' exposure rate readings to NIST measurements for different energy and intensity levels. The responses of the majority of the detectors agreed with NIST-measured values, within acceptable uncertainties, during tests with gamma rays, the report found.

However, low energy X-rays measurements were not up to par. Readings by 14 detectors were 40 to 100 percent below the value of NIST testing equipment. "The deviations were much larger than those stated in manufacturers' specifications," Pibida noted in her report.

The equipment was being tested to see if it met requirements established by the American National Standards Institute, adopted by the Department of Homeland Security in 2004.

"Most of the instrumentation that exists in the market today has been designed for ... occupational monitoring and laboratory use where, generally, the radionucleotide to be detected or measured is known," she wrote. "[In a lab,] corrections to the instrument's reading could be made, if necessary."

But the first responders who use portable units cannot be bothered with delicate calibrations even if they were trained to do so, Pibida said, since the type of radiation they are looking for is unknown.

The radiation detectors of the future will have to be able to operate under a wide range of environments and energies. For now, Pibida suggests greater transparency from suppliers.

"Manufacturers need to do a better job of characterizing their instruments and providing users with better information about their detector's response and performance," read Pibida's paper, contained the May issue of the journal Health Physics.

Results and recommendations will be furnished to the Department of Homeland Security for its use in setting up a program for certifying detectors.