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.