A wide variability exists among commercial radiation detection instruments used to measure exposure rate or ambient dose equivalent rate. These instruments are used to measure both the radiation background and radioactive sources strengths to determine the radiation field be used to test other types of radiation detection systems against different consensus standards. Most radiation fields specified in the ANSI standard are quite low, ranging from 5 to 50 µR/h above background. Due to the radiation fields being such low in intensity, the uncertainty of the measurements made with these instruments can be potentially quite large. As a result of these large uncertainties, it is possible that the response of the various parameters being tested by the standards (e.g., alarm indication, radionuclide identification) will be dependent on the specific radiation detector employed by the testing laboratory. In this work, measurements and calculations were performed with a gamma radiation detector model GE RSS-131ER and compared to previously tested instruments, showing a marked decrease in the uncertainty of the measured radiation field. Consistency in testing results across laboratories could improve with a shift in the standards requirements: For example by specifying for the test the emission rate or activity of the source and a source-to-detector distance instead of specifying the exposure rate or ambient dose equivalent rate of the radiation field.
Technical Note (NIST TN) - 1916
radiation detection for homeland security, ANSI N42 standards, testing of radiation detection equipment