A wipe test counter is a device used to measure for possible radioactive contamination in a variety of environments. When using radioactive materials it is necessary to test for accidental contamination, whether from use of liquid unsealed sources or to check for leaking sealed sources. A swab or small absorbent smear can be used to “wipe” an area, the wipe is then placed into a test tube and counted, typically using a gamma counter. Testing for leaks in this manner is a method described in the ISO 9978 standard.[1]
Survey instruments may be used to detect surface contamination without requiring wiping, however this requires careful calibration and technique to ensure adequate sensitivity is achieved.[2]
A gamma counter is a typical choice for measuring wipe samples for radioactivity as it allows multiple tests to be counted in a largely automated way. These systems detect radiation using a scintillator and photomultiplier tube and may allow the energy spectrum of a sample to be recorded, which can be used to identify the contaminant.[3] [4]
Use of a gamma camera has also been proposed, where collimators are removed to improve sensitivity.[5]
Wipe testing is typically a requirement of licenses to hold radioactive materials. In the United States the Nuclear Regulatory Commission requires wipe testing of sealed sources "periodically" using equipment sensitive down to 185 Becquerels.[6] In the United Kingdom the Health and Safety Executive guidance for the Ionising Radiations Regulations 1999 requires wipe testing (usually every two years) and it is also likely to be a requirement of Environment Agency permits.[7] [8] In Australia licence conditions may require adherence to Australian standard AS2243.4 and ISO 9978 for wipe testing of sealed sources.[9]