The units most commonly found on instruments used for contamination monitoring are:

• counts per second (cs^-1, cps, ps^-1, and s^-1)
• disintegrations per minute (dpm)
• becquerel (Bq)
• becquerels per square centimetre (Bq cm^-2)

If the instrument indicates 'becquerel' or 'becquerel per square centimetre', a calibration factor will have been stored in the instrument. Conversion of counts per second to becquerels or becquerels per square centimetre can be complicated. This task requires a comprehensive knowledge of decay schemes, instrument performance and some estimation of how the local conditions (e.g. surface construction) might effect the observed count rate.

The Radiation Protection Adviser (RPA) should be consulted to provide guidance on the validity of any stored calibration factors.

Good practice online modules

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• Practical radiation monitoring
  
• Practical radiation monitoring units
• Radiation monitoring strategy
• Choice of radiation instrument 
• Radiation monitoring techniques
• Estimating surface radioactivity
• Radiation instrument calibration
• Uncertainties in radiation measurement 
• Troubleshooting in radiation monitoring