Reviewed: Apr 2020
Before measuring for contamination, the surface should be dry. Use a surface contamination meter (direct monitoring) to measure the level of surface contamination if gamma/x-ray or strong beta emitters have been used/stored. To do so:
- Check if your contamination meter meets the U of T criteria for surface contamination (0.5 Bq/cm2), and the proper functioning of the instrument (battery, HV, sound, calibration sticker – the instrument should have been calibrated within the last year). If does not meet the requirements change the instrument or use the indirect monitoring method
- Determine the background reading at a surface that is known to be clean
- Determine the readings of the instrument as close to the surfaces as possible, without touching them (recommended at 1 cm distance) by moving the instrument very slowly (recommended at 1 cm/s)
- Do the calculation to transform the readings from cpm or cps to Bq/cm2
- Record the results
Use the indirect monitoring technique to measure the level of surface contamination if low energy beta or alpha emitters have been used/stored (H-3, C-14, S-35 etc.). To do so:
- Five samples shall be taken from each square meter of the equipment surface (both from inside and outside surfaces of the equipment). Choose the locations most likely to be contaminated (like door handles, the shelf where radioactive material was stored, etc.)
- Swipe 100 cm2 by pressing the filter paper against the surface
- Fold the filter paper and insert it into a liquid scintillation vial
- Add scintillation fluid
- Choose an energy window that is appropriate for the radioisotope, or use a wide-open window
- Perform the measurement
- Perform the calculation
- Record the results
To measure the external radiation field:
- Use a radiation survey meter that was calibrated by a CNSC authorized calibration laboratory within the last year. Check the proper functioning of the instrument (battery, HV, sound, calibration sticker) and adapt the scale to the level of radiation field measured
- Move the survey meter very slowly as close as possible without touching the equipment.
- Record the results (at least five results should be recorded for each square meter of the available surface of the equipment both outside or inside).
The results of all measurements should be kept for three years.