Canada Inc.

Uranium Radiation Safety Toolkit v2.0

Radon Gas Measurement by Delayed Count

Refer to either the VS472 User Manual for the following procedure:

  1. Take a 5 minute background count on a small Aluminum Lucas cell (serial number starts with "A"). This count should be below 50.

  2. Collect a sample as described in the Grab Sampling Setup section of one of the above user's manuals. Alternatively another pump can be used, rather than the radon sniffer's internal pump. Make sure you use an inlet filter.

  3. Wait between 1 and 4 hours.

  4. Count the cell using a 5 minute pre-set time.

  5. Enter the gross count, background count and time between sampling and counting in the form below and hit CALCULATE NOW. (Accept all other default values.) The radon gas concentration will be displayed. As a rule of thumb, 1 count in 5 minutes corresponds to ~ 10 Bq/m3 or 0.25 pCi/L. Longer count times can be used to increase accuracy.

  6. Pump clean air through the cell for about 10 minutes using the radon sniffer's internal pump or a different pump. (Some people prefer dry nitrogen, to ensure extremely low levels of radon in the cell.)

  7. Wait at least 3 hours (preferably overnight) before taking another background reading and re-using the cell. (This allows the radon progeny, attached to the walls of the cell to decay.)

  8. If the background count is high, you may have to purge again and/or wait longer. 

  Input Fields Calculated Fields  
Enter the cell volume (litres):    
Enter the count time (min):    
Enter the gross counts:    
Enter the background counts:    
Enter the cell efficiency:    
Enter the time, t, between sampling and start of count (min):    
    pCi/l Radon



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