When there is a requirement to provide different chamber radon concentration levels, it can be expensive to purchase and maintain a number of different sources in order to provide a range of radon concentration levels inside a radon chamber. Fortunately, there is a simple, low-cost technique that can be used to provide a wide range of radon concentrations in the chamber with only one flow through radon source. This reduces the cost of purchasing and maintaining a number of radon sources.

The technique involves splitting the flow of radon gas from the flow through radon source using two adjustable flow meters. The ratio of the split determines the amount of radon that is flowed into the chamber.

For example, let’s assume that you have a 100 kBq activity flow through radon source and you need a 25 kBq activity flow through radon source to achieve the required concentration in the chamber. In order to meet the requirements using a 100 kBq activity flow through radon source, you need to vent 75% of the gas from the flow through radon source while allowing 25% of the gas to the chamber. This can be achieved by the use of two adjustable flow meters. The following diagram provides an example setup including the recommended addition of a gas drying system.

Using the 100 kBq activity source and the 25 kBq activity requirement for the chamber example above, let’s also assume that the required flow rate is one litre/minute. To achieve the desired activity for the chamber, we will need a flow rate of 0.25 litre/minute in Flow Meter 1 and a flow rate of 0.75 litre/minute in Flow Meter 2.



To set these flow rates up, perform the following steps:

  1. Adjust Flow Meter 2 to provide a flow rate of 0 litre/minute. (i.e., Shut Flow Meter 2 off.)
  2. Turn on the pump and adjust Flow Meter 1 to provide a flow rate of one litre/minute.
  3. Then fully open Flow Meter 2 and adjust the flow rate to 0.75 litre/minute.
  4. After an appropriate period of time, confirm that the chamber concentration is at the desired level. If not adjust the flow meters as appropriate and re-confirm.

Hint – The same setup concept can be used to provide different activities to more than one chamber at a time.

Pylon offers the models RN-1025 and RNC flow through radon sources in a variety of activities. In addition, Pylon also offers the model TH-1025 flow through thoron source in a variety of activities should there be a requirement for a thoron chamber.