CT007-R RADON SNIFFERS
Extremely Fast Radon
Modes of Operation:
For more information, please see the user manuals below.
Principle of Operation:
The CT007-R uses an internal pump to draw air through a scintillation cell. Before air is drawn into the scintillation cell, any radon progeny in the air is removed by a filter. The silicon photomultipliers (SiPM) inside the cell detect the scintillation light from alpha particles emitted by the decay of radon within the cell.
As radon decays inside the cell, the alpha particle emitted hits the wall of the cell, which is coated with scintillation powder, and emits a flash of light. The photomultiplier converts the light into an electronic pulse, which is then counted.
Smart and Standard Modes:
The difficulty with using this principle for measuring radon is that the product of this radon decay is also radioactive. This radon progeny tends to plate out, or stick, on the side of the scintillation cell. The radon progeny continues to emit alpha particles, even after there is no longer radon in the cell. It takes about three hours for radon progeny to decay. In other words, unless one can determine the fraction of the pulses that are due to radon progeny, the time resolution will be quite poor (3 hours).
The 'Smart' algorithm used by the CT007-R assumes that the first count the detector sees is due to radon gas. This is because radon will pass through the filter and radon progeny will not. It is therefore important to start the unit in an area with a low radon concentration. From the amount of radon gas detected, the devices can calculate how much radon progeny is generated. From that, it calculates the number of counts that will be due to radon progeny in the future because the half lives of radon progeny are well known.
At the next time interval, the device knows the number of counts that are due to radon progeny. By subtracting that number from the gross counts recorded, the number of counts due to radon gas is calculated. From the amount of radon gas, the device again calculates the amount of radon progeny that is generated, and so on. This calculation is repeated every 15 seconds.
The 'Standard'/'Non-Smart' algorithm simply assumes that one third of all counts received are due to radon and the rest are due to radon progeny. This is the mode that most other scintillation cell based radon detectors use for their continuous sampling mode. This is a much simpler calculation and the displayed result will be more stable than in the Smart mode. But, the results are only really valid when radon levels are fairly constant and the instrument has been running for a while.
The local display on the CT007-R is always in Smart mode, while the app can enable or disable Smart mode by sliding a toggle switch. (Both calculations are performed all the time and the display just switches which result is displayed.)
Use Smart mode when you want to detect rapid changes in radon concentration. Use Standard mode when you want to see steady values displayed.
The difference in results between the two calculation metods is demonstrated near the end of this video, under controlled conditions, in a radon chamber.