VS472 RADON SNIFFERS
Extremely Fast Radon Detection
Modes of Operation:
Air is continuously pumped through a scintillation cell and the radon concentration in the air is calculated every 3 seconds. This mode is ideal for quickly locating where radon is entering a building because the probe can be inserted into a crack in the foundation and if there is radon entering through the crack, you will know in as little as 15 seconds.
This mode is also useful for doing a short term test. The radon sniffer can be set to run for an adjustable length of time and the keypad can be disabled to ensure it will be an uninterrupted test.
Our radon sniffers can also be used to calculate radon concentrations in air using the standard grab sampling procedure, as described in section 22.214.171.124 of the EPA's Indoor Radon and Radon Decay Product Measurement Device Protocols.
The radon sniffer can be used for both the collection and measurement of grab samples. A grab sampling procedure for our radon sniffers is described in the Radon Gas Measurement by Delayed Count calculator that is available as part of the Uranium Radiation Safety Toolkit v2.0 at www.eic.nu, as well as in the user manuals below.
Principle of Operation:
The radon sniffers use an internal pump to draw air through a scintillation cell. As air is drawn into the scintillation cell, any radon progeny in the air is removed by a filter. The scintillation cell is coupled to a photomultiplier tube (PMT) to detect 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 tube converts the light into an electronic pulse, which is then counted.
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 algorithm used by the VS472 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.
This instrument, therefore, calculates a radon gas reading with a 15 second time resolution.
The instrument can also measure radon by the delayed count method. A scintillation cell can be filled with air using the internal pump and placed on the unit to be counted three hours later.