For short-term radon gas measurements with exposure times between 48 hours and 96 hours, we utilize the liquid scintillation (LS) type of patented pharmaceutical-grade charcoal-silica adsorption material. Near 100% counting efficiencies allow for a monitor that is lighter in weight (0.4 ounce) and easier to handle than traditional charcoal canisters. High efficiency counting also means that fewer samples are lost due to excessive decay time.

Each detector is given a unique bar-coded identification number. A measurement with the LS device in initiated by removing the cap to allow radon-laden air to diffuse into the charcoal packet where the radon is adsorbed. A polyethylene foam plug ensures passive diffusion, preventing distortions caused by drafts and air currents. At the end of the exposure (two days), the device is resealed securely and returned to our lab for analysis.

In the laboratory, the exposed detectors are prepared for analysis by radon desorption techniques. A major fraction of the radon adsorbed on the carbon is transferred into a vial of liquid scintillation fluid. The vials of counting fluid are then loaded into an automated liquid scintillation counter. The total beta activity is then counted for a pre-set time or until the standard deviation of the counts is at 2.5%.

The total beta count, along with the customer supplied exposure data, is used to calculate the radon concentration. The typical uncertainty (standard deviation) of an LS result is ±10% and the minimum reported concentration is 0.5 pCi/l.