Radon in soil gas

This application note describes how to simply and quickly quantify Radon activity concentration in soil gas using a packer probe and a Radon- or Radon-Thoron-Monitor RTM1688-2 or RTM2200 from SARAD GmbH.

Physical and Geo-Physical Basics

The quantifying of Radon activity concentration in soil gas is based on a continuous or clocked taking of soil gas samples via a packer probe located in a suitably sized bore-hole and sealed with respect to ambient air (for instance SARAD soil gas sampling system).

For continuous sampling, the internal pump of the chosen Radon monitor is used mostly. Frequently, well-defined gas volumes have to be investigated and a clocked taking of soil gas samples is necessary. In many of these cases, an external pump is used, possibly a special hand operated one. The risk to suck water out of the soil into the device will be minimised by this procedure.

The Radon activity concentration C [Bq/m³] in soil gas (more generally in aerosols) denotes the ratio (Radon-) activity A [Bq] to the (gas-) volume V [m³]. The unit Bq/m³ reads „Becquerel per cubic meter“, where 1 Bq means that that there is 1 radioactive decay (here with respect to the radioactive inert gas Radon-222) per second.

The Radon activity concentration in soil gas (in a depth of about 1 m) covers normally a range between circa 1.000 and more than 1.000.000 Bq/m³, depending upon where the samples are taken. But also at the same measurement location, the results may differ remarkably, especially in dependence of several parameters as temperature, air pressure, precipitation, moon phases (tides of the earth's crust) and others. 

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