Application of field and laboratory methods determination of radon exhalation raw materials and walls in existing buildings

Accurate measurements of the radon flux of real building materials in existing houses with normalor contaminated walls and/or the mean emanation rate of soil samples, raw materials or building materials are very important for certain studies relating to radon in houses. The two potential sources of errors are that (1). The emanation rate of the disaggregated soil samples (raw materials, building materials), used in the emanation rate procedure outlined below, may be different from the emanation rate under natural setting conditions and (2). the fact that for example, sample disaggregation greatly disturb grain-to grain distances and the natural distribution of moisture within the samples. For porous materials such as the well known Swedish Blue Concrete and soil samples, the Radon emanation rate under certain well-defined conditions is defined to be the number of Rn-222 atoms that escape the solid parts of the material. Often, the emanation rate is given in units of Rn-222 atoms that escape per second per kg dry mass of the material. External conditions known or likely to influence the Rn-222 emanation rate of a given blue concrete, an other building material or a soil sample include: temperature, pressure, stress, packing of the soil and composition of fluids in the
pore space. In the field, exploration activities and measurements of radon flux in existing houses (flats) for example, we can use thin plates of activated charcoal for direct measurements of radon exhalation from the building materials (walls). The charcoal plates (CARBOTEST-S or others) were fixed under a radon barrier (special type of plastic foil) directly on the investigated walls. Some time after the start of such field investigations (Fig.1) with the help of the LLMS 500 (mab) or other instruments we can measure an increasing activity on the charcoal plates.
With the help of well known standard conditions we can calculate also the existing radon flux from the investigated sector of the wall in the fixed charcoal plates. After remedial measures, stopping the radon flux with the help of some types of some types of special wallpaper (PERMAFOIL-S for example there), the activity of the charcoal plates is the same than the background (reference measurements without charcoal plates). The time for the simple determination of the actual radon activity in the charcoal plates is very short (less than 2 minutes) and if we like, with the used instruments automatic determinations of time series may happen any time. In the laboratory, for determination of the emanation rate we are using 4-6 liters of crushed samples (soils, rocks, raw materials) and standard boxes. After filling the boxes we measure with the AB-5 monitor system (PYLON) the increasing radon concentration in steps of 2 hours (Fig.2: Emanation rate measurements for 5 samples of alum-shale).