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The first measurements of radon and gamma radiation in dwellings in the Czech Republic were performed in Jáchymov between 1978 and 1980. The results for Jáchymov, presented in Tab. 1, can be compared with the results of a representative survey of the housing stock in the whole of the Czech Republic, summarized in Tab. 2. The high concentrations in Jáchymov are caused by the former mining activities. (The houses were built on a highly permeable rock slag left behind after silver and uranium ore mining. The radioactive wastes produced during the production of colour pigments from the uranium ore for the ceramic and glass industry were used as filler material for mortars and plasters).
The first remedial measures in the territory of the Czech Republic were also installed in Jáchymov, between 1990 and 1996. Lack of knowledge and experience led to low effectiveness of many of the remedial actions. A positive feature of almost all of the measures was that two different remediation principles were combined – a radon proof membrane with an aluminium carrier, and natural floor air gaps (Fig. 1) or sub slab ventilation (Fig. 2). It was later found that natural air gaps or sub-slab ventilation through vent holes in the perimeter foundations (Fig. 3) are insufficient measures.

Fig. 1 - An air gap in the floor structure formed by the corrugated sheet and ventilated through the vent holes in the perimeter walls.

Fig. 2 - Layer of coarse gravel under the floor structure ventilated through vent holes in the perimeter walls.

Fig. 3 - Vent holes in perimeter foundations or walls serving for soil or air gap ventilation.