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Systematic measurements of indoor radon concentrations and gamma dose rates were carried out in the 730 kindergartens and play schools in Slovenia that, together, care for 65,600 children. The main method for indoor radon measurement was direct sampling in alpha scintillation cells, but in cases with an increased instantaneous radon concentration, the additional methods of track-etch detectors and alpha spectroscopy were applied. In 528 kindergartens and play schools (72%), radon concentrations were below 100 Bq m-3, with a geometric mean of 58 Bq m-3. In 16 kindergartens and play schools (2.2%), radon concentrations exceeded 800 Bq m-3. In all cases, the main reason for a high indoor radon concentration was the geological structure of the soil. Gamma dose rates were measured with a portable scintillation counter, but in the Ljubljana region thermoluminescence dosimeters were also exposed. The results ranged from 30 to 295 nGy h-1, with a geometric mean of 88 nGy h-1.

Remedial actions were carried out in two kindergartens with average heating season radon concentrations of about 2,000 Bq m-3. The first kindergarten is built on sedimentary gravel and the second one on fly ash and cinder fill. In both cases, radon accumulated in a sub-floor channel (service tunnel). The channels were opened at both ends. Natural ventilation of the tunnels did not produce a sufficient reduction in radon concentration. A fan was mounted in one kindergarten to ventilate the channel for 20 min three times each day, thus reducing radon levels to an acceptable value.

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