Radon and its radioactive decay products represent most significant source of human radiation exposure (approximately 43 % of annual radiation effective equivalent). For this reason a special attention is paid to natural radioactivity and potential radon risk. Natural radioactivity is most usually calculated in Gamma radiation dose input.

Data recorded on the territory of Slovakia (63.3 nGy per hour) exceeded set European limit. Average concentrations of K reached 2.52 %, Th 9.4 ppm and U 3.3 ppm. The highest concentrations of U are common for Permian system rocks in which also uranium ore mineralisations are present (Novoveská Huta, Považský Inovec, hronicum system of the Low Tatras).

In 1997, the study ‘Radon Risk Assessment from Geological Bedrock of Towns with Population Exceeding 10 000 and District Towns with Medium and High Radon Risk‘ was completed. Simultaneously, radon risk map at scales 1: 500 000 and 1: 200 000 including the whole territory of Slovakia was created. High potential radon risk was recognised in Spišsko-gemerské rudohorie Mountains area (Smolník, Rožňava, Hnilčík, Poproč, Medzev, Hnilec, Novoveská Huta), in Horehronské podolie basin, in Bratislava, Košice, Banská Bystrica, Kremnica and their surrounding areas as well as in the town of Levice, Rožňava, Žilina, Partizánske, Bytča and mainly Pezinok. High radium and radon values were recorded in water samples taken from different thermal and mineral springs (e.g. Oravice, Bešeňová, Plavnica). However, the highest occurrence of waters with high radon values was registered in waters coming from core areas (such as Malé Karpaty Mountains, Považský Inovec Mountains, Tríbeč Mountains, etc.) and in waters of Veporské and Stolické crystalline mountains.

Importance of radon health risk in indoor facilities (work places and living areas) is stated for different radon volume equivalent activity intervals (EOAR) and is based on representative survey results. The survey was conducted by ÚPKM and included 2 745 housing units and 650 nursery schools and educational facilities, serving as sample material. The above mentioned data represent  approximately 1.5 ‰ of the Slovak housing fund. According to the survey results given in cartographic form it is possible to say that weighted arithmetic mean (AP) EOAR calculated from the population distribution figure equals to 48 Bq per m³. When comparing samples of family houses and blocks of flats the following differences were recorded: family houses - AP - 125 Bq per m³, GN (geometric mean) - 73 Bq per m³ and blocks of flats - AP - 22 Bq per m³, GN - 14 Bq per m³ (EOAR). The maximal recorded value of EOAR is 1 500 Bq per m³ and the average radon decay products inhalation effective dose in indoor facilities per capita is 3 mSv.

EOAR values recorded in indoor facilities (SR)
 

EOAR [Bq.m-3]	Number of flats	Number of flats [%]
< 20 20 – 199 200 – 599 600 – 999 > 1000	728 1 651 336 27 3	26.5 60.2 12.2 1.0 0.1

Districts with the highest average EOAR values and average annual radon and its decay products exposure effective dose in indoor facilities (per capita)
 

	District	EOAR [Bq.m-3]	E [mSv]
1. 2. 3. 4. 5. 6. 7. 8. 9. 10.	Rožňava Košice-vidiek Spišská Nová Ves Rimavská Sobota  Stará Ľubovňa Veľký Krtíš Trebišov  Nitra  Komárno Levice	120 119 94 87 87 79 72 71 66 65	7.5 7.4 5.9 5.4 5.4 4.9 4.5 4.4 4.1 4.1

                                                                                                                   Source: ÚPKM
 
 

	Average annual radon and its decay products inhalation effective dose in indoor
	facilities - based on district  division (per capita)
	Radon risk resulting from geological bedrock evaluated in selected towns
	of the SR and it's comparision with inhalation effective doses of Radon and its
	decay products in indoor facilities according to district of the SR