Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)
Geological factors of radon index in administrative units RIA (NUTS5, Czech Republic) – a proposal of methodics
Abstract
A proposal of a new type of radon index maps of administrative units NUTS5 for the Czech Republic is under preparation for the period of Radon programme 2010-2019 based on 9000 soil gas Rn data (Czech Geological Survey) and 92276 indoor Rn data (National Radiation Protection Institute). The influence of geological factors like lithology, soil gas radon concentrations, permeability, gamma dose rate, density of tectonics and variability of geological basement was correlated to probability of exceeding the action level of indoor radon concentration 200 Bq.m-3 (newly built houses) within 2016 municipalities including more than 10 indoor radon measurements. The georeferencing performed in ArcGIS 9.2. programme has clearly shown, that the leading geological factors for increasing the probability of exceeding the indoor action level are the lithology, soil gas Rn concentration, gamma dose rate and permeability in the intravilans of administrative units, whilst the tectonics and variability of basement does not express any statistically significant influence. The RIA coefficient (Radon Index of Administrative unit) was proposed in two versions using the combination of 2 or 3 variables - the mean soil gas radon concentration in the rock type underlying the intravilan of municipality, the mean gamma dose rate in the cadastre and also including the mean permeability of underlying rocks (variantly - 3 variables). The RIA coefficient in two versions derived from existing soil gas Rn and indoor Rn data from 2016 municipalities was extrapolated to all 6395 municipalities after the corrections for differences of real - calculated values. Two new areas with enhanced probability of exceeding the action level were discovered - in SW Bohemia and Central Moravia, geologically probably connected to occurrence of dyke Variscan granitoids (SW Bohemia) and strongly migmatitized Precambrian crystalline rocks (the latter one).
