Acta Musei Moraviae

Radioactivity and chemistry of granitoids in the eastern part of the Lugicum (Czech Republic)

Two petrographically different types of granitoid bodies cropout in the eastern part of the Lugicum in the territory of the Czech Republic. The first type is represented by small granite or granodiorite massifs (namely Olešnice-Kudowa Massif, Nový Hrádek Stock, Litice Massif and Javorník Massif) and less important granite or granodiorite bodies in the surroundings of the town of Rychnov nad Kněžnou. These rocks contain 2.6 ppm U and 10.8 ppm Th on average, the calculated value of mass activity of ²²⁶Ra equivalent (a_m) is 160 Bq.kg^-1 (379 samples analyzed). The second type is represented by plutonic rocks of a so-called tonalite suite (“tonalites“). Modal composition of these rocks corresponds mainly to granodiorite, quartz diorite and quartz monzodiorite. These rocks outcrop along with metamorphites of the Zábřeh Group in the foothills of the Orlické hory Mountains and in the Staré Město Belt. On average, they contain 2.6 ppm U and 10.2 ppm Th, a_m = 148 Bq.kg^-1 (378 samples analyzed). Natural radioactivity of granitoids in the eastern part of the Lugicum can be evaluated as low, more or less consistent with the average radioactivity of the continental-type crust. Natural radioactivity of the studied granitoids does not pose any health risk.