Peter ANDRÁŠ^1,2, Vojtech DIRNER² & Andrea HORŇÁKOVÁ^3
1Faculty of Natural Sciences, Matej Bel University, Tajovského 40, 974 01 Banská Bystrica, andras@savbb.sk
² VŠB-Technical University of Ostrava, 17. listopadu, 15/2172, 708 33 Ostrava – Poruba, vojtech.dirner@vsb.cz
³ Slovak Environmental Agency, Tajovského 10, 040 01 Košice, andrea.hornakova@sazp.sk

DETERMINATION OF ²³⁸U, ²³²Th AND ⁴⁰K ACTIVITY IN THE ROCKS USED IN CIVIL ENGINEERING FROM THE MALÉ KARPATY MTS. (SLOVAKIA)

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The distribution of natural radionuclides in the main rock-types: granodiorites (granites), biotite-gneisses, black shales and amphibolites from the Malé Karpaty Mts. complex was studied in samples collected from two boreholes. The samples were analyzed by means of gamma-ray spectrometry.
The concentrations of ²³⁸U, ²³²Th and ⁴⁰K were found to be within the range of 0.091 – 37.800 mg/kg (²³⁸U), 0.534 – 13.234 mg/kg (²³²Th), and 0.116 – 5.162 mg/kg (⁴⁰K). The highest average ²³⁸U concentration was in black shale, highest average ²³²Th concentration in granodiorite-granite and highest average ⁴⁰K concentration in granodiorite - granite as well. Activities of ²³⁸U were determined within the range of 1.092 – 48.960 Bq/kg (with exception of one anomalous value – 453.6 Bq/kg), activities of ²³²Th within the range of 2.189 – 54.298 Bq/kg and activities of ⁴⁰K within the range of 30.933 – 1,376.499 Bq/kg. It is considered that the source of ²³⁸U and ²³²Th (and partially also of ⁴⁰K) is in the granitoide intrusion. Uranium was during the metamorphic process mobilised from granitoides to the black shales.

The concentrations and consequently the total activities of ²³⁸U, ²³²Th and ⁴⁰K in the studied rock samples exceed the permitted limit values for building materials. It is possible to recommend their utilisation only for external purposes.