Natural Radionuclides in the Building Materials From the Region of The Small Carpathians

Distribution of radionuclides in the main rock types: granodiorites, biotite-gneisses, black shale and amphibolites at the locality Pezinok - Kolársky vrch was studied in samples from two boreholes. Concentrations of ²³⁸U, ²³²Th and ⁴⁰K in the samples were analysed by gamma spectroscopy (concentrations of ²³⁸U were 0.091 - 37.800 mg/kg, ²³²Th 0.534 - 13.234 mg/kg, ⁴⁰K 0.116 - 5.162 mg/kg). The highest average ²³⁸U concentration was in black shale, highest average ²³²Th concentration in granodiorite and highest average ⁴⁰K concentration in granodiorite. 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. The source of ²³⁸U and ²³²Th (and partially also of ⁴⁰K) is in the granodiorite intrusion. During the metamorphic process, Uranium was mobilised 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.