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

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