Natural radioactivity in granites and gneisses of the Opava Mountains (Poland): a comparison between laboratory and in situ measurements

The natural radioactivities of five characteristic igneous rocks of the eastern foreland of the Opava Mountains (Eastern Sudetes, Poland), obtained in the laboratory and under in situ conditions, are presented. The activity concentrations of ²³²Th, ²³⁸U, and ⁴⁰K were measured using an HPGe gamma-ray spectrometry system. The ranges of the activity concentrations of ²³²Th were 7-71 Bq kg⁻¹ in the laboratory and 6-68 Bq kg⁻¹ for the in situ measurements. For ²³⁸U, the ranges of the activity concentrations were 5-52 Bq kg⁻¹ in the laboratory and 9-48 Bq kg⁻¹ for the in situ measurements, and for ⁴⁰K, the ranges were 520-1560 Bq kg⁻¹ in the laboratory and 537-1700 Bq kg⁻¹ for the in situ measurements. These determined activity concentrations were compared with the average activity concentrations of the radionuclides in similar types of rocks and with data from the Sudetes available in the literature. No significant differences were found between the in situ and laboratory measurements.