Natural radioactivity of rocks from the historic Jeroným Mine in the Czech Republic

This study reports the natural radioactivity of characteristic rocks found in the historic Jeroným Mine of the Czech Republic as measured under the laboratory conditions. The rocks analyzed included granites and schists weathered to varying degrees and collected from different levels of the underground workings of the Jeroným Mine. The mine itself has been subject to metal extraction (mainly tin and tungsten) since the sixteenth century and has recently been developed as a cultural and scientific attraction open to the public. Activity concentrations of 40K, 232Th and 238U were measured from nine rock samples using gamma-ray spectrometry. The activity concentrations of 40K varied from 595 Bq kg−1 to 1244 Bq kg−1, while 232Th varied from 25 Bq kg−1 to 55 Bq kg−1. The activities associated with 238U ranged from 46 Bq kg−1 to 386 Bq kg−1. The measured activities were used to estimate two radiation hazard indices typically applied to building materials, the activity concentration index I and the external hazard index Hex. Mean respective values of 1.02 and 0.77 for I and Hex indicate that the rocks found in the Jeroným Mine meet radiological safety standards for building materials and do not pose a risk to potential tourists and staff.