Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)

Natural radioactivity of the rock environment in Czech show caves (Bozkov Dolomite Caves, Koněprusy Caves, Chýnov Caves)


Jiří Zimák, Jindřich Štelcl

Geoscience Research Reports 38, 2005 (GRR for 2004), pages 126–129

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Concentrations of natural radioactive elements (K, U and Th) were measured using a field gamma-ray spectrometer GS-256 in the rocks in the Bozkov Dolomite Caves, Koněprusy Caves, and Chýnov Cave. Concentrations of these elements were converted to the mass activity of 226Ra equivalent (am) in order to express gamma-ray activity at the studied sites. Average values of am of metamorphic rocks (dolomite marbles and quartzites), sinters, and cave clastic sediments in the Bozkov Dolomite Caves are 99, 70, and 128 Bq . kg-1, respectively. Marbles and cave clastic sediments in certain parts of the Bozkov Dolomite Caves (so-called Nová Cave) have increased contents of uranium (up to 11 ppm U in marbles). The monitored zones of the Koněprusy Caves are characterized by low average am values of Devonian limestones and also sinters (70 and 54 Bq . kg-1, respectively). Average am value of Silurian dolostones in the Koněprusy Caves area is 138 Bq . kg-1 (up to 12 ppm U in the rocks). The relatively high natural radioactivity of cave clastic sediments in the Koněprusy Caves (171 Bq . kg-1 average, 306 Bq . kg-1 maximum) is caused by high contents of K, U, and especially Th (up to 33 ppm). Average am values of marbles, calc-silicate rocks, amphibolites, and cave clastic sediments of the Chýnov Cave are much lower, reaching respective values of 23, 72, 60, and 73 Bq . kg-1.