Natural gamma-radiation in the Aeolian volcanic arc

Pulse-height distributions of gamma -rays, obtained with a field NaI(TI) sc intillation spectrometer in numerous sites of the Lipari and Vulcano island s (Aeolian volcanic are, Italy), were measured to determine the U, Th and K concentrations of the bedrock and the relative values of the air absorbed dose rate. U is spatially related to both Th and K and the Th/U ratio is on average 3.1-3.5. The magmatic evolution is reflected by the concentration of the three radioelements, as they are more abundant within the more felsi c units of the volcanic series. The higher values of U (15.7-20.0 ppm) coin cide with higher Th (48.3-65.9 ppm) and K (4.9-6.1 %) concentrations associ ated with rhyolitic rocks of the third cycle (< 50 ky). The air absorbed do se rate varies from 20 to 470 nGy h(-1). The highest values (> 350 nGy h(-1 )) are observed on outcrops of rhyolitic obsidian lava flows. The cosmic-ra y contribution is also evaluated to estimate the total background radiation dose rate. (C) 2001 Elsevier Science Ltd. All rights reserved.