Natural gamma-radiation in the Aeolian volcanic arc

Pulse-height distributions of γ-rays, obtained with a field NaI(Tl) scintillation spectrometer in numerous sites of the Lipari and Vulcano islands (Aeolian volcanic arc, 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 felsic units of the volcanic series. The higher values of U (15.7–20.0 ppm) coincide with higher Th (48.3–65.9 ppm) and K (4.9–6.1%) concentrations associated with rhyolitic rocks of the third cycle (<50 ky). The air absorbed dose 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-ray contribution is also evaluated to estimate the total background radiation dose rate.