Preliminary survey of outdoor gamma dose rates in Lesvos Island (Greece)

This study reports the first attempt to record the radioactive background due to gamma radiation in Lesvos Island (Greece). The study reports the results from 335 outdoor total gamma effective dose rate measurements conducted using GPS navigation and a Geiger-Mueller detector (Bicron, Micro Sievert) on the whole surface of the island together with a digital map produced by appropriate mapping GIS programme. The study also reports the measurements of outdoor gamma dose rates due to the 238U, 232Th and 40K radionuclides as estimated via in situ gamma-ray spectrometry measurements performed at 26 sites using a 3 x 3 inch NaI (thallium activated) portable detector. The results from the outdoor total gamma effective dose rates range between 0.0023 and 0.28 μSv h-1. The highest outdoor total gamma effective dose rates (0.013-0.28 μSv h-1) were detected in the northeastern part of the island and the intermediate rates (0.066-0.13 μSv h-1) in the central region. The outdoor gamma dose rates due to 238U, 232Th and 40K radionuclides range between 1.7 ± 0.8 and 154 ± 7 nGy h-1 with an average of 86±6 nGy h-1. The average contribution of each of the examined radionuclides (238U, 232Th and 40K) to the total gamma dose rate was found to be equal to 12±4% for 238U, 58±6% for 232Th and 29±7% for 40K, respectively. (authors)