Monte Carlo simulations for under-water radon measurements

The following Master Thesis has been performed as part of the European project ArtEmis, whose main goal is to investigate the possibility of using the increased concentration of the radioactive gas radon as an earthquake precursor. Among the natural disasters, earthquakes are particularly frequent and cause thousands of deaths whenever they hit with a large magnitude. Their high mortality is mainly due to their unpredictability in space and time, even though areas with a higher seismic activity can be identified based on geological studies and statistical records. Before an earthquake, microcracks are formed in the surrounding stone structures due to stress, releasing greater than usual amounts of radon gas within the rock pores. A way of finding an earthquake precursor would be to measure the gamma-ray radiation emitted after the radon decay. With this aim, one can place radiation detectors in areas with high seismicity in order to monitor possible changes in radon activity levels. This could be done in soil, groundwater (via springs, wells, and boreholes), or air. This Master Thesis aims to simulate the detection of γ photons emitted by the decay of radon and other isotopes inside a water environment to find useful results for the project development. In this thesis, it will be found that the real gamma spectrum of the studied site in Italy and the simulated one show similar features, which are useful for performing many studies of the behavior of the radon decay process in water. A reasonable volume of water affecting the detected spectrum will be found to acquire a better knowledge of the physics at the studied site and help perform the simulations. The effects of the potassium in the wall are investigated, and the potent effect of water as a screen for radiation is made evident through the simulations, also in comparison with the case of a detector in an air environment. Moreover, it will be shown that, looking at the variations in the radon concentration, it is convenient to use a broader spectrum instead of a smaller one around a peak.