Three-dimensional localization of Radon source conduits inside the Temperino mine (Tuscany-Italy) with the muon radiography technique

Abstract

Muon radiography, or muography, is a non-invasive technique allowing imaging of the interior of large structures (target) thanks to the study of the absorption of atmospheric muons in materials. The muons absorption effect depends not only on the thickness, but also on the density of the target. Careful comparisons of the muographic results with simulations taking into account a precise description of the target's geometry, allow estimating the two dimensional distribution of the average density of the structure under study as seen from the measurement point of view. In this presentation an application in the geological field for the research and localization of low density anomalies attributable to cavities inside an abandoned mine will be shown. The aim of the study is to identify and locate areas that might be responsible for the production of anomalous concentrations of radon gas inside underground mining sites used for touristic itineraries. Radon is a natural radioactive gas that exposes tourists to ionizing radiation. Radon decay products are the second cause of lung cancer after smoking. It is important therefore to understand where the radon gas comes from before moving through the different galleries. The case study is the Temperino mine near Campiglia Marittima (LI-Italy). Here, the mining activity ended in 1980 and it was primarily focused on the extraction of copper, silver lead and zinc minerals. The area to be explored with muon radiography is part of an area dating back to the Etruscan period that has not yet been completely mapped and that is located above the tourist path of the Temperino mine at a depth of about 40 m from the surface of the hill above. Any nearby cavity could represent a prime conduit that brings radon gas into the tourist trail. The identification and localization in space of these ancient excavations is also interesting from a geological and archaeological point of view. The detector employed for the muographic measurements reported in this presentation, designed in Florence by the National Institute of Nuclear Physics (INFN) and the Department of Physics and Astronomy, is called MIMA (Muon Imaging for Mining and Archaeology) and has cubic shape and approximate dimensions of (50x50x50) cm3. MIMA is equipped with a special protective aluminum mechanism that allows its altazimuth orientation.