Density imaging of volcanos with atmospheric muons

Their long range in matter renders high-energy atmospheric muons a unique probe for geophysical explorations, permitting the cartography of density distributions which can reveal spatial and possibly also temporal variations in extended geological structures. A Collaboration between volcanologists and (astro-)particle physicists, Tomuvol, was formed in 2009 to study tomographic muon imaging of volcanos with high-resolution tracking detectors. Here we discuss preparatory work towards muon tomography as well as the first flux measurements taken at the Puy de Dôme, an inactive lava dome volcano in the Massif Central. 1. The Puy de Dôme as a reference site for muon imaging High-energy atmospheric muons have been considered for more than half a century as a natural probe for geophysical and archaeological prospection. As early as 1955, muon imaging techniques were used to estimate the snow overburden on a mountain tunnel [1] and shortly thereafter, in the early 1960s, to search for hidden chambers in Chepren’s pyramid [2]. Recent developments in particle physics have resulted in scalable tracking detectors with very fine segmentation which facilitate the application of muon imaging to larger structures. This has stimulated an interdisciplinary collaboration between volcanologists and (astro-)particle physicists on the design of a robust, portable system for muon tomography of volcanos with the intention of computing a three-dimensional density model by combining the results of several muon absorption measurements around a volcano. In this way, muon imaging can contribute to the understanding of volcanic structures and might possibly also help in risk prevention. Initiated in 2009, the Tomuvol project aims to turn the Puy de Dôme, an inactive lava dome in the Châıne des Puys [3] (Massif Central, France), into a reference site where muon tomography can be compared to and combined with gravimetric and electrical resistivity measurements. In the initial phase, muon flux measurements have been performed at a site on the flank of the Puy de Dôme and the data are now analyzed for a first radiographic image. The next phase is dedicated to taking a detailed three-dimensional map of the density distribution in the lava dome and to validate the results by comparing with gravimetric and electrical resistivity measurements. In the future, after improvement of the portability of the system, the same methodology might be applied to other targets. Here we report on preparatory work and measurements taken at the Puy de Dôme in the initial phase of the project. In Section 2, the detection site and the experimental setup are described in some detail. Preliminary results of the first months of data taking are then presented in Section 3. Based on this, we assess the prospects of muon imaging in the concluding section. in 2p 300 66 34 46 , v er si on 1 27 J an 2 01 2 Author manuscript, published in "12th International Conference on Topics in Astroparticle and Underground Physics (TAUP 2011), Munich : Germany (2011)"