Abstract
Muography (or muon radiography) is a technique that exploits the penetration capability of muons, elementary particles similar to electrons but with a mass about 200 times larger. High energy muons are naturally produced in the interactions of cosmic rays with the Earth atmosphere. The measurement of their absorption in matter allows the imaging of the inner structure of large bodies. The technological developments in the detection of elementary particles have opened the way to its application in various fields, such as archaeology, studies of geological structures, civil engineering and security issues. We have developed a new approach to the three-dimensional muography of underground structures, capable of directly localising hidden cavities and of reconstructing their shape in space. Our measurements at Mt. Echia, the site of the earliest settlement of the city of Naples in the 8th century BC, have led us to the discovery of a hidden underground cavity, whose existence was not evident with the usual two-dimensional muography graphs. We demonstrate here that our original approach definitely enhances muography discovery potential, especially in case of complex underground systems.
Highlights
Muography is a technique that exploits the penetration capability of muons, elementary particles similar to electrons but with a mass about 200 times larger
Muography is an imaging technique that profits from the penetrating power of elementary particles called muons, similar to electrons but with a mass about two hundred times larger
Almost forty years later, muography was applied to the investigation of the inner structures of volcanic edifices[2,3,4,5,6,7,8,9,10,11,12,13], facing the challenge posed by the observation of the low muon fluxes surviving the traversal of a large rock thickness typical of this application
Summary
The two muon trackers (called MU-RAY and MIMA) used for the measurements reported in this paper are real-time electronic devices that operate autonomously, with remote control and readout. The light generated by muons in the plastic scintillator bars is detected by Silicon Photomultipliers (SiPMs) These photosensors, recently developed, are solid-state devices that, as such, do not require any high voltage supply and have a very low power consumption. The basic module of the MU-RAY muon tracker[7,8,24] is a planar array of 64 plastic scintillator bars. MIMA29 is a smaller muon tracker basically using the same technique, except that the SiPMs are in direct contact with the scintillator bars (i.e. no wavelength shifter is used). The outer XY planes are formed by two orthogonal arrays of 21 scintillator bars. The central XY plane, with a coarser structure and formed by scintillator bars of rectangular section, is used as a constraint in muon tracking.
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