MUCH: An Imaging Cerenkov Telescope for Volcano Muography

Abstract

In the last decades, several attempts have been made to investigate internal structures of large bodies, such as volcanoes, with transmission muography. High spatial resolution and reduction of the strong background noise, due to protons, electrons, and scattered low-energy muons, are the main challenges for this technique. As a possible solution to fulfill these requirements, muography with Imaging Atmospheric Cerenkov Telescopes (IACTs) has been recently proposed and the feasibility demonstrated by our team using GEANT4 simulations. IACTs are telescopes dedicated to gamma-ray astronomy consisting of an optical system that focuses the Cerenkov light into a high-sensitive and fast read-out camera. Muons with energy above about 5 GeV induce Cerenkov radiation which is emitted in a cone with a constant opening angle around their travel direction. As IACTs image in angular space, the Cerenkov light focused onto the camera forms a ring-shaped image centered at a distance from the focal plane center proportional
to the muon incidence angle. None of the previously mentioned sources of background is expected to affect the IACTs muon signal. Here, we present MUCH, a lightweight and compact IACT design, specifically dedicated to volcano muography. The telescope design is based on a SiPMs camera working in the 280 nm–900 nm wavelength band, equipped with fast readout electronics with single-photon counting capability. The proposed Schmidt-like optical system is composed of a 2.5 m aspherical mirror and a 2.5 m PMMA Fresnel lens corrector. It results in a field of view of about 12°, an entrance pupil of 2.5 m diameter, and an angular resolution better than 0.2° throughout the entire FoV which allows us to determine the muon direction with a reconstruction precision better than a few tenths of a degree. A Geant4 framework for the simulation of Fresnel lenses and aspherical mirrors is currently being developed for the telescope prototype achievement.