Development of portable cosmic particle tracking devices for civil engineering
Muons are produced at the end of the decay chain of hadrons generated in the collisions of primary cosmic-rays, mostly protons, with the nuclei of the atmosphere. The relativistic time dilatation makes possible to these energetic particles to reach the surface of the Earth with an average energy of few GeV and penetrate to underground. On the surface of the Earth, typically one muon penetrates across our hand in every second.
Muons are continuously interact with the penetrated matter and loses from its energy mostly via ionization process. The energy loss is proportional with the amount (average density × length) of the material. Muography is an imaging technique which based on this fact. It deduces the spatial distribution (average density) of the investigated object via the tracking of cosmic-ray muons with the knowledge of its average density (spatial distribution).
The first demonstration of muography was conducted by E.P. George, who estimated the snow thickness above Australian mines in 1955. The next pioneering experiment was conducted by L. W. Alvarez, who looked for hidden chambers inside the Khepren pyramid with spark chambers in the middle of 1960th. Thanks to the development of detector technology different projects are ongoing world wide with various aims, such as archaeological excavations of pyramids, explorations of underground ore bodies and cavities.
The aim of the Innovative Gaseous Detector R&D group (REGARD) was the application oriented development of muon tracking devices for various applications. The REGARD developed portable (< 10 kg), compact devices with low power consumption (< 10 W) and reasonable angular resolution of about 10-15 mrad for civil engineering. The advantage of these systems is that all of the main detector system modules, such as DAQ, high- and low-voltage units, electronics, and detector layers are integrated into one compact unit. Our systems can be operated remotely for long time and can be installed by non experts. These advantages together broaden the applicability of tracking systems to various research field:
- Our devices are operated by the MTA ELTE Geological and Geophysics Research Group and applied for the explorations of various tunnel systems under Budapest and natural cave systems with muography since 2011 [4,5,6,7].
- We developed dedicated instruments for the measurement of cosmic-ray background in proposed underground laboratories. These systems are used by HZDR in Felsenkeller, Dresden, Germany and by Wigner RCP in Gyöngyösoroszi, Hungary [8,9].
- We are working together with the Earthquake Research Institute of the University of Tokyo and the Japanese NEC Corporation on the development of new tracking systems for borehole-based muography of building structures, such as pillars, tunnels, dams.
- The REGARD is developing a novel imaging technique and device for the discrimination and identification of low-density materials in collaboration with the University of Novi Sad [10,11]. This new techniques is based on the coincidence of cosmic-ray particles and secondary/tertiary photons which is more sensitive for the low-density than the above detailed absorption or scattering imaging techniques.
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Figure 1. Photographs of portable cosmic-ray muon trackers developed for civil engineering[4-6].
Figure 2. Left: simulation and measurements of underground tunnels . Right: Cosmic background measured inside an proposed accelerator-based experiment in HZDR, Germany .
Figure 3. The first cosmic-ray images of bones taken by University of Novi Sad and REGARD.
Author: László Oláh