Articles | Volume 9, issue 6
Solid Earth, 9, 1517–1533, 2018
Solid Earth, 9, 1517–1533, 2018

Research article 21 Dec 2018

Research article | 21 Dec 2018

The effect of rock composition on muon tomography measurements

Alessandro Lechmann1,*, David Mair1, Akitaka Ariga2, Tomoko Ariga3, Antonio Ereditato2, Ryuichi Nishiyama2, Ciro Pistillo2, Paola Scampoli2,4, Fritz Schlunegger1, and Mykhailo Vladymyrov2 Alessandro Lechmann et al.
  • 1Institute of Geological Sciences, University of Bern, Bern, Switzerland
  • 2Albert Einstein Center for Fundamental Physics, Laboratory for High Energy Physics, University of Bern, Bern, Switzerland
  • 3Faculty of Arts and Science, Kyushu University, Fukuoka, Japan
  • 4Dipartimento di Fisica “E.Pancini”, Università di Napoli Federico II, Naples, Italy
  • * Invited contribution by Alessandro Lechmann, recipient of the EGU Seismology Outstanding Student Poster and PICO Award 2016.

Abstract. In recent years, the use of radiographic inspection with cosmic-ray muons has spread into multiple research and industrial fields. This technique is based on the high-penetration power of cosmogenic muons. Specifically, it allows the resolution of internal density structures of large-scale geological objects through precise measurements of the muon absorption rate. So far, in many previous works, this muon absorption rate has been considered to depend solely on the density of traversed material (under the assumption of a standard rock) but the variation in chemical composition has not been taken seriously into account. However, from our experience with muon tomography in Alpine environments, we find that this assumption causes a substantial bias in the muon flux calculation, particularly where the target consists of high {Z2A} rocks (like basalts and limestones) and where the material thickness exceeds 300 m. In this paper, we derive an energy loss equation for different minerals and we additionally derive a related equation for mineral assemblages that can be used for any rock type on which mineralogical data are available. Thus, for muon tomography experiments in which high {Z2A} rock thicknesses can be expected, it is advisable to plan an accompanying geological field campaign to determine a realistic rock model.

Short summary
Muon tomography is a technology, similar to X-ray tomography, to image the interior of an object, including geologically interesting ones. In this work, we examined the influence of rock composition on the physical measurements, and the possible error that is made by assuming a too-simplistic rock model. We performed numerical simulations for a more realistic rock model and found that beyond 300 m of rock, the composition starts to play a significant role and has to be accounted for.