Project
Muography as a new tool for geophysics

Code EXPL/FIS-OUT/1185/2021

Beneficiary Entity

LIP - Laboratório de Instrumentação e Física Experimental de Partículas

Project summary

Muography is an imaging technique that uses natural cosmic muon radiation, produced at high rate by cosmic rays impinging on the Earth atmosphere. Muons can transverse large depths, the flux attenuated  is measured in cross integrated depths of the order order of kg/cm². They are thus powerful probes for imaging large structures. The use of muography has seen a substantial development in the last years. Our team joins different expertise in particle detectors and cosmic ray analysis from LIP, and long tradition in geophysical surveys and analysis from ICT-UÉvora. With a strong support from the Lousal Science  Centre, which will house the final tests in our project. Our goal is to establish the use of RPC-based muography for Earth subsurface surveys. In this exploratory project we will benchmark it in an accessible but realistic setting. It will significantly boost the preparation of the instrument and methods for future use in a number of applications on subsurface geophysics. There are three fundamental pieces for this project: 1) the instrument - which already exists but will be full characterized and optimized in the laboratory; 2) the analysis methods - which are being developed  together between particle physicists and geophysicists; 3) the test site, at Lousal - which needs to be well characterized with independent geophysical techniques, to provide a reference for the first subsurface muographic survey by the team. At the end of the exploratory project, we will have a better knowledge of the geology of Lousal and a direct assessment of the potential of muography for subsurface geophysics. Both the instrument and the  methods will be ready for larger scale projects. Our instrument, the muographer, is a muon telescope composed of four planes of one square meter Resistive Plate Chambers (RPCs) operating with low gas flux, readout by low-power front-end-electronics.  They were developed by the LIP team for application in large open air cosmic ray observatories, where the detector needs to have high autonomy and reliability as for geophysical application. The muographer is now operating in the LIP detector laboratory. The data acquired there will be used for characterization of the instrument, guiding future upgrades, and to optimize image reconstruction  methods. Testing the full muography machinery in the controlled environment of a building is a first step, before the challenging move to Lousal. Integrating particle physics and geophysics techniques is key in this project. Using particle physics tools we will create a full simulation chain which can include all the details of muon propagation over a  detailed geophysical model. Conversely, we will make the geophysical model inversion starting from the typical coordinate system of muography, which better accounts for the particle physics aspects. At Lousal there is an underground gallery providing a diversity of well-controlled geological structures to analyse at the meter scale. The local setting includes Paleozoic age sedimentary and volcanic rocks and the regional Corona fault. We will first construct a detailed model from existing large scale information and specific local knowledge gathered during the project, with surveying methods independent of  muography. It will be used to guide our muographic survey, configuring different scenarios for observation. The first 2D muographs will be confronted with the one expected from the full simulation, including all the available density information. The full geophysical analysis will be done using only other constraints, in  order to independently obtain the 3D density mapping from the muographic data. We aim at identifying independently the geological structures we already know about, providing an end-to-end test of muography. The muographic data will then be used to increase the precision of the density  mapping at Lousal, in a first real case application. These results will pave the road for future scientific projects and also industrial applications. The test in an underground gallery opened to the public mimics the usage of muography in an operating mine, for  example to prevent accidental explosions from inadverted perforation of gas pockets in salt explorations. This and other uses will become possible by the experience in the use of the instrument and methods  gained in this project.

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Support under

Reforçar a investigação, o desenvolvimento tecnológico e a inovação

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Acknowledgements