Exploring the inner structure of Esztramos Hill using cosmic rays

Cosmic-ray muography is a developing geophysical method that uses high energy cosmic muon particles to explore the inner structure of large objects, such as volcanoes, pyramids or mountains. Cosmic muons originate from upper atmosphere and have a known, steady, angle dependent flux on the surface. Muons are absorbed as they pass through matter, depending on the density of the material along their trajectories. By comparing the expected and the measured muon flux and using geoinformatic models of the observed area it is possible to calculate the density distribution inside these structures. Our research group at the HUN-REN Wigner Research Centre for Phyiscs has been conducting muographic measurements in the abandoned iron ore mine of Esztramos Hill (located in northeastern Hungary) for more than six years. Over the years we created muographic images of the hill from multiple drifts, resulting in a detailed understanding of its inner structure around the abandoned parts of the mine and the Rákóczi cave system, the main cave of which is part of the UNESCO World Heritage List. Based on a 3-D muographic inversion, our results were able to confirm the location of partially collapsed, inaccessible mined-out stopes and indicate the existence of a possible cave nearby, which was published in Scientific Reports last year.