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Observing in‐conduit physical mechanism underlying the switching of eruptive activity between the craters of multi‐vent volcanoes could contribute to hazard assessment at these complex volcanic edifices. We performed monitoring of mass density changes beneath two active craters of Sakurajima volcano in Kyushu, Japan between September 2018 and July 2023 with cosmic‐ray muography. From December 2022, the mass density decreased beneath Minamidake crater and increased beneath Showa crater in accordance with a switch of eruptive activity from Minamidake crater to Showa crater. Plug formation and convective magma degassing processes have been observed with muography in accordance with the deformation of the surface of volcanic edifice measured by Interferometric Synthetic Aperture Radar. We found a moderate inverse correlation with a Pearson's coefficient of −0.52 between the mass densities observed beneath the two active craters throughout the entire period. The inverse correlation of mass densities indicates a magmatic gas flux dynamics which characterizes a branched conduit structure. Muography thus reveals the shallow magmatic processes during switching of eruptive activity between the craters of multi‐vent volcanoes and allows to infer to the conduit structure. Plain Language Summary: Observing the changing of structure and amount of materials in the upper plumbing systems of active volcanoes can contribute to the visualization the ongoing volcanic phenomena and assessing of related hazards. For instance, the increase in mass density indicates the uprise of deep volcanic materials in the conduit that may result in the onset of eruption. We measured the directional dependent yield of naturally occurring cosmic‐ray muon particles across the active Sakurajima volcano in Kyushu, Japan. We utilized muography to visualize the changes in mass density structure beneath the erupting craters over time. The captured muon images revealed that the mass densities varied inversely underneath the Minamidake and Showa craters throughout the measurement period. The observed inverse correlation between the mass densities indicates a branched linkage between the conduits of the two active craters. Key Points: Muography is utilized for visualizing and monitoring the mass density changes beneath the active craters of Sakurajima volcano, Kyushu, JapanInverse correlation is found between the mass densities observed beneath the two active cratersA branched linkage between the conduits of active craters inferred from the changes of eruptive activity and mass densities [ABSTRACT FROM AUTHOR]

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Muography is an innovative imaging technique using naturally produced elementary particles – atmospheric muons – used to determine the distribution of density inside massive objects. The modification of the particles flux – by scattering or absorption – reflects the contrasts in density within the medium and therefore offers the possibility for an image of the crossed volumes. In most muography setups the imaging process is based on the tracking of the particles which accounts for the absorption or the scattering of the muons trajectories. Neither the energy nor the identity of the particles (the so-called PID) is exploited since this information traditionally relies on the use of calorimeters and/or high intensity magnetic fields. Both these techniques hinder detector portability which in the case of muography is important and this renders them impractical for its purpose. In this paper we characterize the performance of a simple and small water Cherenkov detector capable of providing some insights on the energy of muons and the PID for the crossing particles that could potentially improve the background rejection for a muography survey when operating in conjunction with a muon telescope. We tested a prototype of such water Cherenkov detector in combination with two small muon hodoscopes. Both systems are using the same opto-electronics chain – optical fibers and pixellized photosensors – and the same data acquisition (DAQ) readout system which ensures an easy integration and implementation within presently running systems. This article presents the test setup, the detector response to cosmic muons and its performance evaluation against a basic simulation of its geometry and detection principle.

The method for visualizing the internal structure of objects (muography method) based on the analysis of the features of passages of atmospheric muons generated in cosmic ray interactions, is based on the spatial distributions of trajectories of penetrating muons recorded by detectors. The method is at the junction of elementary particle physics with many other areas of natural science, e.g., with archaeology. The article presents the results of a muographic study of two objects in the cave complex of a unique historical and archaeological monument, i.e., the Holy Dormition Pskovo-Pechersky Monastery. The experimental technique is based on nuclear emulsion detectors. [ABSTRACT FROM AUTHOR]

In recent years, the use of high-penetrate cosmic-ray muons has been used in many applications to investigate the internal structure and composition of large material. The muon attenuation is based on multiple Coulomb scattering. This study was aimed to investigate the effect of massive shielding material composition in muon tomography. Muon with various energies between 1 MeV to 100 MeV was used as a source located directly above the shielding material with different density and composition. The output of scattered muon was scored in 2 and 5 km after the material. The simulation was performed using particle and heavy ion transport system (PHITS) software developed by Japan Atomic Energy Agency. The attenuation and scattering of the muon depends predominantly on the shielding material density. The muon energy and flux was decreased with increasing depth of the muon detector. This muon tomography can be applied in investigating the structure and internal composition of unknown materials such as volcanic structures in Indonesia.

Secondary particles will always be generated in particle-to-matter interactions. The interaction of muons with matter produces various secondary particles. In this study, secondary particles produced by the interaction between muons with energies of 5, 50, 100, 200 and 500 MeV with water were analyzed using the PHITS Monte Carlo package. The muon source is placed on the surface of water that has a thickness of 1 km. The muography technique was applied by placed a detector at a depth of 1 km from the source. This detector records the secondary particles produced by the interaction. The results obtained show that this interaction produces secondary particles in the form of photons and neutrons in the detector. The number and energy of these photons and neutrons are strongly influenced by the initial energy of the muon. Muons with the lowest energy of 5 MeV produce more secondary particles than any other energy by a factor of 10. Low-energy muons travel slowly, allowing more interactions to occur and increasing the number of secondary particles in the detector. The energies of neutrons and photons in the detector are at most 3.76 MeV and 5.3 MeV, respectively.

Muography is increasingly used to image the density distribution of volcanic edifices, complementing traditional geophysical tomographies. Here, we present a new muon data processing algorithm, and apply it to a new generation of scintillator-based muon detectors, to image the relative density distribution in La Soufrière de Guadeloupe volcano (Lesser Antilles, France). Our processing method iteratively searches for the best fit of each muon trajectory, accounting for all the hits registered by the detector related to the particular muon event. We test the performance of our algorithm numerically, simulating the interaction of muons with our detector and accounting for its exact assemblage including the scintillator bars and lead shielding. We find that our new data processing mitigates the impact of spurious signals coming from secondary particles, and improves the amount of successfully reconstructed events. The resulting 2-D muon images at La Soufrière have higher angular resolution than previous ones and capture the heterogeneous structure of the dome. They show density anomalies located on the summit southern region, which includes a boiling acid lake and degassing fractures, where the rock is the most porous and fumarolic activity is ongoing. This work shows the importance of combining numerical simulations of muon propagation with precise raw data processing to obtain high-quality results. It is also a first step towards fully assessing the noise contamination sources when performing muon tomography, and their correction, prior to geophysical interpretations. [ABSTRACT FROM AUTHOR]

Transmission-based muography (TM) is an innovative imaging technique based on the measurement and analysis of the cosmic ray muons flux attenuation within the target under investigation. This technique allows imaging inner-body density differences and has successfully been applied in a wide range of research fields: geology, archaeology, engineering geology and civil engineering. The aim of this study is to show the reliability of TM as an innovative, noninvasive geophysical method for ore body prospecting and other mining related studies. The measurements were carried out at the Temperino mine in the San Silvestro Archaeological and Mining Park (Campiglia Marittima, Italy), where several magmatic and metasomatic geological units are embodied. Among them, a Cu–Fe–Zn–Pb(–Ag) sulfide skarn complex primarily composed by hedenbergite and ilvaite minerals. Using the acquired muon imaging data obtained with the MIMA (Muon Imaging for Mining and Archaeology) detector prototype (cubic detector of 0.5 × 0.5 × 0.5 m3), the presence of a high-density vein inside the skarn body within the rock volume above the muon detector was identified, localized and interpreted. Applying a back-projection algorithm to the obtained 2D transmission map made it possible to estimate and visualize as point cloud data, in a 2D or 3D environment, the identified high-density body and its relative distance from the detector. The results of this study highlight the potential of muography as a support tool to other geophysical methods in the field of mining exploration. [ABSTRACT FROM AUTHOR]

Despite the important hydrological and ecological implications of the snowpack, its real time monitoring remains challenging. This is particularly relevant in relation to the Snow Water Equivalent (SWE), as the available technologies which measure it, exhibit a number of limitations that hinder their operational implementation. In this work, we explore the potential of a new technology, Muon Scattering Radiography, to infer the SWE. We coupled snowpack simulations generated by the SNOWPACK model, with a muon scattering simulation program based on GEANT4. The SWE is modeled as a function of the muon scattering distributions. Predictions of the SWE along the year are provided showing a root‐mean‐square error of 12 mm for 5 hr continuous measurements. We also performed laboratory measurements using ice samples, confirming the SWE estimation capabilities and the potential of the technique to operate as a SWE monitoring tool. Plain Language Summary: The monitoring of the seasonal snowpack is important to understand and predict the dynamics of the hydrological and ecological processes, but its continuous monitoring is still a scientific challenge. Particularly in relation to the Snow Water Equivalent (SWE). The available technologies to monitor the SWE exhibit a number of limitations that prevent its use in many real world cases. Here we explore the potential of a new technology, Muon Scattering Radiography (MSR), to quantify the SWE. MSR is a technique based in the detection of the natural and innocuous radiation of muon particles. The technique consists in the measurement of muon deviations, which are larger when the muons cross very large or dense materials. In this analysis, we simulated the snowpack evolution itself and its measurement process. Then, we determined the relation between muon deviations and SWE. Finally, we estimated the precision in the determination of SWE comparing the predictions to the ground truth in simulation. The results yielded a precision of about 12 mm. We also performed laboratory measurements with ice samples, using a 4 layer muon detector based on multiwire proportional chambers, confirming the potential of the technique to operate as a SWE monitoring tool. Key Points: We test the suitability of Muon Scattering Radiography to infer the Snow Water Equivalent (SWE)Numerical simulations show the technique can estimate the SWE with a precision of around 12 mmLaboratory measurements confirm the results obtained with simulation [ABSTRACT FROM AUTHOR]

Muography requires a detailed understanding of the absorption of muons in the material situated between the muon source and the detector. A large-statistics (>3 billion event) Geant4 simulation was run to simulate the absorption of muons in different thicknesses of concrete layers and to determine the effect of the material on the energies of muons that were not absorbed. The Geant4 simulation included a simple detector placed directly behind the absorbing material. A Geant4 simulation was also run for the same detector for alpha sources with no absorbing material and the results of this simulation were compared to the signals from the physical detector built in the laboratory and measured using standard alpha sources. The large-statistics simulations using muons of different energies were compared to the predictions of muon absorption from existing literature. The results of the simulations were in good agreement with both the measured signals from the laboratory as well as the predictions from the literature and the general method is found to be well-suited for studies used for muography involving material layers of uniform thickness. [ABSTRACT FROM AUTHOR]

Cosmic-ray muon imaging is a new non-destructive technique that uses highly penetrating natural muon to reconstruct objects with high atomic number (Z) or subjects hidden in something by applying muon scattering or transmission technique, respectively. Up till now, muography mainly focused on objects with high Z or large volume. But few studies have been reported on objects at small scale with low or medium Z in China. A method that aims to reconstruct 3D image for objects at small scale as well as low or medium Z has been brought out in this paper, which uses the amount of muonic secondary particles and coinciding muon trajectories in different directions to reconstruct objects. A simulation about how muonic secondary particles generate and their performances based on Geant4 toolkit was carried out. The results of this simulation show that the secondary particles are mainly composed of secondary electrons and gamma photons. And as the thickness of the objects increases along one certain direction, the amount of secondary particles increases approximately linearly. Therefore, the amount of them carries the shape and location information of objects. Furthermore, the energy of muonic secondary particles is mainly beyond 01 MeV, so secondary particles can be distinguished with the background noise in the experimental environment. After selecting coincide muon trajectory through injected cosmicray muon and its secondary particles coincide detection technique, the 3D images of three 3 cm×3 cm×3 cm cubes made up from different materials (iron, water, and lead) were reconstructed based on limitedangle computed tomography algorithm. It can be seen from the imaging results that the reconstructed image of iron has best quality. Both water and lead have some voids in their reconstructed images, but the voids of water is apparently less than those of lead. Thus, this imaging method is fit for imaging small scale objects with low or medium Z and the imaging effect of objects at the small scale with medium Z is especially good. A reconstruction of complex objects which is defined as “USC” letter model has also been made. The reconstructed image can match with the size and location of the geometry model in Geant4 and can also distinguish the intervals of 08 cm in the letter “S”. A much better imaging accuracy will be achieved by optimizing the mathematical model of the algorithm. This method extends the application area of muon tomography.

The Muon Telescope, MuTe, is an instrument for imaging volcanoes in Colombia. It consists of a scintillator tracking system and a water Cherenkov detector for particle energy measurement. The Muon Telescope operates autonomously in high-altitude environments where the temperature gradient reaches up to 10 °C. In this work, we characterize the telescope silicon photomultipliers' breakdown voltage, gain, and noise for temperature variations spanning 0 to 40 °C. We demonstrate that the discrimination threshold for the Muon Telescope hodoscope must be above 5 photo-electrons to avoid contamination due to dark count, crosstalk, and afterpulsing. We also assess the detector counting rate depending on day-night temperature variations. [ABSTRACT FROM AUTHOR]

Muons are constantly produced in cosmic-rays and reach the Earth surface with a flux of about 160 particles per second per square meter. The abundance of muons with respect to other cosmic particles and their capability to cross dense materials with low absorption rate allow them to be exploited for large scale geological or human-made object imaging. Muon radiography is based on similar principles as X-ray radiography, measuring the surviving rate of muons escaping the target and relating it to the mass distribution inside the object. In the course of decades, after the first application in 1955, the methodology has been applied in several different fields. Muography allows us to measure the internal density distribution of the investigated object, or to simply highlight the presence of void regions by observing any excess of muons. Most of these applications require the detector to be installed below the rock being probed. In case that possible installation sites are not easily accessible by people, common instrumentation cannot be installed. A novel borehole cylindrical detector for muon radiography has been recently developed to deal with these conditions. It has been realized with a cylindrical geometry to fit typical borehole dimensions. Its design maximizes the geometrical acceptance, minimizing the dead spaces by the use of arc-shaped scintillators. The details of the construction and preliminary results of the first usage are described in this paper. [ABSTRACT FROM AUTHOR]

Abstract Despite the important hydrological and ecological implications of the snowpack, its real time monitoring remains challenging. This is particularly relevant in relation to the Snow Water Equivalent (SWE), as the available technologies which measure it, exhibit a number of limitations that hinder their operational implementation. In this work, we explore the potential of a new technology, Muon Scattering Radiography, to infer the SWE. We coupled snowpack simulations generated by the SNOWPACK model, with a muon scattering simulation program based on GEANT4. The SWE is modeled as a function of the muon scattering distributions. Predictions of the SWE along the year are provided showing a root‐mean‐square error of 12 mm for 5 hr continuous measurements. We also performed laboratory measurements using ice samples, confirming the SWE estimation capabilities and the potential of the technique to operate as a SWE monitoring tool.

A machine learning (ML) algorithm (deep neural network) is presented to suppress background in muography applications mainly targeting volcanoes. Additionally it could be applied for large scale geological structures, such as ophiolites. The detector system investigated in this article is designed to suppress the low energy background by applying up to 5 lead absorber layers arranged among 8 detectors. This complicated system was simulated with a Monte-Carlo based particle simulation to provide training sample for the ML algorithm. It is shown that the developed deep neural network is capable of suppressing the low energy background considerably better than the classical tracking algorithm, therefore this additional suppression with ML yields in a significant improvement. The target areas of volcanoes lie beneath approximately a kilometer of rock that only a fraction of a percent of muons have enough energy to penetrate. The ML algorithm takes advantage of the directional changes in the absorbers, as well as the correlation between the muons energy and the deposited energy in the detectors. Identifying very high energy muons is also a challenge: the classical algorithm discards considerable fraction of 1 TeV muons which create multiple hits due to bremsstrahlung, while the ML algorithm easily adapts to accept such patterns.

We report measurements of muon flux over the sky of the city of Bogotá at 4°35′56′′ north latitude, 74°04′51′′ west longitude, and an altitude of 2657 m above sea level, carried out with a hodoscope composed of four stations of plastic scintillators located equidistant over a distance of 4.8 m. Measurements were taken at different zenith (θ) angles within the range 1.5 °   ≤   θ   ≤ 90 ° , the muon flux data is statistically consistent with a cos 2 θ dependence, with a χ 2 per degree of freedom near unity. If instead, we fit to a cos n θ we obtain n   =   2.145 ± 0.046 with a lower χ 2 per degree of freedom. Integrating the muon flux distribution as a function of the zenith angle over the solid angle of the upper Earth's hemisphere allows an estimation of the atmospheric vertical muon rate at the altitude and latitude of Bogota obtaining a value of 255.1   ±   5.8 m − 2 s − 1 . This estimate is consistent with an independent direct measurement of the vertical muon flux with all detectors stacked horizontally. These measurements play a key role in the further development of detectors, aimed to perform muon imaging of Monserrate Hill, located in Bogotá, where the detectors will be placed at similar locations to those used in the present study. [ABSTRACT FROM AUTHOR]

A cosmic muon imaging system is essentially a particle tracking detector as known from experimental High Energy Physics. The Multiwire Proportional Chamber (MWPC) once revolutionized this field of science, and as such it is a viable choice as the core element of an imaging system. Long term construction and operation experience was gathered from a Japanese–Hungarian collaboration that gave rise to the MWPC-based Muon Observatory System (MMOS), and is being used in Japan at the Sakurajima volcano. The present paper attempts to draw conclusions on the thermal and mechanical limits of the system, based on controlled measurements and detailed simulations. High temperature behavior and effects of thermal cycling and conditioning are presented, which appear to consistently allow one to propose quality control criteria. Regarding mechanical stability, the relation between gluing quality (tensile strength) and expected stress from vibration (during transportation) determines the safety factor to avoid damages. Both of these are presented and quantified in the paper using a conservative and austere approach, with mechanical simulations validated with experimental modal testing data. One can conclude that mechanical stress during industrial standard air freight shipping conditions is nearly a factor of three below the calculated maximum stress. [ABSTRACT FROM AUTHOR]

Transmission muography is a non-invasive and non-destructive imaging method which allows to estimate the integrated density of a volume in a given direction (also referred as opacity). It is used in multiple societal applications like archaeology, nuclear safety or geoscience. It relies on the reconstruction of muon tracks that crossed the studied volume compared to the corresponding open sky expectation. The portable experimental setups developed by CEA/Irfu group operates four Micromegas gaseous detectors, HV and DAQ modules, and an embedded computer allowing remote control. Used Micromegas detectors have a multiplexed readout to optimize the DAQ system, while keeping good spatial resolution. However, the natural muon flux is relatively low, so muography images could have high levels of statistical noise, which would be propagated to the reconstructed 3D images. For this reason, we propose three new methods, using machine learning, which increase significantly the quality of 2D images and 3D tomographies. We developed a new demultiplexing method for the Micromegas. It showed its efficiency both for 1D and 2D multiplexed detectors, in a hodoscopic tracker and a Time Projection Chamber (TPC). In the TPC, this method can embed a particle identification between muon-hits and electron-hits. We demonstrated how neural networks could denoise muography images. In the context of the scanning of a nuclear reactor, we used data augmentation, modeling few hundreds fake nuclear reactors. Muographies from different points of view were simulated to train a denoising neural network. These new methods significantly improved the muography images. Nonetheless, the used 3D tomography algorithm still has some limitations. We proved that it was possible to build a 3D post-process neural network, which was trained to compensate the reconstruction algorithm's limitations. [ABSTRACT FROM AUTHOR]

Muography is an innovative imaging technique using naturally produced elementary particles – atmospheric muons – used to determine the distribution of density inside massive objects. The modification of the particles flux – by scattering or absorption – reflects the contrasts in density within the medium and therefore offers the possibility for an image of the crossed volumes. In most muography setups the imaging process is based on the tracking of the particles which accounts for the absorption or the scattering of the muons trajectories. Neither the energy nor the identity of the particles (the so-called PID) is exploited since this information traditionally relies on the use of calorimeters and/or high intensity magnetic fields. Both these techniques hinder detector portability which in the case of muography is important and this renders them impractical for its purpose. In this paper we characterize the performance of a simple and small water Cherenkov detector capable of providing some insights on the energy of muons and the PID for the crossing particles that could potentially improve the background rejection for a muography survey when operating in conjunction with a muon telescope. We tested a prototype of such water Cherenkov detector in combination with two small muon hodoscopes. Both systems are using the same opto-electronics chain – optical fibers and pixellized photosensors – and the same data acquisition (DAQ) readout system which ensures an easy integration and implementation within presently running systems. This article presents the test setup, the detector response to cosmic muons and its performance evaluation against a basic simulation of its geometry and detection principle. [ABSTRACT FROM AUTHOR]

Muography requires a detailed understanding of the absorption of muons in the material situated between the muon source and the detector. A large-statistics (>3 billion event) Geant4 simulation was run to simulate the absorption of muons in different thicknesses of concrete layers and to determine the effect of the material on the energies of muons that were not absorbed. The Geant4 simulation included a simple detector placed directly behind the absorbing material. A Geant4 simulation was also run for the same detector for alpha sources with no absorbing material and the results of this simulation were compared to the signals from the physical detector built in the laboratory and measured using standard alpha sources. The large-statistics simulations using muons of different energies were compared to the predictions of muon absorption from existing literature. The results of the simulations were in good agreement with both the measured signals from the laboratory as well as the predictions from the literature and the general method is found to be well-suited for studies used for muography involving material layers of uniform thickness.

Muography using cosmic ray muons is a non-invasive and environmentally friendly imaging technique with comprehensive applicability across various fields such as mineral exploration, archaeology, and engineering, etc. Given characteristics of high penetration and broad energy spectrum of cosmic ray muons, three-dimensional density distribution of objects up to hundreds of meters can be well reconstructed. In mineral exploration and archaeology applications, conventional planar detectors are too large and usually deployed in spacious rooms like tunnels or outdoors, which seriously limits the deeper and broader applications of muography. A type of borehole muon detector is highly desired to address this. In the work, we introduce a novel borehole-type muography detector comprising annular and prismatic plastic scintillators, allowing for its deployment in boreholes. In the paper, the structural design of the detector is described in details and its performance is evaluated numerically and experimentally. Comprehensive investigation on components and on the system as a whole were conducted. According to our commissioning tests, the detector we propose has an omnidirectional field of view without blind spots, with an angular uncertainty of 27.4 mrad and a position uncertainty of 2.29 mm in the azimuthal direction, an angular uncertainty of 20.6 mrad and a position uncertainty of 10.31 mm in the zenithal direction. Detection efficiencies for both annular and prismatic scintillators were measured as 90.3 ± 0.53% and 92.27 ± 0.82%. In addition, an underground location was investigated, survival rate distributions being calculated from above-ground and underground measurements. The results indicate its capability to successfully address muography applications This novel borehole-type detector has the potential to address industry demand for lower-cost, more flexible muography solutions. • Achieves high angular resolution and full 360° omnidirectional detection within a compact borehole-sized format. • Maintains >90% detection efficiency across scintillator sections. • Utilizes a simplified single-ended readout design with fewer electronic channels. • Employs low-cost, easy-to-process plastic scintillators as the primary component. [ABSTRACT FROM AUTHOR]

The Muon Telescope, MuTe, is an instrument for imaging volcanoes in Colombia. It consists of a scintillator tracking system and a water Cherenkov detector for particle energy measurement. The Muon Telescope operates autonomously in high-altitude environments where the temperature gradient reaches up to 10 °C. In this work, we characterize the telescope silicon photomultipliers’ breakdown voltage, gain, and noise for temperature variations spanning 0 to 40 °C. We demonstrate that the discrimination threshold for the Muon Telescope hodoscope must be above 5 photo-electrons to avoid contamination due to dark count, crosstalk, and afterpulsing. We also assess the detector counting rate depending on day-night temperature variations.

Muons are constantly produced in cosmic-rays and reach the Earth surface with a flux of about 160 particles per second per square meter. The abundance of muons with respect to other cosmic particles and their capability to cross dense materials with low absorption rate allow them to be exploited for large scale geological or human-made object imaging. Muon radiography is based on similar principles as X-ray radiography, measuring the surviving rate of muons escaping the target and relating it to the mass distribution inside the object. In the course of decades, after the first application in 1955, the methodology has been applied in several different fields. Muography allows us to measure the internal density distribution of the investigated object, or to simply highlight the presence of void regions by observing any excess of muons. Most of these applications require the detector to be installed below the rock being probed. In case that possible installation sites are not easily accessible by people, common instrumentation cannot be installed. A novel borehole cylindrical detector for muon radiography has been recently developed to deal with these conditions. It has been realized with a cylindrical geometry to fit typical borehole dimensions. Its design maximizes the geometrical acceptance, minimizing the dead spaces by the use of arc-shaped scintillators. The details of the construction and preliminary results of the first usage are described in this paper.

Muography uses muons naturally produced in the interactions between cosmic rays and atmosphere for imaging and characterization of density differences and time-sequential changes in solid (e.g. rocks) and liquid (e.g. melts±dissolved gases) materials in scales from tens of metres to up to a few kilometres. In addition to being useful in discovering the secrets of the pyramids, ore prospecting and surveillance of nuclear sites, muography successfully images the internal structure of volcanoes. Several field campaigns have demonstrated that muography can image density changes relating to magma ascent and descent, magma flow rate, magma degassing, the shape of the magma body, an empty conduit diameter, hydrothermal activity and major fault lines. In addition, muography is applied for longterm volcano monitoring in a few selected volcanoes around the world. We propose using muography in volcanomonitoring in conjunction with other existing techniques for predicting volcanic hazards. This approach can provide an early indication of a possible future eruption and potentially the first estimate of its scale by producing direct evidence of magma ascent through its conduit in real time. Knowing these issues as early as possible buy critically important time for those responsible for the local alarm and evacuation protocols. [ABSTRACT FROM AUTHOR]

We report measurements of muon flux over the sky of the city of Bogotá at 4°35′56′′ north latitude, 74°04′51′′ west longitude, and an altitude of 2657 m above sea level, carried out with a hodoscope composed of four stations of plastic scintillators located equidistant over a distance of 4.8 m. Measurements were taken at different zenith (θ) angles within the range 1.5° ≤ θ ≤90°, the muon flux data is statistically consistent with a cos2θ dependence, with a χ2 per degree of freedom near unity. If instead, we fit to a cosnθ we obtain n = 2.145±0.046 with a lower χ2 per degree of freedom. Integrating the muon flux distribution as a function of the zenith angle over the solid angle of the upper Earth’s hemisphere allows an estimation of the atmospheric vertical muon rate at the altitude and latitude of Bogota obtaining a value of 255.1 ± 5.8m−2s−1. This estimate is consistent with an independent direct measurement of the vertical muon flux with all detectors stacked horizontally. These measurements play a key role in the further development of detectors, aimed to perform muon imaging of Monserrate Hill, located in Bogotá, where the detectors will be placed at similar locations to those used in the present study.

A cosmic muon imaging system is essentially a particle tracking detector as known from experimental High Energy Physics. The Multiwire Proportional Chamber (MWPC) once revolutionized this field of science, and as such it is a viable choice as the core element of an imaging system. Long term construction and operation experience was gathered from a Japanese–Hungarian collaboration that gave rise to the MWPC-based Muon Observatory System (MMOS), and is being used in Japan at the Sakurajima volcano. The present paper attempts to draw conclusions on the thermal and mechanical limits of the system, based on controlled measurements and detailed simulations. High temperature behavior and effects of thermal cycling and conditioning are presented, which appear to consistently allow one to propose quality control criteria. Regarding mechanical stability, the relation between gluing quality (tensile strength) and expected stress from vibration (during transportation) determines the safety factor to avoid damages. Both of these are presented and quantified in the paper using a conservative and austere approach, with mechanical simulations validated with experimental modal testing data. One can conclude that mechanical stress during industrial standard air freight shipping conditions is nearly a factor of three below the calculated maximum stress.

Cosmic muon imaging (muography) has gained popularity in recent years for density reconstruction in various applications. However, evaluations of image quality in reconstructed images have been lacking. This work addresses this gap by applying muon transmission imaging to a teaching building on a university campus. Multiple impacts on reconstruction image quality, including filtering methods, total counts, building thickness thresholds, and reconstruction formulas, were integrally studied. The area under the curve (AUC) of the receiver operating characteristic analysis and mean squared error (MSE) were calculated to quantitatively evaluate and optimize these parameters. Based on the simulation using the Geant4 toolkit, the recommended parameters for the building model were median filtering, a total count of 5 × 1 0 4 in the building region, a thickness threshold of 3 m, and either the constant energy loss method or cubic polynomial form fitting method. Implementing these parameters in the experimental data analysis, the reconstructed image well revealed the inner structure of the teaching building from the view angle of the detector. The optimization of the two-dimensional (2D) reconstruction method facilitates the detection of hidden cavities or regions with abnormal density in large-scale objects. [ABSTRACT FROM AUTHOR]

Imaging the internal structure of volcanoes helps highlighting magma pathways and monitoring potential structural weaknesses. We jointly invert gravimetric and muographic data to determine the most precise image of the 3D density structure of the Puy de Dôme volcano (Chaîne des Puys, France) ever obtained. With rock thickness of up to 1,600 m along the muon lines of sight, it is, to our knowledge, the largest volcano ever imaged by combining muography and gravimetry. The inversion of gravimetric data is an ill-posed problem with a non-unique solution and a sensitivity rapidly decreasing with depth. Muography has the potential to constrain the absolute density of the studied structures but the use of the method is limited by the possible number of acquisition view points, by the long acquisition duration and by the noise contained in the data. To take advantage of both types of data in a joint inversion scheme, we develop a robust method adapted to the specificities of both the gravimetric and muographic data. Our method is based on a Bayesian formalism. It includes a smoothing relying on two regularization parameters (an a priori density standard deviation and an isotropic correlation length) which are automatically determined using a leave one out criterion. This smoothing overcomes artifacts linked to the data acquisition geometry of each dataset. A possible constant density offset between both datasets is also determined by least-squares. The potential of the method is shown using the Puy de Dôme volcano as case study as high quality gravimetric and muographic data are both available. Our results show that the dome is dry and permeable. Thanks to the muographic data, we better delineate a trachytic dense core surrounded by a less dense talus.

Muography is a novel imaging method using natural cosmic-ray radiation for characterising and monitoring variation in average material density in a diverse range of objects that cannot be imaged by conventional imaging techniques. Muography includes muon radiography and muon tomography. Cosmic-ray-induced muons were discovered in the 1930's, but rapid development of both muographic techniques has only occurred in the last two decades. With this rapid development, muography has been applied or tested in many fields such as volcano imaging, archaeology, underground structure and tunnel detection, rock mass density measurements, cargo scanning, imaging of nuclear waste and reactors, and monitoring of historical buildings and the inside of blast furnaces. Although applications of muography have already touched mining and rock engineering, such applications are still rare and they are just beginning to enter the market. Based on this background, this paper aims to introduce muography into the fields of mining and rock engineering. First, the basic properties of muons are summarized briefly. Second, potential applications of muography to mining and rock engineering are described. These applications include (1) monitoring temporal changes in the average material density of fracturing and deforming rock mass; (2) detecting geological structures and isolated ore bodies or weak zones in mines; (3) detecting a reservoir or boulders during tunnelling or drifting; (4) monitoring caving bodies to search remaining ore; (5) evaluating and classifying rock masses; (6) exploring new mineral deposits in operating underground mines and their surrounding brownfields. Finally, some issues such as maximum depth muons can reach are discussed. [ABSTRACT FROM AUTHOR]

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Radiographic imaging with muons, also called Muography, is based on the measurement of the absorption of muons, generated by the interaction of cosmic rays with the earth’s atmosphere, in matter. Muons are elementary particles with high penetrating power, a characteristic that makes them capable of crossing bodies of dimensions of the order of hundreds of meters. The interior of bodies the size of a pyramid or a volcano can be seen directly with the use of this technique, which can rely on highly segmented muon trackers. Since the muon flux is distributed in energy over a wide spectrum that depends on the direction of incidence, the main difference with radiography made with X-rays is in the source. The source of muons is not tunable, neither in energy nor in direction; to improve the signal-to-noise ratio, muography requires large instrumentation, long time data acquisition and high background rejection capacity. Here, we present the principles of the Muography, illustrating how radiographic images can be obtained, starting from the measurement of the attenuation of the muon flux through an object. It will then be discussed how recent technologies regarding artificial intelligence can give an impulse to this methodology in order to improve its results.

Several muon telescopes have been developed in the last years at CEA-Saclay. Benefitting from 15 years of R&D on Micro-Pattern Gaseous Detectors (MPGDs) and from several recent innovations, these telescopes yield unprecedented resolution for real-time instruments, and allow for high-definition muography imaging. As a first application, three of them were deployed around Khufu's Pyramid from 2015 to 2017, showing very good performance and stability in harsh conditions. They also provided the first-ever detection of internal structures of a pyramid from the outside, and participated in the discovery of a large void above the Grand Gallery. [ABSTRACT FROM AUTHOR]

Muon tomography, or muography, stands out as a non-invasive technique for the scanning of big objects internal structure. It relies on the measurement of the direction changes or absorption of atmospheric muons when crossing the studied object. For the first case, the trajectory reconstruction of muons upstream and downstream the object, provides information to generate its 3D density map. For bigger objects, a 2D map can be obtained by measuring the absorption for different incident directions. Proposed several decades ago, the performance achieved in particle detectors in the last years, specially in terms of stability, robustness and precision, has enlarged the possible applications of this technique. Bulk Micromegas represent a well-known technology suitable for the construction of muon telescopes based on these detectors. Thus autonomous and portable instruments have been conceived and constructed at Commissariat à l'Énergie Atomique et aux Énergies Alternatives (CEA), being able to perform measurements in-situ , next to the studied objects. Furthermore, a Geant4-based simulation framework, capable to handle 3D models of the studied objects, is also being implemented to be used as support tool during the feasibility studies and for data analysis and results interpretation. [ABSTRACT FROM AUTHOR]

Muography is an innovative imaging technique used for inspecting and monitoring density-length variations of large-sized natural or human-made objects based on the measurement of the absorption rate of cosmic-ray muons. The first large-sized, highresolution muography observatory based on Multi-Wire Proportional Chamber (MWPC) technology is being developed to monitor the mass density variations in the vicinity of Minami-dake crater of Sakurajima volcano. We found that the track rates provided by five ongoing tracking systems with a total surface area of 4 m² are stable within ±3% from the backward direction, which demonstrates that the MWPCbased Muographic Observation System (MMOS) is applicable for the detection of average density variations above 2%, which is well below the practical limit of 5%. We quantified the time resolution of the designed muography observatory by modeling the muon flux across the volcano; the average density-length variation of 5 (10)% is expected to be detected within 5-20 (2-8) days at a 1σ (68%) confidence level (CL) with an MMOS orientation of 10.86° above the horizon. An automated analysis framework was developed as a data base for raw data reconstruction, analysis, and preparation, and which is accessible via webserver. We observed a more than 2σ CL decrease in average density across the West side of Crater A during the ongoing data collection period. The observed density decrease suggests that the amount of material has decreased inside Crater A due to the consecutive eruptions of Minami-dake during the data collection period from November 30, 2018 to January 11, 2019. [ABSTRACT FROM AUTHOR]

A new application of muon radiography (MR) is presented in the context of non-destructive testing of industrial equipment. The long-term operation of industrial facilities frequently involves the deterioration of critical components such as pipes and cauldrons due to corrosion and other processes. The precise determination of the inner state of this equipment is needed to ensure the integrity of the facility. MR can be used to infer the thickness of these components through the comparison and further classification of muon observables with respect to well-known templates. A simulation example is presented where the thickness of a pipe made of steel is studied using the Point of Closest Approach method and simple Kolmogorov–Smirnov statistical tests. A precision of about 2–4 mm is obtained using a simple detector with a spatial resolution of 4 mm and exposure times of about 2 h [ABSTRACT FROM AUTHOR]

High-energy muons that are generated via the reaction between primary cosmic rays and the Earth’s atmosphere can be used to map out the density distribution in shallow parts of a volcano’s interior. This new subterranean imaging technique called muography has been applied to three different kinds of volcano dynamics in Japan: lava dome formation, vulcanian explosions and magma convection. Taking all of the observational data together, it appears that muography can serve as a new and alternative volcano observation technique, providing a fresh approach to understanding eruption mechanism. This review describes observational studies in which muography has been used to explore the volcano’s interior. [ABSTRACT FROM AUTHOR]

By observing the growth of a research community, particularly the factors of size and strength of involvement, it is possible to evaluate the vitality of a new field. The emerging technology of muography, a new visualization technique to look through gigantic objects with an elementary particle called the muon, is the focus of this study. Recently, the initial applications of muography to the study of structures such as pyramids and volcanoes have been expanding to include more commercial interests such as inspecting social infrastructures and energy and mineral resources. Evolutions of the research networks of muography will be discussed with particular attention to the chronological and lateral structures that could be an indicator of the development of this new technology. [ABSTRACT FROM AUTHOR]

Cosmic-ray muons have been studied at IFIN-HH for more than 20 years. Starting as fundamental physics research, the muon flux measurements bring new directions of study regarding muography. Two new directions have been recently developed: underground muon scanning of old mining sites in order to detect the possible presence of unknown cavities and underwater scanning of ships in commercial harbours in order to prevent the illegal traffic of radioactive materials. The main goal of the first direction of study is to improve the security of underground civilian and industrial infrastructures, by starting the development of a new, innovative detection system that can be used to identify potentially dangerous conditions using a non-invasive, totally safe method. The method proposed uses information provided by a device placed underground that measures directional cosmic muon flux and identifies anomalies produced by irregularities in the geological layers above. For the second direction of study, the method proposed is based on the detection and analysis of the cosmic muon flux. The high-density materials (uranium, lead—used for radiation shielding, etc.) cause a decrease in the directional muon flux. The detection system will be submerged underneath the ship that will be scanned, being able to locate illegal radioactive materials without exposing any personnel to radiation or contamination. Correlated with simulations based on the known configuration of the ship scanned, the data provided by the detection system will provide the location and dimensions of the undeclared material transported [ABSTRACT FROM AUTHOR]

We report on the first steps in the development of a small-size muon telescope based on glass resistive plate chambers with small active area (16 × 16 cm²). The long-term goal of this project is to focus on applications of muography where the telescope may have to be operated underground and/or inside small rooms, and in challenging logistic situations. Driving principles in our design are therefore compact size, light weight, gas tightness and robustness. The first data-taking experiences have been encouraging, and we elaborate on the lessons learnt and future directions for development [ABSTRACT FROM AUTHOR]

A multi-wire proportional chamber-based muography observatory is under development for the monitoring of the internal structure of Mt Sakurajima in Kyushu, Japan. We investigated the limits of large-scale and high-definition muography. We adjusted the parameters of a modified Gaisser model and found that the spectral index of γ =−2.64 and normalization factor of C=0.66 reproduce more accurately the measured fluxes than the original parameters at large thickness. A thickness and zenith angle-dependent correction is suggested to the measured muon flux due to the energy cut which is introduced to suppress the background particles. The multiple scattering of muons was simulated across the standard rock and sea-level atmosphere up to the distance of 5 km. We found that multiple scattering decreases from 10 mrad to 4 mrad across the rock due to the decrease in the steepness of muon spectra. The multiple scattering falls down to about 2 mrad after the object in the atmosphere due to the increase in observed arrival zenith angles. The 2 m² sized multi-wire proportional chamber-based Muographic Observation System (MMOS) was operating between February and June 2018. Three tracking systems operated reliably with tracking efficiencies of above 95%. The muon flux has been measured correctly down to 10−3 m−2 sr−1 s−1. The average density map of Mt Sakurajima has been measured with angular resolution of 12 mrad × 12 mrad (spatial resolution of 34 m × 34 m from the distance of 2.8 km). The average density values were found between 1.4 and 2 g cm−3, except at the crater regions where lower densities were observed. [ABSTRACT FROM AUTHOR]

Lingacom Ltd develops detectors for muography— imaging using cosmic-ray muons—together with imaging algorithms and tools. We present selected simulation results from muon imaging of cargo containers, from a joint muon and X-ray imaging algorithm, and for ground surveys using borehole detectors. [ABSTRACT FROM AUTHOR]

Imaging subsurface rock formations or geological objects like oil and gas reservoirs, mineral deposits, cavities or even magmatic plumbing systems under active volcanoes has been for many years a major quest of geoscientists. Since these subsurface objects cannot be observed directly, different indirect methods have been developed. These methods are all based on variations of certain physical properties of the subsurface materials that can be detected from the ground surface or from boreholes. To determine the density distribution, a new imaging technique using cosmic-ray muon detectors deployed in a borehole has been developed and a first prototype of a borehole muon detector successfully tested. In addition to providing a static image of the subsurface density in three dimensions (or three-dimensional tomography), borehole muography can also inform on the variations of density with time, which recently became of major importance with the injection of large volumes of fluids, mainly water and CO2, in porous subsurface reservoirs (e.g. aquifer storage and recovery, wastewater disposal, enhanced oil recovery and carbon sequestration). This raises several concerns about the risk of leakage and the mechanical integrity of the reservoirs. Determining the field scale induced displacement of fluids by geophysical methods like muography is thus a priority [ABSTRACT FROM AUTHOR]

Muon radiography, also known as muography, is an imaging technique that provides information on the mass density distribution inside large objects. Muons are naturally produced in the interactions of cosmic rays in the Earth’s atmosphere. The physical process exploited by muography is the attenuation of the muon flux, that depends on the thickness and density of matter that muons cross in the course of their trajectory. A particle detector with tracking capability allows the measurement of the muons flux as a function of the muon direction. The comparison of the measured muon flux with the expected one gives information on the distribution of the density of matter, in particular, on the presence of cavities. In this article, the measurement performed at Mt. Echia in Naples (Saracino 2017 Sci. Rep. 7, 1181. (doi:10.1038/s41598-017-01277-3)), will be discussed as a practical example of the possible application of muography in archaeology and civil engineering [ABSTRACT FROM AUTHOR]

Cosmic-ray muography uses high-energy particles for imaging applications that are produced by cosmic rays in particle showers in the Earth’s atmosphere. This technology has developed rapidly over the last 15 years, and it is currently branching out into many different applications and moving from academic research to commercial application. As in any new sub-field of research and technology, the nomenclature of the field itself is still developing and has not settled yet as new aspects of the field are appearing and with them the terms to describe them. This overview of the field of muography is not going to focus on the physics, on the reconstruction algorithms or on the involved detector technology. Detailed papers on these aspects are included in this issue of Philosophical Transactions A and I will refer to them. Instead, I will give an overview of the field as it is now, in 2018, and try to give an idea of the future directions in this field as I see them [ABSTRACT FROM AUTHOR]

In the last decade, there has been a surge in the number of academic research groups and commercial companies exploiting naturally occurring cosmic-ray muons for imaging purposes in a range of industrial and geological applications. Since 2009, researchers at the University of Glasgow and the UK National Nuclear Laboratory (NNL) have pioneered this technique for the characterization of shielded nuclear waste containers with significant investment from the UK Nuclear Decommissioning Authority and Sellafield Ltd. Lynkeos Technology Ltd. was formed in 2016 to commercialize the Muon Imaging System (MIS) technology that resulted from this industry-funded academic research. The design, construction and performance of the Lynkeos MIS is presented along with first experimental and commercial results. The high-resolution images include the identification of small fragments of uranium within a surrogate 500-litre intermediate level waste container and metal inclusions within thermally treated GeoMelt® R&D Product Samples. The latter of these are from Lynkeos' first commercial contract with the UK National Nuclear Laboratory. The Lynkeos MIS will be deployed at the NNL Central Laboratory facility on the Sellafield site in Summer 2018 where it will embark upon a series of industry trials. [ABSTRACT FROM AUTHOR]

Significant progress has been made in the last years in the field of volcanic muography. This technique takes advantage of the large penetrating power of atmospheric muons and allows us to infer information about the internal structure of volcanoes observing the differential absorption of muons passing through the target. This, in conjunction with other monitoring techniques, can help to determine the state of activity of a volcano and to reduce the risk related to paroxysmal events. The main challenge in the application of this technique is given by the background noise, that affects detectors. To improve the signal-to-noise ratio it is necessary to use several detection layers and shielding plates that make the detector expensive and difficult to transport. In order to overcome these issues, the use of Imaging Atmospheric Čerenkov Telescopes (IACTs) devoted to muography has been recently proposed. Here we present the MUography CHerenkov (MUCH) telescope, a compact IACT specifically designed for volcano muography. The telescope design is characterized by a Schmidt-like optical system and a Silicon Photo-Multipliers (SiPMs) camera working at wavelengths between 280 nm and 900 nm, equipped with a fast read-out electronics capable to operate SiPMs contemporarily in charge integration and photon counting mode. [ABSTRACT FROM AUTHOR]

In a recent paper, the authors discussed the feasibility study of an innovative technique based on the directionality of Cherenkov light produced in a transparent material to improve the signal to noise ratio in muon imaging applications. In particular, the method was proposed to help in the correct identification of incoming muons direction. After the first study by means of Monte Carlo simulations with Geant4, the first reduced scale prototype of such a detector was built and tested at the Department of Physics and Astronomy "E. Majorana" of the University of Catania (Italy). The characterization technique is based on muon tracking by means of the prototype in coincidence with two scintillating tiles. The results of this preliminary test confirm the validity of the technique and stressed the importance to enhance the Cherenkov photons production to get a signal well distinguishable with respect to sensors and electronic noise.