Muography is a novel method to highly resolve the internal structure of active volcanoes by taking advantage of the cosmic muon's strong penetration power. In this paper, we present the first ...high-definition image in the vicinity of craters of an erupting volcano called Sakurajima, Kyushu, Japan. The muography observation system based on the technique of multi-wire proportional chamber (mMOS) has been operated reliably during the data taking period of 157 days. The mMOS measured precisely the flux of muons up to the thickness of 5,000 meter-water-equivalent. It was shown that high-definition density maps around the Craters A, B and Showa could be determined with a precision of less than 7.5 × 7.5 m
which earlier had not yet been achieved. The observed density distribution suggests that the fall back deposits filled the magma pathway and increased their density underneath Craters A and B.
Investigation of the limits of high-definition muography for observation of Mt Sakurajima Oláh, László; Tanaka, Hiroyuki K M; Hamar, Gergő ...
Philosophical transactions - Royal Society. Mathematical, Physical and engineering sciences/Philosophical transactions - Royal Society. Mathematical, physical and engineering sciences,
12/2018, Volume:
377, Issue:
2137
Journal Article
Peer reviewed
Open access
A multi-wire proportional chamber-based muo- graphy 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
= - 2.64 and normalization factor of
= 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 m
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
m
sr
s
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
, except at the crater regions where lower densities were observed.This article is part of the Theo Murphy meeting issue 'Cosmic-ray muography'.
Sakurajima Muography Observatory captured the formation of a volcanic plug beneath the Showa crater with a spatial resolution of ∼60 m in accordance with the end of the eruption episode of Showa ...crater and the reactivation of Minamidake crater. The increase of average density was observed with above 3 σ standard deviation for both above the floor of Minamidake crater and beneath the floor of Showa crater, respectively, being interpreted as volcanic ejecta deposition and the formation of a volcanic plug laterally extended within a few hundreds of meters.
Plain Language Summary
Muography is an imaging technique that provides information about the amount of material across kilometer‐thick geological structures by the measurement of the yield of cosmic rays, similarly to X‐raying of human body. We applied muography to capture two muon images of Minamidake and Showa craters of Sakurajima volcano before and after the shift of eruption activities occurred between the two craters at the end of 2017. The comparison of the images revealed the presence of increased material across the activated Minamidake and beneath the deactivated Showa crater. Muography detected the formation of a magma plug in the conduit of Showa crater that was not detected earlier by any other geophysical technique. These results demonstrate the applicability of cosmic muon imaging for monitoring of magma movements inside active volcanoes.
Key Points
Two muographic images were taken across the erupting Sakurajima volcano with a spatial resolution of 60 m
Increased average densities were observed beneath the deactivated crater after the shift of eruption sequence
Muography data suggest that uprising magma formed a plug in the conduit of Showa crater
Hole misalignment and gain performance of Gaseous Electron Multipliers Brücken, Erik; Heino, Jouni; Hildén, Timo ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
06/2021, Volume:
1002
Journal Article
Peer reviewed
Open access
It is well known and has been shown that the gain performance of Gaseous Electron Multipliers (GEM) depends on the size of the holes. With an optical scanner it is possible to measure the dimensions ...of the holes, and to predict the performance of GEMs. However, the gain prediction of GEMs that are manufactured with a double mask etching technique is not straightforward. With the hole size information alone, it is not possible to make precise prediction of the gain. We show that the alignment of the photo-masks between the two sides of the GEM foils plays a crucial role. A misalignment of a few microns can lower the gain substantially. The study is performed by using the Helsinki high definition optical scanner for quality control of GEM foils, and this will show its true potential.
Abstract 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.
A tracking detector system has been constructed with an innovative approach to the classical multiwire proportional chamber concept, using contemporary technologies. The detectors, covering an area ...of 0.58 square meters each, are optimized for the application of muon radiography. The main features are high (>99.5%) and uniform detection efficiency, 9 mm FWHM position resolution, and filling gas consumption below 2 liters per hour for the nontoxic, nonflammable argon and carbon dioxide mixture. These parameters, along with the simplicity of the construction and the tolerance for mechanical effects, make the detectors a viable option for a large area muography observation system.
The developed ”Leopard” high resolution scanner measures the single electron response of MPGDs. Therefore it became possible to quantify the amplification of individual holes. A UV light source is ...focused on the MPGD surface and single photoelectron spectra is recorded in every pixel over the selected two dimensional region (map). This way the MPGD gain and the photoelectron yield is clearly separated and can be computed. The single photoelectron spectrum also provides information about the exact distribution shape of the low amplitude responses as well. The MPGD surface structure is well observable on the photoelectron map. As expected, the gain map fluctuates hole by hole, but it is constant around a given hole. This technology reveals the microstructure of photo-efficiency and local gain to quantitatively compare different MPGD geometries and thus provides a powerful tool for e.g. GEM quality assurance.
SUMMARY
Muography is an imaging tool based on the attenuation of cosmic muons for observing density anomalies associated with large objects, such as underground caves or fractured zones. Tomography ...based on muography measurements, that is, 3-D reconstruction of density distribution from 2-D muon flux maps, brings along special challenges. The detector field of view covering must be as balanced as possible, considering the muon flux drop at high zenith angles and the detector placement possibilities. The inversion from directional muon fluxes to a 3-D density map is usually underdetermined (more voxels than measurements). Therefore, the solution of the inversion can be unstable due to partial coverage. The instability can be solved by geologically relevant Bayesian constraints. However, the Bayesian principle results in parameter bias and artefacts. In this work, linearized (density-length based) inversion is applied by formulating the constraints associated with inversion to ensure the stability of parameter fitting. After testing the procedure on synthetic examples, an actual high-quality muography measurement data set from seven positions is used as input for the inversion. The resulting tomographic imaging provides details on the complicated internal structures of karstic fracture zone. The existence of low density zones in the imaged space was verified by samples from core drills, which consist of altered dolomite powder within the intact high density dolomite.
Abstract
Large-scale solid bodies on Earth such as volcanoes and man-made pyramids have been visualized with solid earth muography, and the recently invented technique, acqueous muography, has ...already demonstrated its capability to visualize ocean tides and tsunami. In this work, atmospheric muography, a technique to visualize and monitor the vertical profile of tropic cyclones (TCs) is presented for the first time. The density distribution and time-dependent behavior of several TCs which had approached Kagoshima, Japan, has been investigated with muography. The resultant time-sequential images captured their warm cores, and their movements were consistent with the TC trails and barometric pressure variations observed at meteorological stations. By combining multidirectional muographic images with barometric data, we anticipate that muography will become a useful tool to monitor the three-dimensional density distribution of a targeted mesoscale convective system.
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