High efficiency gaseous tracking detector for cosmic muon radiography

A tracking detector system has been constructed with an innovative approach to the classical multi-wire 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, filling gas consumption below 2 liters per hour for the non toxic, non flammable argon and carbon dioxide mixture. These parameters, along with the simplicity of the construction and the tolerance for mechanical effects, make the detectors to be a viable option for a large area muography observation system.Comment: 15 pages, 15 figure

Low gas consumption in tracking detectors for outdoor applications

Gaseous detectors are one of the popular particle tracking technologies in high energy physics, and there are multiple applications where the detectors must tolerate outdoor conditions, e.g. in the emerging field of muography. Gaseous tracking detectors are attractive choices due to their high efficiency, good resolution and large sensitive area at a reasonable cost and low weight, but to achieve these, the gas system is usually not sealed. Continuous gas flow results gas consumption and thus regular gas cylinder replacement which limits applicability. In this paper we present a practical solution to reduce gas flow to a negligible level, keeping the construction cost-efficient and low weight, by a properly chosen buffer tube at the end of the gas line, which makes the system able to withstand large temperature and pressure fluctuations

Muographic monitoring of hydrogeomorphic changes induced by post-eruptive lahars and erosion of Sakurajima volcano

Post-eruptive destabilization of volcanic edifices by gravity driven debris flows or erosion can catastrophically impact the landscapes, economies and human societies surrounding active volcanoes. In this work, we propose cosmic-ray muon imaging (muography) as a tool for the remote monitoring of hydrogeomorphic responses to volcano landscape disturbances. We conducted the muographic monitoring of Sakurajima volcano, Kyushu, Japan and measured continuous post-eruptive activity with over 30 lahars per year. The sensitive surface area of the Multi-Wire-Proportional-Chamber-based Muography Observation System was upgraded to 7.67 m 2 ; this made it possible for the density of tephra within the crater region to be measured in 40 days. We observed the muon flux decrease from 10 to 40% through the different regions of the crater from September 2019 to October 2020 due to the continuous deposition of tephra fallouts. In spite of the long-term mass increase, significant mass decreases were also observed after the onsets of rain-triggered lahars that induced the erosion of sedimented tephra. The first muographic observation of these post-eruptive phenomena demonstrate that this passive imaging technique has the potential to contribute to the assessment of indirect volcanic hazard

Cosmic Muon Detector Using Proportional Chambers

A set of classical multi-wire proportional chambers were designed and constructed with the main purpose of efficient cosmic muon detection. These detectors are relatively simple to construct, and at the same time are low cost, making them ideal for educational purposes. The detector layers have efficiencies above 99% for minimum ionizing cosmic muons, and their position resolution is about 1 cm, that is, particle trajectories are clearly observable. Visualization of straight tracks is possible using an LED array, with the discriminated and latched signal driving the display. Due to the exceptional operating stability of the chambers, the design can also be used for cosmic muon telescopes.Comment: 11 pages, 11 figures. Submitted to the European Journal of Physic

3D Muographic Inversion in the Exploration of Cavities and Low-density Fractured Zones

Muography is an imaging tool based on the attenuation of cosmic muons to observe the density distribution of large objects, such as underground caves or fractured zones. Tomography based on muography measurements -- that is, three dimensional reconstruction of density distribution from two dimensional muon flux maps -- brings up special challenges. The detector field of view covering must be as balanced as possible, considering the muon flux drop at higher zenith angles and the detector placement possibilities. The inversion from directional muon fluxes to 3D density map is usually underdetermined (more voxels than measurements) which can be unstable due to partial coverage. This can be solved by geologically relevant Bayesian constraints. The Bayesian principle results in parameter bias and artifacts. In this work, the linearized (density-length based) inversion is applied, the methodology is explained, 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 7 positions is used as input for the inversion. The result demonstrates the tomographic imaging of a complex karstic crack zone and provides details on the complicated internal structures. The existence of low density zones in the imaged space was verified by samples from core drills, which consist altered dolomite powder within the intact high density dolomite.Comment: submitted to Geophys. J. In

Improvement of cosmic-ray muography for Earth sciences and civil engineering

Muography is utilizing the cosmic-ray muons to deduce the amount of material across large-sized objects, similarly to X-raying of human body. We specifically developed Multi-Wire Proportional Chamber (MWPC)-based tracking systems with high (> 98 %) efficiency, fair (< 10 mrad) angular resolution and low (< 6 W) power for Earth sciences and civil engineering. A muography observatory is assembled from trackers on a sensitive surface of 5.5 m 2 at 2.8 km distance in South-West from Sakurajima volcano to provide projective density images of the crater regions for future measurements of mass variations occurred during eruptions. An industrial applicability of portable, MWPC-based instruments have been demonstrated with the muographic imaging of an underground iron pillar. We investigated the limits of muography: the Gaisser model is suggested to be modified with an energy exponent of -2.64 and constant scale factor of 0.66 for imaging in near-horizontal directions after large (> 1,000 m.s.r.e.) thicknesses. The multiple scattering of muons across the targeted object is limiting the imaging resolution from 10 mrad to 5 mrad with the increase of thickness between 50 m.s.r.e. and 2,000 m.s.r.e.. The precise measurement of low-energy muon spectra is required to improve muography of small-sized objects. We developed a 5-meter-length, rotatable, MWPC-based spectrometer to precisely measure the energy spectra of muons between 0.5 GeV and 5 GeV from vertical to horizontal directions. It is a consecutive series of thirteen detectors with a positional resolution of approx. 4 mm and lead plates. The spectrometer and the first results are presented

Muography of the active Sakurajima volcano: recent results and future perspectives of hazard assessment

Sakurajima volcano is one of the world’s most active volcanoes with over 3,000 of explosive eruptions during the last five years. A muography observatory is under construction in international collaboration since 2017 at a distance of approx. 2,800 m in south-west direction from the active craters. Currently, the Sakurajima Muography Observatory is operating with 11 Multi-Wire-Proportional-Chamber-based Muography Observation Systems that are covering a sensitive surface area of 8.25 square meters. This work is focusing on the volcanological implications of muographic monitoring of Sakurajima: (i) tephra deposition, and erosion of the surface region exist due to heavy rains and post-eruptive lahars; (ii) magmatic plug formation was observed beneath the active craters after the deactivation of Showa crater in 2018 and after a dormant period of Central craters in 2020; (iii) machine-learning-based processing of daily muographic images achieved a fair area under the receiver operating characteristic curve score of 0.76

Construction and readout system for gaseous muography detectors

Muography instrumentation presents a wide range of practical challenges, since the implementation environment drastically differs from the high energy physics laboratory conditions. This paper briefly overviews the pros and cons of existing technologies, and gaseous detectors in particular. The practical challenges are partially environmental, such as thermal cycling or high humidity, partially connected to the installation such as mechanical shocks, and also include the human factor stipulating minimal non-expert maintenance and troubleshooting. The presentation aims to introduce various solutions to address these challenges, with operational experience spanning five years

Gaseous Tracking Detectors at the Sakurajima Muography Observatory

Muography is a novel imaging technology to reveal density structure of hill-sized objects. The cosmic muons predictably lose their energy and penetrate hundreds of meters into the ground, thus their differential local flux correlates with the crossed density-length. The Sakurajima Muography Observatory in Kagoshima, Japan, is the largest muography experiment targeting an active volcano. A set of multilayered gaseous detectors are used to reconstruct the muon tracks, thus by measuring the flux, imaging of the inner part of the volcano become possible. The paper focuses on the technical challenges of such a particle tracking system, the designed multi-wire proportional chambers, and the recent results from the measurements