High-definition and low-noise muography of the Sakurajima volcano with gaseous tracking detectors

Abstract

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 m2 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.

Long term measurements from the Mátra Gravitational and Geophysical Laboratory

“…The idea is to measure the angular distribution of the highly penetrating muon-component flux of the cosmic-rays, which are created in the upper atmosphere and reach the surface of the Earth. This technique, has been applied successfully by our group for various cases such as cave researches, cosmic background measurements for underground laboratories, civil engineering, and volcano muography [47,48,49,50,51,52].…”

The muon intensity in the Felsenkeller shallow underground laboratory

“…Position 5 at the very end of tunnel IV. 6. Position 6 is located in Messkammer 1 (hereafter called MK1).…”

Plug Formation Imaged Beneath the Active Craters of Sakurajima Volcano With Muography

“…Although the angular resolution of MMOS could in principle resolve the Showa crater region at a resolution of ∼10 m (Oláh et al, 2018), the reduced number of muons arriving across the volcano limited the spatial resolution of our experiment to ∼60 m. The enlargement of the sensitive surface of MMOS is in progress . Furthermore, an optimization of the detection energy threshold of MMOS is suggested to measure accurately the average densities and access information about the physical properties of the magma localized in the conduit of Showa.…”

“…Each tracker consists of at least five MWPCs and five 2‐cm‐thick lead shielding plates. These plates are applied to deflect and absorb the low‐energy (<1 GeV) muons (Oláh et al, ) and electrons (Oláh & Varga, ) that do not penetrate the volcano but appear to come from that direction (Nishiyama et al, ; Ambrosino et al, ). This measurement setting covers the crater region (Figure a) and allows a spatial resolution of less than 10 m at a position of the Minamidake crater rim.…”

“…Off‐line detector calibration and data quality assurance are performed by a reconstruction software that calculates the particle positions on each MWPC, combines the clusters to track candidates, and finds the best fitting tracks with those parameters, for example, the goodness of fit ( χ 2 /ndf), as well as horizontal‐ ( ) and vertical ( ) track slopes. Here the χ 2 /ndf is the sum of squared values of positional residuals (cluster centroids minus track coordinates) divided by the positional resolutions for each MWPC over the number of degrees of freedom (number of MWPCs minus two; Oláh et al, ).…”