Dr. Laszlo Olah (Earthquake Research Institute, University of Tokyo)
"Application of new variant of gaseous tracking detectors for CR detection and muography"

A new variant of multi-wire proportional chambers (MWPC) have been developed with the area of 0.58 square meter, with high (> 99 %) and uniform detection efficiency, and with reasonable position resolution of 4 mm for CR detection and muography [1]. The tracking system consists of 6-8 MWPCs. The chambers require Ar-CO2 gas mixture with the flow of about 1 Liters/hour. The tracking system is operated by Raspberry Pi computer, which allows remote control and data access. The total power consumption of a tracking system is less than 10 Watt. 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 detector system for CR experiments and muography observation systems.

The first prototype of the MWPC-based tracking system are designed for muography [2], which is a technique for the imaging of the interior of large size objects, such as volcanoes and caves with the measurement of the flux of high energy cosmic muons [3,4]. The MWPC-based tracking detector (Muographic Observation System, mMOS) has been installed at the Sakurajima volcano, Kyusu, Japan in the January of 2017. The report on the detector performance and the verification of the applicability of mMOS for muography will be presented.

In cosmic-ray muon imaging, the electrons/positrons, high energy hadrons and low energy muons can contaminate the muon signal. These background sources require a good understanding of the creation processes, as well as reliable simulation frameworks with high predictive power. A simulation framework based on GEANT4 has been established to pin down the key features of the background particles [5]. The particle spectra and ratios have been compared to existing other measurements as well as other simulation programs. The correlation between simultaneously arriving particles have also been quantitatively investigated, demonstrating that electrons and positrons tend to arrive close to each other and with low relative angle. This feature, which is highly relevant for counting detectors, has been experimentally verified at shallow depth underground and under open sky using the new variant of MWPC detectors [5].

[1] D. Varga, G. Nyitrai, G. Hamar, L. Olah: High Efficiency Gaseous Tracking Detector for Cosmic Muon Radiography, Advances in High Energy Physics Volume 2016, Article ID 1962317, 11 pages http://dx.doi.org/10.1155/2016/1962317

[2] T. Kusagaya, G. Hamar, L.Olah, H. K. M. Tanaka, D. Varga: Muographic Observation System, PTZATA153, PATPEND (2016)

[3] H. K. M. Tanaka, T. Kusagaya, H. Shinohara: Radiographic visualization of magma dynamics in an erupting volcano, Nat. Commun. 5:3381 doi: 10.1038/ncomms4381 (2014)

[4] L. Olah, G. G. Barnafoldi, G. Hamar, H. G. Melegh, G. Suranyi, and D. Varga: CCC-based muon telescope for examination of natural caves, Geosci. Instrum. Method. Data Syst., 1, 229-234, 2012 doi:10.5194/gi-1-229-2012

[5] L. Olah, D. Varga: Investigation of soft component in cosmic ray detection, Astroparticle Physics 93 (2017) 17-27 http://dx.doi.org/10.1016/j.astropartphys.2017.06.002