[M-IS13] Atmospheric electricity: Application of technology for reducing disaster risks

[MIS13-09] Directional measurement of MeV gamma gays using the Si pixel detector Timepix3 with electron tracking and its application in winter Hokuriku TGF observation

*Tanaka Atsuya¹, Kazuhiro Nakazawa¹, Keigo Okuma¹, Yuuki Omiya¹, Mii Ando¹, Manari Oguchi¹, Teruaki Enoto², Yuuki Wada³, Yuko Ikkatai⁴, Ting Wu⁵, Daohong Wang ⁵ (1.NAGOYA UNIVERSITY, 2. Kyoto University, 3.Osaka University, 4.Kanazawa University, 5.Gifu University)

Keywords:Terrestrial Gamma-ray Flash (TGF), Directional Instrument, Timepix3 : silicon semiconductor active-pixel detector, Electrons Tracking

Winter thunderclouds are observed from November to March every year along the Sea of Japan coast, and one of their characteristics is the MeV gamma-ray radiation observed on the ground. There are two types of thunderstorm gamma rays: terrestrial gamma ray flashes (TGF), which are emitted on a time scale of less than 1 ms associated with lightning discharges, and gamma-ray glows (Glow), which is emitted from the thunderclouds themselves on a time scale of a few minutes. The GROWTH experiment has been observing the Japan Sea coast in winter since 2006, and we, the Nagoya Univ. group joined the campaign from 2018. As part of the FY2022 project, we introduced a new Terrestrial Gamma-ray Flash (TGF) directional instrument alongside a conventional detector. Remarkably, we achieved successful long-term operation from late November to mid-March. The innovative detector employed include Timepix3, a silicon semiconductor active-pixel detector, and a Cherenkov detector (as presented by Ando at the 2023 meeting and Ohguchi at this meeting). In particular, Timepix3, with 55×55µm² pixels, has a good time resolution of 1.56 ns, allowing for the simultaneous achievement of high-precision imaging and ultra-high temporal resolution. Moreover, utilizing the drift time of charge carriers, this detector has the capability to three-dimensionally trace the trajectories of rapidly moving charged particles generated within the detector. The interaction of MeV gamma-ray generates fast electrons, forming a trackable path within the silicon (Si) that exceeds the size of a pixel. Our focus lies in recognizing that Terrestrial Gamma-ray Flash (TGF), characterized by high-brightness and high-energy gamma-ray emission, allows the estimation of gamma-ray arrival direction through statistical processing of momentum information. We conducted 3D azimuthal measurements of the electron acceleration region using this system. Over a span of approximately four months of observation, the Timepix3 detector identified a Terrestrial Gamma-ray Flash (TGF) event on December 18, 2022. Despite the instantaneous and intensely bright nature of the event surpassing the processing speed of the detector, a portion of the data was successfully recorded. This confirmation establishes that a distinct group of electron trails was captured. In the forthcoming discussion, We will present the latest findings from our observations, placing a particular emphasis on the analysis of the TGF event.