11:15 AM - 11:30 AM
[MIS24-03] Development of Cherenkov detector for directional observation of sudden gamma rays associated with lightning discharges.
Keywords:gamma-rays from lightning activity
Bremsstrahlung gamma rays from electrons accelerated to relativistic energy and amplified by the electrostatic field in thunderclouds are observed along the coast of the Sea of Japan in winter, and their energy can reach 30 MeV. We, the team from Nagoya University, have been participating in the GROWTH (Gamma-ray Observation of Winter Thunderclouds) experiment since 2018, conducting ground-based observations.
There are two types of thunderstorm gamma rays: gamma-ray glow, which is emitted by the thundercloud itself over several minutes, and TGF (Terrestrial Gamma-ray Flash), which is emitted instantaneously at the same time as the lightning discharge. TGF is an extremely bright radiation, with thousands of MeV gamma rays per cm2 arriving within a few hundred µs, and is not easy to observe.
We have been deploying GOOSE, a glow altimetry detector, to observe thunderstorm gamma rays, but it is not suitable for TGF observations because it is optimized for glow detection. By taking advantage of the data acquisition system, which stores information photon-by-photon, we were able to make multi-point observations of TGF and compare them with lightning discharge steps identified by radio observation arrays. However, in the course of this analysis we realized that it is important to determine direction of TGFs independently from that of suspected radio pulses associated with them. We are therefore developing a new detector using Cherenkov light aiming at the first ground-based short-range directional observation of TGFs.
The detector is based on a plastic rod with photo-sensors. To verify the performance of the new detector, prompt gamma irradiation up to 8 MeV were performed at the accelerator-driven neutron source KUANS. By irradiating the detector from various directions, basing angular resolution was confirmed. The prototype Cherenkov detector has been installed in Kanazawa, Ishikawa since December 2022 and has detected two TGF events. Although the statistics are not enough, signals have been obtained and will be analyzed in the future.
There are two types of thunderstorm gamma rays: gamma-ray glow, which is emitted by the thundercloud itself over several minutes, and TGF (Terrestrial Gamma-ray Flash), which is emitted instantaneously at the same time as the lightning discharge. TGF is an extremely bright radiation, with thousands of MeV gamma rays per cm2 arriving within a few hundred µs, and is not easy to observe.
We have been deploying GOOSE, a glow altimetry detector, to observe thunderstorm gamma rays, but it is not suitable for TGF observations because it is optimized for glow detection. By taking advantage of the data acquisition system, which stores information photon-by-photon, we were able to make multi-point observations of TGF and compare them with lightning discharge steps identified by radio observation arrays. However, in the course of this analysis we realized that it is important to determine direction of TGFs independently from that of suspected radio pulses associated with them. We are therefore developing a new detector using Cherenkov light aiming at the first ground-based short-range directional observation of TGFs.
The detector is based on a plastic rod with photo-sensors. To verify the performance of the new detector, prompt gamma irradiation up to 8 MeV were performed at the accelerator-driven neutron source KUANS. By irradiating the detector from various directions, basing angular resolution was confirmed. The prototype Cherenkov detector has been installed in Kanazawa, Ishikawa since December 2022 and has detected two TGF events. Although the statistics are not enough, signals have been obtained and will be analyzed in the future.