Observation of the gradual increases and bursts of energetic radiation in association with winter thunderstorm activity

冬季雷活動による放射線の緩やかな上昇とバーストの観測

鳥居 建男  ; 杉田 武志*; 村木 綏*

Torii, Tatsuo; Sugita, Takeshi*; Muraki, Yasushi*

冬季雷活動時に地上で放射線量率が上昇する事象が観測されることがある。この特徴を把握するために、異なる遮へい材でカバーした長尺比例計数管を用いた放射線検出器によりもんじゅ周辺で放射線変動を測定した。これらの測定結果はもんじゅの環境放射線モニタと比較するとともに、電場計を用いて、雷活動との相関を求めた。その結果、2種類の放射線上昇:落雷前のエネルギーが13MeV程度の約1分間の緩やかな放射線変動と落雷直後の10MeV以上の高エネルギー光子の入射が観測された。

The dose rate increases of the -rays were observed on the ground in the winter season of Japan. To investigate the profile of the radiations during the winter thunderstorms, a four set of the radiation detectors was prepared which consists of the long proportional counters. These detectors have different characteristics of the response for the incident particle energies by mounting different thick shielding covers. Those results were compared with the results measured at the same time by the environmental radiation monitors set up around a nuclear power facility. Electric field was also measured by using a field mill. As a result, the following two types of the radiation enhancements have been found during the winter thunderstorm activities; the gradual variation of photon intensity with energy of a few MeV, and the burst type of the radiation that are attributed to the injection of high energy photons with the energy over 10 MeV.