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

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

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.