Observation of dose-rate increases during winter thunderstorms and Monte-Carlo simulation of bremsstrahlung generation

Publisher Summary This chapter focuses on the observation of dose-rate increases during winter thunderstorms and monte-carlo simulation of bremsstrahlung generation. Increases of environmental gamma-ray dose that seem to originate from a thunderstorm were observed around a nuclear facility in Japan. Dose increases measured by thermoluminescent dosimeters (TLDs) exposed during a period including a large lightning flash were up to about 0.1 mGy. Dose rates indicated by environmental radiation monitors around the facility were also increased transiently at that time. From pulse height analysis of a NaI(Tl) scintillation detector, the photon energy spectrum evaluated by spectral unfolding is continuous with energy up to several MeV, consistent with bremsstrahlung emission from energetic electrons. Furthermore, energy spectra of bremsstrahlung photons emitted from high-energy electrons in thunderstorm electric fields are obtained by Monte-Carlo simulation. These results are discussed in conjunction with observation.