Long-durationγray emissions from 2007 and 2008 winter thunderstorms

摘要: The Gamma-Ray Observation of Winter Thunderclouds (GROWTH) experiment, consisting two radiation detection subsystems, has been operating since 2006 on the premises Kashiwazaki-Kariwa nuclear power plant located at coastal area Japan Sea. By February 2010, GROWTH detected seven long-duration γ ray emissions associated with winter thunderstorms. Of them, events, obtained 13 December 2007 and 25 2008, are reported. On both occasions, all inorganic scintillators (NaI, CsI, BGO) subsystems significant signals lasting for >1 min. Neither these events were any lightning. In cases, energy spectra extend to 10 MeV, suggesting that rays produced by relativistic electrons via bremsstrahlung. Assuming initial photon spectrum source is expressed a law function, observed photons can be interpreted as being radiated from distance 290–560 m event 110–690 2008 one, 90% confidence level. Employing spectra, number estimated 10^(9)–10^(11). estimation generally agrees those calculated basis runaway electron avalanche model. A spectrum, summed over three individual including present another reported previously, similar features cutoff energy, an averaged terrestrial flashes.