ИСТИНА

Ground-based experiments with scintillator gamma-spectrometers were conducted to study the spectral, temporal and spatial characteristics of TGEs as well, as to search the fast hard X-ray and gamma-ray flashes possibly appearing at the moment of lightning. The time of each gamma-quantum interaction was recorded with ~15 µs accuracy together with detailed spectral data. GPS module was used to synchronize the instrument time with UTC with enough accuracy to look at the gamma-ray data at the moment of lightning fixed by radio-wave detector or by any other instrument. The energy range of gamma-spectrometers from ~30 keV to >5MeV includes the region where the radiation of natural isotopes is absent. In this case one can see background changes connected with particles accelerated in thundercloud together with the background increases during the rain caused by Rn-222 daughters. Long-term measurements with two instruments placed in different points of Moscow region were done in 2016 summer season. First one based on CsI(Tl) 80x80 mm has energy range 0.03-6 MeV. The range of the second one based on CsI(Tl) 100x100 mm is 0.05-10 MeV. A dozen of thunderstorms with increase of Rn-222 radiation were detected but no significant increase of gamma-ray flux above 3.2 MeV was observed at these periods. The result of the search for short bursts at the moment of lightning will be discussed as well as the results of the study of slow variations. Continuous observations with 50x50 mm NaI(Tl) gamma-ray spectrometer were provided at mountain altitude in Armenia at Aragatz station. The results of spectral and temporal analysis of readings during the TGE periods, fixed by high-energy gamma-ray and particle flux monitors installed on Aragatz will be presented. The search for fast flashes possibly accompanying lightning was realized by triggering from the UV and optical photometer placed near the gamma-ray instrument. The results of the search for the short flashes in the recorded data will be also discussed.