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 us accuracy together with detailed spectral data. The measurements are similar to ones reported at TEPA-2015 but some important improvement of the instruments was done for summer, 2016 season. First, GPS module was used to synchronize the instrument time with UTC. The accuracy of such synchronization allows one to look at the gamma-ray data at the moment of lightning fixed by radio-wave detector or any other instrument. Second, the energy range of gamma-spectrometers was shifted to higher energies 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 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 fixed by radio-wave detector working in MSU will be discussed as well as the results of the study of slow variations. A lot of data was obtained from the experiment with small gamma-ray spectrometer (40x40 mm NaI(Tl) at mountain altitude in Armenia at Aragatz station. The analysis of readings during the TGE periods indicates on the presence of Rn-222 radiation in low-energy range (E<1 MeV). The use of larger detector with good spectrometric characteristics is necessary for more significant conclusion.