Measurements of the Energy Spectra of TGE Gamma Ray Flux on Aragats Mountain

In 2011 a network of five thallium-doped sodium iodide Nal(Tl) spectrometers was installed on Aragats Space Environmental Center (ASEC) for the research of a new discovered phenomenon, Thunderstorm ground enhancements (TGEs) - an intensive flux of electrons, gamma rays and neutrons originated in the thunderstorm atmospheres. Nal (Tl) crystals measure energy release of gamma rays, most penetrable and intensive specie of TGE. We perform calibration of the Nal(Tl) detectors and data acquisition electronics (DAQ) with gamma rays from the decay of the Caesium-137 (137Cs) isotope and with energy release corresponding to the peak in the energy spectrum of the ambient population of secondary cosmic ray (CR muons with energy ∼60 MeV). Thus, the gamma ray energies used for calibration cover two decades in energy range from 0.662 until 60 MeV. As well, a simulation-based procedure for reconstruction of gamma energy spectrum was developed and influence of a-priory information used in simulation on the accuracy of recovered energy spectra was investigated. (author)