ИСТИНА

The monitoring of secondary cosmic rays, including the surface gamma radiation background (GRB) arriving from the upper hemisphere, has been carried out by the Polar Geophysical Institute since 2009. Scintillation detectors on NaI(Tl) crystals are used. The energy range of 20 keV - 5 МeV is covered by two crystals, of Ø62×20 mm and Ø150×110 mm. The first crystal is effective within the range of 20-400 keV, integral output channels >20 keV and >100 keV are used; the second crystal is effective within the range of 0.2-5 МeV. Based on the second crystal the device to measure the differential energy spectrum was developed. The GRB variations not related to an atmospheric precipitation have been detected. First of all, it is the annual variation whose amplitude is 25% and 50% in Apatity and Barentsburg, respectively. Additional measurements and experiments showed that the annual variation is related to the changes in the energy spectrum up to 450 keV only. In addition, the annual and day variations in other components of secondary cosmic rays have been studied. The transformation of the GRB differential spectrum of of 0.2-5 MeV range into subranges (200-400 keV, 400-600 keV, etc.) allowed us to reveal different bands having the different barometric coefficients increasing with the energy. That means that the radiation within the range of 0.2-5 MeV is generated by different mechanisms and originated from different types of particles. A noncontradictory hypothesis explaining the observed effect is suggested.