ИСТИНА

In the Polar Geophysical Institute a complex set was developed for secondary cosmic rays monitoring. The set integrates detectors of neutron, charged (electron-muon) and electromagnetic components of secondary cosmic rays. Data are recorded continuously with the resolution of 1 minute. Besides, by means of the scintillation detector on a Ø150×110 mm NaI(Tl) crystal, the differential spectrum of background gamma-radiation is measured within the energy range of 0.2-5 MeV. The period of one spectrum gathering is set to 30 minutes. An integral spectrum is recorded by the scintillation detector on a Ø60×20 mm NaI(Tl) crystal within the range of 20-400 keV with two output channels: >20 and >100 keV. The neutron component is measured by two instruments: a conventional neutron monitor 18-NM-64 (NM) and a leadless section (bare NM, bNM). The conventional NM is sensitive to neutrons with energy exceeding ~50 MeV, while bNM is sensitive to neutrons with energy up to hundreds keV only. The detector of a charged component consists of two layers of the Geiger-Muller counters. The output of the upper layer and the coincidence of the two layers are used. The upper layer is sensitive to the charged particles and gamma-quanta both, the scheme of coincidence between the upper and lower layers selects the signal corresponding to a charged particle. The energy threshold for charged particles is estimated ~7 MeV. The set operates since 2009 and a great database has been accumulated and analyzed. Every year 50-70 increase events of 5 to 50 % in amplitude were registered in the gamma-ray background. The increase events are connected with precipitation. An annual variation of the gamma-ray background with amplitude ~30 % were found too. The same set under some reduction is set in Barentsburg station (Spitsbergen). The same increase events and annual variation are present. A noncontradictory hypothesis explaining the observed effect is suggested.