Results of measurements of an environment neutron background at BNO INR RAS objects with the helium proportional counter

Abstract

A method of measurements of the environmental neutron background at the Baksan Neutrino Observatory of the INR RAS are described. Measurements were done by using of a proportional counter filled with mixture of Ar(2 at)+${}^3$He(4 at). The results obtained at the surface and the underground laboratory of the BNO INR RAS are presented. It is shown that a neutron background in the underground laboratory at the 4900 m w.e. depth is decreased by $\sim 260$ times without any special shield in a comparison with the Earth surface. A neutron flux density in the 5-1323.5~cm air height region is constant within the determination error and equal to $(7.1\pm 0.1_{\mathrm{stat}}\pm 0.3_{\mathrm{syst}})\times 10^{-3}$ s${}^{-1}\cdot$cm${}^{-2}$.

5 pages, 4 figures, 2 tables