Skobeltsyn Institute of Nuclear Physics
Lomonosov Moscow State University

Knowing of space distribution and time variations of the neutron fluxes in near-Earth space is of great importance because its contribution to the total radiation dose under the shielding in some tens of g/cm2 on the massive orbital stations can reach fifty and more per cent. Neutrons form significant part of the background during solar neutron, solar and cosmic gamma-ray observations. Information on atmospheric albedo neutrons gives an opportunity to better understand its role in the formation of proton radiation belt. Long and detailed experimental investigations of neutron fluxes in near-Earth space were carried out in SINP. It began in 1970 and continued up to 1997 onboard "Molniya-1", "Kosmos-557" satellites, "Salute", "Salute-4", "Salute-6" orbital stations, orbital complex "Salute-7" - "Kosmos-1686", orbital station "MIR", and CORONAS-I satellite. In this paper methods used, calibrations, experiments, main results and further perspectives of the SINP neutron studying are described. Detailed description of original instruments, designed in SINP for detection of neutrons in the energy range from thermal up to several hundreds MeV, is presented. Latitude dependencies and input to the total flux of albedo neutrons and neutrons, born in nuclear interactions of cosmic rays with the material of the spacecraft (local neutrons) on spacecraft s of various mass were obtained. Estimations of angle distribution and shapes of the spectra were made too. Fluxes of local neutrons were estimated both outside and inside of inner radiation belt. Fluxes of neutrons, born in the solar proton interaction with Earth atmosphere and satellite matter for 25.01.71, 06-08.06.91, 16.06.91 and 10.05.92 events were detected and fluxes of solar proton albedo neutrons were estimated for the first time. For June 1991 and May 1992 solar proton events estimations of spectra of albedo neutrons were produced oo. Dependence of measured flux of neutrons with the energies >20 MeV on spacecraft mass in the range from 1.4 to 120 tons is produced also for the first time. It was shown that on massive orbital stations measured neutron fluxes mainly are due to local neutrons.