Measurements of fast and intermediate neutron energy spectra on MIR space station in the second half of 1991

Abstract

This paper describes the neutron energy spectra measured inside and outside the Mir space station. The measurements were made during the second half of 1991 with nuclear emulsions and a neutron and recoil proton spectrometer, whose output data was telemetry-transmitted. In the fast-neutron ( E n > 1.0 MeV) range, the measurements were carried out using the method of recoil protons in a stack of nuclear photoemulsions (NPE) and in an organic scintillator. To determine spectra of intermediate-energy resonance neutrons (1.0 MeV ≥ E n ≥ 10 −2 MeV), an attempt was made to use the NPE method by adding lithium salts. The measurements are characterized by long-term (133 days) exposures of passive detectors and by sizeable effective shielding thicknesses of the inside detector estimated to be ∼40 g cm −2. The experimental results are compared with each other and with the data published elsewhere. The neutron spectra measured are used to calculate the equivalent dose rates inside and outside the Mir station in various neutron energy ranges. The equivalent neutron dose estimated by measuring the spectra in the (1–10 MeV) range only (as done in earlier works) is observed to entail substantial underestimating of the true neutron dose. Comparison is made of the calculated neutron doses with similar calculations of ionizing-radiation doses for shielding thickness of ∼ 40 g cm −2. It is emphasized that the study should be continued.