L.V. Melkumyan

A study of the radiation environment on board the Space Shuttle flight STS-57

A joint NASA-Russian study of the radiation environment inside a SPACEHAB 2 locker on Space Shuttle flight STS-57 was conducted. The Shuttle flew in a nearly circular orbit of 28.5 degrees inclination and 462 km altitude. The locker carried a charged particle spectrometer, a tissue equivalent proportional counter (TEPC), and two area passive detectors consisting of combined NASA plastic nuclear track detectors (PNTDs) and thermoluminescent detectors (TLDs), and Russian nuclear emulsions, PNTDs and TLDs. All the detector systems were shielded by the same Shuttle mass distribution. This makes possible a direct comparison of the various dose measurement techniques. In addition, measurements of the neutron energy spectrum were made using the proton recoil technique. The results show good agreement between the integral LET spectrum of the combined galactic and trapped particles using the tissue equivalent proportional counter and track detectors between about 15 keV/micrometers and 200 keV/micrometers. The LET spectrum determined from nuclear emulsions was systematically lower by about 50%, possibly due to emulsion fading. The results show that the TEPC measured an absorbed dose 20% higher than the TLDs, due primarily to an increased TEPC response to neutrons and a low sensitivity of TLDs to high LET particles under normal processing techniques. There is a significant flux of high energy neutrons that is currently not taken into consideration in dose equivalent calculations. The results of the analysis of the spectrometer data will be reported separately.

Differential neutron energy spectra measured on spacecraft in low earth orbit

Two methods for measuring neutrons in the range from thermal energies to dozens of MeV were used. In the first method, alpha-particles emitted from the 6Li(n,alpha)T reaction are detected with the help of plastic nuclear track detectors, yielding results on thermal and resonance neutrons. Also, fission foils are used to detect fast neutrons. In the second method, fast neutrons are recorded by nuclear photographic emulsions (NPE). The results of measurements on board various satellites are presented. The neutron flux density does not appear to correlate clearly with orbital parameters. Up to 50% of neutrons are due to albedo neutrons from the atmosphere while the fluxes inside the satellites are 15-20% higher than those on the outside. Estimates show that the neutron contribution to the total equivalent radiation dose reaches 20-30%.

Neutron fluences and energy spectra in the Cosmos-2044 biosatellite orbit

Joint Soviet-American measurements of the neutron component of space radiation (SR) were carried out during the flight of the Soviet biosatellite Cosmos-2044. Neutron flux densities and differential energy spectra were measured inside and on the external surface of the spacecraft. Three energy intervals were employed: thermal (En < or = 0.2 eV), resonance (0.2 eV < En < 1.0 MeV) and fast (En > or = 1.0 MeV) neutrons. The first two groups were measured with U.S. 6LiF detectors, while fast neutrons were recorded both by U.S. fission foils and Soviet nuclear emulsions. Estimations were made of the contributions to absorbed and equivalent doses from each neutron energy interval and a correlation was presented between fast neutron fluxes, measured outside the satellite, and the phase of solar activity (SA). Average dose equivalent rates of 0.018 and 0.14 mrem d-1 were measured for thermal and resonance neutrons, respectively, outside the spacecraft. The corresponding values for fast neutrons were 3.3 (U.S.) and 1.8 (U.S.S.R.) mrem d-1. Inside the spacecraft, a value of 3.5 mrem d-1 was found.

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.

Studying radiation environment on board STS-55 and STS-57 by the method of passive detectors

Abstract Radiation environment onboard STS-55 and 57 is estimated using experimental and calculated data.

Monitoring and forecasting of the geomagnetic and radiation storms during the 23rd solar cycle: Aragats regional space weather center

Abstract The Solar Environment Center located on Mt. Aragats will provide real-time monitoring and forecasting of the extreme Geomagnetic and Radiation Events. Two neutron monitors, a muon telescope and a Solar scintillation telescope operating on Aragats research stations will provide accurate detection of very low fluxes of the most energetic Solar particles and modulation effects of Solar events. The correlation of the Solar Energetic Phenomena with modulations of the Galactic Cosmic Ray flux and direct detection of the high-energy protons and neutrons emitted during Coronal Mass Ejection provide firm grounds for specification and forecasting of the effects of tremendous explosions on the Solar surface. Consequently ground observation of the variations of Cosmic Ray fluxes make it possible to issue alerts to avoid imminent hazard of upcoming Geomagnetic and Radiation Storms.

Some radiation environment estimation data from 10–12 km altitude aircraft

The results of probing the radiation environment on board different civil aviation planes with single-type detectors (nuclear emulsions), with particular emphasis to the cosmic radiation flux measured in-side aircraft, are presented. The measurement results make it possible to find the absorbed and equivalent doses induced by the cosmic radiation neutrons and charged particles.

Determination of cosmic radiation characteristics aboard “salute - 7” orbital station

Abstract The particles fluence was measured, the integral LET spectrum of cosmic radiation in the range of ( 7.55·102 – 4.9·104 ) MeV/cm in the emulsion as well as the integral spectrum of charge distribution of stopping nuclei with Z ⩾ 5 were obtained with the help of registration controlled nuclear emulsion exposed on board the “Salute - 7” orbital station during more than 8 months.