A.B. Akopova

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.

Linear energy transfer (LET) spectra of cosmic radiation in low earth orbit

Integral linear energy transfer (LET) spectra of cosmic radiation (CR) particles were measured on five Cosmos series spacecraft in low Earth orbit (LEO). Particular emphasis is placed on results of the Cosmos 1887 biosatellite which carried a set of joint U.S.S.R.-U.S.A. radiation experiments involving passive detectors that included thermoluminescent detectors (TLDs), plastic nuclear track detectors (PNTDs), fission foils, nuclear photo-emulsions, etc. which were located both inside and outside the spacecraft. Measured LET spectra are compared with those theoretically calculated. Results show that there is some dependence of LET spectra on orbital parameters. The results are used to estimate the CR quality factor (QF) for the Cosmos 1887 mission.

Development of an autoradiographic method of investigation of hot particles from the Chernobyl nuclear power plant

Abstract A method of autoradiographic investigation of hot particles that have risen into the atmosphere and precipitated on the soil and leaves after the Chernobyl accident of April 1986 has been developed. Particular objects of investigation are the α-active radionuclides with their dimensions and activity varying from 0.2 to 200 μm and from 10−6 to 10−1 Bq, respectively. BYa-2 nuclear emulsions were used as detectors. The activity distribution function of particles of different dimension, A = f(d), and the leaf contamination density distribution in the vertical profile are obtained.

Autoradiographic investigation of radionuclide alpha-activity in soil and plant samples from Chernobyl zone

Abstract Alpha-active “hot particles” in soil and plant samples collected in Chernobyl zone have been investigated by the radiographic method. The size and activity of “hot particles” were measured allowing to calculate their contribution into the radiation dose. Correlation between the measured particle parameters was established. The method of the particle size measuring with the help of low sensitive BYa-2 type photoemulsion is described. The measured mean diameter of hot particles varies from 10 to 200 μm and their activity is 10 −1 −10 −5 Bq. The most active particles (10 −1 − 10 −2 Bq) were found only in soil. The leaf samples after the same exposure contained particles with activity not higher than 10 −3 Bq.

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.

Experimental and calculated LET distributions in the Cosmos-2044 biosatellite orbit

During the flight of the Cosmos-2044 biosatellite, joint U.S.S.R.-U.S.A. investigations of different characteristics of cosmic radiation (CR) in the near-Earth environment were carried out. The U.S. dielectric track detectors CR-39 and Soviet BYa- and BR-type nuclear photo-emulsions were used as detectors. The present work shows some results of experimental measurements of linear energy transfer (LET) spectra of CR particles obtained with the use of these detectors, which were placed both inside and outside the satellite. The LET spectra measurement with plastic detectors is composed of two parts: the measurement of galactic cosmic rays (GCR) particles, and of short-range particles. The contributions of these components to the total LET distribution at various thicknesses of the shielding were analyzed and the results of these studies are presented. Calculated LET spectra in the Cosmos-2044 orbit were compared with experimental data. On the basis of experimental and calculated values of the LET spectra, absorbed and equivalent CR doses were calculated. In the shielding range of 1-1.5 g cm-2, outside the spacecraft, the photo-emulsions yielded 10.3 mrad d-1 and 27.5 mrem d-1 (LET > or = 2 MeV cm-1) while the CR-39 yielded averages of 1.43 mrad d-1 and 13.4 mrem d-1 (LET > or = 40 MeV cm-1). Inside the spacecraft (> or = 10 g cm-2) the photo-emulsions yielded 8.9 mrad d-1 and 14.5 mrem d-1.