Radiation protection guidelines for space activities

At the beginning of the space age the dangers of hurtling into space were considerable. Despite this fact, radiation risks were examined in the U.S.S.R. and the U.S.A. and recommendations were made to limit the exposure of the crews to radiation. To date the radiation exposures of crews on missions in low-Earth orbits have been low. Now that missions in low-Earth orbit are becoming longer in duration and new missions into deep space are being considered, radiation protection guidelines become more important. Recently the estimates of the risks of radiation-induced cancer have been increased and new guidelines on radiation exposure limits for crew members must be developed. For deep space missions the guidelines take into account the risks posed by heavy ions. Unfortunately, knowledge about these risks is insufficient. If the new risk estimates are applied, current career dose limits may have to be reduced by a factor of two.     

Cosmic radiation exposure of biological test systems during the EXPOSE-E mission

In the frame of the EXPOSE-E mission on the Columbus external payload facility EuTEF on board the International Space Station, passive thermoluminescence dosimeters were applied to measure the radiation exposure of biological samples. The detectors were located either as stacks next to biological specimens to determine the depth dose distribution or beneath the sample carriers to determine the dose levels for maximum shielding. The maximum mission dose measured in the upper layer of the depth dose part of the experiment amounted to 238±10 mGy, which relates to an average dose rate of 408±16 μGy/d. In these stacks of about 8?mm height, the dose decreased by 5-12% with depth. The maximum dose measured beneath the sample carriers was 215±16 mGy, which amounts to an average dose rate of 368±27 μGy/d. These values are close to those assessed for the interior of the Columbus module and demonstrate the high shielding of the biological experiments within the EXPOSE-E facility. Besides the shielding by the EXPOSE-E hardware itself, additional shielding was experienced by the external structures adjacent to EXPOSE-E, such as EuTEF and Columbus. This led to a dose gradient over the entire exposure area, from 215±16 mGy for the lowest to 121±6 mGy for maximum shielding. Hence, the doses perceived by the biological samples inside EXPOSE-E varied by 70% (from lowest to highest dose). As a consequence of the high shielding, the biological samples were predominantly exposed to galactic cosmic heavy ions, while electrons and a significant fraction of protons of the radiation belts and solar wind did not reach the samples.     

HZE particle effects in space

Among the various particulate components of ionizing radiation in space, heavy ions (the so-called HZE particles) have been of special concern to radiobiologists. To understand the ways by which HZE particles of cosmic radiation interact with biological systems, methods have been developed to precisely localize the trajectory of an HZE particle relative to the biological object and to correlate the physical data of the particle with the biological effects observed along its path. In a variety of test systems, injuries were traced back to the traversal of a single HZE particle, such as somatic mutations, and chromosomal aberrations in plant seeds, development disturbances and malformations in insect and salt shrimp embryos, or cell death in bacterial spores. In the latter case, a long-ranging killing effect around the particle's track was observed. Whereas, from spaceflight experiments, substantial infomation has been accumulated on single HZE particle effects in resting systems and in a few embryonic systems, there is a paucity of data on cosmic radiation effects in whole tissues or animals, especially mammalians.     

航天员空间活动接受辐射剂量限值的研究

空间生物学辐射效应是由空间辐射环境引起的,空间辐射环境的变化受太阳活动性影响。空间辐射水平比地表面水平高,航天员在空间所接受剂量比地面人员接受的吸收剂量高出100倍甚至更高,并且高能重离子的生物效应显著。文章简要阐述了空间辐射环境、空间辐射生物学效应与航天员的辐射剂量限值等问题。     

Effects of sublethal irradiation with helium ions (300 MeV/nucleon) on basic hematological parameters of mice

The aim of the experiment was to obtain new knowledge on the biological effectiveness of high-energy (300 MeV/nucleon) helium ions, which represent a part of the spectrum of cosmic rays. Male (CBA x C57BL)F1 mice, 4 months old, were exposed to a dose of 4 Gy helium ions (exposure rate 0.05 Gy/min). As a comparative standard irradiation the same dose of 4 Gy of 137Cs gamma-rays (exposure rate 0.07 Gy/min) was used. Material sampling was performed 6-8 h, 4 days and 9 days after irradiation for both experimental groups mentioned above. There were 7 animals in each group including the control group of non-irradiated mice. Eight basic hematological parameters of peripheral blood, bone marrow, spleen and thymus were studied. On day 4 after the irradiation with helium ions, the values of leukocyte counts in peripheral blood, bone marrow cellularity and spleen cellularity were reduced to about 10% of the respective control values while the decline after irradiation with gamma-rays amounted to about 50%. These and other results presented reflect a high relative biological effectiveness of 300 MeV/nucleon helium ions.     

R3DE: Radiation Risk Radiometer-Dosimeter on the International Space Station--optical radiation data recorded during 18 months of EXPOSE-E exposure to open space

Radiation Risk Radiometer-Dosimeter E (R3DE) served as a device for measuring ionizing and non-ionizing radiation as well as cosmic radiation reaching biological samples located on the EXPOSE platform EXPOSE-E. The duration of the mission was almost 1.5 years (2008-2009). With four channels, R3DE detected the wavelength ranges of photosynthetically active radiation (PAR, 400-700?nm), UVA (315-400?nm), UVB (280-315?nm), and UVC (<280?nm). In addition, the temperature was recorded. Cosmic ionizing radiation was assessed with a 256-channel spectrometer dosimeter (see separate report in this issue). The light and UV sensors of the device were calibrated with spectral measurement data obtained by the Solar Radiation and Climate Experiment (SORCE) satellite as standard. The data were corrected with respect to the cosine error of the diodes. Measurement frequency was 0.1?Hz. Due to errors in data transmission or temporary termination of EXPOSE power, not all data could be acquired. Radiation was not constant during the mission. At regular intervals of about 2 months, low or almost no radiation was encountered. The radiation dose during the mission was 1823.98 MJ m(-2) for PAR, 269.03 MJ m(-2) for UVA, 45.73 MJ m(-2) for UVB, or 18.28 MJ m(-2) for UVC. Registered sunshine duration during the mission was about 152 days (about 27% of mission time).The surface of EXPOSE was most likely turned away from the Sun for considerably longer. R3DE played a crucial role on EXPOSE-EuTEF (EuTEF, European Technology Exposure Facility), because evaluation of the astrobiology experiments depended on reliability of the data collected by the device. Observed effects in the samples were weighted by radiation doses measured by R3DE.     

Probabilistic assessment of radiation risk for astronauts in space missions

Accurate estimations of the health risks to astronauts due to space radiation exposure are necessary for future lunar and Mars missions. Space radiation consists of solar particle events (SPEs), comprised largely of medium energy protons (less than several hundred MeV); and galactic cosmic rays (GCR), which include high-energy protons and heavy ions. While the frequency distribution of SPEs depends strongly upon the phase within the solar activity cycle, the individual SPE occurrences themselves are random in nature. A solar modulation model has been developed for the temporal characterization of the GCR environment, which is represented by the deceleration potential, ?. The risk of radiation exposure to astronauts as well as to hardware from SPEs during extra-vehicular activities (EVAs) or in lightly shielded vehicles is a major concern for radiation protection. To support the probabilistic risk assessment for EVAs, which could be up to 15% of crew time² on lunar missions, we estimated the probability of SPE occurrence as a function of solar cycle phase using a non-homogeneous Poisson model [1] to fit the historical database of measurements of protons with energy>30 MeV, Φ₃₀. The resultant organ doses and dose equivalents, as well as effective whole body doses, for acute and cancer risk estimations are analyzed for a conceptual habitat module and for a lunar rover during space missions of defined durations. This probabilistic approach to radiation risk assessment from SPE and GCR is in support of mission design and operational planning for future manned space exploration missions.     

Radiation engineering analysis of shielding materials to assess their ability to protect astronauts in deep space from energetic particle radiation

An analysis is performed on four typical materials (aluminum, liquid hydrogen, polyethylene, and water) to assess their impact on the length of time an astronaut can stay in deep space and not exceed a design basis radiation exposure of 150 mSv. A large number of heavy lift launches of pure shielding mass are needed to enable long duration, deep space missions to keep astronauts at or below the exposure value with shielding provided by the vehicle. Therefore, vehicle mass using the assumptions in the paper cannot be the sole shielding mechanism for long duration, deep space missions. As an example, to enable the Mars Design Reference Mission 5.0 with a 400 day transit to and from Mars, not including the 500 day stay on the surface, a minimum of 24 heavy lift launches of polyethylene at 89,375 lbm (40.54 tonnes) each are needed for the 1977 galactic cosmic ray environment. With the assumptions used in this paper, a single heavy lift launch of water or polyethylene can protect astronauts for a 130 day mission before exceeding the exposure value. Liquid hydrogen can only protect the astronauts for 160 days. Even a single launch of pure shielding material cannot protect an astronaut in deep space for more than 180 days using the assumptions adopted in the analysis. It is shown that liquid hydrogen is not the best shielding material for the same mass as polyethylene for missions that last longer than 225 days.     

Time profile of cosmic radiation exposure during the EXPOSE-E mission: the R3DE instrument

The aim of this paper is to present the time profile of cosmic radiation exposure obtained by the Radiation Risk Radiometer-Dosimeter during the EXPOSE-E mission in the European Technology Exposure Facility on the International Space Station's Columbus module. Another aim is to make the obtained results available to other EXPOSE-E teams for use in their data analysis. Radiation Risk Radiometer-Dosimeter is a low-mass and small-dimension automatic device that measures solar radiation in four channels and cosmic ionizing radiation as well. The main results of the present study include the following: (1) three different radiation sources were detected and quantified-galactic cosmic rays (GCR), energetic protons from the South Atlantic Anomaly (SAA) region of the inner radiation belt, and energetic electrons from the outer radiation belt (ORB); (2) the highest daily averaged absorbed dose rate of 426 μGy d(-1) came from SAA protons; (3) GCR delivered a much smaller daily absorbed dose rate of 91.1 μGy d(-1), and the ORB source delivered only 8.6 μGy d(-1). The analysis of the UV and temperature data is a subject of another article (Schuster et al., 2012 ).     

Production of neutrons from interactions of GCR-like particles

In order to help assess the risk to astronauts due to the long-term exposure to the natural radiation environment in space, an understanding of how the primary radiation field is changed when passing through shielding and tissue materials must be obtained. One important aspect of the change in the primary radiation field after passing through shielding materials is the production of secondary particles from the breakup of the primary. Neutrons are an important component of the secondary particle field due to their relatively high biological weighting factors, and due to their relative abundance, especially behind thick shielding scenarios. Because of the complexity of the problem, the estimation of the risk from exposure to the secondary neutron field must be handled using calculational techniques. However, those calculations will need an extensive set of neutron cross section and thicktarget neutron yield data in order to make an accurate assessment of the risk. In this paper we briefly survey the existing neutron-production data sets that are applicable to the space radiation transport problem, and we point out how neutron production from protons is different than neutron production from heavy ions. We also make comparisons of one the heavy-ion data sets with Boltzmann-Uehling-Uhlenbeck (BUU) calculations.     

Intensity/frequency indicator for detection in space: the high values of the incident solar or laser optical radiation in comparison with the appropriate maximum permissible exposure.

The solar or laser optical radiation impact to humans in space depends on the intensity, on the exposure type (direct or indirect) & duration and on the matching of radiation wavelength to tissue characteristics. The main protection factor in space is the application of exposure limits. This paper describes the main biological optical interaction parameters, the optical exposure hazards and the development of a small active lightweight indicator, with output beeper rate depended to the ratio of optical irradiance/exposure limit. The indicator may be used as warning element on the side of helmets, goggles, spectacles, etc, with low power consumption. Electronically the indicator is an intensity/frequency converter, based on the value of the ratio of exposure/exposure limits, with audio & light beepers like the indication output of the ionizing (radioactive) radiation monitors.     

EXPOSE-E: an ESA astrobiology mission 1.5 years in space

The multi-user facility EXPOSE-E was designed by the European Space Agency to enable astrobiology research in space (low-Earth orbit). On 7 February 2008, EXPOSE-E was carried to the International Space Station (ISS) on the European Technology Exposure Facility (EuTEF) platform in the cargo bay of Space Shuttle STS-122 Atlantis. The facility was installed at the starboard cone of the Columbus module by extravehicular activity, where it remained in space for 1.5 years. EXPOSE-E was returned to Earth with STS-128 Discovery on 12 September 2009 for subsequent sample analysis. EXPOSE-E provided accommodation in three exposure trays for a variety of astrobiological test samples that were exposed to selected space conditions: either to space vacuum, solar electromagnetic radiation at >110?nm and cosmic radiation (trays 1 and 3) or to simulated martian surface conditions (tray 2). Data on UV radiation, cosmic radiation, and temperature were measured every 10?s and downlinked by telemetry. A parallel mission ground reference (MGR) experiment was performed on ground with a parallel set of hardware and samples under simulated space conditions. EXPOSE-E performed a successful 1.5-year mission in space.     

Space radiation analysis: Radiation effects and particle interaction outside the Earth's magnetosphere using GRAS and GEANT4

In order to explore the Moon and Mars it is necessary to investigate the hazards due to the space environment and especially ionizing radiation. According to previous papers, much information has been presented in radiation analysis inside the Earth's magnetosphere, but much of this work was not directly relevant to the interplanetary medium. This work intends to explore the effect of radiation on humans inside structures such as the ISS and provide a detailed analysis of galactic cosmic rays (GCRs) and solar proton events (SPEs) using SPENVIS (Space Environment Effects and Information System) and CREME96 data files for particle flux outside the Earth's magnetosphere. The simulation was conducted using GRAS, a European Space Agency (ESA) software based on GEANT4. Dose and equivalent dose have been calculated as well as secondary particle effects and GCR energy spectrum. The calculated total dose effects and equivalent dose indicate the risk and effects that space radiation could have on the crew, these values are calculated using two different types of structures, the ISS and the TransHab modules. Final results indicate the amounts of radiation expected to be absorbed by the astronauts during long duration interplanetary flights; this denotes importance of radiation shielding and the use of proper materials to reduce the effects.     

The biological effectiveness of HZE-particles of cosmic radiation studied in the Apollo 16 and 17 Biostack experiments

The Biostack experiments I and II were flown on board the Apollo 16 and 17 command modules in order to obtain information on the biological damage produced by the bombardment of heavy high-energy (HZE) particles of cosmic radiation during spaceflight. Such data are required for estimating radiation hazards in manned spaceflight. Seven biological systems in resting state (Bacillus subtilis spores, Colpoda cucullus cysts, Arabidopsis thaliana seeds, and eggs of Artemia salina, Tribolium castaneum and of Carausius morosus) were accommodated in the two Biostacks. By using a special sandwich construction of visual track detectors and layers of biological objects, identification of each hit biological object was achieved and the possible biological damage correlated with the physical features of the responsible HZE-particle. In the different systems the degree of damage depended on whether the hit cell was replaceable or not. A high sensitivity to HZE-particle bombardment was observed on Artemia salina eggs; 90% of the embryos, which were induced to develop from hit eggs, died at different developmental stages. Malformations of the abdomen or the extremities of the nauplius were frequently induced. In contrast, the growth of hit Vicia faba radiculae and the germination of hit Arabidopsis thaliana seeds and hit Bacillus subtilis spores were not influenced remarkably. But there was an increase in multicaulous plants and a reduction in the outgrowth of the bacterial spores. In addition, information was obtained on the fluence of the HZE-particles, on their spectrum of charge and energy loss, and on the absorption by the Apollo spacecraft and the Biostack material itself. This will help to improve knowledge concerning radiation conditions inside of spacecrafts, necessary to secure a maximum possible protection to the astronauts.     

Survival of plant seeds, their UV screens, and nptII DNA for 18 months outside the International Space Station

The plausibility that life was imported to Earth from elsewhere can be tested by subjecting life-forms to space travel. Ultraviolet light is the major liability in short-term exposures (Horneck et al., 2001 ), and plant seeds, tardigrades, and lichens-but not microorganisms and their spores-are candidates for long-term survival (Anikeeva et al., 1990 ; Sancho et al., 2007 ; J?nsson et al., 2008 ; de la Torre et al., 2010 ). In the present study, plant seeds germinated after 1.5 years of exposure to solar UV, solar and galactic cosmic radiation, temperature fluctuations, and space vacuum outside the International Space Station. Of the 2100 exposed wild-type Arabidopsis thaliana and Nicotiana tabacum (tobacco) seeds, 23% produced viable plants after return to Earth. Survival was lower in the Arabidopsis Wassilewskija ecotype and in mutants (tt4-8 and fah1-2) lacking UV screens. The highest survival occurred in tobacco (44%). Germination was delayed in seeds shielded from solar light, yet full survival was attained, which indicates that longer space travel would be possible for seeds embedded in an opaque matrix. We conclude that a naked, seed-like entity could have survived exposure to solar UV radiation during a hypothetical transfer from Mars to Earth. Chemical samples of seed flavonoid UV screens were degraded by UV, but their overall capacity to absorb UV was retained. Naked DNA encoding the nptII gene (kanamycin resistance) was also degraded by UV. A fragment, however, was detected by the polymerase chain reaction, and the gene survived in space when protected from UV. Even if seeds do not survive, components (e.g., their DNA) might survive transfer over cosmic distances.     

Monitoring of the time and spatial distribution of neutron-flux spectral density outside the Russian segment of the <Emphasis Type="Italic">International Space Station</Emphasis> based on data from the BTN-Neutron space experiment

Results of measurements of neutron-flux spectral density in the vicinity of the International Space Station (ISS) based on BTN-Neutron space experimental data acquired in 2007–2014 have been presented in this paper. It has been shown that, during the flight of the ISS over different regions of the Earth’s surface, neutron flux in the energy range of 0.4 eV–15 MeV varies from 0.1 n/sm²/s in equatorial regions to 50 n/sm²/s in the South Atlantic anomaly region. The measurements were used to estimate the contribution of the neutron component to the overall exposure dose rate. The total contribution of fast neutrons is about 0.1–0.4 μ Zv/h above the equator area and more than 50 μ Zv/h above the South Atlantic anomaly region. A data analysis of BTN-Neutron data also showed that the time profile of neutron flux has long-periodic variations. It was found that, under the influence of Galactic cosmic rays (GCRs), modulation during 24th solar cycle neutron flux changed almost twofold (above high latitude regions). Maximum values of neutron flux were observed in January 2010 and minimum values were observed in January 2014.     

空间重离子辐照效应评述

文章对生物、半导体、光学材料、金属、聚合物的空间重离子辐照效应的研究工作进行了评述,也阐明了深入开展重离子空间环境模型以及重离子辐照效应与演化规律的研究具有重要意义。研究表明空间环境中重离子的含量虽少,但由于其高的电离能力和穿透力,对生物、半导体、光学材料、金属、聚合物等会产生各种辐射损伤效应,导致卫星信号故障、光学器件失效、金属与聚合物性能及形貌改变,甚至影响航天员的生命安全。     

On the problem of lunar radiation environment

In connection with projects of manned bases on the Moon it becomes topical to estimate radiation danger for their inhabitants. In this paper we describe a method of evaluation of the radiation environment on the lunar surface produced by galactic and solar cosmic rays. The roles of both primary and secondary radiations generated in the depth of the lunar soil under the action of high-energy protons and nuclei are taken into account. Calculated fluxes of particles are used in order to estimate annual averaged absorbed and equivalent local dose rates in tissues. It is established that in the lunar rock the contribution of secondary neutrons to the dose rate exceeds that of protons. The contribution of the secondary particles generated by nuclei of galactic cosmic rays to the dose rate is estimated.     

Cosmic dosimetry using TLD aboard spacecrafts of the "Cosmos" series

Thermoluminescent (TL) detectors were used for dosimetric investigations on the outer surface as well as inside Soviet spacecrafts of the "Cosmos" series. At the outer surface, ultrathin TL detectors, based on CaF2-PTFE and LiF, were arranged in special stacks and exposed to unshielded cosmic radiation. The strong decrease of dose within a few mg/cm2 demonstrates that weakly penetrating radiation is dominating in the radiation field under investigation. On the basis of glow curve analysis of LiF thermoluminescent detectors it could be shown, that the high doses are caused by electrons.     

大容量Flash存储器空间辐射效应试验研究

分析了商用Flash存储器应用于航天器时应考虑的空间辐射效应和机理,并利用钴-60γ射线和重离子加速器对韩国三星公司生产的大容量Flash存储器K9XXG08UXA系列进行了抗电离总剂量试验和抗单粒子试验,以评估其空间应用可行性。试验结果显示：这一系列存储器的累积电离总剂量为50krad（Si）时,器件部分数据丢失,重...