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PubMed1986

Biological effects of heavy ions in Arabidopsis seeds.

Irradiation of dry seeds of Arabidopsis with heavy ions (HZE-particles) produced by UNILAC-accelerator (GSI, Darmstadt) yielded aberrations in varied developmental endpoints such as survival rate and embryo vitality. The damage increased with particle density and charge. Cross sections in the range of 0.2-1.0 micrometer2 for Ne and Ar and 2.0-10.0 micrometers2 for Xe were estimated. Soaked seeds were more sensitive than dry seeds (cross-section 2.0-10.0 micrometers2 for Ar). The induced total damage in the irradiated seeds was estimated adding the different damages weighted by certain factors. These results will be used as base data for the interpretation and evaluation of spaceflight experiments on the biological effects of cosmic radiation.

Arabidopsis↗

PubMed2002

Cosmic rays: are air crew at risk?

This article reviews the current knowledge about cosmic rays and their possible effects on health of air crew, discusses research directions necessary for establishing and measuring the risks, and highlights the need for physicians and air crew to be informed, despite the inconclusiveness of the evidence. A literature review of computerised medical and scientific databases was carried out. Recent reports highlighting increased incidence of cancer among airline pilots and cabin crew have renewed concerns about possible exposure to harmful levels of cosmic radiation at altitude. Such low energy ionising radiation has been shown to cause double stranded DNA deletions and induce genomic instability in human chromosomes. In the field of microelectronics, cosmic rays have been shown to cause "hard" and "soft" errors in computer microchips, in a dose-response fashion with increasing altitude. Pregnant cabin crew members are of special concern. Although the epidemiological evidence is still inconclusive, we know enough to warrant a cautionary stance. The European Union (EU) leads the way in legislation.

Aerospace Medicine↗

PubMed1990

Biological damage induced by ionizing cosmic rays in dry Arabidopsis seeds.

In September 1987 dry seeds containing embryos of the crucifer plant Arabidopsis thaliana (L.) Heynh, were flown in orbit for 13 days on the Kosmos 1887 satellite. The seeds were fixed on CNd detectors and stored in units of Biorack type I/O. One unit was exposed inside, another one outside the satellite. The temperature profile of the flown seeds inside the satellite was simulated on earth in an identical backup control sample (BC). An additional control (SC) was studied with the original seeds sample. By use of the CNd-detector, HZE-tracks were measured with a PC-assisted microscope. The biological damages were investigated by growing the seeds under controlled climatic conditions. The following biological endpoints of the cosmic radiation damage were studied: germination, radicle length, sublethality, morphological aberrations, flower development, tumorization, embryo lethality inside the siliques. The summarized damage (D) and the mutation frequencies of embyronic lethal genes were calculated. The following results were obtained: the damages increase significantly in orbit at all biological endpoints; germination and fiowerings especially, as well as embryo lethality of fruits and lethal mutation frequency, were maximum mostly for HZE-hit seeds. Additionally, an increase of damage was observed for the seeds of the outside-exposed Biorack in comparison to the inside ones, which was probably caused by less radiation shielding and free space vacuum. The significance of the results obtained is discussed with respect to stress and risk and, thus, the quality of the RBE-factors and heavy ionizing radiation all needed for the very definition of radiation protection standards in space.

Arabidopsis↗

PubMed1998

The low earth orbit environment observed using CREAM and CREDO.

The Cosmic Radiation Environment and Dosimetry experiment (CREDO) has been operational on board the Advanced Photovoltaics & Electronics Experiment Spacecraft since August 1994. Extensive measurements of cosmic ray linear energy transfer spectra (using data to January 1996) and total dose (using data to November 1994) have been made, and compared with predictions of standard models. Detailed consideration of spacecraft shielding effects have been made. Predictions are shown to overestimate the measured linear energy transfer spectra. The CREAM experiment was flown on STS-63 in the SpaceHab module. Results show penetration of high energy electrons into the SpaceHab module.

Atlantic Ocean↗

PubMed2003

Materials trade study for lunar/gateway missions.

The National Aeronautics and Space Administration (NASA) administrator has identified protection from radiation hazards as one of the two biggest problems of the agency with respect to human deep space missions. The intensity and strength of cosmic radiation in deep space makes this a 'must solve' problem for space missions. The Moon and two Earth-Moon Lagrange points near Moon are being proposed as hubs for deep space missions. The focus of this study is to identify approaches to protecting astronauts and habitats from adverse effects from space radiation both for single missions and multiple missions for career astronauts to these destinations. As the great cost of added radiation shielding is a potential limiting factor in deep space missions, reduction of mass, without compromising safety, is of paramount importance. The choice of material and selection of the crew profile play major roles in design and mission operations. Material trade studies in shield design over multi-segmented missions involving multiple work and living areas in the transport and duty phase of space mission's to two Earth-Moon co-linear Lagrange points (L1) between Earth and the Moon and (L2) on back side of the moon as seen from Earth, and to the Moon have been studied. It is found that, for single missions, current state-of-the-art knowledge of material provides adequate shielding. On the other hand, the choice of shield material is absolutely critical for career astronauts and revolutionary materials need to be developed for these missions. This study also provides a guide to the effectiveness of multifunctional materials in preparation for more detailed geometry studies in progress.

Astronauts↗

PubMed2006

Comparison of natural background dose rates for residents of the Amargosa Valley, NV, to those in Leadville, CO, and the states of Colorado and Nevada.

In the latter half of 2005, the U.S. Environmental Protection Agency (U.S. EPA) published a Proposed Rule (40 CFR Part 197) for establishing a dose rate standard for limiting radionuclide releases from the proposed Yucca Mountain high-level radioactive waste repository during the time period from 10 to 10 years after closure. The proposed standard was based on the difference in the estimated dose rate from natural background in the Amargosa Valley and the "average annual background radiation" for the State of Colorado. As defined by the U.S. EPA, "natural background radiation consists of external exposures from cosmic and terrestrial sources, and internal exposures from indoor exposures to naturally-occurring radon." On the basis of its assessments, the U.S. EPA estimated that the difference in the dose rate in the two identified areas was 3.5 mSv y. The purpose of this paper is to provide an independent evaluation and review of this estimate. One of the first observations was that, because site-specific dose rate measurements for the Amargosa Valley "were not available," the dose rates for various sources of natural background in that area, used by the U.S. EPA in its assessment, were based on modifications of the average values for the State of Nevada. A second observation was that the conversion coefficient applied in estimating the dose rates due to exposures to indoor radon and its decay products was a factor of >2 higher than the currently internationally accepted value. Further review revealed that site-specific data for many natural background sources in the Amargosa Valley were available. One particularly important observation was that about 91% of the residents of that area live in mobile homes which, due to their construction and design, have indoor radon concentrations comparable to, or less than, those outdoors. For that reason, alone, the U.S. EPA estimate of the average dose rate for residents of the Amargosa Valley, due to exposures to indoor radon, was not valid. For purposes of the comparisons in this paper, site-specific dose rates were estimated for all major natural background sources of exposure to residents of the Amargosa Valley, and those in Leadville, CO. The latter community was selected for comparison because of its altitude (3,200 m) and accompanying relatively high cosmic radiation dose rate, and the fact the size of its population is comparable to that of the Amargosa Valley. Another reason for this selection was that a comparison of the average natural background dose rate in the Amargosa Valley to that for the State of Colorado is not suitable because it fails to consider those locations within the State that have dose rates that are higher than the average. Nonetheless, for completeness, and to provide a number that could be compared to the U.S. EPA estimated difference, similar comparisons of the estimated dose rate in the Amargosa Valley to those for average residents of the States of Colorado and Nevada were included in the assessments that follow. The outcome showed that the estimated dose rates in Leadville, the State of Colorado, and the State of Nevada, were higher than those in the Amargosa Valley by 3.94 +/- 1.09, 2.54 +/- 2.18, and 0.95 +/- 0.82 mSv y, respectively. Associated uncertainties were highest for the estimated dose rates due to exposures to radon and its decay products. Had the systematic errors in the radon dose conversion coefficient and the random distribution in radon concentrations been included, the overall uncertainty in the total dose rate estimates could have been as high as 150%.

Air Pollution, Indoor↗

PubMed1994

An analysis of interplanetary space radiation exposure for various solar cycles.

The radiation dose received by crew members in interplanetary space is influenced by the stage of the solar cycle. Using the recently developed models of the galactic cosmic radiation (GCR) environment and the energy-dependent radiation transport code, we have calculated the dose at 0 and 5 cm water depth; using a computerized anatomical man (CAM) model, we have calculated the skin, eye and blood-forming organ (BFO) doses as a function of aluminum shielding for various solar minima and maxima between 1954 and 1989. These results show that the equivalent dose is within about 15% of the mean for the various solar minima (maxima). The maximum variation between solar minimum and maximum equivalent dose is about a factor of three. We have extended these calculations for the 1976-1977 solar minimum to five practical shielding geometries: Apollo Command Module, the least and most heavily shielded locations in the U.S. space shuttle mid-deck, center of the proposed Space Station Freedom cluster and sleeping compartment of the Skylab. These calculations, using the quality factor of ICRP 60, show that the average CAM BFO equivalent dose is 0.46 Sv/year. Based on an approach that takes fragmentation into account, we estimate a calculation uncertainty of 15% if the uncertainty in the quality factor is neglected.

Cosmic Radiation↗

PubMed2002

The response of a spherical tissue-equivalent proportional counter to iron particles from 200-1000 MeV/nucleon.

The radiation environment on board the space shuttle and the International Space Station includes high-Z and high-energy (HZE) particles that are part of the galactic cosmic radiation (GCR) spectrum. Iron-56 particles are considered to be one of the most biologically important parts of the GCR spectrum. Tissue-equivalent proportional counters (TEPCs) are used as active dosimeters on manned space flights. These TEPCs are further used to determine the average quality factor for each space mission. A TEPC simulating a 1-microm-diameter sphere of tissue was exposed as part of a particle spectrometer to (56)Fe particles at energies from 200-1000 MeV/nucleon. The response of TEPCs in terms of mean lineal energy, y(F), and dose mean lineal energy, y(D), as well as the energy deposited at different impact parameters through the detector was determined for six different incident energies of (56)Fe particles in this energy range. Calculations determined that charged-particle equilibrium was achieved for each of the six experiments. Energy depositions at different impact parameters were calculated using a radial dose distribution model, and the results were compared to experimental data.

Cosmic Radiation↗

PubMed2004

The use of passive personal neutron dosemeters to determine the neutron dose equivalent component of radiation fields in spacecraft.

For the altitude range and inclination of the International Space Station (ISS), secondary neutrons can be a major contributor to dose equivalent inside a spacecraft. The exact proportion is very dependent on the amount of shielding of the primary galactic cosmic radiation and trapped particles, but is likely to lie in the range of 10-50%. Personal neutron dosemeters of simple design, processed using simple techniques developed for personal dosimetry, may be used to estimate this neutron component.

Body Burden↗

PubMed1992

Radiation issues for piloted Mars mission.

Man is now entering an era of colonizing the moon and exploration of Mars. The crewmembers of a piloted mission to Mars will be exposed to inner belt trapped protons, the outer trapped electrons, and the galactic cosmic radiation. In addition there is always the added risk of acute exposure to a solar particle event. Current radiation risk is estimated using the idea of absorbed dose and ICRP-26, LET-dependent quality factors. In a spacecraft with aluminum walls (2 g cm-2) at solar minimum the calculated dose equivalent is 0.73 Sv for a 406-day mission. Based on the current thinking this leads to an excess cancer mortality in a 35 year male of about 1%. About 75% of the dose equivalent is contributed by HZE particles and target fragments with average quality factors of 10.3 and 20, respectively. The entire concept of absorbed dose, quality factor, and dose equivalent as applied to such missions needs to be reexamined, in light of the fact that less than 50% of the nuclei in the body of the astronaut would have been traversed by a single GCR nuclei in the 406-day mission. Clearly, more biologically relevant information about the effects of heavy ions and target fragments is needed and fluence based risk estimation strategy developed for such long term stays in space.

Adult↗

PubMed2006

Dosimetry of environmental radiation--a report on the achievements of EURADOS WG3.

Owing to the fact that a nuclear accident is a border-crossing problem, all national active monitoring systems should measure the same quantity with a comparable level of precision. Also, the sensitivity of the systems must be such that sudden changes in the environmental dose rate are recognised and a radiological incident is clearly identified. Thus, international intercomparisons of the so-called Early Warning Systems are the best method to assure high quality measurements. Supported by the European Commission within the scope of the 4th and 5th Framework Programmes, intercomparisons of these Early Warning Systems were organised by European Radiation Dosimetry (EURADOS) Working Group 3 (WG3) in 1999 and 2002. The methods developed for this purpose are based on controlled irradiation of the systems and the determination of their responses to secondary cosmic radiation. One of the major problems turned out to be the correct subtraction of the internal background. Investigating this problem was only possible by carrying out measurements at almost zero dose rate, as available in the Underground Laboratory for Dosimetry and Spectrometry (UDO) maintained by Physikalisch-Technische Bundesanstalt. Progress was also achieved with regard to including in situ gamma spectroscopy systems in the 2002 intercomparison. For these systems, the UDO irradiation facility provides a unique possibility to measure the spectral responses to monoenergetic photons.

Air Pollution, Radioactive↗

PubMed1996

[Relationship between particle fluence and dose in cabin of recoverable satellite].

Radiation doses in the cabin of the recoverable satellite measured by GJ-III personal dosimeters and LiF thermoluminescent dosimeters were presented. The relationship between the particle fluence calculated from instrument display and the measured doses was studied. It shows that the particle fluence can be directly calculated from the measured dose with a transformation coefficient which is not obviously affected by shielding around the measuring site. The estimated average energy of the particles in the cabin is on the level of Galactic cosmic radiation.

Cosmic Radiation↗

PubMed1988

Physical considerations relevant to HZE-particle transport in matter.

High-energy, highly charged (HZE) heavy nuclei may seem at first sight to be an exotic type of radiation, only remotely connected with nuclear power generation. On closer examination it becomes evident that heavy-ion accelerators are being seriously considered for driving inertial confinement fusion reactors, and high-energy heavy nuclei in the cosmic radiation are likely to place significant constraints on satellite power system deployment and space-based power generation. The use of beams of heavy nuclei in an increasing number of current applications, as well as their importance for the development of the state of the art of the future, makes it necessary to develop at the same time a good understanding of their transport through matter.

Cosmic Radiation↗

PubMed1984

Cosmic ray exposure factors for Shuttle altitudes derived from calculated cut-off rigidities.

The allowed cosmic radiation flux accessible to an earth-orbiting spacecraft is a complex function of the satellite position and the geomagnetic cutoff characteristics at each zenith and azimuth angle at each position. We have determined cosmic ray exposure factors for the galactic cosmic ray spectrum for typical shuttle altitudes and inclinations up to 50 degrees. We have utilized d world grid of trajectory-derived cutoff rigidity calculations at 400 km altitude to determine geomagnetic transmission functions that permit a simple and direct calculation of the allowed cosmic ray spectrum to a 400 km satellite orbit. If the interplanetary cosmic ray spectrum is multiplied by the orbit-averaged geomagnetic transmission function the result is the allowed cosmic ray spectrum at the spacecraft.

Altitude↗

PubMed2000

Do the risks justify action?

The key issues that have been raised at the meeting on Cosmic Radiation Doses to Air Crew and Astronauts are identified. The paper summarizes the radiation environment and radiation risks associated with exposures to both groups. Finally, the summary concludes that the risks do justify action.

Aircraft↗

PubMed2006

A temporal forecast of radiation environments for future space exploration missions.

The understanding of future space radiation environments is an important goal for space mission operations, design, and risk assessment. We have developed a solar cycle statistical model in which sunspot number is coupled to space-related quantities, such as the galactic cosmic radiation (GCR) deceleration potential (phi) and the mean occurrence frequency of solar particle events (SPEs). Future GCR fluxes were derived from a predictive model, in which the temporal dependence represented by phi was derived from GCR flux and ground-based Climax neutron monitor rate measurements over the last four decades. These results showed that the point dose equivalent inside a typical spacecraft in interplanetary space was influenced by solar modulation by up to a factor of three. It also has been shown that a strong relationship exists between large SPE occurrences and phi. For future space exploration missions, cumulative probabilities of SPEs at various integral fluence levels during short-period missions were defined using a database of proton fluences of past SPEs. Analytic energy spectra of SPEs at different ranks of the integral fluences for energies greater than 30 MeV were constructed over broad energy ranges extending out to GeV for the analysis of representative exposure levels at those fluences. Results will guide the design of protection systems for astronauts during future space exploration missions.

Computer Simulation↗

PubMed1965

Satellite biological experiments--major results and problems.

The data on the results of biological experiments carried out on Vostok 5 and Vostok 6 are presented. Space flight factors are shown to cause in hereditary structures of some biological objects (seeds of higher plants, lysogenic bacteria, Tradescantia microspores, etc.) distortions of a small but statistically significant value. Changes in physiological functions of certain objects (seeds of higher plants, etc.) have been also detected. These data are in good agreement with the results of flight experiments carried out in 1960-1962. Prospects of research of the biological effect of cosmic radiation and weightlessness are considered with respect to flight experiments.

Animals↗

PubMed1992

Preliminary total dose measurements on LDEF.

After spending nearly six years in Earth orbit twenty stacks consisting of radiation detectors and biological objects are now back on Earth. These stacks (Experiment A0015 Free Flyer Biostack) are part of the fifty seven science and technology experiments of the Long Duration Exposure Facility (LDEF) of NASA. The major objectives of the Free Flyer Biostack experiments are to investigate the biological effectiveness of single heavy ions of the cosmic radiation in various biological systems and to provide information about the spectral composition of the radiation field and the total dose received in the LDEF orbit. The Biostacks are mounted in two different locations of the LDEF. Up to three layers of Lithium fluoride thermoluminescence dosimeters (TLD) of different isotopic composition were located at different depths of some Biostacks. The preliminary analysis of the TLD yields maximum absorbed dose rates of 2.24 mGy day-1 behind 0.7 g cm-2 shielding and 1.17 mGy day-1 behind 12 g cm-2 shielding. A thermal neutron fluence of 1.7 n cm-2 s-1 is determined from the differences in absorbed dose for different isotopic mixtures of Lithium. The results of this experiment on LDEF are especially valuable and of high importance since LDEF stayed for about six years in the prospected orbit of the Space Station Freedom. There is no knowledge about the effectiveness of the space radiation in long-term spaceflights and the dosimetric data in this orbit are scarce.

Cosmic Radiation↗