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Simple parameterizations of Coulomb dissociation cross sections for use in heavy-ion transport calculations are presented and compared to available experimental dissociation data. The agreement between calculation and experiment is satisfactory considering the simplicity of the calculations.
The concept of advanced manned space missions has captured the interest and imagination of spacefaring nations. However, the physiological and psychological effects of space flight increase in magnitude and significance in the 'extended time-in-space' context. The unencumbered weightless condition enjoyed during short flights might compromise crew productivity upon return to a gravity field and extremely effective countermeasures may be essential. Missions remote from Earth require careful consideration of the medical facilities, psychological support and life support needed. The author discusses pressing issues that must be resolved before the visions of bolder human missions can be realistically fulfilled.
LET variation with the absorber thickness was measured by plastic detectors exposed on COSMOS-1129 satellite.
It is generally accepted that heavy charged particles play an important part in generating the secondary flux of nuclear particles formed by the interaction of space hadrons with nuclei. It is assumed that these particles are responsible for the high biological efficiency of space hadrons in causing cellular damage by their strong interactions. To examine this assumption we investigated the effects of 5.3 MeV alpha particles on bacteriophage T4. This energy provides a LET value of 88.6 KeV/micrometer lying in the range of the highest biological efficiency.
Studies on the response of bacterial spores to accelerated heavy ions (HZE particles) help in understanding problems of space radiobiology and exobiology. Layers of spores of Bacillus subtilis strains, differing in repair capabilities, were irradiated with accelerated boron, carbon and neon ions of linear energy transfer (LET) values up to 14000 MeV cm2/g. Inactivation as measured by loss of colony forming ability and induction of mutations as measured by reversion to histidine prototrophy and resistance to 150 micrograms/ml sodium azide were tested, as well as the influence of repair processes on these effects. For inactivation, the cross-sectional values sigma plotted as a function of LET follow a saturation curve. The plateau, which is reached around a LET of 2000 MeV cm2/g, occurs at 2.5 x 10(-9) cm2, a value in good agreement with the dimensions of the spore protoplast. Lethal damage produced at LET values < 2000 MeV cm2/g is reparable. Recombination repair is more effective than excision repair. At higher LET values, lethal damage could not be reconstituted by the repair mechanisms studied. In addition, at these high LET values, the frequency of induced mutations was drastically decreased. The data support the assumption of at least two qualitatively different types of lesion, depending on the LET of the affecting heavy ion.
The understanding of the radiobiological action of heavy ions requires the knowledge of the dependence of the inactivation probability on the distance between the particle's trajectory and the biological test organism (the impact parameter). Spores of Bacillus subtilis with a cytoplasmic core of about 0.22 micrometer cross section are suitable test objects for the study of this radial inactivation probability in its microscopic details. The spores are irradiated at low fluences of some 10(6) ions/cm2 with very heavy ions at different specific energies up to 10 MeV per atomic mass unit u while in fixed contact with visual nuclear track detectors. The methods are described by which the biological response of individual cells can be evaluated and the impact parameter be determined with an accuracy typically better than 0.2 micrometer. The results demonstrate that the common characteristics of inactivation, e.g., an effective range of inactivation extending to at least 3 micrometers, a nonmonotonic dependence of the inactivation probabilities on the radial distance, and the fact that the inactivation probability even for direct central hits on the cytoplasmic core is substantially below one, are nearly independent of the particle energy and type. The results are incompatible with the assumption that the radiobiological effectiveness can be attributed to the dose of secondary electrons as currently understood. They also demonstrate that the widely held notion of an "overkill" at low impact parameters does not apply for the spores even with the most densely ionizing ions.
Artemia cysts, lettuce and tobacco seeds were flown aboard the Cosmos 1129 for 19 days. A correlative method was used in order to determine the passage of cosmic heavy ions (HZE particles) through the biological test objects. This space flight resulted in a decrease on hatchability, nucleic acid and protein synthesis in hydrated Artemia cysts. HZE particle effects on plant cellular chromosomes are confirmed. In tobacco seeds, a stimulating effect on germination rate and a higher frequency of abnormalities were observed. Dormant biological objects are a very suitable material to study cosmic ray effects: these objects can be arranged in monolayers and sandwiched between visual track detectors in order to determine the passage of the cosmic heavy ions (HZE particles). On the other hand this method allows us to study effects of microgravity and those of the protonic component of cosmic rays in the objects not hit by the HZE articles.
Two experiments with Drosophila melanogaster males were performed aboard the Salyut 6 orbital station. Mutagenic effects of a 8 day space flight on sex chromosome nondisjunction and intergene recombination in chromosome II were studied. The space flight factors (SFF) increased the frequency of chromosome nondisjunction and recombination. The model experiments showed that the combined effects of vibration and acceleration do not cover the whole spectrum of space flight mutagenic factors. These data suggest that heavy space ions are mainly responsible for the observed effect.
Space flights resulted in a stimulating effect on kinetics of proliferation in Paramecium tetraurelia. Additional experiments were performed in order to determine the origin of this phenomena. Paramecia were cultivated in balloon flights or in a slow clinostat, or were exposed to different levels of hypergravity. The results suggest that changes in cell proliferation rate are related to cosmic rays and to a direct effect of microgravity.
High energy, high-Z (HZE) particles are present in high-altitude and high-inclination satellite orbits. Most of the HZE dose above LET = 200 keV/micrometer is due to Fe nuclei. Individual HZE particles can damage several cells adjacent to one another along the particle track in tissue. The outcome has been described as a "microlesion" by D. Grahn. The present study attempts to define conditions for microlesions in specific tissues, to seek biological evidence that microlesions are produced, and to evaluate the microlesion as a potentially useful unit of dose in assessing hazards to spaceworkers. Microlesions in individuals cells and hair follicles have been described. Microbial studies have provided some evidence for independent secondary electron action. Whether or not a few hundred microlesions would be damaging to the whole organism depends upon the nature of damage to critical tissues. For example, cancer may occur if microlesions kill several cells in a straight line and mutate other cells alongside the particle track. Fe particle irradiation of the mouse Harderian gland (Fry et al., this issue) produces tumors efficiently. Microlesions in the lens, cornea, and retina need to be considered. Further dialogue is required before a final decision can be made concerning the most appropriate way to assess the HZE hazard.
The irradiation of grains and/or ices by particles from solar or stellar winds, as well as cosmic rays, induces the synthesis of molecular species. We have shown by in-situ infrared spectroscopy of irradiated samples that this chemistry may be responsible for the presence of organic compounds in a large variety of astrophysical sites such as: lunar and asteroidal regoliths, cometary nucleus, rings and satellites of outer planets, circumstellar shells, interstellar clouds. We present our experimental results concerning the mature and efficiency of C and N irradiation chemistries, and give plausible astrophysical implications.
Types and severeness of biological effects of heavy ions depend crucially on their physical track structure. Recently considerable progress could be made in simulation on fast digital computers the sequence of primary physical events produced by such ions. Such primary distributions represent e.g. adequate starting points for investigations an subsequent non-homogenous chemical and biological re-actions of biological matter. This paper gives a short review of the present state-of-art in physical track structure research and on its open questions.
Computations of the transmission functions of cosmic rays penetrating the geomagnetic field are discussed. Results of LET spectra calculations both inside and outside the spacecraft COSMOS-1129 are presented. Comparison of calculations and measured results shows (in interval 10-5 x 10(3) MeV/cm) a difference of less than 30%. The need for further systematic low altitude particle measurements for the purpose of developing dynamic models of particle populations is stressed.
A CELSS (Controlled Ecological Life Support System) is a device that utilizes photosynthetic organisms and light energy to regenerate waste materials into oxygen and food for a crew in space. The results of theoretical and practical studies conducted by investigators within the CELSS program suggest that a bioregenerative life support system can be a useful and effective method of regenerating consumable materials for crew sustenance. Experimental data suggests that the operation of a CELSS in space will be practical if plants can be made to behave predictably in the space environment. Much of the work currently conducted within the CELSS program centers on the biological components of the CELSS system. The work is particularly directed at ways of achieving high efficiency and long term stability of all components of the system. Included are explorations of the conversion of non-edible cellulose to edible materials, nitrogen fixation by biological and chemical methods, and methods of waste processing. It is the intent of the presentation to provide a description of the extent to which a bioregenerative life support system can meet the constraints of the space environment, and to assess the degree to which system efficiency and stability can be increased during the next decade.
In a study of the biological effects of cosmic HZE particles, lettuce (Lactuca sativa) seeds were flown on the orbital stations Salyut 6 and 7 for varying periods of time (from 40 to 457 days). The dependence of the biological damage on flight duration, physical parameters and the fact of passage of an HZE particle through the seed was estimated using the criterion of the frequency of aberrant cells. The arrangement of the flight biological container Biobloc made it possible to trace the location of tracks of individual HZE particles with Z > or = 6 and LET 200 keV/um. In seeds hit by HZE particles, for all exposure times, a statistically significant much higher yield of aberrant cells and also of cells containing multiple chromosome aberrations was observed than in the control material. The frequency of aberrant cells is markedly higher (by a factor of 1,5) in seeds hit than in non-hit ones. The changes of the yield of aberrant cells as a function of the absorbed dose (3.2-63.4 mGy) and the fluence (4.8-44.2 particles/cm2) are linear for the exposure duration ranging from 40 to 457 days.
CH4, CO, and CO2 are all potential one-carbon molecular repositories in primitive icy objects. These molecules are all found in the Comet Halley coma, and are probable but, (except for CH4 detected on Triton and Pluto) undetected subsurface constituents in icy outer solar system objects. We have investigated the effects of charged particle irradiation by cold plasma discharge upon surfaces of H2O:CH4 clathrate having a 200:1 ratio, as well as upon ices composed of H2O plus C2H6 or C2H2 (sometimes plus NH3) which are also plausible constituents. These materials color and darken noticeably after a dose 10(9) - 10(10) erg cm-2, which is deposited rapidly (< or = 10(4) yr.) in solar system environments. The chromophore is a yellowish to tan organic material (a tholin) which we have studied by UV-VIS reflection and transmission, and IR transmission spectroscopy. Its yield, -1 C keV-1, implies substantial production of organic solids by the action of cosmic rays and radionuclides in cometary crusts and interiors, as well as rapid production in satellite surfaces. This material shows alkane bands which Chyba and Sagan have shown to well match the Halley infrared emission spectrum near 3.4 microns, and also bands due to aldehyde, alcohol and perhaps alkene/aromatic functional groups. We compare the IR spectral properties of these tholins with the spectra of others produced by irradiation of gases and ices containing simple hydrocarbons.
Arabidopsis thaliana offers different possibilities for investigating heavy ion induced early and late damage. Mutations in genetic effective cells can yield early damage, in the form of reduced vitality of the descending cell-lines and/or late damage, such as mutation induction visible in the following generations. Investigation is possible on different levels of ploidy (4n, 2n, n). Different genetic effective cells with equal genomes are available. Additionally, several different biological endpoints for each level of genome ploidy can be observed. Recent results of work in this field are presented.
It is possible to model the time-intensity profile of solar particles expected in space after the occurrence of a significant solar flare on the sun. After the particles are accelerated in the flare process, if conditions are favorable, they may be released into the solar corona and then into space. The heliolongitudinal gradients observed in the inner heliosphere are extremely variable, reflecting the major magnetic structures in the solar corona which extend into space. These magnetic structures control the particle gradients in the inner heliosphere. The most extensive solar particle measurements are those observed by earth-orbiting spacecraft, and forecast and prediction procedures are best for the position of the earth. There is no consensus of how to extend the earth-based models to other locations in space. Local interplanetary conditions and structures exert considerable influence on the time-intensity profiles observed. The interplanetary shock may either reduce or enhance the particle intensity observed at a specific point in space and the observed effects are very dependent on energy.