Fragmentation of 1 GeV/nucleon iron ions in thick targets relevant for space exploration.

We have measured charged nuclear fragments produced by 1 GeV/nucleon 56Fe ions interacting with aluminium, polyethylene and lead. These materials are relevant for assessment of radiation risk for manned space flight. The data will be presented in a form suitable for comparison with models of nuclear fragmentation and transport, including linear energy transfer (LET) spectrum, fluence for iron and fragments, event-tack- and event-dose-averaged LET, total dose and iron contribution to dose.     

A procedure for benchmarking laboratory exposures with 1 A GeV iron ions.

A new version of the HZETRN code capable of simulating HZE ions with either laboratory or space boundary conditions is under development. The computational model consists of combinations of physical perturbation expansions based on the scales of atomic interaction, multiple scattering, and nuclear reactive processes with use of asymptotic/Neumann expansions with non-perturbative corrections. The code contains energy loss with straggling, nuclear attenuation, nuclear fragmentation with energy dispersion and downshifts, and off-axis dispersion with multiple scattering under preparation. The present benchmark is for a broad directed beam for 1 A GeV iron ion beams with 2 A MeV width and four targets of polyethylene, polymethyl metachrylate, aluminum, and lead of varying thickness from 5 to 30 g/cm2. The benchmark quantities will be dose, track averaged LET, dose averaged LET, fraction of iron ion remaining, and fragment energy spectra after 23 g/cm2 of polymethyl metachrylate.     

Monte Carlo transport model comparison with 1A GeV accelerated iron experiment: heavy-ion shielding evaluation of NASA space flight-crew foodstuff.

Deep-space manned flight as a reality depends on a viable solution to the radiation problem. Both acute and chronic radiation health threats are known to exist, with solar particle events as an example of the former and galactic cosmic rays (GCR) of the latter. In this experiment Iron ions of 1A GeV are used to simulate GCR and to determine the secondary radiation field created as the GCR-like particles interact with a thick target. A NASA prepared food pantry locker was subjected to the iron beam and the secondary fluence recorded. A modified version of the Monte Carlo heavy ion transport code developed by Zeitlin at LBNL is compared with experimental fluence. The foodstuff is modeled as mixed nuts as defined by the 71st edition of the Chemical Rubber Company (CRC) Handbook of Physics and Chemistry. The results indicate a good agreement between the experimental data and the model. The agreement between model and experiment is determined using a linear fit to ordered pairs of data. The intercept is forced to zero. The slope fit is 0.825 and the R2 value is 0.429 over the resolved fluence region. The removal of an outlier, Z=14, gives values of 0.888 and 0.705 for slope and R2 respectively.     

Behavioral and neurochemical abnormalities after exposure to low doses of high-energy iron particles.

Exposure of rats to high-energy iron particles (600 MeV/amu) has been found to alter behavior after doses as low as 10 rads. The performance of a task that measures upper body strength was significantly degraded after irradiation. In addition, an impairment in the regulation of dopamine release in the caudate nucleus (a motor center in the brain), lasting at least 6 months, was also found and correlated with the performance deficits. A general indication of behavioral toxicity and an index of nausea and emesis, the conditioned taste aversion, was also evident. The sensitivity to iron particles was 10-600 times greater than to gamma photons. These results suggest that behavioral and neurobiological damage may be a consequence of exposure to low doses of heavy particles and that this possibility should be extensively studied.     

In vitro plant cell growth in microgravity and on clinostat.

For the study of gravity's role in the processes of plant cell differentiation in-vitro, a model "seed-seedling-callus" has been used. Experiments were carried out on board the orbital stations Salyut-7 and Mir as well as on clinostat. They lasted from 18 to 72 days. It was determined that the exclusion of a one-sided action of gravity vector by means of clinostat and spaceflight conditions does not impede the formation and growth of callus tissue; however, at cell and subcellular levels structural and functional changes do take place. No significant changes were observed either on clinostat or in space concerning the accumulation of fresh biomass, while the percentage of dry material in space is lower than in control. Both in microgravity (MG) and in control, even after 72 days of growth, cells with a normally developed ultrastructure are present. In space, however, callus tissue more often contains cells in which the cross-section area of a cell, a nuclei and of mitochondria are smaller and the vacuole area--bigger than in controls. In microgravity a considerable decrease in the number of starch-containing cells and a reduction in the mean area of starch grains in amyloplasts is observed. In space the amount of soluble proteins in callus tissue is 1.5 times greater than in control. However, no differences were observed in fractions when separated by the SDS-PAGE method. In microgravity the changes in cell wall material components was noted. In the space-formed callus changes in the concentration of ions K, Na, Mg, Ca and P were observed. However, the direction of these changes depends on the age of callus. Discussed are the possible reasons for modification of morphological and metabolic parameters of callus cells when grown under changed gravity conditions.     

In vivo and in vitro studies of cartilage differentiation in altered gravities.

The in vivo model our laboratory uses for studies of cartilage differentiation in space is the rat growth plate. Differences between missions, and in rat age and recovery times, provided differing results from each mission. However, in all missions, proliferation and differentiation of chondrocytes in the epiphyseal plate of spaceflown rats was altered as was matrix organization. In vitro systems, necessary complements to in vivo work, provide some advantages over the in vivo situation. In vitro, centrifugation of embryonic limb buds suppressed morphogenesis due to precocious differentiation, and changes in the developmental pattern suggest the involvement of Hox genes. In space, embryonic mouse limb mesenchyme cells differentiating in vitro on IML-1 had smoother membranes and lacked matrix seen in controls. Unusual formations, possibly highly ruffled membranes, were found in flight cultures. These results, coupled with in vivo centrifugation studies, show that in vivo or in vitro, the response of chondrocytes to gravitational changes follows Hert's curve as modified by Simon, i.e. decreased loading decreases differentiation, and increased loading speeds it up, but only to a point. After that, additional increases again slow down chondrogenesis.     

Analysis of cytogenetic effects of the secondary radiation resulting from 70 GeV protons of Chinese hamster cells.

The cell culture of a Chinese hamster was irradiated on a Serpuchov proton synchrotron at a dose of 0.5-4 Gy and a dose rate of 1 Gy/min and by gamma-irradiation at dose 1-5 Gy and dose rate 1.2-1.4 Gy/min. The effect of radiation on the cell culture was judged from chromosomal aberrations in G2-stage of cell cycle and micronuclear test. The relative biological efficience of the secondary radiation was approximately 3. Modifying effect of caffeine on the cells irradiated by secondary radiation of synchrotron was not observed. In the presence of caffeine the effect of gamma-irradiation practically is increased up to the level observed upon secondary irradiation. This suggests that secondary radiation inhibits the repair of the cytogenetic damage.     

Charged-particle mutagenesis II. Mutagenic effects of high energy charged particles in normal human fibroblasts.

The biological effects of high LET charged particles are a subject of great concern with regard to the prediction of radiation risk in space. In this report, mutagenic effects of high LET charged particles are quantitatively measured using primary cultures of human skin fibroblasts, and the spectrum of induced mutations are analyzed. The LET of the charged particles ranged from 25 KeV/micrometer to 975 KeV/micrometer with particle energy (on the cells) between 94-603 MeV/u. The X-chromosome linked hypoxanthine guanine phosphoribosyl transferase (hprt) locus was used as the target gene. Exposure to these high LET charged particles resulted in exponential survival curves; whereas, mutation induction was fitted by a linear model. The Relative Biological Effect (RBE) for cell-killing ranged from 3.73 to 1.25, while that for mutant induction ranged from 5.74 to 0.48. Maximum RBE values were obtained at the LET of 150 keV/micrometer. The inactivation cross-section (alpha i) and the action cross-section for mutant induction (alpha m) ranged from 2.2 to 92.0 micrometer2 and 0.09 to 5.56 x 10(-3) micrometer2, respectively. The maximum values were obtained by 56Fe with an LET of 200 keV/micrometer. The mutagenicity (alpha m/alpha i) ranged from 2.05 to 7.99 x 10(-5) with the maximum value at 150 keV/micrometer. Furthermore, molecular analysis of mutants induced by charged particles indicates that higher LET beams are more likely to cause larger deletions in the hprt locus.     

M-FISH analysis of chromosome aberrations in human fibroblasts exposed to energetic iron ions in vitro.

Confluent human fibroblast cells were exposed to 6 Gy gamma-rays or 200 MeV/nucleon Fe ions at 0.7 or 3 Gy. The cells were allowed to repair for 24 hours after exposure and chromosomes were collected using a premature chromosome condensation technique with calyculin-A. Chromosome aberrations were analyzed using the multicolor FISH (mFISH) technique that allows identification of both complex and truly incomplete exchanges. Results showed that both doses of the Fe ions produced higher ratios of complex to simple exchanges and lower ratio of complete to incomplete exchanges than the 6 Gy gamma-exposure. The ratios of aberration yields were similar for the two doses of Fe ions. After 0.7 Gy of Fe ions, most complex aberrations were found to involve three or four chromosomes, indicating this is the maximum number of chromosome domains traversed by a single Fe ion track.     

Biological effects of galactic radiation HZE particles in experiments on the orbital station Salyut 7.

Lettuce (Lactuca sativa) seeds were flown on-board the orbital station Salyut 7 for 66-457 days. It was found that a single heavy charged particle (HZE) hitting a seed only slightly affects the subsequent plant growth. However, morphological anomalies of varying type in primordial leaves and roots were observed that show good correlation with the location of the particle track. The most severe damage detected by light and an electron microscopy were "channels" in dry and soaked seeds. The appearance of "channels" seems to be related to the LET of the incident particle. This finding is of considerable importance for assessment of space flight radiation hazard.     

In vivo and in vitro measurements of complex-type chromosomal exchanges induced by heavy ions.

Heavy ions are more efficient in producing complex-type chromosome exchanges than sparsely ionizing radiation, and this can potentially be used as a biomarker of radiation quality. We measured the induction of complex-type chromosomal aberrations in human peripheral blood lymphocytes exposed in vitro to accelerated H-, He-, C-, Ar-, Fe- and Au-ions in the LET range of approximately 0.4-1400 keV/micrometers. Chromosomes were analyzed either at the first post-irradiation mitosis, or in interphase, following premature condensation by phosphatase inhibitors. Selected chromosomes were then visualized after FISH-painting. The dose-response curve for the induction of complex-type exchanges by heavy ions was linear in the dose-range 0.2-1.5 Gy, while gamma-rays did not produce a significant increase in the yield of complex rearrangements in this dose range. The yield of complex aberrations after 1 Gy of heavy ions increased up to an LET around 100 keV/micrometers, and then declined at higher LET values. When mitotic cells were analyzed, the frequency of complex rearrangements after 1 Gy was about 10 times higher for Ar- or Fe- ions (the most effective ions, with LET around 100 keV/micrometers) than for 250 MeV protons, and values were about 35 times higher in prematurely condensed chromosomes. These results suggest that complex rearrangements may be detected in astronauts' blood lymphocytes after long-term space flight, because crews are exposed to HZE particles from galactic cosmic radiation. However, in a cytogenetic study of ten astronauts after long-term missions on the Mir or International Space Station, we found a very low frequency of complex rearrangements, and a significant post-flight increase was detected in only one out of the ten crewmembers. It appears that the use of complex-type exchanges as biomarker of radiation quality in vivo after low-dose chronic exposure in mixed radiation fields is hampered by statistical uncertainties.     

Multimodal characteristics of a piezoelectric lead zirconate titanate element impacted with iron particles having velocities above 20 km/s

The responses of a piezoelectric lead zirconate titanate (PZT) element to hypervelocity collisions were experimentally studied. In this study, the particles of masses ranging from 0.3 to 10 fg were made to collide with PZT at velocities between 20 and 96 km/s. The amplitude and the corresponding rise time of the single-pulse output signals that were produced in the piezoelectric PZT element were measured to determine the possible collision states. The results revealed an apparently multimodal output; three classes were assumed to be involved in the pulse formation mechanism. The amplitude and rise time were sensitive to the collision velocity. The multimodal behavior implied that the PZT-based cosmic dust detectors should be calibrated according to the class they belong to.     

Radiation effects in nematodes: results from IML-1 experiments.

The nematode Caenorhabditis elegans was exposed to natural space radiation using the ESA Biorack facility aboard Spacelab on International Microgravity Laboratory 1, STS-42. For the major experimental objective dormant animals were suspended in buffer or on agar or immobilized next to CR-39 plastic nuclear track detectors to correlate fluence of HZE particles with genetic events. This configuration was used to isolate mutations in a set of 350 essential genes as well as in the unc-22 structural gene. From flight samples 13 mutants in the unc-22 gene were isolated along with 53 lethal mutations from autosomal regions balanced by a translocation eT1(III;V). Preliminary analysis suggests that mutants from worms correlated with specific cosmic ray tracks may have a higher proportion of rearrangements than those isolated from tube cultures on a randomly sampled basis. Right sample mutation rate was approximately 8-fold higher than ground controls which exhibited laboratory spontaneous frequencies.     

The iron Kα-line diagnostics of the rotating black hole metric in Seyfert galaxies

Observations of Seyfert galaxies in X-ray region reveal the wide emissive lines in their spectra, which can arise in inner parts of accretion disks, where the effects of General Relativity (GR) must be taken into account. A spectrum of a solitary emission line of a hot spot in Kerr accretion disk is simulated depending on the radial coordinate r and the angular momentum a = J/M of a black hole, under the assumption of equatorial circular motion of a hot spot. It is shown that the characteristic two-peak line profile with the sharp edges arises at a large distance (about r ≈ (3–10) r_g). The inner regions emit the line, which is observed with one maximum and extremely wide red wing. We present results of simulations for the isothermal and Shakura–Sunayev disks.     

Can late effects of neutron irradiation in man be estimated from early responses?1

Slowly-developing tissue changes after neutron irradiation should be more easily predicted from acutely-developing injury than is the case with X rays. The difference between tissue responses to neutrons and X rays is that cell survival in both rapidly and slowly responding tissues is a direct logarithmic function of neutron dose, at least up to about 3 Gy, whereas the X-ray dose-survival relationship differs between the two types of tissue: the target cells for late injury are more susceptible to killing from accumulation of sub-lethal X-ray injury and hence the survival curve diverges from its initial essentially linear region more rapidly than does that for the target cells for acute injury.     

Angular distributions of energetic charged particles observed with HELIOS-1 and -2 between 0.3 amd 1 AU and their relevance to manned interplanetary space missions.

The University of Kiel Cosmic Ray Instrument on board the solar probes HELIOS-1 and -2 measured angular distributions of electrons, protons, and heavier nuclei between 0.3 and 1 AU over one complete solar cycle between 1974 and 1986. Anisotropies are observed mainly during the rising phase of solar particle events or close to the passage of certain interplanetary shocks. The anisotropies are presented as proton data of energies between 27 and 37 MeV. The dependence of the anisotropies on particle energy and distance from the sun is provided based on diffusive propagation in interplanetary space. Strong anisotropies could provide a chance of efficient shielding of the passenger compartment by moving heavier parts of the spacecraft structure into the direction of the highest flux. A reduction of the total radiation dose by less than a factor of 2 might be achievable, however, selection of quiet times for the mission reduces the radiation hazard much more.