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PubMed1994

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.

Cell Death↗
PubMed1983

Chemical evolution in space--a source of prebiotic molecules.

In Laboratory Astrophysics at Leiden University a laboratory analog for following the chemical evolution of interstellar dust in space shows that the dust contains the bulk of organic material in the universe. We follow the photoprocessing of low temperature (10 K) mixtures of ices subjected to vacuum ultraviolet radiation in simulation of interstellar conditions. The most important, but necessary, difference is in the time scales for photo-processing. One hour in the laboratory is equivalent to one thousand years in low density regions of space and as much as, or greater than, ten thousand to one million years in the depths of dense molecular clouds. The ultimate product of photoprocessing of grain material in the laboratory is a complex nonvolatile residue which is yellow in color and soluble in water and methanol. The molecular weight is greater than the mid-hundreds. The infrared absorption spectra indicate the presence of carboxylic acid and amino groups resembling those of other molecules of presumably prebiological significance produced by more classical methods. One of our residues, when subjected to high resolution mass spectroscopy gave a mass of 82 corresponding to C4H6H2 after release of CO2 and trace ammounts of urea suggesting amino pyroline rings. The deposit of prebiotic dust molecules occurred as many as 5 times in the first 500-700 million years on a primitive Earth by accretion during the passage of the solar system through a dense interstellar cloud. The deposition rate during each passage is estimated to be between 10(9) and 10(10) g per year during the million or so years of each passage; i.e., a total deposition of 1O(9)-10(10) metric tons of complex organic material per passage.

Cosmic Dust↗
PubMed2006

Proton-HZE-particle sequential dual-beam exposures increase anchorage-independent growth frequencies in primary human fibroblasts.

The radiation field in deep space contains high levels of high-energy protons and substantially lower levels of high-atomic-number, high-energy (HZE) particles. Calculations indicate that cellular nuclei of human space travelers will be hit during a 3-year Mars mission by approximately 400 protons and approximately 0.4 HZE particles. Thus most cells in astronauts will be hit by a proton(s) before being hit by an HZE particle. To investigate effects of dual ion irradiations on human cells, we irradiated primary human neonatal fibroblasts with protons (1 GeV/nucleon, 20 cGy) followed from 2.5 min to 48 h later by iron or titanium ions (1 GeV/nucleon, 20 cGy) and then measured clonogenic survival and frequency of anchorage-independent growth. This frequency depends on the interval between hydrogen- and iron-ion irradiation, with a critical window between 2.5 min and 1 h producing about three times more anchorage-independent colonies per survivor than expected from simple addition of the two ions separately. The hydrogen-titanium-ion dual-beam irradiation produced similar increases that persisted to approximately 6 h. At longer intervals, anchorage-independent growth frequencies were similar to those expected for additivity. However, irradiation of cells with either an iron or a titanium particle first followed by protons produced only additive levels.

Cell Adhesion↗
PubMed2001

Induction and repair of HZE induced cytogenetic damage.

Wistar rats were exposed to high-mass, high energy (HZE) 56Fe particles (1000 GeV/AMU) using the Alternating Gradient Synchrotron (AGS). The animals were sacrificed at 1-5 hours or after a 30-day recovery period. The frequency of micronuclei in the tracheal and the deep lung epithelial cells were evaluated. The relative effectiveness of 56Fe, for the induction of initial chromosome damage in the form of micronuclei, was compared to damage produced in the same biological system exposed to other types of high and low-LET radiation. It was demonstrated that for animals sacrificed at short times after exposure, the tracheal and lung epithelial cells, the 56Fe particles were 3.3 and 1.3 times as effective as 60Co in production of micronuclei, respectively. The effectiveness was also compared to that for exposure to inhaled radon. With this comparison, the 56Fe exposure of the tracheal epithelial cells and the lung epithelial cells were only 0.18 and 0.20 times as effective as radon in the production of the initial cytogenetic damage. It was suggested that the low relative effectiveness was related to potential for 'wasted energy' from the core of the 56Fe particles. When the animals were sacrificed after 30 days, the slopes of the dose-response relationships, which reflect the remaining level of damage, decreased by a factor of 10 for both the tracheal and lung epithelial cells. In both cases, the slope of the dose-response lines were no longer significantly different from zero, and the r2 values were very high. Lung epithelial cells, isolated from the animals sacrificed hours after exposure, were maintained in culture, and the micronuclei frequency evaluated after 4 and 6 subcultures. These cells were harvested at 24 and 36 days after the exposure. There was no dose-response detected in these cultures and no signs of genomic instability at either sample time.

Alpha Particles↗
PubMed1977

Biological investigations of higher and lower plants aboard Soyuz 19.

Biological investigations carried out aboard Soyuz 19 consisted of three independent complex experiments. All biological materials aboard the spacecraft were kept in "Biocat" thermostats which maintained the required temperature. The objective of the experiment "Genetic investigations" was to determine the effect of space flight factors on the heredity of lower (Chlamydomonas reinhardi Dang) and higher (Crepis capillaris (L) Wallr and Arabidopsis thaliana (L) Heynh) plants, and on the radiosensitivity of plant seeds and the radiation effect of prior gamma-irradiation. The space flight factors decreased the survival of Chlamydomonas cells and A. thaliana plants of the first generation. They decreased the germination of seeds, increased the rate of chlorophyll mutations and embryonal lethals, produced no effect on the rate of visible mutations in unicellular algae, increased the rate of chromosome aberrations in root meristem cells C. capillaris, induced disturbances in mitosis of unicellular algae and modified the effect of prior gamma-irradiation. The experiment "Growth of micro-organisms" was conducted with a culture of Proteus vulgaris in a growth chamber. After return to the laboratory the experimental and control variants were studied for twenty-two tests. The control and experimental material differed in the average cell size, biomass distribution, the character of haemotaxis, the rate of cell migration over the substratum surface, dehydrogenase activity, ribosomal aggregation, and ultrastructural peculiarities of cells. The experiment "Embryological investigations" was carried out to study the effect of space flight factors on embryogenesis of the bony fish Brachyodanio rerio. No abnormalities were noted in the course or rate of the development of spawn cultivated in a special thermostat.

Animals↗
PubMed2004

Astronaut EVA exposure estimates from CAD model spacesuit geometry.

Ongoing assembly and maintenance activities at the International Space Station (ISS) require much more extravehicular activity (EVA) than did the earlier U.S. Space Shuttle missions. It is thus desirable to determine and analyze, and possibly foresee, as accurately as possible what radiation exposures crew members involved in EVAs will experience in order to minimize risks and to establish exposure limits that must not to be exceeded. A detailed CAD model of the U.S. Space Shuttle EVA Spacesuit, developed at NASA Langley Research Center (LaRC), is used to represent the directional shielding of an astronaut; it has detailed helmet and backpack structures, hard upper torso, and multilayer space suit fabric material. The NASA Computerized Anatomical Male and Female (CAM and CAF) models are used in conjunction with the space suit CAD model for dose evaluation within the human body. The particle environments are taken from the orbit-averaged NASA AP8 and AE8 models at solar cycle maxima and minima. The transport of energetic particles through space suit materials and body tissue is calculated by using the NASA LaRC HZETRN code for hadrons and a recently developed deterministic transport code, ELTRN, for electrons. The doses within the CAM and CAF models are determined from energy deposition at given target points along 968 directional rays convergent on the points and are evaluated for several points on the skin and within the body. Dosimetric quantities include contributions from primary protons, light ions, and electrons, as well as from secondary brehmsstrahlung and target fragments. Directional dose patterns are displayed as rays and on spherical surfaces by the use of a color relative intensity representation.

Astronauts↗
PubMed2004

Austrian dose measurements onboard space station MIR and the International Space Station--overview and comparison.

The Atominstitute of the Austrian Universities has conducted various space research missions in the last 12 years in cooperation with the Institute for Biomedical Problems in Moscow. They dealt with the exact determination of the radiation hazards for cosmonauts and the development of precise measurement devices. Special emphasis will be laid on the last experiment on space station MIR the goal of which was the determination of the depth distribution of absorbed dose and dose equivalent in a water filled Phantom. The first results from dose measurements onboard the International Space Station (ISS) will also be discussed. The spherical Phantom with a diameter of 35 cm was developed at the Institute for Biomedical Problems and had 4 channels where dosimeters can be exposed in different depths. The exposure period covered the timeframe from May 1997 to February 1999. Thermoluminescent dosimeters (TLDs) were exposed inside the Phantom, either parallel or perpendicular to the hull of the spacecraft. For the evaluation of the linear energy transfer (LET), the high temperature ratio (HTR) method was applied. Based on this method a mean quality factor and, subsequently, the dose equivalent is calculated according to the Q(LET infinity) relationship proposed in ICRP 26. An increased contribution of neutrons could be detected inside the Phantom. However the total dose equivalent did not increase over the depth of the Phantom. As the first Austrian measurements on the ISS dosimeter packages were exposed for 248 days, starting in February 2001 at six different locations onboard the ISS. The Austrian dosimeter sets for this first exposure on the ISS contained five different kinds of passive thermoluminescent dosimeters. First results showed a position dependent absorbed dose rate at the ISS.

Astronauts↗
PubMed1995

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.

Cosmic Radiation↗
PubMed1987

Light hydrocarbons from plasma discharge in H2-He-CH4: first results and Uranian auroral chemistry.

Voyager 2 found that the Uranian magnetosphere has a substantial flux of energetic charged particles, which becomes rich in higher energies at low magnetospheric L near the orbit of Miranda. The electrons precipitate to produce aurorae, which have been observed in the ultraviolet. The more energetic component of the precipitating electrons can initiate radiation chemistry in the methane-poor stratosphere, near 0.1 mbar where the CH4 mole fraction XCH4 approximately equal to 10(-5). We present laboratory results for cold plasma (glow) discharge in continuous flow H2-He-CH4 atmospheres with mol fractions XCH4 = 10(-2) to 10(-3) and total pressure p = 60 to 0.6 mbar. The yields of simple hydrocarbons in these experiments and an estimate of precipitating electron flux consistent with the Voyager ultraviolet spectroscopy results indicate the globally averaged auroral processing rate of CH4 to higher hydrocarbons approximately equal to 3 x 10(6) C cm-2 s-1, comparable to the globally averaged photochemical production rate. The local rate approximately 2 x 10(8) C cm-2 s-1 in the auroral zones (approximately 20 degrees in diameter) at 15 degrees S and 45 degrees N latitude greatly exceeds the photochemical rate. Even at very low XCH4 approximately equal to 10(-3) the yield (summed over all products) G > approximately 10(-2) C/100 eV and the average slope alpha = > approximately -0.4, where the summation is over all product molecules of a given carbon number eta and the square brackets denote abundance. The yield therefore decreases slowly with molecular complexity: hydrocarbons through C7Hx should be present in auroral zones at abundances > approximately 10(-2) of the simplest C2 hydrocarbons. Saturated hydrocarbons (C2H6, C3H8, C4H10, etc.) are mostly shielded from photodissociation by C2H2 and will therefore persist at the sunlit, as well as the currently dark, magnetic polar regions.

Atmosphere↗
PubMed2005

Predicted inactivation of viruses of relevance to biodefense by solar radiation.

UV radiation from the sun is the primary germicide in the environment. The goal of this study was to estimate inactivation of viruses by solar exposure. We reviewed published reports on 254-nm UV inactivation and tabulated the sensitivities of a wide variety of viruses, including those with double-stranded DNA, single-stranded DNA, double-stranded RNA, or single-stranded RNA genomes. We calculated D(37) values (fluence producing on average one lethal hit per virion and reducing viable virus to 37%) from all available data. We defined "size-normalized sensitivity" (SnS) by multiplying UV(254) sensitivities (D(37) values) by the genome size, and SnS values were relatively constant for viruses with similar genetic composition. In addition, SnS values were similar for complete virions and their defective particles, even when the corresponding D(37) values were significantly different. We used SnS to estimate the UV(254) sensitivities of viruses for which the genome composition and size were known but no UV inactivation data were available, including smallpox virus, Ebola, Marburg, Crimean-Congo, Junin, and other hemorrhagic viruses, and Venezuelan equine encephalitis and other encephalitis viruses. We compiled available data on virus inactivation as a function of wavelength and calculated a composite action spectrum that allowed extrapolation from the 254-nm data to solar UV. We combined our estimates of virus sensitivity with solar measurements at different geographical locations to predict virus inactivation. Our predictions agreed with the available experimental data. This work should be a useful step to understanding and eventually predicting the survival of viruses after their release in the environment.

Cosmic Radiation↗
PubMed1996

Absorbed dose measurements on LDEF and comparisons with predictions.

The radiation environment on LDEF was monitored by cumulative absorbed dose measurements made with TLDs at different locations and shielding depths. The TLDs were included in four experiments: A0015(a) Biostack, P0004 Seeds in Space and P0006 Linear Energy Transfer Spectrum Measurements at the trailing edge (west side) of the satellite; M0004 Fiber Optics Data Link at the leading edge (east side); and A0015(b) Biostack at the Earth side. The shielding depths varied between 0.48 and 15.4 g/cm2, Al equivalent. Both the directional dependence of trapped protons incident on the satellite and the shielding thickness were reflected in absorbed dose values. The trapped proton anisotropy was measured by TLDs at the east and west sides of LDEF. At the east side doses ranged from 2.10 to 2.58 Gy under shielding of 2.90 to 1.37 g/cm2 (M0004) while on the west side doses ranged from 2.66 to 6.48 Gy under shielding of 15.4 to 0.48 g/cm2 (P0006). The west side doses were more than a factor of two higher, where the vertical shielding thicknesses to space were equal. Other west side doses of 3.04 to 4.49 Gy under shielding of 11.7 to 3.85 g/cm2 (A0015(a)) and 2.91 to 6.64 Gy under shielding of 11.1 to 0.48 g/cm2 (P0004) generally agreed with the P0006 results. The Earth side doses of 2.41 to 3.93 Gy under shielding of 10.0 to 1.66 g cm2 (A0015(b)) were intermediate between the east side and west side doses. Calculations utilizing a model of trapped proton spectra were performed by Watts et al. (1993) and comparisons of dose measurement and calculations may be found in a companion paper (Armstrong et al., 1996).

Aluminum↗
PubMed1973

Survival of bacterial isolates exposed to simulated Jovian trapped radiation belt electrons and solar wind protons.

With missions to Jupiter, the spacecraft will be exposed for extended durations to solar wind radiation and the Jovian trapped radiation belt. This study is designed to determine the effect of these radiation environments on spacecraft bacterial isolates. The information can be used in the probability of contamination analysis for these missions. A bacterial subpopulation from Mariner Mars 1971 spacecraft (nine spore-forming and three non-spore-forming isolates) plus two comparative organisms, Staphylococcus epidermidis ATCC 17917 and a strain of Bacillus subtilis var. niger, were exposed to 2, 12, and 25 MeV electrons at different doses with simultaneous exposure to a vacuum of 1.3 x 10(-4) N m-2 at 20 and -20 degrees C. The radioresistance of the subpopulation was dependent on the isolate, dose and energy of electrons. Temperature affected the radioresistance of only the spore-forming isolates. Survival data indicated that spores were reduced approximately 1 log/1500 J kg-1 (10 J kg-1=1 krad), while non-spore-forming isolates (micrococci) were reduced 1.5-2 logs/1500 J kg-1 with the exception of an apparent radioresistant isolate whose resistance approached that of the spores. The subpopulation was found to be less resistant to lower energy than to higher energy electrons. The bacterial isolates were exposed to 3 keV protons under the same conditions as the electrons with a total fluence of 1.5 x 10(13) p cm-2 and a dose rate of 8.6 x 10(9) p cm-2 s-1. The results showed that only 20% of S. epidermidis and 45% of B. subtilis populations survived exposure to the 3 keV protons, while the mean survival of the spacecraft subpopulation was 45% with a range from 31.8% (non-spore-former) to 64.8% (non-spore-former). No significant difference existed between spore-forming and non-spore-forming isolates.

Bacillus subtilis↗
PubMed1989

Space radiation dosimetry with active detections for the scientific program of the second Bulgarian cosmonaut on board the Mir space station.

A dosimetry-radiometry system has been developed at the Space Research Institute of the Bulgarian Academy of Science to measure the fluxes and dose rates on the flight of the second Bulgarian cosmonaut. The dosimetry system is designed for monitoring the different space radiations, such as solar cosmic rays, galactic cosmic rays and trapped particles in the earth radiation belts. The system consists of a battery operated small size detector unit and a "read-write" and telemetry microcomputer unit. The sensitivity of the instrument (3.67 x 10(-8) rad/pulse) permits high resolution measurements of the flux and dose rate along the track of the Mir space station. We report our initial results for the period of the flight between the 7th and 17th June 1988.

Atlantic Ocean↗
PubMed1996

The transfer of viable microorganisms between planets.

There is increasing acceptance that catastrophic cosmic impacts have played an important role in shaping the history of terrestrial life. Large asteroid and cometary impacts are also capable of displacing substantial quantities of planetary surface material into space. The discovery of Martian rocks on Earth suggests that viable microorganisms within such ejecta could be exchanged between planets. If this conjecture is correct, it will have profound implications for the origin and evolution of life in the solar system.

Archaea↗
PubMed2006

Do ambient electromagnetic fields affect behaviour? A demonstration of the relationship between geomagnetic storm activity and suicide.

The relationship between ambient electromagnetic fields and human mood and behaviour is of great public health interest. The relationship between Ap indices of geomagnetic storm activity and national suicide statistics for Australia from 1968 to 2002 was studied. Ap index data was normalised so as to be globally uniform and gave a measure of storm activity for each day. A geomagnetic storm event was defined as a day in which the Ap index was equal to or exceeded 100 nT. Suicide data was a national tally of daily male and female death figures where suicide had been documented as the cause of death. A total of 51 845 males and 16 327 females were included. The average number of suicides was greatest in spring for males and females, and lowest in autumn for males and summer for females. Suicide amongst females increased significantly in autumn during concurrent periods of geomagnetic storm activity (P = .01). This pattern was not observed in males (P = .16). This suggests that perturbations in ambient electromagnetic field activity impact behaviour in a clinically meaningful manner. The study furthermore raises issues regarding other sources of stray electromagnetic fields and their effect on mental health.

Age Distribution↗