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At least 1,063 records · Page 59Linked to original sources
PubMed1997

Simulation of radiation effects on three-dimensional computer optical memories.

A model was developed to simulate the effects of heavy charged-particle (HCP) radiation on the information stored in three-dimensional computer optical memories. The model is based on (i) the HCP track radial dose distribution, (ii) the spatial and temporal distribution of temperature in the track, (iii) the matrix-specific radiation-induced changes that will affect the response, and (iv) the kinetics of transition of photochromic molecules from the colored to the colorless isomeric form (bit flip). It is shown that information stored in a volume of several nanometers radius around the particle's track axis may be lost. The magnitude of the effect is dependent on the particle's track structure.

Biophysical Phenomena↗
PubMed2006

Space radiation dosimetry by combination of integrating dosemeters.

Generally, individual monitoring is performed with a small personal dosemeter which responds to radiation by giving a necessary operational quantity such as personal dose equivalent. In space, however, such a personal dosemeter has not yet been available and a dose equivalent is estimated through elaborate work using etched track detectors. It would be advantageous if we could simply measure the personal dose of an astronaut using conventional integrating dosemeters only. This possibility is discussed based on the concept of efficiency combination.

Cosmic Radiation↗
PubMed1987

Measurement of differential proton spectra onboard the Space Shuttle using a thermoluminescent dosimetry system.

An experimental technique that permits the extraction of orbit-averaged, differential energy spectra of trapped radiation belt protons using simple passive detectors is described. An inversion technique is used for the data analysis. The basic principle of the described system is measurement of the energy deposited in six thermoluminescent (TLD) detector assemblies behind various spherical absorbers. The technique has been applied to a detector assembly flown on four Shuttle flights. Although severe restraints were placed on the flight package, the differential energy spectra derived from these measurements are in good agreement with analytical results using a modified trapped proton environment model. The technique shows good promise for measuring the spectra in low inclination orbits where the flux of high energy galactic cosmic rays protons is small. Modifications to the detector assembly to improve the accuracy and to extend the range of the system to higher energies are suggested.

Cosmic Radiation↗
PubMed1986

Space Station gas-grain simulation facility: application to exobiology.

The Space Station provides an environment in which the forces required to suspend particles during an experiment can be reduced by as much as six orders of magnitude. This reduction in levitation force enables us to perform many new experiments in a variety of disciplines. We have grouped these experiments into two categories: 1) those involving an individual particle or the interaction between a few particles and 2) those involving clouds in particles. We consider only particle experiments at this stage because cloud experiments suffer from electrostatic interactions and levitation-forced coalescence therefore requiring considerably more space, mass and crew interaction. The displacement of a particle resulting from g-jitter for ballistic, Knudsen and Stokes flow regimes is considered in detail and the radiation, acoustic, electrostatic and electromagnetic levitation mechanisms to control this motion are reviewed. We have selected the simulation of organic haze production ion Titan as an example experiment for detailed study. The objective of this experiment is to simulate the photolysis of methane and the subsequent formation of the organic haze particles in the upper atmosphere of Titan.

Aerosols↗
PubMed1989

Quantitative interpretation of heavy ions effects: models for the biological effects of heavy ions.

Heavy ions are an important part of space radiation. Although they contribute only about 1 percent in number the fraction in terms of energy deposited is much higher. Also the quality of radiation is different from the other components since the LET is generally quite high. This poses the problem of Relative Biological Effectiveness (RBE). It is considerably more important in space than on earth because shielding measures are costly and sometimes not even feasible. Radiation hazards appear to be the limiting factor In long term space flights and their evaluation constitutes a major task. There is still no general agreement about RBE of earthbound radiation, and even less concerning the biological weighting of very heavy and very energetic ions in space. Because of the lack of experimental data--particularly for risk estimates in humans-- theoretical approaches may be very helpful in this respect and provide the only means to judge the radiation protection situation in outer space. In order to be useful careful checks of their consistency are necessary. This paper summarizes some of the more common approaches in a critical manner. The unhappy conclusion at the end will be that at present it is not possible to understand even heavy ion action on survival quantitatively with an acceptable precision.

Animals↗
PubMed1998

Role of chromosome instability in long term effect of manned-space missions.

Astronauts are exposed to heavy ions during space missions and heavy ion induced-chromosome damages have been observed in their lymphocytes. This raises the problem of the consequence of longer space flights. Recent studies show that some alterations can appear many cell generations after the initial radiation exposure as a delayed genomic instability. This delayed instability is characterized by the accumulation of cell alterations leading to cell transformation, delayed cell death and mutations. Chromosome instability was shown in vitro in different model systems (Sabatier et al., 1992; Marder and Morgan, 1993, Kadhim et al., 1994 and Holmberg et al., 1993, 1995). All types of radiation used induce a chromosome instability, however, heavy ions cause the most damage. The period of chromosome instability followed by the formation of clones with unbalanced karyotypes seems to be shared by cancer cells. The shortening of telomere sequences leading to the formation of telomere fusions is an important factor in the appearance of this chromosome instability.

Animals↗
PubMed1999

Neutron yields from 155 MeV/nucleon carbon and helium stopping in aluminum.

Neutron fluences have been measured from 155 MeV/nucleon 4He and 12C ions stopping in an Al target at laboratory angles between 10 and 160 deg. The resultant spectra were integrated over angle and energy above 10 MeV to produce total neutron yields. Comparison of the two systems shows that approximately two times as many neutrons are produced from 155 MeV/nucleon 4He stopping in Al and 155 MeV/nucleon 12C stopping in Al. Using an energy-dependent geometric cross-section formula to calculate the expected number of primary nuclear interactions shows that the 12C + Al system has, within uncertainties, the same number of neutrons per interaction (0.99 +/- 0.03) as does the 4He + Al system (1.02 +/- 0.04), despite the fact that 12C has three times as many neutrons as does 4He. Energy and angular distributions for both systems are also reported. No major differences can be seen between the two systems in those distributions, except for the overall magnitude. Where possible, the 4He + Al spectra are compared with previously measured spectra from 160 and 177.5 MeV/nucleon 4He interactions in a variety of stopping targets. The reported spectra are consistent with previously measured spectra. The data were acquired to provide data applicable to problems dealing with the determination of the radiation risk to humans engaged in long-term missions in space; however, the data are also of interest for issues related to the determination of the radiation environment in high-altitude flight, with shielding at high-energy heavy-ion accelerators and with doses delivered outside tumor sites treated with high-energy hadronic beams.

Altitude↗
PubMed1992

Induction of chromosome aberrations in mammalian cells after heavy ion exposure.

The induction of chromosome aberrations by heavy charged particles was studied in V79 Chinese hamster cells over a wide range of energies (3-100 MeV/u) and LET (20-16000 keV/micrometer). For comparison, X-ray experiments were performed. Our data indicate quantitative and qualitative differences in the response of cells to particle and x-ray irradiation. For the same level of cell survival the amount of damaged cells which can be observed is smaller in heavy ion (11.4 MeV/u Ar) irradiated samples. The highest yield of damaged cells is found 8 to 12 hours after particle irradiation and 4 hours after x-irradiation. Differences in the amount of damaged cells are attributed to cell cycle perturbations which interfere with the expression of damage. After heavy ion exposure the amount of cells reaching mitosis (mitotic index) decreases drastically and not all damaged cells reach mitosis within 48 hours after exposure. A portion of cells die in interphase. Cell cycle delays induced by x-ray irradiation are less pronounced and all cells reach the first post-irradiation mitosis within 24 hours after irradiation. Additionally, the damage produced by charged particles seems to be more severe. The disintegration of chromosomes was only observed after high LET radiation: an indication of the high and local energy deposition in the particle track. Only cross sections for the induction of chromosome aberrations in mitotic cells were reported in this paper because of the problems arising from the drastic cell cycle perturbations. In this case, cells were irradiated in mitosis and assayed immediately.

Animals↗
PubMed1994

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.

Animals↗
PubMed2003

Chromosome aberrations as biomarkers of radiation exposure: modelling basic mechanisms.

The space radiation environment is a mixed field consisting of different particles having different energies, including high charge and energy (HZE) ions. Conventional measurements of absorbed doses may not be sufficient to completely characterise the radiation field and perform reliable estimates of health risks. Biological dosimetry, based on the observation of specific radiation-induced endpoints (typically chromosome aberrations), can be a helpful approach in case of monitored exposure to space radiation or other mixed fields, as well as in case of accidental exposure. Furthermore, various ratios of aberrations (e.g. dicentric chromosomes to centric rings and complex exchanges to simple exchanges) have been suggested as possible fingerprints of radiation quality, although all of them have been subjected to some criticisms. In this context a mechanistic model and a Monte Carlo code for the simulation of chromosome aberration induction were developed. The model, able to provide dose-responses for different aberrations (e.g. dicentrics, rings, fragments, translocations, insertions and other complex exchanges), was further developed to assess the dependence of various ratios of aberrations on radiation quality. The predictions of the model were compared with available data, whose experimental conditions were faithfully reproduced. Particular attention was devoted to the scoring criteria adopted in different laboratories and to possible biases introduced by interphase death and mitotic delay. This latter aspect was investigated by taking into account both metaphase data and data obtained with Premature Chromosome Condensation (PCC).

Alpha Particles↗
PubMed2005

Shielding and fragmentation studies.

Radiation dosimetry for manned spaced missions depends on the ability to adequately describe the process of high-energy ion transport through many materials. Since the types of possible nuclear interactions are many and complex, transport models are used which depend upon a reliable source of experimental data. To expand the heavy ion database used in the models we have been measuring charge-changing cross sections and fragment production cross sections from heavy-ion interactions in various elementa targets. These include materials flown on space missions such as carbon and aluminium, as well as those important in radiation dosimetry such as hydrogen, nitrogen and water. Measuring heavy-ion fragmentation through these targets also gives us the ability to determine the effectiveness of new materials proposed for shielding such as graphite composites and polyethylene hybrids. Measurement without a target present gives an indication of the level of contamination of the primary beam, which is also important in radiobiology experiments.

Construction Materials↗
PubMed1979

Radiation danger in prolonged manned space flights.

The author examines methods for prognosticating solar activity for several decades to determine optimum periods for prolonged space flight. The focus of the discussion is the presence of a change in magnetic polarity at the beginning of each 11-year solar cycle, resulting in a 22-year cycle. An historical review of solar cycles determined a super cycle of about 180 years. Using this data, it is determined that solar activity will be weak through the end of the 20th century.

Cosmic Radiation↗
PubMed1999

Organ/Tissue absorbed doses measured with a human phantom torso in the 9th Shuttle-Mir Mission (STS-91).

Organ/Tissue absorbed doses were measured with a life-size human phantom torso in the 9th Shuttle/Mir Mission (STS-91) from June 2 to 12, 1998. This is the first attempt to measure directly organ/tissue doses over a whole human body in space. The absorbed dose was measured by combination of two integrating detectors: thermo- luminescent dosemeter of Mg2SiO4: Tb (TDMS) and plastic nuclear track detector (PNTD). Both detectors were calibrated on ground using high-energy charged-particle beams. The detectors were packed in 59 cases of tissue-equivalent resin; and put into the positions of radiologically important organs and tissues in the phantom. Efficiency reductions of TDMS for high-LET particles were corrected based on the LET-differential particle fluence of space radiation measured with PNTDs. The accumulated absorbed doses during this 9.8-days mission at low-earth orbit (400 km x 51.6 degrees) ranged from 1.6 mGy at colon to 2.6 mGy at bone surface (shoulder) with a variation factor of 1.6. The absorbed doses at some internal organs were higher than the skin dose. This fact is important from the viewpoint of radiological protection for astronauts.

Cosmic Radiation↗
PubMed2001

Space radiation research in the new millenium--from where we come and where we go.

Space radiation research had a significant impact in the past. The physical interaction of heavy charged particles with living matter and the development of models, including microdosimetry, were stimulated by problems encountered in space. New phenomena were discovered. Advanced dosimetric techniques had to be developed and computational methods to describe the radiation field in space. The understanding of the radiobiology of heavy ions, necessary for a well-founded risk assessment and prompted by space radiation research, constitutes also the basis for heavy ion radiotherapy. So far unknown areas like the interaction of microgravity and radiation were opened. The space station will give even more opportunities. For the first time it will be possible to investigate animals for a longer time under the influence of both microgravity and radiation. Living systems can be exposed under well defined conditions with parallel physical measurements. Solar particle events are still an unsolved problem. Significant improvement in their predictability and quantitative description can be expected. All this will not only give exciting opportunities for research but will also translate into immediate benefit for human beings. This paper will attempt to give an overview of the past achievements and glance into the future.

Animals↗
PubMed2005

Comparison of high-energy trapped particle environments at the Earth and Jupiter.

The 'Van Allen belts' of the trapped energetic particles in the Earth's magnetosphere were discovered by the Explorer I satellite in 1958. In addition, in 1959, it was observed that UHF radio emissions from Jupiter probably had a similar source--the Jovian radiation belts. In this paper, the global characteristics of these two planets' trapped radiation environments and respective magnetospheres are compared and state-of-the-art models used to generate estimates of the high-energy electron (> or = 100 keV) and proton (> or = 1 MeV) populations--the dominant radiation particles in these environments. The models used are the AP8/AE8 series for the Earth and the Divine-Garrett/GIRE model for Jupiter. To illustrate the relative magnitude of radiation effects at each planet, radiation transport calculations were performed to compute the total ionising dose levels at the geosynchronous orbit for the Earth and at Europa (Jupiter's 4th largest moon) for Jupiter. The results show that the dose rates are -0.1 krad(Si) d(-1) at the geosynchronous orbit and -30 krad(Si) d((-1) at Europa for a 2.5 mm spherical shell aluminium shield--a factor of -300 between the two planets.

Cosmic Radiation↗
PubMed2005

Validation of the HZETRN code for laboratory exposures with 1A GeV iron ions in several targets.

A new version of the HZETRN code capable of validation with HZE ions in either the laboratory or the space environment is under development. The computational model consists of the lowest order asymptotic approximation followed by a Neumann series expansion with non-perturbative corrections. The physical description includes energy loss with straggling, nuclear attenuation, nuclear fragmentation with energy dispersion and downshift. Measurements to test the model were performed at the Alternating Gradient Synchrotron and the NASA Space Radiation Laboratory at Brookhaven National Laboratory with iron ions. Surviving beam particles and produced fragments were measured with solid-state detectors. Beam analysis software has been written to relate the computational results to the measured energy loss spectra of the incident ions for rapid validation of modeled target transmission functions.

Aluminum↗
PubMed2005

Radiation exposure measurement onboard civil aircraft.

The active dosemeter DOSTEL based on two silicon planar detectors was flown on civil aircraft flights to study the radiation exposure of air crew members. The altitude and latitude dependence of count and dose rates as well as long-term variations are measured. After calibration of the DOSTEL response against measurements of a TEPC instrument, total dose-equivalent values for various flights are compared with H*(10) calculations by EPCARD yielding a ratio of 1.02 +/- 0.09 (standard variation).

Aerospace Medicine↗
PubMed1977

Summary of measurements of high-LET particle radiation in U.S. manned space missions.

A summary of measurements of high-LET particle radiation inside U.S. manned spacecraft is given for ASTP (Apollo Soyuz Test Project), Skylab and Apollo missions. The results include particle fluxes, integral LET spectra, and stopping-density charge distributions derived from measurements made in plastic nuclear track detectors worn by astronauts and located at various positions inside spacecraft. The results presented for different missions cover a wide range of shielding depth and missions type.

Astronauts↗