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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Synchrotron Vacuum Ultraviolet Light and Soft X-Ray Radiation Effects on Aluminized Teflon FEP Investigated

Since the Hubble Space Telescope (HST) was deployed in low Earth orbit in April 1990, two servicing missions have been conducted to upgrade its scientific capabilities. Minor cracking of second-surface metalized Teflon FEP (DuPont; fluorinated ethylene propylene) surfaces from multilayer insulation (MLI) was first observed upon close examination of samples with high solar exposure retrieved during the first servicing mission, which was conducted 3.6 years after deployment. During the second HST servicing mission, 6.8 years after deployment, astronaut observations and photographic documentation revealed significant cracks in the Teflon FEP layer of the MLI on both the solar- and anti-solar-facing surfaces of the telescope. NASA Goddard Space Flight Center directed the efforts of the Hubble Space Telescope MLI Failure Review Board, whose goals included identifying the low-Earth-orbit environmental constituent(s) responsible for the cracking and embrittling of Teflon FEP which was observed during the second servicing mission. The NASA Lewis Research Center provided significant support to this effort. Because soft x-ray radiation from solar flares had been considered as a possible cause for the degradation of the mechanical properties of Teflon FEP (ref. 1), the effects of soft xray radiation and vacuum ultraviolet light on Teflon FEP were investigated. In this Lewisled effort, samples of Teflon FEP with a 100-nm layer of vapor-deposited aluminum (VDA) on the backside were exposed to synchrotron radiation of various vacuum ultraviolet and soft x-ray wavelengths between 18 nm (69 eV) and 0.65 nm (1900 eV). Synchrotron radiation exposures were conducted using the National Synchrotron Light Source at Brookhaven National Laboratory. Samples of FEP/VDA were exposed with the FEP surface facing the synchrotron beam. Doses and fluences were compared with those estimated for the 20-yr Hubble Space Telescope mission.

Dever, Joyce A.↗
NASA NTRS2009

A Monte-Carlo Model for the Formation of Radiation-induced Chromosomal Aberrations

Purpose: To simulate radiation-induced chromosome aberrations in mammalian cells (e.g., rings, translocations, and dicentrics) and to calculate their frequency distributions following exposure to DNA double strand breaks (DSBs) produced by high-LET ions. Methods: The interphase genome was assumed to be comprised of a collection of 2 kbp rigid-block monomers following the random-walk geometry. Additional details for the modeling of chromosomal structure, such as chromosomal domains and chromosomal loops, were included. A radial energy profile for heavy ion tracks was used to simulate the high-LET pattern of induced DSBs. The induced DSB pattern depended on the ion charge and kinetic energy, but always corresponded to the DSB yield of 25 DSBs/cell/Gy. The sum of all energy contributions from Poisson-distributed particle tracks was taken to account for all possible one-track and multi-track effects. The relevant output of the model was DNA fragments produced by DSBs. The DSBs, or breakpoints, were defined by (x, y, z, l) positions, where x, y, z were the Euclidian coordinates of a DSB, and where l was the relative position along the genome. Results: The code was used to carry out Monte Carlo simulations for DSB rejoinings at low doses. The resulting fragments were analyzed to estimate the frequencies of specific types of chromosomal aberrations. Histograms for relative frequencies of chromosomal aberrations and P.D.F.s (probability density functions) of a given aberration type were produced. The relative frequency of dicentrics to rings was compared to empirical data to calibrate rejoining probabilities. Of particular interest was the predicted distribution of ring sizes, irrespective of their frequencies relative to other aberrations. Simulated ring sizes were . 4 kbp, which are far too small to be observed experimentally (i.e., by microscopy) but which, nevertheless, are conjectured to exist. Other aberrations, for example, inversions, translocations, as well as multi-centrics were also recorded. Conclusion: High-LET DNA damage affects the frequencies of chromosomal aberrations. The ratio of rings to dicentrics is correct for the genomic size cut-offs corresponding to available experimental data. The present work predicts a relative abundance of small rings following irradiation by heavy ions.

Ponomarev, Artem L.↗
NASA NTRS2016

Evidence Report: Risk of Acute Radiation Syndromes Due to Solar Particle Events

Crew health and performance may be impacted by a major solar particle event (SPE), multiple SPEs, or the cumulative effect of galactic cosmic rays (GCR) and SPEs. Beyond low-Earth orbit, the protection of the Earth's magnetosphere is no longer available, such that increased shielding and protective mechanisms are necessary in order to prevent acute radiation sickness and impacts to mission success or crew survival. While operational monitoring and shielding are expected to minimize radiation exposures, there are EVA scenarios outside of low-Earth orbit where the risk of prodromal effects, including nausea, vomiting, anorexia, and fatigue, as well as skin injury and depletion of the blood-forming organs (BFO), may occur. There is a reasonable concern that a compromised immune system due to high skin doses from a SPE or due to synergistic space flight factors (e.g., microgravity) may lead to increased risk to the BFO. The primary data available at present are derived from analyses of medical patients and persons accidentally exposed to acute, high doses of low-linear energy transfer (LET) (or terrestrial) radiation. Data more specific to the space flight environment must be compiled to quantify the magnitude of increase of this risk and to develop appropriate protection strategies. In particular, information addressing the distinct differences between solar proton exposures and terrestrial exposure scenarios, including radiation quality, dose-rate effects, and non-uniform dose distributions, is required for accurate risk estimation.

Carnell, Lisa↗
NASA NTRS1983

Late skin damage in rabbits and monkeys after exposure to particulate radiations

Preliminary results are reported of experiments on the late effects of exposure to particulate radiations on stem cell populations. Skin biopsies were taken from the ears of rabbits irradiated 2-5 years previously with 530 MeV/amu Ar ions (LET 90 keV/micron), or 365 MeV/amu Ne ions (LET 35 keV micron), and from the chests and inner thighs of rhesus monkeys irradiated 16-18 years previously with 32-MeV protons (LET about 1.2 keV/micron). Skin fibroblast cultures obtained from the biopsy samples in rabbits were observed to undergo dose-dependent decreases in in vitro life span, with estimated survival curves showing the effects of Ar-ion irradiation to be more severe than those of Ne-ion irradiation. In addition, the healing of the biopsy wound was observed to become slower as radiation dose increased. In the monkey, radiation reduced the average number of fibroblasts at the time of cessation of growth in culture. Results thus demonstrate the capacity of skin sampling to reveal stem cell destruction, and have important implications for astronauts and other persons at risk of particle exposure with regard to healing responses to trauma or surgery.

Bergtold, D. S.↗
NASA NTRS2001

Space Radiation Cancer Risks and Uncertainties for Mars Missions

Projecting cancer risks from exposure to space radiation is highly uncertain because of the absence of data for humans and because of the limited radiobiology data available for estimating late effects from the high-energy and charge (HZE) ions present in the galactic cosmic rays (GCR). Cancer risk projections involve many biological and physical factors, each of which has a differential range of uncertainty due to the lack of data and knowledge. We discuss an uncertainty assessment within the linear-additivity model using the approach of Monte Carlo sampling from subjective error distributions that represent the lack of knowledge in each factor to quantify the overall uncertainty in risk projections. Calculations are performed using the space radiation environment and transport codes for several Mars mission scenarios. This approach leads to estimates of the uncertainties in cancer risk projections of 400-600% for a Mars mission. The uncertainties in the quality factors are dominant. Using safety standards developed for low-Earth orbit, long-term space missions (>90 days) outside the Earth's magnetic field are currently unacceptable if the confidence levels in risk projections are considered. Because GCR exposures involve multiple particle or delta-ray tracks per cellular array, our results suggest that the shape of the dose response at low dose rates may be an additional uncertainty for estimating space radiation risks.

NASA Discipline Radiation Health↗
NASA NTRS1992

Radiation dose to critical body organs for October 1989 proton event

The Geostationary Operational Environmental Satellite (GOES-7) provides high-quality environmental data about the temporal development and energy characteristics of the protons emitted during a solar particle event. The GOES-7 time history of the hourly averaged integral proton flux for various particle kinetic energies are analyzed for the solar proton event occurring October 19-29, 1989. This event is similar to the August 1972 event that has been widely studied to estimate free-space and planetary radiation-protection requirements. By analyzing the time-history data, the dose rates, which can vary over many orders of magnitude in the early phases of the flare, can be estimated as well as the cumulative dose as a function of time. When basic transport results are coupled with detailed body organ thickness distributions calculated with the Computerized Anatomical Man and Computerized Anatomical Female models, the dose rates and cumulative doses to specific organs can be predicted. With these results, the risks of cancer incidence and mortality are estimated for astronauts in free space protected by various water shield thicknesses.

Simonsen, Lisa C.↗
NASA NTRS1994

Radiation protection issues in galactic cosmic ray risk assessment

Radiation protection involves the limitation of exposure to below threshold doses for direct (or deterministic) effects and a knowledge of the risk of stochastic effects after low doses. The principal stochastic risk associated with low dose rate galactic cosmic rays is the increased risk of cancer. Estimates of this risk depend on two factors (a) estimates of cancer risk for low-LET radiation and (b) values of the appropriate radiation weighting factors, WR, for the high-LET radiations of galactic cosmic rays. Both factors are subject to considerable uncertainty. The low-LET cancer risk derived from the late effects of the atomic bombs is vulnerable to a number of uncertainties including especially that from projection in time, and from extrapolation from high to low dose rate. Nevertheless, recent low dose studies of workers and others tend to confirm these estimates. WR, relies on biological effects studied mainly in non-human systems. Additional laboratory studies could reduce the uncertainties in WR and thus produce a more confident estimate of the overall risk of galactic cosmic rays.

NASA Program Radiation Health↗
NASA NTRS2010

Depth Dose Distribution Study within a Phantom Torso after Irradiation with a Simulated Solar Particle Event at NSRL

The adequate knowledge of the radiation environment and the doses incurred during a space mission is essential for estimating an astronaut's health risk. The space radiation environment is complex and variable, and exposures inside the spacecraft and the astronaut's body are compounded by the interactions of the primary particles with the atoms of the structural materials and with the body itself Astronauts' radiation exposures are measured by means of personal dosimetry, but there remains substantial uncertainty associated with the computational extrapolation of skin dose to organ dose, which can lead to over- or underestimation of the health risk. Comparisons of models to data showed that the astronaut's Effective dose (E) can be predicted to within about a +10% accuracy using space radiation transport models for galactic cosmic rays (GCR) and trapped radiation behind shielding. However for solar particle event (SPE) with steep energy spectra and for extra-vehicular activities on the surface of the moon where only tissue shielding is present, transport models predict that there are large differences in model assumptions in projecting organ doses. Therefore experimental verification of SPE induced organ doses may be crucial for the design of lunar missions. In the research experiment "Depth dose distribution study within a phantom torso" at the NASA Space Radiation Laboratory (NSRL) at BNL, Brookhaven, USA the large 1972 SPE spectrum was simulated using seven different proton energies from 50 up to 450 MeV. A phantom torso constructed of natural bones and realistic distributions of human tissue equivalent materials, which is comparable to the torso of the MATROSHKA phantom currently on the ISS, was equipped with a comprehensive set of thermoluminescence detectors and human cells. The detectors are applied to assess the depth dose distribution and radiation transport codes (e.g. GEANT4) are used to assess the radiation field and interactions of the radiation field with the phantom torso. Lymphocyte cells are strategically embedded at selected locations at the skin and internal organs and are processed after irradiation to assess the effects of shielding on the yield of chromosome damage. The initial focus of the present experiment is to correlate biological results with physical dosimetry measurements in the phantom torso. Further on, the results of the passive dosimetry within the anthropomorphic phantoms represent the best tool to generate reliable data to benchmark computational radiation transport models in a radiation field of interest. The presentation will give first results of the physical dose distribution, the comparison with GEANT4 computer simulations based on a Voxel model of the phantom, and a comparison with the data from the chromosome aberration study.

Berger, Thomas↗
NASA NTRSDate not supplied

Analytical Calculation of the Energy Deposition Spectrum and Average Dose to A Spherical Target at All Impact Parameters

Microdosimetry is used to estimate quality factors for risk assessment in radiation protection and to quantify relative biological effectiveness (RBE) for treatment planning of hadron radiation therapy. Radiation physics has shown that energetic ions deposit energy in a complex manner: the track structure. The Local Effect Model (LEM) is often used as an approximation to describe this complex track structure. We have previously calculated an analytical expression for the dose to a spherical target fully located in the penumbra of an ion track using the LEM. In this work, the calculation has been extended to all impact parameters. Furthermore, using these analytical expressions, it was possible to obtain the theoretical energy deposition spectra to a sphere irradiated uniformly.

Ianik Plante↗
NASA NTRS2004

Radiation Risk Assessment of the Individual Astronaut: A Complement to Radiation Interests at the NIH

Predicting human risks following exposure to space radiation is uncertain in part because of unpredictable distribution of high-LET and low-dose-derived damage amongst cells in tissues, unknown synergistic effects of microgravity upon gene- and protein-expression, and inadequately modeled processing of radiation-induced damage within cells to produce rare and late-appearing malignant cancers. Furthermore, estimation of risks of radiogenic outcome within small numbers of astronauts is not possible using classic epidemiologic study. It therefore seems useful to develop strategies of risk-assessment based upon large datasets acquired from correlated biological models useful for resolving radiogenic risk-assessment for irradiated individuals. In this regard, it is suggested that sensitive cellular biodosimeters that simultaneously report 1) the quantity of absorbed dose after exposure to ionizing radiation, 2) the quality of radiation delivering that dose, and 3) the biomolecular risk of malignant transformation be developed in order to resolve these NASA-specific challenges. Multiparametric cellular biodosimeters could be developed using analyses of gene-expression and protein-expression whereby large datasets of cellular response to radiation-induced damage are analyzed for markers predictive for acute response as well as cancer-risk. A new paradigm is accordingly addressed wherein genomic and proteomic datasets are registered and interrogated in order to provide statistically significant dose-dependent risk estimation in individual astronauts. This evaluation of the individual for assessment of radiogenic outcomes connects to NIH program in that such a paradigm also supports assignment of a given patient to a specific therapy, the diagnosis of response of that patient to therapy, and the prediction of risks accumulated by that patient during therapy - such as risks incurred by scatter and neutrons produced during high-energy Intensity-Modulated Radiation Therapy. Value of assessment of radiogenic outcome for individuals exposed to radiation is suggested to be common to both NASA and NIH.

Richmond, Robert C.↗
NASA NTRS2003

Risk of Skin Cancer from Space Radiation

We review the methods for estimating the probability of increased incidence of skin cancers from space radiation exposure, and describe some of the individual factors that may contribute to risk projection models, including skin pigment, and synergistic effects of combined ionizing and UV exposure. The steep dose gradients from trapped electrons, protons, and heavy ions radiation during EVA and limitations in EVA dosimetry are important factors for projecting skin cancer risk of astronauts. We estimate that the probability of increased skin cancer risk varies more than 10-fold for individual astronauts and that the risk of skin cancer could exceed 1 % for future lunar base operations for astronauts with light skin color and hair. Limitations in physical dosimetry in estimating the distribution of dose at the skin suggest that new biodosimetry methods be developed for responding to accidental overexposure of the skin during future space missions.

Cucinotta, Francis A.↗
NASA NTRS2002

Shuttle radiation dose measurements in the International Space Station orbits

The International Space Station (ISS) is now a reality with the start of a permanent human presence on board. Radiation presents a serious risk to the health and safety of the astronauts, and there is a clear requirement for estimating their exposures prior to and after flights. Predictions of the dose rate at times other than solar minimum or solar maximum have not been possible, because there has been no method to calculate the trapped-particle spectrum at intermediate times. Over the last few years, a tissue-equivalent proportional counter (TEPC) has been flown at a fixed mid-deck location on board the Space Shuttle in 51.65 degrees inclination flights. These flights have provided data that cover the expected changes in the dose rates due to changes in altitude and changes in solar activity from the solar minimum to the solar maximum of the current 23rd solar cycle. Based on these data, a simple function of the solar deceleration potential has been derived that can be used to predict the galactic cosmic radiation (GCR) dose rates to within +/-10%. For altitudes to be covered by the ISS, the dose rate due to the trapped particles is found to be a power-law function, rho(-2/3), of the atmospheric density, rho. This relationship can be used to predict trapped dose rates inside these spacecraft to +/-10% throughout the solar cycle. Thus, given the shielding distribution for a location inside the Space Shuttle or inside an ISS module, this approach can be used to predict the combined GCR + trapped dose rate to better than +/-15% for quiet solar conditions.

NASA Discipline Radiation Health↗
NASA NTRS1997

Biodosimetry results from space flight Mir-18

Astronauts are classified as radiation workers due to the presence of ionizing radiation in space. For the assessment of health risks, physical dosimetry has been indispensable. However, the change of the location of dosimeters on the crew members, the variation in dose rate with location inside the spacecraft and the unknown biological effects of microgravity can introduce significant uncertainties in estimating exposure. To circumvent such uncertainty, a study on the cytogenetic effects of space radiation in human lymphocytes was proposed and conducted for Mir-18, a 115-day mission. This study used fluorescence in situ hybridization (FISH) with whole-chromosome painting probes to score chromosomal exchanges and the Giemsa staining method to determine the frequency of dicentrics. The growth kinetics of cells and sister chromatid exchanges (SCEs) were examined to ensure that chromosomal aberrations were scored in the first mitosis and were induced primarily by space radiation. Our results showed that the frequency of chromosomal aberrations increased significantly in postflight samples compared to samples drawn prior to flight, and that the frequency of SCEs was similar for both pre- and postflight samples. Based on a dose-response curve for preflight samples exposed to gamma rays, the absorbed dose received by crew members during the mission was estimated to be about 14.75 cSv. Because the absorbed dose measured by physical dosimeters is 5.2 cGy for the entire mission, the RBE is about 2.8.

NASA Discipline Radiation Health↗
NASA NTRS1998

Effect of track structure and radioprotectors on the induction of oncogenic transformation in murine fibroblasts by heavy ions

The oncogenic potential of high-energy 56Fe particles (1 GeV/nucleon) accelerated with the Alternating Gradient Synchrotron at the Brookhaven National Laboratory was examined utilizing the mouse C3H 10T1/2 cell model. The dose-averaged LET for high-energy 56Fe is estimated to be 143 keV/micrometer with the exposure conditions used in this study. For 56Fe ions, the maximum relative biological effectiveness (RBEmax) values for cell survival and oncogenic transformation were 7.71 and 16.5 respectively. Compared to 150 keV/micrometer 4He nuclei, high-energy 56Fe nuclei were significantly less effective in cell killing and oncogenic induction. The prostaglandin E1 analog misoprostol, an effective oncoprotector of C3H 10T1/2 cells exposed to X rays, was evaluated for its potential as a radioprotector of oncogenic transformation with high-energy 56Fe. Exposure of cells to misoprostol did not alter 56Fe cytotoxicity or the rate of 56Fe-induced oncogenic transformation.

NASA Discipline Radiation Health↗
NASA NTRS1988

Radiation safety in commercial air traffic - A need for further study

The problem of radiation exposure of crewmembers in high altitude supersonic commercial aircraft is addressed. As a result of recent changes in the quality factors for radiological protection, it is found that worst case estimates of radiation exposure are now well above the exposure limits of the general population, and a reassessment of radiation impact on commercial aviation is needed, if the proposed quality factors are adopted. Calculations are presented from a study on neutron dosage equivalent rates. It is shown that a crew flying at altitudes near 13 km (43,000 ft) for 40 hr/mo would receive exposure levels of 47-75 Sv/yr, and it is suggested that such crewmembers be considered as radiation workers, rather than general population members. However, since present exposure estimates need to be improved, and the maximum permissible dose limits are currently under revision, the final exposure limits are, as yet, unclear, suggesting the need for further study to clarify the work status of commercial aircrews.

Wilson, John W.↗
NASA NTRS1989

Approximate angular distribution and spectra for geomagnetically trapped protons in low-earth orbit

The highly anisotropic nature of the radiation in the low-earth orbit has been ignored for most spacecraft shielding calculations made to date because the standard environmental models describe the omnidirectional flux only, because the varying attitude of the spacecraft in the environment is assumed to average out the effect and because of the added complexity of the calculation. The Space Station is planned to be stabilized with respect to the velocity vector and local vertical. Thus it will pass through the South Atlantic Anomaly where most of the radiation flux is encountered in much the same attitude on each pass. Any calculation including a complex shielding geometry should thus consider the angular distributuon of the incident radiation. An approximate trapped proton angular distribution is presented which includes both the 'pan caked' distribution relative to the magnetic field direction and the east-west effect which is energy dependent. This distribution is then used with a planar shielding geometry to obtain an estimate of the effect of the anisotropy on radiation dose rates in spacecraft.

Watts, J. W.↗
NASA NTRS2001

Radiation breakage of DNA: a model based on random-walk chromatin structure

Monte Carlo computer software, called DNAbreak, has recently been developed to analyze observed non-random clustering of DNA double strand breaks in chromatin after exposure to densely ionizing radiation. The software models coarse-grained configurations of chromatin and radiation tracks, small-scale details being suppressed in order to obtain statistical results for larger scales, up to the size of a whole chromosome. We here give an analytic counterpart of the numerical model, useful for benchmarks, for elucidating the numerical results, for analyzing the assumptions of a more general but less mechanistic "randomly-located-clusters" formalism, and, potentially, for speeding up the calculations. The equations characterize multi-track DNA fragment-size distributions in terms of one-track action; an important step in extrapolating high-dose laboratory results to the much lower doses of main interest in environmental or occupational risk estimation. The approach can utilize the experimental information on DNA fragment-size distributions to draw inferences about large-scale chromatin geometry during cell-cycle interphase.

Chromatin/radiation effects↗
NASA NTRS1972

Electron and proton flux models for Jupiter's radiation belts

Estimates of the energetic particle distribution in Jupiter's radiation belts are presented and are compared with previous estimates. Mathematical expressions are developed for the equatorial electron and proton fluxes, shielded electron and proton dose rates, and radiation lifetimes of electronic circuits. It is calculated that a 1 g/sq cm aluminum shield will screen out all protons of energy less than 27.5 MeV, and a 2 g/sq cm shield will screen out protons less than 40.6 MeV. The radiation lifetimes are based on a maximum permissible dose value of 10 million rads, a value 1/2 to 1/3 of the flux at which electronic circuits begin to fail. Estimated increases in lifetimes by using a 3 x 50 orbit instead of a 3 x 3 orbit, and going from 1 to 2 g/sq cm are given.

Klopp, D. A.↗