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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Impulsive solar X-ray bursts. 4: Polarization, directivity and spectrum of the reflected and total bremsstrahlung radiation from a beam of electrons directed toward the photosphere

A Monte Carlo method is described for evaluation of the spectrum, directivity and polarization of X-rays diffusely reflected from stellar photospheres. the accuracy of the technique is evaluated through comparison with analytic results. Using the characteristics of the incident X-rays of the model for solar X-ray flares, the spectrum, directivity and polarization of the reflected and the total X-ray fluxes are evaluated. The results are compared with observations.

Langer, S. H.↗
NASA NTRS1985

Directivity of Bremsstrahlung radiation from relativistic beams and the Gamma-Rays from solar flares

It has been observed that flares with greater than 10 Mev gamma-ray emission are concentrated around the solar limb with a dispersion of 10 to 20 degrees. It is shown that the bremsstrahlung by relativistic electrons is responsible for such gamma-rays and that the expected relativistic beaming cannot explain this dispersion. It is argued that this dispersion is predominately a reflection of the pitch angle distribution of the electrons. Then it is shown that this requires a small variation of the magnetic field from the point where the electrons are injected to the photosphere and a nearly isotropic (in the downward direction) pitch angle distribution at the injection. The influence of other effects on the observed distribution is also discussed.

Petrosian, V.↗
NASA NTRS1985

Directivity of bremsstrahlung radiation from relativistic beams and the gamma rays from solar flares

It has been observed that flares with greater than 10 MeV gamma-ray emission are concentrated around the solar limb with a dispersion of 10 to 20 degrees. It is shown that the bremsstrahlung by relativistic electrons is responsible for such gamma-rays and that the expected relativistic beaming cannot explain this dispersion. It is argued that this dispersion is predominately a reflection of the pitch angle distribution of the electrons. Then it is shown that this requires a small variation of the magnetic field from the point where the electrons are injected to the photosphere and a nearly isotropic (in the downward direction) pitch angle distribution at the injection. The influence of other effects on the observed distribution is also discussed.

Petrosian, V.↗
NASA NTRS1987

Beaming in blazars

Relativistic beaming of radiation is generally invoked to explain the extreme properties of blazars. The simplest synchrotron-self-Compton (SSC) model is applied to all blazars that have been observed in the X-ray region and have known VLBI sizes, and the minimum kinematic Doppler factor for each source is derived. All high polarization quasars (HPQs), but only half of the 30 BL Lac objects in the sample require relativistic enhancement of radiation due to beaming effects. The different Doppler factor distributions for the two classes of sources argue against the hypothesis that BL Lacs could be low-luminosity HPQs whose strong emission lines are swamped out by the boosted nonthermal continuum. Thus HPQs and BL Lacs could be intrinsically different in their physical structure.

Madau, P.↗
DOE OSTI2022

Mode matching method for absorption spectroscopy systems

Systems and methods for controlling optical feedback in an optical system. A resonant optical cavity includes at least two cavity mirrors, one of which is a cavity coupling mirror, and has a plurality of optical resonance cavity modes. A radiation source emits a beam of continuous wave radiation and is capable of being scanned whereby a mean optical frequency of the continuous wave radiation beam is adjustable over a range of frequencies, wherein the radiation source is responsive to optical feedback radiation emerging from the cavity, and wherein the mode matching optics couples the beam of continuous wave radiation to the cavity via the cavity coupling mirror. The radiation source and the mode matching optics are aligned so that a mode fill ratio is reduced relative to a maximum mode fill ratio, wherein the laser beam is coupled with a fundamental cavity mode.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1989

Paraboloidal Antenna Radiates Fan Or Pencil Beams

Shape of beam determined by type of feed. Theory and experiments show same paraboloidal antenna reflector used to radiate pencil beam or fan beam, depending on configuration of feed. Although pencil-shaped beam desirable in many applications, fan-shaped beam preferred in some scanning-radar and mapping-radar systems. Experiment performed with paraboloidal reflector having focal length of 48 in. (1.22 m) and diameter of 3.65 m. Shows fan beams generated in this way and not seriously distorted by feed offsets tested. Also shows because reflector in near field of feed, fan beam not necessarily focused by placing feed at focal plane.

Huang, John↗
NASA NTRS2005

Optical path switching based differential absorption radiometry for substance detection

An optical path switch divides sample path radiation into a time series of alternating first polarized components and second polarized components. The first polarized components are transmitted along a first optical path and the second polarized components along a second optical path. A first gasless optical filter train filters the first polarized components to isolate at least a first wavelength band thereby generating first filtered radiation. A second gasless optical filter train filters the second polarized components to isolate at least a second wavelength band thereby generating second filtered radiation. A beam combiner combines the first and second filtered radiation to form a combined beam of radiation. A detector is disposed to monitor magnitude of at least a portion of the combined beam alternately at the first wavelength band and the second wavelength band as an indication of the concentration of the substance in the sample path.

Sachse, Glen W.↗
NASA NTRS2003

Optical path switching based differential absorption radiometry for substance detection

An optical path switch divides sample path radiation into a time series of alternating first polarized components and second polarized components. The first polarized components are transmitted along a first optical path and the second polarized components along a second optical path. A first gasless optical filter train filters the first polarized components to isolate at least a first wavelength band thereby generating first filtered radiation. A second gasless optical filter train filters the second polarized components to isolate at least a second wavelength band thereby generating second filtered radiation. A beam combiner combines the first and second filtered radiation to form a combined beam of radiation. A detector is disposed to monitor magnitude of at least a portion of the combined beam alternately at the first wavelength band and the second wavelength band as an indication of the concentration of the substance in the sample path.

Sachse, Glen W.↗
NASA NTRS1998

Evaluation of risk from space radiation with high-energy heavy ion beams

The most challenging radiation in space consists of fully ionized atomic elements with high energy for which only the few lowest energy ions can be stopped in shielding materials. The health risk from exposure to these ions and their secondary radiations generated in shield materials is poorly understood since there are few human data and a systematic study in relevant animal model systems has not been made. The accuracy of risk prediction is described as the major limiting factor in the management of space radiation risk. The expected impact of systematic studies is examined using the limited available biological data and models. Given the limitations of current predictions, models must be developed that are able to incorporate the required fundamental scientific data into accurate risk estimates. The important radiation components that can be provided for laboratory testing are identified. The use of ground-based accelerator beams to simulate space radiation is explained and quantitative scientific constraints on such facilities are derived. Three facilities, one each in the United States, in Germany and in Japan, currently have the partial capability to satisfy these constraints. A facility has been proposed using the Brookhaven National Laboratory Booster Synchrotron in the United States; in conjuction with other on-site accelerators, it will be able to provide the full range of heavy ion beams and energies required.

NASA Discipline Radiation Health↗
DOE OSTI2023

Study of the Beam Losses and the Radiation Levels in the Electrostatic Septum for Slowextraction at 8 GEV

Extraction of beam from the Fermilab Delivery Ring for the Mu2e Experiment is hindered by large radiative losses initiated within the electrostatic septum (ESS) components of the resonant extraction system (RES). Of particular concern are beam losses causing potential damages to the support components of the RES, diminished intensity for experimental statistics, and high radiation levels in the area of the RES. Here we present the detailed study of beam energy deposition and radiation levels of components and surrounding regions of the ESS in the RES at Fermilab using the MARS Monte Carlo code system.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Monte Carlo simulations demonstrating physics of equivalency of gamma, electron-beam, and X-ray for radiation sterilization

We report the sterilization of medical devices using the gamma rays from the decay of cobalt-60 has accumulated decades of experience of the performance of the materials and devices that are irradiated. The use of radiation using electron beams and x-rays has much less experience and this leads to questions of equivalency between these three technologies. Computer simulations were conducted to model the relevant physical processes of the interactions of each of the three forms of radiation in order to compare the spectra of electron energies at energies below 500 keV. It is predominantly the electrons below this threshold that produce the sterilization dose. No difference in energy spectra was seen between the three types of initial radiation. It is concluded that there is no energy dependent difference between gamma, e-beam, and x-ray for radiation sterilization.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1987

Generation of plasma waves by thick-target electron beams, and the expected radiation signature

The production of plasma waves by a nonthermal beam of high-energy electrons injected into a background thermal plasma was investigated. The coupled kinetic equations for nonthermal electrons were solved, and the level of the plasma waves produced by the bump-on-tail instability arising as a result of the Coulomb collisions of nonthermal electrons with background plasma was estimated. In addition, the radiation signatures of these waves were examined. It is shown that the wave-particle interactions have a significant effect on the overall distribution of the electrons and that it is unlikely that such effects can be discerned in the observed bremsstrahlung or synchrotron radiation of the nonthermal electrons. However, a significant fraction of the energy lost by the beam is transferred to plasma waves and is then dissipated by the thermal plasma.

Hamilton, Russell J.↗
DOE OSTI2025

Reconstruction of beam parameters and betatron radiation spectra measured with a Compton spectrometer

The photon flux resulting from high-energy electron beam interactions with high-field systems, such as those found in the upcoming FACET-II experiments at the SLAC National Accelerator Laboratory, yields deep insight into the electron beam’s underlying dynamics during the interaction. However, extracting this information is an intricate process. To demonstrate how to approach this challenge using modern methods, this paper utilizes simulated data that models plasma wakefield acceleration-derived betatron radiation in experiments to determine reliable methods of reconstructing key beam and beam-plasma interaction properties. For betatron radiation measurements, translating the observed 200⁢ keV to 30⁢ MeV photon double-differential energy-angle spectra obtained from an advanced Compton spectrometer requires testing multiple methods to optimize the pipeline from its response to incident electron beam information. The paper compares maximum likelihood estimation and machine learning to refine the translation of photon spectra into precise electron beam metrics, such as spot size, energy, and emittance, enhancing the understanding of beam behavior within these dense, high-field environments. We also introduce machine learning and the expected maximization algorithm to reconstruct the primary photon spectrum, employing a multilayer neural network for regression analysis of the energy and angle spectra. With appropriate modifications, the advanced methods reproduce relevant incident beam parameters with high accuracy, even for beam sizes in the <10 μ⁢m range. This capacity is critical to understanding intense beam propagation and its optimization in plasma.

Beam code development & simulation techniques↗
NASA NTRS2024

DNA Break Clustering as a Predictor of Cell Death across Various Radiation Qualities: Influence of Cell Size, Cell Asymmetry, and Beam Orientation

Cosmic radiation, composed of high charge and energy (HZE) particles, causes cellular DNA damage that can result in cell death or mutation that can evolve into cancer. In this work, a cell death model is applied to several cell lines exposed to HZE ions spanning a broad range of linear energy transfer (LET) values. We hypothesize that chromatin movement leads to the clustering of multiple double strand breaks (DSB) within one radiation-induced foci (RIF). The survival probability of a cell population is determined by averaging the survival probabilities of individual cells, which is function of the number of pairwise DSB interactions within RIF. The simulation code RITCARD was used to compute DSB. Two clustering approaches were applied to determine the number of RIF per cell. RITCARD outputs were combined with experimental data from four normal human cell lines to derive the model parameters and expand its predictions in response to ions with LET ranging from ∼0.2keV/μmto∼3000keV/μm. Spherical and ellipsoidal nuclear shapes and two ion beam orientations were modeled to assess the impact of geometrical properties on cell death. The calculated average number of RIF per cell reproduces the saturation trend for high doses and high-LET values that is usually experimentally observed. The cell survival model generates the recognizable bell shape of LET dependence for the relative biological effectiveness (RBE). At low LET, smaller nuclei have lower survival due to increased DNA density and DSB clustering. At high LET, nuclei with a smaller irradiation area either because of a smaller size or a change in beam orientation have a higher survival rate due to a change in the distribution of DSB/RIF per cell. If confirmed experimentally, the geometric characteristics of cells would become a significant factor in predicting radiation-induced biological effects.

cell survival↗
NASA NTRS2001

Shortwave Radiative Fluxes, Solar-Beam Transmissions, and Aerosol Properties: TARFOX and ACE-2 Find More Absorption from Flux Radiometry than from Other Measurements

The Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX) and the Second Aerosol Characterization Experiment (ACE-2) made simultaneous measurements of shortwave radiative fluxes, solar-beam transmissions, and the aerosols affecting those fluxes and transmissions. Besides the measured fluxes and transmissions, other obtained properties include aerosol scattering and absorption measured in situ at the surface and aloft; aerosol single scattering albedo retrieved from skylight radiances; and aerosol complex refractive index derived by combining profiles of backscatter, extinction, and size distribution. These measurements of North Atlantic boundary layer aerosols impacted by anthropogenic pollution revealed the following characteristic results: (1) Better agreement among different types of remote measurements of aerosols (e.g., optical depth, extinction, and backscattering from sunphotometers, satellites, and lidars) than between remote and in situ measurements; 2) More extinction derived from transmission measurements than from in situ measurements; (3) Larger aerosol absorption inferred from flux radiometry than from other measurements. When the measured relationships between downwelling flux and optical depth (or beam transmission) are used to derive best-fit single scattering albedos for the polluted boundary layer aerosol, both TARFOX and ACE-2 yield midvisible values of 0.90 +/- 0.04. The other techniques give larger single scattering albedos (i.e. less absorption) for the polluted boundary layer, with a typical result of 0.95 +/- 0.04. Although the flux-based results have the virtue of describing the column aerosol unperturbed by sampling, they are subject to questions about representativeness and other uncertainties (e.g., unknown gas absorption). Current uncertainties in aerosol single scattering albedo are large in terms of climate effects. They also have an important influence on aerosol optical depths retrieved from satellite radiances. More tests are needed of the consistency among different methods and of the effects of changing humidity on aerosol.

Russell, Philip B.↗
NASA NTRS2024

Final Report on Radiation Measurements Performed Inside of the BEAM Module

Measurements of the radiation environment inside of the Bigelow Expandable Activity Module (BEAM) have been made on a pseudo-continuous basis since June 6, 2016 using both passive and active instrumentation. Passive detectors yield a single cumulative dose value (or average daily dose) over the measurement period from deploy to return to ground. Active Radiation Environment Monitor (REM) sensors yield dose rate, Linear Energy Transfer (LET) spectra, and particle-specific dose, all on a 1-minute cadence. From the initial install in 2016 until early 2018, BEAM was an empty module. In 2018, further testing was approved and stowage began to be moved into BEAM. As a result, it was decided to stop measurements with RAM detectors to avoid potential difficulties with access after stowage was added. The REM sensors remained however in the original deploy locations.

radiation exposure↗