Chemical analysis of surfaces using alpha particles.
Chemical analysis of surfaces using alpha-particle interactions from curium 242 sources and semiconductor silicon detectors
ALPHA RADIATION↗
SEARCH · Engineering Papers
Results for “Scattering, Radiation”
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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Attenuation of radiation in heterogeneous shielding
Primary radiation attenuation in heterogeneous medium and monoenergetic neutron scattering
NEUTRON SCATTERING↗
Reflective scattering from substrates and evaporated films in the far ultraviolet.
Measurement of radiation reflectively scattered from optical surfaces in far UV, noting role of overcoating with metal films
SURFACE ROUGHNESS EFFECT↗
Radiative transfer theory for scattering by layered media
Remote sensing of brightness temperatures of a scattering medium composed of spherical scatterers beneath a homogeneous surface layer is studied by using Mie scattering functions. We illustrate the effects of a surface layer by plotting the brightness temperatures as functions of frequency and viewing angle for different layer thicknesses, dielectric constants, and fractional scattering volumes. It is found that the brightness temperature increases when the loss tangent of the surface layer is increased and when the fractional volume occupied by the scatterers is decreased. In the absence of a surface layer the brightness temperature is usually decreasing as a function of frequency. The presence of a homogeneous layer may cause the brightness temperature to increase with frequency. At all viewing angles the vertical polarization is brighter than the horizontal polarization.
Tsang, L.↗
Abrasion-ablation model for neutron production in heavy ion collisions
In intermediate energy nucleus-nucleus collisions, neutron production at forward angles is observed to occur with a Gaussian shape that is centered near the beam energy and extends to energies well above that of the beam. This paper presents an abrasion-ablation model for making quantitative predictions of the neutron spectrum. To describe neutrons produced from the abrasion step of the reaction where the projectile and target overlap, we use the Glauber model and include effects of final-state interactions. We then use the prefragment mass distribution from abrasion with a statistical evaporation model to estimate the neutron spectrum resulting from ablation. Measurements of neutron production from Ne and Nb beams are compared with calculations, and good agreement is found.
NASA Discipline Radiation Health↗
A new Mars radiation environment model with visualization
A new model for the radiation environment to be found on the planet Mars due to Galactic Cosmic Rays (OCR) has been developed at the NASA Langley Research Center. Solar modulated primary particles rescaled for Mars conditions are transported through the Martian atmosphere, with temporal properties modeled with variable timescales, down to the surface, with altitude and backscattering patterns taken into account. The Martian atmosphere has been modeled by using the Mars Global Reference Atmospheric Model--version 2001 (Mars-GRAM 2001). The altitude to compute the atmospheric thickness profile has been determined by using a model for the topography based on the data provided by the Mars Orbiter Laser Altimeter (MOLA) instrument on board the Mars Global Surveyor (MGS) spacecraft. The Mars surface composition has been modeled based on averages over the measurements obtained from orbiting spacecraft and at various landing sites, taking into account the possible volatile inventory (e.g., CO2 ice, H2O ice) along with its time variation throughout the Martian year. Particle transport has been performed with the HZETRN heavy ion code. The Mars Radiation Environment Model has been made available worldwide through the Space Ionizing Radiation Effects and Shielding Tools (SIREST) website, a project of NASA Langley Research Center. c2004 COSPAR. Published by Elsevier Ltd. All rights reserved.
NASA Center LaRC↗
Compton Scattering of Thermal Disk Radiation with Black Hole Disk Winds
Explore the source record for details and available documents.
Keigo Fukumura↗
A new formulation of electromagnetic wave scattering using an on-surface radiation boundary condition approach
A new formulation of electromagnetic wave scattering by convex, two-dimensional conducting bodies is reported. This formulation, called the on-surface radiation condition (OSRC) approach, is based upon an expansion of the radiation condition applied directly on the surface of a scatterer. It is now shown that application of a suitable radiation condition directly on the surface of a convex conducting scatterer can lead to substantial simplification of the frequency-domain integral equation for the scattered field, which is reduced to just a line integral. For the transverse magnetic case, the integrand is known explicitly. For the transverse electric case, the integrand can be easily constructed by solving an ordinary differential equation around the scatterer surface contour. Examples are provided which show that OSRC yields computed near and far fields which approach the exact results for canonical shapes such as the circular cylinder, square cylinder, and strip. Electrical sizes for the examples are ka = 5 and ka = 10. The new OSRC formulation of scattering may present a useful alternative to present integral equation and uniform high-frequency approaches for convex cylinders larger than ka = 1. Structures with edges or corners can also be analyzed, although more work is needed to incorporate the physics of singular currents at these discontinuities. Convex dielectric structures can also be treated using OSRC.
Kriegsmann, Gregory A.↗
Analytical expressions for radiative properties of planar Rayleigh scattering media, including polarization contributions
The objective of this paper is to provide a convenient and fast way for computing the radiative properties of planar Rayleigh scattering media. Analytical expressions are developed for the three molecular atmospheric functions which are required in remote sensing: the atmospheric reflectance, the transmission function, and the spherical albedo. The expressions are adjusted by using accurate computations performed with successive orders of a scattering code. The accuracy of the code is first checked by using previously published tabulations. The required accuracy of 0.001 in the reflectance unit is achieved by numerical adjustments. The contribution of polarization is considered implicitly. The expressions are shown to be valid for a fairly large range of observational conditions.
Vermote, E.↗
Cosmic gamma rays from inverse Compton scattering.
Background cosmic gamma radiation from inverse Compton scattering of black body photons by galactic cosmic ray electrons
Berkey, G.↗
A Fast Hybrid (3-D/1-D) Model for Thermal Radiative Transfer in Cirrus via Successive Orders of Scattering
We investigate the impact of cirrus cloud heterogeneity on the direct emission by cloud or surface and on the scattering by ice particles in the thermal infrared (TIR). Realistic 3-D cirri are modeled with the 3DCLOUD code, and top-of-atmosphere radiances are simulated by the 3-D Monte Carlo radiative transfer (RT) algorithm 3DMCPOL for two (8.65 micrometers and 12.05 micrometers) channels of the Imaging Infrared Radiometer on CALIPSO. At nadir, comparisons of 1-D and 3-D RT show that 3-D radiances are larger than their 1-D counterparts for direct emission but smaller for scattered radiation. For our cirrus cases, 99% of the 3-D total radiance is computed by the third scattering order, which corresponds to 90% of the total computational effort, but larger optical thicknesses need more scattering orders. To radically accelerate the 3-D RT computations (using only few percent of 3-D RT time with a Monte Carlo code), even in the presence of large optical depths, we develop a hybrid model based on exact 3-D direct emission, the first scattering order from 1-D in each homogenized column, and an empirical adjustment linearly dependent on the optical thickness to account for higher scattering orders. Good agreement is found between the hybrid model and the exact 3-D radiances for two very different cirrus models without changing the empirical parameters. We anticipate that a future deterministic implementation of the hybrid model will be fast enough to process multiangle thermal imagery in a practical tomographic reconstruction of 3-D cirrus fields.
radiative transfer↗
Recent Developments in the Assimilation of Microwave and Radar Observations Into NWP Models
Microwave observations play a very important role in improving the weather forecasts. Although these observations are routinely assimilated into NWP models in clear-sky conditions, assimilation of all-sky microwave observations is very limited. Two main factors contributing to this limitation are inaccuracy in the input cloud and hydrometeor profiles used as input to the radiative transfer model and also error in scattering calculations performed by the radiative transfer model itself. The Mie theory is used by many fast RT models to estimate the optical properties of single particles. The Mie theory assumes spherical shapes for ice or snow particles with mixture of air and ice. However, hydrometeors scattering radiation at microwave frequencies have different shapes, sizes, and orientations. Therefore, using Mie theory to determine their optical properties leads to large uncertainties in all-sky radiative transfer calculations. The discrete dipole approximation (DDA) which approximates the optical properties of large objects in terms of discrete dipoles has shown promise in calculating the scattering properties of particles with different shapes in the microwave frequencies. This presentation focuses on recent advancements in the CRTM scattering calculations for frozen hydrometeors in the microwave frequencies using the DDA technique. In addition to using stand-alone CRTM calculations using collocated ATMS and reanalysis profiles, the data assimilation experiments conducted using the NOAA FV3GFS forecast system are used to evaluate the scattering improvements. Additionally, the backscattering information from the DDA database was used to implement a radar simulator into CRTM. The radar operator takes advantage of CRTM different modules to calculate clouds absorption and scattering properties. In addition to the forward model both adjoint and tangent linear of the radar simulator are implemented and evaluated as well. The radar simulator is currently being tested within the JEDI/GEOS data assimilation framework to facilitate the assimilation of radar measurements such as CloudSat CPR and GPM DPR into the NASA GEOS model.
Isaac Moradi↗
Enhancing CRTM All-Sky Simulations and Implementation of A New Active Sensor Module
Microwave observations play a very important role in improving the weather forecasts. Although these observations are routinely assimilated into NWP models in clear-sky conditions, assimilation of all-sky microwave observations is very limited. Two main factors contributing to this limitation are inaccuracy in the input cloud and hydrometeor profiles used as input to the radiative transfer model and also error in scattering calculations performed by the radiative transfer model itself. The Mie theory is used by many fast RT models to estimate the optical properties of single particles. The Mie theory assumes spherical shapes for ice or snow particles with mixture of air and ice. However, hydrometeors scattering radiation at microwave frequencies have different shapes, sizes, and orientations. Therefore, using Mie theory to determine their optical properties leads to large uncertainties in all-sky radiative transfer calculations. The discrete dipole approximation (DDA) which approximates the optical properties of large objects in terms of discrete dipoles has shown promise in calculating the scattering properties of particles with different shapes in the microwave frequencies. This presentation focuses on recent advancements in the CRTM scattering calculations for frozen hydrometeors in the microwave frequencies using the DDA technique. In addition to using stand-alone CRTM calculations using collocated ATMS and reanalysis profiles, the data assimilation experiments conducted using the NOAA FV3GFS forecast system are used to evaluate the scattering improvements. Additionally, the backscattering information from the DDA database was used to implement a radar simulator into CRTM. The radar operator takes advantage of CRTM different modules to calculate clouds absorption and scattering properties. In addition to the forward model both adjoint and tangent linear of the radar simulator are implemented and evaluated as well. The radar simulator is currently being tested within the JEDI/GEOS data assimilation framework to facilitate the assimilation of radar measurements such as CloudSat CPR and GPM DPR into the NASA GEOS model.
Isaac Moradi↗
Very-high-energy Emission from Pulsars
Air-Cherenkov telescopes have detected pulsations at energies above 50 GeV from a growing number of Fermi pulsars. These include the Crab, Vela, PSR B1706−44, and Geminga, with the first two having pulsed detections above 1 TeV. In some cases, there appears to be very-high-energy (VHE) emission that is an extension of the Fermi spectra to high energies, while in other cases, additional higher-energy spectral components that require a separate emission mechanism may be present. We present results of broadband spectral modeling using global magnetospheric fields and multiple emission mechanisms that include synchro-curvature (SC) and inverse Compton scattered (ICS) radiation from accelerated particles (primaries) and synchrotron self-Compton (SSC) emission from lower-energy pairs. Our models predict three distinct VHE components: SC from primaries whose high-energy tail can extend to 100 GeV, SSC from pairs that can extend to several TeV, and ICS from primary particles accelerated in the current sheet that scatter pair synchrotron radiation, which appears beyond 10 TeV. Our models suggest that H.E.S.S.-II and MAGIC have detected the high-energy tail of the primary SC component that produces the Fermi spectrum in Vela, Geminga, and PSR B1706−44. We argue that the ICS component peaking above 10 TeV from Vela has been seen by H.E.S.S. Detection of this emission component from the Crab and other pulsars is possible with the High Altitude Water Cherenkov Observatory and Cherenkov Telescope Array, and will directly measure the maximum particle energy in pulsars.
Alice K. Harding↗
Instruction manual, Optical Effects Module, Model OEM
The Optical Effects Module Model OEM-1, a laboratory prototype instrument designed for the automated measurement of radiation transmission and scattering through optical samples, is described. The system comprises two main components: the Optical Effects Module Enclosure (OEME) and the Optical Effects Module Electronic Controller and Processor (OEMCP). The OEM is designed for operation in the near UV at approximately 2540A, corresponding to the most intense spectral line activated by the mercury discharge lamp used for illumination. The radiation from this source is detected in transmission and reflection through a number of selectable samples. The basic objective of this operation is to monitor in real time the accretion of possible contamination on the surface of these samples. The optical samples are exposed outside of the OEME proper to define exposure conditions and to separate exposure and measurement environments. Changes in the transmissivity of the sample are attributable to surface contamination or to bulk effects due to radiation. Surface contamination will increase radiation scattering due to Rayleigh-Gans effect or to other phenomena, depending on the characteristics size of the particulate contaminants. Thus, also scattering from the samples becomes a part of the measurement program.
Source record↗
Atmospheric radiation model for water surfaces
An atmospheric correction model was extended to account for various atmospheric radiation components in remotely sensed data. Components such as the atmospheric path radiance which results from singly scattered sky radiation specularly reflected by the water surface are considered. A component which is referred to as the virtual Sun path radiance, i.e. the singly scattered path radiance which results from the solar radiation which is specularly reflected by the water surface is also considered. These atmospheric radiation components are coded into a computer program for the analysis of multispectral remote sensor data over the Great Lakes of the United States. The user must know certain parameters, such as the visibility or spectral optical thickness of the atmosphere and the geometry of the sensor with respect to the Sun and the target elements under investigation.
Turner, R. E.↗
Transport of cosmic ray nuclei in various materials
Cosmic-ray heavy ions have become a concern in space radiation effects analyses. Heavy ions rapidly deposit energy and create dense ionization trails as they traverse materials. Collection of the free charge disrupts the operation of microelectronic circuits. This effect, called the single-event upset, can cause a loss of digital data. Passage of high linear energy transfer particles through the eyes has been observed by Apollo astronauts. These heavy ions have great radiobiological effectiveness and are the primary risk factor for leukemia induction on a manned Mars mission. Models of the transport of heavy cosmic-ray nuclei through materials depend heavily on our understanding of the cosmic-ray environment, nuclear spallation cross sections, and computer transport codes. Our group has initiated and pursued the development of a full capability for modeling these transport processes. A recent review of this ongoing effort is presented in Ref. 5. In this paper, we discuss transport methods and present new results comparing the attenuation of cosmic rays in various materials.
NASA Discipline Radiation Health↗
Spallation processes and nuclear interaction products of cosmic rays
Most cosmic-ray nuclei heavier than helium have suffered nuclear collisions in the interstellar gas, with transformation of nuclear composition. The isotopic and elemental composition at the sources has to be inferred from the observed composition near the Earth. The source composition permits tests of current ideas on sites of origin, nucleosynthesis in stars, evolution of stars, the mixing and composition of the interstellar medium and injection processes prior to acceleration. The effects of nuclear spallation, production of radioactive nuclides and the time dependence of their decay provide valuable information on the acceleration and propagation of cosmic rays, their nuclear transformations, and their confinement time in the Galaxy. The formation of spallation products that only decay by electron capture and are relatively long-lived permits an investigation of the nature and density fluctuations (like clouds) of the interstellar medium. Since nuclear collisions yield positrons, antiprotons, gamma rays and neutrinos, we shall discuss these topics briefly.
Non-NASA Center↗