Precision methods using soft penetrating radiation for bone densitometry
Soft X-ray-radiation for bone densitometry using gamma radioisotope source in precision X-ray tube
DENSITOMETER↗
SEARCH · Search NASA
Results for “X 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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Spectral-luminosity evolution of active galactic nuclei and the cosmic X-ray background
Black hole accretion disk dynamo processes are generally regarded as the central power source for AGN (Rees, 1984). If the precursor active galaxies for such AGN are formed at redshift z greater than about 4 and contain initial central seed black holes about 10 exp 6 solar masses, then the Eddington limited X-ray radiation emitted during their lifetime will undergo the phenomenon of 'spectral-luminosity evolution'. When accretion disks are first formed at the onset of galaxy formation, the accretion rate occurs at high values of luminosity/size compactness parameter L/R greater than 10 exp 30 erg/cm-sec. Such high values of L/R generate dynamic constraints which suppress nonthermal black hole accretion disk dynamo processes in favor of thermal processes. This causes the spectrum of X-radiation emitted by early AGN to be predominantly thermal. A superposition of such thermal, comptonized PAG sources can account for the residual cosmic X-ray background and can act as a source of X-ray heating of the intergalactic medium for z greater than about 4.
Leiter, Darryl↗
Improving the Science Observing Efficiency of the Chandra X-Ray Observatory via the Chandra Radiation Model
The Chandra X-ray Observatory (CXO), NASA's latest "Great Observatory", was launched on July 23, 1999 and reached its final orbit on August 7, 1999. The CXO is in a highly elliptical orbit, approximately 140,000 km x 10,000 km, and has a period of approximately 63.5 hours (N 2.65 days). It transits the Earth's Van Allen belts once per orbit during which no science observations can be performed due to the high radiation environment. The Chandra X-ray Observatory Center currently uses the National Space Science Data Center's "near Earth" AP-8/AE-8 radiation belt model to predict the start and end times of passage through the radiation belts. Our earlier analysis demonstrated that our implementation of the AP-8/AE-8 model (a simple dipole model of the Earth's magnetic field) does not always give sufficiently accurate predictions of the start and end times of transit of the Van Allen belts. This led to a change in our operating procedure whereby we "padded" the start and end times of transit by 10 kiloseconds (ks) so that ACIS, the primary science instrument on-board Chandra, would not be exposed to the "fringes" of the Van Allen belts on ingress and egress for any given transit. This additional 20 ks per orbit during which Chandra is unable to perform science observations sums to approximately 3 Ms of "lost" science time per year and therefore reduces the science observing efficiency of the Observatory. To address the need for a higher fidelity radiation model appropriate for the Chandra orbit, the Chandra Radiation Model (CRM) was developed. The CRM is an ion model for the outer magnetosphere and is based on data from the EPIC/ICS instrument on-board the Geotail satellite as well as data from the CEPPAD/IPS instrument on-board the Polar satellite. With the production and Implementation of the CRM, we present the results of a study designed to investigate the science observing time that may be recovered by using the CRM as a function of the additional low-energy proton exposure to ACIS.
Virani, Shanil↗
The radiation monitor cosmic X-ray experiment OSO-1
A comprehensive technical description is presented of the Radiation Monitor which is part of the GSFC cosmic X-ray experiment to be flown on the OSO-1 satellite. The theory of operation, fabrication and assembly, and cone angle determination are reported.
Randall, R. F.↗
X-ray detector physics and applications; Proceedings of the Meeting, San Diego, CA, July 23, 24, 1992
Recent developments in X-ray and hard X-ray imaging detector, high-intensity sources, hard X-ray imaging optics, calibration, and detection technologies are discussed. Particular attention is given to a high-MTF X-ray image intensifier, application of monolithic CdZnTe linear solid state ionization detectors for X-ray imaging, magnetic response of high-Tc superconductors to X-ray radiation and detection of X-rays, laboratory soft X-ray source with foil target, detection of explosive materials using nuclear radiation, energy response of astronomical CCD X-ray detectors, calibration techniques for high-flux X-ray detectors, fabrication of grazing-incidence optics using flow-polishing techniques, and numerical simulations for capillary-based X-ray optics. (No individual items are abstracted in this volume)
Hoover, Richard B.↗
Impulsive solar X-ray bursts: Bremsstrahlung radiation from a beam of electrons in the solar chromosphere and the total energy of solar flares
Analysis of various aspects of impulsive X-ray bursts (IXB's) has lead to the consideration of a model where the X-rays are produced by bremsstrahlung radiation from a beam of electrons directed toward the photosphere. It was found that in general the X-ray spectrum from such a beam will fall off more rapidly than when the effect of the beaming of radiation is neglected. Furthermore, the spectral index of the resulting X-rays appears to increase by about unity for X-ray energies 100 kev, a fact which may explain the observed cutoff in the spectrum of the IXB's. It is also shown that in such a model there is sufficient energy in the form of nonthermal electrons to explain the total energy (approximately 10 to the 32nd power ergs) of a flare.
Petrosian, V.↗
Late evolution of very low mass X-ray binaries sustained by radiation from their primaries
The accretion-powered radiation from the X-ray pulsar system Her X-1 (McCray et al. 1982) is studied. The changes in the soft X-ray and gamma-ray flux and in the accompanying electron-positron wind are discussed. These are believed to be associated with the inward movement of the inner edge of the accretion disk corresponding to the boundary with the neutron star's corotating magnetosphere (Alfven radius). LMXB evolution which is self-sustained by secondary winds intercepting the radiation emitted near an LMXB neutron star is investigated as well.
Ruderman, M.↗
Microstructural, optical and electrical properties of CdS thin films grown by spray pyrolysis technique as a function of substrate temperature
In this research, nanocrystalline cadmium sulfide thin films were produced by the spray pyrolysis technique on glass substrates. The effects of substrate temperature in the range 400–550 °C on the structural, morphological, optical, and electrical properties of the thin films were investigated. The thin films have been characterized by investigating their X-ray diffraction, field emission scanning electron microscope (FE-SEM), and optical absorption (UV–Vis) measurements. X-ray analysis revealed that thin films were a polycrystalline structure with the hexagonal phase in all cases and by increasing in substrate temperature, crystallite size decreases, and dislocation density increases. The FE-SEM images showed that the surface of the thin films is uniform, homogeneous and without cracks. The average sizes of the grains are at the range of 210–235 nm. The obtained values for optical band gap have been in the range of 2.18–2.41 eV, where the value of optical band gap for the thin films decreases by increasing substrate temperature. The Urbach energies of the thin films increase as the substrate temperature is increased. When substrate temperature increased from 400 to 550 °C, electrical resistivity increased from 531 to 2817 Ω cm, carrier concentration decreased from 15.96 × 10{sup 14} to 3.71 × 10{sup 14} cm{sup −3}, Hall mobility decreased from 7.37 to 5.98 cm{sup 2}/V s. Hall effect analysis indicated that the thin films exhibited n-type conductivity.
77 NANOSCIENCE AND NANOTECHNOLOGY↗
Accretion of matter and spectra of binary X-ray sources in massive gravity
We study low-mass binary X-ray sources involving stellar mass black holes within massive gravity. Regarding the accretion disk, we adopt the standard model for an optically thick, cool, and geometrically thin disk by Shakura–Sunyaev. For the gravitational field generated by the black hole, we consider the analogue of the Schwarzschild–de Sitter space–time of Einstein’s theory in massive gravity, for which we found an additional term linear in the radial coordinate. Then, we compute the radial velocity, the energy density and the pressure as a function of the radial coordinate, and the X-ray emission’s soft spectral component expected from the disk. We also investigated in detail the impact of this new geometry. Our result indicates that by using observed spectra from confirmed X-ray binaries involving astrophysical black holes, we can put strong constraints on alternative theories of gravity.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Effect of polycarboxylate ether on the expansion of ye'elimite hydration in the presence of anhydrite
Polycarboxylate ether (PCE), a commonly used superplasticizer, is known to influence the morphology of ettringite during the early hydration of C{sub 3}A- and ye'elimite-containing cements. According to existing theories, such morphological changes may be crucial to the expansive behavior of these cements. This paper studied the expansion of ye'elimite-anhydrite pastes and found the use of PCE to reduce expansion after 4 days of curing. Hydration studies were conducted by calorimetry, X-ray diffractometry, scanning electron microscopy, mercury intrusion porosimetry, inductively coupled plasma–optical emission spectrometry, and X-ray microtomography. The results show that the influences of PCE on the morphology of ettringite and the hydration of ye'elimite were quite small after 2 days. Based on the crystal growth theory, the range of pores in which ettringite can grow was calculated to explain the observed expansive behaviors. The presence of ettringite nano-crystals in aluminum hydroxide was also revealed and considered as a possible expansion mechanism.
36 MATERIALS SCIENCE↗
Coordination environment of Si in calcium silicate hydrates, silicate minerals, and blast furnace slags: A XANES database
Understanding the silicate polymerization of calcium silicate hydrate (C-S-H) gel and its crystalline polymorphs is important in cement science. NMR can determine Si environments, but the measurement can be time-consuming and provides no spatial information. X-ray absorption near-edge structure (XANES) spectroscopy is a fast tool for probing Si coordination, possibly with spatial information. However, there lacks an understanding of Si K-edge XANES spectra of cement-related silicate phases. Here, a Si K-edge XANES spectral database of nanocrystalline C-S-H, C-S-H minerals, blast-furnace slags, and metakaolin is provided. Si K-edge of C-S-H minerals shifts to higher energies with higher polymerized Si and lower CaSi connectivity in the Si second nearest neighbor shell. Si K-edge energy shows weak correlations with Ca/Si ratio, average SiO bond length, and SiO{sub 4} distortion due to the structural complexity of silicates. The substitution of Al for Si shifts the Si K-edge of tobermorite and slags to higher energies.
36 MATERIALS SCIENCE↗
Carbonation of model cement pastes: The mineralogical origin of microstructural changes and shrinkage
This study explored the reactive processes of atmospheric carbonation and the consequences with respect to cementitious materials. Two model pastes were used: hydrated C{sub 3}S (including C-S-H and portlandite) and a paste prepared by hydrating a blend of C{sub 3}S and nanosilica (including C-S-H only). The two pastes were carbonated under accelerated conditions in the laboratory. The resulting mineralogical assemblage was examined using X-ray diffraction, thermogravimetric analysis and nuclear magnetic resonance. The microstructural changes were studied by X-ray tomography and porosimetry, and their macroscopic impacts were evaluated through gas diffusion and shrinkage measurements. The use of model pastes allowed for the evaluation of the change in solid volume induced by the carbonation of C-S-H. C-S-H decalcification and subsequent silica chain polymerisation were found responsible for carbonation shrinkage (and potentially cracking). Finally, the results highlight the protective role of portlandite: portlandite helped in limiting C-S-H decalcification and then reducing carbonation shrinkage and cracking.
36 MATERIALS SCIENCE↗
Temperature-dependent x-ray fluorescent response from thermographic phosphors under x-ray excitation
Phosphor thermometry has been successfully applied within several challenging environments. Typically, the thermographic phosphors are excited by an ultraviolet light source, and the temperature-dependent spectral or temporal response is measured. However, this is challenging or impossible in optically thick environments. In addition, emission from other sources (e.g., a flame) may interfere with the optical phosphor emission. Furthermore, a temperature dependent x-ray excitation/emission could alleviate these issues as x-rays could penetrate obscurants with no interference from flame luminosity. In addition, x-ray emission could allow for thermometry within solids while simultaneously x-ray imaging the structural evolution. In this study, select thermographic phosphors were excited via x-ray radiation, and their x-ray emission characteristics were measured at various temperatures. Several of the phosphors showed varying levels of temperature dependence with the strongest sensitivity occurring for YAG:Dy and ZnGa 2 O 4 :Mn. This approach opens a path for less intrusive temperature measurements, particularly in optically opaque multiphase and solid phase combustion environments.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
HD 63021: Chromospheric Activity and Mass Transfer in a Close Binary
Prompted by X-ray detections from multiple surveys, we investigated the A-type star HD 63021 and found that it is a double-lined spectroscopic binary with highly variable emission associated with the primary star. Analysis of our multiepoch spectroscopic observations, the majority of which were carried out on small-aperture telescopes, indicates a very short orbital period of just 2.9 days and a mass ratio M {sub 2}/M {sub 1} of 0.23. The A1 V star is a slow rotator, with a rotational speed of ∼34 km s{sup −1}. Assuming that its mass is 2.3 M {sub ⊙}, the present-day secondary is an evolved star of ∼0.5 M {sub ⊙} that nearly fills its Roche lobe. This secondary star rotates comparatively rapidly at ∼44 km s{sup −1}, and we see evidence that it is chromospherically active. Analysis of a photometric light curve from TESS reveals two strong periods, one at the orbital period for the system and another at half the orbital period. These findings suggest that HD 63021 is a close binary system undergoing mass transfer from the secondary star onto the primary star—in all ways like an Algol eclipsing binary system, except without the eclipse. We discuss the system’s mass transfer, which is not steady but seems to run in fits and bursts, and infer the system’s basic physical properties from an orbital parameter study, the Roche lobe geometry, and its extant X-ray emission.
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
X-Rays in Cepheids: XMM-Newton Observations of η Aql
X-ray bursts have recently been discovered in the Cepheids δ Cep and β Dor modulated by the pulsation cycle. We have obtained an observation of the Cepheid η Aql with the XMM-Newton satellite at the phase of maximum radius; the phase at which there is a burst of X-rays in δ Cep. No X-rays were seen from the Cepheid η Aql at this phase, and the implications for Cepheid upper atmospheres are discussed. We have also used the combination of X-ray sources, as well as Gaia and 2MASS data, to search for a possible grouping around the young intermediate mass Cepheid. No indication of such a group was found.
79 ASTRONOMY AND ASTROPHYSICS↗
Reflex feed system for dual frequency antenna with frequency cutoff means
A reflex feed system is described for a dual frequency antenna such as one which transmits and receives both S and X band signals. The dichroic plate, normally employed for directing X band radiation away from the X band horn, is replaced by a flange about the opening of the X band horn.
Hartop, R. W.↗
Computational Aeroheating Predictions for X-34
Radiative equilibrium surface temperatures, heating rates, streamlines, surface pressures, and flow-field features as predicted by the Langley Aerothermodynamic Upwind Relaxation Algorithm (Laura) are presented for the X-34 Technology Demonstrator. Results for two trajectory points corresponding to entry peak heating and two control surface deflections are discussed. This data is also discussed in context of Thermal Protection System (TPS) design issues. The work presented in this report is part of a larger effort to define the X-34 aerothermal environment, including the application of engineering codes and wind-tunnel studies.
Kelb, William L.↗
Computational Aeroheating Predictions for X-34
Radiative equilibrium surface temperatures, heating rates, streamlines, surface pressures, and flow-field features as predicted by the Langley Aerothermodynamic Upwind Relaxation Algorithm (LAURA) are presented for the X-34 Technology Demonstrator. Results for two trajectory points corresponding to entry peak heating and two control surface deflections are discussed. This data is also discussed in the context of Thermal Protection System (TPS) design issues. The work presented in this report is part of a larger effort to define the X-34 aerothermal environment, including the application of engineering codes and wind-tunnel studies.
Kleb,William H.↗