grazing incidence


Also found in: Dictionary, Thesaurus, Medical.
Related to grazing incidence: Glancing angle

grazing incidence

X-rays reflect from surfaces for the same physical reason that light reflects, mainly due to coherent scattering in the surface material. However, since X-ray photon energies are large, the refractive index, n, is slightly less than unity and reflection occurs only up to a critical angle, θ, where cos θ = n. The angle θ is usually small and thus X-ray reflection is only high for rays that graze the surface; hence ‘grazing incidence’. For example θ is about 1° for a gold surface and X-rays of wavelengths of about 0.3 nm (4 keV). θ is proportional to X-ray wavelength and also increases with the atomic number of the reflecting surface.

The space station Skylab was the first space mission to carry a large grazing incidence X-ray telescope, in fact two, both of which produced many high-resolution X-ray images of the solar corona in 1973–74. With two coaxial reflectors (usually a paraboloid/hyperboloid pair), high-quality X-ray images are produced over a field of view of order of the grazing angle. The great potential of such optical systems for cosmic X-ray astronomy was first demonstrated with the flight of a 60-cm diameter grazing incidence telescope on the Einstein Observatory in 1978–81. Subsequently, most X-ray astronomy satellites have employed or will employ this technique.

grazing incidence

[′graz·iŋ ‚in·sə·dəns]
(physics)
Incidence at a small glancing angle.
References in periodicals archive ?
Measurements at grazing incidence and reflectivity have been carried out to quantify the surface roughness in systems of spin valves [26].
Michael Burgess University of Alabama, Huntsville "Advanced Grazing Incidence Neutron Imaging System" Daniella Della-Guistina University of Arizona "The Martian Bus Schedule: an Innovative Technique for Protecting Humans on a Journey to Mars" Jonathan Sharma Georgia Institute of Technology, Atlanta, Ga.
With its non-contact, grazing incidence, stitching interferometer based on Corning Tropel's existing FlatMaster technology, the FlatMaster 1400 rasters the surface of the image mask and stitches together a series of 200 mm x 200 mm measurements.
The assembly and alignment of the eight grazing incidence HRMA mirrors, some weighing up to 450 pounds, to fractions of an arc-second tilt accuracy was a magnificent accomplishment," said Jeff Wynn, program manager of Kodak's AXAF telescope project.
The mounting of the grazing incidence mirrors in the HRMA by Kodak is a truly remarkable engineering achievement,'' said Steven Loer, manager of TRW's AXAF telescope project.
These mirrors are Silicon substrates (reflectivity 35 %) with B4C coating (reflectivity 25-30 %), and the measurements will be carried out in normal incidence and grazing incidence.
It must be equipped mainly as follows - A source high brightness (average power) and a high-performance detection system enabling rapid acquisitions, : - A source for high energy diffraction studies and dissemination : - Capabilities addressed in depth analysis (In-plane grazing incidence diffraction) : - The analysis capabilities of very thin films (brightness, 2D detection microfocus) and highly resolved (optical) : This equipment will be installed on the platform of nano characterization (PFNC) within Minatec.
This contract involves the design, manufacture, testing and delivery of a pair of long mirrors at grazing incidence and horizontal deflection, and the mechanical positioning system to accurately place the mirrors in the beam of photons, and the first bender necessary to mirror the beam focus.