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Physics of generation of bremsstrahlung
Published in Rolf Behling, Modern Diagnostic X-Ray Sources, 2021
For medical imaging, characteristic radiation is intentionally employed in mammography. Boneless, compressed breast tissue of a mamma is sufficiently transparent for soft X-ray photons. A transparency of up to about 10% is achieved with tube voltages of about 30 kV. Softer radiation delivers a superior image contrast in comparison with harder radiation. The visibility of small lesions is better as long as the transparency of the patient and the X-ray flux suffice to overcome quantum and electronic noise. The ratio between contrast and image noise for minimal radiation dose is optimal for a single photon energy only. Therefore, monochromatic radiation is appreciated. CT systems, which allow for spectral differentiation, offer the option to reconstruct “monochromatic” images, which look as though they were generated with the optimal monochromatic radiation. With often striking results, the user may then “scroll through the kVs” and search for the optimal contrast resolution.
Physical Methods for Characterizing Solids
Published in Elaine A. Moore, Lesley E. Smart, Solid State Chemistry, 2020
Normally, in X-ray diffraction, monochromatic radiation (single wavelength or a very narrow range of wavelengths) is required. Usually the Kα line is selected and the Kβ line is filtered out by using a filter made of a thin metal foil of the element adjacent (Z−1) in the periodic table; thus nickel effectively filters out the Kβ line of copper, and niobium is used for molybdenum. A drawback to using filters is the very high background (from the white X-ray spectrum) and the fact that the X-ray beam is still not purely monochromatic and unpolarised. A monochromatic beam of higher quality, lower background, and of pure Kα1 radiation can be obtained by reflecting the beam from a plane in a single crystal, normally made of graphite, silicon, or germanium (the reasons why this works will become obvious after you have read the next section).
Force-System Resultants and Equilibrium
Published in Richard C. Dorf, The Engineering Handbook, 2018
In the stimulated emission process a photon produced by a recombination event stimulates the recombination of another free electron with a hole. This results in the emission of a second photon. The two photons are exactly at the same frequency and phase, and travel in the same direction. These photons then stimulate the recombination of another free electron and hole. This results in the emission of another photon. These photons will be at exactly the same frequency and phase, and travel in the same direction. This process of the stimulated emission of radiation can then continue through the active region of the device. Indeed, the word laser is an acronym for light amplification by the stimulated emission of radiation. The resulting emission is of photons that are at the same frequency, and hence this is monochromatic radiation. The photons are all in phase with each other, so this is coherent radiation. The photons are all traveling in the same direction resulting in a collimated beam of light. In actuality, both spontaneous and stimulated emission processes occur.
Study of C.I. Reactive Yellow 145, C.I. Reactive Red 238, and C.I. Reactive Blue 235 dyestuffs in order to use them in color formulation. Part 1: characterization and compatibility
Published in The Journal of The Textile Institute, 2019
Sabrine Chaouch, Ali Moussa, Imed Ben Marzoug, Neji Ladhari
The transmission of monochromatic radiation through a dye solution is governed by the Beer-Lambert law, which essentially states that the absorption of light is proportional to the number of absorbing molecules. This law relates the transmittance of light to absorbance as follows (Beer, 1852; Lambert, 1760):