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Basics of x-ray tubes
Published in Gavin Poludniowski, Artur Omar, Pedro Andreo, Calculating X-ray Tube Spectra, 2022
Gavin Poludniowski, Artur Omar, Pedro Andreo
However, since the electric field lines in a conductor are always perpendicular to the surface, the trajectory of incident electrons will be modified such that they are deflected towards normal incidence as they approach the target. The true angle of incidence will be somewhere between the oblique angle of approach and zero degrees. Detailed simulations suggest that it may typically be closer to the latter [31]. In any case, the electrons quickly undergo multiple elastic scattering in the target and their direction at depth rapidly loses correlation with the original trajectory.
Total Skin Electron Irradiation
Published in W. P. M. Mayles, A. E. Nahum, J.-C. Rosenwald, Handbook of Radiotherapy Physics, 2021
David Thwaites, Alan McKenzie, W. P. M. Mayles
The penetration needs to be matched to the required clinical depth. Generally, for superficial involvement only, or where shallow plaques are present, this requires the therapeutic range (see Section 24.2.2) to be between 3 mm and 6 mm. The beam penetration of interest here is the final effective penetration achieved by the total combination of all field positions and directions. This produces a significantly smaller depth of dose maximum and therapeutic range than for a single field due to the effects of oblique incidence (see Section 24.2.7), scattering, etc., although the practical range and bremsstrahlung are similar, all other things being equal. The beam energies that are used for TSEI are generally chosen to be in the range of 6 MeV to 10 MeV as they emerge from the accelerator. These are typically reduced to 3 MeV to 6 MeV at the patient surface partly by the energy loss in the air (approximately 0.25 MeV m−1) and partly by the addition of plastic energy-degrader sheets, typically of 5 mm to 10 mm thickness, close to the patient (i.e. approximately 20 cm gap).* The depth doses of the single field vary with angle of incidence across the beam (i.e. around the patient surface, as illustrated in Figure 42.5; Bjarngard et al. 1977; Pla et al. 1988).
Bioengineering Aids to Reproductive Medicine
Published in Sujoy K. Guba, Bioengineering in Reproductive Medicine, 2020
A single optical fiber consists of a central core cylinder of a transparent material usually glass, but could be plastics, having a refractive index σ1 covered with a closely fitting concentric hollow tube known as the “cladding”, also made of glass or plastic but having a different refractive index σ2 (Figure 3.23). The refractive index of the core material is higher than that of the cladding. Recalling elementary high school physics that when a light ray traveling in a medium of high refractive index strikes an interface with a material of lower refractive index, the ray can take three possible paths. If the angle of incidence (the angle between the direction of the ray and the normal to the interface) is low the light ray will escape into the low refractive index material. If the angle of incidence is high, the ray will be subject to ‘total internal reflection’ and will traverse back into the high refractive index material. At a critical angle of incidence (the angle equal to inverse sine of the ratio of the refractive index of the core medium to that of the cladding medium), the ray will neither escape nor travel back into the original material but will travel along a path just bordering the interface. Optical fibers function with the high angle of incidence as in the diagram (Figure 3.23) where at the point a the angle i being greater than the critical angle the ray is reflected back into the core. Similar reflections occur at B and C and so on till the ray emerges from the other end of the fiber.
Dosimetry and uncertainty approaches for the million person study of low-dose radiation health effects: overview of the recommendations in NCRP Report No. 178
Published in International Journal of Radiation Biology, 2022
Lawrence T. Dauer, André Bouville, Richard E. Toohey, John D. Boice, Harold L. Beck, Keith F. Eckerman, Derek Hagemeyer, Richard W. Leggett, Michael T. Mumma, Bruce Napier, Kathy H. Pryor, Marvin Rosenstein, David A. Schauer, Sami Sherbini, Daniel O. Stram, James L. Thompson, John E. Till, R. Craig Yoder, Cary Zeitlin
The Report provides several dose coefficients [relating Hp(10) and organ dose] that could be applicable to various external exposure scenarios and geometries for the MPS populations where personal dosimeter data were available. Figure 3 provides an example of dose coefficients for AP exposure geometry. The use of dose coefficients typically assumes uniform irradiation of the body from a designated angle of incidence, particularly for the torso where most of the radiosensitive organs reside. Some exposure scenarios and radiation environments do not result in relative uniform irradiation of the torso and head. In these situations, the estimate of Hp(10) may need to be modified to reflect the nonuniform irradiation of different regions of the body. In the absence of detailed information on the irradiation geometry related to work activities, it is recommended to assume typical or representative geometries such as 100% AP or 50% AP plus 50% ROT (NCRP, 2009b), or 50% AP plus 50% isotropic (Thierry-Chef et al. 2007). In some facilities, multiple personal monitoring dosimeters may have been used by a single person during conditions of very nonuniform irradiation of the body. In such cases, the estimate of Hp(10) from the dosimeter located nearest the organ of interest should be used. ANSI/HPS (2011) prescribes a procedure in which the body is divided into compartments for which a separate compartment-weighted Hp(10) value is assessed from a dosimeter located nearest that compartment.
Steering light in fiber-optic medical devices: a patent review
Published in Expert Review of Medical Devices, 2022
Merle S. Losch, Famke Kardux, Jenny Dankelman, Benno H. W. Hendriks
Refraction is defined as the change in direction of a transmitted light beam after it enters a second medium. Reflection is defined as the change in direction of a light beam at an interface that returns the light beam back to the original medium. The angle of incidence of the light beam on the surface and the material properties of the two media determine the intensity and direction of the refracted and reflected light beam. Another way to steer light is scattering: multiple changes in refractive index force the light beam to randomly change direction in a series of reflection events, resulting in diffuse light scattering. Lastly, a fundamentally different method to steer a light beam is diffraction. Diffraction is defined as the bending of light after encountering a small opening or obstacle. The light beam does not bend in one direction; instead, a diffraction pattern is generated by the interference of different wave fronts. Diffraction is predominant for apertures and obstacles with sizes in the range of the wavelength of the incident light.
Applications of mid-infrared spectroscopy in the clinical laboratory setting
Published in Critical Reviews in Clinical Laboratory Sciences, 2018
Sander De Bruyne, Marijn M. Speeckaert, Joris R. Delanghe
ATR-FTIR is able to overcome these potential problems. ATR-FTIR operates on the principles of total internal reflection. A radiation beam entering a crystal will undergo total internal reflection when the angle of incidence is greater than the critical angle, which is function of the refractive indices of the two surfaces. The beam loses energy when a material that selectively absorbs radiation is in contact with the internal reflecting element (IRE) [7,53,56]. One limitation of this approach is the fact that samples have to be in close contact with the IRE, which is sometimes difficult in the case of solid samples. Because of the small light penetration depth, the ATR technique is ideal for highly absorbing samples, surfaces and thin-film measurements [56]. The major benefits of ATR-FTIR, in contrast to transmission and transflection experiments, are its sample thickness independent measurements, the ability to probe highly IR absorbing materials without the need for complex sample preparations and the improved spatial resolution [57]. Furthermore, expensive IR transparent substrates are not needed [7].