Articles you may be interested inFinal Aperture Superposition Technique applied to fast calculation of electron output factors and depth dose curves Med. A practical method for the calculation of multileaf collimator shaped fields output factors Med. Phys. 26, 2385 (1999); 10.1118/1.598754 Monte Carlo investigation of electron beam output factors versus size of square cutout Med. Phys. 26, 743 (1999); 10.1118/1.598582Calculating output factors for photon beam radiotherapy using a convolution/superposition method based on a dual source photon beam model Med.An empirical model is presented that uses a sector-integration method for calculating the output factors of irregularly shaped electron fields. The sector-integration method accounts for changes in electron fluence, lateral scatter equilibrium, and scatter from the edge of a cutout shield. This method is tested for elliptical and rectangular fields with a ratio of the long-to-short axis as great as 4 to 1. Differences between measured and calculated values for output factors were less than Ϯ1%.Comparisons were also carried out for a large number of cutout shields that were used in the clinic and similar levels of accuracy were obtained. © 1997 American Association of Physicists in Medicine. ͓S0094-2405͑97͒01211-X͔

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The power reflection coefficient is derived for an electromagnetic H wave incident on a semi‐infinite magnetized ferrite medium, moving perpendicular to the plane of incidence. Both the speed of the moving media and the anisotropy of the ferrite contribute to hybrid modes of the reflected and transmitted electromagnetic field components. Double refraction at an anisotropic boundary is not new but what is interesting in this article is the effect of the speed of the moving ferrite on both the propagation constants and the power reflection coefficient.

Wave vector surfaces, phase velocity surfaces, and ray velocity surfaces have been evaluated for electromagnetic waves traveling through magnetized ferrite. These surfaces are shown to have unique shapes depending upon the precessional, magnetization, and excitation frequencies. Double refraction of the waves occur at the interface between different ferrites. A transcendental equation for determining the angle of transmission is presented and a discussion is made on the possibility of total reflection. Since the direction of propagation, boundary surface normal, and direction of magnetization each present a degree of freedom to the incident plane wave problem a general set of coordinates is introduced that takes into account their relative orientation. The two cases for which the static magnetization is parallel and perpendicular to the plane of incidence is solved in detail and expressions are given for the reflection and transmission coefficients. It is shown that for the parallel magnetic polarization case the reflected component of the electric vector can be eliminated if the incident wave strikes the boundary plane at a magnetically dependent Brewster angle.

The electromagnetic fields generated by a superluminal electron in longitudinally magnetized, microwave ferrite have been derived for a narrow band of frequencies in the X band. For a superluminal electron, Cerenkov radiation is emitted in two circular cones for the ordinary and extraordinary wave modes. Using a Huygens' construction of wavelets, conditions for Cerenkov radiation were related to the propagation of plane waves through the ferrite. It was found that a slow relativistic electron will radiate only in the extraordinary wave mode. It is too slow to generate radiation in the ordinary wave mode. INTRODUCTIONThe generation of coherent microwave energy represents an area of continual interest for applications in space communications, microwave spectroscopy, and plasma diagnostics. Boundary value problems in Cerenkov theory [Bolotovskii, 1957[Bolotovskii, , 1962 Nag and Sayied, 1956] are important in connection with the theory of linear accelerators and waveguide systems. The emission of Cerenkov radiation was investigated for an electron moving with uniform velocity in an infinite, unbounded, anisotropic ferrite medium.The use of the Cerenkov effect as a means of generating microwave energy was first proposed by Ginsburg [1947]. He mentioned that it was unlikely to be an efficient way of producing microwave radiation and it would be difficult to obtain high powers. The source would give a continuous spectrum, whereas in most communication applications the aim is to produce oscillators that run at a single frequency. Three years after Cerenkov experimented with fluorescent light produced by gamma rays passing through uranyl salt solutions, Frank and Tarnrn [1937] explained the phenomenon using the classical electromagnetic theory of macroscopic media. Cerenkov radiation in anisotropic media has been studied, for the most part, in the optical spectrum [Ginsburg, 1940a, b;Tanaka, 1954;Muzikar and