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Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
The objective of this research is to develop and implement an algorithm that can accurately and efficiently predict backscatter yield and the trajectories and energies of electrons backscattered by solids. Taking into account the energy and direction of an incident electron, as well as the atomic number, atomic mass and density of the solid, our program determines a statistically reasonable path for the electron through the solid via Monte Carlo techniques. Such a model can and has been used in a variety of applications, but in this case we are interested in predicting the behavior of backscattered electrons. When applied to large numbers of electrons, the program provides statistically accurate results. In particular, excellent agreement is seen between the backscatter coefficients measured by Hunger and Kuchler and those predicted by our program. Furthermore, the angular distributions and energy distributions of backscattered electrons predicted by our program are consistent with those measured by Bishop.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
The objective of this research is to develop and implement an algorithm that can accurately and efficiently predict backscatter yield and the trajectories and energies of electrons backscattered by solids. Taking into account the energy and direction of an incident electron, as well as the atomic number, atomic mass and density of the solid, our program determines a statistically reasonable path for the electron through the solid via Monte Carlo techniques. Such a model can and has been used in a variety of applications, but in this case we are interested in predicting the behavior of backscattered electrons. When applied to large numbers of electrons, the program provides statistically accurate results. In particular, excellent agreement is seen between the backscatter coefficients measured by Hunger and Kuchler and those predicted by our program. Furthermore, the angular distributions and energy distributions of backscattered electrons predicted by our program are consistent with those measured by Bishop.
Author: David C. Joy Publisher: Oxford University Press, USA ISBN: 0195088743 Category : Electron microscopy Languages : en Pages : 225
Book Description
This book describes for the first time how Monte Carlo modeling methods can be applied to electron microscopy and microanalysis. Computer programs for two basic types of Monte Carlo simulation are developed from physical models of the electron scattering process--a single scattering program capable of high accuracy but requiring long computation times, and a plural scattering program which is less accurate but much more rapid. Optimized for use on personal computers, the programs provide a real time graphical display of the interaction. The programs are then used as the starting point for the development of programs aimed at studying particular effects in the electron microscope, including backscattering, secondary electron production, EBIC and cathodo-luminescence imaging, and X-ray microanalysis. The computer code is given in a fully annotated format so that it may be readily modified for specific problems. Throughout, the author includes numerous examples of how such applications can be used. Students and professionals using electron microscopes will want to read this important addition to the literature.
Author: David C. Joy Publisher: Oxford University Press ISBN: 0195358465 Category : Computers Languages : en Pages : 225
Book Description
This book describes for the first time how Monte Carlo modeling methods can be applied to electron microscopy and microanalysis. Computer programs for two basic types of Monte Carlo simulation are developed from physical models of the electron scattering process--a single scattering program capable of high accuracy but requiring long computation times, and a plural scattering program which is less accurate but much more rapid. Optimized for use on personal computers, the programs provide a real time graphical display of the interaction. The programs are then used as the starting point for the development of programs aimed at studying particular effects in the electron microscope, including backscattering, secondary electron production, EBIC and cathodo-luminescence imaging, and X-ray microanalysis. The computer code is given in a fully annotated format so that it may be readily modified for specific problems. Throughout, the author includes numerous examples of how such applications can be used. Students and professionals using electron microscopes will want to read this important addition to the literature.
Author: Samantha A. M. Lloyd Publisher: ISBN: Category : Languages : en Pages :
Book Description
This work establishes a framework for Monte Carlo simulations of complex, modulated electron fields produced by Varian's TrueBeam medical linear accelerator for investigations into modulated electron radiation therapy (MERT) and combined modulated photon and electron radiation therapy (MPERT). Both MERT and MPERT have shown potential for reduced low dose to normal tissue without compromising target coverage in the external beam radiation therapy of some breast, chest wall, head and neck, and scalp cancers. This reduction in low dose could translate into the reduction of immediate radiation side effects as well as long term morbidities and incidence of secondary cancers.Monte Carlo dose calculations are widely accepted as the gold standard for complex radiation therapy dose modelling, and are used almost exclusively for modelling the complex electron fields involved in MERT and MPERT. The introduction of Varian's newest linear accelerator, the TrueBeam, necessitated the development of new Monte Carlo models in order to further research into the potential role of MERT and MPERT in radiation therapy. This was complicated by the fact that the field independent internal schematics of TrueBeam were kept proprietary, unlike in previous generations of Varian accelerators.Two approaches are presented for performing Monte Carlo simulations of complex electron fields produced by TrueBeam. In the first approach, the dosimetric characteristics of electron fields produced by the TrueBeam were first compared with those produced by an older Varian accelerator, the Clinac 21EX. Differences in depth and profile characteristics of fields produced by the TrueBeam and those produced by the Clianc 21EX were found to be within 3%/3 mm. Given this information, complete accelerator models of the Clinac 21EX, based on its known internal geometry, were then successfully modified in order to simulate 12 and 20 MeV electron fields produced by the TrueBeam to within 2%/2 mm of measured depth and profile curves and to within 3.7% of measured relative output. While the 6 MeV TrueBeam model agreed with measured depth and profile data to within 3%/3 mm, the modified Clinac 21EX model was unable to reproduce trends in relative output as a function of fieldsize with acceptable accuracy.The second approach to modelling TrueBeam electron fields used phase-space source files provided by Varian that were scored below the field-independent portions of the accelerator head geometry. These phase-spaces were first validated for use in MERT and MPERT applications, in which simulations using the phase-space source files were shown to model depth dose curves that agreed with measurement within 2%/2 mm and profile curves that agreed with measurement within 3%/3 mm. Simulated changes in output as a function of field size fell within 2.7%, for the most part.In order to inform the positioning of jaws in MLC-shaped electron field delivery, the change in output as a function of jaw position for fixed MLC-apertures was investigated using the phase-space source files. In order to achieve maximum output and minimize treatment time, a jaw setting between 5 and 10 cm beyond the MLC- field setting is recommended at 6 MeV, while 5 cm or closer is recommended for 12 and 20 MeV with the caveat that output is most sensitive to jaw position when the jaws are very close to the MLC-field periphery. Additionally, output was found to be highly sensitive to jaw model. A change in divergence of the jaw faces from a point on the source plane to a 3x3 mm^2 square in the source plane changed the shape of the output curve dramatically.Finally, electron backscatter from the jaws into the monitor ionization chamber of the TrueBeam was measured and simulated to enable accurate absolute dose calculations. Two approaches were presented for measuring backscatter into the monitor ionization chamber without specialized electronics by turning o the dose and pulse forming network servos. Next, a technique was applied for simulating backscatter factors for the TrueBeam phase-space source models without the exact specifications of the monitor ionization chamber. By using measured backscatter factors, the forwarddose component in a virtual chamber was determined and then used to calculate backscatter factors for arbitrary fields to within 0.21%. Backscatter from the jaws was found to contribute up to 2.6% of the overall monitor chamber signal. The measurement techniques employed were not sensitive enough to quantify backscatter from the MLC, however, Monte Carlo simulations predicted this contribution to be 0.3%, at most, verifying that this component can be neglected.
Author: CLINTON TROY BALLINGER Publisher: ISBN: Category : Languages : en Pages : 420
Book Description
particularly attractive for use on sub-MeV electrons, because analog Monte Carlo calculations are too time-consuming and condensed history calculations are inaccurate.
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Author: Dustin Frederick Kapraun
Author: Kurt F. J. Heinrich
Author: David C. Joy
Author: Kurt F. J. Heinrich
Author: Tran Duy Ly
Author: David C. Joy
Author: Samantha A. M. Lloyd
Author: Solar Energy Research Institute
Author: CLINTON TROY BALLINGER