Bremsstrahlung and Photoneutrons from Thick Tungsten and Tantalum Targets
TL;DR: In this paper, Monte Carlo calculations have been made of electron-photon cascades in thick tungsten targets bombarded by electrons with energies up to 60 MeV, and the following information has been obtained: (1) the bremsstrahlung efficiency, (2) the angular distribution of the emitted bremstrahlsung intensity, (3) the spectra of the bremstrung emitted in various directions, (4) the transmission of primary and secondary electrons through the target, (5) energy deposition as function of the depth in the target
Abstract: Monte Carlo calculations have been made of electron-photon cascades in thick tungsten targets bombarded by electrons with energies up to 60 MeV. The following information has been obtained: (1) the bremsstrahlung efficiency, (2) the angular distribution of the emitted bremsstrahlung intensity, (3) the spectra of the bremsstrahlung emitted in various directions, (4) the transmission of primary and secondary electrons through the target, (5) energy deposition as function of the depth in the target, (6) the differential photon track length distribution inside the target, and (7) the yield of photoneutrons. The paper also includes various comparisons with experimental data.
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TL;DR: There has been an enormous increase in Monte Carlo studies dealing specifically with the subject of the present review, i.e., external photon beam Monte Carlo calculations, aided by the advent of new codes and fast computers.
Abstract: An essential requirement for successful radiation therapy is that the discrepancies between dose distributions calculated at the treatment planning stage and those delivered to the patient are minimized. An important component in the treatment planning process is the accurate calculation of dose distributions. The most accurate way to do this is by Monte Carlo calculation of particle transport, first in the geometry of the external or internal source followed by tracking the transport and energy deposition in the tissues of interest. Additionally, Monte Carlo simulations allow one to investigate the influence of source components on beams of a particular type and their contaminant particles. Since the mid 1990s, there has been an enormous increase in Monte Carlo studies dealing specifically with the subject of the present review, i.e., external photon beam Monte Carlo calculations, aided by the advent of new codes and fast computers. The foundations for this work were laid from the late 1970s until the early 1990s. In this paper we will review the progress made in this field over the last 25 years. The review will be focused mainly on Monte Carlo modelling of linear accelerator treatment heads but sections will also be devoted to kilovoltage x-ray units and 60Co teletherapy sources.
423 citations
02 Nov 1991
TL;DR: The ITS system as discussed by the authors is a powerful and user-friendly software package permitting state-of-the-art Monte Carlo solution of linear time-independent coupled electron/photon radiation transport problems, with or without the presence of macroscopic electric and magnetic fields of arbitrary spatial dependence.
Abstract: The ITS system is a powerful and user-friendly software package permitting state-of-the-art Monte Carlo solution of linear time-independent coupled electron/photon radiation transport problems, with or without the presence of macroscopic electric and magnetic fields of arbitrary spatial dependence. Version 3.0 is a major upgrade of the system with important improvements in the physical model, variance reduction, I/O, and user friendliness. Improvements to the cross-section generator include the replacement of Born-approximation bremsstrahlung cross section with the results of numerical phase-shift calculations, the addition of coherent scattering and binding effects in incoherent scattering, an upgrade of collisional and radiative stopping powers, and a complete rewrite to Fortran 77 standards emphasizing Block-IF structure. Improvements in the Monte Carlo codes are also described. >
392 citations
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KEK1
TL;DR: With the release of the EGS4 version, a deliberate attempt was made to present example problems in order to help the user ''get started'', and that spirit is followed in this report.
Abstract: In the nineteen years since EGS4 was released, it has been used in a wide variety of applications, particularly in medical physics, radiation measurement studies, and industrial development. Every new user and every new application bring new challenges for Monte Carlo code designers, and code refinements and bug fixes eventually result in a code that becomes difficult to maintain. Several of the code modifications represented significant advances in electron and photon transport physics, and required a more substantial invocation than code patching. Moreover, the arcane MORTRAN3[48] computer language of EGS4, was highest on the complaint list of the users of EGS4. The size of the EGS4 user base is difficult to measure, as there never existed a formal user registration process. However, some idea of the numbers may be gleaned from the number of EGS4 manuals that were produced and distributed at SLAC: almost three thousand. Consequently, the EGS5 project was undertaken. It was decided to employ the FORTRAN 77 compiler, yet include as much as possible, the structural beauty and power of MORTRAN3. This report consists of four chapters and several appendices. Chapter 1 is an introduction to EGS5 and to this report in general. We suggest that youmore » read it. Chapter 2 is a major update of similar chapters in the old EGS4 report[126] (SLAC-265) and the old EGS3 report[61] (SLAC-210), in which all the details of the old physics (i.e., models which were carried over from EGS4) and the new physics are gathered together. The descriptions of the new physics are extensive, and not for the faint of heart. Detailed knowledge of the contents of Chapter 2 is not essential in order to use EGS, but sophisticated users should be aware of its contents. In particular, details of the restrictions on the range of applicability of EGS are dispersed throughout the chapter. First-time users of EGS should skip Chapter 2 and come back to it later if necessary. With the release of the EGS4 version, a deliberate attempt was made to present example problems in order to help the user ''get started'', and we follow that spirit in this report. A series of elementary tutorial user codes are presented in Chapter 3, with more sophisticated sample user codes described in Chapter 4. Novice EGS users will find it helpful to read through the initial sections of the EGS5 User Manual (provided in Appendix B of this report), proceeding then to work through the tutorials in Chapter 3. The User Manuals and other materials found in the appendices contain detailed flow charts, variable lists, and subprogram descriptions of EGS5 and PEGS. Included are step-by-step instructions for developing basic EGS5 user codes and for accessing all of the physics options available in EGS5 and PEGS. Once acquainted with the basic structure of EGS5, users should find the appendices the most frequently consulted sections of this report.« less
350 citations
Cites background or methods or result from "Bremsstrahlung and Photoneutrons fr..."
...Even though other low-energy radiation transport codes were available, most notably ETRAN[15, 18, 19] and its progeny[46, 68], there had been many requests to extend EGS3 down to lower energies and this was a major, but not the only, reason for creating EGS4....
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...We refer to the ETRAN Monte Carlo shower code written by Berger and Seltzer[19]5....
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...In addition, comparisons of backscattered photon fluence as computed by EGS2 versus unpublished HEPL data, as well as bremsstrahlung angular distribution calculations comparing EGS2 results with those of Berger and Seltzer using ETRAN[19], suggested that EGS2 might be predicting values in the backward direction that were low by up to a factor of two....
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TL;DR: Experimental and theoretical studies of runaway electrons in toroidal devices are reviewed in this article, with particular reference to tokamaks, and the complex phenomenology of runaway effects, which have been the subject of research for the past twenty years, is organized within the framework of a number of physical models.
Abstract: Experimental and theoretical studies of runaway electrons in toroidal devices are reviewed here, with particular reference to tokamaks. The complex phenomenology of runaway effects, which have been the subject of research for the past twenty years, is organized within the framework of a number of physical models. The mechanisms and rates for runaway production are discussed first, followed by sections on runaway-driven kinetic relaxation processes and runaway orbit confinement. Next, the equilibrium and stability of runaway-dominated discharges are reviewed. Models for runaway production at early times in the discharge and the scaling of runaway phenomena to larger devices are also discussed. Finally, detection techniques and possible applications of runaways are mentioned.
305 citations
TL;DR: In general, the model S700 Source exhibited depth dose behavior similar to low-energy photon-emitting low dose rate sources I125 and Pd103, yet with capability for variable and much higher dose rates and subsequently adjustable penetration capabilities.
Abstract: A new x-ray source, the model S700 Axxent X-Ray Source (Source), has been developed by Xoft Inc. for electronic brachytherapy. Unlike brachytherapy sources containing radionuclides, this Source may be turned on and off at will and may be operated at variable currents and voltages to change the dose rate and penetration properties. The in-water dosimetry parameters for this electronic brachytherapy source have been determined from measurements and calculations at 40, 45, and 50 kV settings. Monte Carlo simulations of radiation transport utilized the MCNP5 code and the EPDL97-based mcplib04 cross-section library. Inter-tube consistency was assessed for 20 different Sources, measured with a PTW 34013 ionization chamber. As the Source is intended to be used for a maximum of ten treatment fractions, tube stability was also assessed. Photon spectra were measured using a high-purity germanium (HPGe) detector, and calculated using MCNP. Parameters used in the two-dimensional (2D) brachytherapy dosimetry formalism were determined. While the Source was characterized as a point due to the small anode size, < 1 mm, use of the one-dimensional (1D) brachytherapy dosimetry formalism is not recommended due to polar anisotropy. Consequently, 1D brachytherapy dosimetry parameters were not sought. Calculated point-source model radial dose functions at gP(5) were 0.20, 0.24, and 0.29 for the 40, 45, and 50 kV voltage settings, respectively. For 1
167 citations
References
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TL;DR: The quantenmechanische Theorie der elastischen Einzelstreuung am abgeschirmten Coulomb - Feld wird unter Berücksichtigung der Abschirmung nach the Thomas - Fermi - Methode in analytischer form entwickelt as discussed by the authors.
Abstract: Die quantenmechanische Theorie der elastischen Einzelstreuung am abgeschirmten Coulomb - Feld wird unter Berücksichtigung der Abschirmung nach der Thomas - Fermi - Methode in analytischer Form entwickelt. Die Theorie ist gültig für beliebige Werte des Parameters α ≡ zZI( 137 ß) [Z = Ordnungszahl der streuenden Atome, ± z e = Ladung der gestreuten Teilchen, v deren Geschwindigkeit, ß = v/c] sowie für Streuwinkel x 90 ° und für kinetische Energie der Teilchen Ekinz≳zZ4/3 • 100 eV. Der Spineinfluß, der bei kleinen Streuwinkeln gering ist, wurde vernachlässigt, womit die Theorie für alle Sorten geladener Teilchen gilt. Als Ergebnis wurde für das Verhältnis q(χ) ≡ ] Q ( χ ) / 0,9 ergibt. Im übrigen Bereich kann der Verlauf der Funktion q (χ) mit Hilfe von Interpolationsformeln der Gestalt χq = χo( Aq+ Bq a2) 1/2 ermittelt werden, wobei χq denjenigen Winkel bedeutet, für den das Verhältnis Q/QRuth. den festen Wert q annimmt. Die Zahlen Aq und Bq sind für eine Reihe von Werten q tabuliert (vergl. S. 143). Der so konstruierte Funktionsverlauf von q (χ) ist exakt für die Grenzfälle kleiner und großer α und stellt für Zwischenwerte von α eine gute Näherung dar, wie der Vergleich mit einigen durch numerische Auswertung erhaltenen Punkten zeigt (vergl. Abb. 2 S. 143). - Der letzte § (9) dient der Vorbereitung der im Tl. II behandelten Theorie der Vielfachstreuung.
1,017 citations
966 citations
TL;DR: Theorie der inkohärenten Mehrfach-und Vielfach-streuung zu (absolut) kleinen Winkeln wird neu entwickelt as discussed by the authors.
Abstract: Abstract Die Theorie der inkohärenten Mehrfach-und Vielfachstreuung zu (absolut) kleinen Winkeln wird neu entwickelt. Gegenüber den bisherigen Theorien, auf deren Methoden z.Tl. aufgebaut wird, werden folgende Fortschritte erzielt: 1. Es wird das in Tl. I abgeleitete, für beliebige Werte von a = zZ/(137ß) gültige Einzelstreugesetz zugrunde gelegt.
697 citations
TL;DR: In this paper, a systematische Einleitung zu der Behandlung des kontinuierlichen Rontgenspektrums im II. Teil is presented.
Abstract: Ubersicht: Der I. Teil bildet eine systematische Einleitung zu der Behandlung des kontinuierlichen Rontgenspektrums im II. Teil. Der I. Teil geht nur in der Methode, nicht in den Resultaten uber die Arbeiten von Gordon, Mott, Temple hinaus. Der II. Teil setzt, im Gegensatz zu Arbeiten von Oppenheimer und Sugiura den Endzustand des gebremsten Elektrons als ebene, durch Beugung modifizierte Welle an. Polarisation und Intensitat im kontinuierlichen Spektrum werden nach der Methode der Matrixelemente berechnet. Um die azimutale Verteilung der Intensitat, insbesondere die Voreilung des Maximums zu erhalten, mus die Rechenmethode verfeinert werden durch Berucksichtigung der Retardierung. Die Resultate werden mit Messungen von Kulenkampff verglichen.
678 citations
TL;DR: In this paper, a theoretical treatment of multiple Rutherford scattering is given which is exact if one considers electrons with the same total path length in the scatterer, and it is shown that this distribution depends in a sensitive way upon the deviation from the Rutherford law for small angle scattering due to screening by electrons.
Abstract: A theoretical treatment of multiple Rutherford scattering is given which is exact if one considers electrons with the same total path length in the scatterer. The approximations necessary for the actual solution of the problem for a thin scatterer can be shown to have little effect on the results for small angle scattering. The distribution of scattering is expressed as a series in Legendre polynomials which has been evaluated numerically; the final result for thin scattering is approximately a Gaussian curve. It is shown that this distribution depends in a sensitive way upon the deviation from the Rutherford law for small angle scattering due to screening by electrons. This may perhaps explain the discrepancies between experiments and theory.
503 citations