Search results for "anisotropy"
showing 10 items of 912 documents
A Monte Carlo investigation of the dosimetric characteristics of the CSM11 137Cs source from CIS
2000
The purpose of this study is to calculate basic dosimetry data for a CSM11 low dose rate 137Cs source in water. This source is widely used in afterloadable dome cylinders designed to homogeneously irradiate the vaginal cuff alone or additional areas of the vagina in hysterectomized patients. In this study, the Monte Carlo simulation code GEANT, incorporating in detail source geometry, is used to investigate the dosimetric characteristics of the source. The calculated data were analyzed using a fitting procedure that is described in detail. Absolute dose rate distributions in water were calculated around this source and are presented as conventional 2D Cartesian lookup tables (classically al…
Coherent forward-scattering amplitude in transmission and grazing incidence Mössbauer spectroscopy
1996
The theory of both transmission and grazing incidence M\"ossbauer spectroscopy is re-analyzed. Starting with the nuclear susceptibility tensor a common concise first order perturbation formulation is given by introducing the forward scattering amplitude into an anisotropic optical scheme. Formulae of Blume and Kistner as well as those of Andreeva are re-derived for the forward scattering and grazing incidence geometries, respectively. Limitations of several previously intuitively introduced approximations are pointed out. The grazing incidence integral propagation matrices are written in a form built up from 2x2 matrix exponentials which is particularly suitable for numerical calculations a…
Polarization instability in anisotropic-cavity degenerate four-wave mixing
2000
Abstract The emission and stability properties of a plane-wave model of intracavity degenerate four-wave mixing including self- and cross-phase modulation are studied. A Kerr medium inside an anisotropic cavity in which a linearly polarized field is injected is considered. Cavity anisotropy leads to qualitative new phenomena such as a subcritical polarization instability.
Dyakonov surface waves in lossy metamaterials
2015
We analyze the existence of localized waves in the vicinities of the interface between two dielectrics, provided one of them is uniaxial and lossy. We found two families of surface waves, one of them approaching the well-known Dyakonov surface waves (DSWs). In addition, a new family of wave fields exists which are tightly bound to the interface. Although its appearance is clearly associated with the dissipative character of the anisotropic material, the characteristic propagation length of such surface waves might surpass the working wavelength by nearly two orders of magnitude. This research was funded by the Spanish Ministry of Economy and Competitiveness under the Project TEC2013-50416-E…
Dyakonov-like surface waves in the THz regime
2016
Abstract Here we examine Dyakonov-like surface waves (DSWs) in the THz regime traveling along the plane interface between a non-conducting isotropic medium and a low-loss graphene-based uniaxial metamaterial with the optic axis (OA) oriented along with the interface. New insights concerning the propagation characteristics of DSWs are given by analyzing the dispersion relation in such configuration, that is evaluated using the effective medium theory. The range of angles with respect to the OA which is determined for the in-plane wave vector can be conveniently tuned with extremely flexibility in opposition with DSWs excited in natural anisotropic media. The properties discussed here are of …
Unusual optical properties of the dense nonequilibrium plasmas
2005
A concise overview of new optical properties of dense nonequilibrium plasma formed on the solid state target boundary is given. In this chapter, we describe phenomena such as the third harmonic generation in the skin layer, collisionless electron heating in the high frequency skin-effect regime, absorption, and reflection and transmission of radiation by a plasma with anisotropic electron distribution.
Observation of an Intense Quasicontinuum of Superdeformed Rotational Transitions inEu143
1996
Quasicontinuum spectra in coincidence with transitions belonging to the different potential wells of {sup 143}Eu are studied with an increasing number of coincidence folds. An intense bump of rotationally correlated transitions is observed to develop in the high spin region. Fold distributions, angular anisotropies, moment of inertia determinations, and lower limits of lifetimes as a function of the rotational frequency show that the bump originates from highly collective rotationally damped {ital E}2 transitions generated by superdeformed states. {copyright} {ital 1996 The American Physical Society.}
A two-dimensional liquid-filled ionization chamber array prototype for small-field verification: characterization and first clinical tests.
2012
In this work we present the design, characterization and first clinical tests of an in-house developed two-dimensional liquid-filled ionization chamber prototype for the verification of small radiotherapy fields and treatments containing such small fields as in radiosurgery, which consists of 2 mm × 2 mm pixels arranged on a 16×8 rectangular grid. The ionization medium is isooctane. The characterization of the device included the study of depth, field-size and dose-rate dependences, which are sufficiently moderate for a good operation at therapy radiation levels. However, the detector presents an important anisotropic response, up to ≃ 12% for front versus near-lateral incidence, which can …
SU-FF-T-14: Monte Carlo Derivation of TG-43 Dosimetric Parameters for Radiation Therapy Resources and 3M Cs-137 Sources
2005
Purpose: In clinical brachytherapydosimetry a detailed dose rate distribution of the radioactive source in water is needed to make a quality treatment planning. Two Cs‐137 sources are considered in this study the Radiation Therapy Resources 67–800 source(Radiation Therapy Resources Inc., Valencia, CA) and the 3M model 6500/6D6C source.Material and methods: A complete dosimetric dataset for both sources has been obtained by means of the Monte Carlo GEANT4 code. Results:Dose rate distributions are presented in two different ways, following the TG43 formalism and in a 2D rectangular dose rate table. Conclusion: This 2D dose rate table is helpful for the TPS quality control and it is fully cons…
Technical note: Monte-Carlo dosimetry of the HDR 12i and Plus 192Ir sources.
2001
In this study a complete set of dosimetric data for the GammaMed high dose rate (HDR) 12i and Plus 192 Ir sources are presented. These data have been calculated by means of the Monte Carlo simulation code GEANT3. Absolute dose rate distributions in water are presented as conventional two dimensional (2D) Cartesian look-up tables, and in the TG43 formalism.