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S P Heluani - One of the best experts on this subject based on the ideXlab platform.
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non steady state transport of charge carriers an approach based on Invariant Embedding method
Journal of Applied Physics, 2020Co-Authors: C Figueroa, B Straube, M Villafuerte, G Bridoux, J M Ferreyra, Nadia Celeste Vega, S P HeluaniAbstract:In this work, we report on a model that describes the microscopic electrical transport as a transmission problem using the Invariant Embedding technique. Analytical expressions for the transport coefficients under non-steady-state conditions are derived allowing us to calculate carrier concentration and time-dependent conductivity. Employing measurable magnitudes, our theoretical results allow us to determine defect concentrations, carrier generation rates, cross sections of recombination, and capture by traps. This model can be employed to study the conduction processes of semiconductors and test their band and defect structure. In particular, time-dependent photoconductivity measurements of a ZnO microwire have been well fitted using our model indicating a relevant role of intrinsic point defects in this material.
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backscattering and absorption coefficients for electrons solutions of Invariant Embedding transport equations using a method of convergence
Journal of Applied Physics, 2014Co-Authors: C Figueroa, H Brizuela, S P HeluaniAbstract:The backscattering coefficient is a magnitude whose measurement is fundamental for the characterization of materials with techniques that make use of particle beams and particularly when performing microanalysis. In this work, we report the results of an analytic method to calculate the backscattering and absorption coefficients of electrons in similar conditions to those of electron probe microanalysis. Starting on a five level states ladder model in 3D, we deduced a set of integro-differential coupled equations of the coefficients with a method know as Invariant Embedding. By means of a procedure proposed by authors, called method of convergence, two types of approximate solutions for the set of equations, namely complete and simple solutions, can be obtained. Although the simple solutions were initially proposed as auxiliary forms to solve higher rank equations, they turned out to be also useful for the estimation of the aforementioned coefficients. In previous reports, we have presented results obtain...
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convergence method for calculating solutions to the 3d Invariant Embedding integro differential equations describing electron transport processes
Journal of Materials Science, 2010Co-Authors: C Figueroa, H Brizuela, S P HeluaniAbstract:The electron and photon transport processes in spectroscopy techniques described by the Invariant Embedding theory is here revisited. We report a convergence method to obtain closed analytical solutions to the 3D integro-differential equations. This method was successfully used in calculating the dependence of the electron backscattered fraction on the atomic number and on the energy. Also the fraction of absorbed electron as a function of incident angles was calculated. This method, using a states ladder model for the electron energies, provides a tool for testing physical parameters involved in the transport theory, such as the elastic and inelastic cross sections. The outstanding feature of the Invariant Embedding differential equations of considering observable quantities (such as the emergent flux of particles) as independent variables makes them a suitable tool to describe experimental situations.
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3d Invariant Embedding model for backscattering electrons applied to materials characterization
Physica B-condensed Matter, 2007Co-Authors: C Figueroa, N Nieva, S P HeluaniAbstract:In this work, the results of a 3D model used to describe the fraction of backscattered electrons, together with its energy and angular distributions, are reported. This 3D model is the result of improvements in the Invariant Embedding Approach to Microanalysis (IEAM). Comparisons with experiment show that the theoretical results follow the general trend of experimental data, when parameters (such as atomic number, energy of the impinging electrons and tilted angle) are changed.
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Invariant Embedding approach to microanalysis procedure to thin film characterization
Journal of Applied Physics, 2006Co-Authors: C Figueroa, H Brizuela, S P HeluaniAbstract:By the use of invariance principles a procedure to characterize thin films using an electron microprobe is reported. Experimental quantities such as the detected intensities and electron fluxes in the boundaries of a solid system are described by the Invariant Embedding method. In addition, differential equations are given for the probabilities of the different “destinations” of the electrons inside a solid as functions of the sample thickness. The procedure reported here makes it possible to perform microanalysis without the need of making approaches to estimate the ionization distribution function. The decaying in the energy of the electrons is described by a state ladder model. A few but usual cases for which this method gives fairly good agreement with experimental results are reported. The method seems to be promising to obtain procedures in microanalysis.
Akinao Shimizu - One of the best experts on this subject based on the ideXlab platform.
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calculation of gamma ray buildup factors up to depths of 100 mfp by the method of Invariant Embedding iii generation of an improved data set
Journal of Nuclear Science and Technology, 2004Co-Authors: Akinao Shimizu, Takashi Onda, Yukio SakamotoAbstract:An improved data set of gamma-ray buildup factors for point isotropic sources in infinite homogeneous media has been generated by the method of Invariant Embedding. The points of improvement compared with the standard data set ANSI/ANS-6.4.3 include (1) extension of the buildup factors up to depths of 100 mean free paths, (2) improved treatment of bremsstrahlung, (3) addition of the effective dose buildup factors, (4) consistent use of the cross-section PHOTX to all materials and (5) a quantitative evaluation about the accuracy in transport calculation. The data set obtained are compared precisely with the standard data set ANSI/ANS-6.4.3.
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calculation of gamma ray buildup factors up to depths of 100 mfp by the method of Invariant Embedding ii improved treatment of bremsstrahlung
Journal of Nuclear Science and Technology, 2003Co-Authors: Akinao Shimizu, Hideo HirayamaAbstract:An improved method to calculate the gamma-ray buildup factors including bremsstrahlung has been developed. The exposure buildup factors with bremsstrahlung were computed by the present method for lead, iron and water at the source energy of 10.0 MeV up to depths of 100 mfp. The accuracy of the present method was checked by comparison with the calculations by use of EGS4. Excellent agreement was obtained between the calculations by both methods about the exposure buildup factors per energy (energy spectrum of transmitted photons) for lead up to depths of 10 mfp and the ratio of the exposure buildup factor with bremsstrahlung to that without bremsstrahlung for lead, iron and water up to depths of 40 mfp. It is confirmed that the present method has an accuracy sufficient to be used to the generation of an improved set of gamma-ray buildup factors including bremsstrahlung.
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calculation of gamma ray buildup factors up to depths of 100 mfp by the method of Invariant Embedding i analysis of accuracy and comparison with other data
Journal of Nuclear Science and Technology, 2002Co-Authors: Akinao ShimizuAbstract:The method of Invariant Embedding has been applied to calculations of gamma-ray buildup factors for point isotropic sources in infinite homogeneous media up to depths of 100 mean free paths (mfp) without bremsstrahlung. A comprehensive survey of buildup factors was performed to estimate errors due to energy, angle and space meshes adopted in the transport calculations by the present method. It is confirmed numerically that the exposure buildup factors can be calculated up to depths of 100 mfp with an error less than 10% by using the present method. The exposure buildup factors for water, iron and lead for typical source energies of 10 MeV, 1.0 MeV and 0.1 MeV are provided up to depths of 100 mfp. Those buildup factors are found to agree well with other data including the moments method calculations and the Monte Calro calculations by EGS4. These results indicate that the method of Invariant Embedding is able to provide gamma-ray buildup factor up to depths of 100 mfp with an accuracy enough to be used in shielding calculations.
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gamma ray albedo data generated by the Invariant Embedding method
Journal of Nuclear Science and Technology, 1998Co-Authors: Hiroyuki Kadotani, Akinao ShimizuAbstract:The energy-and-angle dependent doubly differential γ-ray albedos for homogeneous semi-infinite medium have been calculated for water, ordinary concrete, soil, heavy concrete, iron, tin and lead. The procedure of calculation employed in the present paper is the Invariant Embedding method which is being developed to solve neutral particle transport problems in homogeneous one dimensional medium. The calculated γ-ray albedos are stored in the data base. One can easily obtain from this data base the various kinds of albedos (number, dose, energy, etc.) with a simple interface program. The accuracy of the calculated γ-ray albedos is ascertained by comparing with the Monte Carlo calculations (MCNP4A and EGS4).
C Figueroa - One of the best experts on this subject based on the ideXlab platform.
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non steady state transport of charge carriers an approach based on Invariant Embedding method
Journal of Applied Physics, 2020Co-Authors: C Figueroa, B Straube, M Villafuerte, G Bridoux, J M Ferreyra, Nadia Celeste Vega, S P HeluaniAbstract:In this work, we report on a model that describes the microscopic electrical transport as a transmission problem using the Invariant Embedding technique. Analytical expressions for the transport coefficients under non-steady-state conditions are derived allowing us to calculate carrier concentration and time-dependent conductivity. Employing measurable magnitudes, our theoretical results allow us to determine defect concentrations, carrier generation rates, cross sections of recombination, and capture by traps. This model can be employed to study the conduction processes of semiconductors and test their band and defect structure. In particular, time-dependent photoconductivity measurements of a ZnO microwire have been well fitted using our model indicating a relevant role of intrinsic point defects in this material.
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backscattering and absorption coefficients for electrons solutions of Invariant Embedding transport equations using a method of convergence
Journal of Applied Physics, 2014Co-Authors: C Figueroa, H Brizuela, S P HeluaniAbstract:The backscattering coefficient is a magnitude whose measurement is fundamental for the characterization of materials with techniques that make use of particle beams and particularly when performing microanalysis. In this work, we report the results of an analytic method to calculate the backscattering and absorption coefficients of electrons in similar conditions to those of electron probe microanalysis. Starting on a five level states ladder model in 3D, we deduced a set of integro-differential coupled equations of the coefficients with a method know as Invariant Embedding. By means of a procedure proposed by authors, called method of convergence, two types of approximate solutions for the set of equations, namely complete and simple solutions, can be obtained. Although the simple solutions were initially proposed as auxiliary forms to solve higher rank equations, they turned out to be also useful for the estimation of the aforementioned coefficients. In previous reports, we have presented results obtain...
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convergence method for calculating solutions to the 3d Invariant Embedding integro differential equations describing electron transport processes
Journal of Materials Science, 2010Co-Authors: C Figueroa, H Brizuela, S P HeluaniAbstract:The electron and photon transport processes in spectroscopy techniques described by the Invariant Embedding theory is here revisited. We report a convergence method to obtain closed analytical solutions to the 3D integro-differential equations. This method was successfully used in calculating the dependence of the electron backscattered fraction on the atomic number and on the energy. Also the fraction of absorbed electron as a function of incident angles was calculated. This method, using a states ladder model for the electron energies, provides a tool for testing physical parameters involved in the transport theory, such as the elastic and inelastic cross sections. The outstanding feature of the Invariant Embedding differential equations of considering observable quantities (such as the emergent flux of particles) as independent variables makes them a suitable tool to describe experimental situations.
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3d Invariant Embedding model for backscattering electrons applied to materials characterization
Physica B-condensed Matter, 2007Co-Authors: C Figueroa, N Nieva, S P HeluaniAbstract:In this work, the results of a 3D model used to describe the fraction of backscattered electrons, together with its energy and angular distributions, are reported. This 3D model is the result of improvements in the Invariant Embedding Approach to Microanalysis (IEAM). Comparisons with experiment show that the theoretical results follow the general trend of experimental data, when parameters (such as atomic number, energy of the impinging electrons and tilted angle) are changed.
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Invariant Embedding approach to microanalysis procedure to thin film characterization
Journal of Applied Physics, 2006Co-Authors: C Figueroa, H Brizuela, S P HeluaniAbstract:By the use of invariance principles a procedure to characterize thin films using an electron microprobe is reported. Experimental quantities such as the detected intensities and electron fluxes in the boundaries of a solid system are described by the Invariant Embedding method. In addition, differential equations are given for the probabilities of the different “destinations” of the electrons inside a solid as functions of the sample thickness. The procedure reported here makes it possible to perform microanalysis without the need of making approaches to estimate the ionization distribution function. The decaying in the energy of the electrons is described by a state ladder model. A few but usual cases for which this method gives fairly good agreement with experimental results are reported. The method seems to be promising to obtain procedures in microanalysis.
C Hoffmann - One of the best experts on this subject based on the ideXlab platform.
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thin film characterization with x ray microanalysis extending and improving Invariant Embedding results
X-Ray Spectrometry, 2003Co-Authors: S P Heluani, C HoffmannAbstract:Invariant Embedding theoretical results for the recorded x-ray intensities in electron probe microanalysis were used to develop a procedure for thin films. The method presented here gives the possibility of achieving thin-film characterization directly from characteristic x-rays intensities measurements, without the necessity to make an explicit calculation of the ϕ(ρz) function. Theoretical results are found to follow the general trend of experimental data. Copyright © 2003 John Wiley & Sons, Ltd.
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theoretical modelling of x ray production in thin films characterization with electron probe Invariant Embedding results
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2002Co-Authors: S P Heluani, C HoffmannAbstract:Abstract Employing the Invariant Embedding principle, theoretical expressions for the detected characteristic X-ray intensities generated in electron probe microanalysis of thin films are obtained. Characteristic X-ray emission from the elements present in a solid is calculated from the probabilities of the backscattered and transmitted electron trajectories within the film and the substrate. The theoretical expressions mentioned provide for the possibility of developing procedures for microanalysis directly from the experimental results without making approaches for the estimation of the φ(ρz) function. The procedure used permits to calculate the recorded X-rays as a function of incident beam voltage and also as a function of the sample thickness. The method presented here gives the possibility of obtaining calibration curves for thin films and multi-layers. The results obtained are found to agree with experimental ones.
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states ladder model for electrons backscattered in x ray microanalysis application of the Invariant Embedding method
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2000Co-Authors: S P Heluani, C HoffmannAbstract:Abstract The advantage of the Invariant Embedding method for the study of transport process in electron probe microanalysis (EPMA), is illustrated considering a model where the energy of the impinging electrons slows down on a ladder of states. Differential equations systems for the probability of the electrons being backscattered and for the contribution of these electrons to the detected X-ray intensity are obtained. Theoretical predictions of the model are compared with experimental results. It is shown that the proposed model describes the general trend of experimental data and leads to a good agreement for a wide range of atomic numbers.
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application of the Invariant Embedding method to x ray microanalysis
X-Ray Spectrometry, 1998Co-Authors: S P Heluani, C HoffmannAbstract:The Invariant Embedding principle was applied to obtain closed analytical expressions of several magnitudes of interest in electron probe microanalysis [ionization distribution function, ϕ(ρz) backscattering probability, etc.]. This approach permits one easily to obtain solutions for a model which explicitly considers the mean free path between effective electron collisions. © 1998 John Wiley & Sons, Ltd.
H Brizuela - One of the best experts on this subject based on the ideXlab platform.
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backscattering and absorption coefficients for electrons solutions of Invariant Embedding transport equations using a method of convergence
Journal of Applied Physics, 2014Co-Authors: C Figueroa, H Brizuela, S P HeluaniAbstract:The backscattering coefficient is a magnitude whose measurement is fundamental for the characterization of materials with techniques that make use of particle beams and particularly when performing microanalysis. In this work, we report the results of an analytic method to calculate the backscattering and absorption coefficients of electrons in similar conditions to those of electron probe microanalysis. Starting on a five level states ladder model in 3D, we deduced a set of integro-differential coupled equations of the coefficients with a method know as Invariant Embedding. By means of a procedure proposed by authors, called method of convergence, two types of approximate solutions for the set of equations, namely complete and simple solutions, can be obtained. Although the simple solutions were initially proposed as auxiliary forms to solve higher rank equations, they turned out to be also useful for the estimation of the aforementioned coefficients. In previous reports, we have presented results obtain...
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convergence method for calculating solutions to the 3d Invariant Embedding integro differential equations describing electron transport processes
Journal of Materials Science, 2010Co-Authors: C Figueroa, H Brizuela, S P HeluaniAbstract:The electron and photon transport processes in spectroscopy techniques described by the Invariant Embedding theory is here revisited. We report a convergence method to obtain closed analytical solutions to the 3D integro-differential equations. This method was successfully used in calculating the dependence of the electron backscattered fraction on the atomic number and on the energy. Also the fraction of absorbed electron as a function of incident angles was calculated. This method, using a states ladder model for the electron energies, provides a tool for testing physical parameters involved in the transport theory, such as the elastic and inelastic cross sections. The outstanding feature of the Invariant Embedding differential equations of considering observable quantities (such as the emergent flux of particles) as independent variables makes them a suitable tool to describe experimental situations.
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Invariant Embedding approach to microanalysis procedure to thin film characterization
Journal of Applied Physics, 2006Co-Authors: C Figueroa, H Brizuela, S P HeluaniAbstract:By the use of invariance principles a procedure to characterize thin films using an electron microprobe is reported. Experimental quantities such as the detected intensities and electron fluxes in the boundaries of a solid system are described by the Invariant Embedding method. In addition, differential equations are given for the probabilities of the different “destinations” of the electrons inside a solid as functions of the sample thickness. The procedure reported here makes it possible to perform microanalysis without the need of making approaches to estimate the ionization distribution function. The decaying in the energy of the electrons is described by a state ladder model. A few but usual cases for which this method gives fairly good agreement with experimental results are reported. The method seems to be promising to obtain procedures in microanalysis.
