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1

Vectorized Monte Carlo Photon Transport.  

National Technical Information Service (NTIS)

The results of current research in the development of a CRAY algorithm for time-dependent Monte Carlo photon radiation transport is presented. The method that has been developed is a fully vectorized particle-vector scheme. This technique tracks groups of...

F. W. Bobrowicz J. E. Lynch K. J. Fisher J. E. Tabor

1983-01-01

2

Monte Carlo electron/photon transport  

SciTech Connect

A review of nonplasma coupled electron/photon transport using Monte Carlo method is presented. Remarks are mainly restricted to linerarized formalisms at electron energies from 1 keV to 1000 MeV. Applications involving pulse-height estimation, transport in external magnetic fields, and optical Cerenkov production are discussed to underscore the importance of this branch of computational physics. Advances in electron multigroup cross-section generation is reported, and its impact on future code development assessed. Progress toward the transformation of MCNP into a generalized neutral/charged-particle Monte Carlo code is described. 48 refs.

Mack, J.M.; Morel, J.E.; Hughes, H.G.

1985-01-01

3

A vectorized Monte Carlo code for modeling photon transport in SPECT  

Microsoft Academic Search

A vectorized Monte Carlo computer code has been developed for modeling photon transport in single photon emission computed tomography (SPECT). The code models photon transport in a uniform attenuating region and photon detection by a gamma camera. It is adapted from a history-based Monte Carlo code in which photon history data are stored in scalar variables and photon histories are

Mark F. Smith; C. E. Jr. Floyd; R. J. Jaszczak

1993-01-01

4

Electron and Photon Transport in Multi-Layer Media: Notes on the Monte Carlo Code ZTRAN,  

National Technical Information Service (NTIS)

The report provides a brief description and running instructions for the one-dimensional Monte Carlo code ZTRAN. The program is used to calculate the transport of electrons and photons in heterogeneous multi-layer media.

S. M. Seltzer M. J. Berger

1984-01-01

5

Overview of physical interaction models for photon and electron transport used in Monte Carlo codes  

Microsoft Academic Search

The physical principles and approximations employed in Monte Carlo simulations of coupled electron-photon transport are reviewed. After a brief analysis of the assumptions underlying the trajectory picture used to generate random particle histories, we concentrate on the physics of the various interaction processes of photons and electrons. For each of these processes we describe the theoretical models and approximations that

Francesc Salvat; José M. Fernández-Varea

2009-01-01

6

Monte Carlo photon transport on vector and parallel supercomputers: Final report  

Microsoft Academic Search

The University of Michigan has been investigating the implementation of vectorized and parallelized Monte Carlo algorithms for the analysis of photon transport in an inertially-confined fusion (ICF) plasma. The goal of this work is to develop and test Monte Carlo algorithms for vector\\/parallel supercomputers such as the Cray X-MP and Cray-2. Previous effort has resulted in the development of a

W. R. Martin; P. F. Nowak

1986-01-01

7

Monte Carlo photon transport on vector and parallel superconductors: Final report  

Microsoft Academic Search

The vectorized Monte Carlo photon transport code VPHOT has been developed for the Cray-1, Cray-XMP, and Cray-2 computers. The effort in the current project was devoted to multitasking the VPHOT code and implement it on the Cray X-MP and Cray-2 parallel-vector supercomputers, examining the robustness of the vectorized algorithm for changes in the physics of the test problems, and evaluating

W. R. Martin; P. F. Nowak

1987-01-01

8

A GPU implementation of EGSnrc's Monte Carlo photon transport for imaging applications  

NASA Astrophysics Data System (ADS)

EGSnrc is a well-known Monte Carlo simulation package for coupled electron-photon transport that is widely used in medical physics application. This paper proposes a parallel implementation of the photon transport mechanism of EGSnrc for graphics processing units (GPUs) using NVIDIA's Compute Unified Device Architecture (CUDA). The implementation is specifically designed for imaging applications in the diagnostic energy range and does not model electrons. No approximations or simplifications of the original EGSnrc code were made other than using single floating-point precision instead of double precision and a different random number generator. To avoid performance penalties due to the random nature of the Monte Carlo method, the simulation was divided into smaller steps that could easily be performed in a parallel fashion suitable for GPUs. Speedups of 20 to 40 times for 643 to 2563 voxels were observed while the accuracy of the simulation was preserved. A detailed analysis of the differences between the CUDA simulation and the original EGSnrc was conducted. The two simulations were found to produce equivalent results for scattered photons and an overall systematic deviation of less than 0.08% was observed for primary photons.

Lippuner, Jonas; Elbakri, Idris A.

2011-11-01

9

TART 2000: A Coupled Neutron-Photon, 3-D, Combinatorial Geometry, Time Dependent, Monte Carlo Transport Code.  

National Technical Information Service (NTIS)

TART2000 is a coupled neutron-photon, 3 Dimensional, combinatorial geometry, time dependent Monte Carlo radiation transport code. This code can run on any modern computer. It is a complete system to assist you with input Preparation, running Monte Carlo c...

D. E. Cullen

2000-01-01

10

Monte Carlo photon transport on vector and parallel superconductors: Final report  

SciTech Connect

The vectorized Monte Carlo photon transport code VPHOT has been developed for the Cray-1, Cray-XMP, and Cray-2 computers. The effort in the current project was devoted to multitasking the VPHOT code and implement it on the Cray X-MP and Cray-2 parallel-vector supercomputers, examining the robustness of the vectorized algorithm for changes in the physics of the test problems, and evaluating the efficiency of alternative algorithms such as the ''stack-driven'' algorithm of Bobrowicz for possible incorporation into VPHOT. These tasks are discussed in this paper. 4 refs.

Martin, W.R.; Nowak, P.F.

1987-09-30

11

TART97 a coupled neutron-photon 3-D, combinatorial geometry Monte Carlo transport code  

SciTech Connect

TART97 is a coupled neutron-photon, 3 Dimensional, combinatorial geometry, time dependent Monte Carlo transport code. This code can on any modern computer. It is a complete system to assist you with input preparation, running Monte Carlo calculations, and analysis of output results. TART97 is also incredibly FAST; if you have used similar codes, you will be amazed at how fast this code is compared to other similar codes. Use of the entire system can save you a great deal of time and energy. TART97 is distributed on CD. This CD contains on- line documentation for all codes included in the system, the codes configured to run on a variety of computers, and many example problems that you can use to familiarize yourself with the system. TART97 completely supersedes all older versions of TART, and it is strongly recommended that users only use the most recent version of TART97 and its data riles.

Cullen, D.E.

1997-11-22

12

MCNP: a general Monte Carlo code for neutron and photon transport  

SciTech Connect

MCNP is a very general Monte Carlo neutron photon transport code system with approximately 250 person years of Group X-6 code development invested. It is extremely portable, user-oriented, and a true production code as it is used about 60 Cray hours per month by about 150 Los Alamos users. It has as its data base the best cross-section evaluations available. MCNP contains state-of-the-art traditional and adaptive Monte Carlo techniques to be applied to the solution of an ever-increasing number of problems. Excellent user-oriented documentation is available for all facets of the MCNP code system. Many useful and important variants of MCNP exist for special applications. The Radiation Shielding Information Center (RSIC) in Oak Ridge, Tennessee is the contact point for worldwide MCNP code and documentation distribution. A much improved MCNP Version 3A will be available in the fall of 1985, along with new and improved documentation. Future directions in MCNP development will change the meaning of MCNP to Monte Carlo N Particle where N particle varieties will be transported.

Forster, R.A.; Godfrey, T.N.K.

1985-01-01

13

Monte Carlo evaluation of kerma at a point for photon transport problems  

Microsoft Academic Search

Estimation of collision kerma at a geometric point arising from scattered photons is a potentially important application of Monte Carlo simulation, especially in the presence of steep flux gradients. We examine the usual method of extracting point-kerma estimates from randomly generated photon trajectories which consists of tallying the energy lost by photon collisions occurring in the vicinity of the point

Jeffrey F. Williamson

1987-01-01

14

Radiation transport calculations for 50 MV photon therapy beam using the Monte Carlo code GEANT4.  

PubMed

A new thin transmission target technique for fast dose delivery using narrow scanned photon beams has been developed. High-energy, 50-100 MeV, electron beams of low emittance incident on thin low-Z targets produce narrow and intense high-energy bremsstrahlung beams. However, electrons transmitted through the target are bent from the therapeutic beam by a purging magnet and have to be effectively absorbed in a dedicated electron collector. The electron-photon transport through a treatment head has been studied using the Monte Carlo simulation toolkit Geant4. The Geant4 electromagnetic physics processes have been compared with experimental data of radial dose profiles. The differences between calculated and measured radial dose distributions are approximately 2-10%. Preliminary investigations of the collector design have been carried out in order to minimise secondary electron and photon contamination of the therapeutic beam. The toolkit presented here is promising for further development of narrow photon beam therapy. PMID:16381775

Larsson, Susanne; Svensson, Roger; Gudowska, Irena; Ivanchenko, Vladimir; Brahme, Anders

2005-01-01

15

ITS Version 6 : the integrated TIGER series of coupled electron/photon Monte Carlo transport codes.  

SciTech Connect

ITS is a powerful and user-friendly software package permitting state-of-the-art Monte Carlo solution of lineartime-independent coupled electron/photon radiation transport problems, with or without the presence of macroscopic electric and magnetic fields of arbitrary spatial dependence. Our goal has been to simultaneously maximize operational simplicity and physical accuracy. Through a set of preprocessor directives, the user selects one of the many ITS codes. The ease with which the makefile system is applied combines with an input scheme based on order-independent descriptive keywords that makes maximum use of defaults and internal error checking to provide experimentalists and theorists alike with a method for the routine but rigorous solution of sophisticated radiation transport problems. Physical rigor is provided by employing accurate cross sections, sampling distributions, and physical models for describing the production and transport of the electron/photon cascade from 1.0 GeV down to 1.0 keV. The availability of source code permits the more sophisticated user to tailor the codes to specific applications and to extend the capabilities of the codes to more complex applications. Version 6, the latest version of ITS, contains (1) improvements to the ITS 5.0 codes, and (2) conversion to Fortran 90. The general user friendliness of the software has been enhanced through memory allocation to reduce the need for users to modify and recompile the code.

Franke, Brian Claude; Kensek, Ronald Patrick; Laub, Thomas William

2008-04-01

16

Ant colony algorithm implementation in electron and photon Monte Carlo transport: Application to the commissioning of radiosurgery photon beams  

SciTech Connect

Purpose: In this work, the authors describe an approach which has been developed to drive the application of different variance-reduction techniques to the Monte Carlo simulation of photon and electron transport in clinical accelerators. Methods: The new approach considers the following techniques: Russian roulette, splitting, a modified version of the directional bremsstrahlung splitting, and the azimuthal particle redistribution. Their application is controlled by an ant colony algorithm based on an importance map. Results: The procedure has been applied to radiosurgery beams. Specifically, the authors have calculated depth-dose profiles, off-axis ratios, and output factors, quantities usually considered in the commissioning of these beams. The agreement between Monte Carlo results and the corresponding measurements is within {approx}3%/0.3 mm for the central axis percentage depth dose and the dose profiles. The importance map generated in the calculation can be used to discuss simulation details in the different parts of the geometry in a simple way. The simulation CPU times are comparable to those needed within other approaches common in this field. Conclusions: The new approach is competitive with those previously used in this kind of problems (PSF generation or source models) and has some practical advantages that make it to be a good tool to simulate the radiation transport in problems where the quantities of interest are difficult to obtain because of low statistics.

Garcia-Pareja, S.; Galan, P.; Manzano, F.; Brualla, L.; Lallena, A. M. [Servicio de Radiofisica Hospitalaria, Hospital Regional Universitario ''Carlos Haya'', Avda. Carlos Haya s/n, E-29010 Malaga (Spain); Unidad de Radiofisica Hospitalaria, Hospital Xanit Internacional, Avda. de los Argonautas s/n, E-29630 Benalmadena (Malaga) (Spain); NCTeam, Strahlenklinik, Universitaetsklinikum Essen, Hufelandstr. 55, D-45122 Essen (Germany); Departamento de Fisica Atomica, Molecular y Nuclear, Universidad de Granada, E-18071 Granada (Spain)

2010-07-15

17

Space applications of the MITS electron-photon Monte Carlo transport code system  

SciTech Connect

The MITS multigroup/continuous-energy electron-photon Monte Carlo transport code system has matured to the point that it is capable of addressing more realistic three-dimensional adjoint applications. It is first employed to efficiently predict point doses as a function of source energy for simple three-dimensional experimental geometries exposed to simulated uniform isotropic planar sources of monoenergetic electrons up to 4.0 MeV. Results are in very good agreement with experimental data. It is then used to efficiently simulate dose to a detector in a subsystem of a GPS satellite due to its natural electron environment, employing a relatively complex model of the satellite. The capability for survivability analysis of space systems is demonstrated, and results are obtained with and without variance reduction.

Kensek, R.P.; Lorence, L.J.; Halbleib, J.A. [Sandia National Labs., Albuquerque, NM (United States); Morel, J.E. [Los Alamos National Lab., NM (United States)

1996-07-01

18

Monte Carlo simulation of photon transport in a randomly oriented sphere-cylinder scattering medium  

NASA Astrophysics Data System (ADS)

A Monte Carlo simulation tool for simulating photon transport in a randomly oriented sphere-cylinder medium has been developed. The simulated medium represents a paper pulp suspension where the constituents are assumed to be mono-disperse micro-spheres, representing dispersed fiber fragments, and infinitely long, straight, randomly oriented cylinders representing fibers. The diameter of the micro-spheres is considered to be about the order of the wavelength and is described by Mie scattering theory. The fiber diameter is considerably larger than the wavelength and the photon scattering is therefore determined by an analytical solution of Maxwell's equation for scattering at an infinitely long cylinder. By employing a Stokes-Mueller formalism, the software tracks the polarization of the light while propagating through the medium. The effects of varying volume concentrations and sizes of the scattering components on reflection, transmission and polarization of the incident light are investigated. It is shown that not only the size but also the shape of the particles has a big impact on the depolarization.

Linder, T.; Löfqvist, T.

2011-11-01

19

A method for photon beam Monte Carlo multileaf collimator particle transport.  

PubMed

Monte Carlo (MC) algorithms are recognized as the most accurate methodology for patient dose assessment. For intensity-modulated radiation therapy (IMRT) delivered with dynamic multileaf collimators (DMLCs), accurate dose calculation, even with MC, is challenging. Accurate IMRT MC dose calculations require inclusion of the moving MLC in the MC simulation. Due to its complex geometry, full transport through the MLC can be time consuming. The aim of this work was to develop an MLC model for photon beam MC IMRT dose computations. The basis of the MC MLC model is that the complex MLC geometry can be separated into simple geometric regions, each of which readily lends itself to simplified radiation transport. For photons, only attenuation and first Compton scatter interactions are considered. The amount of attenuation material an individual particle encounters while traversing the entire MLC is determined by adding the individual amounts from each of the simplified geometric regions. Compton scatter is sampled based upon the total thickness traversed. Pair production and electron interactions (scattering and bremsstrahlung) within the MLC are ignored. The MLC model was tested for 6 MV and 18 MV photon beams by comparing it with measurements and MC simulations that incorporate the full physics and geometry for fields blocked by the MLC and with measurements for fields with the maximum possible tongue-and-groove and tongue-or-groove effects, for static test cases and for sliding windows of various widths. The MLC model predicts the field size dependence of the MLC leakage radiation within 0.1% of the open-field dose. The entrance dose and beam hardening behind a closed MLC are predicted within +/- 1% or 1 mm. Dose undulations due to differences in inter- and intra-leaf leakage are also correctly predicted. The MC MLC model predicts leaf-edge tongue-and-groove dose effect within +/- 1% or 1 mm for 95% of the points compared at 6 MV and 88% of the points compared at 18 MV. The dose through a static leaf tip is also predicted generally within +/- 1% or 1 mm. Tests with sliding windows of various widths confirm the accuracy of the MLC model for dynamic delivery and indicate that accounting for a slight leaf position error (0.008 cm for our MLC) will improve the accuracy of the model. The MLC model developed is applicable to both dynamic MLC and segmental MLC IMRT beam delivery and will be useful for patient IMRT dose calculations, pre-treatment verification of IMRT delivery and IMRT portal dose transmission dosimetry. PMID:12361220

Siebers, Jeffrey V; Keall, Paul J; Kim, Jong Oh; Mohan, Radhe

2002-09-01

20

Parallel Monte Carlo Electron and Photon Transport Simulation Code (PMCEPT code)  

NASA Astrophysics Data System (ADS)

Simulations for customized cancer radiation treatment planning for each patient are very useful for both patient and doctor. These simulations can be used to find the most effective treatment with the least possible dose to the patient. This typical system, so called ``Doctor by Information Technology", will be useful to provide high quality medical services everywhere. However, the large amount of computing time required by the well-known general purpose Monte Carlo(MC) codes has prevented their use for routine dose distribution calculations for a customized radiation treatment planning. The optimal solution to provide ``accurate" dose distribution within an ``acceptable" time limit is to develop a parallel simulation algorithm on a beowulf PC cluster because it is the most accurate, efficient, and economic. I developed parallel MC electron and photon transport simulation code based on the standard MPI message passing interface. This algorithm solved the main difficulty of the parallel MC simulation (overlapped random number series in the different processors) using multiple random number seeds. The parallel results agreed well with the serial ones. The parallel efficiency approached 100% as was expected.

Kum, Oyeon

2004-11-01

21

Accuracy of Monte Carlo photon transport simulation in characterizing brachytherapy dosimeter energy-response artefacts  

NASA Astrophysics Data System (ADS)

Practical dosimeters in brachytherapy, such as thermoluminescent dosimeters (TLD) and diodes, are usually calibrated against low-energy megavoltage beams. To measure absolute dose rate near a brachytherapy source, it is necessary to establish the energy response of the detector relative to that of the calibration energy. The purpose of this paper is to assess the accuracy of Monte Carlo photon transport (MCPT) simulation in modelling the absolute detector response as a function of detector geometry and photon energy. We have exposed two different sizes of TLD-100 (LiF chips) and p-type silicon diode detectors to calibrated , HDR source and superficial x-ray beams. For the Scanditronix electron-field diode, the relative detector response, defined as the measured detector readings per measured unit of air kerma, varied from (40 kVp beam) to ( beam). Similarly for the large and small chips the same quantity varied from and , respectively. Monte Carlo simulation was used to calculate the absorbed dose to the active volume of the detector per unit air kerma. If the Monte Carlo simulation is accurate, then the absolute detector response, which is defined as the measured detector reading per unit dose absorbed by the active detector volume, and is calculated by Monte Carlo simulation, should be a constant. For the diode, the absolute response is . For TLDs of size the absolute response is and for TLDs of it is . From the above results we can conclude that the absolute response function of detectors (TLDs and diodes) is directly proportional to absorbed dose by the active volume of the detector and is independent of beam quality.

Das, R. K.; Li, Z.; Perera, H.; Williamson, J. F.

1996-06-01

22

Qualitative Simulation of Photon Transport in Free Space Based on Monte Carlo Method and Its Parallel Implementation  

PubMed Central

During the past decade, Monte Carlo method has obtained wide applications in optical imaging to simulate photon transport process inside tissues. However, this method has not been effectively extended to the simulation of free-space photon transport at present. In this paper, a uniform framework for noncontact optical imaging is proposed based on Monte Carlo method, which consists of the simulation of photon transport both in tissues and in free space. Specifically, the simplification theory of lens system is utilized to model the camera lens equipped in the optical imaging system, and Monte Carlo method is employed to describe the energy transformation from the tissue surface to the CCD camera. Also, the focusing effect of camera lens is considered to establish the relationship of corresponding points between tissue surface and CCD camera. Furthermore, a parallel version of the framework is realized, making the simulation much more convenient and effective. The feasibility of the uniform framework and the effectiveness of the parallel version are demonstrated with a cylindrical phantom based on real experimental results.

Chen, Xueli; Gao, Xinbo; Qu, Xiaochao; Chen, Duofang; Ma, Bin; Wang, Lin; Peng, Kuan; Liang, Jimin; Tian, Jie

2010-01-01

23

Monte Carlo evaluation of kerma at a point for photon transport problems  

SciTech Connect

Estimation of collision kerma at a geometric point arising from scattered photons is a potentially important application of Monte Carlo simulation, especially in the presence of steep flux gradients. We examine the usual method of extracting point-kerma estimates from randomly generated photon trajectories which consists of tallying the energy lost by photon collisions occurring in the vicinity of the point of interest. Several other methods derived from the equivalence of track length per unit volume and flux are evaluated as to accuracy and efficiency. Finally, a next-flight estimator is discussed in which the expected contribution of each simulated photon collision to kerma at the point of interest is calculated regardless of proximity of the collision to the point. All of these techniques are shown to involve a trade-off between statistical precision and spatial resolution: increasing the number of contributing collisions requires averaging kerma over a larger volume. Based upon both analytic models and realistic Monte Carlo simulations, use of next-flight and track-length estimators is shown to improve simulation efficiencies by factors of 2 to 20 compared to analog scoring. Practical guidelines as to choice of estimator and successful implementation are presented.

Williamson, J.F.

1987-07-01

24

Variance reduction unique to coupled electron/photon Monte Carlo transport  

SciTech Connect

The disparity between the mean free paths of electrons and photons leads to unique variance-reduction procedures for the coupled transport at intermediate energies. It is electrons that ultimately deposit charge and energy, yet electron transport is much more expensive than photon transport. The objective, then, is to control the variance of the energy, angular, and spatially dependent populations of the two species within the generation and transport of the cascade in such a way that all contributions to electron flux in the vicinity of the detector are represented to a degree commensurate with their importance. However, in [beta]/[gamma] transport, biasing techniques are often unique to one or the other of the species.

Halbleib, J.A.; Kensek, R.P.; Valdez, G.D.

1993-01-01

25

Development of a GPU-based Monte Carlo dose calculation code for coupled electron-photon transport  

NASA Astrophysics Data System (ADS)

Monte Carlo simulation is the most accurate method for absorbed dose calculations in radiotherapy. Its efficiency still requires improvement for routine clinical applications, especially for online adaptive radiotherapy. In this paper, we report our recent development on a GPU-based Monte Carlo dose calculation code for coupled electron-photon transport. We have implemented the dose planning method (DPM) Monte Carlo dose calculation package (Sempau et al 2000 Phys. Med. Biol. 45 2263-91) on the GPU architecture under the CUDA platform. The implementation has been tested with respect to the original sequential DPM code on the CPU in phantoms with water-lung-water or water-bone-water slab geometry. A 20 MeV mono-energetic electron point source or a 6 MV photon point source is used in our validation. The results demonstrate adequate accuracy of our GPU implementation for both electron and photon beams in the radiotherapy energy range. Speed-up factors of about 5.0-6.6 times have been observed, using an NVIDIA Tesla C1060 GPU card against a 2.27 GHz Intel Xeon CPU processor.

Jia, Xun; Gu, Xuejun; Sempau, Josep; Choi, Dongju; Majumdar, Amitava; Jiang, Steve B.

2010-06-01

26

Accelerating Monte Carlo simulations of photon transport in a voxelized geometry using a massively parallel graphics processing unit  

SciTech Connect

Purpose: It is a known fact that Monte Carlo simulations of radiation transport are computationally intensive and may require long computing times. The authors introduce a new paradigm for the acceleration of Monte Carlo simulations: The use of a graphics processing unit (GPU) as the main computing device instead of a central processing unit (CPU). Methods: A GPU-based Monte Carlo code that simulates photon transport in a voxelized geometry with the accurate physics models from PENELOPE has been developed using the CUDA programming model (NVIDIA Corporation, Santa Clara, CA). Results: An outline of the new code and a sample x-ray imaging simulation with an anthropomorphic phantom are presented. A remarkable 27-fold speed up factor was obtained using a GPU compared to a single core CPU. Conclusions: The reported results show that GPUs are currently a good alternative to CPUs for the simulation of radiation transport. Since the performance of GPUs is currently increasing at a faster pace than that of CPUs, the advantages of GPU-based software are likely to be more pronounced in the future.

Badal, Andreu; Badano, Aldo [Division of Imaging and Applied Mathematics, OSEL, CDRH, U.S. Food and Drug Administration, Silver Spring, Maryland 20993-0002 (United States)

2009-11-15

27

Application of discrete ordinates and Monte Carlo methods to transport of photons from environmental sources  

SciTech Connect

Federal Guidance Report No. 12 tabulates dose coefficients for external exposure to photons and electrons emitted by radionuclides distributed in air, water, and soil. Although the dose coefficients of this report are based on previously developed dosimetric methodologies, they are derived from new, detailed calculations of energy and angular distributions of the radiations incident on the body and the transport of these radiations within the body. Effort was devoted to expanding the information available for assessment of radiation dose from radionuclides distributed on or below the surface of the ground. A companion paper (External Exposure to Radionuclides in Air, Water, and Soil) discusses the significance of the new tabulations of coefficients and provides detiled comparisons to previously published values. This paper discusses details of the photon transport calculations.

Ryman, J.C.; Eckerman, K.F. [Oak Ridge National Lab., TN (United States); Shultis, J.K.; Faw, R.E. [Kansas State Univ., Manhattan, KS (United States). Dept. of Nuclear Engineering; Dillman, L.T. [Ohio Wesleyan Univ., Delaware, OH (United States). Dept. of Physics

1996-04-01

28

ITS version 5.0 : the integrated TIGER series of coupled electron/photon Monte Carlo transport codes.  

SciTech Connect

ITS is a powerful and user-friendly software package permitting state of the art Monte Carlo solution of linear time-independent couple electron/photon radiation transport problems, with or without the presence of macroscopic electric and magnetic fields of arbitrary spatial dependence. Our goal has been to simultaneously maximize operational simplicity and physical accuracy. Through a set of preprocessor directives, the user selects one of the many ITS codes. The ease with which the makefile system is applied combines with an input scheme based on order-independent descriptive keywords that makes maximum use of defaults and internal error checking to provide experimentalists and theorists alike with a method for the routine but rigorous solution of sophisticated radiation transport problems. Physical rigor is provided by employing accurate cross sections, sampling distributions, and physical models for describing the production and transport of the electron/photon cascade from 1.0 GeV down to 1.0 keV. The availability of source code permits the more sophisticated user to tailor the codes to specific applications and to extend the capabilities of the codes to more complex applications. Version 5.0, the latest version of ITS, contains (1) improvements to the ITS 3.0 continuous-energy codes, (2)multigroup codes with adjoint transport capabilities, and (3) parallel implementations of all ITS codes. Moreover the general user friendliness of the software has been enhanced through increased internal error checking and improved code portability.

Franke, Brian Claude; Kensek, Ronald Patrick; Laub, Thomas William

2004-06-01

29

Monte Carlo study of coherent diffuse photon transport in a homogeneous turbid medium: a degree-of-coherence based approach.  

PubMed

We employ a Monte Carlo (MC) algorithm to investigate the decoherence of diffuse photons in turbid media. For the MC simulation of coherent photons, the degree of coherence, defined as a random variable for a photon packet, is associated with a decoherence function that depends on the scattering angle and is updated as a photon interacts with a medium via scattering. Using a slab model, the effects of medium scattering properties were studied, which reveals that a linear random variable model for the degree of coherence is in better agreement with experimental results than a sinusoidal model and that decoherence is quick for the initial few scattering events followed by a slow and gradual decrease of coherence. PMID:18204720

Moon, Seyoung; Kim, Donghyun; Sim, Eunji

2008-01-20

30

The MC21 Monte Carlo Transport Code  

SciTech Connect

MC21 is a new Monte Carlo neutron and photon transport code currently under joint development at the Knolls Atomic Power Laboratory and the Bettis Atomic Power Laboratory. MC21 is the Monte Carlo transport kernel of the broader Common Monte Carlo Design Tool (CMCDT), which is also currently under development. The vision for CMCDT is to provide an automated, computer-aided modeling and post-processing environment integrated with a Monte Carlo solver that is optimized for reactor analysis. CMCDT represents a strategy to push the Monte Carlo method beyond its traditional role as a benchmarking tool or ''tool of last resort'' and into a dominant design role. This paper describes various aspects of the code, including the neutron physics and nuclear data treatments, the geometry representation, and the tally and depletion capabilities.

Sutton TM, Donovan TJ, Trumbull TH, Dobreff PS, Caro E, Griesheimer DP, Tyburski LJ, Carpenter DC, Joo H

2007-01-09

31

Development and implementation of photonuclear cross- section data for mutually coupled neutron-photon transport calculations in the Monte Carlo N-particle (MCNP) radiation transport code  

Microsoft Academic Search

The fundamental motivation for the research presented in this dissertation was the need to develop a more accurate prediction method for characterization of mixed radiation fields around medical electron accelerators (MEAs). Specifically, a model is developed for simulation of neutron and other particle production from photonuclear reactions and incorporated in the Monte Carlo N-Particle (MCNP) radiation transport code. This extension

Morgan Curtis White

2000-01-01

32

Super-Monte Carlo: A photon\\/electron dose calculation algorithm for radiotherapy  

Microsoft Academic Search

Super-Monte Carlo (SMC) is a method of dose calculation for radiotherapy which combines both analytical calculations and Monte Carlo electron transport. Analytical calculations are used where possible, such as the determination of photon interaction density, to decrease computation time. A Monte Carlo method is used for the electron transport in order to obtain high accuracy of results. To further speed

P. J. Keall; P. W. Hoban; M. P. West

1998-01-01

33

Verification of external exposure assessment for the upper Techa riverside by luminescence measurements and Monte Carlo photon transport modeling.  

PubMed

An area located in the Southern Urals was contaminated in 1949-1956 as a result of radioactive waste releases into the Techa river by the Mayak Production Association. The external dose reconstruction of the Techa river dosimetry system (TRDS-2000) for the exposed population is based on an assessment of dose rates in air (DRA) obtained by modeling transport and deposition of radionuclides along the river for the time before 1952 and by gamma dose rate measurements since 1952. The aim of this paper is to contribute to a verification of the TRDS-2000 external dose assessment. Absorbed doses in bricks from a 130-year-old building in the heavily exposed Metlino settlement were measured by a luminescence technique. By the autumn of 1956 the population of Metlino had been evacuated, and then a water reservoir was created at the village location, which led to a change in the radioactive source geometry. Radiation transport calculations for assumed environmental sources before and since 1957 were performed with the MCNP Monte Carlo code. In combination with TRDS-2000 estimates for annual dose rates in air at the shore of the Techa river for the period 1949-1956 and contemporary dose rate in air measurements, absorbed doses in bricks were calculated. These calculations were performed deterministically with best estimates of the modeling parameters and stochastically by propagating uncertainty distributions through the calculation scheme. Assessed doses in bricks were found to be consistent with measured values within the uncertainty bounds, while their best estimates were approximately 15% lower than the luminescence measurements. PMID:12687379

Taranenko, V; Meckbach, R; Degteva, M O; Bougrov, N G; Göksu, Y; Vorobiova, M I; Jacob, P

2003-04-10

34

ITS version 5.0 :the integrated TIGER series of coupled electron/Photon monte carlo transport codes with CAD geometry.  

SciTech Connect

ITS 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. Our goal has been to simultaneously maximize operational simplicity and physical accuracy. Through a set of preprocessor directives, the user selects one of the many ITS codes. The ease with which the makefile system is applied combines with an input scheme based on order-independent descriptive keywords that makes maximum use of defaults and internal error checking to provide experimentalists and theorists alike with a method for the routine but rigorous solution of sophisticated radiation transport problems. Physical rigor is provided by employing accurate cross sections, sampling distributions, and physical models for describing the production and transport of the electron/photon cascade from 1.0 GeV down to 1.0 keV. The availability of source code permits the more sophisticated user to tailor the codes to specific applications and to extend the capabilities of the codes to more complex applications. Version 5.0, the latest version of ITS, contains (1) improvements to the ITS 3.0 continuous-energy codes, (2) multigroup codes with adjoint transport capabilities, (3) parallel implementations of all ITS codes, (4) a general purpose geometry engine for linking with CAD or other geometry formats, and (5) the Cholla facet geometry library. Moreover, the general user friendliness of the software has been enhanced through increased internal error checking and improved code portability.

Franke, Brian Claude; Kensek, Ronald Patrick; Laub, Thomas William

2005-09-01

35

Treatment of Compton scattering of linearly polarized photons in Monte Carlo codes  

Microsoft Academic Search

The basic formalism of Compton scattering of linearly polarized photons is reviewed, and some simple prescriptions to deal with the transport of polarized photons in Monte Carlo simulation codes are given. Fortran routines, based on the described method, have been included in MCNP, a widely used code for neutrons, photons and electrons transport. As this improved version of the code

Giorgio Matt; Marco Feroci; Massimo Rapisarda; Enrico Costa

1996-01-01

36

PHOTON – An optical Monte Carlo code for simulating scintillation detector responses  

Microsoft Academic Search

A Monte Carlo code, PHOTON, has been developed to simulate optical photon transport in scintillation detectors. The code supports arbitrarily complex geometry models, flexible models for material and surface properties specification, detailed treatment of complex refractive index materials, thin-film surface coatings and interactive simulation with graphical display. This paper concentrates on the photon transport simulation and a simple benchmarking study,

James Tickner; Greg Roach

2007-01-01

37

Modified Monte Carlo Procedure for Particle Transport Problems.  

National Technical Information Service (NTIS)

The simulation of photon transport in the atmosphere with the Monte Carlo method forms part of the EURASEP-programme. The specifications for the problems posed for a solution were such that the direct application of the analogue Monte Carlo method was not...

W. Matthes

1978-01-01

38

Integrated Tiger Series of electron/photon Monte Carlo transport codes: a user's guide for use on IBM mainframes  

SciTech Connect

The ITS (Integrated Tiger Series) Monte Carlo code package developed at Sandia National Laboratories and distributed as CCC-467/ITS by the Radiation Shielding Information Center (RSIC) at Oak Ridge National Laboratory (ORNL) consists of eight codes - the standard codes, TIGER, CYLTRAN, ACCEPT; the P-codes, TIGERP, CYLTRANP, ACCEPTP; and the M-codes ACCEPTM, CYLTRANM. The codes have been adapted to run on the IBM 3081, VAX 11/780, CDC-7600, and Cray 1 with the use of the update emulator UPEML. This manual should serve as a guide to a user running the codes on IBM computers having 370 architecture. The cases listed were tested on the IBM 3033, under the MVS operating system using the VS Fortran Level 1.3.1 compiler.

Kirk, B.L.

1985-12-01

39

PHOTON An optical Monte Carlo code for simulating scintillation detector responses  

NASA Astrophysics Data System (ADS)

A Monte Carlo code, PHOTON, has been developed to simulate optical photon transport in scintillation detectors. The code supports arbitrarily complex geometry models, flexible models for material and surface properties specification, detailed treatment of complex refractive index materials, thin-film surface coatings and interactive simulation with graphical display. This paper concentrates on the photon transport simulation and a simple benchmarking study, comparing the experimental and calculated light yields from a rectangular plastic scintillator block.

Tickner, James; Roach, Greg

2007-10-01

40

Optimization of the Monte Carlo code for modeling of photon migration in tissue  

Microsoft Academic Search

The Monte Carlo method is frequently used to simulate light transport in turbid media because of its simplicity and flexibility, allowing to analyze complicated geometrical structures. Monte Carlo simulations are, however, time consuming because of the necessity to track the paths of individual photons. The time consuming computation is mainly associated with the calculation of the logarithmic and trigonometric functions

Norbert S. Zolek; Adam Liebert; Roman Maniewski

2006-01-01

41

Investigation of variance reduction techniques for Monte Carlo photon dose calculation using XVMC  

Microsoft Academic Search

Several variance reduction techniques, such as photon splitting, electron history repetition, Russian roulette and the use of quasi-random numbers are investigated and shown to significantly improve the efficiency of the recently developed XVMC Monte Carlo code for photon beams in radiation therapy. It is demonstrated that it is possible to further improve the efficiency by optimizing transport parameters such as

Iwan Kawrakow; Matthias Fippel

2000-01-01

42

Automated Monte Carlo biasing for photon-generated electrons near surfaces.  

SciTech Connect

This report describes efforts to automate the biasing of coupled electron-photon Monte Carlo particle transport calculations. The approach was based on weight-windows biasing. Weight-window settings were determined using adjoint-flux Monte Carlo calculations. A variety of algorithms were investigated for adaptivity of the Monte Carlo tallies. Tree data structures were used to investigate spatial partitioning. Functional-expansion tallies were used to investigate higher-order spatial representations.

Franke, Brian Claude; Crawford, Martin James; Kensek, Ronald Patrick

2009-09-01

43

THE MCNPX MONTE CARLO RADIATION TRANSPORT CODE  

SciTech Connect

MCNPX (Monte Carlo N-Particle eXtended) is a general-purpose Monte Carlo radiation transport code with three-dimensional geometry and continuous-energy transport of 34 particles and light ions. It contains flexible source and tally options, interactive graphics, and support for both sequential and multi-processing computer platforms. MCNPX is based on MCNP4B, and has been upgraded to most MCNP5 capabilities. MCNP is a highly stable code tracking neutrons, photons and electrons, and using evaluated nuclear data libraries for low-energy interaction probabilities. MCNPX has extended this base to a comprehensive set of particles and light ions, with heavy ion transport in development. Models have been included to calculate interaction probabilities when libraries are not available. Recent additions focus on the time evolution of residual nuclei decay, allowing calculation of transmutation and delayed particle emission. MCNPX is now a code of great dynamic range, and the excellent neutronics capabilities allow new opportunities to simulate devices of interest to experimental particle physics; particularly calorimetry. This paper describes the capabilities of the current MCNPX version 2.6.C, and also discusses ongoing code development.

WATERS, LAURIE S. [Los Alamos National Laboratory; MCKINNEY, GREGG W. [Los Alamos National Laboratory; DURKEE, JOE W. [Los Alamos National Laboratory; FENSIN, MICHAEL L. [Los Alamos National Laboratory; JAMES, MICHAEL R. [Los Alamos National Laboratory; JOHNS, RUSSELL C. [Los Alamos National Laboratory; PELOWITZ, DENISE B. [Los Alamos National Laboratory

2007-01-10

44

Fast photon-boundary intersection computation for Monte Carlo simulation of photon migration  

NASA Astrophysics Data System (ADS)

Monte Carlo (MC) method is generally used as a "gold standard" technique to simulate photon transport in biomedical optics. However, it is quite time-consuming since abundant photon propagations need to be simulated in order to achieve an accurate result. In the case of complicated geometry, the computation speed is bound up with the calculation of the intersection between the photon transmission path and media boundary. The ray-triangle-based method is often used to calculate the photon-boundary intersection in the shape-based MC simulation for light propagation, but it is still relatively time-consuming. We present a fast way to determine the photon-boundary intersection. Triangle meshes are used to describe the boundary structure. A line segment instead of a ray is used to check if there exists a photon-boundary intersection, as the next location of the photon in light transports is determined by the step size. Results suggest that by simply replacing the conventional ray-triangle-based method with the proposed line segment-triangle-based method, the MC simulation for light propagation in the mouse model can be speeded up by more than 35%.

Zhao, Xiaofen; Liu, Hongyan; Zhang, Bin; Liu, Fei; Luo, Jianwen; Bai, Jing

2013-01-01

45

Improved geometry representations for Monte Carlo radiation transport.  

SciTech Connect

ITS (Integrated Tiger Series) permits a state-of-the-art Monte Carlo solution of linear time-integrated coupled electron/photon radiation transport problems with or without the presence of macroscopic electric and magnetic fields of arbitrary spatial dependence. ITS allows designers to predict product performance in radiation environments.

Martin, Matthew Ryan (Cornell University)

2004-08-01

46

Applications of the Monte Carlo radiation transport toolkit at LLNL  

Microsoft Academic Search

Modern Monte Carlo radiation transport codes can be applied to model most applications of radiation, from optical to TeV photons, from thermal neutrons to heavy ions. Simulations can include any desired level of detail in three-dimensional geometries using the right level of detail in the reaction physics. The technology areas to which we have applied these codes include medical applications,

Kenneth E. Sale; Paul M. Bergstrom; Richard M. Buck; Dermot Cullen; D. Fujino; Christine Hartmann-Siantar

1999-01-01

47

Patient-dependent beam-modifier physics in Monte Carlo photon dose calculations  

Microsoft Academic Search

Model pencil-beam on slab calculations are used as well as a series of detailed calculations of photon and electron output from commercial accelerators to quantify level(s) of physics required for the Monte Carlo transport of photons and electrons in treatment-dependent beam modifiers, such as jaws, wedges, blocks, and multileaf collimators, in photon teletherapy dose calculations. The physics approximations investigated comprise

A. E. Schach von Wittenau; P. M. Jr. Bergstrom; L. J. Cox

2000-01-01

48

Coupled electron-photon radiation transport  

SciTech Connect

Massively-parallel computers allow detailed 3D radiation transport simulations to be performed to analyze the response of complex systems to radiation. This has been recently been demonstrated with the coupled electron-photon Monte Carlo code, ITS. To enable such calculations, the combinatorial geometry capability of ITS was improved. For greater geometrical flexibility, a version of ITS is under development that can track particles in CAD geometries. Deterministic radiation transport codes that utilize an unstructured spatial mesh are also being devised. For electron transport, the authors are investigating second-order forms of the transport equations which, when discretized, yield symmetric positive definite matrices. A novel parallelization strategy, simultaneously solving for spatial and angular unknowns, has been applied to the even- and odd-parity forms of the transport equation on a 2D unstructured spatial mesh. Another second-order form, the self-adjoint angular flux transport equation, also shows promise for electron transport.

Lorence, L.; Kensek, R.P.; Valdez, G.D.; Drumm, C.R.; Fan, W.C.; Powell, J.L.

2000-01-17

49

The use of Monte Carlo radiation transport codes in radiation physics and dosimetry  

Microsoft Academic Search

Transport and interaction of electromagnetic radiation Interaction models and simulation schemes implemented in modern Monte Carlo codes for the simulation of coupled electron-photon transport will be briefly reviewed. In these codes, photon transport is simulated by using the detailed scheme, i.e., interaction by interaction. Detailed simulation is easy to implement, and the reliability of the results is only limited by

F Salvat-Gavada; Alfredo Ferrari; Marco Silari

2006-01-01

50

Vectorization of Monte Carlo particle transport  

SciTech Connect

Fully vectorized versions of the Los Alamos National Laboratory benchmark code Gamteb, a Monte Carlo photon transport algorithm, were developed for the Cyber 205/ETA-10 and Cray X-MP/Y-MP architectures. Single-processor performance measurements of the vector and scalar implementations were modeled in a modified Amdahl's Law that accounts for additional data motion in the vector code. The performance and implementation strategy of the vector codes are related to architectural features of each machine. Speedups between fifteen and eighteen for Cyber 205/ETA-10 architectures, and about nine for CRAY X-MP/Y-MP architectures are observed. The best single processor execution time for the problem was 0.33 seconds on the ETA-10G, and 0.42 seconds on the CRAY Y-MP. 32 refs., 12 figs., 1 tab.

Burns, P.J.; Christon, M.; Schweitzer, R.; Lubeck, O.M.; Wasserman, H.J.; Simmons, M.L.; Pryor, D.V. (Colorado State Univ., Fort Collins, CO (USA). Computer Center; Los Alamos National Lab., NM (USA); Supercomputing Research Center, Bowie, MD (USA))

1989-01-01

51

Full-band Monte Carlo simulation of high-energy carrier transport in single photon avalanche diodes with multiplication layers made of InP, InAlAs, and GaAs  

NASA Astrophysics Data System (ADS)

We investigate the high-energy charge dynamics of electrons and holes in the multiplication process of single photon avalanche diodes. The technologically important multiplication layer materials InP and In0.52Al0.48As, used in near infrared photon detectors, are analyzed and compared with GaAs. We use the full-band Monte Carlo technique to solve the Boltzmann transport equation which improves the state-of-the-art treatment of high-field carrier transport in the multiplication process. As a result of the computationally efficient treatment of the scattering rates and the parallel central processing unit power of modern computer clusters, the full-band Monte Carlo calculation of the breakdown characteristics has become feasible. The breakdown probability features a steeper rise versus the reverse bias for smaller multiplication layer widths for InP, In0.52Al0.48As, and GaAs. Both the time to avalanche breakdown and jitter decrease with shrinking size of the multiplication region for the three examined III-V semiconductors.

Dolgos, Denis; Meier, Hektor; Schenk, Andreas; Witzigmann, Bernd

2012-05-01

52

Fast Monte Carlo dose calculation for photon beams based on the VMC electron algorithm.  

PubMed

A new Monte Carlo algorithm for 3D photon dose calculation in radiation therapy is presented, which is based on the previously developed Voxel Monte Carlo (VMC) for electron beams. The main result is that this new version of VMC (now called XVMC) is more efficient than EGS4/PRESTA photon dose calculation by a factor of 15-20. Therefore, a standard treatment plan for photons can be calculated by Monte Carlo in about 20 min. on a "normal" personal computer. The improvement is caused mainly by the fast electron transport algorithm and ray tracing technique, and an initial ray tracing method to calculate the number of electrons created in each voxel by the primary photon beam. The model was tested in comparison to calculations by EGS4 using several fictive phantoms. In most cases a good coincidence has been found between both codes. Only within lung substitute dose differences have been observed. PMID:10501045

Fippel, M

1999-08-01

53

NOTE: An efficient framework for photon Monte Carlo treatment planning  

NASA Astrophysics Data System (ADS)

Currently photon Monte Carlo treatment planning (MCTP) for a patient stored in the patient database of a treatment planning system (TPS) can usually only be performed using a cumbersome multi-step procedure where many user interactions are needed. This means automation is needed for usage in clinical routine. In addition, because of the long computing time in MCTP, optimization of the MC calculations is essential. For these purposes a new graphical user interface (GUI)-based photon MC environment has been developed resulting in a very flexible framework. By this means appropriate MC transport methods are assigned to different geometric regions by still benefiting from the features included in the TPS. In order to provide a flexible MC environment, the MC particle transport has been divided into different parts: the source, beam modifiers and the patient. The source part includes the phase-space source, source models and full MC transport through the treatment head. The beam modifier part consists of one module for each beam modifier. To simulate the radiation transport through each individual beam modifier, one out of three full MC transport codes can be selected independently. Additionally, for each beam modifier a simple or an exact geometry can be chosen. Thereby, different complexity levels of radiation transport are applied during the simulation. For the patient dose calculation, two different MC codes are available. A special plug-in in Eclipse providing all necessary information by means of Dicom streams was used to start the developed MC GUI. The implementation of this framework separates the MC transport from the geometry and the modules pass the particles in memory; hence, no files are used as the interface. The implementation is realized for 6 and 15 MV beams of a Varian Clinac 2300 C/D. Several applications demonstrate the usefulness of the framework. Apart from applications dealing with the beam modifiers, two patient cases are shown. Thereby, comparisons are performed between MC calculated dose distributions and those calculated by a pencil beam or the AAA algorithm. Interfacing this flexible and efficient MC environment with Eclipse allows a widespread use for all kinds of investigations from timing and benchmarking studies to clinical patient studies. Additionally, it is possible to add modules keeping the system highly flexible and efficient. This work was presented in part at the First European Workshop on Monte Carlo Treatment Planning (EWG-MCTP) held in Gent, Belgium from 22 to 25 October 2006.

Fix, Michael K.; Manser, Peter; Frei, Daniel; Volken, Werner; Mini, Roberto; Born, Ernst J.

2007-09-01

54

MCNP photon transport benchmarking calculations performed at SRP. Revision 1  

SciTech Connect

Monte Carlo methods have long been used at the Savannah River Laboratory (SRL) to perform criticality calculations for many different processes. To perform transport analyses (both neutron and photon) a two-dimensional infinite lattice integral transport code (GLASS) has been used. The neutron transport portion of the code has been benchmarked against other codes and experimental data. The photon transport portion of the code, which is used to calculate gamma redistribution in the event of a loss of moderator and/or coolant, had not been benchmarked against either. For this reason, the Monte Carlo code MCNP was used to benchmark the photon transport portion of the GLASS code. Preceding this, a brief description of the geometry of the Savannah River Plant`s (SRP) reactor cores and how they were modeled using MCNP will be given.

White, A.M.

1989-12-31

55

Conformal photon-beam therapy with transverse magnetic fields: Monte Carlo study  

Microsoft Academic Search

This work studies the use of strong transverse magnetic (B) fields with high-energy photon beams to enhance dose distributions for conformal radiotherapy. EGS4 Monte Carlo code is modified to incorporate charged particle transport in B fields and is used to calculate effects of B fields on dose distributions for a variety of high-energy photon beams. Two types of hypothetical B

X. Allen Li; L. Reiffel; J. Chu; S. Naqvi

2000-01-01

56

Implict Monte Carlo Radiation Transport Simulations of Four Test Problems  

SciTech Connect

Radiation transport codes, like almost all codes, are difficult to develop and debug. It is helpful to have small, easy to run test problems with known answers to use in development and debugging. It is also prudent to re-run test problems periodically during development to ensure that previous code capabilities have not been lost. We describe four radiation transport test problems with analytic or approximate analytic answers. These test problems are suitable for use in debugging and testing radiation transport codes. We also give results of simulations of these test problems performed with an Implicit Monte Carlo photonics code.

Gentile, N

2007-08-01

57

The MCNPX Monte Carlo Radiation Transport Code  

Microsoft Academic Search

MCNPX (Monte Carlo N-Particle eXtended) is a general-purpose Monte Carlo radiation transport code with three-dimensional geometry and continuous-energy transport of 34 particles and light ions. It contains flexible source and tally options, interactive graphics, and support for both sequential and multi-processing computer platforms. MCNPX is based on MCNP4c and has been upgraded to most MCNP5 capabilities. MCNP is a highly

Laurie S. Waters; Gregg W. McKinney; Joe W. Durkee; Michael L. Fensin; John S. Hendricks; Michael R. James; Russell C. Johns; Denise B. Pelowitz

2007-01-01

58

An efficient framework for photon Monte Carlo treatment planning.  

PubMed

Currently photon Monte Carlo treatment planning (MCTP) for a patient stored in the patient database of a treatment planning system (TPS) can usually only be performed using a cumbersome multi-step procedure where many user interactions are needed. This means automation is needed for usage in clinical routine. In addition, because of the long computing time in MCTP, optimization of the MC calculations is essential. For these purposes a new graphical user interface (GUI)-based photon MC environment has been developed resulting in a very flexible framework. By this means appropriate MC transport methods are assigned to different geometric regions by still benefiting from the features included in the TPS. In order to provide a flexible MC environment, the MC particle transport has been divided into different parts: the source, beam modifiers and the patient. The source part includes the phase-space source, source models and full MC transport through the treatment head. The beam modifier part consists of one module for each beam modifier. To simulate the radiation transport through each individual beam modifier, one out of three full MC transport codes can be selected independently. Additionally, for each beam modifier a simple or an exact geometry can be chosen. Thereby, different complexity levels of radiation transport are applied during the simulation. For the patient dose calculation, two different MC codes are available. A special plug-in in Eclipse providing all necessary information by means of Dicom streams was used to start the developed MC GUI. The implementation of this framework separates the MC transport from the geometry and the modules pass the particles in memory; hence, no files are used as the interface. The implementation is realized for 6 and 15 MV beams of a Varian Clinac 2300 C/D. Several applications demonstrate the usefulness of the framework. Apart from applications dealing with the beam modifiers, two patient cases are shown. Thereby, comparisons are performed between MC calculated dose distributions and those calculated by a pencil beam or the AAA algorithm. Interfacing this flexible and efficient MC environment with Eclipse allows a widespread use for all kinds of investigations from timing and benchmarking studies to clinical patient studies. Additionally, it is possible to add modules keeping the system highly flexible and efficient. PMID:17881793

Fix, Michael K; Manser, Peter; Frei, Daniel; Volken, Werner; Mini, Roberto; Born, Ernst J

2007-09-14

59

Patient-dependent beam-modifier physics in Monte Carlo photon dose calculations  

SciTech Connect

Model pencil-beam on slab calculations are used as well as a series of detailed calculations of photon and electron output from commercial accelerators to quantify level(s) of physics required for the Monte Carlo transport of photons and electrons in treatment-dependent beam modifiers, such as jaws, wedges, blocks, and multileaf collimators, in photon teletherapy dose calculations. The physics approximations investigated comprise (1) not tracking particles below a given kinetic energy, (2) continuing to track particles, but performing simplified collision physics, particularly in handling secondary particle production, and (3) not tracking particles in specific spatial regions. Figures-of-merit needed to estimate the effects of these approximations are developed, and these estimates are compared with full-physics Monte Carlo calculations of the contribution of the collimating jaws to the on-axis depth-dose curve in a water phantom. These figures of merit are next used to evaluate various approximations used in coupled photon/electron physics in beam modifiers. Approximations for tracking electrons in air are then evaluated. It is found that knowledge of the materials used for beam modifiers, of the energies of the photon beams used, as well as of the length scales typically found in photon teletherapy plans, allows a number of simplifying approximations to be made in the Monte Carlo transport of secondary particles from the accelerator head and beam modifiers to the isocenter plane. (c)

Schach von Wittenau, A. E. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Bergstrom, P. M. Jr. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Cox, L. J. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)

2000-05-01

60

Parallel processing Monte Carlo radiation transport codes  

SciTech Connect

Issues related to distributed-memory multiprocessing as applied to Monte Carlo radiation transport are discussed. Measurements of communication overhead are presented for the radiation transport code MCNP which employs the communication software package PVM, and average efficiency curves are provided for a homogeneous virtual machine.

McKinney, G.W.

1994-02-01

61

Overview of Monte Carlo radiation transport codes  

Microsoft Academic Search

The Radiation Safety Information Computational Center (RSICC) is the designated central repository of the United States Department of Energy (DOE) for nuclear software in radiation transport, safety, and shielding. Since the center was established in the early 60’s, there have been several Monte Carlo (MC) particle transport computer codes contributed by scientists from various countries. An overview of the neutron

B. L. Kirk; Bernadette Lugue

2010-01-01

62

Parallel processing Monte Carlo radiation transport codes  

Microsoft Academic Search

Issues related to distributed-memory multiprocessing as applied to Monte Carlo radiation transport are discussed. Measurements of communication overhead are presented for the radiation transport code MCNP which employs the communication software package PVM, and average efficiency curves are provided for a homogeneous virtual machine.

1994-01-01

63

Overview of Monte Carlo radiation transport codes  

SciTech Connect

The Radiation Safety Information Computational Center (RSICC) is the designated central repository of the United States Department of Energy (DOE) for nuclear software in radiation transport, safety, and shielding. Since the center was established in the early 60's, there have been several Monte Carlo particle transport (MC) computer codes contributed by scientists from various countries. An overview of the neutron transport computer codes in the RSICC collection is presented.

Kirk, Bernadette Lugue [ORNL

2010-01-01

64

A NEW MONTE CARLO METHOD FOR TIME-DEPENDENT NEUTRINO RADIATION TRANSPORT  

SciTech Connect

Monte Carlo approaches to radiation transport have several attractive properties such as simplicity of implementation, high accuracy, and good parallel scaling. Moreover, Monte Carlo methods can handle complicated geometries and are relatively easy to extend to multiple spatial dimensions, which makes them potentially interesting in modeling complex multi-dimensional astrophysical phenomena such as core-collapse supernovae. The aim of this paper is to explore Monte Carlo methods for modeling neutrino transport in core-collapse supernovae. We generalize the Implicit Monte Carlo photon transport scheme of Fleck and Cummings and gray discrete-diffusion scheme of Densmore et al. to energy-, time-, and velocity-dependent neutrino transport. Using our 1D spherically-symmetric implementation, we show that, similar to the photon transport case, the implicit scheme enables significantly larger timesteps compared with explicit time discretization, without sacrificing accuracy, while the discrete-diffusion method leads to significant speed-ups at high optical depth. Our results suggest that a combination of spectral, velocity-dependent, Implicit Monte Carlo and discrete-diffusion Monte Carlo methods represents a robust approach for use in neutrino transport calculations in core-collapse supernovae. Our velocity-dependent scheme can easily be adapted to photon transport.

Abdikamalov, Ernazar; Ott, Christian D.; O'Connor, Evan [TAPIR, California Institute of Technology, MC 350-17, 1200 E California Blvd., Pasadena, CA 91125 (United States); Burrows, Adam; Dolence, Joshua C. [Department of Astrophysical Sciences, Princeton University, Peyton Hall, Ivy Lane, Princeton, NJ 08544 (United States); Loeffler, Frank; Schnetter, Erik, E-mail: abdik@tapir.caltech.edu [Center for Computation and Technology, Louisiana State University, 216 Johnston Hall, Baton Rouge, LA 70803 (United States)

2012-08-20

65

A New Monte Carlo Method for Time-dependent Neutrino Radiation Transport  

NASA Astrophysics Data System (ADS)

Monte Carlo approaches to radiation transport have several attractive properties such as simplicity of implementation, high accuracy, and good parallel scaling. Moreover, Monte Carlo methods can handle complicated geometries and are relatively easy to extend to multiple spatial dimensions, which makes them potentially interesting in modeling complex multi-dimensional astrophysical phenomena such as core-collapse supernovae. The aim of this paper is to explore Monte Carlo methods for modeling neutrino transport in core-collapse supernovae. We generalize the Implicit Monte Carlo photon transport scheme of Fleck & Cummings and gray discrete-diffusion scheme of Densmore et al. to energy-, time-, and velocity-dependent neutrino transport. Using our 1D spherically-symmetric implementation, we show that, similar to the photon transport case, the implicit scheme enables significantly larger timesteps compared with explicit time discretization, without sacrificing accuracy, while the discrete-diffusion method leads to significant speed-ups at high optical depth. Our results suggest that a combination of spectral, velocity-dependent, Implicit Monte Carlo and discrete-diffusion Monte Carlo methods represents a robust approach for use in neutrino transport calculations in core-collapse supernovae. Our velocity-dependent scheme can easily be adapted to photon transport.

Abdikamalov, Ernazar; Burrows, Adam; Ott, Christian D.; Löffler, Frank; O'Connor, Evan; Dolence, Joshua C.; Schnetter, Erik

2012-08-01

66

MCNP (Monte Carlo Neutron Photon) capabilities for nuclear well logging calculations  

SciTech Connect

The Los Alamos Radiation Transport Code System (LARTCS) consists of state-of-the-art Monte Carlo and discrete ordinates transport codes and data libraries. The general-purpose continuous-energy Monte Carlo code MCNP (Monte Carlo Neutron Photon), part of the LARTCS, provides a computational predictive capability for many applications of interest to the nuclear well logging community. The generalized three-dimensional geometry of MCNP is well suited for borehole-tool models. SABRINA, another component of the LARTCS, is a graphics code that can be used to interactively create a complex MCNP geometry. Users can define many source and tally characteristics with standard MCNP features. The time-dependent capability of the code is essential when modeling pulsed sources. Problems with neutrons, photons, and electrons as either single particle or coupled particles can be calculated with MCNP. The physics of neutron and photon transport and interactions is modeled in detail using the latest available cross-section data. A rich collections of variance reduction features can greatly increase the efficiency of a calculation. MCNP is written in FORTRAN 77 and has been run on variety of computer systems from scientific workstations to supercomputers. The next production version of MCNP will include features such as continuous-energy electron transport and a multitasking option. Areas of ongoing research of interest to the well logging community include angle biasing, adaptive Monte Carlo, improved discrete ordinates capabilities, and discrete ordinates/Monte Carlo hybrid development. Los Alamos has requested approval by the Department of Energy to create a Radiation Transport Computational Facility under their User Facility Program to increase external interactions with industry, universities, and other government organizations. 21 refs.

Forster, R.A.; Little, R.C.; Briesmeister, J.F.

1989-01-01

67

Particle Monte Carlo Transport in HYDRA  

Microsoft Academic Search

Accurate simulation of diagnostics for thermonuclear burn requires detailed modeling of the spatial and energy distributions of particle sources, in-flight reaction kinematics, and Doppler effects. In the ALE multiphysics code HYDRA, this is now achieved using a new Monte Carlo particle transport package based on LLNL's Arrakis library. It tracks neutrons, gammas, and light ions on 2D quadrilateral and 3D

S. M. Sepke; M. V. Patel; M. M. Marinak; M. S. McKinley; M. J. O'Brien; R. J. Procassini

2010-01-01

68

Morse Monte Carlo Radiation Transport Code System  

Microsoft Academic Search

The report contains sections containing descriptions of the MORSE and PICTURE codes, input descriptions, sample problems, deviations of the physical equations and explanations of the various error messages. The MORSE code is a multipurpose neutron and gamma-ray transport Monte Carlo code. Time dependence for both shielding and criticality problems is provided. General three-dimensional geometry may be used with an albedo

Emmett

1975-01-01

69

Applications of the Monte Carlo radiation transport toolkit at LLNL  

NASA Astrophysics Data System (ADS)

Modern Monte Carlo radiation transport codes can be applied to model most applications of radiation, from optical to TeV photons, from thermal neutrons to heavy ions. Simulations can include any desired level of detail in three-dimensional geometries using the right level of detail in the reaction physics. The technology areas to which we have applied these codes include medical applications, defense, safety and security programs, nuclear safeguards and industrial and research system design and control. The main reason such applications are interesting is that by using these tools substantial savings of time and effort (i.e. money) can be realized. In addition it is possible to separate out and investigate computationally effects which can not be isolated and studied in experiments. In model calculations, just as in real life, one must take care in order to get the correct answer to the right question. Advancing computing technology allows extensions of Monte Carlo applications in two directions. First, as computers become more powerful more problems can be accurately modeled. Second, as computing power becomes cheaper Monte Carlo methods become accessible more widely. An overview of the set of Monte Carlo radiation transport tools in use a LLNL will be presented along with a few examples of applications and future directions.

Sale, Kenneth E.; Bergstrom, Paul M.; Buck, Richard M.; Cullen, Dermot; Fujino, D.; Hartmann-Siantar, Christine

1999-09-01

70

Hybrid Monte-Carlo method for simulating neutron and photon radiography  

NASA Astrophysics Data System (ADS)

We present a Hybrid Monte-Carlo method (HMCM) for simulating neutron and photon radiographs. HMCM utilizes the combination of a Monte-Carlo particle simulation for calculating incident film radiation and a statistical post-processing routine to simulate film noise. Since the method relies on MCNP for transport calculations, it is easily generalized to most non-destructive evaluation (NDE) simulations. We verify the method's accuracy through ASTM International's E592-99 publication, Standard Guide to Obtainable Equivalent Penetrameter Sensitivity for Radiography of Steel Plates [1]. Potential uses for the method include characterizing alternative radiological sources and simulating NDE radiographs.

Wang, Han; Tang, Vincent

2013-11-01

71

Simulation of Photon, Exciton and Charge Transports in Organic Photovoltaics based on the Dynamic Monte Carlo Method coupled with the Maxwell Equation  

NASA Astrophysics Data System (ADS)

Organic photovoltaics(OPVs) have received increasing attention as alternatives to inorganic solar cells. To understand the physics of OPVs, the dynamic Monte Carlo(DMC) method for simulating exciton and charge carrier movements has been regarded as a suitable method. However, simulation of light absorption has been ignored. We presented a simulation of the performance of OPVs by DMC method with solving the Maxwell equation for light absorption. We especially focused on the ordered bulk heterojunction(OBHJ) OPV which is composed of P3HT and PCBM. Our analysis indicated that locations of light absorption are different at different wavelength, which suggests that the simulation of light absorption is essential. In the wavelength of 300 to 400 nm, light absorption occurred dominantly nearby the interface between the P3HT and PCBM. This implies that the generated exciton can be more efficiently dissociated into the free charges. For wavelength longer than 400 nm, most of light are absorbed away from the interface between the P3HT and PCBM. As a result of this, the internal quantum efficiencies gradually decrease from 44.6% to 30.2% as the wavelength increases from 300 to 700 nm.

Jung, Buyoung

2012-02-01

72

Photon beam characterization and modelling for Monte Carlo treatment planning  

NASA Astrophysics Data System (ADS)

Photon beams of 4, 6 and 15 MV from Varian Clinac 2100C and 2300C/D accelerators were simulated using the EGS4/BEAM code system. The accelerators were modelled as a combination of component modules (CMs) consisting of a target, primary collimator, exit window, flattening filter, monitor chamber, secondary collimator, ring collimator, photon jaws and protection window. A full phase space file was scored directly above the upper photon jaws and analysed using beam data processing software, BEAMDP, to derive the beam characteristics, such as planar fluence, angular distribution, energy spectrum and the fractional contributions of each individual CM. A multiple-source model has been further developed to reconstruct the original phase space. Separate sources were created with accurate source intensity, energy, fluence and angular distributions for the target, primary collimator and flattening filter. Good agreement (within 2%) between the Monte Carlo calculations with the source model and those with the original phase space was achieved in the dose distributions for field sizes of 4 cm × 4 cm to 40 cm × 40 cm at source surface distances (SSDs) of 80-120 cm. The dose distributions in lung and bone heterogeneous phantoms have also been found to be in good agreement (within 2%) for 4, 6 and 15 MV photon beams for various field sizes between the Monte Carlo calculations with the source model and those with the original phase space.

Deng, Jun; Jiang, Steve B.; Kapur, Ajay; Li, Jinsheng; Pawlicki, Todd; Ma, C.-M.

2000-02-01

73

TOPICAL REVIEW: Monte Carlo modelling of external radiotherapy photon beams  

Microsoft Academic Search

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

Frank Verhaegen; Jan Seuntjens

2003-01-01

74

3D extension of the Monte Carlo code MCSHAPE for photon–matter interactions in heterogeneous media  

Microsoft Academic Search

MCSHAPE is a Monte Carlo code for the simulation of gamma and X-ray diffusion in matter which gives a general description of the evolution of the polarisation state of the photons. The model is derived from the so-called ‘vector’ transport equation. The three-dimensional (3D) version of the code can accurately simulate the propagation of photons in heterogeneous media originating from

V. Scot; J. E. Fernandez; L. Vincze; K. Janssens

2007-01-01

75

Advantages of Analytical Transformations in Monte Carlo Methods for Radiation Transport  

SciTech Connect

Monte Carlo methods for radiation transport typically attempt to solve an integral by directly sampling analog or weighted particles, which are treated as physical entities. Improvements to the methods involve better sampling, probability games or physical intuition about the problem. We show that significant improvements can be achieved by recasting the equations with an analytical transform to solve for new, non-physical entities or fields. This paper looks at one such transform, the difference formulation for thermal photon transport, showing a significant advantage for Monte Carlo solution of the equations for time dependent transport. Other related areas are discussed that may also realize significant benefits from similar analytical transformations.

McKinley, M S; Brooks III, E D; Daffin, F

2004-12-13

76

Shape based Monte Carlo code for light transport in complex heterogeneous Tissues  

Microsoft Academic Search

A Monte Carlo code for the calculation of light transport in heterogeneous scattering media is presented together with its validation. Triangle meshes are used to define the interfaces between different materials, in contrast with techniques based on individual volume elements. This approach allows to address realistic problems in a flexible way. A hierarchical spatial organisation enables a fast photon-surface intersection

Eduardo Margallo-Balbás; Patrick J. French

2007-01-01

77

Overview and applications of the Monte Carlo radiation transport kit at LLNL  

Microsoft Academic Search

Modern Monte Carlo radiation transport codes can be applied to model most applications of radiation, from optical to TeV photons, from thermal neutrons to heavy ions. Simulations can include any desired level of detail in three-dimensional geometries using the right level of detail in the reaction physics. The technology areas to which we have applied these codes include medical applications,

Sale

1999-01-01

78

Accelerating execution of the integrated TIGER series Monte Carlo radiation transport codes  

Microsoft Academic Search

Execution of the integrated TIGER series (ITS) of coupled electron\\/photon Monte Carlo radiation transport codes has been accelerated by modifying the FORTRAN source code for more efficient computation. Each member code of ITS was benchmarked and profiled with a specific test case that directed the acceleration effort toward the most computationally intensive subroutines. Techniques for accelerating these subroutines included replacing

L. Montgomery Smith; Reuben D. Hochstedler

1997-01-01

79

Investigation of variance reduction techniques for Monte Carlo photon dose calculation using XVMC  

NASA Astrophysics Data System (ADS)

Several variance reduction techniques, such as photon splitting, electron history repetition, Russian roulette and the use of quasi-random numbers are investigated and shown to significantly improve the efficiency of the recently developed XVMC Monte Carlo code for photon beams in radiation therapy. It is demonstrated that it is possible to further improve the efficiency by optimizing transport parameters such as electron energy cut-off, maximum electron energy step size, photon energy cut-off and a cut-off for kerma approximation, without loss of calculation accuracy. These methods increase the efficiency by a factor of up to 10 compared with the initial XVMC ray-tracing technique or a factor of 50 to 80 compared with EGS4/PRESTA. Therefore, a common treatment plan (6 MV photons, 10×10 cm2 field size, 5 mm voxel resolution, 1% statistical uncertainty) can be calculated within 7 min using a single CPU 500 MHz personal computer. If the requirement on the statistical uncertainty is relaxed to 2%, the calculation time will be less than 2 min. In addition, a technique is presented which allows for the quantitative comparison of Monte Carlo calculated dose distributions and the separation of systematic and statistical errors. Employing this technique it is shown that XVMC calculations agree with EGSnrc on a sub-per cent level for simulations in the energy and material range of interest for radiation therapy.

Kawrakow, Iwan; Fippel, Matthias

2000-08-01

80

Applications of the COG multiparticle Monte Carlo transport code to simulated imaging of complex objects  

Microsoft Academic Search

COG is a major multiparticle simulation code in the LLNL Monte Carlo radiation transport toolkit. It was designed to solve deep-penetration radiation shielding problems in arbitrarily complex 3D geometries, involving coupled transport of photons, neutrons, and electrons. COG was written to provide as much accuracy as the underlying cross-sections will allow, and has a number of variance-reduction features to speed

Richard M. Buck; James M. Hall

81

Applications of the COG multiparticle Monte Carlo transport code to simulated imaging of complex objects  

Microsoft Academic Search

COG is a major multiparticle simulation code in the LLNL Monte Carlo radiation transport toolkit. It was designed to solve deep-penetration radiation shielding problems in arbitrarily complex 3D geometries, involving coupled transport of photons, neutrons, and electrons. COG was written to provide as much accuracy as the underlying cross-sections will allow, and has a number of variance-reduction features to speed

Richard M. Buck; James M. Hall

1999-01-01

82

The all particle method: Coupled neutron, photon, electron, charged particle Monte Carlo calculations  

SciTech Connect

At the present time a Monte Carlo transport computer code is being designed and implemented at Lawrence Livermore National Laboratory to include the transport of: neutrons, photons, electrons and light charged particles as well as the coupling between all species of particles, e.g., photon induced electron emission. Since this code is being designed to handle all particles this approach is called the ''All Particle Method''. The code is designed as a test bed code to include as many different methods as possible (e.g., electron single or multiple scattering) and will be data driven to minimize the number of methods and models ''hard wired'' into the code. This approach will allow changes in the Livermore nuclear and atomic data bases, used to described the interaction and production of particles, to be used to directly control the execution of the program. In addition this approach will allow the code to be used at various levels of complexity to balance computer running time against the accuracy requirements of specific applications. This paper describes the current design philosophy and status of the code. Since the treatment of neutrons and photons used by the All Particle Method code is more or less conventional, emphasis in this paper is placed on the treatment of electron, and to a lesser degree charged particle, transport. An example is presented in order to illustrate an application in which the ability to accurately transport electrons is important. 21 refs., 1 fig.

Cullen, D.E.; Perkins, S.T.; Plechaty, E.F.; Rathkopf, J.A.

1988-06-01

83

Errors in glass photon transport calculation  

SciTech Connect

A calculational capability for photon sources and photon transport in a reactor lattice was added to the GLASS system in 1973. The calculation has been used in a variety of applications since 1973, and has always produced results that appear reasonable. The GLASS photon transport calculation, however, was never compared to an independent photon transport calculation at any state of its development. Recently, the GLASS calculation was compared to calculations performed by the SHIELD system module SNONE (SHIELD system version of LASL DTF-IV code) and significant differences were found in the calculation of deposited photon heat. This led to discovery of certain errors in the GLASS calculations, as discussed in this report.

Finch, D.R.

1981-03-03

84

Particle Monte Carlo Transport in HYDRA  

NASA Astrophysics Data System (ADS)

Accurate simulation of diagnostics for thermonuclear burn requires detailed modeling of the spatial and energy distributions of particle sources, in-flight reaction kinematics, and Doppler effects. In the ALE multiphysics code HYDRA, this is now achieved using a new Monte Carlo particle transport package based on LLNL's Arrakis library. It tracks neutrons, gammas, and light ions on 2D quadrilateral and 3D hexahedral meshes. Neutrons and gammas track using the latest LLNL nuclear data; light ions undergo continuous slowing down with corrections for Fermi degeneracy, small angle Coulomb deflections at track end points, nuclear collisions, and direct Coulomb collisions with plasma ions. The package agrees well with idealized analytical problems as well as high resolution diffusion burn ICF capsule and hohlraum simulations as shown and achieves run times commensurate with production requirements. An overview of the charged particle physics models used is given.

Sepke, S. M.; Patel, M. V.; Marinak, M. M.; McKinley, M. S.; O'Brien, M. J.; Procassini, R. J.

2010-11-01

85

Efficient, automated Monte Carlo methods for radiation transport  

Microsoft Academic Search

Monte Carlo simulations provide an indispensible model for solving radiative transport problems, but their slow convergence inhibits their use as an everyday computational tool. In this paper, we present two new ideas for accelerating the convergence of Monte Carlo algorithms based upon an efficient algorithm that couples simulations of forward and adjoint transport equations. Forward random walks are first processed

Rong Kong; Martin Ambrose; Jerome Spanier

2008-01-01

86

Conformal photon-beam therapy with transverse magnetic fields: a Monte Carlo study.  

PubMed

This work studies the idea of using strong transverse magnetic (B) fields with high-energy photon beams to enhance dose distributions for conformal radiotherapy. EGS4 Monte Carlo code is modified to incorporate charged particle transport in B fields and is used to calculate effects of B fields on dose distributions for a variety of high-energy photon beams. Two types of hypothetical B fields, curl-free linear fields and dipole fields, are used to demonstrate the idea. The major results from the calculation for the linear B fields are: (1) strong transverse B fields (> 1 T) with high longitudinal gradients (G) (> 0.5 T/cm) can produce dramatic dose enhancement as well as dose reduction in localized regions for high-energy photon beams; (2) the magnitude of the enhancement (reduction) and the geometric extension and the location of this enhancement (reduction) depend on the strength and gradient of the B field, and photon-beam energy; (3) for a given B field, the dose enhancement generally increases with photon-beam energy; (4) for a 5 T B field with infinite longitudinal gradient (solenoidal field), up to 200% of dose enhancement and 40% of dose reduction were obtained along the central axis of a 15 MV photon beam; and (5) a 60% of dose enhancement was observed over a 2 cm depth region for the 15 MV beam when B = 5 T and G = 2.5 T/cm. These results are also observed, qualitatively, in the calculation with the dipole B fields. Calculations for a variety of B fields and beam configurations show that, by employing a well-designed B field in photon-beam radiotherapy, it is possible to achieve a significant dose enhancement within the target, while obtaining a substantial dose reduction over critical structures. PMID:11243334

Li, X A; Reiffel, L; Chu, J; Naqvi, S

2001-02-01

87

Neutron transport calculations using Quasi-Monte Carlo methods  

SciTech Connect

This paper examines the use of quasirandom sequences of points in place of pseudorandom points in Monte Carlo neutron transport calculations. For two simple demonstration problems, the root mean square error, computed over a set of repeated runs, is found to be significantly less when quasirandom sequences are used ({open_quotes}Quasi-Monte Carlo Method{close_quotes}) than when a standard Monte Carlo calculation is performed using only pseudorandom points.

Moskowitz, B.S.

1997-07-01

88

Monte Carlo simulation of time-dependent, transport-limited fluorescent boundary measurements in frequency domain.  

PubMed

Recently, we have presented and experimentally validated a unique numerical solver of the coupled radiative transfer equations (RTEs) for rapidly computing time-dependent excitation and fluorescent light propagation in small animal tomography. Herein, we present a time-dependent Monte Carlo algorithm to validate the forward RTE solver and investigate the impact of physical parameters upon transport-limited measurements in order to best direct the development of the RTE solver for optical tomography. Experimentally, the Monte Carlo simulations for both transport-limited and diffusion-limited propagations are validated using frequency domain photon migration measurements for 1.0%, 0.5%, and 0.2% intralipid solutions containing 1 microM indocyanine green in a 49 cm3 cylindrical phantom corresponding to the small volume employed in small animal tomography. The comparisons between Monte Carlo simulations and the numerical solutions result in mean percent error in amplitude and the phase shift less than 5.0% and 0.7 degrees, respectively, at excitation and emission wavelengths for varying anisotropic factors, lifetimes, and modulation frequencies. Monte Carlo simulations indicate that the accuracy of the forward model is enhanced using (i) suitable source models of photon delivery, (ii) accurate anisotropic factors, and (iii) accurate acceptance angles of collected photons. Monte Carlo simulations also show that the accuracy of the diffusion approximation in the small phantom depends upon (i) the ratio d(phantom)/l(tr), where d(phantom) is the phantom diameter and l(tr) is the transport mean free path; and (ii) the anisotropic factor of the medium. The Monte Carlo simulations validates and guides the future development of an appropriate RTE solver for deployment in small animal optical tomography. PMID:17500461

Pan, Tianshu; Rasmussen, John C; Lee, Jae Hoon; Sevick-Muraca, Eva M

2007-04-01

89

PARALLELIZATION OF THE PENELOPE MONTE CARLO PARTICLE TRANSPORT SIMULATION PACKAGE  

Microsoft Academic Search

We have parallelized the PENELOPE Monte Carlo particle transport simulation package (1). The motivation is to increase efficiency of Monte Carlo simulations for medical applications. Our parallelization is based on the standard MPI message passing interface. The parallel code is especially suitable for a distributed memory environment, and has been run on up to 256 processors on the Indiana University

R. B. Cruise; R. W. Sheppard; V. P. Moskvin

2003-01-01

90

ITS: the integrated TIGER series of electron\\/photon transport codes-Version 3.0  

Microsoft Academic Search

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. Improvements in the Monte Carlo codes

John A. Halbleib; Ronald P. Kensek; Greg D. Valdez; Stephen M. Seltzer; Martin J. Berger

1992-01-01

91

Monte Carlo Simulation of the Turbulent Transport of Airborne Contaminants.  

National Technical Information Service (NTIS)

A generalized, three-dimensional Monte Carlo model and computer code (SPOOR) are described for simulating atmospheric transport and dispersal of small pollutant clouds. A cloud is represented by a large number of particles that we track by statistically s...

C. W. Watson S. Barr

1975-01-01

92

Vectorization on Monte Carlo particle transport: an architectural study using the LANL benchmark “GAMTEB”  

Microsoft Academic Search

Fully vectorized versions of the Los Alamos National Laboratory benchmark code Gamteb, a Monte Carlo photon transport algorithm, were developed for the Cyber 205\\/ETA-10 and Cray X-MP\\/Y-MP architectures. Single-processor performance measurements of the vector and scalar implementations were modeled in a modified Amdahl's Law that accounts for additional data motion in the vector code. The performance and implementation strategy of

Patrick J. Burns; Mark Christon; Roland Schweitzer; O. M. Lubeck; H. J. Wasserman

1989-01-01

93

Applications of the COG multiparticle Monte Carlo transport code to simulated imaging of complex objects  

SciTech Connect

COG is a major multiparticle simulation code in the LLNL Monte Carlo radiation transport toolkit. It was designed to solve deep-penetration radiation shielding problems in arbitrarily complex 3D geometries, involving coupled transport of photons, neutrons, and electrons. COG was written to provide as much accuracy as the underlying cross-sections will allow, and has a number of variance-reduction features to speed computations. Recently COG has been applied to the simulation of high- resolution radiographs of complex objects and the evaluation of contraband detection schemes. In this paper we will give a brief description of the capabilities of the COG transport code and show several examples of neutron and gamma-ray imaging simulations. Keywords: Monte Carlo, radiation transport, simulated radiography, nonintrusive inspection, neutron imaging.

Buck, R M; Hall, J M

1999-06-01

94

Study of scattered photons from the collimator system of Leksell Gamma Knife using the EGS4 Monte Carlo Code  

SciTech Connect

In the algorithm of Leksell GAMMAPLAN (the treatment planning software of Leksell Gamma Knife), scattered photons from the collimator system are presumed to have negligible effects on the Gamma Knife dosimetry. In this study, we used the EGS4 Monte Carlo (MC) technique to study the scattered photons coming out of the single beam channel of Leksell Gamma Knife. The PRESTA (Parameter Reduced Electron-Step Transport Algorithm) version of the EGS4 (Electron Gamma Shower version 4) MC computer code was employed. We simulated the single beam channel of Leksell Gamma Knife with the full geometry. Primary photons were sampled from within the {sup 60}Co source and radiated isotropically in a solid angle of 4{pi}. The percentages of scattered photons within all photons reaching the phantom space using different collimators were calculated with an average value of 15%. However, this significant amount of scattered photons contributes negligible effects to single beam dose profiles for different collimators. Output spectra were calculated for the four different collimators. To increase the efficiency of simulation by decreasing the semiaperture angle of the beam channel or the solid angle of the initial directions of primary photons will underestimate the scattered component of the photon fluence. The generated backscattered photons from within the {sup 60}Co source and the beam channel also contribute to the output spectra.

Cheung, Joel Y.C.; Yu, K.N. [Gamma Knife Centre, Canossa Hospital, 1 Old Peak Road, Hong Kong (China); Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Hong Kong (China)

2006-01-15

95

Study of scattered photons from the collimator system of Leksell Gamma Knife using the EGS4 Monte Carlo code.  

PubMed

In the algorithm of Leksell GAMMAPLAN (the treatment planning software of Leksell Gamma Knife), scattered photons from the collimator system are presumed to have negligible effects on the Gamma Knife dosimetry. In this study, we used the EGS4 Monte Carlo (MC) technique to study the scattered photons coming out of the single beam channel of Leksell Gamma Knife. The PRESTA (Parameter Reduced Electron-Step Transport Algorithm) version of the EGS4 (Electron Gamma Shower version 4) MC computer code was employed. We simulated the single beam channel of Leksell Gamma Knife with the full geometry. Primary photons were sampled from within the 60Co source and radiated isotropically in a solid angle of 4pi. The percentages of scattered photons within all photons reaching the phantom space using different collimators were calculated with an average value of 15%. However, this significant amount of scattered photons contributes negligible effects to single beam dose profiles for different collimators. Output spectra were calculated for the four different collimators. To increase the efficiency of simulation by decreasing the semiaperture angle of the beam channel or the solid angle of the initial directions of primary photons will underestimate the scattered component of the photon fluence. The generated backscattered photons from within the 60Co source and the beam channel also contribute to the output spectra. PMID:16485407

Cheung, Joel Y C; Yu, K N

2006-01-01

96

Development of heavy ion transport Monte Carlo code  

Microsoft Academic Search

We developed a heavy ion transport Monte Carlo code HETC-CYRIC which can treat the fragments produced by heavy ion reactions. The HETC-CYRIC code is made by incorporating a heavy ion reaction calculation routine, which consists of the HIC code, the SPAR code, and the Shen formula, into the hadron transport Monte Carlo code HETC-3-STEP. The results calculated with the HETC-CYRIC

Hiroshi Iwase; Tadahiro Kurosawa; Takashi Nakamura; Nobuaki Yoshizawa; Jun Funabiki

2001-01-01

97

Coupled Electron-Photon Transport Calculations Using the Method of Discrete Ordinates.  

National Technical Information Service (NTIS)

A new discrete-ordinates method for coupled electron-photon transport is presented and applied to space shielding calculations. It is found that the discrete-ordinates method is as accurate as the standard Monte Carlo method, but is much more efficient. (...

L. J. Lorence W. E. Nelson J. E. Morel

1985-01-01

98

Efficient photon treatment planning by the use of Swiss Monte Carlo Plan  

NASA Astrophysics Data System (ADS)

Currently photon Monte Carlo treatment planning (MCTP) for a patient stored in the patient database of a treatment planning system (TPS) usually can only be performed using a cumbersome multi-step procedure where many user interactions are needed. Automation is needed for usage in clinical routine. In addition, because of the long computing time in MCTP, optimization of the MC calculations is essential. For these purposes a new GUI-based photon MC environment has been developed resulting in a very flexible framework, namely the Swiss Monte Carlo Plan (SMCP). Appropriate MC transport methods are assigned to different geometric regions by still benefiting from the features included in the TPS. In order to provide a flexible MC environment the MC particle transport has been divided into different parts: source, beam modifiers, and patient. The source part includes: Phase space-source, source models, and full MC transport through the treatment head. The beam modifier part consists of one module for each beam modifier. To simulate the radiation transport through each individual beam modifier, one out of three full MC transport codes can be selected independently. Additionally, for each beam modifier a simple or an exact geometry can be chosen. Thereby, different complexity levels of radiation transport are applied during the simulation. For the patient dose calculation two different MC codes are available. A special plug-in in Eclipse providing all necessary information by means of Dicom streams was used to start the developed MC GUI. The implementation of this framework separates the MC transport from the geometry and the modules pass the particles in memory, hence no files are used as interface. The implementation is realized for 6 and 15 MV beams of a Varian Clinac 2300 C/D. Several applications demonstrate the usefulness of the framework. Apart from applications dealing with the beam modifiers, three patient cases are shown. Thereby, comparisons between MC calculated dose distributions and those calculated by a pencil beam or the AAA algorithm. Interfacing this flexible and efficient MC environment with Eclipse allows a widespread use for all kinds of investigations from timing and benchmarking studies to clinical patient studies. Additionally, it is possible to add modules keeping the system highly flexible and efficient.

Fix, M. K.; Manser, P.; Frei, D.; Volken, W.; Mini, R.; Born, E. J.

2007-06-01

99

Computational methods of electron/photon transport  

SciTech Connect

A review of computational methods simulating the non-plasma transport of electrons and their attendant cascades is presented. Remarks are mainly restricted to linearized formalisms at electron energies above 1 keV. The effectiveness of various metods is discussed including moments, point-kernel, invariant imbedding, discrete-ordinates, and Monte Carlo. Future research directions and the potential impact on various aspects of science and engineering are indicated.

Mack, J.M.

1983-01-01

100

A hybrid (Monte Carlo/deterministic) approach for multi-dimensional radiation transport  

SciTech Connect

Highlights: {yields} We introduce a variance reduction scheme for Monte Carlo (MC) transport. {yields} The primary application is atmospheric remote sensing. {yields} The technique first solves the adjoint problem using a deterministic solver. {yields} Next, the adjoint solution is used as an importance function for the MC solver. {yields} The adjoint problem is solved quickly since it ignores the volume. - Abstract: A novel hybrid Monte Carlo transport scheme is demonstrated in a scene with solar illumination, scattering and absorbing 2D atmosphere, a textured reflecting mountain, and a small detector located in the sky (mounted on a satellite or a airplane). It uses a deterministic approximation of an adjoint transport solution to reduce variance, computed quickly by ignoring atmospheric interactions. This allows significant variance and computational cost reductions when the atmospheric scattering and absorption coefficient are small. When combined with an atmospheric photon-redirection scheme, significant variance reduction (equivalently acceleration) is achieved in the presence of atmospheric interactions.

Bal, Guillaume, E-mail: gb2030@columbia.edu [Department of Applied Physics and Applied Mathematics, Columbia University, 200 S.W. Mudd Building, 500 W. 120th Street, New York, NY 10027 (United States); Davis, Anthony B., E-mail: Anthony.B.Davis@jpl.nasa.gov [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Mail Stop 169-237, Pasadena, CA 91109 (United States); Kavli Institute for Theoretical Physics, Kohn Hall, University of California, Santa Barbara, CA 93106-4030 (United States); Langmore, Ian, E-mail: ianlangmore@gmail.com [Department of Applied Physics and Applied Mathematics, Columbia University, 200 S.W. Mudd Building, 500 W. 120th Street, New York, NY 10027 (United States)

2011-08-20

101

Experimental investigation of a fast Monte Carlo photon beam dose calculation algorithm  

Microsoft Academic Search

An experimental verification of the recently developed XVMC code, a fast Monte Carlo algorithm to calculate dose distributions of photon beams in treatment planning, is presented. The treatment head is modelled by a point source with energy distribution (primary photons) and an additional head scatter contribution. Utility software is presented, allowing the determination of the parameters for this model using

Matthias Fippel; Wolfram Laub; Bernd Huber; Fridtjof Nüsslin

1999-01-01

102

Generalized coupled photon transport equations for handling correlated photon streams with distinct frequencies.  

PubMed

A generalized form of coupled photon transport equations that can handle correlated light beams with distinct frequencies is introduced. The derivation is based on the principle of energy conservation. For a single frequency, the current formulation reduces to a standard photon transport equation, and for fluorescence and phosphorescence, the diffusion models derived from the proposed photon transport model match for homogenous media. The generalized photon transport model is extended to handle wideband inputs in the frequency domain. PMID:23381285

Handapangoda, Chintha C; Premaratne, Malin; Nahavandi, Saeid

2012-08-15

103

Polarization of the Tagged Compton Backscattered Laser Photons. Results of Monte Carlo Simulation  

Microsoft Academic Search

Polarization characteristics of the gamma beam obtained by the Compton back\\u000ascattering of laser photons on high energy electrons are evaluated by\\u000aMonte-Carlo simulations.\\u000a It is assumed that outgoing photons are tagged; the energy dispersion of the\\u000atagging photons and emittance of the initial electrons are taken into account.\\u000aDependence of the final photon polarization parameters on measured photon\\u000aenergy

V. G. Nedorezov; Yu. P. Peresunko; Yu. M. Ranyuk; I. M. Shapoval

1998-01-01

104

MORSE Monte Carlo radiation transport code system  

Microsoft Academic Search

This report is an addendum to the MORSE report, ORNL-4972, originally published in 1975. This addendum contains descriptions of several modifications to the MORSE Monte Carlo Code, replacement pages containing corrections, Part II of the report which was previously unpublished, and a new Table of Contents. The modifications include a Klein Nishina estimator for gamma rays. Use of such an

Emmett

1983-01-01

105

Generation of photon energy deposition kernels using the EGS Monte Carlo code  

Microsoft Academic Search

The EGS Monte Carlo code was used to generate photon energy deposition kernels which describe the energy deposited by charged particles set in motion by primary, first scattered, second scattered, multiple scattered and bremsstrahlung plus annihilation photons. These were calculated for a water medium irradiated with monoenergetic photons with energies in the range 0.1-50 MeV. In addition to the primary

T. R. Mackie; A. F. Bielajew; D. W. O. Rogers; J. J. Battista

1988-01-01

106

Monte Carlo simulations of the transport of sputtered particles  

NASA Astrophysics Data System (ADS)

Program SPATS models the transport of neutral particles during magnetron sputtering deposition. The 3D Monte Carlo simulation provides information about spatial distribution of the fluxes, density of the sputtered particles in the chamber glow discharge area, and kinetic energy distribution of the arrival flux. Collision events are modelled by scattering in Biersack's potential, Lennard-Jones potential, or by binary hard sphere collision approximation. The code has an interface for Monte Carlo TRIM simulated results of the sputtered particles.

Macàk, Karol; Macàk, Peter; Helmersson, Ulf

1999-08-01

107

Coupled proton/neutron transport calculations using the S sub N and Monte Carlo methods  

SciTech Connect

Coupled charged/neutral article transport calculations are most often carried out using the Monte Carol technique. For example, the ITS, EGS, and MCNP (Version 4) codes are used extensively for electron/photon transport calculations while HETC models the transport of protons, neutrons and heavy ions. In recent years there has been considerable progress in deterministic models of electron transport, and many of these models are applicable to protons. However, even with these new models (and the well established models for neutron transport) deterministic coupled neutron/proton transport calculations have not been feasible for most problems of interest, due to a lack of coupled multigroup neutron/proton cross section sets. Such cross sections sets are now being developed at Los Alamos. Using these cross sections we have carried out coupled proton/neutron transport calculations using both the S{sub N} and Monte Carlo methods. The S{sub N} calculations used a code called SMARTEPANTS (simulating many accumulative Rutherford trajectories, electron, proton and neutral transport slover) while the Monte Carlo calculations are done with the multigroup option of the MCNP code. Both SMARTEPANTS and MCNP require standard multigroup cross section libraries. HETC on the other hand, avoids the need for precalculated nuclear cross sections by modeling individual nucleon collisions as the transporting neutrons and protons interact with nuclei. 21 refs., 1 fig.

Filippone, W.L. (Arizona Univ., Tucson, AZ (USA). Dept. of Nuclear and Energy Engineering); Little, R.C.; Morel, J.E.; MacFarlane, R.E.; Young, P.G. (Los Alamos National Lab., NM (USA))

1991-01-01

108

Correlated histogram representation of Monte Carlo derived medical accelerator photon-output phase space  

SciTech Connect

We present a method for condensing the photon energy and angular distributions obtained from Monte Carlo simulations of medical accelerators. This method represents the output as a series of correlated histograms and as such is well-suited for inclusion as the photon-source package for Monte Carlo codes used to determine the dose distributions in photon teletherapy. The method accounts for the isocenter-plane variations of the photon energy spectral distributions with increasing distance from the beam central axis for radiation produced in the bremsstrahlung target as well as for radiation scattered by the various treatment machine components within the accelerator head. Comparison of the isocenter energy fluence computed by this algorithm with that of the underlying full-physics Monte Carlo photon phase space indicates that energy fluence errors are less than 1{percent} of the maximum energy fluence for a range of open-field sizes. Comparison of jaw-edge penumbrae shows that the angular distributions of the photons are accurately reproduced. The Monte Carlo sampling efficiency (the fraction of generated photons which clear the collimator jaws) of the algorithm is approximately 83{percent} for an open 10{times}10 field, rising to approximately 96{percent} for an open 40{times}40 field. Data file sizes for a typical medical accelerator, at a given energy, are approximately 150 kB, compared to the 1 GB size of the underlying full-physics phase space file. {copyright} {ital 1999 American Association of Physicists in Medicine.}

Schach von Wittenau, A.E.; Cox, L.J.; Bergstrom, P.M. Jr.; Chandler, W.P.; Siantar, C.L. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Mohan, R. [Medical College of Virginia/Virginia Commonwealth University, Richmond, Virginia 23298 (United States)

1999-07-01

109

Response of thermoluminescent dosimeters to photons simulated with the Monte Carlo method  

NASA Astrophysics Data System (ADS)

Personal monitors composed of thermoluminescent dosimeters (TLDs) made of natural fluorite (CaF2:NaCl) and lithium fluoride (Harshaw TLD-100) were exposed to gamma and X rays of different qualities. The GEANT4 radiation transport Monte Carlo toolkit was employed to calculate the energy depth deposition profile in the TLDs. X-ray spectra of the ISO/4037-1 narrow-spectrum series, with peak voltage (kVp) values in the range 20 300 kV, were obtained by simulating a X-ray Philips MG-450 tube associated with the recommended filters. A realistic photon distribution of a 60Co radiotherapy source was taken from results of Monte Carlo simulations found in the literature. Comparison between simulated and experimental results revealed that the attenuation of emitted light in the readout process of the fluorite dosimeter must be taken into account, while this effect is negligible for lithium fluoride. Differences between results obtained by heating the dosimeter from the irradiated side and from the opposite side allowed the determination of the light attenuation coefficient for CaF2:NaCl (mass proportion 60:40) as 2.2 mm-1.

Moralles, M.; Guimarães, C. C.; Okuno, E.

2005-06-01

110

Transport properties of nonlinear photonic crystals  

NASA Astrophysics Data System (ADS)

Keen interest has been shown in exploiting the transport properties of nonlinear photonic crystals for modulation, switching and routing applications at telecommunication frequencies. This is due to the rich anisotropy evidenced by a highly-textured dispersion surface, and its dependence on the permittivity profile of the structure. We consider a two-dimensional photonic crystal, presume an instantaneous change in profile due to an optical Kerr effect, and show how the beam's refraction angle depends on its intensity. For computational simplicity, we employ a self-consistent approach and the linear eigenvalue equation, which we solve using a finite element method. Previous studies have extracted directions of optical power flow from equifrequency contour gradients. Such gradients, more formally the group velocity, lack local definition and are only meaningful in the context of a spatial average over the unit cell. As a result, the relationship between the local character of the optical transport and the induced permittivity profile is obscured. By contrast, we explicitly consider the spatial dependence of the Poynting's vector, from which we also extract mean transport directions with much greater computational efficiency. We thereby demonstrate the interrelationship between optical transport and nonlinear response at the nanoscale. A consequent analysis of refraction in the context of the superprism effect reveals new aspects to the optical transport in such nonlinear systems.

Schriemer, Henry P.; Wheeldon, Jeffrey; Hall, Trevor

2005-09-01

111

Modelling of electron contamination in clinical photon beams for Monte Carlo dose calculation  

NASA Astrophysics Data System (ADS)

The purpose of this work is to model electron contamination in clinical photon beams and to commission the source model using measured data for Monte Carlo treatment planning. In this work, a planar source is used to represent the contaminant electrons at a plane above the upper jaws. The source size depends on the dimensions of the field size at the isocentre. The energy spectra of the contaminant electrons are predetermined using Monte Carlo simulations for photon beams from different clinical accelerators. A 'random creep' method is employed to derive the weight of the electron contamination source by matching Monte Carlo calculated monoenergetic photon and electron percent depth-dose (PDD) curves with measured PDD curves. We have integrated this electron contamination source into a previously developed multiple source model and validated the model for photon beams from Siemens PRIMUS accelerators. The EGS4 based Monte Carlo user code BEAM and MCSIM were used for linac head simulation and dose calculation. The Monte Carlo calculated dose distributions were compared with measured data. Our results showed good agreement (less than 2% or 2 mm) for 6, 10 and 18 MV photon beams.

Yang, J.; Li, J. S.; Qin, L.; Xiong, W.; Ma, C.-M.

2004-06-01

112

Using Monte Carlo simulations to commission photon beam output factors—a feasibility study  

NASA Astrophysics Data System (ADS)

This study investigates the feasibility of using Monte Carlo methods to assist the commissioning of photon beam output factors from a medical accelerator. The Monte Carlo code, BEAMnrc, was used to model 6 MV and 18 MV photon beams from a Varian linear accelerator. When excellent agreements were obtained between the Monte Carlo simulated and measured dose distributions in a water phantom, the entire geometry including the accelerator head and the water phantom was simulated to calculate the relative output factors. Simulated output factors were compared with measured data, which consist of a typical commission dataset for the output factors. The measurements were done using an ionization chamber in a water phantom at a depth of 10 cm with a source-detector distance of 100 cm. Square fields and rectangular fields with widths and lengths ranging from 4 cm to 40 cm were studied. The result shows a very good agreement (<1.5%) between the Monte Carlo calculated and the measured relative output factors for a typical commissioning dataset. The Monte Carlo calculated backscatter factors to the beam monitor chamber agree well with measured data in the literature. Monte Carlo simulations have also been shown to be able to accurately predict the collimator exchange effect and its component for rectangular fields. The information obtained is also useful to develop an algorithm for accurate beam modelling. This investigation indicates that Monte Carlo methods can be used to assist commissioning of output factors for photon beams.

Ding, George X.

2003-12-01

113

Monte Carlo Assessments of Absorbed Doses to the Hands of Radiopharmaceutical Workers Due to Photon Emitters  

SciTech Connect

This paper describes the characterization of radiation doses to the hands of nuclear medicine technicians resulting from the handling of radiopharmaceuticals. Radiation monitoring using ring dosimeters indicates that finger dosimeters that are used to show compliance with applicable regulations may overestimate or underestimate radiation doses to the skin depending on the nature of the particular procedure and the radionuclide being handled. To better understand the parameters governing the absorbed dose distributions, a detailed model of the hands was created and used in Monte Carlo simulations of selected nuclear medicine procedures. Simulations of realistic configurations typical for workers handling radiopharmaceuticals were performedfor a range of energies of the source photons. The lack of charged-particle equilibrium necessitated full photon-electron coupled transport calculations. The results show that the dose to different regions of the fingers can differ substantially from dosimeter readings when dosimeters are located at the base of the finger. We tried to identify consistent patterns that relate the actual dose to the dosimeter readings. These patterns depend on the specific work conditions and can be used to better assess the absorbed dose to different regions of the exposed skin.

Ilas, Dan [ORNL; Eckerman, Keith F [ORNL; Karagiannis, Harriet [ORNL

2009-01-01

114

Overview of Monte Carlo Neutron Transport Codes.  

National Technical Information Service (NTIS)

The Radiation Safety Information Computational Center (RSICC) is the designated central repository of the United States Department of Energy (DOE) for nuclear software in radiation transport, safety, and shielding. Since the center was established in the ...

B. L. Kirk

2013-01-01

115

Monte Carlo simulation of the turbulent transport of airborne contaminants  

Microsoft Academic Search

A generalized, three-dimensional Monte Carlo model and computer code ; (SPOOR) are described for simulating atmospheric transport and dispersal of small ; pollutant clouds. A cloud is represented by a large number of particles that we ; track by statistically sampling simulated wind and turbulence fields. These ; fields are based on generalized wind data for large-scale flow and turbulent

C. W. Watson; S. Barr

1975-01-01

116

Clinical implementation of the Peregrine Monte Carlo dose calculations system for photon beam therapy  

Microsoft Academic Search

PEREGRINE is a 3D Monte Carlo dose calculation system designed to serve as a dose calculation engine for clinical radiation therapy treatment planning systems. Taking advantage of recent advances in low-cost computer hardware, modern multiprocessor architectures and optimized Monte Carlo transport algorithms, PEREGRINE performs mm-resolution Monte Carlo calculations in times that are reasonable for clinical use. PEREGRINE has been developed

N Albright; P M Bergstrom; T P Daly; M Descalle; D Garrett; R K House; D K Knapp; S May; R W Patterson; C L Siantar; L Verhey; R S Walling; D Welczorek

1999-01-01

117

MORSE Monte Carlo radiation transport code system  

SciTech Connect

This report is an addendum to the MORSE report, ORNL-4972, originally published in 1975. This addendum contains descriptions of several modifications to the MORSE Monte Carlo Code, replacement pages containing corrections, Part II of the report which was previously unpublished, and a new Table of Contents. The modifications include a Klein Nishina estimator for gamma rays. Use of such an estimator required changing the cross section routines to process pair production and Compton scattering cross sections directly from ENDF tapes and writing a new version of subroutine RELCOL. Another modification is the use of free form input for the SAMBO analysis data. This required changing subroutines SCORIN and adding new subroutine RFRE. References are updated, and errors in the original report have been corrected. (WHK)

Emmett, M.B.

1983-02-01

118

Equivalence of four Monte Carlo methods for photon migration in turbid media.  

PubMed

In the field of photon migration in turbid media, different Monte Carlo methods are usually employed to solve the radiative transfer equation. We consider four different Monte Carlo methods, widely used in the field of tissue optics, that are based on four different ways to build photons' trajectories. We provide both theoretical arguments and numerical results showing the statistical equivalence of the four methods. In the numerical results we compare the temporal point spread functions calculated by the four methods for a wide range of the optical properties in the slab and semi-infinite medium geometry. The convergence of the methods is also briefly discussed. PMID:23201658

Sassaroli, Angelo; Martelli, Fabrizio

2012-10-01

119

Parallel MCNP Monte Carlo transport calculations with MPI  

SciTech Connect

The steady increase in computational performance has made Monte Carlo calculations for large/complex systems possible. However, in order to make these calculations practical, order of magnitude increases in performance are necessary. The Monte Carlo method is inherently parallel (particles are simulated independently) and thus has the potential for near-linear speedup with respect to the number of processors. Further, the ever-increasing accessibility of parallel computers, such as workstation clusters, facilitates the practical use of parallel Monte Carlo. Recognizing the nature of the Monte Carlo method and the trends in available computing, the code developers at Los Alamos National Laboratory implemented the message-passing general-purpose Monte Carlo radiation transport code MCNP (version 4A). The PVM package was chosen by the MCNP code developers because it supports a variety of communication networks, several UNIX platforms, and heterogeneous computer systems. This PVM version of MCNP has been shown to produce speedups that approach the number of processors and thus, is a very useful tool for transport analysis. Due to software incompatibilities on the local IBM SP2, PVM has not been available, and thus it is not possible to take advantage of this useful tool. Hence, it became necessary to implement an alternative message-passing library package into MCNP. Because the message-passing interface (MPI) is supported on the local system, takes advantage of the high-speed communication switches in the SP2, and is considered to be the emerging standard, it was selected.

Wagner, J.C.; Haghighat, A. [Pennsylvania State Univ., University Park, PA (United States)

1996-12-31

120

Monte Carlo simulation of photon densities inside the dermis in LLLT (low level laser therapy)  

NASA Astrophysics Data System (ADS)

In this work, the photon distribution of He:Ne laser within dermis tissue is studied. The dermis as a highly scattering media was irradiated by a low power laser. The photon densities as well as the corresponding isothermal contours were obtained by two different numerical methods, i.e., Lambert-Beer and Welch. The results were compared to that of Monte Carlo subsequently.

Parvin, Parviz; Eftekharnoori, Somayeh; Dehghanpour, Hamid Reza

2009-09-01

121

Testing Monte Carlo computer codes for simulations of electron transport in matter.  

PubMed

In this paper, three Monte Carlo codes were tested for electron transport in various materials. MCNPX (version 2.4.0), Penelope (version 2003) and EGSnrc codes were used for modeling simple problems. These problems were focused on bremsstrahlung, energy deposition in matter, electron ranges and production of secondary electrons by gamma radiation. The electrons were primary particles, except in the last exercise, where photons were used. Various materials, e.g., water, lead and tungsten were used. The energy of the primary particles was within the energy range from 20 to 450 keV. The simulation results were compared with each other. PMID:20116266

Sídlová, Vera; Trojek, Tomás

2009-12-21

122

Efficient, automated Monte Carlo methods for radiation transport  

SciTech Connect

Monte Carlo simulations provide an indispensible model for solving radiative transport problems, but their slow convergence inhibits their use as an everyday computational tool. In this paper, we present two new ideas for accelerating the convergence of Monte Carlo algorithms based upon an efficient algorithm that couples simulations of forward and adjoint transport equations. Forward random walks are first processed in stages, each using a fixed sample size, and information from stage k is used to alter the sampling and weighting procedure in stage k+1. This produces rapid geometric convergence and accounts for dramatic gains in the efficiency of the forward computation. In case still greater accuracy is required in the forward solution, information from an adjoint simulation can be added to extend the geometric learning of the forward solution. The resulting new approach should find widespread use when fast, accurate simulations of the transport equation are needed.

Kong Rong; Ambrose, Martin [Claremont Graduate University, 150 E. 10th Street, Claremont, CA 91711 (United States); Spanier, Jerome [Claremont Graduate University, 150 E. 10th Street, Claremont, CA 91711 (United States); Beckman Laser Institute and Medical Clinic, University of California, 1002 Health Science Road E., Irvine, CA 92612 (United States)], E-mail: jspanier@uci.edu

2008-11-20

123

Monte Carlo calculations of efficiencies for photon interactions in plastic scintillators  

Microsoft Academic Search

Energy absorption and total peak efficiencies for plastic scintillators have been calculated by means of the Monte Carlo method. These results are of interest for potential uses of plastic scintillators as dosimetric or spectrometric devices. The calculations were carried out for photon energies from 2 keV up to 1 MeV. We considered all of the physical effects involved in each

Edgardo V. Bonzi; Raúl T. Mainardi

1992-01-01

124

Efficient particle transport simulation through beam modulating devices for Monte Carlo treatment planning.  

PubMed

For Monte Carlo treatment planning it is essential to model efficiently patient dependent beam modifying devices, e.g., Multi-Leaf Collimators (MLC). Therefore a Monte Carlo geometry tracking procedure is presented allowing the simulation of photon and electron transport through these devices within short calculation time. The tracking procedure is based on elemental regions, on surfaces (mainly planes) to separate the regions as well as on bit patterns and bit masks to identify the regions. Photon cross sections for photoelectric absorption, Compton scattering and pair production as well as electron stopping powers and ranges are provided by the Physical Reference Data of the National Institute of Standards and Technology (NIST). The tracking procedure is implemented in c + + with object-oriented design based on c + + class hierarchies and inheritance. Using the geometry technique, several MLC models are constructed. Some of them take into account tongue-and-groove effects as well as curved leaf ends. The models are integrated into the Monte Carlo dose calculation engine XVMC for treatment planning. The system is tested by comparing different MLC implementations and by verification with measurement. PMID:15191314

Fippel, Matthias

2004-05-01

125

GPU-accelerated object-oriented Monte Carlo modeling of photon migration in turbid media  

NASA Astrophysics Data System (ADS)

Due to the recent intense developments in lasers and optical technologies a number of novel revolutionary imaging and photonic-based diagnostic modalities have arisen. Utilizing various features of light these techniques provide new practical solutions in a range of biomedical, environmental and industrial applications. Conceptual engineering design of new optical diagnostic systems requires a clear understanding of the light-tissue interaction and the peculiarities of optical radiation propagation therein. Description of photon migration within the random media is based on the radiative transfer that forms a basis of Monte Carlo modelling of light propagation in complex turbid media like biological tissues. In current presentation with a further development of the Monte Carlo technique we introduce a novel Object-Oriented Programming (OOP) paradigm accelerated by Graphics Processing Unit that provide an opportunity to escalate the performance of standard Monte Carlo simulation over 100 times.

Doronin, Alex; Meglinski, Igor

2010-10-01

126

Applications of the COG multiparticle Monte Carlo transport code to simulated imaging of complex objects  

NASA Astrophysics Data System (ADS)

COG is a major multiparticle simulation code in the LLNL Monte Carlo radiation transport toolkit. It was designed to solve deep-penetration radiation shielding problems in arbitrarily complex 3D geometries, involving coupled transport of photons, neutrons, and electrons. COG was written to provide as much accuracy as the underlying cross-sections will allow, and has a number of variance-reduction features to speed computations. Recently COG has been applied to the simulation of high- resolution radiographs of complex objects and the evaluation of contraband detection schemes. In this paper we will give a brief description of the capabilities of the COG transport code and show several examples of neutron and gamma-ray imaging simulations.

Buck, Richard M.; Hall, James M.

1999-09-01

127

Response kernel density estimation Monte Carlo method for electron transport  

NASA Astrophysics Data System (ADS)

Electron transport simulation plays an important role in the dose calculation in electron cancer therapy as well as in many other fields. Traditional numerical solutions for particle transport are inadequate because of the extremely anisotropic collisions between electrons and the background medium. In principle, analog Monte Carlo (AMC) can be used, however, the large cross section for coulombic interactions makes it of limited use due to the large amount of computer time required for typical simulations. Several techniques, such as the condensed history random walk technique, have been proposed and investigated to improve the efficiency of AMC. However, the approximations used in these techniques either reduce their accuracy, or restrict them to certain applications. The response kernel density estimation Monte Carlo method (RKMC) proposed in this study attempts to improve the efficiency of AMC without sacrificing accuracy. A complete Monte Carlo electron transport calculation is divided into two steps in RKMC. In the first step, or local calculation, a series of AMC simulations are performed to collect electron state data in phase space after the electrons experience multiple scattering. In the second step, or global calculation, the adaptive kernel density estimation method is used to construct the probability density functions (pdf's) from the recorded data set, which are sampled efficiently by a specially designed Monte Carlo sampling scheme. Since the electron multiple scattering pdf's come from the AMC simulations, all the effects of multiple scattering are taken into consideration. Therefore, RKMC is expected to be both accurate and efficient. A RKMC code was developed first to test the method against an AMC code. The test case results showed that the RKMC code was approximately 100 times faster than the AMC code. The method was also incorporated into EGS4, an industry standard electron transport condensed history Monte Carlo (CHMC) code, as a replacement for Moliere's multiple scattering theory (MMST). A clear improvement in both accuracy and efficiency over EGS4 was observed for the low and intermediate energy range (10 keV to 20 MeV) electron transport simulations, because lateral displacements are considered in RKMC and the restrictions on transport step size are eliminated. All the results of our study show that RKMC is a promising method for electron transport simulations.

Du, Jie

128

Monte Carlo Modeling of Photon Interrogation Methods for Characterization of Special Nuclear Material  

SciTech Connect

This work illustrates a methodology based on photon interrogation and coincidence counting for determining the characteristics of fissile material. The feasibility of the proposed methods was demonstrated using a Monte Carlo code system to simulate the full statistics of the neutron and photon field generated by the photon interrogation of fissile and non-fissile materials. Time correlation functions between detectors were simulated for photon beam-on and photon beam-off operation. In the latter case, the correlation signal is obtained via delayed neutrons from photofission, which induce further fission chains in the nuclear material. An analysis methodology was demonstrated based on features selected from the simulated correlation functions and on the use of artificial neural networks. We show that the methodology can reliably differentiate between highly enriched uranium and plutonium. Furthermore, the mass of the material can be determined with a relative error of about 12%. Keywords: MCNP, MCNP-PoliMi, Artificial neural network, Correlation measurement, Photofission

Pozzi, Sara A [ORNL; Downar, Thomas J [ORNL; Padovani, Enrico [Nuclear Engineering Department Politecnico di Milano, Milan, Italy; Clarke, Shaun D [ORNL

2006-01-01

129

Status of the MORSE multigroup Monte Carlo radiation transport code  

Microsoft Academic Search

There are two versions of the MORSE multigroup Monte Carlo radiation transport computer code system at Oak Ridge National Laboratory. MORSE-CGA is the most well-known and has undergone extensive use for many years. MORSE-SGC was originally developed in about 1980 in order to restructure the cross-section handling and thereby save storage. However, with the advent of new computer systems having

Emmett

1993-01-01

130

Acceleration of a Monte Carlo radiation transport code  

Microsoft Academic Search

Execution time for the Integrated TIGER Series (ITS) Monte Carlo radiation transport code has been reduced by careful re-coding of computationally intensive subroutines. Three test cases for the TIGER (1-D slab geometry), CYLTRAN (2-D cylindrical geometry), and ACCEPT (3-D arbitrary geometry) codes were identified and used to benchmark and profile program execution. Based upon these results, sixteen top time-consuming subroutines

Reuben D. Hochstedler; L. Montgomery Smith

1996-01-01

131

Neutron streaming Monte Carlo radiation transport code MORSE-CG  

SciTech Connect

Calculations have been performed using the Monte Carlo code, MORSE-CG, to determine the neutron streaming through various straight and stepped gaps between radiation shield sectors in the conceptual tokamak fusion power plant design STARFIRE. This design calls for ''pie-shaped'' radiation shields with gaps between segments. It is apparent that some type of offset, or stepped gap, configuration will be necessary to reduce neutron streaming through these gaps. To evaluate this streaming problem, a MORSE-to-MORSE coupling technique was used, consisting of two separate transport calculations, which together defined the entire transport problem. The results define the effectiveness of various gap configurations to eliminate radiation streaming.

Halley, A.M.; Miller, W.H.

1986-11-01

132

Monte Carlo calculation of dose rate conversion factors for external exposure to photon emitters in soil.  

PubMed

The dose rate conversion factors D(CF) (absorbed dose rate in air per unit activity per unit of soil mass, nGy h(-1) per Bq kg(-1)) are calculated 1 m above ground for photon emitters of natural radionuclides uniformly distributed in the soil. Three Monte Carlo codes are used: 1) The MCNP code of Los Alamos; 2) The GEANT code of CERN; and 3) a Monte Carlo code developed in the Nuclear Technology Laboratory of the Aristotle University of Thessaloniki. The accuracy of the Monte Carlo results is tested by the comparison of the unscattered flux obtained by the three Monte Carlo codes with an independent straightforward calculation. All codes and particularly the MCNP calculate accurately the absorbed dose rate in air due to the unscattered radiation. For the total radiation (unscattered plus scattered) the D(CF) values calculated from the three codes are in very good agreement between them. The comparison between these results and the results deduced previously by other authors indicates a good agreement (less than 15% of difference) for photon energies above 1,500 keV. Antithetically, the agreement is not as good (difference of 20-30%) for the low energy photons. PMID:10688452

Clouvas, A; Xanthos, S; Antonopoulos-Domis, M; Silva, J

2000-03-01

133

Monte Carlo radiation transport: A revolution in science  

SciTech Connect

When Enrico Fermi, Stan Ulam, Nicholas Metropolis, John von Neuman, and Robert Richtmyer invented the Monte Carlo method fifty years ago, little could they imagine the far-flung consequences, the international applications, and the revolution in science epitomized by their abstract mathematical method. The Monte Carlo method is used in a wide variety of fields to solve exact computational models approximately by statistical sampling. It is an alternative to traditional physics modeling methods which solve approximate computational models exactly by deterministic methods. Modern computers and improved methods, such as variance reduction, have enhanced the method to the point of enabling a true predictive capability in areas such as radiation or particle transport. This predictive capability has contributed to a radical change in the way science is done: design and understanding come from computations built upon experiments rather than being limited to experiments, and the computer codes doing the computations have become the repository for physics knowledge. The MCNP Monte Carlo computer code effort at Los Alamos is an example of this revolution. Physicians unfamiliar with physics details can design cancer treatments using physics buried in the MCNP computer code. Hazardous environments and hypothetical accidents can be explored. Many other fields, from underground oil well exploration to aerospace, from physics research to energy production, from safety to bulk materials processing, benefit from MCNP, the Monte Carlo method, and the revolution in science.

Hendricks, J. [Los Alamos National Lab., CA (United States)

1993-04-01

134

Modelling 6 MV photon beams of a stereotactic radiosurgery system for Monte Carlo treatment planning  

NASA Astrophysics Data System (ADS)

The goal of this work is to build a multiple source model to represent the 6 MV photon beams from a Cyberknife stereotactic radiosurgery system for Monte Carlo treatment planning dose calculations. To achieve this goal, the 6 MV photon beams have been characterized and modelled using the EGS4/BEAM Monte Carlo system. A dual source model has been used to reconstruct the particle phase space at a plane immediately above the secondary collimator. The proposed model consists of two circular planar sources for the primary photons and the scattered photons, respectively. The dose contribution of the contaminant electrons was found to be in the order of 10-3 of the total maximum dose and therefore has been omitted in the source model. Various comparisons have been made to verify the dual source model against the full phase space simulated using the EGS4/BEAM system. The agreement in percent depth dose (PDD) curves and dose profiles between the phase space and the source model was generally within 2%/1 mm for various collimators (5 to 60 mm in diameter) at 80 to 100 cm source-to-surface distances (SSD). Excellent agreement (within 1%/1 mm) was also found between the dose distributions in heterogeneous lung and bone geometry calculated using the original phase space and those calculated using the source model. These results demonstrated the accuracy of the dual source model for Monte Carlo treatment planning dose calculations for the Cyberknife system.

Deng, Jun; Guerrero, Thomas; Ma, C.-M.; Nath, Ravinder

2004-05-01

135

Modelling 6 MV photon beams of a stereotactic radiosurgery system for Monte Carlo treatment planning.  

PubMed

The goal of this work is to build a multiple source model to represent the 6 MV photon beams from a Cyberknife stereotactic radiosurgery system for Monte Carlo treatment planning dose calculations. To achieve this goal, the 6 MV photon beams have been characterized and modelled using the EGS4/BEAM Monte Carlo system. A dual source model has been used to reconstruct the particle phase space at a plane immediately above the secondary collimator. The proposed model consists of two circular planar sources for the primary photons and the scattered photons, respectively. The dose contribution of the contaminant electrons was found to be in the order of 10(-3) of the total maximum dose and therefore has been omitted in the source model. Various comparisons have been made to verify the dual source model against the full phase space simulated using the EGS4/BEAM system. The agreement in percent depth dose (PDD) curves and dose profiles between the phase space and the source model was generally within 2%/1 mm for various collimators (5 to 60 mm in diameter) at 80 to 100 cm source-to-surface distances (SSD). Excellent agreement (within 1%/1 mm) was also found between the dose distributions in heterogeneous lung and bone geometry calculated using the original phase space and those calculated using the source model. These results demonstrated the accuracy of the dual source model for Monte Carlo treatment planning dose calculations for the Cyberknife system. PMID:15152924

Deng, Jun; Guerrero, Thomas; Ma, C M; Nath, Ravinder

2004-05-01

136

Monte Carlo simulation of charged particle transport in biomatter.  

PubMed

Knowledge of the microscopic distribution of interactions in irradiated matter is of fundamental importance for a mechanistic understanding of subsequent effects. This may be obtained by Monte Carlo codes which simulate event-by-event the transport of charged particles in matter. The development of such codes necessitates accurate interaction cross-sections for all the important collision processes. A semi-theoretical formalism has been developed and implemented in a Monte Carlo code which fairly accurately predicts energy-loss spectra for charged particle impact on water molecules. The extension of the formalism for establishing the necessary cross-sections for liquid/solid water (i.e. more realistic biomatter) is discussed and preliminary results are presented. PMID:11770524

Emfietzoglou, D; Papamichael, G; Moscovitch, M

2001-01-01

137

Photon transport in dense plant canopies  

SciTech Connect

With the main challenges in the numerical solution of the neutron transport equation having largely been met (i.e., multidimensional geometries, full matrix scattering, time dependence, etc.), numerical transport specialists have sought new applications with new transport equations. One such application is radiative transfer associated with satellite remote sensing for environmental monitoring. To reliably apply remote sensing techniques to obtain information about plant coverings (called plant canopies), an understanding of how radiant energy interacts with the elements of the plant canopy is essential. For example, in the investigation of the photosynthesis process and leaf respiration, plant physiologists are primarily concerned with the complex biochemistry driven by radiant energy in the visible portion of the sun`s spectrum. The agronomist, on the other hand, is concerned with how the features of the canopy influence the biochemical processes to promote photosynthesis. For both applications, knowledge of the amount photosynthesis. For both applications, knowledge of the amount of radiant energy input and the amount and wavelength spectrum of the reflected radiant energy is required. Currently, there are several approaches leading to estimates of the canopy reflectance (the angular response at the canopy surface), and one common formulation is the solution to the appropriate radiative transfer equation. The solution to the radiative transfer equation is complicated by the complexity of photon scattering interaction. In this paper, the solution to the one-angle radiative transfer equation for a dense canopy, with leaves assumed to scatter as Lambertian surfaces, is solved using a technique originally applied to the conventional radiative transfer equation.

Ganapol, B.D.

1994-12-31

138

Neutron and photon transport in seagoing cargo containers  

SciTech Connect

Factors affecting sensing of small quantities of fissionable material in large seagoing cargo containers by neutron interrogation and detection of {beta}-delayed photons are explored. The propagation of variable-energy neutrons in cargos, subsequent fission of hidden nuclear material and production of the {beta}-delayed photons, and the propagation of these photons to an external detector are considered explicitly. Detailed results of Monte Carlo simulations of these stages in representative cargos are presented. Analytical models are developed both as a basis for a quantitative understanding of the interrogation process and as a tool to allow ready extrapolation of our results to cases not specifically considered here.

Pruet, J.; Descalle, M.-A.; Hall, J.; Pohl, B.; Prussin, S.G. [Lawrence Livermore National Laboratory, N-Division, 7000 East Avenue, Livermore, California 94550 (United States); Department of Nuclear Engineering, University of California at Berkeley (United States)

2005-05-01

139

Low-energy photons in high-energy photon fields--Monte Carlo generated spectra and a new descriptive parameter.  

PubMed

The varying low-energy contribution to the photon spectra at points within and around radiotherapy photon fields is associated with variations in the responses of non-water equivalent dosimeters and in the water-to-material dose conversion factors for tissues such as the red bone marrow. In addition, the presence of low-energy photons in the photon spectrum enhances the RBE in general and in particular for the induction of second malignancies. The present study discusses the general rules valid for the low-energy spectral component of radiotherapeutic photon beams at points within and in the periphery of the treatment field, taking as an example the Siemens Primus linear accelerator at 6 MV and 15 MV. The photon spectra at these points and their typical variations due to the target system, attenuation, single and multiple Compton scattering, are described by the Monte Carlo method, using the code BEAMnrc/EGSnrc. A survey of the role of low energy photons in the spectra within and around radiotherapy fields is presented. In addition to the spectra, some data compression has proven useful to support the overview of the behaviour of the low-energy component. A characteristic indicator of the presence of low-energy photons is the dose fraction attributable to photons with energies not exceeding 200 keV, termed P(D)(200 keV). Its values are calculated for different depths and lateral positions within a water phantom. For a pencil beam of 6 or 15 MV primary photons in water, the radial distribution of P(D)(200 keV) is bellshaped, with a wide-ranging exponential tail of half value 6 to 7 cm. The P(D)(200 keV) value obtained on the central axis of a photon field shows an approximately proportional increase with field size. Out-of-field P(D)(200 keV) values are up to an order of magnitude higher than on the central axis for the same irradiation depth. The 2D pattern of P(D)(200 keV) for a radiotherapy field visualizes the regions, e.g. at the field margin, where changes of detector responses and dose conversion factors, as well as increases of the RBE have to be anticipated. Parameter P(D)(200 keV) can also be used as a guidance supporting the selection of a calibration geometry suitable for radiation dosimeters to be used in small radiation fields. PMID:21530198

Chofor, Ndimofor; Harder, Dietrich; Willborn, Kay; Rühmann, Antje; Poppe, Björn

2011-05-06

140

Resonance fluorescence near a photonic band edge: Dressed-state Monte Carlo wave-function approach  

NASA Astrophysics Data System (ADS)

We introduce a dressed-state Monte Carlo wave-function technique to describe resonance fluorescence in a broad class of non-Markovian reservoirs with strong atom-reservoir interaction. The method recaptures photon localization effects which are beyond the Born and Markovian approximations, and describes the influence of the driving field on the atom-reservoir interaction. Using this approach, we predict a number of fundamentally new features in resonance fluorescence near the edge of a photonic band gap. In particular, the atomic population exhibits inversion for moderate applied field intensity. For a low external field intensity, the atomic system retains a long-time memory of its initial state.

Quang, Tran; John, Sajeev

1997-11-01

141

A photon transport model code for use in scintillation detectors  

Microsoft Academic Search

A Monte Carlo code, PHOTRACK, has been written to simulate the behaviour of light photons in scintillation detectors, with and without light guides. It has been tested by reproducing the results of other workers, and then used in preliminary studies of a small lithium glass neutron detector.

N Ghal-Eh; M. C Scott; R Koohi-Fayegh; M. F Rahimi

2004-01-01

142

A high-order photon Monte Carlo method for radiative transfer in direct numerical simulation  

SciTech Connect

A high-order photon Monte Carlo method is developed to solve the radiative transfer equation. The statistical and discretization errors of the computed radiative heat flux and radiation source term are isolated and quantified. Up to sixth-order spatial accuracy is demonstrated for the radiative heat flux, and up to fourth-order accuracy for the radiation source term. This demonstrates the compatibility of the method with high-fidelity direct numerical simulation (DNS) for chemically reacting flows. The method is applied to address radiative heat transfer in a one-dimensional laminar premixed flame and a statistically one-dimensional turbulent premixed flame. Modifications of the flame structure with radiation are noted in both cases, and the effects of turbulence/radiation interactions on the local reaction zone structure are revealed for the turbulent flame. Computational issues in using a photon Monte Carlo method for DNS of turbulent reacting flows are discussed.

Wu, Y. [Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, 130 Research Building E, University Park, PA 16802 (United States); Modest, M.F. [Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, 130 Research Building E, University Park, PA 16802 (United States); Haworth, D.C. [Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, 130 Research Building E, University Park, PA 16802 (United States)]. E-mail: dch12@psu.edu

2007-05-01

143

Piecewise linear discretization of Symbolic Implicit Monte Carlo radiation transport in the difference formulation  

SciTech Connect

We describe a Monte Carlo solution for time dependent photon transport, in the difference formulation with the material in local thermodynamic equilibrium (LTE), that is piecewise linear in its treatment of the material state variable. Our method employs a Galerkin solution for the material energy equation while using Symbolic Implicit Monte Carlo (SIMC) to solve the transport equation. In constructing the scheme, one has the freedom to choose between expanding the material temperature, or the equivalent black body radiation energy density at the material temperature, in terms of finite element basis functions. The former provides a linear treatment of the material energy while the latter provides a linear treatment of the radiative coupling between zones. Subject to the conditional use of a lumped material energy in the vicinity of strong gradients, possible with a linear treatment of the material energy, our approach provides a robust solution for time dependent transport of thermally emitted radiation that can address a wide range of problems. It produces accurate results in the diffusion limit.

Brooks III, E D; Szoke, A; Peterson, J L

2005-11-15

144

Comparison of Monte Carlo Dose Calculation with Advanced Kernel Methods in External Photon Beam Treatment Planning  

Microsoft Academic Search

After successful implementation in commercial treatment planning systems (TPS) for high energy electron beams, Monte Carlo\\u000a dose calculation algorithms are becoming also commercially available for high energy photon beams. On the other hand, advanced\\u000a kernel based methods are in clinical use for many years. The aim of this study was to compare the accuracy of both types of\\u000a dose calculation

I. Fotina; B. Kroupa; D. Georg

145

Adaptively Learning an Importance Function Using Transport Constrained Monte Carlo  

SciTech Connect

It is well known that a Monte Carlo estimate can be obtained with zero-variance if an exact importance function for the estimate is known. There are many ways that one might iteratively seek to obtain an ever more exact importance function. This paper describes a method that has obtained ever more exact importance functions that empirically produce an error that is dropping exponentially with computer time. The method described herein constrains the importance function to satisfy the (adjoint) Boltzmann transport equation. This constraint is provided by using the known form of the solution, usually referred to as the Case eigenfunction solution.

Booth, T.E.

1998-06-22

146

Infrared nerve stimulation: modelling of photon transport and heat conduction  

NASA Astrophysics Data System (ADS)

Infrared neural stimulation (INS) is a novel technique for stimulating neurons with infrared light, rather than the traditional electrical means. There has been significant discussion in the literature on the mechanisms behind INS, while recent work has shown that infrared light stimulates neurons by causing a reversible change in their membrane capacitance. Nevertheless, the effect of different laser parameters on neuronal responses is still not well understood. To better understand this and to assist in designing light delivery systems, modelling of spatial and temporal characteristics of light delivery during INS has been performed. Monte Carlo modelling of photon transport in tissue allows the spatial characteristics of light to be determined during INS and allows comparisons of varying geometries and fibre designs. Finite element analysis of heat conduction can then be used to reveal the behavior of different pulse durations and the resulting temperature decay. The combination of the two methods allows for further insights into the mechanisms of INS and assists in understanding different mechanisms which promote INS. The model suggests there may be two regimes of INS, namely temperature limited for pulses under 100 ?s and temperature gradient limited for longer pulses. this is compatible with previously published data, but requires further experimentation for confirmation. The model also provides a tool for optimising the design of emitters and implants.

Thompson, Alexander C.; Wade, Scott A.; Cadusch, Peter J.; Brown, William G. A.; Stoddart, Paul R.

2013-02-01

147

Characterization of a novel micro-irradiator using Monte Carlo radiation transport simulations.  

PubMed

Small animals are highly valuable resources for radiobiology research. While rodents have been widely used for decades, zebrafish embryos have recently become a very popular research model. However, unlike rodents, zebrafish embryos lack appropriate irradiation tools and methodologies. Therefore, the main purpose of this work is to use Monte Carlo radiation transport simulations to characterize dosimetric parameters, determine dosimetric sensitivity and help with the design of a new micro-irradiator capable of delivering irradiation fields as small as 1.0 mm in diameter. The system is based on a miniature x-ray source enclosed in a brass collimator with 3 cm diameter and 3 cm length. A pinhole of 1.0 mm diameter along the central axis of the collimator is used to produce a narrow photon beam. The MCNP5, Monte Carlo code, is used to study the beam energy spectrum, percentage depth dose curves, penumbra and effective field size, dose rate and radiation levels at 50 cm from the source. The results obtained from Monte Carlo simulations show that a beam produced by the miniature x-ray and the collimator system is adequate to totally or partially irradiate zebrafish embryos, cell cultures and other small specimens used in radiobiology research. PMID:18475008

Rodriguez, Manuel; Jeraj, Robert

2008-05-12

148

Investigation of variance reduction techniques for Monte Carlo photon dose calculation using XVMC.  

PubMed

Several variance reduction techniques, such as photon splitting, electron history repetition, Russian roulette and the use of quasi-random numbers are investigated and shown to significantly improve the efficiency of the recently developed XVMC Monte Carlo code for photon beams in radiation therapy. It is demonstrated that it is possible to further improve the efficiency by optimizing transpon parameters such as electron energy cut-off, maximum electron energy step size, photon energy cut-off and a cut-off for kerma approximation, without loss of calculation accuracy. These methods increase the efficiency by a factor of up to 10 compared with the initial XVMC ray-tracing technique or a factor of 50 to 80 compared with EGS4/PRESTA. Therefore, a common treatment plan (6 MV photons, 10 x 10 cm2 field size, 5 mm voxel resolution, 1% statistical uncertainty) can be calculated within 7 min using a single CPU 500 MHz personal computer. If the requirement on the statistical uncertainty is relaxed to 2%, the calculation time will be less than 2 min. In addition, a technique is presented which allows for the quantitative comparison of Monte Carlo calculated dose distributions and the separation of systematic and statistical errors. Employing this technique it is shown that XVMC calculations agree with EGSnrc on a sub-per cent level for simulations in the energy and material range of interest for radiation therapy. PMID:10958187

Kawrakow, I; Fippel, M

2000-08-01

149

Optimization of Monte Carlo transport simulations in stochastic media  

SciTech Connect

This paper presents an accurate and efficient approach to optimize radiation transport simulations in a stochastic medium of high heterogeneity, like the Very High Temperature Gas-cooled Reactor (VHTR) configurations packed with TRISO fuel particles. Based on a fast nearest neighbor search algorithm, a modified fast Random Sequential Addition (RSA) method is first developed to speed up the generation of the stochastic media systems packed with both mono-sized and poly-sized spheres. A fast neutron tracking method is then developed to optimize the next sphere boundary search in the radiation transport procedure. In order to investigate their accuracy and efficiency, the developed sphere packing and neutron tracking methods are implemented into an in-house continuous energy Monte Carlo code to solve an eigenvalue problem in VHTR unit cells. Comparison with the MCNP benchmark calculations for the same problem indicates that the new methods show considerably higher computational efficiency. (authors)

Liang, C.; Ji, W. [Dept. of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Inst., 110 8th street, Troy, NY (United States)

2012-07-01

150

Multidimensional Monte Carlo model for two-photon laser-induced fluorescence and amplified spontaneous emission  

NASA Astrophysics Data System (ADS)

This paper describes the development of a multidimensional model based on the Monte Carlo (MC) method for the modeling of laser-induced fluorescence (LIF) and amplified spontaneous emission (ASE) signals involved in multi-photon processes. Multi-photon LIF finds applications in a broad range of topics; however, the interpretation of the LIF signal is plagued by the nonlinear effects caused by the ASE. Past work focused on developing one-dimensional (1D) models. Therefore, this work developed an MC method to solve the governing equations of ASE and LIF in multidimension. The results were validated using existing 1D data, both experimental and modeling. The results suggest that past 1D models cause noticeable error in the ASE signal even when the measurement volume has a large aspect ratio. We expect this work to facilitate the ongoing research of multi-photon LIF, and to stimulate new experiments that can provide data to validate the model in 2D.

Zhao, Yan; Li, Xuesong; Ma, Lin

2012-08-01

151

A Monte Carlo simulation of ion transport at finite temperatures  

NASA Astrophysics Data System (ADS)

We have developed a Monte Carlo simulation for ion transport in hot background gases, which is an alternative way of solving the corresponding Boltzmann equation that determines the distribution function of ions. We consider the limit of low ion densities when the distribution function of the background gas remains unchanged due to collision with ions. Special attention has been paid to properly treating the thermal motion of the host gas particles and their influence on ions, which is very important at low electric fields, when the mean ion energy is comparable to the thermal energy of the host gas. We found the conditional probability distribution of gas velocities that correspond to an ion of specific velocity which collides with a gas particle. Also, we have derived exact analytical formulae for piecewise calculation of the collision frequency integrals. We address the cases when the background gas is monocomponent and when it is a mixture of different gases. The techniques described here are required for Monte Carlo simulations of ion transport and for hybrid models of non-equilibrium plasmas. The range of energies where it is necessary to apply the technique has been defined. The results we obtained are in excellent agreement with the existing ones obtained by complementary methods. Having verified our algorithm, we were able to produce calculations for Ar+ ions in Ar and propose them as a new benchmark for thermal effects. The developed method is widely applicable for solving the Boltzmann equation that appears in many different contexts in physics.

Ristivojevic, Zoran; Petrovi?, Zoran Lj

2012-06-01

152

Photon-mediated electron transport in hybrid circuit-QED  

NASA Astrophysics Data System (ADS)

We investigate photon-mediated transport processes in a hybrid circuit-QED structure consisting of two double quantum dots coupled to a common microwave cavity. Under suitable resonance conditions, electron transport in one double quantum dot is facilitated by the transport in the other dot via photon-mediated processes through the cavity. We calculate the average current in the quantum dots, the mean cavity photon occupation, and the current cross-correlations with both a full numerical simulation and a recursive perturbation scheme that allows us to include the influence of the cavity order-by-order in the couplings between the cavity and the quantum dot systems. We can then clearly identify the photon-mediated transport processes.

Lambert, Neill; Flindt, Christian; Nori, Franco

2013-07-01

153

The derivation of Particle Monte Carlo methods for plasma modeling from transport equations  

Microsoft Academic Search

We analyze here in some detail, the derivation of the Particle and Monte Carlo methods of plasma simulation, such as Particle in Cell (PIC), Monte Carlo (MC) and Particle in Cell \\/ Monte Carlo (PIC\\/MC) from formal manipulation of transport equations.

Savino Longo

2008-01-01

154

COMPARISON OF SYNCHROTRON RADIATION CALCULATIONS BETWEEN ANALYTIC CODES (STAC8, PHOTON) AND MONTE CARLO CODES (FLUKA, EGS4)  

Microsoft Academic Search

Significantly improved upon its predecessor PHOTON, STAC8 is a valuable analytic code for quick and conservative beamline shielding designs for synchrotron radiation (SR) facilities. To check the applicability, accuracy, and limitations of STAC8, studies were conducted to compare STAC8 and PHOTON results with calculations using the FLUKA and EGS4 Monte Carlo codes. Doses and spectra for scattered SR in a

J. C. Liu; A. Fasso; A. Prinz; S. Rokni; Y. Asano

2004-01-01

155

Accelerating execution of the integrated TIGER series Monte Carlo radiation transport codes  

SciTech Connect

Execution of the integrated TIGER series (ITS) of coupled electron/photon Monte Carlo radiation transport codes has been accelerated by modifying the FORTRAN source code for more efficient computation. Each member code of ITS was benchmarked and profiled with a specific test case that directed the acceleration effort toward the most computationally intensive subroutines. Techniques for accelerating these subroutines included replacing linear search algorithms with binary versions, replacing the pseudo-random number generator, reducing program memory allocation, and proofing the input files for geometrical redundancies. All techniques produced identical or statistically similar results to the original code. Final benchmark timing of the accelerated code resulted in speed-up factors of 2.00 for TIGER (the one-dimensional slab geometry code), 1.74 for CYLTRAN (the two-dimensional cylindrical geometry code), and 1.90 for ACCEPT (the arbitrary three-dimensional geometry code).

Smith, L.M.; Hochstedler, R.D. [Univ of Tennessee Space Inst., Tullahoma, TN (United States). Dept. of Electrical Engineering

1997-02-01

156

Dissipationless electron transport in photon-dressed nanostructures.  

PubMed

It is shown that the electron coupling to photons in field-dressed nanostructures can result in the ground electron-photon state with a nonzero electric current. Since the current is associated with the ground state, it flows without the Joule heating of the nanostructure and is nondissipative. Such a dissipationless electron transport can be realized in strongly coupled electron-photon systems with the broken time-reversal symmetry--particularly, in quantum rings and chiral nanostructures dressed by circularly polarized photons. PMID:21981519

Kibis, O V

2011-08-31

157

Generalized free-space diffuse photon transport model based on the influence analysis of a camera lens diaphragm.  

PubMed

The camera lens diaphragm is an important component in a noncontact optical imaging system and has a crucial influence on the images registered on the CCD camera. However, this influence has not been taken into account in the existing free-space photon transport models. To model the photon transport process more accurately, a generalized free-space photon transport model is proposed. It combines Lambertian source theory with analysis of the influence of the camera lens diaphragm to simulate photon transport process in free space. In addition, the radiance theorem is also adopted to establish the energy relationship between the virtual detector and the CCD camera. The accuracy and feasibility of the proposed model is validated with a Monte-Carlo-based free-space photon transport model and physical phantom experiment. A comparison study with our previous hybrid radiosity-radiance theorem based model demonstrates the improvement performance and potential of the proposed model for simulating photon transport process in free space. PMID:20935713

Chen, Xueli; Gao, Xinbo; Qu, Xiaochao; Chen, Duofang; Ma, Xiaopeng; Liang, Jimin; Tian, Jie

2010-10-10

158

Light transport in trabecular bone: Monte Carlo simulation based on 3D triangle meshes  

NASA Astrophysics Data System (ADS)

Light transport in trabecular bone is not well understood despite its clinical interest. Recent experimental studies on optical bone biopsy are lacking models that relate their measurements to the underlying morphology and thus to tissue condition. Laser surgery can also benefit from a better understanding of energy distribution in cancellous bone. A Monte Carlo (MC) simulation environment, able to efficiently compute complex geometries and account for refraction and reflection on tissue boundaries has been developed to provide the missing insight. The geometry description is based on a 3D triangle mesh organised in a bounding-volume hierarchy. This efficient structure allows a fast photon-surface intersection test, ensuring a sufficient number of photon paths and thus a good signal-to-noise ratio. The simulation program has been validated against well-known problems of refractive optics and turbid media. This new tool has been applied to a set of numerical phantoms indicating that morphology may have a fundamental impact on long-range light transport. The simulation environment has also been used on high-resolution models of trabecular bone, based on micro-CT scans. Calculation of time resolved signals in transmission and reflectance geometries has been demonstrated, paving the way to numerical evaluation of new minimally invasive diagnostic techniques, and offering a link to evaluation of Optical Coherence Tomography (OCT) in complex heterogeneous geometries. Preliminary experimental results in support of the mentioned effects are presented.

Margallo-Balbás, Eduardo; French, Patrick J.; Wieringa, Peter A.

2006-03-01

159

Electron transport through a quantum dot assisted by cavity photons.  

PubMed

We investigate transient transport of electrons through a single quantum dot controlled by a plunger gate. The dot is embedded in a finite wire with length Lx assumed to lie along the x-direction with a parabolic confinement in the y-direction. The quantum wire, originally with hard-wall confinement at its ends, ±Lx/2, is weakly coupled at t = 0 to left and right leads acting as external electron reservoirs. The central system, the dot and the finite wire, is strongly coupled to a single cavity photon mode. A non-Markovian density-matrix formalism is employed to take into account the full electron-photon interaction in the transient regime. In the absence of a photon cavity, a resonant current peak can be found by tuning the plunger-gate voltage to lift a many-body state of the system into the source-drain bias window. In the presence of an x-polarized photon field, additional side peaks can be found due to photon-assisted transport. By appropriately tuning the plunger-gate voltage, the electrons in the left lead are allowed to undergo coherent inelastic scattering to a two-photon state above the bias window if initially one photon was present in the cavity. However, this photon-assisted feature is suppressed in the case of a y-polarized photon field due to the anisotropy of our system caused by its geometry. PMID:24132041

Abdullah, Nzar Rauf; Tang, Chi-Shung; Manolescu, Andrei; Gudmundsson, Vidar

2013-10-17

160

Electron transport through a quantum dot assisted by cavity photons  

NASA Astrophysics Data System (ADS)

We investigate transient transport of electrons through a single quantum dot controlled by a plunger gate. The dot is embedded in a finite wire with length Lx assumed to lie along the x-direction with a parabolic confinement in the y-direction. The quantum wire, originally with hard-wall confinement at its ends, ±Lx/2, is weakly coupled at t = 0 to left and right leads acting as external electron reservoirs. The central system, the dot and the finite wire, is strongly coupled to a single cavity photon mode. A non-Markovian density-matrix formalism is employed to take into account the full electron–photon interaction in the transient regime. In the absence of a photon cavity, a resonant current peak can be found by tuning the plunger-gate voltage to lift a many-body state of the system into the source–drain bias window. In the presence of an x-polarized photon field, additional side peaks can be found due to photon-assisted transport. By appropriately tuning the plunger-gate voltage, the electrons in the left lead are allowed to undergo coherent inelastic scattering to a two-photon state above the bias window if initially one photon was present in the cavity. However, this photon-assisted feature is suppressed in the case of a y-polarized photon field due to the anisotropy of our system caused by its geometry.

Abdullah, Nzar Rauf; Tang, Chi-Shung; Manolescu, Andrei; Gudmundsson, Vidar

2013-11-01

161

Acceleration of a Monte Carlo radiation transport code  

SciTech Connect

Execution time for the Integrated TIGER Series (ITS) Monte Carlo radiation transport code has been reduced by careful re-coding of computationally intensive subroutines. Three test cases for the TIGER (1-D slab geometry), CYLTRAN (2-D cylindrical geometry), and ACCEPT (3-D arbitrary geometry) codes were identified and used to benchmark and profile program execution. Based upon these results, sixteen top time-consuming subroutines were examined and nine of them modified to accelerate computations with equivalent numerical output to the original. The results obtained via this study indicate that speedup factors of 1.90 for the TIGER code, 1.67 for the CYLTRAN code, and 1.11 for the ACCEPT code are achievable. {copyright} {ital 1996 American Institute of Physics.}

Hochstedler, R.D.; Smith, L.M. [The University of Tennessee Space Institute, B. H. Goethert Parkway, MS 21, Tullahoma, Tennessee 37388-8897 (United States)

1996-03-01

162

Monte Carlo simulation of charge transport in amorphous chalcogenides  

NASA Astrophysics Data System (ADS)

The I(V) characteristics of amorphous GST devices show a peculiar S-shape behavior, that is a swift rise of the current along with a voltage snap-back. This type of characteristics led to a growing research interest in view of the future application of such materials to the manufacturing of phase-change memory devices. In this work we adopt a generalization of the variable-range hopping theory to simulate charge transport in a layer of amorphous Ge2Sb2Te5 sandwiched between two planar metallic electrodes. The numerical implementation of a current-driven Monte Carlo code allows one both to provide a complete microscopic particle picture of electrical conduction in the device and to better analyze the mechanisms governing the snap-back effect.

Piccinini, E.; Buscemi, F.; Rudan, M.; Brunetti, R.; Jacoboni, C.

2009-11-01

163

Response of thermoluminescent dosimeters to photons simulated with the Monte Carlo method  

Microsoft Academic Search

Personal monitors composed of thermoluminescent dosimeters (TLDs) made of natural fluorite (CaF2:NaCl) and lithium fluoride (Harshaw TLD-100) were exposed to gamma and X rays of different qualities. The GEANT4 radiation transport Monte Carlo toolkit was employed to calculate the energy depth deposition profile in the TLDs. X-ray spectra of the ISO\\/4037-1 narrow-spectrum series, with peak voltage (kVp) values in the

M. Moralles; C. C. Guimarães; E. Okuno

2005-01-01

164

Parallelization of a Monte Carlo particle transport simulation code  

NASA Astrophysics Data System (ADS)

We have developed a high performance version of the Monte Carlo particle transport simulation code MC4. The original application code, developed in Visual Basic for Applications (VBA) for Microsoft Excel, was first rewritten in the C programming language for improving code portability. Several pseudo-random number generators have been also integrated and studied. The new MC4 version was then parallelized for shared and distributed-memory multiprocessor systems using the Message Passing Interface. Two parallel pseudo-random number generator libraries (SPRNG and DCMT) have been seamlessly integrated. The performance speedup of parallel MC4 has been studied on a variety of parallel computing architectures including an Intel Xeon server with 4 dual-core processors, a Sun cluster consisting of 16 nodes of 2 dual-core AMD Opteron processors and a 200 dual-processor HP cluster. For large problem size, which is limited only by the physical memory of the multiprocessor server, the speedup results are almost linear on all systems. We have validated the parallel implementation against the serial VBA and C implementations using the same random number generator. Our experimental results on the transport and energy loss of electrons in a water medium show that the serial and parallel codes are equivalent in accuracy. The present improvements allow for studying of higher particle energies with the use of more accurate physical models, and improve statistics as more particles tracks can be simulated in low response time.

Hadjidoukas, P.; Bousis, C.; Emfietzoglou, D.

2010-05-01

165

Soft Photons from transport and hydrodynamics at FAIR energies  

NASA Astrophysics Data System (ADS)

Direct photon spectra from uranium-uranium collisions at FAIR energies (Elab = 35 AGeV) are calculated within the hadronic Ultra-relativistic Quantum Molecular Dynamics transport model. In this microscopic model, one can optionally include a macroscopic intermediate hydrodynamic phase. The hot and dense stage of the collision is then modeled by a hydro dynamical calculation. Photon emission from transport-hydro hybrid calculations is examined for purely hadronic matter and matter that has a cross-over phase transition and a critical end point to deconfined and chirally restored matter at high temperatures. We find the photon spectra in both scenarios to be dominated by Bremsstrahlung. Comparing flow of photons in both cases suggests a way to distinguish these two scenarios.

Grimm, Andreas; Bäuchle, Bjørn

2013-03-01

166

All-band photonic transport system and its device technologies  

NASA Astrophysics Data System (ADS)

To open up new optical frequency resources for communications, a concept called all-band photonics is proposed. This concept focuses on 1-?m waveband photonic transmission and device technologies, thereby pioneering a new waveband for photonic transport systems (PTSs). To construct the 1-?m PTS, a novel semiconductor light-source, optical-fiber transmission lines, and optical amplifiers are developed. In this paper, we demonstrate a 1-?m waveband, high bit-rate (>10 Gbps), and long-distance photonic transmission system by using attractive photonic devices such as mode-locked semiconductor lasers (MLL), wavelength tunable quantum dot (QD) lasers, QD optical frequency comb lasers (QD-CMLs), holey-fiber transmission lines, and Ytterbium-doped fiber amplifiers (YDFAs).

Yamamoto, Naokatsu; Sotobayashi, Hideyuki

2009-01-01

167

Improvements of low-energy photon transport in EGS4  

NASA Astrophysics Data System (ADS)

The treatment of low-energy (<=1 MeV) photon transport in the EGS4 code [Nelson, W.R., Hirayama, H. and Rogers, D.W.O., 1985. The EGS4 Code System SLAC-265 Stanford Linear Accelerator Center] has been improved. This also includes an improvement of the treatment of the electrons generated from low-energy photons and photons generated from low-energy electrons. The phenomena treated are: (i) linearly polarized photon scattering, (ii) Doppler broadening of Compton-scattered photons, (iii) L-X-ray and L-photoelectron production and (iv) electron impact ionization. We made measurements to verify the improved EGS4 code using monochromatized synchrotron radiation.

Namito, Y.; Hirayama, H.; Ban, S.

1998-09-01

168

Monte Carlo simulation of photon migration in 3D turbid media accelerated by graphics processing units.  

PubMed

We report a parallel Monte Carlo algorithm accelerated by graphics processing units (GPU) for modeling time-resolved photon migration in arbitrary 3D turbid media. By taking advantage of the massively parallel threads and low-memory latency, this algorithm allows many photons to be simulated simultaneously in a GPU. To further improve the computational efficiency, we explored two parallel random number generators (RNG), including a floating-point-only RNG based on a chaotic lattice. An efficient scheme for boundary reflection was implemented, along with the functions for time-resolved imaging. For a homogeneous semi-infinite medium, good agreement was observed between the simulation output and the analytical solution from the diffusion theory. The code was implemented with CUDA programming language, and benchmarked under various parameters, such as thread number, selection of RNG and memory access pattern. With a low-cost graphics card, this algorithm has demonstrated an acceleration ratio above 300 when using 1792 parallel threads over conventional CPU computation. The acceleration ratio drops to 75 when using atomic operations. These results render the GPU-based Monte Carlo simulation a practical solution for data analysis in a wide range of diffuse optical imaging applications, such as human brain or small-animal imaging. PMID:19997242

Fang, Qianqian; Boas, David A

2009-10-26

169

Monte Carlo simulation of photon migration in 3D turbid media accelerated by graphics processing units  

PubMed Central

We report a parallel Monte Carlo algorithm accelerated by graphics processing units (GPU) for modeling time-resolved photon migration in arbitrary 3D turbid media. By taking advantage of the massively parallel threads and low-memory latency, this algorithm allows many photons to be simulated simultaneously in a GPU. To further improve the computational efficiency, we explored two parallel random number generators (RNG), including a floating-point-only RNG based on a chaotic lattice. An efficient scheme for boundary reflection was implemented, along with the functions for time-resolved imaging. For a homogeneous semi-infinite medium, good agreement was observed between the simulation output and the analytical solution from the diffusion theory. The code was implemented with CUDA programming language, and benchmarked under various parameters, such as thread number, selection of RNG and memory access pattern. With a low-cost graphics card, this algorithm has demonstrated an acceleration ratio above 300 when using 1792 parallel threads over conventional CPU computation. The acceleration ratio drops to 75 when using atomic operations. These results render the GPU-based Monte Carlo simulation a practical solution for data analysis in a wide range of diffuse optical imaging applications, such as human brain or small-animal imaging.

Boas, David A.

2010-01-01

170

Monte Carlo-based energy response studies of diode dosimeters in radiotherapy photon beams.  

PubMed

This study presents Monte Carlo-calculated absolute and normalized (relative to a (60)Co beam) sensitivity values of silicon diode dosimeters for a variety of commercially available silicon diode dosimeters for radiotherapy photon beams in the energy range of (60)Co-24 MV. These values were obtained at 5 cm depth along the central axis of a water-equivalent phantom of 10 cm × 10 cm field size. The Monte Carlo calculations were based on the EGSnrc code system. The diode dosimeters considered in the calculations have different buildup materials such as aluminum, brass, copper, and stainless steel + epoxy. The calculated normalized sensitivity values of the diode dosimeters were then compared to previously published measured values for photon beams at (60)Co-20 MV. The comparison showed reasonable agreement for some diode dosimeters and deviations of 5-17 % (17 % for the 3.4 mm brass buildup case for a 10 MV beam) for some diode dosimeters. Larger deviations of the measurements reflect that these models of the diode dosimeter were too simple. The effect of wall materials on the absorbed dose to the diode was studied and the results are presented. Spencer-Attix and Bragg-Gray stopping power ratios (SPRs) of water-to-diode were calculated at 5 cm depth in water. The Bragg-Gray SPRs of water-to-diode compare well with Spencer-Attix SPRs for ? = 100 keV and above at all beam qualities. PMID:23180010

Arun, C; Palani Selvam, T; Dinkar, Verma; Munshi, Prabhat; Kalra, Manjit Singh

2012-11-20

171

Photon-cell interactive Monte Carlo model based on the geometric optics theory for photon migration in blood by incorporating both extra- and intracellular pathways.  

PubMed

A photon-cell interactive Monte Carlo (pciMC) that tracks photon migration in both the extra- and intracellular spaces is developed without using macroscopic scattering phase functions and anisotropy factors, as required for the conventional Monte Carlos (MCs). The interaction of photons at the plasma-cell boundary of randomly oriented 3-D biconcave red blood cells (RBCs) is modeled using the geometric optics. The pciMC incorporates different photon velocities from the extra- to intracellular space, whereas the conventional MC treats RBCs as points in the space with a constant velocity. In comparison to the experiments, the pciMC yielded the mean errors in photon migration time of 9.8±6.8 and 11.2±8.5% for suspensions of small and large RBCs (RBC(small), RBC(large)) averaged over the optically diffusing region from 2000 to 4000 ?m, while the conventional random walk Monte Carlo simulation gave statistically higher mean errors of 19.0±5.8 (?p?photon migration in the optically diffusing, turbid medium. PMID:21198165

Sakota, Daisuke; Takatani, Setsuo

172

Monte Carlo impurity transport modeling in the DIII-D transport  

SciTech Connect

A description of the carbon transport and sputtering physics contained in the Monte Carlo Impurity (MCI) transport code is given. Examples of statistically significant carbon transport pathways are examined using MCI`s unique tracking visualizer and a mechanism for enhanced carbon accumulation on the high field side of the divertor chamber is discussed. Comparisons between carbon emissions calculated with MCI and those measured in the DIII-D tokamak are described. Good qualitative agreement is found between 2D carbon emission patterns calculated with MCI and experimentally measured carbon patterns. While uncertainties in the sputtering physics, atomic data, and transport models have made quantitative comparisons with experiments more difficult, recent results using a physics based model for physical and chemical sputtering has yielded simulations with about 50% of the total carbon radiation measured in the divertor. These results and plans for future improvement in the physics models and atomic data are discussed.

Evans, T.E. [General Atomics, San Diego, CA (United States); Finkenthal, D.F. [Palomar College, San Marcos, CA (United States)

1998-04-01

173

Study on photon transport problem based on the platform of molecular optical simulation environment.  

PubMed

As an important molecular imaging modality, optical imaging has attracted increasing attention in the recent years. Since the physical experiment is usually complicated and expensive, research methods based on simulation platforms have obtained extensive attention. We developed a simulation platform named Molecular Optical Simulation Environment (MOSE) to simulate photon transport in both biological tissues and free space for optical imaging based on noncontact measurement. In this platform, Monte Carlo (MC) method and the hybrid radiosity-radiance theorem are used to simulate photon transport in biological tissues and free space, respectively, so both contact and noncontact measurement modes of optical imaging can be simulated properly. In addition, a parallelization strategy for MC method is employed to improve the computational efficiency. In this paper, we study the photon transport problems in both biological tissues and free space using MOSE. The results are compared with Tracepro, simplified spherical harmonics method (SP(n)), and physical measurement to verify the performance of our study method on both accuracy and efficiency. PMID:20445737

Peng, Kuan; Gao, Xinbo; Liang, Jimin; Qu, Xiaochao; Ren, Nunu; Chen, Xueli; Ma, Bin; Tian, Jie

2010-04-22

174

MULTIDIMENSIONAL COUPLED PHOTON-ELECTRON TRANSPORT SIMULATIONS USING NEUTRAL PARTICLE SN CODES  

SciTech Connect

During the past two years a study was underway at ORNL to assess the suitability of the popular SN neutral particle codes ANISN, DORT and TORT for coupled photon-electron calculations specific to external beam therapy of medical physics applications. The CEPXS-BFP code was used to generate the cross sections. The computational tests were performed on phantoms typical of those used in medical physics for external beam therapy, with materials simulated by water at different densities and the comparisons were made against Monte Carlo simulations that served as benchmarks. Although the results for one-dimensional calculations were encouraging, it appeared that the higher dimensional transport codes had fundamental difficulties in handling the electron transport. The results of two-dimensional simulations using the code DORT with an S16 fully symmetric quadrature set agree fairly with the reference Monte Carlo results but not well enough for clinical applications. While the photon fluxes are in better agreement (generally, within less than 5% from the reference), the discrepancy increases, sometimes very significantly, for the electron fluxes. The paper, however, focuses on the results obtained with the three-dimensional code TORT which had convergence difficulties for the electron groups. Numerical instabilities occurred in these groups. These instabilities were more pronounced with the degree of anisotropy of the problem.

Ilas, Dan [ORNL; Williams, Mark L [ORNL; Peplow, Douglas E. [ORNL; Kirk, Bernadette Lugue [ORNL

2008-01-01

175

Experimental investigation of a fast Monte Carlo photon beam dose calculation algorithm.  

PubMed

An experimental verification of the recently developed XVMC code, a fast Monte Carlo algorithm to calculate dose distributions of photon beams in treatment planning, is presented. The treatment head is modelled by a point source with energy distribution (primary photons) and an additional head scatter contribution. Utility software is presented, allowing the determination of the parameters for this model using a single measured depth dose curve in water. The simple beam model is considered to be a starting point for more complex models being planned for future versions of the code. This paper is mainly focused on the influence of the different techniques on variance reduction and material property determination for dose distributions. It is demonstrated that XVMC and the simple beam model reproduce measured (by a diamond detector) relative dose distributions with an accuracy of better than +/-2% in various homogeneous and inhomogeneous phantoms. Furthermore, relative dose distributions in solid state phantoms have been measured by film. Also for these cases, measured and calculated dose distributions agree within experimental uncertainty. The short calculation time (depending on voxel resolution, statistical accuracy, field size and energy, a span of 1 min to 1 h using a present-day personal computer) and an interface to a commercial planning system will allow the implementation of the code for routine treatment planning of clinical electron and photon beams. PMID:10616153

Fippel, M; Laub, W; Huber, B; Nüsslin, F

1999-12-01

176

Coupled proton/neutron transport calculations using the S(sub N) and Monte Carlo methods.  

National Technical Information Service (NTIS)

Coupled charged/neutral article transport calculations are most often carried out using the Monte Carol technique. For example, the ITS, EGS, and MCNP (Version 4) codes are used extensively for electron/photon transport calculations while HETC models the ...

W. L. Filippone R. C. Little J. E. Morel R. E. MacFarlane P. G. Young

1991-01-01

177

Determining superficial dosimetry for the internal canthus from the Monte Carlo simulation of kV photon and MeV electron beams.  

PubMed

This paper presents the findings of an investigation into the Monte Carlo simulation of superficial cancer treatments of an internal canthus site using both kilovoltage photons and megavoltage electrons. The EGSnrc system of codes for the Monte Carlo simulation of the transport of electrons and photons through a phantom representative of either a water phantom or treatment site in a patient is utilised. Two clinical treatment units are simulated: the Varian Medical Systems Clinac 2100C accelerator for 6 MeV electron fields and the Pantak Therapax SXT 150 X-ray unit for 100 kVp photon fields. Depth dose, profile and isodose curves for these simulated units are compared against those measured by ion chamber in a PTW Freiburg MP3 water phantom. Good agreement was achieved away from the surface of the phantom between simulated and measured data. Dose distributions are determined for both kV photon and MeV electron fields in the internal canthus site containing lead and tungsten shielding, rapidly sloping surfaces and different density interfaces. There is a relatively high level of deposition of dose in tissue-bone and tissue-cartilage interfaces in the kV photon fields in contrast to the MeV electron fields. This is reflected in the maximum doses in the PTV of the internal canthus field being 12 Gy for kV photons and 4.8 Gy for MeV electrons. From the dose distributions, DVH and dose comparators are used to assess the simulated treatment fields. Any indication as to which modality is preferable to treat the internal canthus requires careful consideration of many different factors, this investigation provides further perspective in being able to assess which modality is appropriate. PMID:19623857

Currie, B E

2009-06-01

178

Effect of transverse magnetic fields on dose distribution and RBE of photon beams: comparing PENELOPE and EGS4 Monte Carlo codes.  

PubMed

The application of a strong transverse magnetic field to a volume undergoing irradiation by a photon beam can produce localized regions of dose enhancement and dose reduction. This study uses the PENELOPE Monte Carlo code to investigate the effect of a slice of uniform transverse magnetic field on a photon beam using different magnetic field strengths and photon beam energies. The maximum and minimum dose yields obtained in the regions of dose enhancement and dose reduction are compared to those obtained with the EGS4 Monte Carlo code in a study by Li et al (2001), who investigated the effect of a slice of uniform transverse magnetic field (1 to 20 Tesla) applied to high-energy photon beams. PENELOPE simulations yielded maximum dose enhancements and dose reductions as much as 111% and 77%, respectively, where most results were within 6% of the EGS4 result. Further PENELOPE simulations were performed with the Sheikh-Bagheri and Rogers (2002) input spectra for 6, 10 and 15 MV photon beams, yielding results within 4% of those obtained with the Mohan et al (1985) spectra. Small discrepancies between a few of the EGS4 and PENELOPE results prompted an investigation into the influence of the PENELOPE elastic scattering parameters C(1) and C(2) and low-energy electron and photon transport cut-offs. Repeating the simulations with smaller scoring bins improved the resolution of the regions of dose enhancement and dose reduction, especially near the magnetic field boundaries where the dose deposition can abruptly increase or decrease. This study also investigates the effect of a magnetic field on the low-energy electron spectrum that may correspond to a change in the radiobiological effectiveness (RBE). Simulations show that the increase in dose is achieved predominantly through the lower energy electron population. PMID:18723929

Nettelbeck, H; Takacs, G J; Rosenfeld, A B

2008-08-22

179

Effect of transverse magnetic fields on dose distribution and RBE of photon beams: comparing PENELOPE and EGS4 Monte Carlo codes  

NASA Astrophysics Data System (ADS)

The application of a strong transverse magnetic field to a volume undergoing irradiation by a photon beam can produce localized regions of dose enhancement and dose reduction. This study uses the PENELOPE Monte Carlo code to investigate the effect of a slice of uniform transverse magnetic field on a photon beam using different magnetic field strengths and photon beam energies. The maximum and minimum dose yields obtained in the regions of dose enhancement and dose reduction are compared to those obtained with the EGS4 Monte Carlo code in a study by Li et al (2001), who investigated the effect of a slice of uniform transverse magnetic field (1 to 20 Tesla) applied to high-energy photon beams. PENELOPE simulations yielded maximum dose enhancements and dose reductions as much as 111% and 77%, respectively, where most results were within 6% of the EGS4 result. Further PENELOPE simulations were performed with the Sheikh-Bagheri and Rogers (2002) input spectra for 6, 10 and 15 MV photon beams, yielding results within 4% of those obtained with the Mohan et al (1985) spectra. Small discrepancies between a few of the EGS4 and PENELOPE results prompted an investigation into the influence of the PENELOPE elastic scattering parameters C1 and C2 and low-energy electron and photon transport cut-offs. Repeating the simulations with smaller scoring bins improved the resolution of the regions of dose enhancement and dose reduction, especially near the magnetic field boundaries where the dose deposition can abruptly increase or decrease. This study also investigates the effect of a magnetic field on the low-energy electron spectrum that may correspond to a change in the radiobiological effectiveness (RBE). Simulations show that the increase in dose is achieved predominantly through the lower energy electron population.

Nettelbeck, H.; Takacs, G. J.; Rosenfeld, A. B.

2008-09-01

180

Status of the MORSE multigroup Monte Carlo radiation transport code  

SciTech Connect

There are two versions of the MORSE multigroup Monte Carlo radiation transport computer code system at Oak Ridge National Laboratory. MORSE-CGA is the most well-known and has undergone extensive use for many years. MORSE-SGC was originally developed in about 1980 in order to restructure the cross-section handling and thereby save storage. However, with the advent of new computer systems having much larger storage capacity, that aspect of SGC has become unnecessary. Both versions use data from multigroup cross-section libraries, although in somewhat different formats. MORSE-SGC is the version of MORSE that is part of the SCALE system, but it can also be run stand-alone. Both CGA and SGC use the Multiple Array System (MARS) geometry package. In the last six months the main focus of the work on these two versions has been on making them operational on workstations, in particular, the IBM RISC 6000 family. A new version of SCALE for workstations is being released to the Radiation Shielding Information Center (RSIC). MORSE-CGA, Version 2.0, is also being released to RSIC. Both SGC and CGA have undergone other revisions recently. This paper reports on the current status of the MORSE code system.

Emmett, M.B.

1993-06-01

181

An automated variance reduction method for global Monte Carlo neutral particle transport problems  

NASA Astrophysics Data System (ADS)

A method to automatically reduce the variance in global neutral particle Monte Carlo problems by using a weight window derived from a deterministic forward solution is presented. This method reduces a global measure of the variance of desired tallies and increases its associated figure of merit. Global deep penetration neutron transport problems present difficulties for analog Monte Carlo. When the scalar flux decreases by many orders of magnitude, so does the number of Monte Carlo particles. This can result in large statistical errors. In conjunction with survival biasing, a weight window is employed which uses splitting and Russian roulette to restrict the symbolic weights of Monte Carlo particles. By establishing a connection between the scalar flux and the weight window, two important concepts are demonstrated. First, such a weight window can be constructed from a deterministic solution of a forward transport problem. Also, the weight window will distribute Monte Carlo particles in such a way to minimize a measure of the global variance. For Implicit Monte Carlo solutions of radiative transfer problems, an inefficient distribution of Monte Carlo particles can result in large statistical errors in front of the Marshak wave and at its leading edge. Again, the global Monte Carlo method is used, which employs a time-dependent weight window derived from a forward deterministic solution. Here, the algorithm is modified to enhance the number of Monte Carlo particles in the wavefront. Simulations show that use of this time-dependent weight window significantly improves the Monte Carlo calculation.

Cooper, Marc Andrew

182

Photonic antenna system for light harvesting, transport and trapping  

Microsoft Academic Search

Host¿guest composites with photonic antenna properties are described. The material consists of cylindrical zeolite L crystals the channels of which are filled with chains of joined but electronically non-interacting dye molecules. Light shining on a crystal is first absorbed and the energy is then transported by the dye molecules inside the tubes to the desired part. Data on crystals in

G. Calzaferri; M. Pauchard; H. Maas; S. Huber; A. Khatyr; T. J. Schaafsma

2002-01-01

183

Implicit Monte Carlo Methods and Non-Equilibrium Marshak Wave Radiative Transport.  

National Technical Information Service (NTIS)

Two enhancements to the Fleck implicit Monte Carlo method for radiative transport are described, for use in transparent and opaque media respectively. The first introduces a spectral mean cross section, which applies to pseudoscattering in transparent reg...

J. E. Lynch

1985-01-01

184

Neutron and photon doses in high energy radiotherapy facilities and evaluation of shielding performance by Monte Carlo method  

Microsoft Academic Search

Medical accelerators operating above 10MV are a source of undesirable neutron radiations which contaminate the therapeutic photon beam. These photoneutrons can also generate secondary gamma rays which increases undesirable dose to the patient body and to personnel and general public. In this study, the Monte Carlo N-Particle MCNP5 code has been used to model the radiotherapy room of a medical

J. Ghassoun; N. Senhou; A. Jehouani

2011-01-01

185

Extension of the Integrated Tiger Series (ITS) of electron-photon Monte Carlo codes to 100 GeV  

SciTech Connect

Version 2.1 of the Integrated Tiger Series (ITS) of electron-photon Monte Carlo codes was modified to extend their ability to model interactions up to 100 GeV. Benchmarks against experimental results conducted at 10 and 15 GeV confirm the accuracy of the extended codes. 12 refs., 2 figs., 2 tabs.

Miller, S.G.

1989-10-01

186

Extension of the Integrated Tiger Series (ITS) of electron-photon Monte Carlo codes to 100 GeV  

SciTech Connect

Version 2.1 of the Integrated Tiger Series (ITS) of electron-photon Monte Carlo codes was modified to extend their ability to model interactions up to 100 GeV. Benchmarks against experimental results conducted at 10 and 15 GeV confirm the accuracy of the extended codes. 12 refs., 2 figs., 2 tabs.

Miller, S.G.

1988-08-01

187

Calculation of Dose from External Photon Exposures Using Reference Human Phantoms and Monte-Carlo Methods. Pt. 1.  

National Technical Information Service (NTIS)

By the help of a Monte-Carlo program the dose that single organs, organ groups and bigger or smaller parts of body would receive on an average, caused by an irradiation definitely fixed by the geometry of irradiation and photon energy, can be determined. ...

R. Kramer M. Zankl G. Williams G. Drexler

1982-01-01

188

Validation of Monte Carlo calculated surface doses for megavoltage photon beams.  

PubMed

Recent work has shown that there is significant uncertainty in measuring build-up doses in mega-voltage photon beams especially at high energies. In this present investigation we used a phantom-embedded extrapolation chamber (PEEC) made of Solid Water to validate Monte Carlo (MC)-calculated doses in the dose build-up region for 6 and 18 MV x-ray beams. The study showed that the percentage depth ionizations (PDIs) obtained from measurements are higher than the percentage depth doses (PDDs) obtained with Monte Carlo techniques. To validate the MC-calculated PDDs, the design of the PEEC was incorporated into the simulations. While the MC-calculated and measured PDIs in the dose build-up region agree with one another for the 6 MV beam, a non-negligible difference is observed for the 18 MV x-ray beam. A number of experiments and theoretical studies of various possible effects that could be the source of this discrepancy were performed. The contribution of contaminating neutrons and protons to the build-up dose region in the 18 MV x-ray beam is negligible. Moreover, the MC calculations using the XCOM photon cross-section database and the NIST bremsstrahlung differential cross section do not explain the discrepancy between the MC calculations and measurement in the dose build-up region for the 18 MV. A simple incorporation of triplet production events into the MC dose calculation increases the calculated doses in the build-up region but does not fully account for the discrepancy between measurement and calculations for the 18 MV x-ray beam. PMID:15719980

Abdel-Rahman, Wamied; Seuntjens, Jan P; Verhaegen, Frank; Deblois, François; Podgorsak, Ervin B

2005-01-01

189

A 3D Monte Carlo code for plasma transport in island divertors  

Microsoft Academic Search

A fully 3D self-consistent Monte Carlo code EMC3 (edge Monte Carlo 3D) for modelling the plasma transport in island divertors has been developed. In a first step, the code solves a simplified version of the 3D time-independent plasma fluid equations. Coupled to the neutral transport code EIRENE, the EMC3 code has been used to study the particle, energy and neutral

Y. Feng; F. Sardei; J. Kisslinger; P. Grigull

1997-01-01

190

Hybrid Description of Outflowing Ionospheric Plasma: A Monte Carlo\\/n-Moment Transport Equations Model  

Microsoft Academic Search

At terrestrial high latitudes, the plasma flows along ``open'' field lines, gradually going from a collision-dominated region into a collisionless region. Over several decades, the (fluid-like) generalized transport equations, TE, and the particle-based Monte Carlo, MC, approaches evolved as two of the most powerful simulation techniques that address this problem. In contrast to the computationally intensive Monte Carlo, the transport

J. Ji; A. R. Barakat; R. W. Schunk

2009-01-01

191

Disorder-enhanced transport in photonic quasi-crystals: Anderson localization and delocalization  

Microsoft Academic Search

We demonstrate experimentally that disorder enhances transport of waves in Penrose-type photonic quasicrystals. Increasing disorder gives rise to a transition from “bumpy ride” to diffusive transport.

Liad Levi; Mikael Rechtsman; Barak Freedman; Tal Schwartz; Ofer Manela; Mordechai Segev

2010-01-01

192

FZ2MC: A Tool for Monte Carlo Transport Code Geometry Manipulation  

SciTech Connect

The process of creating and validating combinatorial geometry representations of complex systems for use in Monte Carlo transport simulations can be both time consuming and error prone. To simplify this process, a tool has been developed which employs extensions of the Form-Z commercial solid modeling tool. The resultant FZ2MC (Form-Z to Monte Carlo) tool permits users to create, modify and validate Monte Carlo geometry and material composition input data. Plugin modules that export this data to an input file, as well as parse data from existing input files, have been developed for several Monte Carlo codes. The FZ2MC tool is envisioned as a 'universal' tool for the manipulation of Monte Carlo geometry and material data. To this end, collaboration on the development of plug-in modules for additional Monte Carlo codes is desired.

Hackel, B M; Nielsen Jr., D E; Procassini, R J

2009-02-25

193

Utilization of a Photon Transport Code to Investigate Radiation Therapy Treatment Planning Quantities and Techniques.  

NASA Astrophysics Data System (ADS)

A versatile computer program MORSE, based on neutron and photon transport theory has been utilized to investigate radiation therapy treatment planning quantities and techniques. A multi-energy group representation of transport equation provides a concise approach in utilizing Monte Carlo numerical techniques to multiple radiation therapy treatment planning problems. A general three dimensional geometry is used to simulate radiation therapy treatment planning problems in configurations of an actual clinical setting. Central axis total and scattered dose distributions for homogeneous and inhomogeneous water phantoms are calculated and the correction factor for lung and bone inhomogeneities are also evaluated. Results show that Monte Carlo calculations based on multi-energy group transport theory predict the depth dose distributions that are in good agreement with available experimental data. Improved correction factors based on the concepts of lung-air-ratio and bone-air-ratio are proposed in lieu of the presently used correction factors that are based on tissue-air-ratio power law method for inhomogeneity corrections. Central axis depth dose distributions for a bremsstrahlung spectrum from a linear accelerator is also calculated to exhibit the versatility of the computer program in handling multiple radiation therapy problems. A novel approach is undertaken to study the dosimetric properties of brachytherapy sources. Dose rate constants for various radionuclides are calculated from the numerically generated dose rate versus source energy curves. Dose rates can also be generated for any point brachytherapy source with any arbitrary energy spectrum at various radial distances from this family of curves.

Palta, Jatinder Raj

194

A virtual photon energy fluence model for Monte Carlo dose calculation.  

PubMed

The presented virtual energy fluence (VEF) model of the patient-independent part of the medical linear accelerator heads, consists of two Gaussian-shaped photon sources and one uniform electron source. The planar photon sources are located close to the bremsstrahlung target (primary source) and to the flattening filter (secondary source), respectively. The electron contamination source is located in the plane defining the lower end of the filter. The standard deviations or widths and the relative weights of each source are free parameters. Five other parameters correct for fluence variations, i.e., the horn or central depression effect. If these parameters and the field widths in the X and Y directions are given, the corresponding energy fluence distribution can be calculated analytically and compared to measured dose distributions in air. This provides a method of fitting the free parameters using the measurements for various square and rectangular fields and a fixed number of monitor units. The next step in generating the whole set of base data is to calculate monoenergetic central axis depth dose distributions in water which are used to derive the energy spectrum by deconvolving the measured depth dose curves. This spectrum is also corrected to take the off-axis softening into account. The VEF model is implemented together with geometry modules for the patient specific part of the treatment head (jaws, multileaf collimator) into the XVMC dose calculation engine. The implementation into other Monte Carlo codes is possible based on the information in this paper. Experiments are performed to verify the model by comparing measured and calculated dose distributions and output factors in water. It is demonstrated that open photon beams of linear accelerators from two different vendors are accurately simulated using the VEF model. The commissioning procedure of the VEF model is clinically feasible because it is based on standard measurements in air and water. It is also useful for IMRT applications because a full Monte Carlo simulation of the treatment head would be too time-consuming for many small fields. PMID:12674229

Fippel, Matthias; Haryanto, Freddy; Dohm, Oliver; Nüsslin, Fridtjof; Kriesen, Stephan

2003-03-01

195

Determination of peripheral underdosage at the lung-tumor interface using Monte Carlo radiation transport calculations  

SciTech Connect

Prediction of dose distributions in close proximity to interfaces is difficult. In the context of radiotherapy of lung tumors, this may affect the minimum dose received by lesions and is particularly important when prescribing dose to covering isodoses. The objective of this work is to quantify underdosage in key regions around a hypothetical target using Monte Carlo dose calculation methods, and to develop a factor for clinical estimation of such underdosage. A systematic set of calculations are undertaken using 2 Monte Carlo radiation transport codes (EGSnrc and GEANT4). Discrepancies in dose are determined for a number of parameters, including beam energy, tumor size, field size, and distance from chest wall. Calculations were performed for 1-mm{sup 3} regions at proximal, distal, and lateral aspects of a spherical tumor, determined for a 6-MV and a 15-MV photon beam. The simulations indicate regions of tumor underdose at the tumor-lung interface. Results are presented as ratios of the dose at key peripheral regions to the dose at the center of the tumor, a point at which the treatment planning system (TPS) predicts the dose more reliably. Comparison with TPS data (pencil-beam convolution) indicates such underdosage would not have been predicted accurately in the clinic. We define a dose reduction factor (DRF) as the average of the dose in the periphery in the 6 cardinal directions divided by the central dose in the target, the mean of which is 0.97 and 0.95 for a 6-MV and 15-MV beam, respectively. The DRF can assist clinicians in the estimation of the magnitude of potential discrepancies between prescribed and delivered dose distributions as a function of tumor size and location. Calculation for a systematic set of 'generic' tumors allows application to many classes of patient case, and is particularly useful for interpreting clinical trial data.

Taylor, Michael, E-mail: michael.taylor@rmit.edu.au [School of Applied Sciences, College of Science, Engineering and Health, RMIT University, Melbourne, Victoria (Australia); Physical Sciences, Peter MacCallum Cancer Centre, East Melbourne, Victoria (Australia); Dunn, Leon; Kron, Tomas; Height, Felicity; Franich, Rick [School of Applied Sciences, College of Science, Engineering and Health, RMIT University, Melbourne, Victoria (Australia); Physical Sciences, Peter MacCallum Cancer Centre, East Melbourne, Victoria (Australia)

2012-04-01

196

3D Monte Carlo model of optical transport in laser-irradiated cutaneous vascular malformations  

NASA Astrophysics Data System (ADS)

We have developed a three-dimensional Monte Carlo (MC) model of optical transport in skin and applied it to analysis of port wine stain treatment with sequential laser irradiation and intermittent cryogen spray cooling. Our MC model extends the approaches of the popular multi-layer model by Wang et al.1 to three dimensions, thus allowing treatment of skin inclusions with more complex geometries and arbitrary irradiation patterns. To overcome the obvious drawbacks of either "escape" or "mirror" boundary conditions at the lateral boundaries of the finely discretized volume of interest (VOI), photons exiting the VOI are propagated in laterally infinite tissue layers with appropriate optical properties, until they loose all their energy, escape into the air, or return to the VOI, but the energy deposition outside of the VOI is not computed and recorded. After discussing the selection of tissue parameters, we apply the model to analysis of blood photocoagulation and collateral thermal damage in treatment of port wine stain (PWS) lesions with sequential laser irradiation and intermittent cryogen spray cooling.

Majaron, Boris; Milani?, Matija; Jia, Wangcun; Nelson, J. S.

2010-06-01

197

Neutrino transport in type II supernovae: Boltzmann solver vs. Monte Carlo method  

Microsoft Academic Search

We have coded a Boltzmann solver based on a finite difference scheme (S_N method) aiming at calculations of neutrino transport in type II supernovae. Close comparison between the Boltzmann solver and a Monte Carlo transport code has been made for realistic atmospheres of post bounce core models under the assumption of a static background. We have also investigated in detail

Shoichi Yamada; Hans-Thomas Janka; Hideyuki Suzuki

1999-01-01

198

INTEGRATED KENO MONTE CARLO TRANSPORT FOR 3-D DEPLETION WITH SCALE  

Microsoft Academic Search

Accurate calculation of the depletion of nuclear materials requires careful determination of the neutron flux density and spectrum in the region(s) of interest. Increasing complexity in reactor designs, evolutionary concepts, and nonreactor applications such as safeguards, security, and nonproliferation, is beginning to require robust geometrical modeling capabilities to capture neutron transport for complex configurations. Monte Carlo transport methods offer the

Stephen M. Bowman; Mark D. DeHart; Lester M. Petrie

199

Monte Carlo simulation of small electron fields collimated by the integrated photon MLC  

NASA Astrophysics Data System (ADS)

In this study, a Monte Carlo (MC)-based beam model for an ELEKTA linear accelerator was established. The beam model is based on the EGSnrc Monte Carlo code, whereby electron beams with nominal energies of 10, 12 and 15 MeV were considered. For collimation of the electron beam, only the integrated photon multi-leaf-collimators (MLCs) were used. No additional secondary or tertiary add-ons like applicators, cutouts or dedicated electron MLCs were included. The source parameters of the initial electron beam were derived semi-automatically from measurements of depth-dose curves and lateral profiles in a water phantom. A routine to determine the initial electron energy spectra was developed which fits a Gaussian spectrum to the most prominent features of depth-dose curves. The comparisons of calculated and measured depth-dose curves demonstrated agreement within 1%/1 mm. The source divergence angle of initial electrons was fitted to lateral dose profiles beyond the range of electrons, where the imparted dose is mainly due to bremsstrahlung produced in the scattering foils. For accurate modelling of narrow beam segments, the influence of air density on dose calculation was studied. The air density for simulations was adjusted to local values (433 m above sea level) and compared with the standard air supplied by the ICRU data set. The results indicate that the air density is an influential parameter for dose calculations. Furthermore, the default value of the BEAMnrc parameter 'skin depth' for the boundary crossing algorithm was found to be inadequate for the modelling of small electron fields. A higher value for this parameter eliminated discrepancies in too broad dose profiles and an increased dose along the central axis. The beam model was validated with measurements, whereby an agreement mostly within 3%/3 mm was found.

Mihaljevic, Josip; Soukup, Martin; Dohm, Oliver; Alber, Markus

2011-02-01

200

Experiences with different parallel programming paradigms for Monte Carlo particle transport leads to a portable toolkit for parallel Monte Carlo  

SciTech Connect

Monte Carlo particle transport is easy to implement on massively parallel computers relative to other methods of transport simulation. This paper describes experiences of implementing a realistic demonstration Monte Carlo code on a variety of parallel architectures. Our pool of tasks'' technique, which allows reproducibility from run to run regardless of the number of processors, is discussed. We present detailed timing studies of simulations performed on the 128 processor BBN-ACI TC2000 and preliminary timing results for the 32 processor Kendall Square Research KSR-1. Given sufficient workload to distribute across many computational nodes, the BBN achieves nearly linear speedup for a large number of nodes. The KSR, with which we have had less experience, performs poorly with more than ten processors. A simple model incorporating known causes of overhead accurately predicts observed behavior. A general-purpose communication and control package to facilitate the implementation of existing Monte Carlo packages is described together with timings on the BBN. This package adds insignificantly to the computational costs of parallel simulations.

Martin, W.R.; Majumdar, A. (Michigan Univ., Ann Arbor, MI (United States). Dept. of Nuclear Engineering); Rathkopf, J.A. (Lawrence Livermore National Lab., CA (United States)); Litvin, M. (Phillips Academy, Andover, MA (United States))

1993-04-01

201

Experiences with different parallel programming paradigms for Monte Carlo particle transport leads to a portable toolkit for parallel Monte Carlo  

SciTech Connect

Monte Carlo particle transport is easy to implement on massively parallel computers relative to other methods of transport simulation. This paper describes experiences of implementing a realistic demonstration Monte Carlo code on a variety of parallel architectures. Our ``pool of tasks`` technique, which allows reproducibility from run to run regardless of the number of processors, is discussed. We present detailed timing studies of simulations performed on the 128 processor BBN-ACI TC2000 and preliminary timing results for the 32 processor Kendall Square Research KSR-1. Given sufficient workload to distribute across many computational nodes, the BBN achieves nearly linear speedup for a large number of nodes. The KSR, with which we have had less experience, performs poorly with more than ten processors. A simple model incorporating known causes of overhead accurately predicts observed behavior. A general-purpose communication and control package to facilitate the implementation of existing Monte Carlo packages is described together with timings on the BBN. This package adds insignificantly to the computational costs of parallel simulations.

Martin, W.R.; Majumdar, A. [Michigan Univ., Ann Arbor, MI (United States). Dept. of Nuclear Engineering; Rathkopf, J.A. [Lawrence Livermore National Lab., CA (United States); Litvin, M. [Phillips Academy, Andover, MA (United States)

1993-04-01

202

Monte Carlo linear accelerator simulation of megavoltage photon beams: Independent determination of initial beam parameters  

SciTech Connect

Purpose: To individually benchmark the incident electron parameters in a Monte Carlo model of an Elekta linear accelerator operating at 6 and 15 MV. The main objective is to establish a simplified but still precise benchmarking procedure that allows accurate dose calculations of advanced treatment techniques. Methods: The EGSnrc Monte Carlo user codes BEAMnrc and DOSXYZnrc are used for photon beam simulations and dose calculations, respectively. A 5 x 5 cm{sup 2} field is used to determine both the incident electron energy and the electron radial intensity. First, the electron energy is adjusted to match the calculated depth dose to the measured one. Second, the electron radial intensity is adjusted to make the calculated dose profile in the penumbrae region match the penumbrae measured by GafChromic EBT film. Finally, the mean angular spread of the incident electron beam is determined by matching calculated and measured cross-field profiles of large fields. The beam parameters are verified for various field sizes and shapes. Results: The penumbrae measurements revealed a non-circular electron radial intensity distribution for the 6 MV beam, while a circular electron radial intensity distribution could best describe the 15 MV beam. These electron radial intensity distributions, given as the standard deviation of a Gaussian distribution, were found to be 0.25 mm (in-plane) and 1.0 mm (cross-plane) for the 6 MV beam and 0.5 mm (both in-plane and cross-plane) for the 15 MV beam. Introducing a small mean angular spread of the incident electron beam has a considerable impact on the lateral dose profiles of large fields. The mean angular spread was found to be 0.7 deg. and 0.5 deg. for the 6 and 15 MV beams, respectively. Conclusions: The incident electron beam parameters in a Monte Carlo model of a linear accelerator could be precisely and independently determined by the benchmarking procedure proposed. As the dose distribution in the penumbra region is insensitive to moderate changes in electron energy and angular spread, accurate penumbra measurements is feasible for benchmarking the electron radial intensity distribution. This parameter is particularly important for accurate dosimetry of mlc-shaped fields and small fields.

Almberg, Sigrun Saur; Frengen, Jomar; Kylling, Arve; Lindmo, Tore [Department of Physics, Norwegian University of Science and Technology, NO-7491 Trondheim (Norway) and Department of Oncology and Radiotherapy, St. Olavs University Hospital, NO-7006 Trondheim (Norway); Department of Oncology and Radiotherapy, St. Olavs University Hospital, NO-7006 Trondheim (Norway); Department of Oncology and Radiotherapy, Aalesund Hospital, NO-6026 Aalesund (Norway); Department of Physics, Norwegian University of Science and Technology, NO-7491 Trondheim (Norway)

2012-01-15

203

Magnetic fields with photon beams: Monte Carlo calculations for a model magnetic field.  

PubMed

Strong transverse magnetic fields can produce very large dose enhancements and reductions in localized regions of a patient under irradiation by a photon beam. We have suggested a model magnetic field which can be expected to produce such large dose enhancements and reductions, and we have carried out EGS4 Monte Carlo calculations to examine this effect for a 6x6 cm2 photon beam of energy 15, 30, or 45 MV penetrating a water phantom. Our model magnetic field has a nominal (center) strength B0 ranging between 1 and 5 T, and a maximum strength within the geometric beam which is 2.2xB0. For all three beam energies, there is significant dose enhancement for B0 = 2 T which increases greatly for B0 = 3 T, but stronger magnetic fields increase the enhancement further only for the 45-MV beam. Correspondingly, there is major reduction in the dose just distal to this region of large dose enhancement, resulting from secondary electrons and positrons originating upstream which are depositing energy in the dose-enhancement region rather than continuing further into the patient. The dose peak region is fairly narrow (in depth), but the magnetic field can be shifted along the longitudinal axis to produce a flat peak region of medium width (approximately 2 cm) or of large width (approximately 4 cm), with rapid dose dropoffs on either side. For the 30-MV beam with B0 = 3 T, we found a dose enhancement of 55% for the narrow-width configuration, 32% for the medium-width configuration, and 23% for the large-width configuration; for the 45-MV beam with B0 = 3 T, the enhancements were quite similar, but for the 15-MV beam they were considerably less. For all of these 30-MV configurations, the dose reductions were approximately 30%, and they were approximately 40% for the 45-MV configurations. PMID:11190956

Jette, D

2000-12-01

204

Neutron streaming Monte Carlo radiation transport code MORSE-CG  

Microsoft Academic Search

Calculations have been performed using the Monte Carlo code, MORSE-CG, to determine the neutron streaming through various straight and stepped gaps between radiation shield sectors in the conceptual tokamak fusion power plant design STARFIRE. This design calls for ''pie-shaped'' radiation shields with gaps between segments. It is apparent that some type of offset, or stepped gap, configuration will be necessary

A. M. Halley; W. H. Miller

1986-01-01

205

Technique of Neutral Transport Simulation Using the DEGAS Monte-Carlo Code Application to GAMMA 10-  

Microsoft Academic Search

Techniques for the neutral transport simulation using a Monte-Carlo code are briefly reviewed by explaining the examples of the simulation with the DEGAS Monte-Carlo code. Tandem mirror plasma produced in GAMMA 10 is employed as a target plasma for the simulation. An axisymmetric simulation using the ver.35 code is applied for the central-region and a three-dimensional simulation in non-axisymmetric anchor

Yousuke Nakashima

2004-01-01

206

Electron and photon transport calculations between 1 MeV and 1 eV. Final report, November 1982-May 1986  

SciTech Connect

This report describes the development and application of numerical methods for predicting dose and variation in multi-layered structures due to x rays and gamma rays and the charge buildup in dielectrics due to electron-beam irradiation. The scope of the work included: development and implementation of: 1) discrete-ordinates electron-transport calculations for electron sources both within and incident of solid structures; 2) discrete-ordinates electron-transport calculations for photon sources incident on layered solids; and 3) Monte Carlo calculations and statistical analysis programs for low-energy electron transport in insulating structures. In addition, several photon-transport calculations were made to determine the scattered-photon energy spectra characteristic of various standard irradiation test facilities.

Woolf, S.

1988-04-01

207

Peer-to-peer Monte Carlo simulation of photon migration in topical applications of biomedical optics  

NASA Astrophysics Data System (ADS)

In the framework of further development of the unified approach of photon migration in complex turbid media, such as biological tissues we present a peer-to-peer (P2P) Monte Carlo (MC) code. The object-oriented programming is used for generalization of MC model for multipurpose use in various applications of biomedical optics. The online user interface providing multiuser access is developed using modern web technologies, such as Microsoft Silverlight, ASP.NET. The emerging P2P network utilizing computers with different types of compute unified device architecture-capable graphics processing units (GPUs) is applied for acceleration and to overcome the limitations, imposed by multiuser access in the online MC computational tool. The developed P2P MC was validated by comparing the results of simulation of diffuse reflectance and fluence rate distribution for semi-infinite scattering medium with known analytical results, results of adding-doubling method, and with other GPU-based MC techniques developed in the past. The best speedup of processing multiuser requests in a range of 4 to 35 s was achieved using single-precision computing, and the double-precision computing for floating-point arithmetic operations provides higher accuracy.

Doronin, Alexander; Meglinski, Igor

2012-09-01

208

Peer-to-peer Monte Carlo simulation of photon migration in topical applications of biomedical optics.  

PubMed

In the framework of further development of the unified approach of photon migration in complex turbid media, such as biological tissues we present a peer-to-peer (P2P) Monte Carlo (MC) code. The object-oriented programming is used for generalization of MC model for multipurpose use in various applications of biomedical optics. The online user interface providing multiuser access is developed using modern web technologies, such as Microsoft Silverlight, ASP.NET. The emerging P2P network utilizing computers with different types of compute unified device architecture-capable graphics processing units (GPUs) is applied for acceleration and to overcome the limitations, imposed by multiuser access in the online MC computational tool. The developed P2P MC was validated by comparing the results of simulation of diffuse reflectance and fluence rate distribution for semi-infinite scattering medium with known analytical results, results of adding-doubling method, and with other GPU-based MC techniques developed in the past. The best speedup of processing multiuser requests in a range of 4 to 35 s was achieved using single-precision computing, and the double-precision computing for floating-point arithmetic operations provides higher accuracy. PMID:23085901

Doronin, Alexander; Meglinski, Igor

2012-09-01

209

Application of the full-spectrum k-distribution method to photon Monte Carlo solvers  

NASA Astrophysics Data System (ADS)

Accurate prediction of radiative heat transfer is key in most high temperature applications, such as combustion devices and fires. Among the various solution methods for the radiative transfer equation (RTE), the photon Monte Carlo (PMC) method is potentially the most accurate and the most versatile. The implementation of a PMC method in multidimensional inhomogeneous problems, however, can be limited by its demand for large computer storage space and its CPU time consumption. This is particularly true if the spectral absorption coefficient is to be accurately represented, due to its irregular behavior. On the other hand, the recently developed full-spectrum k-distribution (FSK) method reorders the irregular absorption coefficient into smooth k-distributions and, therefore, provides an efficient and accurate scheme for the spectral integration of radiative quantities of interest. In this paper the accuracy of the PMC method in solving the RTE and the efficiency and storage advantage provided by the FSK method are combined. The advantages of the proposed PMC/FSK method is described in detail. The accuracy and the efficiency of the method are demonstrated by sample calculations that consider inhomogeneous problems.

Wang, L.; Yang, J.; Modest, M. F.; Haworth, D. C.

2007-03-01

210

Ion beam transport in tissue-like media using the Monte Carlo code SHIELD-HIT  

Microsoft Academic Search

The development of the Monte Carlo code SHIELD-HIT (heavy ion transport) for the simulation of the transport of protons and heavier ions in tissue-like media is described. The code SHIELD-HIT, a spin-off of SHIELD (available as RSICC CCC-667), extends the transport of hadron cascades from standard targets to that of ions in arbitrary tissue-like materials, taking into account ionization energy-loss

Irena Gudowska; Nikolai Sobolevsky; Pedro Andreo; Dževad Belki?; Anders Brahme

2004-01-01

211

Monte Carlo simulation of X-ray fluorescence spectra: Part 4. Photon scattering at high X-ray energies  

Microsoft Academic Search

The photon scattering model of a Monte Carlo simulation code for synchrotron radiation X-ray fluorescence (SRXRF) spectrometers is evaluated at high X-ray energies (60–100 keV) by means of a series of validation experiments performed at Beamline BW5 of HASYLAB. Using monochromatic X-rays, Compton\\/Rayleigh multiple scattering experiments were performed on polypropylene, Al and Cu samples. Especially in the case of the

L. Vincze; K Janssens; B Vekemans; F Adams

1999-01-01

212

Monte Carlo simulation of the backscatter region in photon-excited energy dispersive X-ray fluorescence spectra  

Microsoft Academic Search

The backscatter region of energy-dispersive X-ray fluorescence spectra obtained by a typical radioisotope system is examined\\u000a in detail. A Monte Carlo simulation program which incorporates all the information on photon scattering processes including\\u000a electron momentum distributions in target atoms, form factors and scattering factors for the cross-sections is presented.\\u000a The program uses extensive variance reduction techniques and has the option

F. ARINff; R. P. Gardner

1979-01-01

213

Monte-Carlo-based perturbation and beam quality correction factors for thimble ionization chambers in high-energy photon beams  

Microsoft Academic Search

This paper presents a detailed investigation into the calculation of perturbation and beam quality correction factors for ionization chambers in high-energy photon beams with the use of Monte Carlo simulations. For a model of the NE2571 Farmer-type chamber, all separate perturbation factors as found in the current dosimetry protocols were calculated in a fixed order and compared to the currently

J. Wulff; J. T. Heverhagen; K. Zink

2008-01-01

214

The validity of the density scaling method in primary electron transport for photon and electron beams  

Microsoft Academic Search

In the convolution\\/superposition method of photon beam dose calculations, inhomogeneities are usually handled by using some form of scaling involving the relative electron densities of the inhomogeneities. In this paper the accuracy of density scaling as applied to primary electrons generated in photon interactions is examined. Monte Carlo calculations are compared with density scaling calculations for air and cork slab

M. K. Woo; J. R. Cunningham

1990-01-01

215

Transport of Neutrons and Photons Through Iron and Water Layers  

NASA Astrophysics Data System (ADS)

The neutron and photon spectra were measured after iron and water plates placed at the horizontal channel of the Dresden University reactor AK-2. The measurements have been performed with the multiparameter spectrometer [1] with a stilbene cylindrical crystal, 10 × 10 mm or 45 × 45 mm; the neutron and photon spectra have been measured simultaneously. The calculations were performed with the MCNP code and nuclear data libraries ENDF/B VI.2, ENDF/BVII.0, JENDL 3.3 and JEFF 3.1. The measured channel leakage spectrum was used as the input spectrum for the transport calculation. Photons, the primary photons from the reactor - as well as the ones induced by neutron interaction - were calculated. The comparison of the measurements and calculations through 10 cm of iron and 20 cm thickness of water are presented. Besides that, the attenuation of the radiation mixed field by iron layers from 5 to 30 cm is presented; the measured and calculated data are compared.

Koš?ál, Michal; Cvachovec, František; Ošmera, Bohumil; Hansen, Wolfgang; Noack, Klaus

2009-08-01

216

The FERMI-Elettra FEL Photon Transport System  

SciTech Connect

The FERMI-Elettra free electron laser (FEL) user facility is under construction at Sincrotrone Trieste (Italy), and it will be operative in late 2010. It is based on a seeded scheme providing an almost perfect transform-limited and fully spatially coherent photon beam. FERMI-Elettra will cover the wavelength range 100 to 3 nm with the fundamental harmonics, and down to 1 nm with higher harmonics. We present the layout of the photon beam transport system that includes: the first common part providing on-line and shot-to-shot beam diagnostics, called PADReS (Photon Analysis Delivery and Reduction System), and 3 independent beamlines feeding the experimental stations. Particular emphasis is given to the solutions adopted to preserve the wavefront, and to avoid damage on the different optical elements. Peculiar FEL devices, not common in the Synchrotron Radiation facilities, are described in more detail, e.g. the online photon energy spectrometer measuring shot-by-shot the spectrum of the emitted radiation, the beam splitting and delay line system dedicated to cross/auto correlation and pump-probe experiments, and the wavefront preserving active optics adapting the shape and size of the focused spot to meet the needs of the different experiments.

Zangrando, M. [Laboratorio TASC INFM-CNR, S.S. 14 km 163.5 in Area Science Park, 34149 Trieste (Italy); Cudin, I.; Fava, C.; Godnig, R.; Kiskinova, M.; Masciovecchio, C.; Parmigiani, F.; Rumiz, L.; Svetina, C.; Turchet, A.; Cocco, D. [Sincrotrone Trieste SCpA, S.S. 14 km 163.5 in Area Science Park, 34149 Trieste (Italy)

2010-06-23

217

The FERMIatElettra FEL Photon Transport System  

NASA Astrophysics Data System (ADS)

The FERMIatElettra free electron laser (FEL) user facility is under construction at Sincrotrone Trieste (Italy), and it will be operative in late 2010. It is based on a seeded scheme providing an almost perfect transform-limited and fully spatially coherent photon beam. FERMIatElettra will cover the wavelength range 100 to 3 nm with the fundamental harmonics, and down to 1 nm with higher harmonics. We present the layout of the photon beam transport system that includes: the first common part providing on-line and shot-to-shot beam diagnostics, called PADReS (Photon Analysis Delivery and Reduction System), and 3 independent beamlines feeding the experimental stations. Particular emphasis is given to the solutions adopted to preserve the wavefront, and to avoid damage on the different optical elements. Peculiar FEL devices, not common in the Synchrotron Radiation facilities, are described in more detail, e.g. the online photon energy spectrometer measuring shot-by-shot the spectrum of the emitted radiation, the beam splitting and delay line system dedicated to cross/auto correlation and pump-probe experiments, and the wavefront preserving active optics adapting the shape and size of the focused spot to meet the needs of the different experiments.

Zangrando, M.; Cudin, I.; Fava, C.; Godnig, R.; Kiskinova, M.; Masciovecchio, C.; Parmigiani, F.; Rumiz, L.; Svetina, C.; Turchet, A.; Cocco, D.

2010-06-01

218

Simplified spherical harmonic method for coupled electron-photon transport calculations  

NASA Astrophysics Data System (ADS)

In this paper we apply the simplified spherical harmonic (SPN) approximation to coupled electron-photon transport problems in two-dimensional cylindrical geometry in the energy range from roughly 10 keV to 10 MeV. The SPN equations represent an asymptotic approximation that does not necessarily converge to the exact transport solution as N-->?, but can sometimes produce solutions that are much more accurate than diffusion theory at a fraction of the cost of a full transport treatment. To our knowledge, the SPN approximation has previously been applied only to neutron transport problems. We investigate the applicability of the SPN method to satellite electronics shielding calculations. In addition to applying the approximation, we generalize certain iterative convergence acceleration techniques originally developed for the one-dimensional SN (discrete ordinates) equations, and apply them to the two-dimensional SPN equations. We present numerical comparisons with Monte Carlo calculations for the purpose of examining both the accuracy of the SPN approximation and the computational efficiency of our solution techniques.

Josef, J. A.; Morel, J. E.

1998-05-01

219

A Monte Carlo model for out-of-field dose calculation from high-energy photon therapy  

SciTech Connect

As cancer therapy becomes more efficacious and patients survive longer, the potential for late effects increases, including effects induced by radiation dose delivered away from the treatment site. This out-of-field radiation is of particular concern with high-energy radiotherapy, as neutrons are produced in the accelerator head. We recently developed an accurate Monte Carlo model of a Varian 2100 accelerator using MCNPX for calculating the dose away from the treatment field resulting from low-energy therapy. In this study, we expanded and validated our Monte Carlo model for high-energy (18 MV) photon therapy, including both photons and neutrons. Simulated out-of-field photon doses were compared with measurements made with thermoluminescent dosimeters in an acrylic phantom up to 55 cm from the central axis. Simulated neutron fluences and energy spectra were compared with measurements using moderated gold foil activation in moderators and data from the literature. The average local difference between the calculated and measured photon dose was 17%, including doses as low as 0.01% of the central axis dose. The out-of-field photon dose varied substantially with field size and distance from the edge of the field but varied little with depth in the phantom, except at depths shallower than 3 cm, where the dose sharply increased. On average, the difference between the simulated and measured neutron fluences was 19% and good agreement was observed with the neutron spectra. The neutron dose equivalent varied little with field size or distance from the central axis but decreased with depth in the phantom. Neutrons were the dominant component of the out-of-field dose equivalent for shallow depths and large distances from the edge of the treatment field. This Monte Carlo model is useful to both physicists and clinicians when evaluating out-of-field doses and associated potential risks.

Kry, Stephen F.; Titt, Uwe; Followill, David; Poenisch, Falk; Vassiliev, Oleg N.; White, R. Allen; Stovall, Marilyn; Salehpour, Mohammad [Department of Radiation Physics, University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030 (United States); Medizinische Fakultaet Carl Gustav Carus, Technische Universitaet Dresden, Dresden, 01307 (Germany); Department of Radiation Physics, University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030 (United States); Department of Biostatistics and Applied Mathematics, University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030 (United States); Department of Radiation Physics, University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030 (United States)

2007-09-15

220

Quantum Zeno switch for single-photon coherent transport  

SciTech Connect

Using a dynamical quantum Zeno effect, we propose a general approach to control the coupling between a two-level system (TLS) and its surroundings, by modulating the energy-level spacing of the TLS with a high-frequency signal. We show that the TLS-surroundings interaction can be turned off when the ratio between the amplitude and the frequency of the modulating field is adjusted to be a zero of a Bessel function. The quantum Zeno effect of the TLS can also be observed by the vanishing of the photon reflection at these zeros. Based on these results, we propose a quantum switch to control the transport of a single photon in a one-dimensional waveguide. Our analytical results agree well with numerical results using Floquet theory.

Zhou Lan [Department of Physics, Hunan Normal University, Changsha 410081 (China); Advanced Science Institute, Institute of Physical and Chemical Research (RIKEN), Wako-shi 351-0198 (Japan); Yang, S. [Institute of Theoretical Physics, The Chinese Academy of Sciences, Beijing 100080 (China); Liu Yuxi [Advanced Science Institute, Institute of Physical and Chemical Research (RIKEN), Wako-shi 351-0198 (Japan); CREST, Japan Science and Technology Agency (JST), Kawaguchi, Saitama 332-0012 (Japan); Sun, C. P. [Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100080 (China); Advanced Science Institute, Institute of Physical and Chemical Research (RIKEN), Wako-shi 351-0198 (Japan); Nori, Franco [Advanced Science Institute, Institute of Physical and Chemical Research (RIKEN), Wako-shi 351-0198 (Japan); CREST, Japan Science and Technology Agency (JST), Kawaguchi, Saitama 332-0012 (Japan); Center for Theoretical Physics, Physics Department, Center for the Study of Complex Systems, University of Michigan, Ann Arbor, Michigan 48109-1040 (United States)

2009-12-15

221

Monte Carlo simulation of light transport in tissue for optimizing light delivery in photoacoustic imaging of the sentinel lymph node.  

PubMed

ABSTRACT. Noninvasive or minimally invasive identification of sentinel lymph node (SLN) is essential to reduce the surgical effects of SLN biopsy. Photoacoustic (PA) imaging of SLN in animal models has shown its promise for clinical use in the future. Here, we present a Monte Carlo simulation for light transport in the SLN for various light delivery configurations with a clinical ultrasound probe. Our simulation assumes a realistic tissue layer model and also can handle the transmission/reflectance at SLN-tissue boundary due to the mismatch of refractive index. Various light incidence angles show that for deeply situated SLNs the maximum absorption of light in the SLN is for normal incidence. We also show that if a part of the diffused reflected photons is reflected back into the skin using a reflector, the absorption of light in the SLN can be increased significantly to enhance the PA signal. PMID:24108574

Periyasamy, Vijitha; Pramanik, Manojit

2013-10-01

222

Verification measurements and clinical evaluation of the iPlan RT Monte Carlo dose algorithm for 6 MV photon energy  

NASA Astrophysics Data System (ADS)

This study presents data for verification of the iPlan RT Monte Carlo (MC) dose algorithm (BrainLAB, Feldkirchen, Germany). MC calculations were compared with pencil beam (PB) calculations and verification measurements in phantoms with lung-equivalent material, air cavities or bone-equivalent material to mimic head and neck and thorax and in an Alderson anthropomorphic phantom. Dosimetric accuracy of MC for the micro-multileaf collimator (MLC) simulation was tested in a homogeneous phantom. All measurements were performed using an ionization chamber and Kodak EDR2 films with Novalis 6 MV photon beams. Dose distributions measured with film and calculated with MC in the homogeneous phantom are in excellent agreement for oval, C and squiggle-shaped fields and for a clinical IMRT plan. For a field with completely closed MLC, MC is much closer to the experimental result than the PB calculations. For fields larger than the dimensions of the inhomogeneities the MC calculations show excellent agreement (within 3%/1 mm) with the experimental data. MC calculations in the anthropomorphic phantom show good agreement with measurements for conformal beam plans and reasonable agreement for dynamic conformal arc and IMRT plans. For 6 head and neck and 15 lung patients a comparison of the MC plan with the PB plan was performed. Our results demonstrate that MC is able to accurately predict the dose in the presence of inhomogeneities typical for head and neck and thorax regions with reasonable calculation times (5-20 min). Lateral electron transport was well reproduced in MC calculations. We are planning to implement MC calculations for head and neck and lung cancer patients.

Petoukhova, A. L.; van Wingerden, K.; Wiggenraad, R. G. J.; van de Vaart, P. J. M.; van Egmond, J.; Franken, E. M.; van Santvoort, J. P. C.

2010-08-01

223

Verification measurements and clinical evaluation of the iPlan RT Monte Carlo dose algorithm for 6 MV photon energy.  

PubMed

This study presents data for verification of the iPlan RT Monte Carlo (MC) dose algorithm (BrainLAB, Feldkirchen, Germany). MC calculations were compared with pencil beam (PB) calculations and verification measurements in phantoms with lung-equivalent material, air cavities or bone-equivalent material to mimic head and neck and thorax and in an Alderson anthropomorphic phantom. Dosimetric accuracy of MC for the micro-multileaf collimator (MLC) simulation was tested in a homogeneous phantom. All measurements were performed using an ionization chamber and Kodak EDR2 films with Novalis 6 MV photon beams. Dose distributions measured with film and calculated with MC in the homogeneous phantom are in excellent agreement for oval, C and squiggle-shaped fields and for a clinical IMRT plan. For a field with completely closed MLC, MC is much closer to the experimental result than the PB calculations. For fields larger than the dimensions of the inhomogeneities the MC calculations show excellent agreement (within 3%/1 mm) with the experimental data. MC calculations in the anthropomorphic phantom show good agreement with measurements for conformal beam plans and reasonable agreement for dynamic conformal arc and IMRT plans. For 6 head and neck and 15 lung patients a comparison of the MC plan with the PB plan was performed. Our results demonstrate that MC is able to accurately predict the dose in the presence of inhomogeneities typical for head and neck and thorax regions with reasonable calculation times (5-20 min). Lateral electron transport was well reproduced in MC calculations. We are planning to implement MC calculations for head and neck and lung cancer patients. PMID:20668337

Petoukhova, A L; van Wingerden, K; Wiggenraad, R G J; van de Vaart, P J M; van Egmond, J; Franken, E M; van Santvoort, J P C

2010-07-29

224

Monte Carlo study of photon beams from medical linear accelerators: Optimization, benchmark and spectra  

NASA Astrophysics Data System (ADS)

BEAM is a general purpose EGS4 user code for simulating radiotherapy sources (Rogers et al. Med. Phys. 22, 503-524, 1995). The BEAM code is optimized by first minimizing unnecessary electron transport (a factor of 3 improvement in efficiency). The efficiency of the uniform bremsstrahlung splitting (UBS) technique is assessed and found to be 4 times more efficient. The Russian Roulette technique used in conjunction with UBS is substantially modified to make simulations additionally 2 times more efficient. Finally, a novel and robust technique, called selective bremsstrahlung splitting (SBS), is developed and shown to improve the efficiency of photon beam simulations by an additional factor of 3-4, depending on the end- point considered. The optimized BEAM code is benchmarked by comparing calculated and measured ionization distributions in water from the 10 and 20 MV photon beams of the NRCC linac. Unlike previous calculations, the incident e - energy is known independently to 1%, the entire extra-focal radiation is simulated and e- contamination is accounted for. Both beams use clinical jaws, whose dimensions are accurately measured, and which are set for a 10 x 10 cm2 field at 110 cm. At both energies, the calculated and the measured values of ionization on the central-axis in the buildup region agree within 1% of maximum dose. The agreement is well within statistics elsewhere on the central-axis. Ionization profiles match within 1% of maximum dose, except at the geometrical edges of the field, where the disagreement is up to 5% of dose maximum. Causes for this discrepancy are discussed. The benchmarked BEAM code is then used to simulate beams from the major commercial medical linear accelerators. The off-axis factors are matched within statistical uncertainties, for most of the beams at the 1 ? level and for all at the 2 ? level. The calculated and measured depth-dose data agree within 1% (local dose), at about 1% (1 ? level) statistics, at all depths past depth of maximum dose for almost all beams. The calculated photon spectra and average energy distributions are compared to those published by Mohan et al. and decomposed into direct and scattered photon components.

Sheikh-Bagheri, Daryoush

1999-12-01

225

Comparison of space radiation calculations for deterministic and Monte Carlo transport codes  

NASA Astrophysics Data System (ADS)

For space radiation protection of astronauts or electronic equipments, it is necessary to develop and use accurate radiation transport codes. Radiation transport codes include deterministic codes, such as HZETRN from NASA and UPROP from the Naval Research Laboratory, and Monte Carlo codes such as FLUKA, the Geant4 toolkit and HETC-HEDS. The deterministic codes and Monte Carlo codes complement each other in that deterministic codes are very fast while Monte Carlo codes are more elaborate. Therefore it is important to investigate how well the results of deterministic codes compare with those of Monte Carlo transport codes and where they differ. In this study we evaluate these different codes in their space radiation applications by comparing their output results in the same given space radiation environments, shielding geometry and material. Typical space radiation environments such as the 1977 solar minimum galactic cosmic ray environment are used as the well-defined input, and simple geometries made of aluminum, water and/or polyethylene are used to represent the shielding material. We then compare various outputs of these codes, such as the dose-depth curves and the flux spectra of different fragments and other secondary particles. These comparisons enable us to learn more about the main differences between these space radiation transport codes. At the same time, they help us to learn the qualitative and quantitative features that these transport codes have in common.

Lin, Zi-Wei; Adams, James; Barghouty, Abdulnasser; Randeniya, Sharmalee; Tripathi, Ram; Watts, John; Yepes, Pablo

226

Conditional photon-assisted transport in coupled quantum dot  

NASA Astrophysics Data System (ADS)

We theoretically study the photon-assisted transport (PAT) in a double quantum dot (QD) which is conditionally controlled by the optical excitation in an adjacent QD. Based on a real three-QD model, a double-electron level configuration needed for the conditional PAT is designed. Interesting conditional dynamics are demonstrated for the double QD and its adjacent QD. Depending on various conditional frequencies, the conditional behaviors can be manifested as the current peaks or collapses of the PAT. They correspond to coherent excitations or trapping of double-electron states. Our results present a possible way to optically manipulate electron states and monitor them via the signals of current spectrum.

Xie, Yan; Xie, Weidong; Duan, Suqing; Yang, Ning; Chen, Jing; Zhang, Wei; Chu, Weidong; Zhao, Xian-Geng

2012-04-01

227

Calibration and Monte Carlo modelling of neutron long counters  

Microsoft Academic Search

The Monte Carlo technique has become a very powerful tool in radiation transport as full advantage is taken of enhanced cross-section data, more powerful computers and statistical techniques, together with better characterisation of neutron and photon source spectra. At the National Physical Laboratory, calculations using the Monte Carlo radiation transport code MCNP-4B have been combined with accurate measurements to characterise

Hamid Tagziria; David J Thomas

2000-01-01

228

Monte Carlo calculated correction factors for diodes and ion chambers in small photon fields.  

PubMed

The application of small photon fields in modern radiotherapy requires the determination of total scatter factors Scp or field factors ?(f(clin), f(msr))(Q(clin), Q(msr)) with high precision. Both quantities require the knowledge of the field-size-dependent and detector-dependent correction factor k(f(clin), f(msr))(Q(clin), Q(msr)). The aim of this study is the determination of the correction factor k(f(clin), f(msr))(Q(clin), Q(msr)) for different types of detectors in a clinical 6 MV photon beam of a Siemens KD linear accelerator. The EGSnrc Monte Carlo code was used to calculate the dose to water and the dose to different detectors to determine the field factor as well as the mentioned correction factor for different small square field sizes. Besides this, the mean water to air stopping power ratio as well as the ratio of the mean energy absorption coefficients for the relevant materials was calculated for different small field sizes. As the beam source, a Monte Carlo based model of a Siemens KD linear accelerator was used. The results show that in the case of ionization chambers the detector volume has the largest impact on the correction factor k(f(clin), f(msr))(Q(clin), Q(msr)); this perturbation may contribute up to 50% to the correction factor. Field-dependent changes in stopping-power ratios are negligible. The magnitude of k(f(clin), f(msr))(Q(clin), Q(msr)) is of the order of 1.2 at a field size of 1 × 1 cm(2) for the large volume ion chamber PTW31010 and is still in the range of 1.05-1.07 for the PinPoint chambers PTW31014 and PTW31016. For the diode detectors included in this study (PTW60016, PTW 60017), the correction factor deviates no more than 2% from unity in field sizes between 10 × 10 and 1 × 1 cm(2), but below this field size there is a steep decrease of k(f(clin), f(msr))(Q(clin), Q(msr)) below unity, i.e. a strong overestimation of dose. Besides the field size and detector dependence, the results reveal a clear dependence of the correction factor on the accelerator geometry for field sizes below 1 × 1 cm(2), i.e. on the beam spot size of the primary electrons hitting the target. This effect is especially pronounced for the ionization chambers. In conclusion, comparing all detectors, the unshielded diode PTW60017 is highly recommended for small field dosimetry, since its correction factor k(f(clin), f(msr))(Q(clin), Q(msr)) is closest to unity in small fields and mainly independent of the electron beam spot size. PMID:23514734

Czarnecki, D; Zink, K

2013-03-21

229

Effect of statistical fluctuation in Monte Carlo based photon beam dose calculation on gamma index evaluation  

NASA Astrophysics Data System (ADS)

The ?-index test has been commonly adopted to quantify the degree of agreement between a reference dose distribution and an evaluation dose distribution. Monte Carlo (MC) simulation has been widely used for the radiotherapy dose calculation for both clinical and research purposes. The goal of this work is to investigate both theoretically and experimentally the impact of the MC statistical fluctuation on the ?-index test when the fluctuation exists in the reference, the evaluation, or both dose distributions. To the first order approximation, we theoretically demonstrated in a simplified model that the statistical fluctuation tends to overestimate ?-index values when existing in the reference dose distribution and underestimate ?-index values when existing in the evaluation dose distribution given the original ?-index is relatively large for the statistical fluctuation. Our numerical experiments using realistic clinical photon radiation therapy cases have shown that (1) when performing a ?-index test between an MC reference dose and a non-MC evaluation dose, the average ?-index is overestimated and the gamma passing rate decreases with the increase of the statistical noise level in the reference dose; (2) when performing a ?-index test between a non-MC reference dose and an MC evaluation dose, the average ?-index is underestimated when they are within the clinically relevant range and the gamma passing rate increases with the increase of the statistical noise level in the evaluation dose; (3) when performing a ?-index test between an MC reference dose and an MC evaluation dose, the gamma passing rate is overestimated due to the statistical noise in the evaluation dose and underestimated due to the statistical noise in the reference dose. We conclude that the ?-index test should be used with caution when comparing dose distributions computed with MC simulation.

Jiang Graves, Yan; Jia, Xun; Jiang, Steve B.

2013-03-01

230

Methods of Monte Carlo electron transport in particle-in-cell codes  

SciTech Connect

An algorithm has been implemented in CCUBE and ISIS to treat electron transport in materials using a Monte Carlo method in addition to the electron dynamics determined by the self-consistent electromagnetic, relativistic, particle-in-cell simulation codes that have been used extensively to model generation of electron beams and intense microwave production. Incorporation of a Monte Carlo method to model the transport of electrons in materials (conductors and dielectrics) in a particle-in-cell code represents a giant step toward realistic simulation of the physics of charged-particle beams. The basic Monte Carlo method used in the implementation includes both scattering of electrons by background atoms and energy degradation.

Kwan, T.J.T.; Snell, C.M.

1985-01-01

231

Neutron-induced photon production in MCNP  

SciTech Connect

An improved method of neutron-induced photon production has been incorporated into the Monte Carlo transport code MCNP. The new method makes use of all partial photon-production reaction data provided by ENDF/B evaluators including photon-production cross sections as well as energy and angular distributions of secondary photons. This faithful utilization of sophisticated ENDF/B evaluations allows more precise MCNP calculations for several classes of coupled neutron-photon problems.

Little, R.C.; Seamon, R.E.

1983-01-01

232

Implicit Monte Carlo Radiation Transport Simulations of Four Test Problems  

Microsoft Academic Search

Radiation transport codes, like almost all codes, are difficult to develop and debug. It is helpful to have small, easy to\\u000a run test problems with known answers to use in development and debugging. It is also prudent to re-run test problems periodically\\u000a during development to ensure that previous code capabilities have not been lost. We describe four radiation transport test

N. A. Gentile

2007-01-01

233

Multidimensional electron-photon transport with standard discrete ordinates codes  

SciTech Connect

A method is described for generating electron cross sections that are comparable with standard discrete ordinates codes without modification. There are many advantages of using an established discrete ordinates solver, e.g. immediately available adjoint capability. Coupled electron-photon transport capability is needed for many applications, including the modeling of the response of electronics components to space and man-made radiation environments. The cross sections have been successfully used in the DORT, TWODANT and TORT discrete ordinates codes. The cross sections are shown to provide accurate and efficient solutions to certain multidimensional electron-photon transport problems. The key to the method is a simultaneous solution of the continuous-slowing-down (CSD) portion and elastic-scattering portion of the scattering source by the Goudsmit-Saunderson theory. The resulting multigroup-Legendre cross sections are much smaller than the true scattering cross sections that they represent. Under certain conditions, the cross sections are guaranteed positive and converge with a low-order Legendre expansion.

Drumm, C.R.

1997-04-01

234

Implicitly causality enforced solution of multidimensional transient photon transport equation.  

PubMed

A novel method for solving the multidimensional transient photon transport equation for laser pulse propagation in biological tissue is presented. A Laguerre expansion is used to represent the time dependency of the incident short pulse. Owing to the intrinsic causal nature of Laguerre functions, our technique automatically always preserve the causality constrains of the transient signal. This expansion of the radiance using a Laguerre basis transforms the transient photon transport equation to the steady state version. The resulting equations are solved using the discrete ordinates method, using a finite volume approach. Therefore, our method enables one to handle general anisotropic, inhomogeneous media using a single formulation but with an added degree of flexibility owing to the ability to invoke higher-order approximations of discrete ordinate quadrature sets. Therefore, compared with existing strategies, this method offers the advantage of representing the intensity with a high accuracy thus minimizing numerical dispersion and false propagation errors. The application of the method to one, two and three dimensional geometries is provided. PMID:20052050

Handapangoda, Chintha C; Premaratne, Malin

2009-12-21

235

Electron and Hole Transport in Bulk ZnO: A Full Band Monte Carlo Study  

Microsoft Academic Search

Electron and hole transport in wurtzite phase ZnO is studied using an ensemble full band Monte Carlo method. The model includes\\u000a an accurate description of the electronic structure obtained with the nonlocal pseudopotential method and numerically calculated\\u000a impact ionization transition rates based on a wavevector-dependent dielectric function. Results of transport simulations at\\u000a both low and high electric fields are presented.

Francesco Bertazzi; Michele Goano; Enrico Bellotti

2007-01-01

236

Measured performances on vectorization and multitasking with a Monte Carlo code for neutron transport problems  

Microsoft Academic Search

This paper summarized two improvements of a real production code by using vectorization and multitasking techniques. After a short description of Monte Carlo algorithms employed in our neutron transport problems, we briefly describe the work we have done in order to get a vector code. Vectorization principles will be presented and measured performances on the CRAY 1S, CYBER 205 and

Yves Chauvet

1985-01-01

237

SRNA - MONTE CARLO CODES FOR PROTON TRANSPORT SIMULATION IN COMBINED AND VOXELIZED GEOMETRIES  

Microsoft Academic Search

This paper describes new Monte Carlo codes for proton transport simulations in complex geometrical forms and in materials of different composition. The SRNA codes were developed for 3D dose distribution calculation in proton therapy and dosimetry. The model of these codes is based on the theory of proton multiple scattering and a simple model of compound nucleus decay. The developed

Radovan D. ILI; Darko LALI; Srboljub J. STANKOVI

238

Reference solutions for 3-D radiation transport benchmarks by a Monte Carlo code GMVP  

Microsoft Academic Search

Reference Solutions for the 3-D transport benchmark problems proposed by Kobayashi are presented. They were obtained by the multigroup Monte Carlo code GMVP with the point-detector estimator. The statistical uncertainties (1?) are less than 1% at all the calculation points. The GMVP results show good agreement with the analytical solutions by Kobayashi and the MCNP solutions for the pure absorber

Yasunobu Nagaya

2001-01-01

239

Investigating M87 through GRMHD and Novel Monte Carlo Radiation Transport Tools  

NASA Astrophysics Data System (ADS)

Results from general relativistic magneto-hydrodynamic simulations of M87 are presented. Spectra are obtained through the use of a unique Monte Carlo radiation transport code, specialized to consider radiation in a region of high velocity shear and magnetic field anisotropy. Ramifications for constraints on physical parameters, such as black hole spin and flare mechanism, will be discussed.

Hilburn, Guy L.; Liang, E. P.

2011-09-01

240

Characterization of a novel micro-irradiator using Monte Carlo radiation transport simulations  

Microsoft Academic Search

Small animals are highly valuable resources for radiobiology research. While rodents have been widely used for decades, zebrafish embryos have recently become a very popular research model. However, unlike rodents, zebrafish embryos lack appropriate irradiation tools and methodologies. Therefore, the main purpose of this work is to use Monte Carlo radiation transport simulations to characterize dosimetric parameters, determine dosimetric sensitivity

Manuel Rodriguez; Robert Jeraj

2008-01-01

241

Applications of the Monte Carlo Code for Radiation Transport Simulation for Use in Radiotherapy  

Microsoft Academic Search

The simulation of electron beam transport by the Monte Carlo method in arbitrary, user-defined, complex geometries made of any chemical element or material was used to examine an influence of a beam forming system on absorbed dose distributions for electron beams from medical accelerators. The typical beam defining system consists of scattering foils, adjustable collimators and electron applicators. The scattering

Izabella Zychor

242

Improvements to the Integrated TIGER Series Monte Carlo radiation transport codes  

Microsoft Academic Search

This paper describes two areas in which the usability of the Integrated TIGER Series (ITS) Monte Carlo radiation transport codes has been improved for use in the design and analysis of tests conducted with the DECADE nuclear weapons effects simulator. The first area is in improving the speed of execution. By benchmarking and profiling the member codes of the ITS

L. Montgomery Smith; Reuben D. Hochstedler

1997-01-01

243

Automatic Computation of Importance Sampling Functions for Monte Carlo Transport Codes - Phase Ii.  

National Technical Information Service (NTIS)

The report covers the second phase of a program, now in progress at MAGI, to develop procedures for the automatic generation of importance functions for use in three-dimensional Monte Carlo radiation transport codes. The availability of an automatic impor...

H. A. Steinberg M. H. Kalos E. Troubetzkoy

1970-01-01

244

Response matrix Monte Carlo based on a general geometry local calculation for electron transport  

SciTech Connect

A Response Matrix Monte Carlo (RMMC) method has been developed for solving electron transport problems. This method was born of the need to have a reliable, computationally efficient transport method for low energy electrons (below a few hundred keV) in all materials. Today, condensed history methods are used which reduce the computation time by modeling the combined effect of many collisions but fail at low energy because of the assumptions required to characterize the electron scattering. Analog Monte Carlo simulations are prohibitively expensive since electrons undergo coulombic scattering with little state change after a collision. The RMMC method attempts to combine the accuracy of an analog Monte Carlo simulation with the speed of the condensed history methods. Like condensed history, the RMMC method uses probability distributions functions (PDFs) to describe the energy and direction of the electron after several collisions. However, unlike the condensed history method the PDFs are based on an analog Monte Carlo simulation over a small region. Condensed history theories require assumptions about the electron scattering to derive the PDFs for direction and energy. Thus the RMMC method samples from PDFs which more accurately represent the electron random walk. Results show good agreement between the RMMC method and analog Monte Carlo. 13 refs., 8 figs.

Ballinger, C.T.; Rathkopf, J.A. (Lawrence Livermore National Lab., CA (USA)); Martin, W.R. (Michigan Univ., Ann Arbor, MI (USA). Dept. of Nuclear Engineering)

1991-01-01

245

Domain Decomposition Models for Parallel Monte Carlo Transport  

Microsoft Academic Search

We present a strategy for parallelizing computations that use the transport method. It combines spatial domain decomposition with domain replication to realize the scaling benefits of replication while allowing for problems whose computational mesh will not fit in a single processor's memory. The mesh is decomposed into a small number of spatial domains—typically fewer domains than there are processors—and heuristics

Henry J. Alme; Garry H. Rodrigue; George B. Zimmerman

2001-01-01

246

Monte Carlo simulation on pre-clinical irradiation: A heterogeneous phantom study on monoenergetic kilovoltage photon beams  

NASA Astrophysics Data System (ADS)

This study investigated radiation dose variations in pre-clinical irradiation due to the photon beam energy and presence of tissue heterogeneity. Based on the same mouse computed tomography image dataset, three phantoms namely, heterogeneous, homogeneous and bone homogeneous were used. These phantoms were generated by overriding the relative electron density of no voxel (heterogeneous), all voxel (homogeneous) and the bone voxel (bone homogeneous) to one. 360° photon arcs with beam energies of 50 - 1250 keV were used in mouse irradiations. Doses in the above phantoms were calculated using the EGSnrc-based DOSXYZnrc code through the DOSCTP. Monte Carlo simulations were carried out in parallel using multiple nodes in a high-performance computing cluster. It was found that the dose conformity increased with the increase of the photon beam energy from the keV to MeV range. For the heterogeneous mouse phantom, increasing the photon beam energy from 50 keV to 1250 keV increased seven times the dose deposited at the isocenter. For the bone dose enhancement, the mean dose was 2.7 times higher when the bone heterogeneity was not neglected using the 50 keV photon beams in the mouse irradiation. Bone dose enhancement affecting the mean dose was found in the photon beams with energy range of 50 - 200 keV and the dose enhancement decreased with an increase of the beam energy. Moreover, the MeV photon beam had a higher dose at the isocenter, and a better dose conformity compared to the keV beam.

Chow, James C. L.

2012-10-01

247

Photon maps in bidirectional Monte Carlo ray tracing of complex objects  

Microsoft Academic Search

This paper describes a bidirectional Monte Carlo ray tracing method simulating global illumination in models containing complex objects that do not have to be tessellated. The two pass method combines a first pass light ray tracing (ray casting) with a second pass optimized Monte Carlo ray tracing. In the first pass, the light emitted from the light sources hit objects

Henrik Wann Jensen; Niels Jørgen Christensen

1995-01-01

248

Simulation of diffuse photon migration in tissue by a Monte Carlo method derived from the optical scattering of spheroids.  

PubMed

A Monte Carlo method was derived from the optical scattering properties of spheroidal particles and used for modeling diffuse photon migration in biological tissue. The spheroidal scattering solution used a separation of variables approach and numerical calculation of the light intensity as a function of the scattering angle. A Monte Carlo algorithm was then developed which utilized the scattering solution to determine successive photon trajectories in a three-dimensional simulation of optical diffusion and resultant scattering intensities in virtual tissue. Monte Carlo simulations using isotropic randomization, Henyey-Greenstein phase functions, and spherical Mie scattering were additionally developed and used for comparison to the spheroidal method. Intensity profiles extracted from diffusion simulations showed that the four models differed significantly. The depth of scattering extinction varied widely among the four models, with the isotropic, spherical, spheroidal, and phase function models displaying total extinction at depths of 3.62, 2.83, 3.28, and 1.95 cm, respectively. The results suggest that advanced scattering simulations could be used as a diagnostic tool by distinguishing specific cellular structures in the diffused signal. For example, simulations could be used to detect large concentrations of deformed cell nuclei indicative of early stage cancer. The presented technique is proposed to be a more physical description of photon migration than existing phase function methods. This is attributed to the spheroidal structure of highly scattering mitochondria and elongation of the cell nucleus, which occurs in the initial phases of certain cancers. The potential applications of the model and its importance to diffusive imaging techniques are discussed. PMID:24085080

Hart, Vern P; Doyle, Timothy E

2013-09-01

249

A Comparison of Monte Carlo Particle Transport Algorithms for Binary Stochastic Mixtures  

SciTech Connect

Two Monte Carlo algorithms originally proposed by Zimmerman and Zimmerman and Adams for particle transport through a binary stochastic mixture are numerically compared using a standard set of planar geometry benchmark problems. In addition to previously-published comparisons of the ensemble-averaged probabilities of reflection and transmission, we include comparisons of detailed ensemble-averaged total and material scalar flux distributions. Because not all benchmark scalar flux distribution data used to produce plots in previous publications remains available, we have independently regenerated the benchmark solutions including scalar flux distributions. Both Monte Carlo transport algorithms robustly produce physically-realistic scalar flux distributions for the transport problems examined. The first algorithm reproduces the standard Levermore-Pomraning model results for the probabilities of reflection and transmission. The second algorithm generally produces significantly more accurate probabilities of reflection and transmission and also significantly more accurate total and material scalar flux distributions.

Brantley, P S

2009-02-23

250

Monte Carlo path sampling approach to modeling aeolian sediment transport  

NASA Astrophysics Data System (ADS)

Coastal communities and vital infrastructure are subject to coastal hazards including storm surge and hurricanes. Coastal dunes offer protection by acting as natural barriers from waves and storm surge. During storms, these landforms and their protective function can erode; however, they can also erode even in the absence of storms due to daily wind and waves. Costly and often controversial beach nourishment and coastal construction projects are common erosion mitigation practices. With a more complete understanding of coastal morphology, the efficacy and consequences of anthropogenic activities could be better predicted. Currently, the research on coastal landscape evolution is focused on waves and storm surge, while only limited effort is devoted to understanding aeolian forces. Aeolian transport occurs when the wind supplies a shear stress that exceeds a critical value, consequently ejecting sand grains into the air. If the grains are too heavy to be suspended, they fall back to the grain bed where the collision ejects more grains. This is called saltation and is the salient process by which sand mass is transported. The shear stress required to dislodge grains is related to turbulent air speed. Subsequently, as sand mass is injected into the air, the wind loses speed along with its ability to eject more grains. In this way, the flux of saltating grains is itself influenced by the flux of saltating grains and aeolian transport becomes nonlinear. Aeolian sediment transport is difficult to study experimentally for reasons arising from the orders of magnitude difference between grain size and dune size. It is difficult to study theoretically because aeolian transport is highly nonlinear especially over complex landscapes. Current computational approaches have limitations as well; single grain models are mathematically simple but are computationally intractable even with modern computing power whereas cellular automota-based approaches are computationally efficient but evolve the system according to rules that are abstractions of the governing physics. This work presents the Green function solution to the continuity equations that govern sediment transport. The Green function solution is implemented using a path sampling approach whereby sand mass is represented as an ensemble of particles that evolve stochastically according to the Green function. In this approach, particle density is a particle representation that is equivalent to the field representation of elevation. Because aeolian transport is nonlinear, particles must be propagated according to their updated field representation with each iteration. This is achieved using a particle-in-cell technique. The path sampling approach offers a number of advantages. The integral form of the Green function solution makes it robust to discontinuities in complex terrains. Furthermore, this approach is spatially distributed, which can help elucidate the role of complex landscapes in aeolian transport. Finally, path sampling is highly parallelizable, making it ideal for execution on modern clusters and graphics processing units.

Hardin, E. J.; Mitasova, H.; Mitas, L.

2011-12-01

251

Backscatter towards the monitor ion chamber in high-energy photon and electron beams: charge integration versus Monte Carlo simulation  

NASA Astrophysics Data System (ADS)

In some linear accelerators, the charge collected by the monitor ion chamber is partly caused by backscattered particles from accelerator components downstream from the chamber. This influences the output of the accelerator and also has to be taken into account when output factors are derived from Monte Carlo simulations. In this work, the contribution of backscattered particles to the monitor ion chamber response of a Varian 2100C linac was determined for photon beams (6, 10 MV) and for electron beams (6, 12, 20 MeV). The experimental procedure consisted of charge integration from the target in a photon beam or from the monitor ion chamber in electron beams. The Monte Carlo code EGS4/BEAM was used to study the contribution of backscattered particles to the dose deposited in the monitor ion chamber. Both measurements and simulations showed a linear increase in backscatter fraction with decreasing field size for photon and electron beams. For 6 MV and 10 MV photon beams, a 2-3% increase in backscatter was obtained for a 0.5×0.5 cm2 field compared to a 40×40 cm2 field. The results for the 6 MV beam were slightly higher than for the 10 MV beam. For electron beams (6, 12, 20 MeV), an increase of similar magnitude was obtained from measurements and simulations for 6 MeV electrons. For higher energy electron beams a smaller increase in backscatter fraction was found. The problem is of less importance for electron beams since large variations of field size for a single electron energy usually do not occur.

Verhaegen, F.; Symonds-Tayler, R.; Liu, H. H.; Nahum, A. E.

2000-11-01

252

Data decomposition of Monte Carlo particle transport simulations via tally servers  

NASA Astrophysics Data System (ADS)

An algorithm for decomposing large tally data in Monte Carlo particle transport simulations is developed, analyzed, and implemented in a continuous-energy Monte Carlo code, OpenMC. The algorithm is based on a non-overlapping decomposition of compute nodes into tracking processors and tally servers. The former are used to simulate the movement of particles through the domain while the latter continuously receive and update tally data. A performance model for this approach is developed, suggesting that, for a range of parameters relevant to LWR analysis, the tally server algorithm should perform with minimal overhead on contemporary supercomputers. An implementation of the algorithm in OpenMC is then tested on the Intrepid and Titan supercomputers, supporting the key predictions of the model over a wide range of parameters. We thus conclude that the tally server algorithm is a successful approach to circumventing classical on-node memory constraints en route to unprecedentedly detailed Monte Carlo reactor simulations.

Romano, Paul K.; Siegel, Andrew R.; Forget, Benoit; Smith, Kord

2013-11-01

253

Study on dynamics of photon migration in human breast based on three-dimensional Monte Carlo modeling  

NASA Astrophysics Data System (ADS)

The scattering and absorption properties of human breast are very important for cancer diagnosis based on diffuse optical tomography (DOT). In this study, the dynamics of photon migration in three-dimensional human breast model with various source-detector separations is simulated based on a Monte Carlo algorithm. The three-dimensional human breast structure is obtained from in vivo MRI image. The breast model consists of skin, fatty tissue, glandular tissue, sternum and ribcage. The backscattered diffuse photons from each layer in breast are recorded by marking the deepest layer which every photon can reach. The experimental results indicate that the re-emitted photons contain more information from deep tissue regions with the source-detector separations because of the strong dependence to the resolution and sensitivity in DOT imaging. The geometric position of the source-detector separations were optimized in this study. The different sizes of breast tumor were modeled to analysis of optical image characterizations. Finally, the tumor images from different deep information were obtained with temporal profiles.

Chuang, Ching-Cheng; Chen, Chung-Ming; Lee, Chia-Yen; Tsai, Jui-Che; Lu, Chih-Wei; Sun, Chia-Wei

2010-02-01

254

A Novel Implementation of Massively Parallel Three Dimensional Monte Carlo Radiation Transport  

NASA Astrophysics Data System (ADS)

The goal of our summer project was to implement the difference formulation for radiation transport into Cosmos++, a multidimensional, massively parallel, magneto hydrodynamics code for astrophysical applications (Peter Anninos - AX). The difference formulation is a new method for Symbolic Implicit Monte Carlo thermal transport (Brooks and Szöke - PAT). Formerly, simultaneous implementation of fully implicit Monte Carlo radiation transport in multiple dimensions on multiple processors had not been convincingly demonstrated. We found that a combination of the difference formulation and the inherent structure of Cosmos++ makes such an implementation both accurate and straightforward. We developed a "nearly nearest neighbor physics" technique to allow each processor to work independently, even with a fully implicit code. This technique coupled with the increased accuracy of an implicit Monte Carlo solution and the efficiency of parallel computing systems allows us to demonstrate the possibility of massively parallel thermal transport. This work was performed under the auspices of the U.S. Department of Energy by University of California Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48

Robinson, P. B.; Peterson, J. D. L.

2005-12-01

255

Correlated histogram representation of Monte Carlo derived medical accelerator photon-output phase space  

DOEpatents

A method is provided to represent the calculated phase space of photons emanating from medical accelerators used in photon teletherapy. The method reproduces the energy distributions and trajectories of the photons originating in the bremsstrahlung target and of photons scattered by components within the accelerator head. The method reproduces the energy and directional information from sources up to several centimeters in radial extent, so it is expected to generalize well to accelerators made by different manufacturers. The method is computationally both fast and efficient overall sampling efficiency of 80% or higher for most field sizes. The computational cost is independent of the number of beams used in the treatment plan.

Schach Von Wittenau, Alexis E. (Livermore, CA)

2003-01-01

256

Evaluation of the Difference Formulation for Photon Transport in a Two Level System.  

National Technical Information Service (NTIS)

In this paper we extend the difference formulation for radiation transport to the case of a single atomic line. We examine the accuracy, performance and stability of the difference formulation within the framework of the Symbolic Implicit Monte Carlo meth...

F. C. Daffin M. S. McKinley E. D. Brooks A. Szoke

2005-01-01

257

Design and commissioning of the photon monitors and optical transport lines for the advanced photon source positron accumulator ring  

SciTech Connect

Two photon monitors have been designed and installed in the positron accumulator ring (PAR) of the Advanced Photon Source. The photon monitors characterize the beam`s transverse profile, bunch length, emittance, and energy spread in a nonintrusive manner. An optical transport line delivers synchrotron light from the PAR out of a high radiation environment. Both charge-coupled device and fast-gated, intensified cameras are used to measure the transverse beam profile (0.11 - 1 mm for damped beam) with a resolution of 0.06 mm. A streak camera ({theta}{sub {tau}} =I ps) is used to measure the bunch length which is in the range of 0.3-1 ns. The design of the various transport components and commissioning results of the photon monitors will be discussed.

Berg, W.; Yang, B.; Lumpkin, A.; Jones, J.

1996-12-31

258

Light transport regimes in slow light photonic crystal waveguides  

NASA Astrophysics Data System (ADS)

The dispersive properties of waves are strongly affected by inevitable residual disorder in man-made propagating media, in particular in the slow wave regime. By a direct measurement of the dispersion curve in k space, we show that the nature of the guided modes in real photonic crystal waveguides undergoes an abrupt transition in the vicinity of a band edge. Such a transition that is not highlighted by standard optical transmission measurement, defines the limit where k can be considered as a good quantum number. In the framework of a mean-field theory we propose a qualitative description of this effect and attribute it to the transition from the “dispersive” regime to the diffusive regime. In particular we prove that a scaling law exists between the strength of the disorder and the group velocity. As a result, for group velocities vg smaller than c/25 the diffusive contribution to the light transport is predominant. In this regime the group velocity vg loses its relevance and the energy transport velocity vE is the proper light speed to consider.

Le Thomas, N.; Zhang, H.; Jágerská, J.; Zabelin, V.; Houdré, R.; Sagnes, I.; Talneau, A.

2009-09-01

259

Implicit Monte Carlo methods and non-equilibrium Marshak wave radiative transport  

SciTech Connect

Two enhancements to the Fleck implicit Monte Carlo method for radiative transport are described, for use in transparent and opaque media respectively. The first introduces a spectral mean cross section, which applies to pseudoscattering in transparent regions with a high frequency incident spectrum. The second provides a simple Monte Carlo random walk method for opaque regions, without the need for a supplementary diffusion equation formulation. A time-dependent transport Marshak wave problem of radiative transfer, in which a non-equilibrium condition exists between the radiation and material energy fields, is then solved. These results are compared to published benchmark solutions and to new discrete ordinate S-N results, for both spatially integrated radiation-material energies versus time and to new spatially dependent temperature profiles. Multigroup opacities, which are independent of both temperature and frequency, are used in addition to a material specific heat which is proportional to the cube of the temperature. 7 refs., 4 figs.

Lynch, J.E.

1985-01-01

260

A simplified spherical harmonic method for coupled electron-photon transport calculations  

SciTech Connect

In this thesis we have developed a simplified spherical harmonic method (SP{sub N} method) and associated efficient solution techniques for 2-D multigroup electron-photon transport calculations. The SP{sub N} method has never before been applied to charged-particle transport. We have performed a first time Fourier analysis of the source iteration scheme and the P{sub 1} diffusion synthetic acceleration (DSA) scheme applied to the 2-D SP{sub N} equations. Our theoretical analyses indicate that the source iteration and P{sub 1} DSA schemes are as effective for the 2-D SP{sub N} equations as for the 1-D S{sub N} equations. Previous analyses have indicated that the P{sub 1} DSA scheme is unstable (with sufficiently forward-peaked scattering and sufficiently small absorption) for the 2-D S{sub N} equations, yet is very effective for the 1-D S{sub N} equations. In addition, we have applied an angular multigrid acceleration scheme, and computationally demonstrated that it performs as well for the 2-D SP{sub N} equations as for the 1-D S{sub N} equations. It has previously been shown for 1-D S{sub N} calculations that this scheme is much more effective than the DSA scheme when scattering is highly forward-peaked. We have investigated the applicability of the SP{sub N} approximation to two different physical classes of problems: satellite electronics shielding from geomagnetically trapped electrons, and electron beam problems. In the space shielding study, the SP{sub N} method produced solutions that are accurate within 10% of the benchmark Monte Carlo solutions, and often orders of magnitude faster than Monte Carlo. We have successfully modeled quasi-void problems and have obtained excellent agreement with Monte Carlo. We have observed that the SP{sub N} method appears to be too diffusive an approximation for beam problems. This result, however, is in agreement with theoretical expectations.

Josef, J.A.

1996-12-01

261

[Verification of the VEF photon beam model for dose calculations by the Voxel-Monte-Carlo-Algorithm].  

PubMed

The VEF linac head model (VEF, virtual energy fluence) was developed at the University of Tübingen to determine the primary fluence for calculations of dose distributions in patients by the Voxel-Monte-Carlo-Algorithm (XVMC). This analytical model can be fitted to any therapy accelerator head by measuring only a few basic dose data; therefore, time-consuming Monte-Carlo simulations of the linac head become unnecessary. The aim of the present study was the verification of the VEF model by means of water-phantom measurements, as well as the comparison of this system with a common analytical linac head model of a commercial planning system (TMS, formerly HELAX or MDS Nordion, respectively). The results show that both the VEF and the TMS models can very well simulate the primary fluence. However, the VEF model proved superior in the simulations of scattered radiation and in the calculations of strongly irregular MLC fields. Thus, an accurate and clinically practicable tool for the determination of the primary fluence for Monte-Carlo-Simulations with photons was established, especially for the use in IMRT planning. PMID:16008081

Kriesen, Stephan; Fippel, Matthias

2005-01-01

262

Point KENO V.a: A Continuous-energy Monte Carlo Code for Transport Applications  

Microsoft Academic Search

KENO V.a is a multigroup Monte Carlo code that solves the Boltzmann transport equation and is used extensively in the criticality safety community to calculate the effective multiplication factor of systems with fissionable material. In this work, a continuous-energy or pointwise version of KENO V.a has been developed by first designing a new continuous-energy cross-section format and then by developing

Michael E. Dunn; N. Maurice Greene; Lester M. Petrie

2004-01-01

263

MONTE CARLO PARTICLE TRANSPORT IN MEDIA WITH EXPONENTIALLY VARYING TIME-DEPENDENT CROSS-SECTIONS  

SciTech Connect

A probability density function (PDF) and random sampling procedure for the distance to collision were derived for the case of exponentially varying cross-sections. Numerical testing indicates that both are correct. This new sampling procedure has direct application in a new method for Monte Carlo radiation transport, and may be generally useful for analyzing physical problems where the material cross-sections change very rapidly in an exponential manner.

F. BROWN; W. MARTIN

2001-02-01

264

Modeling complex vapor-transport systems using Monte-Carlo techniques: Radioactive ion beam applications  

Microsoft Academic Search

A Monte-Carlo code has been developed that can be used to optimally design vapor transport systems for isotope-separator-on-line-based radioactive ion beam facilities in lieu of costly iterative trial and error design methods. The code provides a powerful means for delineating diffusion-release and effusive-flow (molecular-flow) processes, in combination, the delay times of which are principal intensity limiters of short-lived radioactive species

Y. Zhang; G. D. Alton

2005-01-01

265

Monte Carlo study of electron transport in strained silicon-carbon alloy  

Microsoft Academic Search

Electron transport characteristics of strained Si(1 - y)C(y) random alloy grown in a Si (100) substrate are studied theoretically using the Monte Carlo technique. The value of alloy scattering potential has a strong influence on the low-field electron mobility. Valley repopulation effect combined with decreased scattering rate of electrons in strained Si(1 - y)C(y) material can give rise to the

M. Ershov; V. Ryzhii

1994-01-01

266

Modular, object-oriented redesign of a large-scale Monte Carlo neutron transport program  

SciTech Connect

This paper describes the modular, object-oriented redesign of a large-scale Monte Carlo neutron transport program. This effort represents a complete 'white sheet of paper' rewrite of the code. In this paper, the motivation driving this project, the design objectives for the new version of the program, and the design choices and their consequences will be discussed. The design itself will also be described, including the important subsystems as well as the key classes within those subsystems.

Moskowitz, B.S.

2000-02-01

267

Analytic band Monte Carlo model for electron transport in Si including acoustic and optical phonon dispersion  

Microsoft Academic Search

We describe the implementation of a Monte Carlo model for electron transport in silicon. The model uses analytic, nonparabolic electron energy bands, which are computationally efficient and sufficiently accurate for future low-voltage (<1 V) nanoscale device applications. The electron-lattice scattering is incorporated using an isotropic, analytic phonon-dispersion model, which distinguishes between the optical\\/acoustic and the longitudinal\\/transverse phonon branches. We show

Eric Pop; Robert W. Dutton; Kenneth E. Goodson

2004-01-01

268

Practical aspects of Monte Carlo simulation of charged particle transport: Mixed algorithms and variance reduction techniques  

Microsoft Academic Search

This paper is concerned with the practical implementation of Monte Carlo simulation methods for charged particle transport.\\u000a The emphasis is on light particles (electrons and positrons) because of the larger scattering and energy straggling effects.\\u000a Differential cross sections (DCS) for the various interaction mechanisms are described. As the average number of interactions\\u000a along the particle track increases with the initial

F. Salvat; J. M. Fernández-Varea; J. Sempau; J. Mazurier

1999-01-01

269

RADIATION TRANSPORT THROUGH COMPLEX SHIELD PENETRATIONS IN ACCELERATOR ENVIRONMENTS USING HYBRID MONTE CARLO\\/DISCRETE ORDINATES CALCULATIONS  

Microsoft Academic Search

SUMMARY Shielding calculations for penetrations in the SNS accelerator environment are presented based on hybrid Monte Carlo and discrete ordinates particle transport methods. This methodology relies on coupling tools that map boundary surface leakage information from the Monte Carlo calculations to boundary sources for one-, two-, and three- dimensional discrete ordinates calculations. I. BACKGROUND Evaluating bulk shielding in accelerator environments

Franz X. Gallmeier

270

Monte Carlo study of the energy and angular dependence of the response of plastic scintillation detectors in photon beams  

SciTech Connect

Purpose: By using Monte Carlo simulations, the authors investigated the energy and angular dependence of the response of plastic scintillation detectors (PSDs) in photon beams. Methods: Three PSDs were modeled in this study: A plastic scintillator (BC-400) and a scintillating fiber (BCF-12), both attached by a plastic-core optical fiber stem, and a plastic scintillator (BC-400) attached by an air-core optical fiber stem with a silica tube coated with silver. The authors then calculated, with low statistical uncertainty, the energy and angular dependences of the PSDs' responses in a water phantom. For energy dependence, the response of the detectors is calculated as the detector dose per unit water dose. The perturbation caused by the optical fiber stem connected to the PSD to guide the optical light to a photodetector was studied in simulations using different optical fiber materials. Results: For the energy dependence of the PSDs in photon beams, the PSDs with plastic-core fiber have excellent energy independence within about 0.5% at photon energies ranging from 300 keV (monoenergetic) to 18 MV (linac beam). The PSD with an air-core optical fiber with a silica tube also has good energy independence within 1% in the same photon energy range. For the angular dependence, the relative response of all the three modeled PSDs is within 2% for all the angles in a 6 MV photon beam. This is also true in a 300 keV monoenergetic photon beam for PSDs with plastic-core fiber. For the PSD with an air-core fiber with a silica tube in the 300 keV beam, the relative response varies within 1% for most of the angles, except in the case when the fiber stem is pointing right to the radiation source in which case the PSD may over-response by more than 10%. Conclusions: At {+-}1% level, no beam energy correction is necessary for the response of all three PSDs modeled in this study in the photon energy ranges from 200 keV (monoenergetic) to 18 MV (linac beam). The PSD would be even closer to water equivalent if there is a silica tube around the sensitive volume. The angular dependence of the response of the three PSDs in a 6 MV photon beam is not of concern at 2% level.

Wang, Lilie L. W.; Klein, David; Beddar, A. Sam [Department of Radiation Physics, University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030 (United States)

2010-10-15

271

Epp - A C++ EGSnrc user code for Monte Carlo simulation of radiation transport  

NASA Astrophysics Data System (ADS)

Easy particle propagation (Epp) is a Monte Carlo simulation EGSnrc user code that we have developed for dose calculation in a voxelized volume, and to generate images of an arbitrary geometry irradiated by a particle source. The dose calculation aspect is a reimplementation of the function of DOSXYZnrc with new features added and some restrictions removed. Epp is designed for x-ray application, but can be readily extended to trace other kinds of particles. Epp is based on the EGSnrc C++ class library (egspp) which makes modeling particle sources and simulation geometries simpler than in DOSXYZnrc and other BEAM user codes based on EGSnrc code system. With Epp geometries can be modeled analytically or voxelized geometries, such as those in DOSXYZnrc, can be used. Compared to DOSXYZnrc (slightly modified from the official version for saving phase space information of photons leaving the geometry), Epp is at least two times faster. Photon propagation to the image plane is integrated into Epp (other particles possible with minor extension to the current code) with an ideal detector defined. When only the resultant images are needed, there is no need to save the particle data. This results in significant savings of data storage space, network load, and time for file I/O. Epp was validated against DOSXYZnrc for imaging and dose calculation by comparing simulation results with the same input. Epp can be used as a Monte Carlo simulation tool for faster imaging and radiation dose applications.

Cui, Congwu; Lippuner, Jonas; Ingleby, Harry R.; di Valentino, David N. M.; Elbakri, Idris A.

2010-03-01

272

Monte Carlo sensitivity analysis of unknown parameters in hazardous materials transportation risk assessment.  

PubMed

The US Department of Transportation was interested in the risks associated with transporting Hydrazine in tanks with and without relief devices. Hydrazine is both highly toxic and flammable, as well as corrosive. Consequently, there was a conflict as to whether a relief device should be used or not. Data were not available on the impact of relief devices on release probabilities or the impact of Hydrazine on the likelihood of fires and explosions. In this paper, a Monte Carlo sensitivity analysis of the unknown parameters was used to assess the risks associated with highway transport of Hydrazine. To help determine whether or not relief devices should be used, fault trees and event trees were used to model the sequences of events that could lead to adverse consequences during transport of Hydrazine. The event probabilities in the event trees were derived as functions of the parameters whose effects were not known. The impacts of these parameters on the risk of toxic exposures, fires, and explosions were analyzed through a Monte Carlo sensitivity analysis and analyzed statistically through an analysis of variance. The analysis allowed the determination of which of the unknown parameters had a significant impact on the risks. It also provided the necessary support to a critical transportation decision even though the values of several key parameters were not known. PMID:10765455

Pet-Armacost, J J; Sepulveda, J; Sakude, M

1999-12-01

273

Simulation of Cherenkov photons emitted in photomultiplier windows induced by Compton diffusion using the Monte Carlo code GEANT4.  

PubMed

The implementation of the TDCR method (Triple to Double Coincidence Ratio) is based on a liquid scintillation system which comprises three photomultipliers; at LNHB, this counter can also be used in the beta-channel of a 4pi(LS)beta-gamma coincidence counting equipment. It is generally considered that the gamma-sensitivity of the liquid scintillation detector comes from the interaction of the gamma-photons in the scintillation cocktail but when introducing solid gamma-ray emitting sources instead of the scintillation vial, light emitted by the surrounding of the counter is observed. The explanation proposed in this article is that this effect comes from the emission of Cherenkov photons induced by Compton diffusion in the photomultiplier windows. In order to support this assertion, the creation and the propagation of Cherenkov photons inside the TDCR counter is simulated using the Monte Carlo code GEANT4. Stochastic calculations of double coincidences confirm the hypothesis of Cherenkov light produced in the photomultiplier windows. PMID:20031429

Thiam, C; Bobin, C; Bouchard, J

2009-12-02

274

A portable, parallel, object-oriented Monte Carlo neutron transport code in C++  

SciTech Connect

We have developed a multi-group Monte Carlo neutron transport code using C++ and the Parallel Object-Oriented Methods and Applications (POOMA) class library. This transport code, called MC++, currently computes k and {alpha}-eigenvalues and is portable to and runs parallel on a wide variety of platforms, including MPPs, clustered SMPs, and individual workstations. It contains appropriate classes and abstractions for particle transport and, through the use of POOMA, for portable parallelism. Current capabilities of MC++ are discussed, along with physics and performance results on a variety of hardware, including all Accelerated Strategic Computing Initiative (ASCI) hardware. Current parallel performance indicates the ability to compute {alpha}-eigenvalues in seconds to minutes rather than hours to days. Future plans and the implementation of a general transport physics framework are also discussed.

Lee, S.R.; Cummings, J.C. [Los Alamos National Lab., NM (United States); Nolen, S.D. [Texas A and M Univ., College Station, TX (United States)]|[Los Alamos National Lab., NM (United States)

1997-05-01

275

Monte Carlo impurity transport modeling in the DIII-D Tokamak  

SciTech Connect

A description of the carbon transport and sputtering physics contained in the Monte Carlo Impurity (MCI) transport code is given. Examples of statistically significant carbon transport pathways are examined using MCI's unique tracking visualizer and a mechanism for enhanced carbon accumulation on the high field side of the divertor chamber is discussed. Comparisons between carbon emissions calculated with MCI and those measured in the DIII-D tokamak are described. Good qualitative agreement is found between 2D carbon emission patterns calculated with MCI and experimentally measured carbon patterns. While uncertainties in the sputtering physics, atomic data, and transport models have made quantitative comparisons with experiments more difficult, recent results using a physics based model for physical and chemical sputtering has yielded simulations with about 50% of the total carbon radiation measured in the divertor. These results and plans for future improvement in the physics models and atomic data are discussed.

Evans, T. E. [General Atomics, PO Box 85608, San Diego, California 92186 (United States); Finkenthal, D. F. [Palomar College, 1140 West Mission Road, San Marcos, California 92069 (United States)

1998-09-28

276

Evaluation of the EGSnrc Monte Carlo code for interface dosimetry near high-Z media exposed to kilovolt and 60Co photons  

Microsoft Academic Search

High atomic number (Z) heterogeneities in tissue exposed to photons with energies of up to about 1 MeV can cause significant dose perturbations in their immediate vicinity. The recently released Monte Carlo (MC) code EGSnrc (Kawrakow 2000a Med. Phys. 27 485-98) was used to investigate the dose perturbation of high-Z heterogeneities in tissue in kilovolt (kV) and 60Co photon beams.

Frank Verhaegen

2002-01-01

277

Monte Carlo Simulation of the Electron Transport Through Air Slabs: A Comparative Study of penelope, geant3, geant4 and egsnrc Monte Carlo Codes  

Microsoft Academic Search

The Monte Carlo simulation of the electron transport through air slabs is studied with four codes: PENELOPE, GEANT3, Geant4 and EGSnrc. Monoenergetic electron beams with energies 6, 12 and 18 MeV are considered to impinge on air slabs with thicknesses ranging from 10 to 100 cm. The angular and radial distributions of the transmitted electrons are used to make a

M. Vilches; S. Garcia-Pareja; R. Guerrero; M. Anguiano; A. M. Lallena

2008-01-01

278

Multigroup Boltzmann-Fokker-Planck electron-photon transport capability in MCNP  

SciTech Connect

The MCNP code system has a robust multigroup transport capability that includes a Boltzmann-Fokker-Planck (MGBFP) transport algorithm to perform coupled electron-photon or other coupled charged and neutral particle transport in either a forward or adjoint mode. This paper discusses this capability.

Adams, K.J.; Hart, M. [Los Alamos National Lab., NM (United States)

1995-12-31

279

Monte Carlo simulation of the photon beam characteristics from medical linear accelerators.  

PubMed

The MCNPX code has been employed on a personal computer to calculate the dosimetric characteristics of the photon beams from the 6 MV Siemens MX2 and the 10 MV Varian Clinac 2100C linear accelerators. A model of the treatment head includes the major geometric structure within the beam path. The model was used to calculate the energy spectra of the photon beam, percentage depth dose and the dose profiles. The accuracy of the calculated results is examined by comparing them with the measured dose distributions for the two machines. The computed and measured depth dose curves agree to within 2% for all the depths beyond the build-up region for both treatment machines. The calculations agree to within 2% of the measured profiles within the 100-50% dose level. It has been found that the MCNPX code is an effective tool for simulating the clinical photon beam. PMID:16644954

Kim, H K; Han, S J; Kim, J L; Kim, B H; Chang, S Y; Lee, J K

2006-04-27

280

Quantifying the number of color centers in single fluorescent nanodiamonds by photon correlation spectroscopy and Monte Carlo simulation  

SciTech Connect

The number of negatively charged nitrogen-vacancy centers (N-V){sup -} in fluorescent nanodiamond (FND) has been determined by photon correlation spectroscopy and Monte Carlo simulations at the single particle level. By taking account of the random dipole orientation of the multiple (N-V){sup -} fluorophores and simulating the probability distribution of their effective numbers (N{sub e}), we found that the actual number (N{sub a}) of the fluorophores is in linear correlation with N{sub e}, with correction factors of 1.8 and 1.2 in measurements using linearly and circularly polarized lights, respectively. We determined N{sub a}=8{+-}1 for 28 nm FND particles prepared by 3 MeV proton irradiation.

Hui, Y.Y.; Chang, Y.-R.; Lee, H.-Y.; Chang, H.-C. [Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan (China); Lim, T.-S. [Department of Physics, Tunghai University, Taichung 407, Taiwan (China); Fann Wunshain [Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan (China); Department of Physics, National Taiwan University, Taipei 106, Taiwan (China)

2009-01-05

281

On Monte Carlo modeling of megavoltage photon beams: A revisited study on the sensitivity of beam parameters  

SciTech Connect

Purpose: To commission Monte Carlo beam models for five Varian megavoltage photon beams (4, 6, 10, 15, and 18 MV). The goal is to closely match measured dose distributions in water for a wide range of field sizes (from 2x2 to 35x35 cm{sup 2}). The second objective is to reinvestigate the sensitivity of the calculated dose distributions to variations in the primary electron beam parameters. Methods: The GEPTS Monte Carlo code is used for photon beam simulations and dose calculations. The linear accelerator geometric models are based on (i) manufacturer specifications, (ii) corrections made by Chibani and Ma [''On the discrepancies between Monte Carlo dose calculations and measurements for the 18 MV Varian photon beam,'' Med. Phys. 34, 1206-1216 (2007)], and (iii) more recent drawings. Measurements were performed using pinpoint and Farmer ionization chambers, depending on the field size. Phase space calculations for small fields were performed with and without angle-based photon splitting. In addition to the three commonly used primary electron beam parameters (E{sub AV} is the mean energy, FWHM is the energy spectrum broadening, and R is the beam radius), the angular divergence ({theta}) of primary electrons is also considered. Results: The calculated and measured dose distributions agreed to within 1% local difference at any depth beyond 1 cm for different energies and for field sizes varying from 2x2 to 35x35 cm{sup 2}. In the penumbra regions, the distance to agreement is better than 0.5 mm, except for 15 MV (0.4-1 mm). The measured and calculated output factors agreed to within 1.2%. The 6, 10, and 18 MV beam models use {theta}=0 deg., while the 4 and 15 MV beam models require {theta}=0.5 deg. and 0.6 deg., respectively. The parameter sensitivity study shows that varying the beam parameters around the solution can lead to 5% differences with measurements for small (e.g., 2x2 cm{sup 2}) and large (e.g., 35x35 cm{sup 2}) fields, while a perfect agreement is maintained for the 10x10 cm{sup 2} field. The influence of R on the central-axis depth dose and the strong influence of {theta} on the lateral dose profiles are demonstrated. Conclusions: Dose distributions for very small and very large fields were proved to be more sensitive to variations in E{sub AV}, R, and {theta} in comparison with the 10x10 cm{sup 2} field. Monte Carlo beam models need to be validated for a wide range of field sizes including small field sizes (e.g., 2x2 cm{sup 2}).

Chibani, Omar; Moftah, Belal; Ma, C.-M. Charlie [Department of Biomedical Physics, King Faisal Specialist Hospital and Research Center, Riyadh 11211 (Saudi Arabia) and Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111 (United States); Department of Biomedical Physics, King Faisal Specialist Hospital and Research Center, Riyadh 11211 (Saudi Arabia); Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111 (United States)

2011-01-15

282

Are neutrons responsible for the dose discrepancies between Monte Carlo calculations and measurements in the build-up region for a high-energy photon beam?  

Microsoft Academic Search

This study presents measured neutron dose using a neutron dosimeter in a water phantom and investigates a hypothesis that neutrons in a high-energy photon beam may be responsible for the reported significant dose discrepancies between Monte Carlo calculations and measurements at the build-up region in large fields. Borated polyethylene slabs were inserted between the accelerator head and the phantom in

George X. Ding; Cheryl Duzenli; Nina I. Kalach

2002-01-01

283

SAF values for internal photon emitters calculated for the RPI-P pregnant-female models using Monte Carlo methods  

PubMed Central

Estimates of radiation absorbed doses from radionuclides internally deposited in a pregnant woman and her fetus are very important due to elevated fetal radiosensitivity. This paper reports a set of specific absorbed fractions (SAFs) for use with the dosimetry schema developed by the Society of Nuclear Medicine’s Medical Internal Radiation Dose (MIRD) Committee. The calculations were based on three newly constructed pregnant female anatomic models, called RPI-P3, RPI-P6, and RPI-P9, that represent adult females at 3-, 6-, and 9-month gestational periods, respectively. Advanced Boundary REPresentation (BREP) surface-geometry modeling methods were used to create anatomically realistic geometries and organ volumes that were carefully adjusted to agree with the latest ICRP reference values. A Monte Carlo user code, EGS4-VLSI, was used to simulate internal photon emitters ranging from 10 keV to 4 MeV. SAF values were calculated and compared with previous data derived from stylized models of simplified geometries and with a model of a 7.5-month pregnant female developed previously from partial-body CT images. The results show considerable differences between these models for low energy photons, but generally good agreement at higher energies. These differences are caused mainly by different organ shapes and positions. Other factors, such as the organ mass, the source-to-target-organ centroid distance, and the Monte Carlo code used in each study, played lesser roles in the observed differences in these. Since the SAF values reported in this study are based on models that are anatomically more realistic than previous models, these data are recommended for future applications as standard reference values in internal dosimetry involving pregnant females.

Shi, C. Y.; Xu, X. George; Stabin, Michael G.

2008-01-01

284

Monte Carlo modeling for photoacoustic-based transport-regime optical property estimation  

NASA Astrophysics Data System (ADS)

We developed a unique reflection-mode photoacoustic technique sensitive to optical scattering in turbid media. We focused a small laser spot on to the surface of a turbid medium and captured the photoacoustic signal by a focused ultrasound transducer. The amplitude of the photoacoustic signal for different surface illumination spot locations is an effective estimate of the Green's function of light transport in turbid media. Our results for different concentrations of Intralipid indicate that this method is capable of distinguishing small changes in the reduced scattering coefficient. In this work, we present experimental measurements for an Intralipid phantom with reduced scattering coefficients of 3, 4, and 5 cm-1, and show that Monte Carlo simulations of light transport accurately reproduce experimental curves. This means that we can estimate transport-regime optical properties of the media given a suitable fitting algorithm.

Ranasinghesagara, Janaka C.; Zemp, Roger J.

2010-02-01

285

A 3D photon superposition/convolution algorithm and its foundation on results of Monte Carlo calculations  

NASA Astrophysics Data System (ADS)

Based on previous publications on a triple Gaussian analytical pencil beam model and on Monte Carlo calculations using Monte Carlo codes GEANT-Fluka, versions 95, 98, 2002, and BEAMnrc/EGSnrc, a three-dimensional (3D) superposition/convolution algorithm for photon beams (6 MV, 18 MV) is presented. Tissue heterogeneity is taken into account by electron density information of CT images. A clinical beam consists of a superposition of divergent pencil beams. A slab-geometry was used as a phantom model to test computed results by measurements. An essential result is the existence of further dose build-up and build-down effects in the domain of density discontinuities. These effects have increasing magnitude for field sizes <=5.5 cm2 and densities <=0.25 g cm-3, in particular with regard to field sizes considered in stereotaxy. They could be confirmed by measurements (mean standard deviation 2%). A practical impact is the dose distribution at transitions from bone to soft tissue, lung or cavities. This work has partially been presented at WC 2003, Sydney.

Ulmer, W.; Pyyry, J.; Kaissl, W.

2005-04-01

286

Diffusion of photons with arbitrary state of polarization: the Monte Carlo code MCSHAPE  

Microsoft Academic Search

When X-rays penetrate in the matter, they interact with the atoms, producing secondary radiation that carries important information about the composition of the target. The polarization state is one of the properties of the incoming photons which changes as a consequence of the number and the type of the undergone interaction. Therefore, to study properly the atomic properties of a

J. E Fernandez; V. G Molinari; M Bastiano; V Scot

2004-01-01

287

Discrepancies in the Monte Carlo simulations of propagation of ultra-high energy cosmic-ray photons in the geomagnetic field  

NASA Astrophysics Data System (ADS)

The discrepancies in the results produced by the two most commonly used Monte Carlo programs for simulation of propagation of ultra-high energy cosmic ray photons in the presence of the geomagnetic field are presented. Although photons have not yet been discovered in the cosmic ray flux at highest energies, the capabilities of the present cosmic ray detectors make their discovery possible, according to the predictions of conventional models, within the next few years. It is therefore necessary to have a reliable and well maintained software for relevant simulations. The results of this paper are important for simulations of propagation of photons at energies above 1019 eV. Photons of such high energies might interact with the geomagnetic field giving rise to a cascade of particles even above the atmosphere. This effect is called a "preshower effect". The preshower effect is important for air shower evolution and has to be accounted for in full Monte Carlo simulations of propagation of highest energy cosmic-ray photons. In this paper we compare the two most frequently used Monte Carlo codes for preshower simulations: PRESHOWER, used as a stand-alone program or as a part of CORSIKA, and MaGICS, used as a part of AIRES.

Homola, P.; Rygielski, M.

2013-05-01

288

Monte Carlo simulation of phonon transport in silicon including a realistic dispersion relation  

NASA Astrophysics Data System (ADS)

Thermal conductivities in bulk Si and Si films are analyzed using a Monte Carlo method to solve the phonon Boltzmann transport equation. By taking into account the realistic phonon dispersion relation calculated from the adiabatic bond charge model along with pure diffuse boundary scattering based on Lambert's law, simulated results that were in good agreement with the experimental ones were obtained. In addition, it was found that the approximated dispersion curves fitted along the [100] direction underestimate the density of states for mobile phonons, which results in a smaller specific heat and a longer phonon mean free path. The resulting impact on the simulation of heat transfer in nanostructures is discussed.

Kukita, K.; Kamakura, Y.

2013-10-01

289

Monte Carlo analysis of ultrafast electron transport in quantum well infrared photodetectors  

NASA Astrophysics Data System (ADS)

A self-consistent ensemble Monte Carlo simulation is used to study ultrafast electron transport in quantum well infrared photodetectors (QWIPs). It is shown that transient photocurrent triggered by a short infrared radiation pulse reveals a sharp peak followed by a relatively slow decay. The photocurrent peak is associated with the electron velocity overshoot effect while the slow component of the photocurrent is determined by the electron transit time and capture effects. The velocity overshoot effect results in the existence of a plateau in the QWIP frequency-dependent responsivity in the range of terahertz frequencies.

Ryzhii, M.; Ryzhii, V.

1998-02-01

290

On the discrepancies between Monte Carlo dose calculations and measurements for the 18 MV varian photon beam.  

PubMed

Significant discrepancies between Monte Carlo dose calculations and measurements for the Varian 18 MV photon beam with a large field size (40 x 40 cm2) were reported by different investigators. In this work, we investigated these discrepancies based on a new geometry model ("New Model") of the Varian 21EX linac using the GEPTS Monte Carlo code. Some geometric parameters used in previous investigations (Old Model) were inaccurate, as suggested by Chibani in his AAPM presentation (2004) and later confirmed by the manufacturer. The entrance and exit radii of the primary collimator of the New Model are 2 mm larger than previously thought. In addition to the corrected dimensions of the primary collimator, the New Model includes approximate models for the lead shield and the mirror frame between the monitor chamber and the Y jaws. A detailed analysis of the phase space data shows the effects of these corrections on the beam characteristics. The individual contributions from the linac component to the photon and electron fluences are calculated. The main source of discrepancy between measurements and calculations based on the Old Model is the underestimated electron contamination. The photon and electron fluences at the isocenter are 5.3% and 36% larger in the New Model in comparison with the Old Model. The flattening filter and the lead shield (plus the mirror frame) contribute 48.7% and 13% of the total electron contamination at the isocenter, respectively. For both open and filtered (2 mm Pb) fields, the calculated (New Model) and measured dose distributions are within 1% for depths larger than 1 cm. To solve the residual problem of large differences at shallow depths (8% at 0.25 cm depth), the detailed geometry of an IC-10 ionization chamber was simulated and the dose in the air cavity was calculated for different positions on the central axis including at the surface, where half of the chamber is outside the phantom. The calculated and measured chamber responses are within 3% even at the zero depth. PMID:17500452

Chibani, Omar; Ma, C M Charlie

2007-04-01

291

Review of Hybrid (Deterministic\\/Monte Carlo) Radiation Transport Methods, Codes, and Applications at Oak Ridge National Laboratory  

Microsoft Academic Search

This paper provides a review of the hybrid (Monte Carlo\\/deterministic) radiation transport methods and codes used at the Oak Ridge National Laboratory and examples of their application for increasing the efficiency of real-world, fixed-source Monte Carlo analyses. The two principal hybrid methods are (1) Consistent Adjoint Driven Importance Sampling (CADIS) for optimization of a localized detector (tally) region (e.g., flux,

John C Wagner; Douglas E. Peplow; Scott W Mosher; Thomas M Evans

2010-01-01

292

Review of Hybrid (Deterministic\\/Monte Carlo) Radiation Transport Methods, Codes, and Applications at Oak Ridge National Laboratory  

Microsoft Academic Search

This paper provides a review of the hybrid (Monte Carlo\\/deterministic) radiation transport methods and codes used at the Oak Ridge National Laboratory and examples of their application for increasing the efficiency of real-world, fixed-source Monte Carlo analyses. The two principal hybrid methods are (1) Consistent Adjoint Driven Importance Sampling (CADIS) for optimization of a localized detector (tally) region (e.g., flux,

John C Wagner; Douglas E. Peplow; Scott W Mosher; Thomas M Evans

2011-01-01

293

Two-dimensional discrete ordinates photon transport calculations for brachytherapy dosimetry applications  

SciTech Connect

The DANTSYS discrete ordinates computer code system is applied to quantitative estimation of water kerma rate distributions in the vicinity of discrete photon sources with energies in the 20- to 800-keV range in two-dimensional cylindrical r-z geometry. Unencapsulated sources immersed in cylindrical water phantoms of 40-cm diameter and 40-cm height are modeled in either homogeneous phantoms or shielded by Ti, Fe, and Pb filters with thicknesses of 1 and 2 mean free paths. The obtained dose results are compared with corresponding photon Monte Carlo simulations. A 210-group photon cross-section library for applications in this energy range is developed and applied, together with a general-purpose 42-group library developed at Los Alamos National Laboratory, for DANTSYS calculations. The accuracy of DANTSYS with the 42-group library relative to Monte Carlo exhibits large pointwise fluctuations from {minus}42 to +84%. The major cause for the observed discrepancies is determined to be the inadequacy of the weighting function used for the 42-group library derivation. DANTSYS simulations with a finer 210-group library show excellent accuracy on and off the source transverse plane relative to Monte Carlo kerma calculations, varying from {minus}4.9 to 3.7%. The P{sub 3} Legendre polynomial expansion of the angular scattering function is shown to be sufficient for accurate calculations. The results demonstrate that DANTSYS is capable of calculating photon doses in very good agreement with Monte Carlo and that the multigroup cross-section library and efficient techniques for mitigation of ray effects are critical for accurate discrete ordinates implementation.

Daskalov, G.M.; Baker, R.S.; Little, R.C.; Rogers, D.W.O.; Williamson, J.F.

2000-02-01

294

Efficient ohmic boundary conditions for the Monte Carlo simulation of electron transport  

SciTech Connect

The development of macroscopic transport models, accurate for studying hot-electron transport in semiconductors, involves a direct consideration of higher-moment terms. All hydrodynamic transport models (HTMs), derived from moments of the Boltzmann transport equation, require the introduction of closure relations to terminate the resulting infinite set of macroscopic equations. These closure relations are used as analytical approximations to distributional-dependent integral coefficients. The most popular theoretical approach employed for the construction and evaluation of these higher-moment transport-parameter closures is the Monte Carlo (MC) method. Since the MC method is computationally intensive, the discovery and implementation of efficient MC modeling techniques (either numerical or physical) is of significant value. This paper reports on a relationship between device boundary conditions and the convergence range of higher-moment terms in time-independent MC simulations. Specifically, a set of ohmic BC's which offer computational advantages is presented. This particular mathematical approach, which allows for two degrees of freedom, is shown to be more efficient in generating the full electron distribution function than conventional BC methods (i.e., strictly equilibrium-based).

Woolard, D.L.; Tian, H.; Littlejohn, M.A.; Kim, K.W. (North Carolina State Univ., Raleigh, NC (United States). Electrical and Computer Engineering Dept.)

1994-04-01

295

Considerations and limitations of fast Monte Carlo electron transport in radiation therapy based on precalculated data.  

PubMed

The purpose of this work is to revisit the impediments and characteristics of fast Monte Carlo techniques for applications in radiation therapy treatment planning using new methods of utilizing pregenerated electron tracks. The limitations of various techniques for the improvement of speed and accuracy of electron transport have been evaluated. A method is proposed that takes advantage of large available memory in current computer hardware for extensive generation of precalculated data. Primary tracks of electrons are generated in the middle of homogeneous materials (water, air, bone, lung) and with energies between 0.2 and 18 MeV using the EGSnrc code. Secondary electrons are not transported, but their position, energy, charge, and direction are saved and used as a primary particle. Based on medium type and incident electron energy, a track is selected from the precalculated set. The performance of the method is tested in various homogeneous and heterogeneous configurations and the results were generally within 2% compared to EGSnrc but with a 40-60 times speed improvement. In a second stage the authors studied the obstacles for further increased speed-ups in voxel geometries by including ray-tracing and particle fluence information in the pregenerated track information. The latter method leads to speed increases of about a factor of 500 over EGSnrc for voxel-based geometries. In both approaches, no physical calculation is carried out during the runtime phase after the pregenerated data has been stored even in the presence of heterogeneities. The precalculated data are generated for each particular material and this improves the performance of the precalculated Monte Carlo code both in terms of accuracy and speed. Precalculated Monte Carlo codes are accurate, fast, and physics independent and therefore applicable to different radiation types including heavy-charged particles. PMID:19291992

Jabbari, Keyvan; Keall, Paul; Seuntjens, Jan

2009-02-01

296

Hybrid two-dimensional Monte-Carlo electron transport in self-consistent electromagnetic fields  

SciTech Connect

The physics and numerics of the hybrid electron transport code ANTHEM are described. The need for the hybrid modeling of laser generated electron transport is outlined, and a general overview of the hybrid implementation in ANTHEM is provided. ANTHEM treats the background ions and electrons in a laser target as coupled fluid components moving relative to a fixed Eulerian mesh. The laser converts cold electrons to an additional hot electron component which evolves on the mesh as either a third coupled fluid or as a set of Monte Carlo PIC particles. The fluids and particles move in two-dimensions through electric and magnetic fields calculated via the Implicit Moment method. The hot electrons are coupled to the background thermal electrons by Coulomb drag, and both the hot and cold electrons undergo Rutherford scattering against the ion background. Subtleties of the implicit E- and B-field solutions, the coupled hydrodynamics, and large time step Monte Carlo particle scattering are discussed. Sample applications are presented.

Mason, R.J.; Cranfill, C.W.

1985-01-01

297

Two-photon fluorescence correlation microscopy reveals the two-phase nature of transport in tumors  

Microsoft Academic Search

Transport parameters determine the access of drugs to tumors. However, technical difficulties preclude the measurement of these parameters deep inside living tissues. To this end, we adapted and further optimized two-photon fluorescence correlation microscopy (TPFCM) for in vivo measurement of transport parameters in tumors. TPFCM extends the detectable range of diffusion coefficients in tumors by one order of magnitude, and

George Alexandrakis; Edward B Brown; Ricky T Tong; Trevor D McKee; Robert B Campbell; Yves Boucher; Rakesh K Jain

2004-01-01

298

Development of Monte Carlo automatic modeling functions of MCAM for TRIPOLI-ITER application  

Microsoft Academic Search

TRIPOLI is a Monte Carlo particle transport code simulating the three-dimensional transport of neutrons and photons with the Monte Carlo method, and it can be used for many applications to nuclear devices with complex geometries; however, modeling of a complex geometry is a time-consuming and error-prone task. The recently developed functions of Monte Carlo Automatic Modeling (MCAM) system, which is

L. Lu; Y. K. Lee; J. J. Zhang; Y. Li; Q. Zeng; Y. C. Wu

2009-01-01

299

Photon-cell interactive monte carlo (pciMC) model to describe both intracellular and extracellular optical pathways for biconcave red blood cells: phase function and albedo  

NASA Astrophysics Data System (ADS)

A photon-cell interactive Monte Carlo ("pciMC") model was developed to quantify the intracellular optical propagation in a 3-dimensional biconcave red blood cell (RBC) model having a finite volume and intracellular hemoglobin. The orientation of RBCs with respect to the incident photons was randomized to allow either extra- or intra-cellular propagation depending on the incident point and angles where the photon propagation at the plasma-cell interface was determined by the Snell's law and Fresnell's law. In this study, the photon propagation through single RBC using the pciMC was compared against the Henyey-Greenstein phase function. The absorption dependent intracellular optical path length was evaluated in comparison to Mie theory. Both results showed good agreement. The pciMC can contribute to photo-spectroscopy of blood and tissues by quantifying both extra- and intra-cellular optical propagation.

Sakota, D.; Takatani, S.

2010-02-01

300

Improved electron transport mechanics in the PENELOPE Monte-Carlo model  

NASA Astrophysics Data System (ADS)

We describe a new model of electron transport mechanics, the method by which an electron is transported geometrically in an infinite medium as a function of pathlength, s, the accumulated elastic multiple-scattering angular deflection characterized by /?(s), the polar scattering angle, and /?, a random azimuthal angle. This model requires only one sample of the multiple-scattering angle yet it reproduces exactly the following spatial moments and space-angular correlations: /, /, /, /, , and . Moreover, the distributions associated with these moments exhibit a good improvement over the PENELOPE transport mechanics model when compared self-consistently with the results of analog simulations. When we split the transport step into two steps with equal pathlength, we observe excellent agreement with the distributions, indicating that the algorithm nearly matches higher order moments when employed in this way. The equations described herein are relatively inexpensive to employ in an iterative Monte-Carlo code. We have employed the new model to demonstrate the usefulness of the new mechanics for several examples that span the dynamic range of application.

Bielajew, A. F.; Salvat, F.

2001-01-01

301

Monte Carlo simulation of phonon transport in UO2 single crystals  

NASA Astrophysics Data System (ADS)

The Monte Carlo (MC) method is applied to solve the Boltzmann transport equation for phonons in uranium dioxide single crystals, with the objective of understanding thermal transport in this material at the mesoscale. The overall solution scheme tracks the phonon density as it evolves in space and time due to phonon drift and phonon-phonon scattering by normal and Umklapp processes. Unlike most previous works on solving the Boltzmann transport equation for phonons by the MC technique, our scheme for calculating phonon lifetime, based on normal and Umklapp scattering, eliminates the need for using many fitting parameters. Instead, the Grüneisen parameter, which is a well-characterized material property, is the only parameter of the problem. The results elucidate the simulation domain size over which the computed conductivity is size dependent; this helps to determine the minimum domain size required to simulate bulk thermal transport and hence calculate the thermal conductivity. The latter is computed over the temperature range 300-1000 K. The computed conductivity values are in good agreement with the previously published experimental and molecular dynamics simulation results.

Deskins, W. R.; El-Azab, A.

2013-03-01

302

Generalized Particle Concept for Adjoint Monte Carlo Calculations of Coupled Gamma-Ray-Electron-Positron Transport  

SciTech Connect

Adjoint Monte Carlo methods for coupled transport are developed. The phase-space is extended by the introduction of an additional discrete coordinate (particle type of so-called generalized particle). The generalized particle concept allows the treatment of the transport of mixed radiation as a process with only one particle outgoing from a collision regardless of the physical picture of the interaction. In addition to the forward equation for the generalized particle, the adjoint equation is also derived. The proposed concept is applied to the adjoint equation of the coupled gamma-ray-electron-positron transport. Charged particle transport is considered in continuous slowing down approximation and Moliere's theory of multiple scattering, for which special adjoint sampling methods are suggested. A new approach to simulation of fixed-energy secondary radiation is implemented into the generalized particle concept. This approach performs fixed-energy secondary radiation simulation as the local energy estimator through the intermediate state with fixed energy. A comparison of forward and adjoint calculations for energy absorption shows the same results for radionuclide energies with and without electron equilibrium. Adjoint methods show greater efficiency in thin slabs.

Borisov, N.M. [Thomas Jefferson University (United States); Panin, M.P. [Moscow Engineering Physics Institute (State University) (Russian Federation)

2005-07-15

303

Monte Carlo simulation based on dynamic disorder model in organic semiconductors: From coherent to incoherent transport  

NASA Astrophysics Data System (ADS)

The dynamic disorder model for charge carrier transport in organic semiconductors has been extensively studied in recent years. Although it is successful on determining the value of bandlike mobility in the organic crystalline materials, the incoherent hopping, the typical transport characteristic in amorphous molecular semiconductors, cannot be described. In this work, the decoherence process is taken into account via a phenomenological parameter, say, decoherence time, and the projective and Monte Carlo method are applied for this model to determine the waiting time and thus the diffusion coefficient. It is obtained that the type of transport is changed from coherent to incoherent with a sufficiently short decoherence time, which indicates the essential role of decoherence time in determining the type of transport in organics. We have also discussed the spatial extent of carriers for different decoherence time, and the transition from delocalization (carrier resides in about 10 molecules) to localization is observed. Based on the experimental results of spatial extent, we estimate that the decoherence time in pentacene has the order of 1 ps. Furthermore, the dependence of diffusion coefficient on decoherence time is also investigated, and corresponding experiments are discussed.

Yao, Yao; Si, Wei; Hou, Xiaoyuan; Wu, Chang-Qin

2012-06-01

304

Monte Carlo impurity transport modeling in the DIII{endash}D Tokamak  

SciTech Connect

A description of the carbon transport and sputtering physics contained in the Monte Carlo Impurity (MCI) transport code is given. Examples of statistically significant carbon transport pathways are examined using MCI{close_quote}s unique tracking visualizer and a mechanism for enhanced carbon accumulation on the high field side of the divertor chamber is discussed. Comparisons between carbon emissions calculated with MCI and those measured in the DIII{endash}D tokamak are described. Good qualitative agreement is found between 2D carbon emission patterns calculated with MCI and experimentally measured carbon patterns. While uncertainties in the sputtering physics, atomic data, and transport models have made quantitative comparisons with experiments more difficult, recent results using a physics based model for physical and chemical sputtering has yielded simulations with about 50{percent} of the total carbon radiation measured in the divertor. These results and plans for future improvement in the physics models and atomic data are discussed. {copyright} {ital 1998 American Institute of Physics.}

Evans, T.E. [General Atomics, PO Box 85608, San Diego, California 92186 (United States); Finkenthal, D.F. [Palomar College, 1140 West Mission Road, San Marcos, California 92069 (United States)

1998-09-01

305

Dosimetric validation of Acuros XB with Monte Carlo methods for photon dose calculations  

SciTech Connect

Purpose: The dosimetric accuracy of the recently released Acuros XB advanced dose calculation algorithm (Varian Medical Systems, Palo Alto, CA) is investigated for single radiation fields incident on homogeneous and heterogeneous geometries, and a comparison is made to the analytical anisotropic algorithm (AAA). Methods: Ion chamber measurements for the 6 and 18 MV beams within a range of field sizes (from 4.0x4.0 to 30.0x30.0 cm{sup 2}) are used to validate Acuros XB dose calculations within a unit density phantom. The dosimetric accuracy of Acuros XB in the presence of lung, low-density lung, air, and bone is determined using BEAMnrc/DOSXYZnrc calculations as a benchmark. Calculations using the AAA are included for reference to a current superposition/convolution standard. Results: Basic open field tests in a homogeneous phantom reveal an Acuros XB agreement with measurement to within {+-}1.9% in the inner field region for all field sizes and energies. Calculations on a heterogeneous interface phantom were found to agree with Monte Carlo calculations to within {+-}2.0%({sigma}{sub MC}=0.8%) in lung ({rho}=0.24 g cm{sup -3}) and within {+-}2.9%({sigma}{sub MC}=0.8%) in low-density lung ({rho}=0.1 g cm{sup -3}). In comparison, differences of up to 10.2% and 17.5% in lung and low-density lung were observed in the equivalent AAA calculations. Acuros XB dose calculations performed on a phantom containing an air cavity ({rho}=0.001 g cm{sup -3}) were found to be within the range of {+-}1.5% to {+-}4.5% of the BEAMnrc/DOSXYZnrc calculated benchmark ({sigma}{sub MC}=0.8%) in the tissue above and below the air cavity. A comparison of Acuros XB dose calculations performed on a lung CT dataset with a BEAMnrc/DOSXYZnrc benchmark shows agreement within {+-}2%/2mm and indicates that the remaining differences are primarily a result of differences in physical material assignments within a CT dataset. Conclusions: By considering the fundamental particle interactions in matter based on theoretical interaction cross sections, the Acuros XB algorithm is capable of modeling radiotherapy dose deposition with accuracy only previously achievable with Monte Carlo techniques.

Bush, K.; Gagne, I. M.; Zavgorodni, S.; Ansbacher, W.; Beckham, W. [Department of Medical Physics, British Columbia Cancer Agency-Vancouver Island Center, Victoria, British Columbia V8R 6V5 (Canada)

2011-04-15

306

Intercomparision of Monte Carlo Radiation Transport Codes MCNPX, GEANT4, and FLUKA for Simulating Proton Radiotherapy of the Eye.  

PubMed

Monte Carlo simulations of an ocular treatment beam-line consisting of a nozzle and a water phantom were carried out using MCNPX, GEANT4, and FLUKA to compare the dosimetric accuracy and the simulation efficiency of the codes. Simulated central axis percent depth-dose profiles and cross-field dose profiles were compared with experimentally measured data for the comparison. Simulation speed was evaluated by comparing the number of proton histories simulated per second using each code. The results indicate that all the Monte Carlo transport codes calculate sufficiently accurate proton dose distributions in the eye and that the FLUKA transport code has the highest simulation efficiency. PMID:20865141

Randeniya, S D; Taddei, P J; Newhauser, W D; Yepes, P

2009-12-01

307

Study of photon migration with various source-detector separations in near-infrared spectroscopic brain imaging based on three-dimensional Monte Carlo modeling  

NASA Astrophysics Data System (ADS)

We have simulated photon migration with various sourcedetector separations based on a three-dimensional Monte Carlo code. Whole brain MRI structure images are introduced in the simulation, and the brain model is more accurate than in previous studies. The brain model consists of the scalp, skull, CSF layer, gray matter, and white matter. We demonstrate dynamic propagating movies under different source-detector separations. The multiple backscattered intensity from every layer of the brain model is obtained by marking the deepest layer that every photon can reach. Also, the influences of an absorption target on the brain cortex are revealed.

Lee, Cheng-Kuang; Sun, Chia-Wei; Lee, Hsiang-Chieh; Yang, C. C.; Jiang, Cho-Pei; Tong, Yuh-Ping; Lee, Po-Lei; Hsieh, Jen-Chuen

2005-10-01

308

Adiabatic Deceleration of Solar Energetic Particles as Deduced from Monte Carlo Simulations of Interplanetary Transport  

NASA Astrophysics Data System (ADS)

Monte Carlo simulations of interplanetary transport are employed to study adiabatic energy losses of solar protons during propagation in the interplanetary medium. We consider four models. The first model is based on the diffusion-convection equation. Three other models employ the focused transport approach. In the focused transport models, we simulate elastic scattering in the local solar wind frame and magnetic focusing. We adopt three methods to treat scattering. In two models, we simulate a pitch-angle diffusion as successive isotropic or anisotropic small-angle scatterings. The third model treats large-angle scatterings as numerous small-chance isotropizations. The deduced intensity time profiles are compared with each other, with Monte Carlo solutions to the diffusion-convection equation, and with results of the finite-difference scheme by Ruffolo (1995). A numerical agreement of our Monte Carlo simulations with results of the finite-difference scheme is good. For the period shortly after the maximum intensity time, including deceleration can increase the decay rate of the near-Earth intensity essentially more than would be expected based on advection from higher momenta. We, however, find that the excess in the exponential-decay rate is time dependent. Being averaged over a reasonably long period, the decay rate of the near-Earth intensity turns out to be close to that expected based on diffusion, convection, and advection from higher momenta. We highlight a variance of the near-Earth energy which is not small in comparison with the energy lost. It leads to blurring of any fine details in the accelerated particle spectra. We study the impact of realistic spatial dependencies of the mean free path on adiabatic deceleration and on the near-Earth intensity magnitude. We find that this impact is essential whenever adiabatic deceleration itself is important. It is also found that the initial angular distribution of particles near the Sun can markedly affect MeV-proton energy losses and intensities observed at 1 AU. Computations invoked during the study are described in detail.

Kocharov, L.; Vainio, R.; Kovaltsov, G. A.; Torsti, J.

1998-09-01

309

Composition PDF\\/photon Monte Carlo modeling of moderately sooting turbulent jet flames  

Microsoft Academic Search

A comprehensive model for luminous turbulent flames is presented. The model features detailed chemistry, radiation and soot models and state-of-the-art closures for turbulence-chemistry interactions and turbulence-radiation interactions. A transported probability density function (PDF) method is used to capture the effects of turbulent fluctuations in composition and temperature. The PDF method is extended to include soot formation. Spectral gas and soot

R. S. Mehta; D. C. Haworth; M. F. Modest

2010-01-01

310

Composition PDF\\/photon Monte Carlo modeling of moderately sooting turbulent jet flames  

Microsoft Academic Search

A comprehensive model for luminous turbulent flames is presented. The model features detailed chemistry, radiation and soot models and state-of-the-art closures for turbulence–chemistry interactions and turbulence–radiation interactions. A transported probability density function (PDF) method is used to capture the effects of turbulent fluctuations in composition and temperature. The PDF method is extended to include soot formation. Spectral gas and soot

R. S. Mehta; D. C. Haworth; M. F. Modest

2010-01-01

311

Modeling the Global Short-Period Wavefield with a Monte Carlo Seismic Photon Method  

NASA Astrophysics Data System (ADS)

At high frequencies (~1 Hz), much of the seismic energy arriving at teleseismic distances is not found in the main phases (e.g., P, PP, S, etc.) but is contained in the extended coda that follows these arrivals. This coda results from scattering off small-scale velocity and density perturbations within the crust and mantle and contains valuable information regarding the depth dependence and strength of this heterogeneity as well as the relative importance of intrinsic vs. scattering attenuation. Most analyses of seismic coda to date have concentrated on S-wave coda generated from lithospheric scattering for events recorded at local and regional distances. Here we examine the globally averaged teleseismic (>20° range) vertical-component, 1-Hz wavefield for earthquakes recorded in the IRIS FARM archive from 1989 to 1999. We apply an envelope-function stacking technique to image the average time-distance behavior of the wavefield. Unlike regional records, our images are dominated by P and P-coda owing to the large effect of attenuation on PP and S at high frequencies. Modeling our results is complicated by the need to include a variety of ray paths, the likely contributions of multiple scattering, and the possible importance of P-to-S and S-to-P scattering. We adopt a stochastic, particle-based approach in which millions of seismic ``photons'' are randomly sprayed from the source and tracked through the Earth. Each photon represents an energy packet that travels along the appropriate ray path until it is affected by a discontinuity or a scatterer. Discontinuities are modeled by treating the energy normalized reflection and transmission coefficients as probabilities. Scattering probabilities and scattering angles are computed in a similar fashion, assuming random velocity and density perturbations characterized by an exponential autocorrelation function. Intrinsic attenuation is included by reducing the energy contained in each particle as an appropriate function of travel time. Results suggest that most scattering occurs in the lithosphere and upper mantle, as previous results have indicated, but that some lower mantle scattering is likely also required. One-dimensional models found to date that successfully predict observed P-coda amplitudes for deep earthquakes underestimate P-coda amplitudes for shallow earthquakes. The origin of this discrepancy is not clear, but may indicate greater-than-average scattering in shallow earthquake source regions or differences in average 1-Hz S-to-P energy ratios between shallow and deep earthquakes.

Shearer, P. M.; Earle, P. S.

2002-12-01

312

Study of the response of plastic scintillation detectors in small-field 6 MV photon beams by Monte Carlo simulations  

SciTech Connect

Purpose: To investigate the response of plastic scintillation detectors (PSDs) in a 6 MV photon beam of various field sizes using Monte Carlo simulations. Methods: Three PSDs were simulated: A BC-400 and a BCF-12, each attached to a plastic-core optical fiber, and a BC-400 attached to an air-core optical fiber. PSD response was calculated as the detector dose per unit water dose for field sizes ranging from 10x10 down to 0.5x0.5 cm{sup 2} for both perpendicular and parallel orientations of the detectors to an incident beam. Similar calculations were performed for a CC01 compact chamber. The off-axis dose profiles were calculated in the 0.5x0.5 cm{sup 2} photon beam and were compared to the dose profile calculated for the CC01 chamber and that calculated in water without any detector. The angular dependence of the PSDs' responses in a small photon beam was studied. Results: In the perpendicular orientation, the response of the BCF-12 PSD varied by only 0.5% as the field size decreased from 10x10 to 0.5x0.5 cm{sup 2}, while the response of BC-400 PSD attached to a plastic-core fiber varied by more than 3% at the smallest field size because of its longer sensitive region. In the parallel orientation, the response of both PSDs attached to a plastic-core fiber varied by less than 0.4% for the same range of field sizes. For the PSD attached to an air-core fiber, the response varied, at most, by 2% for both orientations. Conclusions: The responses of all the PSDs investigated in this work can have a variation of only 1%-2% irrespective of field size and orientation of the detector if the length of the sensitive region is not more than 2 mm long and the optical fiber stems are prevented from pointing directly to the incident source.

Wang, Lilie L. W.; Beddar, Sam [Department of Radiation Physics, University of Texas MD Anderson Cancer Center, Houston, Texas 77030 (United States)

2011-03-15

313

Photon migration through a turbid slab described by a model based on diffusion approximation. II. Comparison with Monte Carlo results.  

PubMed

In our companion paper we presented a model to describe photon migration through a diffusing slab. The model, developed for a homogeneous slab, is based on the diffusion approximation and is able to take into account reflection at the boundaries resulting from the refractive index mismatch. In this paper the predictions of the model are compared with solutions of the radiative transfer equation obtained by Monte Carlo simulations in order to determine the applicability limits of the approximated theory in different physical conditions. A fitting procedure, carried out with the optical properties as fitting parameters, is used to check the application of the model to the inverse problem. The results show that significant errors can be made if the effect of the refractive index mismatch is not properly taken into account. Errors are more important when measurements of transmittance are used. The effects of using a receiver with a limited angular field of view and the angular distribution of the radiation that emerges from the slab have also been investigated. PMID:18259255

Martelli, F; Contini, D; Taddeucci, A; Zaccanti, G

1997-07-01

314

Development of red blood cell-photon simulator for optical propagation analysis in blood using Monte Carlo method.  

PubMed

We have developed a "red blood cell (RBC)-photon simulator" to reveal optical propagation in prethrombus blood for various levels of RBC density and aggregation. The simulator investigates optical propagation in the prethrombus blood and will be applied to detect it noninvasively for thrombosis prevention in an earlier stage. In our simulator, Lambert-Beer's law is employed to simulate the absorption of RBCs with hemoglobin, while the Monte Carlo method is applied to simulate scattering through iterative calculations. One advantage of our simulator is that concentrations and distributions of RBCs can be arbitrarily chosen to exhibit the prethrombus, while conventional models cannot. Using the simulator, we found that various levels of RBC density and aggregation have different effects on the optical propagation of near-infrared response light in blood. The same different effects were acquired in in vitro experiments with 12 bovine blood samples, which were performed to evaluate the simulator. We measured RBC density using the clinical hematocrit index and RBC aggregation using activated whole blood clotting time. The experimental results correspond to the simulator results well. Therefore, we could show that our simulator exhibits the correct optical propagation for prethrombus blood and is applicable for the prethrombus detection using multiple detectors. PMID:21342854

Oshima, Shiori; Sankai, Yoshiyuki

2011-02-22

315

a Next-To Monte Carlo Study of Photon Pairs and the Search for the Intermediate Mass Higgs Boson.  

NASA Astrophysics Data System (ADS)

Symmetry breaking and the question of the origin of mass are the reasons the Superconducting Super Collider and the Large Hadron Collider are being built. The Standard Model of particle physics provides a solution to this problem by proposing the existence of a neutral scalar particle, the Higgs boson. This particle, via its interactions, gives mass to all of the particles in the Standard Model. The question of whether the Higgs boson can be detected at these machines depends critically on its final state decays. These decays in turn depend crucially on the mass of the Higgs boson, an unknown parameter of the theory. A lower bound of the Higgs mass has been set by experiment and a upper bound via theoretical arguments. Throughout much of the mass range Higgs decays via weak gauge bosons yield a clear signal. However, near the lower limit, the so-called intermediate mass region, the situation is less clear. In this region Higgs decays into photon pairs have been suggested as a viable signal. The significance of such a signal depends on other competing processes or backgrounds. This dissertation attempts to answer the question, "Can the Intermediate mass Higgs boson be detected via its electromagnetic decays?" To answer this question various Standard Model processes are calculated to the leading-log and next-to-leading-log level in a Monte Carlo environment.

Bailey, Bobby R.

316

Bone and mucosal dosimetry in skin radiation therapy: a Monte Carlo study using kilovoltage photon and megavoltage electron beams  

NASA Astrophysics Data System (ADS)

This study examines variations of bone and mucosal doses with variable soft tissue and bone thicknesses, mimicking the oral or nasal cavity in skin radiation therapy. Monte Carlo simulations (EGSnrc-based codes) using the clinical kilovoltage (kVp) photon and megavoltage (MeV) electron beams, and the pencil-beam algorithm (Pinnacle3 treatment planning system) using the MeV electron beams were performed in dose calculations. Phase-space files for the 105 and 220 kVp beams (Gulmay D3225 x-ray machine), and the 4 and 6?MeV electron beams (Varian 21 EX linear accelerator) with a field size of 5 cm diameter were generated using the BEAMnrc code, and verified using measurements. Inhomogeneous phantoms containing uniform water, bone and air layers were irradiated by the kVp photon and MeV electron beams. Relative depth, bone and mucosal doses were calculated for the uniform water and bone layers which were varied in thickness in the ranges of 0.5-2 cm and 0.2-1 cm. A uniform water layer of bolus with thickness equal to the depth of maximum dose (dmax) of the electron beams (0.7 cm for 4 MeV and 1.5 cm for 6 MeV) was added on top of the phantom to ensure that the maximum dose was at the phantom surface. From our Monte Carlo results, the 4 and 6 MeV electron beams were found to produce insignificant bone and mucosal dose (<1%), when the uniform water layer at the phantom surface was thicker than 1.5 cm. When considering the 0.5 cm thin uniform water and bone layers, the 4 MeV electron beam deposited less bone and mucosal dose than the 6 MeV beam. Moreover, it was found that the 105 kVp beam produced more than twice the dose to bone than the 220 kVp beam when the uniform water thickness at the phantom surface was small (0.5 cm). However, the difference in bone dose enhancement between the 105 and 220 kVp beams became smaller when the thicknesses of the uniform water and bone layers in the phantom increased. Dose in the second bone layer interfacing with air was found to be higher for the 220 kVp beam than that of the 105 kVp beam, when the bone thickness was 1 cm. In this study, dose deviations of bone and mucosal layers of 18% and 17% were found between our results from Monte Carlo simulation and the pencil-beam algorithm, which overestimated the doses. Relative depth, bone and mucosal doses were studied by varying the beam nature, beam energy and thicknesses of the bone and uniform water using an inhomogeneous phantom to model the oral or nasal cavity. While the dose distribution in the pharynx region is unavailable due to the lack of a commercial treatment planning system commissioned for kVp beam planning in skin radiation therapy, our study provided an essential insight into the radiation staff to justify and estimate bone and mucosal dose.

Chow, James C. L.; Jiang, Runqing

2012-06-01

317

Bone and mucosal dosimetry in skin radiation therapy: a Monte Carlo study using kilovoltage photon and megavoltage electron beams.  

PubMed

This study examines variations of bone and mucosal doses with variable soft tissue and bone thicknesses, mimicking the oral or nasal cavity in skin radiation therapy. Monte Carlo simulations (EGSnrc-based codes) using the clinical kilovoltage (kVp) photon and megavoltage (MeV) electron beams, and the pencil-beam algorithm (Pinnacle(3) treatment planning system) using the MeV electron beams were performed in dose calculations. Phase-space files for the 105 and 220 kVp beams (Gulmay D3225 x-ray machine), and the 4 and 6?MeV electron beams (Varian 21 EX linear accelerator) with a field size of 5 cm diameter were generated using the BEAMnrc code, and verified using measurements. Inhomogeneous phantoms containing uniform water, bone and air layers were irradiated by the kVp photon and MeV electron beams. Relative depth, bone and mucosal doses were calculated for the uniform water and bone layers which were varied in thickness in the ranges of 0.5-2 cm and 0.2-1 cm. A uniform water layer of bolus with thickness equal to the depth of maximum dose (d(max)) of the electron beams (0.7 cm for 4 MeV and 1.5 cm for 6 MeV) was added on top of the phantom to ensure that the maximum dose was at the phantom surface. From our Monte Carlo results, the 4 and 6 MeV electron beams were found to produce insignificant bone and mucosal dose (<1%), when the uniform water layer at the phantom surface was thicker than 1.5 cm. When considering the 0.5 cm thin uniform water and bone layers, the 4 MeV electron beam deposited less bone and mucosal dose than the 6 MeV beam. Moreover, it was found that the 105 kVp beam produced more than twice the dose to bone than the 220 kVp beam when the uniform water thickness at the phantom surface was small (0.5 cm). However, the difference in bone dose enhancement between the 105 and 220 kVp beams became smaller when the thicknesses of the uniform water and bone layers in the phantom increased. Dose in the second bone layer interfacing with air was found to be higher for the 220 kVp beam than that of the 105 kVp beam, when the bone thickness was 1 cm. In this study, dose deviations of bone and mucosal layers of 18% and 17% were found between our results from Monte Carlo simulation and the pencil-beam algorithm, which overestimated the doses. Relative depth, bone and mucosal doses were studied by varying the beam nature, beam energy and thicknesses of the bone and uniform water using an inhomogeneous phantom to model the oral or nasal cavity. While the dose distribution in the pharynx region is unavailable due to the lack of a commercial treatment planning system commissioned for kVp beam planning in skin radiation therapy, our study provided an essential insight into the radiation staff to justify and estimate bone and mucosal dose. PMID:22642985

Chow, James C L; Jiang, Runqing

2012-05-30

318

Monte Carlo Study of Fetal Dosimetry Parameters for 6 MV Photon Beam  

PubMed Central

Because of the adverse effects of ionizing radiation on fetuses, prior to radiotherapy of pregnant patients, fetal dose should be estimated. Fetal dose has been studied by several authors in different depths in phantoms with various abdomen thicknesses (ATs). In this study, the effect of maternal AT and depth in fetal dosimetry was investigated, using peripheral dose (PD) distribution evaluations. A BEAMnrc model of Oncor linac using out of beam components was used for dose calculations in out of field border. A 6 MV photon beam was used to irradiate a chest phantom. Measurements were done using EBT2 radiochromic film in a RW3 phantom as abdomen. The followings were measured for different ATs: Depth PD profiles at two distances from the field's edge, and in-plane PD profiles at two depths. The results of this study show that PD is depth dependent near the field's edge. The increase in AT does not change PD depth of maximum and its distribution as a function of distance from the field's edge. It is concluded that estimating the maximum fetal dose, using a flat phantom, i.e., without taking into account the AT, is possible. Furthermore, an in-plane profile measured at any depth can represent the dose variation as a function of distance. However, in order to estimate the maximum PD the depth of Dmax in out of field should be used for in-plane profile measurement.

Atarod, Maryam; Shokrani, Parvaneh

2013-01-01

319

Tissue classifications in Monte Carlo simulations of patient dose for photon beam tumor treatments  

NASA Astrophysics Data System (ADS)

The purpose of this work was to study the calculated dose uncertainties induced by the material classification that determined the interaction cross-sections and the water-to-material stopping-power ratios. Calculations were made for a head- and neck-cancer patient treated with five intensity-modulated radiotherapy fields using 6 MV photon beams. The patient's CT images were reconstructed into two voxelized patient phantoms based on different CT-to-material classification schemes. Comparisons of the depth-dose curve of the anterior-to-posterior field and the dose-volume-histogram of the treatment plan were used to evaluate the dose uncertainties from such schemes. The results indicated that any misassignment of tissue materials could lead to a substantial dose difference, which would affect the treatment outcome. To assure an appropriate material assignment, it is desirable to have different conversion tables for various parts of the body. The assignment of stopping-power ratio should be based on the chemical composition and the density of the material.

Lin, Mu-Han; Chao, Tsi-Chian; Lee, Chung-Chi; Tung-Chieh Chang, Joseph; Tung, Chuan-Jong

2010-07-01

320

Energy transport analysis in ultrashort pulse laser ablation through combined molecular dynamics and Monte Carlo simulation  

SciTech Connect

Mechanisms of energy transport during ultrashort laser pulses (USLPs) ablation are investigated in this paper. Nonequilibrium electron-transport, material ionization, as well as density change effects, are studied using atomistic models--the molecular dynamics (MD) and Monte Carlo (MC) methods, in addition to the previously studied laser absorption, heat conduction, and stress wave propagation. The target material is treated as consisting of two subsystems: valence-electron system and lattice system. MD method is applied to analyze the motion of atoms while MC method is applied for simulating electron dynamics and multiscattering events between particles. Early-time laser-energy absorption and redistribution as well as later-time material ablation and expansion processes are analyzed. This model is validated in terms of ablation depth, lattice/electron temperature distribution as well as evolution, and plume front velocity, through comparisons with experimental or theoretical results in literature. It is generally believed that the hydrodynamic motion of the ablated material is negligible for USLP but this study shows it is true only for its effect on laser-energy deposition. This study shows that the consideration of hydrodynamic expansion and fast density change in both electron and lattice systems is important for obtaining a reliable energy transport mechanism in the locally heated zone.

Hu Wenqian; Shin, Yung C.; King, Galen [School of Mechanical Engineering, Purdue University, West Lafayette, Indiana 47907 (United States)

2010-09-01

321

Monte Carlo transient phonon transport in silicon and germanium at nanoscales  

NASA Astrophysics Data System (ADS)

Heat transport at nanoscales in semiconductors is investigated with a statistical method. The Boltzmann transport equation (BTE), which characterizes phonon motion and interaction within the crystal lattice, has been simulated with a Monte Carlo technique. Our model takes into account media frequency properties through the dispersion curves for longitudinal and transverse acoustic branches. The BTE collisional term involving phonon scattering processes is simulated with the relaxation times approximation theory. A new distribution function accounting for the collisional processes has been developed in order to respect energy conservation during phonons scattering events. This nondeterministic approach provides satisfactory results in what concerns phonon transport in both ballistic and diffusion regimes. The simulation code has been tested with silicon and germanium thin films; temperature propagation within samples is presented and compared to analytical solutions (in the diffusion regime). The two-material bulk thermal conductivity is retrieved for temperature ranging between 100 K and 500 K. Heat transfer within a plane wall with a large thermal gradient (250 K to 500 K) is proposed in order to expose the model ability to simulate conductivity thermal dependence on heat exchange at nanoscales. Finally, size effects and validity of heat conduction law are investigated for several slab thicknesses.

Lacroix, David; Joulain, Karl; Lemonnier, Denis

2005-08-01

322

Space Charge Limited Transient Transport Simulation by the Monte Carlo Technique  

NASA Astrophysics Data System (ADS)

Recently (Murayama & Mitsunori, 1992), a mechanism of transient dispersive transport has been proposed for the explanation of the temperature dependence of the dispersion parameters of a-Si:H. By contructing several percolation clusters in a cubic lattice, each one with a different factor of filled sites, they calculated the transient current of particles through the clusters. The occupied sites factor for the percolation clusters and the density of states of the system were related by means of the fraction of space allowed to particles with energy E, i.e. the number of occupied states at energy E divided by the total number of states. The percolaction path was related to the minimum energy barrier path. They showed that the simulated results fit quite well the experimental data of a-Si:H transient currents. Modifying the above model it is possible to simulate the effect of space charge in the transient transport. If we consider that the non-equilibrium charge carriers ganerated near to one electrode and they are space limited in the same region, the released charge carriers will have a time distribution and the transient current will be directly affected. In the present work a set of Monte Carlo experiments, for different applied electric fields and trapping probabilities, was performed in order to compare with the experimental results of the transient transport measured with the time of flight (TOF) technique.

Picos-Vega, Abraham; Ramirez-Bon, Rafael; Espinoza-Beltran, Francisco; Zelaya-Angel, Orlando

1998-03-01

323

Towards scalable parellelism in Monte Carlo particle transport codes using remote memory access  

SciTech Connect

One forthcoming challenge in the area of high-performance computing is having the ability to run large-scale problems while coping with less memory per compute node. In this work, they investigate a novel data decomposition method that would allow Monte Carlo transport calculations to be performed on systems with limited memory per compute node. In this method, each compute node remotely retrieves a small set of geometry and cross-section data as needed and remotely accumulates local tallies when crossing the boundary of the local spatial domain. initial results demonstrate that while the method does allow large problems to be run in a memory-limited environment, achieving scalability may be difficult due to inefficiencies in the current implementation of RMA operations.

Romano, Paul K [Los Alamos National Laboratory; Brown, Forrest B [Los Alamos National Laboratory; Forget, Benoit [MIT

2010-01-01

324

Monte Carlo simulation study of spin transport in multilayer graphene with Bernal stacking  

NASA Astrophysics Data System (ADS)

In this work, we model spin transport in multilayer graphene (MLG) stacks with Bernal (ABA) stacking using semi-classical Monte Carlo simulations and the results are compared to bi-layer graphene. Both the D'yakonov-Perel and Elliot-Yafet mechanisms for spin relaxation are considered for modeling purposes. Varying the number of layers alters the band structure of the MLG. We study the effect of the band structures in determining the spin relaxation lengths of the different multilayer graphene stacks. We observe that as the number of layers increases the spin relaxation length increases up to a maximum value for 16 layers and then stays the same irrespective of the number of layers. We explain this trend in terms of the changing band structures which affects the scattering rates of the spin carriers.

Misra, Soumya; Ghosh, Bahniman; Nandal, Vikas; Dubey, Lalit

2012-07-01

325

Domain Decomposition of a Constructive Solid Geometry Monte Carlo Transport Code  

SciTech Connect

Domain decomposition has been implemented in a Constructive Solid Geometry (CSG) Monte Carlo neutron transport code. Previous methods to parallelize a CSG code relied entirely on particle parallelism; but in our approach we distribute the geometry as well as the particles across processors. This enables calculations whose geometric description is larger than what could fit in memory of a single processor, thus it must be distributed across processors. In addition to enabling very large calculations, we show that domain decomposition can speed up calculations compared to particle parallelism alone. We also show results of a calculation of the proposed Laser Inertial-Confinement Fusion-Fission Energy (LIFE) facility, which has 5.6 million CSG parts.

O'Brien, M J; Joy, K I; Procassini, R J; Greenman, G M

2008-12-07

326

Practical aspects of Monte Carlo simulation of charged particle transport: mixed algorithms and variance reduction techniques.  

PubMed

This paper is concerned with the practical implementation of Monte Carlo simulation methods for charged particle transport. The emphasis is on light particles (electrons and positrons) because of the larger scattering and energy straggling effects. Differential cross sections (DCS) for the various interaction mechanisms are described. As the average number of interactions along the particle track increases with the initial energy, detailed simulation becomes unfeasible at high energies. We can then rely on mixed simulation algorithms: hard events (i.e. individual interactions with angular deflection or energy loss larger than given cutoff values) are sampled from the DCS whereas soft events are simulated by means of a multiple scattering approach. Too frequently, the statistical uncertainty of analogue simulation (i.e. strict simulation of the physical interaction process) is found to be so large that results are meaningless. This problem can be partially solved by applying simple variance reduction techniques. PMID:10384951

Salvat, F; Fernández-Varea, J M; Sempau, J; Mazurier, J

1999-05-01

327

The effect of collisional broadening on Monte Carlo simulations of high-field transport in semiconductor devices  

Microsoft Academic Search

Some important consequences of the uncertainty principle on Monte Carlo simulations of very high field transport are discussed. It is shown that recent values of the phonon scattering rates reported for GaAs by Shichijo and Hess lead to an unrealistically high collisional broadening (0.3-0.6eV) of the electronic states, thus rendering questionable any attempt to relate transport properties to the band

F. Capasso; T. P. Pearsall; K. K. Thornber

1981-01-01

328

Monte Carlo simulation of high-field electron transport in alternating-current thin-film electroluminescent devices  

Microsoft Academic Search

An ensemble Monte Carlo simulation of electron transport in bulk ZnS at high electric fields is presented. Scattering mechanisms associated with polar optical phonons, acoustic phonons (through deformation potential coupling), intervalley scattering, and impurities (neutral and ionized) are included in a nonparabolic multi-valley model. The simulated results show that energetic electrons are available for impact excitation at fields exceeding 1

K. Bhattacharyya; S. M. Goodnick; J. F. Wager

1993-01-01

329

Integrating Circuit Level Simulation and Monte-Carlo Radiation Transport Code for Single Event Upset Analysis in SEU Hardened Circuitry  

Microsoft Academic Search

Monte-Carlo radiation transport code is coupled with SPICE circuit level simulation to identify regions of single event upset vulnerability in an SEU hardened flip-flop, as well as predict single event upset cross sections and on-orbit soft error rates under static and dynamic operating conditions.

Kevin M. Warren; Andrew L. Sternberg; Robert A. Weller; Mark P. Baze; Lloyd W. Massengill; Robert A. Reed; Marcus H. Mendenhall; Ronald D. Schrimpf

2008-01-01

330

Fast CT\\/SPECT derived 3D Monte Carlo dose computations for 131I internal emitter therapy  

Microsoft Academic Search

The DPM (Dose Planning Method) Monte Carlo electron and photon transport program, designed for fast computation of radiation dose in external electron beam radiotherapy, has been adapted to the determination of dose in patient-specific I-131 internal emitter therapy. Because both its photon and electron transport mechanics algorithms have been optimized for computation in 3D voxelized geometries (in particular, those from

S. J. Wilderman; R. B. Gunnett; K. J. Kearfott; Y. K. Dewaraja

2004-01-01

331

Method for Fast CT\\/SPECT-Based 3D Monte Carlo Absorbed Dose Computations in Internal Emitter Therapy  

Microsoft Academic Search

The DPM (Dose Planning Method) Monte Carlo electron and photon transport program, designed for fast computation of radiation absorbed dose in external beam radiotherapy, has been adapted to the calculation of absorbed dose in patient-specific internal emitter therapy. Because both its photon and electron transport mechanics algorithms have been optimized for fast computation in 3D voxelized geometries (in particular, those

S. J. Wilderman; Y. K. Dewaraja

2007-01-01

332

Experimental validation of GADRAS's coupled neutron-photon inverse radiation transport solver.  

SciTech Connect

Sandia National Laboratories has developed an inverse radiation transport solver that applies nonlinear regression to coupled neutron-photon deterministic transport models. The inverse solver uses nonlinear regression to fit a radiation transport model to gamma spectrometry and neutron multiplicity counting measurements. The subject of this paper is the experimental validation of that solver. This paper describes a series of experiments conducted with a 4.5 kg sphere of {alpha}-phase, weapons-grade plutonium. The source was measured bare and reflected by high-density polyethylene (HDPE) spherical shells with total thicknesses between 1.27 and 15.24 cm. Neutron and photon emissions from the source were measured using three instruments: a gross neutron counter, a portable neutron multiplicity counter, and a high-resolution gamma spectrometer. These measurements were used as input to the inverse radiation transport solver to evaluate the solver's ability to correctly infer the configuration of the source from its measured radiation signatures.

Mattingly, John K.; Mitchell, Dean James; Harding, Lee T.

2010-08-01

333

Atomistic Monte Carlo simulations of heat transport in Si and SiGe nanostructured materials  

NASA Astrophysics Data System (ADS)

Efficient thermoelectric energy conversion depends on the design of materials with low thermal conductivity and/or high electrical conductivity and Seebeck coefficient [1]. Semiconducting nanostructured materials are promising candidates to exhibit high thermoelectric efficiency, as they may have much lower thermal conductivity than their bulk counterparts [1]. Atomistic simulations capable of handling large samples and describing accurately phonon dispersions and lifetimes at the nanoscale could greatly advance our understanding of heat transport in such materials [2]. We will present an atomistic Monte Carlo method to solve the Boltzmann transport equation [3] that enables the computation of the thermal conductivity of large systems with both empirical and first principles Hamiltonians (e.g. up to several thousand atoms in the case of Tersoff potentials). We will demonstrate how this new approach allows one to rationalize trends in the thermal conductivity of a range of Si and SiGe based nanostructures, as a function of size, dimensionality and morphology [3]. [1] See e.g. A. J. Minnich et al. Energy Environ. Sci. 2, 466 (2009). [2] Y. He, I. Savic, D. Donadio, and G. Galli, accepted in Phys. Chem. Chem. Phys. [3] I. Savic, D. Donadio, F. Gygi, and G. Galli, submitted.

Savic, Ivana; Donadio, Davide; Murray, Eamonn; Gygi, Francois; Galli, Giulia

2013-03-01

334

One-dimensional hopping transport in disordered organic solids. II. Monte Carlo simulations  

NASA Astrophysics Data System (ADS)

Drift mobility of charge carriers in strongly anisotropic disordered organic media is studied by Monte Carlo computer simulations. Results for the nearest-neighbor hopping are in excellent agreement with those of the analytic theory (Cordes et al., preceding paper). It is widely believed that the low-field drift mobility in disordered organic solids has the form ?~exp[-(T0/T)2] with characteristic temperature T0 depending solely on the scale of the energy distribution of localized states responsible for transport. Taking into account electron transitions to more distant sites than the nearest neighbors, we show that this dependence is not universal and parameter T0 depends also on the concentration of localized states and on the decay length of the electron wave function in localized states. The results of computer simulation evidence that correlations in the distribution of localized states influence essentially not only the field dependence as known from the literature, but also the temperature dependence of the drift mobility. In particular, strong space-energy correlations diminish the role of long-range hopping transitions in the charge carrier transport.

Kohary, K.; Cordes, H.; Baranovskii, S. D.; Thomas, P.; Yamasaki, S.; Hensel, F.; Wendorff, J.-H.

2001-03-01

335

RAFFLE V general purpose Monte Carlo code for neutron and gamma transport. Revision 1  

SciTech Connect

The RAFFLE V general-purpose Monte Carlo code is an extensively-modified version of the original RAFFLE code developed at INEL. This document describes the RAFFLE V code, emphasizing the modifications made since prior documentation. The major modifications implemented into the RAFFLE V code are: (1) implementation of the processed ENDF-B version V neutron data and an expansion of the energy range to include above-10-MeV reactions important in fusion devices; (2) incorporation of the Combinatorial Geometry subroutines developed by the Mathematical Applications Group Incorporated (MAGI) of White Plains, New York; (3) use of the Probability Table method in the unresolved resonance energy region so that neutron transport and flux shielding can be better represented; (4) the capability to perform gamma-ray transport calculations; (5) the inclusion of flux-at-a-point detectors; (6) the option to obtain microscopic reaction rates and generalized response functions by region or point; and (7) the capability to obtain time-dependent reaction rates and fluxes for fixed-source problems with no fission.

Wheeler, F.J.; Easson, S.A.; Grimesey, R.A.; Wessol, D.W.

1983-10-01

336

A simplified spherical harmonic method for coupled electron-photon transport calculations  

Microsoft Academic Search

In this thesis we have developed a simplified spherical harmonic method (SP{sub N} method) and associated efficient solution techniques for 2-D multigroup electron-photon transport calculations. The SP{sub N} method has never before been applied to charged-particle transport. We have performed a first time Fourier analysis of the source iteration scheme and the P⁠diffusion synthetic acceleration (DSA) scheme applied to

Josef

1996-01-01

337

A Comparison of Monte Carlo Particle Transport Algorithms for an Interior Source Binary Stochastic Medium Benchmark Suite  

SciTech Connect

Particle transport through binary stochastic mixtures has received considerable research attention in the last two decades. Zimmerman and Adams proposed a Monte Carlo algorithm (Algorithm A) that solves the Levermore-Pomraning equations and another Monte Carlo algorithm (Algorithm B) that should be more accurate as a result of improved local material realization modeling. Zimmerman and Adams numerically confirmed these aspects of the Monte Carlo algorithms by comparing the reflection and transmission values computed using these algorithms to a standard suite of planar geometry binary stochastic mixture benchmark transport solutions. The benchmark transport problems are driven by an isotropic angular flux incident on one boundary of a binary Markovian statistical planar geometry medium. In a recent paper, we extended the benchmark comparisons of these Monte Carlo algorithms to include the scalar flux distributions produced. This comparison is important, because as demonstrated, an approximate model that gives accurate reflection and transmission probabilities can produce unphysical scalar flux distributions. Brantley and Palmer recently investigated the accuracy of the Levermore-Pomraning model using a new interior source binary stochastic medium benchmark problem suite. In this paper, we further investigate the accuracy of the Monte Carlo algorithms proposed by Zimmerman and Adams by comparing to the benchmark results from the interior source binary stochastic medium benchmark suite, including scalar flux distributions. Because the interior source scalar flux distributions are of an inherently different character than the distributions obtained for the incident angular flux benchmark problems, the present benchmark comparison extends the domain of problems for which the accuracy of these Monte Carlo algorithms has been investigated.

Brantley, P S

2009-06-30

338

Suppression of population transport and control of exciton distributions by entangled photons  

PubMed Central

Entangled photons provide an important tool for secure quantum communication, computing and lithography. Low intensity requirements for multi-photon processes make them idealy suited for minimizing damage in imaging applications. Here we show how their unique temporal and spectral features may be used in nonlinear spectroscopy to reveal properties of multiexcitons in chromophore aggregates. Simulations demostrate that they provide unique control tools for two-exciton states in the bacterial reaction centre of Blastochloris viridis. Population transport in the intermediate single-exciton manifold may be suppressed by the absorption of photon pairs with short entanglement time, thus allowing the manipulation of the distribution of two-exciton states. The quantum nature of the light is essential for achieving this degree of control, which cannot be reproduced by stochastic or chirped light. Classical light is fundamentally limited by the frequency-time uncertainty, whereas entangled photons have independent temporal and spectral characteristics not subjected to this uncertainty.

Schlawin, Frank; Dorfman, Konstantin E.; Fingerhut, Benjamin P.; Mukamel, Shaul

2013-01-01

339

Monte Carlo simulation of gas Cerenkov detectors  

SciTech Connect

Theoretical study of selected gamma-ray and electron diagnostic necessitates coupling Cerenkov radiation to electron/photon cascades. A Cerenkov production model and its incorporation into a general geometry Monte Carlo coupled electron/photon transport code is discussed. A special optical photon ray-trace is implemented using bulk optical properties assigned to each Monte Carlo zone. Good agreement exists between experimental and calculated Cerenkov data in the case of a carbon-dioxide gas Cerenkov detector experiment. Cerenkov production and threshold data are presented for a typical carbon-dioxide gas detector that converts a 16.7 MeV photon source to Cerenkov light, which is collected by optics and detected by a photomultiplier.

Mack, J.M.; Jain, M.; Jordan, T.M.

1984-01-01

340

Recommendations for a Production Discrete-Ordinates Coupled Electron-Photon Transport Capability.  

National Technical Information Service (NTIS)

The purpose of this study was to determine if a production capability for discrete-ordinates coupled electron-photon transport calculations should be developed and, if so, to recommend how it should be done. It is concluded that such a capability should b...

J. E. Morel W. E. Nelson

1984-01-01

341

Event-by-event Monte Carlo simulation of radiation transport in vapor and liquid water  

NASA Astrophysics Data System (ADS)

A Monte-Carlo Simulation is presented for Radiation Transport in water. This process is of utmost importance, having applications in oncology and therapy of cancer, in protecting people and the environment, waste management, radiation chemistry and on some solid-state detectors. It's also a phenomenon of interest in microelectronics on satellites in orbit that are subject to the solar radiation and in space-craft design for deep-space missions receiving background radiation. The interaction of charged particles with the medium is primarily due to their electromagnetic field. Three types of interaction events are considered: Elastic scattering, impact excitation and impact ionization. Secondary particles (electrons) can be generated by ionization. At each stage, along with the primary particle we explicitly follow all secondary electrons (and subsequent generations). Theoretical, semi-empirical and experimental formulae with suitable corrections have been used in each case to model the cross sections governing the quantum mechanical process of interactions, thus determining stochastically the energy and direction of outgoing particles following an event. Monte-Carlo sampling techniques have been applied to accurate probability distribution functions describing the primary particle track and all secondary particle-medium interaction. A simple account of the simulation code and a critical exposition of its underlying assumptions (often missing in the relevant literature) are also presented with reference to the model cross sections. Model predictions are in good agreement with existing computational data and experimental results. By relying heavily on a theoretical formulation, instead of merely fitting data, it is hoped that the model will be of value in a wider range of applications. Possible future directions that are the object of further research are pointed out.

Papamichael, Georgios Ioannis

342

Monte Carlo calculation of ion, electron, and photon spectra of xenon atoms in x-ray free-electron laser pulses  

NASA Astrophysics Data System (ADS)

When atoms and molecules are irradiated by an x-ray free-electron laser (XFEL), they are highly ionized via a sequence of one-photon ionization and relaxation processes. To describe the ionization dynamics during XFEL pulses, a rate equation model has been employed. Even though this model is straightforward for the case of light atoms, it generates a huge number of coupled rate equations for heavy atoms like xenon, which are not trivial to solve directly. Here, we employ the Monte Carlo method to address this problem and we investigate ionization dynamics of xenon atoms induced by XFEL pulses at a photon energy of 4500 eV. Charge-state distributions, photoelectron and Auger electron spectra, and fluorescence spectra are presented for x-ray fluences of up to 1013 photons/?m2. With the photon energy of 4500 eV, xenon atoms can be ionized up to +44 through multiphoton absorption characterized by sequential one-photon single-electron interactions.

Son, Sang-Kil; Santra, Robin

2012-06-01

343

Effect of resonance structure on 14-MeV Monte Carlo neutron transport in nitrogen and air  

SciTech Connect

The results of Monte Carlo calculations can be sensitive to methods used to treat cross sections. This sensitivity can be emphasized by studying one isotope of an element or material that has a resonance region. Very few naturally occurring materials exist in a mono-isotopic form, but when such a material is an important part of a problem, care should be exercised in the selection of a code to be used for the calculations. It is recommended that the ALICE code, that uses a multiband treatment for cross sections, be used at LLNL for neutronic and neutron-induced photonic problems.

Plechaty, E.F.

1982-10-20

344

Deriving attenuation coefficients from 3D CT data for SPECT Monte Carlo simulations  

Microsoft Academic Search

Quantitation of nuclear medicine data is a major goal in medical imaging. It implies that photon attenuation, scatter and depth dependent spatial resolution be corrected for. Realistic, anthropomorphic numerical phantoms are needed to understand how these phenomena degrade nuclear medicine images, and to validate correction methods. We developed a Monte Carlo simulator which simulates photon transport in an anthropomorphic phantom.

Veronique Baccarne; A. Turzo; Y. Bizais; M. Farine

1997-01-01

345

Robust volume calculations for Constructive Solid Geometry (CSG) components in Monte Carlo transport calculations  

SciTech Connect

In this paper we consider a new generalized algorithm for the efficient calculation of component object volumes given their equivalent constructive solid geometry (CSG) definition. The new method relies on domain decomposition to recursively subdivide the original component into smaller pieces with volumes that can be computed analytically or stochastically, if needed. Unlike simpler brute-force approaches, the proposed decomposition scheme is guaranteed to be robust and accurate to within a user-defined tolerance. The new algorithm is also fully general and can handle any valid CSG component definition, without the need for additional input from the user. The new technique has been specifically optimized to calculate volumes of component definitions commonly found in models used for Monte Carlo particle transport simulations for criticality safety and reactor analysis applications. However, the algorithm can be easily extended to any application which uses CSG representations for component objects. The paper provides a complete description of the novel volume calculation algorithm, along with a discussion of the conjectured error bounds on volumes calculated within the method. In addition, numerical results comparing the new algorithm with a standard stochastic volume calculation algorithm are presented for a series of problems spanning a range of representative component sizes and complexities. (authors)

Millman, D. L. [Dept. of Computer Science, Univ. of North Carolina at Chapel Hill (United States); Griesheimer, D. P.; Nease, B. R. [Bechtel Marine Propulsion Corporation, Bertis Atomic Power Laboratory (United States); Snoeyink, J. [Dept. of Computer Science, Univ. of North Carolina at Chapel Hill (United States)

2012-07-01

346

Core-scale solute transport model selection using Monte Carlo analysis  

NASA Astrophysics Data System (ADS)

Model applicability to core-scale solute transport is evaluated using breakthrough data from column experiments conducted with conservative tracers tritium (3H) and sodium-22 (22Na ), and the retarding solute uranium-232 (232U). The three models considered are single-porosity, double-porosity with single-rate mobile-immobile mass-exchange, and the multirate model, which is a deterministic model that admits the statistics of a random mobile-immobile mass-exchange rate coefficient. The experiments were conducted on intact Culebra Dolomite core samples. Previously, data were analyzed using single-porosity and double-porosity models although the Culebra Dolomite is known to possess multiple types and scales of porosity, and to exhibit multirate mobile-immobile-domain mass transfer characteristics at field scale. The data are reanalyzed here and null-space Monte Carlo analysis is used to facilitate objective model selection. Prediction (or residual) bias is adopted as a measure of the model structural error. The analysis clearly shows single-porosity and double-porosity models are structurally deficient, yielding late-time residual bias that grows with time. On the other hand, the multirate model yields unbiased predictions consistent with the late-time -5/2 slope diagnostic of multirate mass transfer. The analysis indicates the multirate model is better suited to describing core-scale solute breakthrough in the Culebra Dolomite than the other two models.

Malama, Bwalya; Kuhlman, Kristopher L.; James, Scott C.

2013-06-01

347

Parallel domain decomposition methods in fluid models with Monte Carlo transport  

SciTech Connect

To examine the domain decomposition code coupled Monte Carlo-finite element calculation, it is important to use a domain decomposition that is suitable for the individual models. We have developed a code that simulates a Monte Carlo calculation ( ) on a massively parallel processor. This code is used to examine the load balancing behavior of three domain decomposition ( ) for a Monte Carlo calculation. Results are presented.

Alme, H.J.; Rodrigues, G.H. [California Univ., Davis, CA (United States). Dept. of Applied Science; Zimmerman, G.B. [Lawrence Livermore National Lab., CA (United States)

1996-12-01

348

A novel approach for including band-structure effects in a Monte Carlo simulation of electron transport in silicon  

Microsoft Academic Search

We present a novel approach for including the effects of realistic silicon band structure in the simulation of electron transport with a Monte Carlo method. This will be achieved by an electron effective-mass and energy–over–wave-vector relation, which are derived directly from the density of states. Consistent with this model, the scattering rates as well as the equations of motion are

Th. Vogelsang; W. Hänsch

1991-01-01

349

Ultrashort n-MOSFETs with strained Si: device performance and the effect of ballistic transport using Monte Carlo simulation  

Microsoft Academic Search

Semi-classical Monte Carlo simulation is used to study the electrical performance of 18-nm-long n-MOSFETs including a strained Si channel. In particular, the impact of extrinsic series resistance on the drive current Ion is quantified: we show that the large on-current improvement induced by the strain is preserved, even by including an external parasitic resistance. The importance of ballistic transport is

Valérie Aubry-Fortuna; Arnaud Bournel; Philippe Dollfus; Sylvie Galdin-Retailleau

2006-01-01

350

A Kinetic Theory for Nonanalog Monte Carlo Particle Transport Algorithms: Exponential Transform with Angular Biasing in Planar-Geometry Anisotropically Scattering Media  

Microsoft Academic Search

We show that Monte Carlo simulations of neutral particle transport in planar-geometry anisotropically scattering media, using the exponential transform with angular biasing as a variance reduction device, are governed by a new “Boltzmann Monte Carlo” (BMC) equation, which includes particle weight as an extra independent variable. The weight moments of the solution of the BMC equation determine the moments of

Taro Ueki; Edward W Larsen

1998-01-01

351

Monte Carlo next-event estimates from thermal collisions  

SciTech Connect

A new approximate method has been developed by Richard E. Prael to allow S({alpha},{beta}) thermal collision contributions to next-event estimators in Monte Carlo calculations. The new technique is generally applicable to next-event estimator contributions from any discrete probability distribution. The method has been incorporated into Version 4 of the production Monte Carlo neutron and photon radiation transport code MCNP. 9 refs.

Hendricks, J.S.; Prael, R.E.

1990-01-01

352

Energy spectra, angular spread, fluence profiles and dose distributions of 6 and 18 MV photon beams: results of Monte Carlo simulations for a Varian 2100EX accelerator  

NASA Astrophysics Data System (ADS)

The purpose of this study is to provide detailed characteristics of incident photon beams for different field sizes and beam energies. This information is critical to the future development of accurate treatment planning systems. It also enhances our knowledge of radiotherapy photon beams. The EGS4 Monte Carlo code, BEAM, has been used to simulate 6 and 18 MV photon beams from a Varian Clinac-2100EX accelerator. A simulated realistic beam is stored in a phase space data file, which contains details of each particle's complete history including where it has been and where it has interacted. The phase space files are analysed to obtain energy spectra, angular distribution, fluence profile and mean energy profiles at the phantom surface for particles separated according to their charge and history. The accuracy of a simulated beam is validated by the excellent agreement between the Monte Carlo calculated and measured dose distributions. Measured depth-dose curves are obtained from depth-ionization curves by accounting for newly introduced chamber fluence corrections and the stopping-power ratios for realistic beams. The study presents calculated depth-dose components from different particles as well as calculated surface dose and contribution from different particles to surface dose across the field. It is shown that the increase of surface dose with the increase of the field size is mainly due to the increase of incident contaminant charged particles. At 6 MV, the incident charged particles contribute 7% to 21% of maximum dose at the surface when the field size increases from 10 × 10 to 40 × 40 cm2. At 18 MV, their contributions are up to 11% and 29% of maximum dose at the surface for 10 × 10 cm2 and 40 × 40 cm2 fields respectively. However, the fluence of these incident charged particles is less than 1% of incident photon fluence in all cases.

Ding, George X.

2002-04-01

353

Are neutrons responsible for the dose discrepancies between Monte Carlo calculations and measurements in the build-up region for a high-energy photon beam?  

NASA Astrophysics Data System (ADS)

This study presents measured neutron dose using a neutron dosimeter in a water phantom and investigates a hypothesis that neutrons in a high-energy photon beam may be responsible for the reported significant dose discrepancies between Monte Carlo calculations and measurements at the build-up region in large fields. Borated polyethylene slabs were inserted between the accelerator head and the phantom in order to remove neutrons generated in the accelerator head. The thickness of the slab ranged from 2.5 cm to 10 cm. A lead slab of 3 mm thickness was also used in the study. The superheated drop neutron dosimeter was used to measure the depth-dose curve of neutrons in a high-energy photon beam and to verify the effectiveness of the slab to remove these neutrons. Total dose measurements were performed in water using a WELLHOFER WP700 beam scanner with an IC-10 ionization chamber. The Monte Carlo code BEAM was used to simulate an 18 MV photon beam from a Varian Clinac-2100EX accelerator. Both EGS4/DOSXYZ and EGSnrc/DOSRZnrc were used in the dose calculations. Measured neutron dose equivalents as a function of depth per unit total dose in water were presented for 10 × 10 and 40 × 40 cm2 fields. The measured results have shown that a 5-10 cm thick borated polyethylene slab can reduce the neutron dose by a factor of 2 when inserted between the accelerator head and the detector. In all cases the measured neutron dose equivalent was less than 0.5% of the photon dose. In order to study if the ion chamber was highly sensitive to the neutron dose, we have investigated the disagreement between the Monte Carlo calculated and measured central-axis depth-dose curves in the build-up region when different shielding materials were used. The result indicated that the IC-10 chamber was not highly sensitive to the neutron dose. Therefore, neutrons present in a high-energy photon beam were unlikely to be responsible for the reported discrepancies in the build-up region for large fields.

Ding, George X.; Duzenli, Cheryl; Kalach, Nina I.

2002-09-01

354

Monte Carlo Uncertainty Assessment of Water, Sediment and Nutrient Transport Predictions with a Distributed Catchment Model  

Microsoft Academic Search

There are many sources of uncertainty in the input data of distributed catchment models. Monte Carlo simulation can be used to quantify the impact of input data uncertainty on the simulated results. In this study, we present Monte Carlo simulations with the spatially distributed eco-hydrological model SWAT-G applied to the Aar catchment in Germany. We focus on the impact of

L. Breuer; J. A. Huisman; K. Eckhardt; H.-G. Frede

2003-01-01

355

Monte Carlo simulation of the cascade decay processes in gaseous boron initiated by photons with energies scanned through L- and K-ionization thresholds  

NASA Astrophysics Data System (ADS)

The Monte Carlo technique is applied to simulate the processes of the cascade relaxation of gaseous boron at atomic density of 2.5 × 1022 m-3 ionized by photons with the energies of 0.7-25 Ryd passing through a cylindrical interaction zone along its axis. The trajectories of electrons are simulated based on photoionization and electron-impact ionization cross sections calculated in the one-electron configuration-average Pauli-Fock approximation. Numbers of electrons and photons leaving the interaction zone per one initial photoionization, their energy spectra, the energy transferred to the medium and the probabilities of final ion formations are shown to change noticeably as the incident photon energy is scanned through boron atom ionization thresholds. These variations can be explained only if secondary electron-impact-produced processes are considered. The density of secondary events decreases when going from the zone axis to its border, and the profiles of the density along the radial direction are found to be similar for all the initial exciting photon energies.

Brühl, S.; Kochur, A. G.

2012-07-01

356

Organic cation transport in the rat kidney in vivo visualized by time-resolved two-photon microscopy  

Microsoft Academic Search

Secretion of cationic drugs and endogenous metabolites is a major function of the kidney accomplished by tubular organic cation transport systems. A cationic styryl dye (ASP+) was developed as a fluorescent substrate for renal organic cation transporters. The dye was injected intravenously and continuously monitored in externalized rat kidneys by time-resolved two-photon laser scanning microscopy. To investigate changes in transport

M Hörbelt; C Wotzlaw; T A Sutton; B A Molitoris; T Philipp; A Kribben; J Fandrey; F Pietruck

2007-01-01

357

Travel to France to attend seminar on advanced Monte Carlo Computer Program for Radiation Transport. Foreign trip report, April 25--May 2, 1993.  

National Technical Information Service (NTIS)

The traveler attended the Organization for Economic Cooperation and Development (OECD) Nuclear Energy Agency (NEA) Seminar on Advanced Monte Carlo Computer Programs for Radiation Transport at Centre d'Etudes, Saclay, France, to present an invited paper on...

J. O. Johnson

1993-01-01

358

ITS Version 4.0: Electron/photon Monte Carlo transport codes  

SciTech Connect

The current publicly released version of the Integrated TIGER Series (ITS), Version 3.0, has been widely distributed both domestically and internationally, and feedback has been very positive. This feedback as well as our own experience have convinced us to upgrade the system in order to honor specific user requests for new features and to implement other new features that will improve the physical accuracy of the system and permit additional variance reduction. This presentation we will focus on components of the upgrade that (1) improve the physical model, (2) provide new and extended capabilities to the three-dimensional combinatorial-geometry (CG) of the ACCEPT codes, and (3) permit significant variance reduction in an important class of radiation effects applications.

Halbleib, J.A,; Kensek, R.P. [Sandia National Labs., Albuquerque, NM (United States); Seltzer, S.M. [National Inst. of Standards and Technology, Gaithersburg, MD (United States)

1995-07-01

359

Report of the AAPM Task Group No. 105: Issues associated with clinical implementation of Monte Carlo-based photon and electron external beam treatment planning  

SciTech Connect

The Monte Carlo (MC) method has been shown through many research studies to calculate accurate dose distributions for clinical radiotherapy, particularly in heterogeneous patient tissues where the effects of electron transport cannot be accurately handled with conventional, deterministic dose algorithms. Despite its proven accuracy and the potential for improved dose distributions to influence treatment outcomes, the long calculation times previously associated with MC simulation rendered this method impractical for routine clinical treatment planning. However, the development of faster codes optimized for radiotherapy calculations and improvements in computer processor technology have substantially reduced calculation times to, in some instances, within minutes on a single processor. These advances have motivated several major treatment planning system vendors to embark upon the path of MC techniques. Several commercial vendors have already released or are currently in the process of releasing MC algorithms for photon and/or electron beam treatment planning. Consequently, the accessibility and use of MC treatment planning algorithms may well become widespread in the radiotherapy community. With MC simulation, dose is computed stochastically using first principles; this method is therefore quite different from conventional dose algorithms. Issues such as statistical uncertainties, the use of variance reduction techniques, the ability to account for geometric details in the accelerator treatment head simulation, and other features, are all unique components of a MC treatment planning algorithm. Successful implementation by the clinical physicist of such a system will require an understanding of the basic principles of MC techniques. The purpose of this report, while providing education and review on the use of MC simulation in radiotherapy planning, is to set out, for both users and developers, the salient issues associated with clinical implementation and experimental verification of MC dose algorithms. As the MC method is an emerging technology, this report is not meant to be prescriptive. Rather, it is intended as a preliminary report to review the tenets of the MC method and to provide the framework upon which to build a comprehensive program for commissioning and routine quality assurance of MC-based treatment planning systems.

Chetty, Indrin J.; Curran, Bruce; Cygler, Joanna E.; DeMarco, John J.; Ezzell, Gary; Faddegon, Bruce A.; Kawrakow, Iwan; Keall, Paul J.; Liu, Helen; Ma, C.-M. Charlie; Rogers, D. W. O.; Seuntjens, Jan; Sheikh-Bagheri, Daryoush; Siebers, Jeffrey V. [University of Michigan, Ann Arbor, Michigan 48109 and University of Nebraska Medical Center, Omaha, Nebraska 68198-7521 (United States) and University of Michigan, Ann Arbor, Michigan 48109 (United States) and Ottawa Hospital Regional Cancer Center, Ottawa, Ontario K1H 1C4 (Canada); University of California, Los Angeles, Callifornia 90095 (United States) and Mayo Clinic Scottsdale, Scottsdale, Arizona 85259 (United States) and University of California, San Francisco, California 94143 (United States); National Research Council of Canada, Ottawa, Ontario K1A 0R6 (Canada); Stanford University Cancer Center, Stanford, California 94305-5847 (United States); University of Texas MD Anderson Cancer Center, Houston, Texas 77030 (United States); Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111 (United States); Carleton University, Ottawa, Ontario K1S 5B6 (Canada); McGill University, Montreal, Quebec H3G 1A4 (Canada); Regional Cancer Center, Erie, Pennsylvania 16505 (United States); Virginia Commonwealth University, Richmond, Virginia 23298 (United States)

2007-12-15

360

Thermal effects on photon-induced quantum transport in a single quantum dot.  

PubMed

We theoretically investigate laser induced quantum transport in a single quantum dot attached to electrical contacts. Our approach, based on a nonequilibrium Green function technique, allows us to include thermal effects on the photon-induced quantum transport and excitonic dynamics, enabling the study of non-Markovian effects. By solving a set of coupled integrodifferential equations, involving correlation and propagator functions, we obtain the photocurrent and the dot occupation as a function of time. Two distinct sources of decoherence, namely, incoherent tunneling and thermal fluctuations, are observed in the Rabi oscillations. As temperature increases, a thermally activated Pauli blockade results in a suppression of these oscillations. Additionally, the interplay between photon and thermally induced electron populations results in a switch of the current sign as time evolves and its stationary value can be maximized by tuning the laser intensity. PMID:23462318

Assunção, M O; de Oliveira, E J R; Villas-Bôas, J M; Souza, F M

2013-03-05

361

Generalized Fokker-Planck theory for electron and photon transport in biological tissues: application to radiotherapy.  

PubMed

In this paper, we study a deterministic method for particle transport in biological tissues. The method is specifically developed for dose calculations in cancer therapy and for radiological imaging. Generalized Fokker-Planck (GFP) theory [Leakeas and Larsen, Nucl. Sci. Eng. 137 (2001), pp. 236-250] has been developed to improve the Fokker-Planck (FP) equation in cases where scattering is forward-peaked and where there is a sufficient amount of large-angle scattering. We compare grid-based numerical solutions to FP and GFP in realistic medical applications. First, electron dose calculations in heterogeneous parts of the human body are performed. Therefore, accurate electron scattering cross sections are included and their incorporation into our model is extensively described. Second, we solve GFP approximations of the radiative transport equation to investigate reflectance and transmittance of light in biological tissues. All results are compared with either Monte Carlo or discrete-ordinates transport solutions. PMID:20924856

Olbrant, Edgar; Frank, Martin

2010-12-01

362

A parallel Monte Carlo code for planar and SPECT imaging: implementation, verification and applications in 131I SPECT  

Microsoft Academic Search

This paper reports the implementation of the SIMIND Monte Carlo code on an IBM SP2 distributed memory parallel computer. Basic aspects of running Monte Carlo particle transport calculations on parallel architectures are described. Our parallelization is based on equally partitioning photons among the processors and uses the Message Passing Interface (MPI) library for interprocessor communication and the Scalable Parallel Random

Yuni K. Dewaraja; Michael Ljungberg; Amitava Majumdar; Abhijit Bose; Kenneth F. Koral

2002-01-01

363

Theory for transport and temperature effects on two-photon photoemission: Application to Cu  

NASA Astrophysics Data System (ADS)

Using a theory that treats on equal footing transport of excited electrons and electron-phonon scattering, we are able to explain the temperature dependence of the relaxation time in Cu as recently observed by Petek, Nagano, and Ogawa. We show that the unexpected increase of the relaxation time with temperature results from the drastic change of the electron motion due to the efficiency of electron-phonon scattering: the transport is ballistic at low temperature and becomes diffusive at room temperature. Finally, our theory also reproduces the experimental measurements of the two-photon photoemission intensity as a function of the pump-probe delay.

Knorren, R.; Bouzerar, G.; Bennemann, K. H.

2001-03-01

364

Snow shielding factors for cosmogenic nuclide dating inferred from Monte Carlo neutron transport simulations  

NASA Astrophysics Data System (ADS)

Conventional formulations of changes in cosmogenic nuclide production rates with snow cover are based on a mass-shielding approach, which neglects the role of neutron moderation by hydrogen. This approach can produce erroneous correction factors and add to the uncertainty of the calculated cosmogenic exposure ages. We use a Monte Carlo particle transport model to simulate fluxes of secondary cosmic-ray neutrons near the surface of the Earth and vary surface snow depth to show changes in neutron fluxes above rock or soil surface. To correspond with shielding factors for spallation and low-energy neutron capture, neutron fluxes are partitioned into high-energy, epithermal and thermal components. The results suggest that high-energy neutrons are attenuated by snow cover at a significantly higher rate (shorter attenuation length) than indicated by the commonly-used mass-shielding formulation. As thermal and epithermal neutrons derive from the moderation of high-energy neutrons, the presence of a strong moderator such as hydrogen in snow increases the thermal neutron flux both within the snow layer and above it. This means that low-energy production rates are affected by snow cover in a manner inconsistent with the mass-shielding approach and those formulations cannot be used to compute snow correction factors for nuclides produced by thermal neutrons. Additionally, as above-ground low-energy neutron fluxes vary with snow cover as a result of reduced diffusion from the ground, low-energy neutron fluxes are affected by snow even if the snow is at some distance from the site where measurements are made.

Zweck, Christopher; Zreda, Marek; Desilets, Darin

2013-10-01

365

Input-output formalism for few-photon transport in one-dimensional nanophotonic waveguides coupled to a qubit  

SciTech Connect

We extend the input-output formalism of quantum optics to analyze few-photon transport in waveguides with an embedded qubit. We provide explicit analytical derivations for one- and two-photon scattering matrix elements based on operator equations in the Heisenberg picture.

Fan Shanhui; Kocabas, Suekrue Ekin [Ginzton Laboratory, Department of Electrical Engineering, Stanford University, Stanford, California 94305 (United States); Shen, Jung-Tsung [Department of Electrical and Systems Engineering, Washington University, St. Louis, Missouri 63130 (United States)

2010-12-15

366

Program EPICP: Electron photon interaction code, photon test module. Version 94.2  

SciTech Connect

The computer code EPICP performs Monte Carlo photon transport calculations in a simple one zone cylindrical detector. Results include deposition within the detector, transmission, reflection and lateral leakage from the detector, as well as events and energy deposition as a function of the depth into the detector. EPICP is part of the EPIC (Electron Photon Interaction Code) system. EPICP is designed to perform both normal transport calculations and diagnostic calculations involving only photons, with the objective of developing optimum algorithms for later use in EPIC. The EPIC system includes other modules that are designed to develop optimum algorithms for later use in EPIC; this includes electron and positron transport (EPICE), neutron transport (EPICN), charged particle transport (EPICC), geometry (EPICG), source sampling (EPICS). This is a modular system that once optimized can be linked together to consider a wide variety of particles, geometries, sources, etc. By design EPICP only considers photon transport. In particular it does not consider electron transport so that later EPICP and EPICE can be used to quantitatively evaluate the importance of electron transport when starting from photon sources. In this report I will merely mention where we expect the results to significantly differ from those obtained considering only photon transport from that obtained using coupled electron-photon transport.

Cullen, D.E.

1994-09-01

367

Monte Carlo evaluations of the absorbed dose and quality dependence of Al{sub 2}O{sub 3} in radiotherapy photon beams  

SciTech Connect

Purpose: The purpose of this work was to evaluate the absorbed dose to Al{sub 2}O{sub 3} dosimeter at various depths of water phantom in radiotherapy photon beams by Monte Carlo simulation and evaluate the beam quality dependence. Methods: The simulations were done using EGSnrc. The cylindrical Al{sub 2}O{sub 3} dosimeter ({Phi}4 mmx1 mm) was placed at the central axis of the water phantom ({Phi}16 cmx16 cm) at depths between 0.5 and 8 cm. The incident beams included monoenergetic photon beams ranging from 1 to 18 MeV, {sup 60}Co {gamma} beams, Varian 6 MV beams using phase space files based on a full simulation of the linac, and Varian beams between 4 and 24 MV using Mohan's spectra. The absorbed dose to the dosimeter and the water at the corresponding position in the absence of the dosimeter, as well as absorbed dose ratio factor f{sub md}, was calculated. Results: The results show that f{sub md} depends obviously on the photon energy at the shallow depths. However, as the depth increases, the change in f{sub md} becomes small, beyond the buildup region, the maximum discrepancy of f{sub md} to the average value is not more than 1%. Conclusions: These simulation results confirm the use of Al{sub 2}O{sub 3} dosimeter in radiotherapy photon beams and clearly indicate that more attention should be paid when using such a dosimeter in the buildup region of high-energy radiotherapy photon beams.

Chen Shaowen; Wang Xuetao; Chen Lixin; Tang Qiang; Liu Xiaowei [School of Physics Science and Engineering, Sun Yat-Sen University, Guangzhou 510275 (China) and School of Electron Engineering, Dongguan University of Technology, Dongguan 523808 (China); Guangdong Province Hospital of TCM, Guangzhou 510120 (China); Cancer Center of Sun Yat-Sen University, Guangzhou 510060 (China); School of Physics Science and Engineering, Sun Yat-Sen University, Guangzhou 510275 (China)

2009-10-15

368

A probability-conserving cross-section biasing mechanism for variance reduction in Monte Carlo particle transport calculations  

NASA Astrophysics Data System (ADS)

In Monte Carlo particle transport codes, it is often important to adjust reaction cross-sections to reduce the variance of calculations of relatively rare events, in a technique known as non-analog Monte Carlo. We present the theory and sample code for a Geant4 process which allows the cross-section of a G4VDiscreteProcess to be scaled, while adjusting track weights so as to mitigate the effects of altered primary beam depletion induced by the cross-section change. This makes it possible to increase the cross-section of nuclear reactions by factors exceeding 104 (in appropriate cases), without distorting the results of energy deposition calculations or coincidence rates. The procedure is also valid for bias factors less than unity, which is useful in problems that involve the computation of particle penetration deep into a target (e.g. atmospheric showers or shielding studies).

Mendenhall, Marcus H.; Weller, Robert A.

2012-03-01

369

Multilevel Monte Carlo for two phase flow and Buckley-Leverett transport in random heterogeneous porous media  

NASA Astrophysics Data System (ADS)

Monte Carlo (MC) is a well known method for quantifying uncertainty arising for example in subsurface flow problems. Although robust and easy to implement, MC suffers from slow convergence. Extending MC by means of multigrid techniques yields the multilevel Monte Carlo (MLMC) method. MLMC has proven to greatly accelerate MC for several applications including stochastic ordinary differential equations in finance, elliptic stochastic partial differential equations and also hyperbolic problems. In this study, MLMC is combined with a streamline-based solver to assess uncertain two phase flow and Buckley-Leverett transport in random heterogeneous porous media. The performance of MLMC is compared to MC for a two dimensional reservoir with a multi-point Gaussian logarithmic permeability field. The influence of the variance and the correlation length of the logarithmic permeability on the MLMC performance is studied.

Müller, Florian; Jenny, Patrick; Meyer, Daniel W.

2013-10-01

370

Neutron\\/photon\\/electron shielding study for a laser-fusion facility  

Microsoft Academic Search

A Monte Carlo shielding study encompassing neutron, photon, and electron transport was conducted. The application of the Monte Carlo technique and several variance reduction schemes to the study is described. The calculations involve a geometry which is complicated in all three dimensions, a very intense 14 MeV neutron source, skyshine and deep penetrations. The facility design with 1.83 m concrete

W. L. Thompson

1977-01-01

371

Monte Carlo simulation for temporal characteristics of pulse laser propagation in discrete random medium  

NASA Astrophysics Data System (ADS)

Study the laser pulses transmission time characteristics in discrete random medium using the Monte Carlo method. Firstly, the medium optical parameters have been given by OPAC software. Then, create a Monte Carlo model and Monte Carlo simulation of photon transport behavior of a large number of tracking, statistics obtain the photon average arrival time and average pulse broadening case, the calculation result with calculation results of two-frequency mutual coherence function are compared, the results are very consistent. Finally, medium impulse response function given by polynomial fitting method can be used to correct discrete random medium inter-symbol interference in optical communications and reduce the rate of system error.

Wang, Ping; Yuan, Hongwu; Mei, Haiping; Zhang, Qianghua

2013-08-01

372

Evaluation of PENFAST – A fast Monte Carlo code for dose calculations in photon and electron radiotherapy treatment planning  

Microsoft Academic Search

The aim of the present study is to demonstrate the potential of accelerated dose calculations, using the fast Monte Carlo (MC) code referred to as PENFAST, rather than the conventional MC code PENELOPE, without losing accuracy in the computed dose. For this purpose, experimental measurements of dose distributions in homogeneous and inhomogeneous phantoms were compared with simulated results using both

B. Habib; B. Poumarede; F. Tola; J. Barthe

2010-01-01

373

Monte Carlo simulation of the photon-tagger focal-plane electronics at the MAX IV laboratory  

NASA Astrophysics Data System (ADS)

Rate-dependent effects in the electronics used to instrument the tagger focal plane at the MAX IV Laboratory have been investigated using the novel approach of Monte Carlo simulation. Results are compared to analytical calculations as well as experimental data for both specialized testing and production running to demonstrate a thorough understanding of the behavior of the detector system.

Myers, L. S.; Feldman, G.; Fissum, K. G.; Isaksson, L.; Kovash, M. A.; Nathan, A. M.; Pywell, R. E.; Schröder, B.

2013-11-01

374

Cascaded two-photon spectroscopy of Yb atoms with a transportable effusive atomic beam apparatus  

NASA Astrophysics Data System (ADS)

We present a transportable effusive atomic beam apparatus for cascaded two-photon spectroscopy of the dipole-forbidden transition (6s2 1S0<--> 6s7s 1S0) of Yb atoms. An ohmic-heating effusive oven is designed to have a reservoir volume of 1.6 cm3 and a high degree of atomic beam collimation angle of 30 mrad. The new atomic beam apparatus allows us to detect the spontaneously cascaded two-photons from the 6s7s1S0 state via the intercombination 6s6p3P1 state with a high signal-to-noise ratio even at the temperature of 340 °C. This is made possible in our apparatus because of the enhanced atomic beam flux and superior detection solid angle.

Song, Minsoo; Yoon, Tai Hyun

2013-02-01

375

Comparative Calculation of Electron Transport Properties in Anisotropic Ramp Model Gas of Reid by Monte-Carlo Simulation  

NASA Astrophysics Data System (ADS)

Adopting the model differential cross sections used by Reid (1979) and by Haddad et al. (1981), an investigation to asses the discrepancies observed in the transverse diffusion coefficients D T and other transport properties are performed by the Monte-Carlo simulation. The results show that the values of ND T drastically vary with the change of anisotropy in the scattering property against the common sense that ND T is determined solely by the reduced field E/N under a given momentum transfer cross section. Cross sections so far derived from the D T/µ data may be necessary to be reassesed if anisotropy in the scattering properties is considered.

Yamamoto, Kohji; Ikuta, Nobuaki

1994-03-01

376

Benchmark of PENELOPE code for low-energy photon transport: dose comparisons with MCNP4 and EGS4.  

PubMed

The expanding clinical use of low-energy photon emitting 125I and 103Pd seeds in recent years has led to renewed interest in their dosimetric properties. Numerous papers pointed out that higher accuracy could be obtained in Monte Carlo simulations by utilizing newer libraries for the low-energy photon cross-sections, such as XCOM and EPDL97. The recently developed PENELOPE 2001 Monte Carlo code is user friendly and incorporates photon cross-section data from the EPDL97. The code has been verified for clinical dosimetry of high-energy electron and photon beams, but has not yet been tested at low energies. In the present work, we have benchmarked the PENELOPE code for 10-150 keV photons. We computed radial dose distributions from 0 to 10 cm in water at photon energies of 10-150 keV using both PENELOPE and MCNP4C with either DLC-146 or DLC-200 cross-section libraries, assuming a point source located at the centre of a 30 cm diameter and 20 cm length cylinder. Throughout the energy range of simulated photons (except for 10 keV), PENELOPE agreed within statistical uncertainties (at worst +/- 5%) with MCNP/DLC-146 in the entire region of 1-10 cm and with published EGS4 data up to 5 cm. The dose at 1 cm (or dose rate constant) of PENELOPE agreed with MCNP/DLC-146 and EGS4 data within approximately +/- 2% in the range of 20-150 keV, while MCNP/DLC-200 produced values up to 9% lower in the range of 20-100 keV than PENELOPE or the other codes. However, the differences among the four datasets became negligible above 100 keV. PMID:15012008

Ye, Sung-Joon; Brezovich, Ivan A; Pareek, Prem; Naqvi, Shahid A

2004-02-01

377

Benchmark of PENELOPE code for low-energy photon transport: dose comparisons with MCNP4 and EGS4  

NASA Astrophysics Data System (ADS)

The expanding clinical use of low-energy photon emitting 125I and 103Pd seeds in recent years has led to renewed interest in their dosimetric properties. Numerous papers pointed out that higher accuracy could be obtained in Monte Carlo simulations by utilizing newer libraries for the low-energy photon cross-sections, such as XCOM and EPDL97. The recently developed PENELOPE 2001 Monte Carlo code is user friendly and incorporates photon cross-section data from the EPDL97. The code has been verified for clinical dosimetry of high-energy electron and photon beams, but has not yet been tested at low energies. In the present work, we have benchmarked the PENELOPE code for 10-150 keV photons. We computed radial dose distributions from 0 to 10 cm in water at photon energies of 10-150 keV using both PENELOPE and MCNP4C with either DLC-146 or DLC-200 cross-section libraries, assuming a point source located at the centre of a 30 cm diameter and 20 cm length cylinder. Throughout the energy range of simulated photons (except for 10 keV), PENELOPE agreed within statistical uncertainties (at worst ±5%) with MCNP/DLC-146 in the entire region of 1-10 cm and with published EGS4 data up to 5 cm. The dose at 1 cm (or dose rate constant) of PENELOPE agreed with MCNP/DLC-146 and EGS4 data within approximately ±2% in the range of 20-150 keV, while MCNP/DLC-200 produced values up to 9% lower in the range of 20-100 keV than PENELOPE or the other codes. However, the differences among the four datasets became negligible above 100 keV.

Ye, Sung-Joon; Brezovich, Ivan A.; Pareek, Prem; Naqvi, Shahid A.

2004-02-01

378

Coupling of kinetic Monte Carlo simulations of surface reactions to transport in a fluid for heterogeneous catalytic reactor modeling.  

PubMed

We have developed a method to couple kinetic Monte Carlo simulations of surface reactions at a molecular scale to transport equations at a macroscopic scale. This method is applicable to steady state reactors. We use a finite difference upwinding scheme and a gap-tooth scheme to efficiently use a limited amount of kinetic Monte Carlo simulations. In general the stochastic kinetic Monte Carlo results do not obey mass conservation so that unphysical accumulation of mass could occur in the reactor. We have developed a method to perform mass balance corrections that is based on a stoichiometry matrix and a least-squares problem that is reduced to a non-singular set of linear equations that is applicable to any surface catalyzed reaction. The implementation of these methods is validated by comparing numerical results of a reactor simulation with a unimolecular reaction to an analytical solution. Furthermore, the method is applied to two reaction mechanisms. The first is the ZGB model for CO oxidation in which inevitable poisoning of the catalyst limits the performance of the reactor. The second is a model for the oxidation of NO on a Pt(111) surface, which becomes active due to lateral interaction at high coverages of oxygen. This reaction model is based on ab initio density functional theory calculations from literature. PMID:23406093

Schaefer, C; Jansen, A P J

2013-02-01

379

Dense wavelength division multiplexing photonic transport for radio frequency and microwave wireless services  

NASA Astrophysics Data System (ADS)

The expected increase in space and terrestrial services that include two-way fixed, SATCOM, CATV and mobile wireless services require expanding the system capacity. This expansion has created an opportunity for the utilization of the demonstrated photonic transport systems in wireless networks. System demonstrations and architectural developments have been proposed for distribution of communication services over fiber. Termed Fiber Radio and Hybrid Fiber Wireless, these systems offer the potential to improve services and reduce base station costs through increased bandwidth and ease of installation. We have developed and demonstrated DWDM broadband photonic transport systems able to meet the requirements for IS-95 Personal Communications Services operating at 1.9 GHz and Broadband Wireless Internet operating over the band of 2.5 to 2.7 GHz. Each DWDM channel operates from 1 to 3 GHz transporting services up to 80 Km. Solutions are being sought for low cost transmitters to meet DWDM SATCOM system requirements include extending the transmission distance to over 100 Km with a bandwidth that exceeds multiple octaves. These new requirements put high performance demands on the optical components. We have developed high performance transmitters based on electro-absorption modulated lasers (EML) that can meet SATCOM requirements. We have shown that the EML is capable of providing the required CNR of 32 dB for satellite transmission in the band of 950 to 2150 MHz over a 100 Km distance. In addition, we are investigating a new modulation technique, Microwave Photonic Vector Modulation (MPVM), which has the potential for wideband transmission in DWDM systems.

Paolella, Arthur C.; Jemison, William D.; Borlando, Javier; Wang, Jun

2004-10-01

380

Calculation of effective dose-equivalent responses for external exposure from residual photon emitters in soil  

Microsoft Academic Search

Effective dose-equivalent responses have been calculated for external exposure from residual photon emitters in soil. The calculations are based on the assumption that the receptor is located 1 m above the contaminated ground. A Monte Carlo algorithm was developed to perform the photon transport calculation for the soil\\/air configuration, in which the soil constituents were assumed to be similar to

S. Y. Chen

1991-01-01

381

The effect of energy weighting on x-ray imaging based on photon counting detector: a Monte Carlo simulation  

NASA Astrophysics Data System (ADS)

Photon counting detector based on semiconductor materials is a promising imaging modality and provides many benefits for x-ray imaging compared with conventional detectors. This detector is able to measure the x-ray photon energy deposited by each event and provide the x-ray spectrum formed by detected photon. Recently, photon counting detectors have been developed for x-ray imaging. However, there has not been done many works for developing the novel x-ray imaging techniques and evaluating the image quality in x-ray system based on photon counting detectors. In this study, we simulated computed tomography (CT) images using projection-based and image-based energy weighting techniques and evaluate the effect of energy weighting in CT images. We designed the x-ray CT system equipped with cadmium telluride (CdTe) detector operating in the photon counting mode using Geant4 Application for Tomographic Emission (GATE) simulation. A micro focus X-ray source was modeled to reduce the flux of photons and minimize the spectral distortion. The phantom had a cylindrical shape of 30 mm diameter and consisted of ploymethylmethacrylate (PMMA) which includes the blood (1.06 g/cm3), iodine, and gadolinium (50 mg/cm3). The reconstructed images of phantom were acquired with projection-based and image-based energy weighting techniques. To evaluate the image quality, the contrast-to-noise ratio (CNR) is calculated as a function of the number of energy-bins. The CNR of both images acquired with energy weighting techniques were improved compared with those of integrating and counting images and increased as a function of the number of energy-bins. When the number of energy-bins was increased, the CNR in the image-based energy weighting image is higher than the projection-based energy weighting image. The results of this study show that the energy weighting techniques based on the photon counting detector can improve the image quality and the number of energy-bins used for generating the image is important.

Lee, Seung-Wan; Choi, Yu-Na; Cho, Hyo-Min; Lee, Young-Jin; Ryu, Hyun-Ju; Kim, Hee-Joung

2012-02-01

382

Use of single scatter electron monte carlo transport for medical radiation sciences  

DOEpatents

The single scatter Monte Carlo code CREEP models precise microscopic interactions of electrons with matter to enhance physical understanding of radiation sciences. It is designed to simulate electrons in any medium, including materials important for biological studies. It simulates each interaction individually by sampling from a library which contains accurate information over a broad range of energies.

Svatos, Michelle M. (Oakland, CA)

2001-01-01

383

Efficient Evaluation of Ionized-Impurity Scattering in Monte Carlo Transport Calculations  

Microsoft Academic Search

Carrier scattering by ionized impurities is strongly anisotropic, and events with small scattering angles are highly preferred. On the Monte Carlo technique applied to semiconductor device modeling this behavior imposes several problems which are discussed. We present a method which reduces the amount of low-angle scattering very effectively. Instead of the anisotropic scattering mechanism an equivalent isotropic mechanism is defined

H. Kosina

1997-01-01

384

Low pressure semiconductor processing transport property modeling using direct simulation Monte Carlo  

Microsoft Academic Search

Summary form only given. In order to extend the capability of the Hybrid Plasma Equipment Model (HPEM)1 simulation code to increasingly lower operating pressure conditions, the direct simulation Monte Carlo (DSMC)2 method is used to improve the modeling of the heavy particle species in a hollow cathode magnetron (HCM) plasma reactor, a device used to implement the Ionized Metal Physical

Zheng Li; Hao Deng; D. A. Levin

2010-01-01

385

Monte Carlo Transport Code Study of the Space Radiation Environment Using FLUKA and ROOT.  

National Technical Information Service (NTIS)

We report on the progress of a current study aimed at developing a state-of-the-art Monte-Carlo computer simulation of the space radiation environment using advanced computer software techniques recently available at CERN, the European Laboratory for Part...

A. Empl A. Ferrari F. Carminati J. MacGibbon L. Pinsky P. Sala R. Brun T. Wilson

2001-01-01

386

Epp - A C++ EGSnrc user code for Monte Carlo simulation of radiation transport  

Microsoft Academic Search

Easy particle propagation (Epp) is a Monte Carlo simulation EGSnrc user code that we have developed for dose calculation in a voxelized volume, and to generate images of an arbitrary geometry irradiated by a particle source. The dose calculation aspect is a reimplementation of the function of DOSXYZnrc with new features added and some restrictions removed. Epp is designed for

Congwu Cui; Jonas Lippuner; Harry R. Ingleby; David N. M. di Valentino; Idris A. Elbakri

2010-01-01

387

Monte-Carlo Treatment of Nonlinear Collisional Effects in Charged-Particle Transport.  

National Technical Information Service (NTIS)

The effects of two-body coulomb collisions of the simulation particles against a background material are often treated by a Monte-Carlo collisional process in which the collision probability is determined by a Fokker-Planck treatment. This procedure is no...

D. L. Weiss K. H. Witte M. G. Sheppard T. A. Oliphant

1985-01-01

388

Verification measurements and clinical evaluation of the iPlan RT Monte Carlo dose algorithm for 6 MV photon energy  

Microsoft Academic Search

This study presents data for verification of the iPlan RT Monte Carlo (MC) dose algorithm (BrainLAB, Feldkirchen, Germany). MC calculations were compared with pencil beam (PB) calculations and verification measurements in phantoms with lung-equivalent material, air cavities or bone-equivalent material to mimic head and neck and thorax and in an Alderson anthropomorphic phantom. Dosimetric accuracy of MC for the micro-multileaf

A L Petoukhova; K van Wingerden; R G J Wiggenraad; P J M van de Vaart; J van Egmond; E M Franken; J P C van Santvoort

2010-01-01

389

Evaluation of Shutdown Gamma-ray Dose Rates around the Duct Penetration by Three-Dimensional Monte Carlo Decay Gamma-ray Transport Calculation with Variance Reduction Method  

Microsoft Academic Search

For the evaluation of gamma-ray dose rates around the duct penetrations after shutdown of nuclear fusion reactor, the calculation method is proposed with an application of the Monte Carlo neutron and decay gamma-ray transport calculation. For the radioisotope production rates during operation, the Monte Carlo calculation is conducted by the modification of the nuclear data library replacing a prompt gamma-ray

Satoshi SATO; Hiromasa IIDA; Takeo NISHITANI

2002-01-01

390

Simulation of Cherenkov photons emitted in photomultiplier windows induced by Compton diffusion using the Monte Carlo code GEANT4  

Microsoft Academic Search

The implementation of the TDCR method (Triple to Double Coincidence Ratio) is based on a liquid scintillation system which comprises three photomultipliers; at LNHB, this counter can also be used in the ?-channel of a 4?(LS)?–? coincidence counting equipment. It is generally considered that the ?-sensitivity of the liquid scintillation detector comes from the interaction of the ?-photons in the

C. Thiam; C. Bobin; J. Bouchard

2010-01-01

391

A hybrid hydrodynamic-Monte Carlo simulation of the transport of neutral radicals in low-pressure remote plasma sources  

SciTech Connect

In low pressure electron cyclotron resonance and remote plasma enhanced chemical vapor deposition reactors (milliTorr to hundreds of milliTorr) the mean free path of excited state neutrals can be commensurate with the vessel dimensions. Deposition species may collide with the wall several times before encountering the substrate. While the movement of these particles is essentially ballistic, the advective flow of the background gas is a significant factor in the determination of the transport of the neutral radicals. To address these conditions, a hybrid hydrodynamic-Monte Carlo model has been developed. The advective flow field is calculated from the mass and momentum equations. Radical transport is then simulated using Monte Carlo techniques that include inelastic collisions with the background species and other MC particles, absorbing or reflective collisions with reactor surfaces, or momentum transfer with the advective fluid. Presented are the results describing the effects of geometry, pressure and gas flow for gas mixtures containing SiH[sub 4]. Identity, uniformity, and angle of incidence of the radical flux to the substrate will be addressed with the goal of optimizing the fluxes of selected species.

Hartig, M.J.

1993-01-01

392

a Hybrid Hydrodynamic-Monte Carlo Simulation of the Transport of Neutral Radicals in Low-Pressure Remote Plasma Sources.  

NASA Astrophysics Data System (ADS)

In low pressure electron cyclotron resonance and remote plasma enhanced chemical vapor deposition reactors (milliTorr to hundreds of milliTorr) the mean free path of excited state neutrals can be commensurate with the vessel dimensions. Deposition species may collide with the wall several times before encountering the substrate. While the movement of these particles is essentially ballistic, the advective flow of the background gas is a significant factor in the determination of the transport of the neutral radicals. To address these conditions, a hybrid hydrodynamic -Monte Carlo model has been developed. The advective flow field is calculated from the mass and momentum equations. Radical transport is then simulated using Monte Carlo techniques that include inelastic collisions with the background species and other MC particles, absorbing or reflective collisions with reactor surfaces, or momentum transfer with the advective fluid. Presented here are the results describing the effects of geometry, pressure and gas flow for gas mixtures containing SiH_4. Identity, uniformity, and angle of incidence of the radical flux to the substrate will be addressed with the goal of optimizing the fluxes of selected species.

Hartig, Michael Joseph

393

Thermal Scattering Law Data: Implementation and Testing Using the Monte Carlo Neutron Transport Codes COG, MCNP and TART  

SciTech Connect

Recently we implemented the ENDF/B-VI thermal scattering law data in our neutron transport codes COG and TART. Our objective was to convert the existing ENDF/B data into double differential form in the Livermore ENDL format. This will allow us to use the ENDF/B data in any neutron transport code, be it a Monte Carlo, or deterministic code. This was approached as a multi-step project. The first step was to develop methods to directly use the thermal scattering law data in our Monte Carlo codes. The next step was to convert the data to double-differential form. The last step was to verify that the results obtained using the data directly are essentially the same as the results obtained using the double differential data. Part of the planned verification was intended to insure that the data as finally implemented in the COG and TART codes, gave the same answer as the well known MCNP code, which includes thermal scattering law data. Limitations in the treatment of thermal scattering law data in MCNP have been uncovered that prevented us from performing this part of our verification.

Cullen, D E; Hansen, L F; Lent, E M; Plechaty, E F

2003-05-17

394

Experimental benchmarks of the Monte Carlo code penelope  

Microsoft Academic Search

The physical algorithms implemented in the latest release of the general-purpose Monte Carlo code penelope for the simulation of coupled electron–photon transport are briefly described. We discuss the mixed (class II) scheme used to transport intermediate- and high-energy electrons and positrons and, in particular, the approximations adopted to account for the energy dependence of the interaction cross-sections. The reliability of

J. Sempau; J. M. Fernández-Varea; E. Acosta; F. Salvat

2003-01-01

395

Sampling function of single-X-ray-photon counting hybrid pixel detectors: combining an analytical approach to Monte-Carlo simulations and Finite-Element-Modeling  

NASA Astrophysics Data System (ADS)

Spectroscopic and imaging performance parameters of hybrid pixel detectors operated in single-X-ray photon-counting mode can be inferred from the dependence of their sampling function (or aperture function) on the detection energy threshold. In a previous paper, it was shown that this dependence could be modelled using a simple analytical method. Measurements were performed on typical synchrotron X-ray detectors and fitted to the analytical formulas in order to obtain detector parameters such as charge-sharing width, energy dispersion and fill-factor at 50% threshold. In the present paper, we use Monte-Carlo (MC) and Finite-Element-Modeling (FEM) software tools to perform a more detailed simulation of image formation processes taking place in photon-counting hybrid pixel detectors of various pixel sizes associated to standard silicon sensor thickness and exposed to 15 keV monochromatic X-rays. We show that the MC/FEM simulation results can be used to produce detector parameters required in the analytical expressions of the sampling function of these detectors.

McGrath, J.; Marchal, J.; Medjoubi, K.

2013-10-01

396

Correlated two-photon transport in a one-dimensional waveguide side-coupled to a nonlinear cavity  

SciTech Connect

We investigate the transport properties of two photons inside a one-dimensional waveguide side-coupled to a single-mode nonlinear cavity. The cavity is filled with a nonlinear Kerr medium. Based on the Laplace transform method, we present an analytic solution for the quantum states of the two transmitted and reflected photons, which are initially prepared in a Lorentzian wave packet. The solution reveals how quantum correlation between the two photons emerges after the scattering by the nonlinear cavity. In particular, we show that the output wave function of the two photons in position space can be localized in relative coordinates, which is a feature that might be interpreted as a two-photon bound state in this waveguide-cavity system.

Liao Jieqiao; Law, C. K. [Department of Physics and Institute of Theoretical Physics, Chinese University of Hong Kong, Shatin, Hong Kong Special Administrative Region (Hong Kong)

2010-11-15

397

Lead and tungsten pinhole inserts for I-131 SPECT tumor imaging: experimental measurements and photon transport simulations  

Microsoft Academic Search

The potential use of lead and tungsten pinhole inserts for high-resolution SPECT imaging of intratumor activity in I-131 radioimmunotherapy was investigated using experimental point source measurements and photon transport simulations. I-131 imaging is challenging because the primary photon emission is at 364 keV and penetration through the insert near the pinhole aperture is significant. Point source response functions (PSRF's) for

Mark F. Smith; Ronald J. Jaszczak; Huili Wang; Jianying Li

1997-01-01

398

NonRelativistic Electron Transport in Metals: A Monte Carlo Approach  

Microsoft Academic Search

A simple Monte Carlo procedure is described for simulating the multiple scattering and absorption of electrons with the incident energy in the range 1-50 keV moving through a slab of uniformly distributed material of given atomic number, density and thickness. The simulation is based on a screened Rutherford cross-section and Bethe continuous energy-loss equation. A FORTRAN program is written to

Nima Ghal-eh; Mohammad Farhad Rahimi; Mehrnoush Manouchehri

2001-01-01

399

Heat generation and transport in nanoscale semiconductor devices via Monte Carlo and hydrodynamic simulations  

Microsoft Academic Search

Purpose – The purpose of this paper is to set up a consistent off-equilibrium thermodynamic theory to deal with the self-heating of electronic nano-devices. Design\\/methodology\\/approach – From the Bloch-Boltzmann-Peierls kinetic equations for the coupled system formed by electrons and phonons, an extended hydrodynamic model (HM) has been obtained on the basis of the maximum entropy principle. An electrothermal Monte Carlo

Orazio Muscato; Vincenza Di Stefano

2011-01-01

400

A Monte Carlo transport code study of the space radiation environment using FLUKA and ROOT  

Microsoft Academic Search

We report on the progress of a current study aimed at developing a state-of-the-art Monte-Carlo computer simulation of the space radiation environment using advanced computer software techniques recently available at CERN, the European Laboratory for Particle Physics in Geneva, Switzerland. By taking the next-generation computer software appearing at CERN and adapting it to known problems in the implementation of space

Thomas Wilson; Lawrence Pinsky; Federico Carminati; René Brun; Alfredo Ferrari; Paola Sala; A. Empl; Jane MacGibbon

2001-01-01

401

RAFFLE V general purpose Monte Carlo code for neutron and gamma transport. Revision 1  

Microsoft Academic Search

The RAFFLE V general-purpose Monte Carlo code is an extensively-modified version of the original RAFFLE code developed at INEL. This document describes the RAFFLE V code, emphasizing the modifications made since prior documentation. The major modifications implemented into the RAFFLE V code are: (1) implementation of the processed ENDF-B version V neutron data and an expansion of the energy range

F. J. Wheeler; S. A. Easson; R. A. Grimesey; D. W. Wessol

1983-01-01

402

Dosimetry of interface region near closed air cavities for Co-60, 6 MV and 15 MV photon beams using Monte Carlo simulations  

PubMed Central

Underdosing of treatment targets can occur in radiation therapy due to electronic disequilibrium around air-tissue interfaces when tumors are situated near natural air cavities. These effects have been shown to increase with the beam energy and decrease with the field size. Intensity modulated radiation therapy (IMRT) and tomotherapy techniques employ combinations of multiple small radiation beamlets of varying intensities to deliver highly conformal radiation therapy. The use of small beamlets in these techniques may therefore result in underdosing of treatment target in the air-tissue interfaces region surrounding an air cavity. This work was undertaken to investigate dose reductions near the air-water interfaces of 1×1×1 and 3×3×3 cm3 air cavities, typically encountered in the treatment of head and neck cancer utilizing radiation therapy techniques such as IMRT and tomotherapy using small fields of Co-60, 6 MV and 15 MV photons. Additional investigations were performed for larger photon field sizes encompassing the entire air-cavity, such as encountered in conventional three dimensional conformal radiation therapy (3DCRT) techniques. The EGSnrc/DOSXYZnrc Monte Carlo code was used to calculate the dose reductions (in water) in air-water interface region for single, parallel opposed and four field irradiations with 2×2 cm2 (beamlet), 10×2 cm2 (fan beam), 5×5 and 7×7 cm2 field sizes. The magnitude of dose reduction in water near air-water interface increases with photon energy; decreases with distance from the interface as well as decreases as the number of beams are increased. No dose reductions were observed for large field sizes encompassing the air cavities. The results demonstrate that Co-60 beams may provide significantly smaller interface dose reductions than 6 MV and 15 MV irradiations for small field irradiations such as used in IMRT and tomotherapy.

Joshi, Chandra P.; Darko, Johnson; Vidyasagar, P. B.; Schreiner, L. John

2010-01-01

403

Influence of photon energy spectra from brachytherapy sources on Monte Carlo simulations of kerma and dose rates in water and air  

SciTech Connect

Purpose: For a given radionuclide, there are several photon spectrum choices available to dosimetry investigators for simulating the radiation emissions from brachytherapy sources. This study examines the dosimetric influence of selecting the spectra for {sup 192}Ir, {sup 125}I, and {sup 103}Pd on the final estimations of kerma and dose. Methods: For {sup 192}Ir, {sup 125}I, and {sup 103}Pd, the authors considered from two to five published spectra. Spherical sources approximating common brachytherapy sources were assessed. Kerma and dose results from GEANT4, MCNP5, and PENELOPE-2008 were compared for water and air. The dosimetric influence of {sup 192}Ir, {sup 125}I, and {sup 103}Pd spectral choice was determined. Results: For the spectra considered, there were no statistically significant differences between kerma or dose results based on Monte Carlo code choice when using the same spectrum. Water-kerma differences of about 2%, 2%, and 0.7% were observed due to spectrum choice for {sup 192}Ir, {sup 125}I, and {sup 103}Pd, respectively (independent of radial distance), when accounting for photon yield per Bq. Similar differences were observed for air-kerma rate. However, their ratio (as used in the dose-rate constant) did not significantly change when the various photon spectra were selected because the differences compensated each other when dividing dose rate by air-kerma strength. Conclusions: Given the standardization of radionuclide data available from the National Nuclear Data Center (NNDC) and the rigorous infrastructure for performing and maintaining the data set evaluations, NNDC spectra are suggested for brachytherapy simulations in medical physics applications.

Rivard, Mark J.; Granero, Domingo; Perez-Calatayud, Jose; Ballester, Facundo [Department of Radiation Oncology, Tufts University School of Medicine, Boston, Massachusetts 02111 (United States); Department of Radiation Oncology, ERESA, Hospital General Universitario, E-46014 Valencia (Spain); Department of Radiation Oncology, La Fe University Hospital, E-46009 Valencia (Spain); Department of Atomic, Molecular, and Nuclear Physics, University of Valencia, E-46100 Burjassot, Spain and IFIC, CSIC-University of Valencia, E-46100 Burjassot (Spain)

2010-02-15

404

A Monte Carlo method for calculating the energy response of plastic scintillators to polarized photons below 100 keV  

Microsoft Academic Search

The energy response of plastic scintillators (Eljen Technology EJ-204) to polarized soft gamma-ray photons below 100keV has been studied, primarily for the balloon-borne polarimeter, PoGOLite. The response calculation includes quenching effects due to low-energy recoil electrons and the position dependence of the light collection efficiency in a 20cm long scintillator rod. The broadening of the pulse-height spectrum, presumably caused by

T. Mizuno; Y. Kanai; J. Kataoka; M. Kiss; K. Kurita; M. Pearce; H. Tajima; H. Takahashi; T. Tanaka; M. Ueno; Y. Umeki; H. Yoshida; M. Arimoto; M. Axelsson; C. Marini Bettolo; G. Bogaert; P. Chen; W. Craig; Y. Fukazawa; S. Gunji; T. Kamae; J. Katsuta; N. Kawai; S. Kishimoto; W. Klamra; S. Larsson; G. Madejski; J. S. T. Ng; F. Ryde; S. Rydström; T. Takahashi; T. S. Thurston; G. Varner

2009-01-01

405

Consistent treatment of transport properties for five-species air direct simulation Monte Carlo/Navier-Stokes applications  

NASA Astrophysics Data System (ADS)

A general approach for achieving consistency in the transport properties between direct simulation Monte Carlo (DSMC) and Navier-Stokes (CFD) solvers is presented for five-species air. Coefficients of species diffusion, viscosity, and thermal conductivities are considered. The transport coefficients that are modeled in CFD solvers are often obtained by expressions involving sets of collision integrals, which are obtained from more realistic intermolecular potentials (i.e., ab initio calculations). In this work, the self-consistent effective binary diffusion and Gupta et al.-Yos tranport models are considered. The DSMC transport coefficients are approximated from Chapman-Enskog theory in which the collision integrals are computed using either the variable hard sphere (VHS) and variable soft sphere (VSS) (phenomenological) collision cross section models. The VHS and VSS parameters are then used to adjust the DSMC transport coefficients in order to achieve a best-fit to the coefficients computed from more realistic intermolecular potentials over a range of temperatures. The best-fit collision model parameters are determined for both collision-averaged and collision-specific pairing approaches using the Nelder-Mead simplex algorithm. A consistent treatment of the diffusion, viscosity, and thermal conductivities is presented, and recommended sets of best-fit VHS and VSS collision model parameters are provided for a five-species air mixture.

Stephani, K. A.; Goldstein, D. B.; Varghese, P. L.

2012-07-01

406

Monte Carlo simulation of light transport in dark-field confocal photoacoustic microscopy  

Microsoft Academic Search

A modified MC convolution method for integration extension of MC simulation is developed for finite photon beam with random shape of translational or rotational invariance, which is proven consistent with the conventional convolution extension of MC simulation for normal incident finite beam. The method is applied to analyze the positions of fluence foci and ratios of fluence at the focus

Zhixing Xie; Lihong V. Wang; Hao F. Zhang

2009-01-01

407

A Modified Treatment of Sources in Implicit Monte Carlo Radiation Transport  

SciTech Connect

We describe a modification of the treatment of photon sources in the IMC algorithm. We describe this modified algorithm in the context of thermal emission in an infinite medium test problem at equilibrium and show that it completely eliminates statistical noise.

Gentile, N A; Trahan, T J

2011-03-22

408

Review of Hybrid (Deterministic/Monte Carlo) Radiation Transport Methods, Codes, and Applications at Oak Ridge National Laboratory  

SciTech Connect

This paper provides a review of the hybrid (Monte Carlo/deterministic) radiation transport methods and codes used at the Oak Ridge National Laboratory and examples of their application for increasing the efficiency of real-world, fixed-source Monte Carlo analyses. The two principal hybrid methods are (1) Consistent Adjoint Driven Importance Sampling (CADIS) for optimization of a localized detector (tally) region (e.g., flux, dose, or reaction rate at a particular location) and (2) Forward Weighted CADIS (FW-CADIS) for optimizing distributions (e.g., mesh tallies over all or part of the problem space) or multiple localized detector regions (e.g., simultaneous optimization of two or more localized tally regions). The two methods have been implemented and automated in both the MAVRIC sequence of SCALE 6 and ADVANTG, a code that works with the MCNP code. As implemented, the methods utilize the results of approximate, fast-running 3-D discrete ordinates transport calculations (with the Denovo code) to generate consistent space- and energy-dependent source and transport (weight windows) biasing parameters. These methods and codes have been applied to many relevant and challenging problems, including calculations of PWR ex-core thermal detector response, dose rates throughout an entire PWR facility, site boundary dose from arrays of commercial spent fuel storage casks, radiation fields for criticality accident alarm system placement, and detector response for special nuclear material detection scenarios and nuclear well-logging tools. Substantial computational speed-ups, generally O(10{sup 2-4}), have been realized for all applications to date. This paper provides a brief review of the methods, their implementation, results of their application, and current development activities, as well as a considerable list of references for readers seeking more information about the methods and/or their applications.

Wagner, John C [ORNL; Peplow, Douglas E. [ORNL; Mosher, Scott W [ORNL; Evans, Thomas M [ORNL

2010-01-01

409

Review of Hybrid (Deterministic/Monte Carlo) Radiation Transport Methods, Codes, and Applications at Oak Ridge National Laboratory  

SciTech Connect

This paper provides a review of the hybrid (Monte Carlo/deterministic) radiation transport methods and codes used at the Oak Ridge National Laboratory and examples of their application for increasing the efficiency of real-world, fixed-source Monte Carlo analyses. The two principal hybrid methods are (1) Consistent Adjoint Driven Importance Sampling (CADIS) for optimization of a localized detector (tally) region (e.g., flux, dose, or reaction rate at a particular location) and (2) Forward Weighted CADIS (FW-CADIS) for optimizing distributions (e.g., mesh tallies over all or part of the problem space) or multiple localized detector regions (e.g., simultaneous optimization of two or more localized tally regions). The two methods have been implemented and automated in both the MAVRIC sequence of SCALE 6 and ADVANTG, a code that works with the MCNP code. As implemented, the methods utilize the results of approximate, fast-running 3-D discrete ordinates transport calculations (with the Denovo code) to generate consistent space- and energy-dependent source and transport (weight windows) biasing parameters. These methods and codes have been applied to many relevant and challenging problems, including calculations of PWR ex-core thermal detector response, dose rates throughout an entire PWR facility, site boundary dose from arrays of commercial spent fuel storage casks, radiation fields for criticality accident alarm system placement, and detector response for special nuclear material detection scenarios and nuclear well-logging tools. Substantial computational speed-ups, generally O(102-4), have been realized for all applications to date. This paper provides a brief review of the methods, their implementation, results of their application, and current development activities, as well as a considerable list of references for readers seeking more information about the methods and/or their applications.

Wagner, John C [ORNL; Peplow, Douglas E. [ORNL; Mosher, Scott W [ORNL; Evans, Thomas M [ORNL

2011-01-01

410

The HETC\\/LHI\\/SGS Radiation Transport Code System  

Microsoft Academic Search

In this tutorial paper the authors discuss the High Energy Transport (HETC)\\/Light Heavy Ion (LHI)\\/Spallation Gamma Source (SGS) Monte Carlo radiation transport computer code system, used to transport nucleons, pions, muons, photons, and ''light heavy'' nuclei with 2 less than or equal to A less than or equal to 10 through complex materials and geometries. In particular, they present for

David Dietz

1986-01-01

411

Vectorization and multitasking with a Monte Carlo code for neutron transport problems  

Microsoft Academic Search

This paper summarizes two improvements of a Monte Carlo code by resorting to vectorization and multitasking techniques.\\u000a \\u000a After a short presentation of the physical problem to solve and a description of main difficulties to produce an efficient\\u000a coding, this paper introduces the vectorization principles employed and briefly describes the vectorized algorithm functioning.\\u000a \\u000a \\u000a \\u000a Next, measured performances on CRAY 1S. CYBER 205

Yves Chauvet

1985-01-01

412

Monte-Carlo treatment of nonlinear collisional effects in charged-particle transport  

SciTech Connect

The effects of two-body coulomb collisions of the simulation particles against a background material are often treated by a Monte-Carlo collisional process in which the collision probability is determined by a Fokker-Planck treatment. This procedure is nonlinear if the properties of the background material are allowed to change as a result of the scattering of the simulation particles. A more completely, nonlinear problem is obtained if the simulation particles themselves form all or part of the background distribution. A new method is presented here for doing this, and examples will be discussed that illustrate the power of the technique.

Weiss, D.L.; Witte, K.H.; Sheppard, M.G.; Oliphant, T.A.

1985-01-01

413

Transport anisotropy of the pnictides studied via Monte Carlo simulations of the Spin-Fermion model  

SciTech Connect

An undoped three-orbital spin-fermion model for the Fe-based superconductors is studied via Monte Carlo techniques in two-dimensional clusters. At low temperatures, the magnetic and one-particle spectral properties are in agreement with neutron and photoemission experiments. Our main results are the resistance versus temperature curves that display the same features observed in BaFe{sub 2}As{sub 2} detwinned single crystals (under uniaxial stress), including a low-temperature anisotropy between the two directions followed by a peak at the magnetic ordering temperature, that qualitatively appears related to short-range spin order and concomitant Fermi surface orbital order.

Liang, Shuhua [ORNL; Alvarez, Gonzalo [ORNL; Sen, Cengiz [ORNL; Moreo, Adriana [ORNL; Dagotto, Elbio R [ORNL

2012-01-01

414

Monte Carlo Sensitivity Analysis of Unknown Parameters in Hazardous Materials Transportation Risk Assessment  

Microsoft Academic Search

The US Department of Transportation was interested in the risks associated with transporting Hydrazine in tanks with and without relief devices. Hydrazine is both highly toxic and flammable, as well as corrosive. Consequently, there was a conflict as to whether a relief device should be used or not. Data were not available on the impact of relief devices on release

Julia J. Pet-Armacost; Jose Sepulveda; Milton Sakude

1999-01-01

415

From force-fields to photons: MD simulations of dye-labeled nucleic acids and Monte Carlo modeling of FRET  

NASA Astrophysics Data System (ADS)

Fluorescence resonance energy transfer (FRET) is a powerful technique for understanding the structural fluctuations and transformations of RNA, DNA and proteins. Molecular dynamics (MD) simulations provide a window into the nature of these fluctuations on a different, faster, time scale. We use Monte Carlo methods to model and compare FRET data from dye-labeled RNA with what might be predicted from the MD simulation. With a few notable exceptions, the contribution of fluorophore and linker dynamics to these FRET measurements has not been investigated. We include the dynamics of the ground state dyes and linkers in our study of a 16mer double-stranded RNA. Water is included explicitly in the simulation. Cyanine dyes are attached at either the 3' or 5' ends with a 3 carbon linker, and differences in labeling schemes are discussed.[4pt] Work done in collaboration with Peker Milas, Benjamin D. Gamari, and Louis Parrot.

Goldner, Lori

2012-02-01

416

From force-fields to photons: MD simulations of dye-labeled nucleic acids and Monte Carlo modeling of FRET  

NASA Astrophysics Data System (ADS)

Fluorescence resonance energy transfer (FRET) is a powerful experimental technique for understanding the structural fluctuations and transformations of RNA, DNA and proteins. Molecular dynamics (MD) simulations provide a window into the nature of these fluctuations on a faster time scale inaccessible to experiment. We use Monte Carlo methods to model and compare FRET data from dye-labeled RNA with what might be predicted from the MD simulation. With a few notable exceptions, the contribution of fluorophore and linker dynamics to these FRET measurements has not been investigated. We include the dynamics of the ground state dyes and linkers along with an explicit water solvent in our study of a 16mer double-stranded RNA. Cyanine dyes are attached at either the 3' or 5' ends with a three carbon linker, providing a basis for contrasting the dynamics of similar but not identical molecular structures.

Milas, Peker; Gamari, Ben; Parrot, Louis; Buckman, Richard; Goldner, Lori

2011-11-01

417

Self-Adjoint Angular Flux Equation for Coupled Electron-Photon Transport  

SciTech Connect

Recently, Morel and McGhee described an alternate second-order form of the transport equation called the self adjoint angular flux (SAAF) equation that has the angular flux as its unknown. The SAAF formulation has all the advantages of the traditional even- and odd-parity self-adjoint equations, with the added advantages that it yields the full angular flux when it is numerically solved, it is significantly easier to implement reflective and reflective-like boundary conditions, and in the appropriate form it can be solved in void regions. The SAAF equation has the disadvantage that the angular domain is the full unit sphere and, like the even- and odd- parity form, S{sub n} source iteration cannot be implemented using the standard sweeping algorithm. Also, problems arise in pure scattering media. Morel and McGhee demonstrated the efficacy of the SAAF formulation for neutral particle transport. Here we apply the SAAF formulation to coupled electron-photon transport problems using multigroup cross-sections from the CEPXS code and S{sub n} discretization.

Liscum-Powell, J.L.; Lorence, L.J. Jr.; Morel, J.E.; Prinja, A.K.

1999-07-08

418

Self-adjoint angular flux equation for coupled electron-photon transport  

SciTech Connect

Recently, Morel and McGhee described an alternate second-order form of the transport equation called the self-adjoint angular flux (SAAF) equation that has the angular flux as its unknown. The SAAF formulation has all the advantages of the traditional even- and odd-parity self-adjoint equations, with the added advantages that it yields the full angular flux when it is numerically solved, it is significantly easier to implement reflective and reflective-like boundary conditions, and in the appropriate form it can be solved in void regions. The SAAF equation has the disadvantage that the angular domain is the full unit sphere, and, like the even- and odd-parity form, S{sub n} source iteration cannot be implemented using the standard sweeping algorithm. Also, problems arise in pure scattering media. Morel and McGhee demonstrated the efficacy of the SAAF formulation for neutral particle transport. Here, the authors apply the SAAF formulation to coupled electron-photon transport problems using multigroup cross sections from the CEPXS code and S{sub n} discretization.

Liscum-Powell, J.L.; Prinja, A.K.; Morel, J.E.; Lorence, L.J. Jr.

1999-07-01

419

Enhancements to the Combinatorial Geometry Particle Tracker in the Mercury Monte Carlo Transport Code: Embedded Meshes and Domain Decomposition  

SciTech Connect

Two enhancements to the combinatorial geometry (CG) particle tracker in the Mercury Monte Carlo transport code are presented. The first enhancement is a hybrid particle tracker wherein a mesh region is embedded within a CG region. This method permits efficient calculations of problems with contain both large-scale heterogeneous and homogeneous regions. The second enhancement relates to the addition of parallelism within the CG tracker via spatial domain decomposition. This permits calculations of problems with a large degree of geometric complexity, which are not possible through particle parallelism alone. In this method, the cells are decomposed across processors and a particles is communicated to an adjacent processor when it tracks to an interprocessor boundary. Applications that demonstrate the efficacy of these new methods are presented.

Greenman, G M; O'Brien, M J; Procassini, R J; Joy, K I

2009-03-09

420

3D dose distribution calculation in a voxelized human phantom by means of Monte Carlo method  

Microsoft Academic Search

The aim of this work is to provide the reconstruction of a real human voxelized phantom by means of a MatLab® program and the simulation of the irradiation of such phantom with the photon beam generated in a Theratron 780® (MDS Nordion) 60Co radiotherapy unit, by using the Monte Carlo transport code MCNP (Monte Carlo N-Particle), version 5. The project

V. Abella; R. Miró; B. Juste; G. Verdú

2010-01-01