Monte Carlo simulation for Kaonic deuterium studies
International Nuclear Information System (INIS)
Full text: The SIDDHARTA experiment at the DAFNE collider measured the shift and with of the ground level in kaonic hydrogen caused by the strong interaction between the kaons and protons. The measurement of the X-ray transitions to the 1s level in kaonic deuterium will allow, together with the available results from kaonic hydrogen, to extract the isospin- dependent antikaon-nucleon scattering lengths. I will present the Monte Carlo simulation of the SIDDHARTA-2 setup, in the framework of GEANT4. The program is used to optimize the critical parameters of the setup in order to perform the kaonic deuterium measurement. (author)
Polarization Properties of Ferroelectric Superlattice Studied by Monte Carlo Simulation
Institute of Scientific and Technical Information of China (English)
Guiwu LU; Hairui XIA; Pijun LIU
2001-01-01
The polarization property of a ferroelectric superlattice formed from two alternating materials was studied using Monte Carlo computer simulation. Our study has been developed in a framework of the transverse Ising model with nearest-neighbor interactions. Both the effect of the transverse field and interface coupling strength have been taken into consideration. In view of our results which is in good agreement with previous theoretical results, it is concluded that the Curie temperature of the superlattice increases with the increase of the interface coupling strength JAB.The remanent polarization and saturation coercive force of the superlattice are also presented.
Monte Carlo simulations and dosimetric studies of an irradiation facility
Belchior, A.; Botelho, M. L.; Vaz, P.
2007-09-01
There is an increasing utilization of ionizing radiation for industrial applications. Additionally, the radiation technology offers a variety of advantages in areas, such as sterilization and food preservation. For these applications, dosimetric tests are of crucial importance in order to assess the dose distribution throughout the sample being irradiated. The use of Monte Carlo methods and computational tools in support of the assessment of the dose distributions in irradiation facilities can prove to be economically effective, representing savings in the utilization of dosemeters, among other benefits. One of the purposes of this study is the development of a Monte Carlo simulation, using a state-of-the-art computational tool—MCNPX—in order to determine the dose distribution inside an irradiation facility of Cobalt 60. This irradiation facility is currently in operation at the ITN campus and will feature an automation and robotics component, which will allow its remote utilization by an external user, under REEQ/996/BIO/2005 project. The detailed geometrical description of the irradiation facility has been implemented in MCNPX, which features an accurate and full simulation of the electron-photon processes involved. The validation of the simulation results obtained was performed by chemical dosimetry methods, namely a Fricke solution. The Fricke dosimeter is a standard dosimeter and is widely used in radiation processing for calibration purposes.
Study of Gamma spectra by Monte Carlo simulation
International Nuclear Information System (INIS)
The purpose of this paper is obtaining gamma ray spectra by means of a scintillation detector applying the Monte Carlo statistic simulation method using the EGS4 program. The Monte Carlo algorithm implies that the physical system is described by the probability density function which allows generating random figures and the result is taken as an average of numbers which were observed. The EGS4 program allows the simulation of the following physical processes: the photo-electrical effect, the Compton effect, the electron positron pairs generation and the Rayleigh diffusion. The gamma rays recorded by the detector are converted into electrical pulses and the gamma ray spectra are acquired and processed by means of the Nomad Plus portable spectrometer connected to a computer. As a gamma ray sources 137Cs and 60Co are used whose spectra drawn and used for study the interaction of the gamma radiations with the scintillation detector. The parameters which varied during the acquisition of the gamma ray spectra are the distance between source and detector and the measuring time. Due to the statistical processes in the detector, the peak looks like a Gauss distribution. The identification of the gamma quantum energy value is achieved by the experimental spectra peaks, thus gathering information about the position of the peak, the width and the area of the peak respectively. By means of the EGS4 program a simulation is run using these parameters and an 'ideal' spectrum is obtained, a spectrum which is not influenced by the statistical processes which take place inside the detector. Then, the convolution of the spectra is achieved by means of a normalised Gauss function. There is a close match between the experimental results and those simulated in the EGS4 program because the interactions which occurred during the simulation have a statistical behaviour close to the real one. (authors)
Monte Carlo simulations and benchmark studies at CERN's accelerator chain
AUTHOR|(CDS)2083190; Brugger, Markus
2015-01-01
Mixed particle and energy radiation fields present at the Large Hadron Collider (LHC) and its accelerator chain are responsible for failures on electronic devices located in the vicinity of the accelerator beam lines. These radiation effects on electronics and, more generally, the overall radiation damage issues have a direct impact on component and system lifetimes, as well as on maintenance requirements and radiation exposure to personnel who have to intervene and fix existing faults. The radiation environments and respective radiation damage issues along the CERN’s accelerator chain were studied in the framework of the CERN Radiation to Electronics (R2E) project and are hereby presented. The important interplay between Monte Carlo simulations and radiation monitoring is also highlighted.
A Monte Carlo simulation study of branched polymers.
Yethiraj, Arun
2006-11-28
Monte Carlo simulations are presented for the static properties of highly branched polymer molecules. The molecules consist of a semiflexible backbone of hard-sphere monomers with semiflexible side chains, also composed of hard-sphere monomers, attached to either every backbone bead or every other backbone bead. The conformational properties and structure factor of this model are investigated as a function of the stiffness of the backbone and side chains. The average conformations of the side chains are similar to self-avoiding random walks. The simulations show that there is a stiffening of the backbone as degree of crowding is increased, for example, if the branch spacing is decreased or side chain length is increased. The persistence length of the backbone is relatively insensitive to the stiffness of the side chains over the range investigated. The simulations reproduce most of the qualitative features of the structure factor observed in experiment, although the magnitude of the stiffening of the backbone is smaller than in experiment. PMID:17144734
Study of the quantitative analysis approach of maintenance by the Monte Carlo simulation method
International Nuclear Information System (INIS)
This study is examination of the quantitative valuation by Monte Carlo simulation method of maintenance activities of a nuclear power plant. Therefore, the concept of the quantitative valuation of maintenance that examination was advanced in the Japan Society of Maintenology and International Institute of Universality (IUU) was arranged. Basis examination for quantitative valuation of maintenance was carried out at simple feed water system, by Monte Carlo simulation method. (author)
Using Monte Carlo simulations to commission photon beam output factors: a feasibility study
International Nuclear Information System (INIS)
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
Monte Carlo simulations for generic granite repository studies
International Nuclear Information System (INIS)
In a collaborative study between Los Alamos National Laboratory (LANL) and Sandia National Laboratories (SNL) for the DOE-NE Office of Fuel Cycle Technologies Used Fuel Disposition (UFD) Campaign project, we have conducted preliminary system-level analyses to support the development of a long-term strategy for geologic disposal of high-level radioactive waste. A general modeling framework consisting of a near- and a far-field submodel for a granite GDSE was developed. A representative far-field transport model for a generic granite repository was merged with an integrated systems (GoldSim) near-field model. Integrated Monte Carlo model runs with the combined near- and farfield transport models were performed, and the parameter sensitivities were evaluated for the combined system. In addition, a sub-set of radionuclides that are potentially important to repository performance were identified and evaluated for a series of model runs. The analyses were conducted with different waste inventory scenarios. Analyses were also conducted for different repository radionuelide release scenarios. While the results to date are for a generic granite repository, the work establishes the method to be used in the future to provide guidance on the development of strategy for long-term disposal of high-level radioactive waste in a granite repository.
Monte Carlo simulations for generic granite repository studies
Energy Technology Data Exchange (ETDEWEB)
Chu, Shaoping [Los Alamos National Laboratory; Lee, Joon H [SNL; Wang, Yifeng [SNL
2010-12-08
In a collaborative study between Los Alamos National Laboratory (LANL) and Sandia National Laboratories (SNL) for the DOE-NE Office of Fuel Cycle Technologies Used Fuel Disposition (UFD) Campaign project, we have conducted preliminary system-level analyses to support the development of a long-term strategy for geologic disposal of high-level radioactive waste. A general modeling framework consisting of a near- and a far-field submodel for a granite GDSE was developed. A representative far-field transport model for a generic granite repository was merged with an integrated systems (GoldSim) near-field model. Integrated Monte Carlo model runs with the combined near- and farfield transport models were performed, and the parameter sensitivities were evaluated for the combined system. In addition, a sub-set of radionuclides that are potentially important to repository performance were identified and evaluated for a series of model runs. The analyses were conducted with different waste inventory scenarios. Analyses were also conducted for different repository radionuelide release scenarios. While the results to date are for a generic granite repository, the work establishes the method to be used in the future to provide guidance on the development of strategy for long-term disposal of high-level radioactive waste in a granite repository.
International Nuclear Information System (INIS)
In the report, research results discussed in 1999 fiscal year at Nuclear Code Evaluation Committee of Nuclear Code Research Committee were summarized. Present status of Monte Carlo simulation on nuclear energy study was described. Especially, besides of criticality, shielding and core analyses, present status of applications to risk and radiation damage analyses, high energy transport and nuclear theory calculations of Monte Carlo Method was described. The 18 papers are indexed individually. (J.P.N.)
Kim, Su-Young
2012-01-01
Just as growth mixture models are useful with single-phase longitudinal data, multiphase growth mixture models can be used with multiple-phase longitudinal data. One of the practically important issues in single- and multiphase growth mixture models is the sample size requirements for accurate estimation. In a Monte Carlo simulation study, the…
Local dose enhancement in radiation therapy: Monte Carlo simulation study
International Nuclear Information System (INIS)
The development of nanotechnology has boosted the use of nanoparticles in radiation therapy in order to achieve greater therapeutic ratio between tumor and healthy tissues. Gold has been shown to be most suitable to this task due to the high biocompatibility and high atomic number, which contributes to a better in vivo distribution and for the local energy deposition. As a result, this study proposes to study, nanoparticle in the tumor cell. At a range of 11 nm from the nanoparticle surface, results have shown an absorbed dose 141 times higher for the medium with the gold nanoparticle compared to the water for an incident energy spectrum with maximum photon energy of 50 keV. It was also noted that when only scattered radiation is interacting with the gold nanoparticles, the dose was 134 times higher compared to enhanced local dose that remained significant even for scattered radiation. (author)
International Nuclear Information System (INIS)
There are several methods of measuring radon concentrations but nuclear track detector cylindrical dosimeters are widely employed. In this investigation, the consequence of effective volumes of the dosimeters on the registration of alpha tracks in a CR-39 detector was studied. In a series of experiments an optimum radius for a CR-39-based open cylindrical radon dosimeter was found to be about 3 cm. Monte Carlo simulation techniques hav been employed to verify the experimental results. In this context, a computer code Monte Carlo simulation dosimetry (MOCSID) was developed. Monte Carlo simulation experiments gave the optimum radius of the dosimeters as 3.0 cm. The experimental results are in good agreement with those obtained by Monte Carlo design calculations. In addition to this, plate-out effects of radon progeny were also studied. It was observed that the contribution of radon progeny (218Po and 214Po) plated-out on the wall of the dosimeters increases with an increase of dosimeter radii and then decrease to 0 at a radius of about 3 cm if a point detector has been installed at the center of the dosimeter base. In the code MOCSID different types of random number generators were employed. The results of this research are very useful for designing an optimum size of radon dosimeters
International Nuclear Information System (INIS)
Purpose: To validate the MCNPX Monte Carlo simulation for radiobiologic studies of megavoltage grid radiotherapy. Methods and Materials: EDR2 films, a scanning water phantom with microionization chamber and MCNPX Monte Carlo code, were used to study the dosimetric characteristics of a commercially available megavoltage grid therapy collimator. The measured dose profiles, ratios between maximum and minimum doses at 1.5 cm depth, and percentage depth dose curve were compared with those obtained in the simulations. The simulated two-dimensional dose profile and the linear-quadratic formalism of cell survival were used to calculate survival statistics of tumor and normal cells for the treatment of melanoma with a list of doses of the fractionated grid therapy. Results: A good agreement between the simulated and measured dose data was found. The therapeutic ratio based on normal cell survival has been defined and calculated for treating both the acute and late responding melanoma tumors. The grid therapy in this study was found to be advantageous for treating the acutely responding tumors, but not for late responding tumors. Conclusions: Monte Carlo technique was demonstrated to be able to provide the dosimetric characteristics for grid therapy. The therapeutic ratio was dependent not only on the single α/β value, but also on the individual α and β values. Acutely responding tumors and radiosensitive normal tissues are more suitable for using the grid therapy
Domain-growth kinetics and aspects of pinning: A Monte Carlo simulation study
DEFF Research Database (Denmark)
Castán, T.; Lindgård, Per-Anker
1991-01-01
By means of Monte Carlo computer simulations we study the domain-growth kinetics after a quench across a first-order line to very low and moderate temperatures in a multidegenerate system with nonconserved order parameter. The model is a continuous spin model relevant for martensitic transformati......By means of Monte Carlo computer simulations we study the domain-growth kinetics after a quench across a first-order line to very low and moderate temperatures in a multidegenerate system with nonconserved order parameter. The model is a continuous spin model relevant for martensitic...... transformations, surface reconstructions, and magnetic transitions. No external impurities are introduced, but the model has a number of intrinsic, annealable pinning mechanisms, which strongly influences the growth kinetics. It allows a study of pinning effects of three kinds: (a) pinning of domain walls by...
Dynamic phase transitions in a ferromagnetic thin film system: A Monte Carlo simulation study
International Nuclear Information System (INIS)
Dynamic phase transition properties of a ferromagnetic thin film system under the influence of both bias and time-dependent magnetic fields have been elucidated by means of kinetic Monte Carlo simulation with local spin update Metropolis algorithm. The obtained results after a detailed analysis suggest that the bias field is the conjugate field to dynamic order parameter, and it also appears to define a phase line between two antiparallel dynamic ordered states depending on the considered system parameters. Moreover, the data presented in this study well qualitatively reproduce the recently published experimental findings where time-dependent magnetic behavior of a uniaxial cobalt films is studied in the neighborhood of dynamic phase transition point. - Highlights: • A ferromagnetic thin film system is examined. • The system is exposed to both bias and time-dependent magnetic fields. • Kinetic Monte Carlo simulation technique is used. • Bias field is the conjugate field to the dynamic order parameter
International Nuclear Information System (INIS)
Monte Carlo simulation has been used to study the critical behaviors and the magnetic properties of a ferromagnetic thin Ising film with a plaquette four spin interaction. The effects of the ratio rs=Js/J of the surface exchange interaction to the bulk one and the four spin interaction on phase diagrams are investigated. A number of characteristic behaviors have been found, which include the first- and second-order phase transitions, thus also the tricritical points, triple point and isolated critical point. - Highlights: ► The magnetic behavior of an Ising ferromagnetic film has been studied using Monte Carlo simulation. ► The effects of the four spin interaction on the phase diagrams have been examined. ► The thermal variations of magnetizations have been investigated. ► The dependence of the total susceptibility on the temperature is investigated
M. Valiskó; D. Boda
2005-01-01
A systematic Monte Carlo (MC) simulation and perturbation theoretical (PT) study is reported for the dielectric constant of the polarizable dipolar hard sphere (PDHS) fluid. We take the polarizability of the molecules into account in two different ways. In a continuum approach we place the permanent dipole of the molecule into a sphere of dielectric constant ε∞ in the spirit of Onsager. The high frequency dielectric constant ε∞ is calculated from the Clausius-Mosotti relation, while the diele...
The proton therapy nozzles at Samsung Medical Center: A Monte Carlo simulation study using TOPAS
Chung, Kwangzoo; Kim, Jinsung; Kim, Dae-Hyun; Ahn, Sunghwan; Han, Youngyih
2015-07-01
To expedite the commissioning process of the proton therapy system at Samsung Medical Center (SMC), we have developed a Monte Carlo simulation model of the proton therapy nozzles by using TOol for PArticle Simulation (TOPAS). At SMC proton therapy center, we have two gantry rooms with different types of nozzles: a multi-purpose nozzle and a dedicated scanning nozzle. Each nozzle has been modeled in detail following the geometry information provided by the manufacturer, Sumitomo Heavy Industries, Ltd. For this purpose, the novel features of TOPAS, such as the time feature or the ridge filter class, have been used, and the appropriate physics models for proton nozzle simulation have been defined. Dosimetric properties, like percent depth dose curve, spreadout Bragg peak (SOBP), and beam spot size, have been simulated and verified against measured beam data. Beyond the Monte Carlo nozzle modeling, we have developed an interface between TOPAS and the treatment planning system (TPS), RayStation. An exported radiotherapy (RT) plan from the TPS is interpreted by using an interface and is then translated into the TOPAS input text. The developed Monte Carlo nozzle model can be used to estimate the non-beam performance, such as the neutron background, of the nozzles. Furthermore, the nozzle model can be used to study the mechanical optimization of the design of the nozzle.
International Nuclear Information System (INIS)
The results of Monte Carlo simulation studies of the timing calibration accuracy required by the NEMO underwater neutrino telescope are presented. The NEMO Collaboration is conducting a long term R and D activity toward the installation of a km3 apparatus in the Mediterranean Sea. An optimal site has been found and characterized at 3500 m depth off the Sicilian coast. Monte Carlo simulation shows that the angular resolution of the telescope remains approximately unchanged if the offset errors of timing calibration are less than 1 ns. This value is tolerable because the apparatus performance is not significantly changed when such inaccuracies are added to the other sources of error (e.g., the accuracy position of optical modules). We also discuss the optical background rate effect on the angular resolution of the apparatus and we compare the present version of the NEMO telescope with a different configuration.
Optimization of Monte Carlo simulations
Bryskhe, Henrik
2009-01-01
This thesis considers several different techniques for optimizing Monte Carlo simulations. The Monte Carlo system used is Penelope but most of the techniques are applicable to other systems. The two mayor techniques are the usage of the graphics card to do geometry calculations, and raytracing. Using graphics card provides a very efficient way to do fast ray and triangle intersections. Raytracing provides an approximation of Monte Carlo simulation but is much faster to perform. A program was ...
Radiation doses in volume-of-interest breast computed tomography—A Monte Carlo simulation study
Energy Technology Data Exchange (ETDEWEB)
Lai, Chao-Jen, E-mail: cjlai3711@gmail.com; Zhong, Yuncheng; Yi, Ying; Wang, Tianpeng; Shaw, Chris C. [Department of Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030-4009 (United States)
2015-06-15
Purpose: Cone beam breast computed tomography (breast CT) with true three-dimensional, nearly isotropic spatial resolution has been developed and investigated over the past decade to overcome the problem of lesions overlapping with breast anatomical structures on two-dimensional mammographic images. However, the ability of breast CT to detect small objects, such as tissue structure edges and small calcifications, is limited. To resolve this problem, the authors proposed and developed a volume-of-interest (VOI) breast CT technique to image a small VOI using a higher radiation dose to improve that region’s visibility. In this study, the authors performed Monte Carlo simulations to estimate average breast dose and average glandular dose (AGD) for the VOI breast CT technique. Methods: Electron–Gamma-Shower system code-based Monte Carlo codes were used to simulate breast CT. The Monte Carlo codes estimated were validated using physical measurements of air kerma ratios and point doses in phantoms with an ion chamber and optically stimulated luminescence dosimeters. The validated full cone x-ray source was then collimated to simulate half cone beam x-rays to image digital pendant-geometry, hemi-ellipsoidal, homogeneous breast phantoms and to estimate breast doses with full field scans. 13-cm in diameter, 10-cm long hemi-ellipsoidal homogeneous phantoms were used to simulate median breasts. Breast compositions of 25% and 50% volumetric glandular fractions (VGFs) were used to investigate the influence on breast dose. The simulated half cone beam x-rays were then collimated to a narrow x-ray beam with an area of 2.5 × 2.5 cm{sup 2} field of view at the isocenter plane and to perform VOI field scans. The Monte Carlo results for the full field scans and the VOI field scans were then used to estimate the AGD for the VOI breast CT technique. Results: The ratios of air kerma ratios and dose measurement results from the Monte Carlo simulation to those from the physical
International Nuclear Information System (INIS)
The resulting neutron captures in 10B are used for radiation therapy. The occurrence point of the characteristic 478 keV prompt gamma rays agrees with the neutron capture point. If these prompt gamma rays are detected by external instruments such as a gamma camera or single photon emission computed tomography (SPECT), the therapy region can be monitored during the treatment using images. A feasibility study and analysis of a reconstructed image using many projections (128) were conducted. The optimization of the detection system and a detailed neutron generator simulation were beyond the scope of this study. The possibility of extracting a 3D BNCT-SPECT image was confirmed using the Monte Carlo simulation and OSEM algorithm. The quality of the prompt gamma ray SPECT image obtained from BNCT was evaluated quantitatively using three different boron uptake regions and was shown to depend on the location and size relations. The prospects for obtaining an actual BNCT-SPECT image were also estimated from the quality of the simulated image and the simulation conditions. When multi tumor regions should be treated using the BNCT method, a reasonable model to determine how many useful images can be obtained from SPECT can be provided to the BNCT facilities based on the preceding imaging research. However, because the scope of this research was limited to checking the feasibility of 3D BNCT-SPECT image reconstruction using multiple projections, along with an evaluation of the image, some simulation conditions were taken from previous studies. In the future, a simulation will be conducted that includes optimized conditions for an actual BNCT facility, along with an imaging process for motion correction in BNCT. Although an excessively long simulation time was required to obtain enough events for image reconstruction, the feasibility of acquiring a 3D BNCT-SPECT image using multiple projections was confirmed using a Monte Carlo simulation, and a quantitative image analysis was
A study on the radioactivity analysis of decommissioning concrete using Monte Carlo simulation
International Nuclear Information System (INIS)
In order to decommission the shielding concrete of KRR(Korea Research Reactor)-1 and 2, it must be exactly determined activated level and range by neutron irradiation during operation. To determine the activated level and range, it must be sampled and analyzed the core sample. But, there are difficulties in sample preparation and determination of the measurement efficiency by self-absorption. In the study, the full energy efficiency of the HPGe detector was compared with the measured value using standard source and the calculated one using Monte Carlo simulation. Also, self-absorption effects due to the density and component change of the concrete were calculated using the Monte Carlo method. Its results will be used radioactivity analysis of the real concrete core sample in the future
A study on the radioactivity analysis of decommissioning concrete using Monte Carlo simulation
Energy Technology Data Exchange (ETDEWEB)
Seo, Bum Kyoung; Kim, Gye Hong; Chung, Un Soo; Lee, Keun Woo; Oh, Won Zin; Park, Jin Ho [KAERI, Taejon (Korea, Republic of)
2004-07-01
In order to decommission the shielding concrete of KRR(Korea Research Reactor)-1 and 2, it must be exactly determined activated level and range by neutron irradiation during operation. To determine the activated level and range, it must be sampled and analyzed the core sample. But, there are difficulties in sample preparation and determination of the measurement efficiency by self-absorption. In the study, the full energy efficiency of the HPGe detector was compared with the measured value using standard source and the calculated one using Monte Carlo simulation. Also, self-absorption effects due to the density and component change of the concrete were calculated using the Monte Carlo method. Its results will be used radioactivity analysis of the real concrete core sample in the future.
Study of the effect of usual heterogeneities in brachytherapy using Monte Carlo simulation
International Nuclear Information System (INIS)
The majority of current planning in brachytherapy systems don't count the composition of materials they form applicators, or the characteristics of the main interfaces present in the treatments. The objective of this study It is to compare the dosimetry distributions obtained by Monte Carlo simulations in geometric mannequins that they represent general features of the treatments that we find in our clinical practice, with results calculated according to the TG-43 formalism based on the existing consensus data for Ir-192 mHDR-v2 source. (Author)
Institute of Scientific and Technical Information of China (English)
WANG Mao-Xiang
2009-01-01
We use dynamic Monte Carlo simulations to study the athermal relaxation of bulk extended chains and the isothermal crystallization in intermediately relaxed melts. It is found that the memory of chain orientations in the melt can significantly enhance the crystallization rates. The crystal orientation and lamellar thickness essentially depend on the orientational relaxation. Moreover, there is a transition of the nucleation mechanism during the isothermal crystallization from the intermediately relaxed melts. These results explain the mechanism of the self-nucleation by orientation and suggest that in flow-induced polymer crystallization, the orientational relaxation of chains decides the crystal orientation.
International Nuclear Information System (INIS)
The main goal of this work is focused on testing the applicability of Geant4 electromagnetic models for studying mass attenuations for different types of composite materials at 59.5, 80, 356, 661.6, 1173.2 and 1332.5 keV photon energies. The simulated results of mass attenuation coefficients were compared with the experimental and theoretical data for the same samples and a good agreement has been observed. The results indicate that this process can be followed to determine the data on the attenuation of gamma-rays with the several energies in different materials. - Highlights: • We measure mass attenuation of gamma rays through different materials. • We model a design of a simple model using Geant-4 Monte Carlo Simulation for calculating mass attenuation of different composite materials. • We compare the model with the theoretical calculation of NIST XCOM code
Kadoura, Ahmad
2011-06-06
Lennard‐Jones (L‐J) and Buckingham exponential‐6 (exp‐6) potential models were used to produce isotherms for methane at temperatures below and above critical one. Molecular simulation approach, particularly Monte Carlo simulations, were employed to create these isotherms working with both canonical and Gibbs ensembles. Experiments in canonical ensemble with each model were conducted to estimate pressures at a range of temperatures above methane critical temperature. Results were collected and compared to experimental data existing in literature; both models showed an elegant agreement with the experimental data. In parallel, experiments below critical temperature were run in Gibbs ensemble using L‐J model only. Upon comparing results with experimental ones, a good fit was obtained with small deviations. The work was further developed by adding some statistical studies in order to achieve better understanding and interpretation to the estimated quantities by the simulation. Methane phase diagrams were successfully reproduced by an efficient molecular simulation technique with different potential models. This relatively simple demonstration shows how powerful molecular simulation methods could be, hence further applications on more complicated systems are considered. Prediction of phase behavior of elemental sulfur in sour natural gases has been an interesting and challenging field in oil and gas industry. Determination of elemental sulfur solubility conditions helps avoiding all kinds of problems caused by its dissolution in gas production and transportation processes. For this purpose, further enhancement to the methods used is to be considered in order to successfully simulate elemental sulfur phase behavior in sour natural gases mixtures.
International Nuclear Information System (INIS)
The coincidence Doppler broadening (CDB) technique in positron annihilation studies is used to study the momentum distribution of the electrons with which the positrons are annihilating. The relative momentum distribution curves of different samples become reliable under stringent stability conditions of the acquisition system. The CDB spectra were simulated by Monte Carlo method to study the effect of various instrumental parameters on the information extracted from CDB spectra. (author)
Solvent effect on Rb+ to K+ ion mutation: Monte Carlo simulation study
International Nuclear Information System (INIS)
The solvent effects on the relative free energies of solvation and the difference in partition coefficients (log P) for Rb+ to K+ mutation in several solvents have been investigated using Monte Carlo simulation (MCS) of statistical perturbation theory (SPT). In comparing the relative free energies for interconversion of one ion pair, Rb+ to K+, in H2O (TIP4P) in this study with the relative free energies of the computer simulations and the experimental, we found that the figure in this study is -5.00 ± 0.11 kcal/mol. There is good agreement among various studies, taking into account both methods used to obtain the hydration free energies and standard deviations. There is also good agreement between the calculated structural properties of this study and the simulations, ab initio and the experimental results. We have explained the deviation of the relationship between the free energy difference and the Onsager dielectric function of solvents by the electron pair donor properties of the solvents. For the Rb+ and K+ ion pair, the Onsager dielectric function of solvents (or solvent permittivity), donor number of solvent and the differences in solvation dominate the differences in the relative free energies of solvation and partition coefficients
Computed tomography with a low-intensity proton flux: results of a Monte Carlo simulation study
Schulte, Reinhard W.; Klock, Margio C. L.; Bashkirov, Vladimir; Evseev, Ivan G.; de Assis, Joaquim T.; Yevseyeva, Olga; Lopes, Ricardo T.; Li, Tianfang; Williams, David C.; Wroe, Andrew J.; Schelin, Hugo R.
2004-10-01
Conformal proton radiation therapy requires accurate prediction of the Bragg peak position. This problem may be solved by using protons rather than conventional x-rays to determine the relative electron density distribution via proton computed tomography (proton CT). However, proton CT has its own limitations, which need to be carefully studied before this technique can be introduced into routine clinical practice. In this work, we have used analytical relationships as well as the Monte Carlo simulation tool GEANT4 to study the principal resolution limits of proton CT. The GEANT4 simulations were validated by comparing them to predictions of the Bethe Bloch theory and Tschalar's theory of energy loss straggling, and were found to be in good agreement. The relationship between phantom thickness, initial energy, and the relative electron density uncertainty was systematically investigated to estimate the number of protons and dose needed to obtain a given density resolution. The predictions of this study were verified by simulating the performance of a hypothetical proton CT scanner when imaging a cylindrical water phantom with embedded density inhomogeneities. We show that a reasonable density resolution can be achieved with a relatively small number of protons, thus providing a possible dose advantage over x-ray CT.
Monte Carlo simulation study of melittin: Protein folding and temperature dependence
Monajjemi, M.; Ketabi, S.; Amiri, A.
2006-11-01
The tetramerization of melittin, a 26-amino-acid peptide, is considered as a model for protein folding. The Monte Carlo simulation was used to study the folding arrangement of melittin, and the results are compared with the experiment. An acceptance rate of 50% for new configurations is achieved by using ranges of ±0.001 Å for the translations and ±15°C for the rotations. Around 311 K, the folded structure of the protein has the greatest stability; the range from -40 to -80 shows the best ϕ angles for melittin. The final optimized structure of melittin strongly depends on the temperature. The melittin tetramer is found to have a temperature of maximum stability ranging from 35.5 to 43°C.
Study of dose distribution in dental radiology using the Monte Carlo Simulation
International Nuclear Information System (INIS)
Full text: The purpose of this study was to study the absorbed dose in mouth due to scattering in teeth in dental radiography using the monte carlo simulation. The Electron Gamma Shower (EGS-4) system of computer codes was used, which is a general purpose package for monte carlo simulation of the coupled transport of electrons and photons in an arbitrary geometry for particles with energies above a few keV up to several TeV. In the case of a X ray dental the low energy photons beam, are removed of the spectrum by the filtration. These low energy photons beam do not contribute in the obtaining of the radiographic image, but they will be contribute in the dose to the patient, however when the incident radiation crosses the tooth it generates a scattering radiation that contributes in the dose received by the patient in the oral cavity (cheek, tooth and oral cavity). Dental radiography is one of the largest single groups of radiographic examination accounting for 32% of radiographs taken in the Brazil. A number of relatively recent improvements in technology, equipment and techniques have the potential to reduce patient radiation dose and improve image quality. To optimize radiation protection all reasonable means should be employed to minimize the dose of each exposure. Dentists therefore need to keep up to date with changes in techniques and equipment and modify their own practice. In preliminary analysis could be notice that the energy below the 30 keV (low energy) is deposited in the cheek. To 30 keV photons there is the maximum absorbed energy in the tooth (about 60%). In 40 keV could be notice that deposited energy is same to teeth and cheek, but up to 40 keV just a small part of energy is deposited, e.g., the great part of energy is transmitted to the inner mouth (oral cavity). (orig.)
International Nuclear Information System (INIS)
Using fast lattice Monte Carlo (FLMC) simulations [Q. Wang, Soft Matter 5, 4564 (2009)] and the corresponding lattice self-consistent field (LSCF) calculations, we studied a model system of grafted homopolymers, in both the brush and mushroom regimes, in an explicit solvent compressed by an impenetrable surface. Direct comparisons between FLMC and LSCF results, both of which are based on the same Hamiltonian (thus without any parameter-fitting between them), unambiguously and quantitatively reveal the fluctuations/correlations neglected by the latter. We studied both the structure (including the canonical-ensemble averages of the height and the mean-square end-to-end distances of grafted polymers) and thermodynamics (including the ensemble-averaged reduced energy density and the related internal energy per chain, the differences in the Helmholtz free energy and entropy per chain from the uncompressed state, and the pressure due to compression) of the system. In particular, we generalized the method for calculating pressure in lattice Monte Carlo simulations proposed by Dickman [J. Chem. Phys. 87, 2246 (1987)], and combined it with the Wang-Landau–Optimized Ensemble sampling [S. Trebst, D. A. Huse, and M. Troyer, Phys. Rev. E 70, 046701 (2004)] to efficiently and accurately calculate the free energy difference and the pressure due to compression. While we mainly examined the effects of the degree of compression, the distance between the nearest-neighbor grafting points, the reduced number of chains grafted at each grafting point, and the system fluctuations/correlations in an athermal solvent, the θ-solvent is also considered in some cases
Phase transitions of bulk statistical copolymers studied by dynamic Monte Carlo simulations
Hu, W.; Mathot, V.B.F.; Frenkel, D.
2003-01-01
We report a numerical study of crystallization and melting in bulk statistical homogeneous (random), homogeneous (slightly alternating), and heterogeneous (produced in a batch reaction) copolymers formed by crystallizable monomers and noncrystallizable comonomers. In our dynamic Monte Carlo simulati
Proton Upset Monte Carlo Simulation
O'Neill, Patrick M.; Kouba, Coy K.; Foster, Charles C.
2009-01-01
The Proton Upset Monte Carlo Simulation (PROPSET) program calculates the frequency of on-orbit upsets in computer chips (for given orbits such as Low Earth Orbit, Lunar Orbit, and the like) from proton bombardment based on the results of heavy ion testing alone. The software simulates the bombardment of modern microelectronic components (computer chips) with high-energy (.200 MeV) protons. The nuclear interaction of the proton with the silicon of the chip is modeled and nuclear fragments from this interaction are tracked using Monte Carlo techniques to produce statistically accurate predictions.
Directory of Open Access Journals (Sweden)
M.Valiskó
2005-01-01
Full Text Available A systematic Monte Carlo (MC simulation and perturbation theoretical (PT study is reported for the dielectric constant of the polarizable dipolar hard sphere (PDHS fluid. We take the polarizability of the molecules into account in two different ways. In a continuum approach we place the permanent dipole of the molecule into a sphere of dielectric constant ε∞ in the spirit of Onsager. The high frequency dielectric constant ε∞ is calculated from the Clausius-Mosotti relation, while the dielectric constant of the polarizable fluid is obtained from the Kirkwood-Fröhlich equation. In the molecular approach, the polarizability is built into the model on the molecular level, which makes the interactions non-pairwise additive. Here we use Wertheim's renormalized PT method to calculate the induced dipole moment, while the dielectric constant is calculated from our recently introduced formula. We also apply a series expansion for the dielectric constant both in the continuum and the molecular approach. These series expansions ensure a better agreement with simulation results. The agreement between our MC data and the PT results in the molecular approach is excellent for low to moderate dipole moments and polarizabilities. At stronger dipolar interactions ergodicity problems and anizotropic behaviour appear where simulation results become uncertain and the theoretical approach becomes invalid.
Directory of Open Access Journals (Sweden)
Amharrak H.
2016-01-01
Full Text Available The nuclear heating measurements in Material Testing Reactors (MTRs are crucial for the study of nuclear materials and fuels under irradiation. The reference measurements of this nuclear heating are especially performed by a differential calorimeter including a graphite sample material. Then these measurements are used for other materials, other geometries, or other experimental conditions in order to predict the nuclear heating and thermal conditions induced in the irradiation devices. This paper will present new simulations with MCNP Monte-Carlo transport code to determine the gamma heating profile inside the calorimeter. The whole complex geometry of the sensor has been considered. We use as an input source in the model, the photon spectra calculated in various positions of CARMEN-1 irradiation program in OSIRIS reactor. After a description of the differential calorimeter device, the MCNP modeling used for the calculations of radial profile of nuclear heating inside the calorimeter elements will be introduced. The obtained results of different simulations will be detailed and discussed in this paper. The charged particle equilibrium inside the calorimeter elements will be studied. Then we will focus on parametric studies of the various components of the calorimeter. The influence of source type will be also took into account. Moreover the influence of the material used for the sample will be described.
International Nuclear Information System (INIS)
Uranium hexafluoride physical adsorption on armchair carbon nano tubes is studied with Monte Carlo Simulations in a wide range of temperatures and pressures. All of the particle particle interaction are modeled with Lennard-Jones potential. We have written a FORTRAN program for Monte Carlo simulation and then calculated the inside density of carbon nano tube, out side density of carbon nano tube and total density of carbon nano tube. The conclusions drown from theses calculations are then contrasted and compared. Result show that the total amount of uranium hexafluoride adsorption on single-walled carbon nano tube, increases with high pressure and low temperature
Hysteresis loop behaviors of ferroelectric thin films:A Monte Carlo simulation study
Institute of Scientific and Technical Information of China (English)
C. M. Bedoya-Hincapi´e; H. H. Ortiz-´Alvarez; E. Restrepo-Parra; J. J. Olaya-Fl´orez; J. E. Alfonso
2015-01-01
The ferroelectric response of bismuth titanate Bi4Ti3O12 (BIT) thin film is studied through a Monte Carlo simulation of hysteresis loops. The ferroelectric system is described by using a Diffour Hamiltonian with three terms: the electric field applied in the z direction, the nearest dipole–dipole interaction in the transversal (x–y) direction, and the nearest dipole–dipole interaction in the direction perpendicular to the thin film (the z axis). In the sample construction, we take into consideration the dipole orientations of the monoclinic and orthorhombic structures that can appear in BIT at low temperature in the ferroelectric state. The effects of temperature, stress, and the concentration of pinned dipole defects are assessed by using the hysteresis loops. The results indicate the changes in the hysteresis area with temperature and stress, and the asymmetric hysteresis loops exhibit evidence of the imprint failure mechanism with the emergence of pinned dipolar defects. The simulated shift in the hysteresis loops conforms to the experimental ferroelectric response.
Hysteresis loop behaviors of ferroelectric thin films: A Monte Carlo simulation study
M. Bedoya-Hincapié, C.; H. Ortiz-Álvarez, H.; Restrepo-Parra, E.; J. Olaya-Flórez, J.; E. Alfonso, J.
2015-11-01
The ferroelectric response of bismuth titanate Bi4Ti3O12 (BIT) thin film is studied through a Monte Carlo simulation of hysteresis loops. The ferroelectric system is described by using a Diffour Hamiltonian with three terms: the electric field applied in the z direction, the nearest dipole-dipole interaction in the transversal (x-y) direction, and the nearest dipole-dipole interaction in the direction perpendicular to the thin film (the z axis). In the sample construction, we take into consideration the dipole orientations of the monoclinic and orthorhombic structures that can appear in BIT at low temperature in the ferroelectric state. The effects of temperature, stress, and the concentration of pinned dipole defects are assessed by using the hysteresis loops. The results indicate the changes in the hysteresis area with temperature and stress, and the asymmetric hysteresis loops exhibit evidence of the imprint failure mechanism with the emergence of pinned dipolar defects. The simulated shift in the hysteresis loops conforms to the experimental ferroelectric response. Project sponsored by the research departments of the Universidad Nacional de Colombia DIMA and DIB under Project 201010018227-“Crecimiento y caracterización eléctrica y estructural de películas delgadas de BixTiyOz producidas mediante Magnetrón Sputtering” and Project 12920-“Desarrollo teóricoexperimental de nanoestructuras basadas en Bismuto y materiales similares” and “Bisnano Project.”
Monte Carlo simulation of the microcanonical ensemble
International Nuclear Information System (INIS)
We consider simulating statistical systems with a random walk on a constant energy surface. This combines features of deterministic molecular dynamics techniques and conventional Monte Carlo simulations. For discrete systems the method can be programmed to run an order of magnitude faster than other approaches. It does not require high quality random numbers and may also be useful for nonequilibrium studies. 10 references
A Monte Carlo simulation of photomultiplier resolution
International Nuclear Information System (INIS)
A Monte Carlo simulation of dynode statistics has been used to generate multiphotoelectron distributions to compare with actual photomultiplier resolution results. In place of Poission of Polya statistics, in this novel approach, the basis for the simulation is an experimentally determined single electron response. The relevance of this method to the study of intrinsic line widths of scintillators is discussed
Local and chain dynamics in miscible polymer blends: A Monte Carlo simulation study
Luettmer-Strathmann, Jutta; Mantina, Manjeera
2005-01-01
Local chain structure and local environment play an important role in the dynamics of polymer chains in miscible blends. In general, the friction coefficients that describe the segmental dynamics of the two components in a blend differ from each other and from those of the pure melts. In this work, we investigate polymer blend dynamics with Monte Carlo simulations of a generalized bond-fluctuation model, where differences in the interaction energies between non-bonded nearest neighbors distin...
Renormalization group studies and Monte Carlo simulation for quantum spin systems
International Nuclear Information System (INIS)
Extended application of various real-space renormalization group methods to quantum spin systems is discussed. At finite temperature, both the reliability and range of application of the decimation renormalization group method (DRG) are extended for calculating the thermal and magnetic properties of low-dimensional quantum spin chains, in which general models of the three-state Potts model and the general Heisenberg model are proposed. Some interesting finite-temperature behavior of the models was obtained. Also proposed is a general formula for the critical properties of the n-dimensional q-state Potts model by using a modified Migdal-Kadanoff approach which is in very good agreement with all available results for general q and d. For high-spin systems, the famous Haldane's prediction was studied by using a modified block renormalization group approach in spin-1/2, spin-1, and spin-3/2 cases. The results supports Haldane's prediction and a novel property of the spin-1 Heisenberg antiferromagnet has been predicted. A modified quantum Monte Carlo simulation approach was developed in this study and used to treat quantum interacting problems (only quantum spin systems are studied) without the negative sign problem
Quantum Monte Carlo simulation study of two-dimensional Hubbard model
International Nuclear Information System (INIS)
The physical properties of strongly correlated fermionic systems, described by two-dimensional Hubbard model with nearest neighbour hopping have been studied using the path integral formulation along with quantum Monte Carlo simulation technique. The partition function of the fermionic system is evaluated within the usual path integral formulation, treating β, the inverse temperature as imaginary time and dividing it into small discrete intervals. The singlet and triplet pairing correlation functions, nearest-neighbour charge density correlations, local squared magnetic moments, double occupancy and total energy are studied as a function of interaction strength for various band fillings at different temperatures. This study leads to the conclusions that the singlet pairing correlation decreases with increasing interaction strength. The triplet pairing correlations for parallel spins show abrupt behaviour. The extended singlet pairing correlation and triplet pairing correlations for anti-parallel spins show the slightly fluctuating behaviour of finite temperatures. The enhancement of local squared magnetic moment and decrement of double occupancy and increment of total energy with U at finite temperatures for half-filled, one-third-filled and one-fourth-filled bands are also noted. (author)
Monte Carlo simulation in proton computed tomography: a study of image reconstruction technique
Energy Technology Data Exchange (ETDEWEB)
Inocente, Guilherme Franco; Stenico, Gabriela V.; Hormaza, Joel Mesa [Universidade Estadual Paulista Julio de Mesquita Filho (UNESP), Botucatu, SP (Brazil). Inst. de Biociencias. Dept. de Fisica e Biofisica
2012-07-01
Full text: The radiation method is one of the most used for cancer treatment. In this context arises therapy with proton beams in front of conventional radiotherapy. It is known that with proton therapy there are more advantages to the patient treated when compared with more conventional methods. The dose distributed along the path, especially in healthy tissues - neighbor the tumor, is smaller and the accuracy of treatment is much better. To carry out the treatment, the patient undergoes a plan through images for visualization and location of the target volume. The main method for obtaining these images is computed tomography X-ray (XCT). For treatment with proton beam this imaging technique can to generate some uncertainties. The purpose of this project is to study the feasibility of reconstructing images generated from the irradiation with proton beams, thereby reducing some inaccuracies, as it will be the same type of radiation as treatment planning, and also to drastically reduce some errors location, since the planning can be done at the same place and just before where the patient is treated. This study aims to obtain a relationship between the intrinsic property of the interaction of photons and protons with matter. For this we use computational simulation based on Monte Carlo method with the code SRIM 2008 and MCNPX v.2.5.0, to reconstruct images using the technique used in conventional computed tomography. (author)
Concentrating bacterial cells using a ratchet system: a lattice Monte Carlo simulation study
Tao, Yuguo; Slater, Gary
2012-02-01
Rectification of motile E. coli bacteria has been observed in the presence of funnel-like channels. We present a lattice Monte Carlo model which takes into account both the size and the mechanical and thermodynamic properties of autonomous bacterial cells. The motion of the cells is composed of alternating run and tumble periods. We show that the rectification effect of the funnels is strongly dependent upon the effective random walk step length of the run/tumble cycle as well as the size of the funnel's aperture. Our results agree with experimental observations, and also confirm some conclusions from a previous simulation model of point-like bacteria. We also explore series of funnels as a means to pump and concentrate cells. We observe deviations from theoretical predictions when the size of the cells is comparable to that of the aperture of the funnel. The current model can be extended to study cells with different shapes, e.g. cigar-shape bacteria.
Energy Technology Data Exchange (ETDEWEB)
Quesada-Pérez, Manuel; Maroto-Centeno, José Alberto [Departamento de Física, Escuela Politécnica Superior de Linares, Universidad de Jaén, 23700 Linares, Jaén (Spain); Adroher-Benítez, Irene [Grupo de Física de Fluidos y Biocoloides, Departamento de Física Aplicada, Facultad de Ciencias, Universidad de Granada, 18071 Granada (Spain)
2014-05-28
In this work, the size-exclusion partitioning of neutral solutes in crosslinked polymer networks has been studied through Monte Carlo simulations. Two models that provide user-friendly expressions to predict the partition coefficient have been tested over a wide range of volume fractions: Ogston's model (especially devised for fibrous media) and the pore model. The effects of crosslinking and bond stiffness have also been analyzed. Our results suggest that the fiber model can acceptably account for size-exclusion effects in crosslinked gels. Its predictions are good for large solutes if the fiber diameter is assumed to be the effective monomer diameter. For solutes sizes comparable to the monomer dimensions, a smaller fiber diameter must be used. Regarding the pore model, the partition coefficient is poorly predicted when the pore diameter is estimated as the distance between adjacent crosslinker molecules. On the other hand, our results prove that the pore sizes obtained from the pore model by fitting partitioning data of swollen gels are overestimated.
Breast tomosynthesis with monochromatic beams: a feasibility study using Monte Carlo simulations
International Nuclear Information System (INIS)
The aim of this study is to investigate the impact on image quality of using monochromatic beams for lower dose breast tomosynthesis (BT). For this purpose, modeling and simulation of BT and mammography imaging processes have been performed using two x-ray beams: one at 28 kVp and a monochromatic one at 19 keV at different entrance surface air kerma ranging between 0.16 and 5.5 mGy. Two 4 cm thick computational breast models, in a compressed state, were used: one simple homogeneous and one heterogeneous based on CT breast images, with compositions of 50% glandular–50% adipose and 40% glandular–60% adipose tissues by weight, respectively. Modeled lesions, representing masses and calcifications, were inserted within these breast phantoms. X-ray transport in the breast models was simulated with previously developed and validated Monte Carlo application. Results showed that, for the same incident photon fluence, the use of the monochromatic beam in BT resulted in higher image quality compared to the one using polychromatic acquisition, especially in terms of contrast. For the homogenous phantom, the improvement ranged between 15% and 22% for calcifications and masses, respectively, while for the heterogeneous one this improvement was in the order of 33% for the masses and 17% for the calcifications. For different exposures, comparable image quality in terms of signal-difference-to-noise ratio and higher contrast for all features was obtained when using a monochromatic 19 keV beam at a lower mean glandular dose, compared to the polychromatic one. Monochromatic images also provide better detail and, in combination with BT, can lead to substantial improvement in visualization of features, and particularly better edge detection of low-contrast masses. (paper)
Breast tomosynthesis with monochromatic beams: a feasibility study using Monte Carlo simulations
Malliori, A.; Bliznakova, K.; Sechopoulos, I.; Kamarianakis, Z.; Fei, B.; Pallikarakis, N.
2014-08-01
The aim of this study is to investigate the impact on image quality of using monochromatic beams for lower dose breast tomosynthesis (BT). For this purpose, modeling and simulation of BT and mammography imaging processes have been performed using two x-ray beams: one at 28 kVp and a monochromatic one at 19 keV at different entrance surface air kerma ranging between 0.16 and 5.5 mGy. Two 4 cm thick computational breast models, in a compressed state, were used: one simple homogeneous and one heterogeneous based on CT breast images, with compositions of 50% glandular-50% adipose and 40% glandular-60% adipose tissues by weight, respectively. Modeled lesions, representing masses and calcifications, were inserted within these breast phantoms. X-ray transport in the breast models was simulated with previously developed and validated Monte Carlo application. Results showed that, for the same incident photon fluence, the use of the monochromatic beam in BT resulted in higher image quality compared to the one using polychromatic acquisition, especially in terms of contrast. For the homogenous phantom, the improvement ranged between 15% and 22% for calcifications and masses, respectively, while for the heterogeneous one this improvement was in the order of 33% for the masses and 17% for the calcifications. For different exposures, comparable image quality in terms of signal-difference-to-noise ratio and higher contrast for all features was obtained when using a monochromatic 19 keV beam at a lower mean glandular dose, compared to the polychromatic one. Monochromatic images also provide better detail and, in combination with BT, can lead to substantial improvement in visualization of features, and particularly better edge detection of low-contrast masses.
Energy Technology Data Exchange (ETDEWEB)
Kim, Moo-Sub; Jung, Joo-Young; Suh, Tae Suk [College of Medicine, Catholic University of Korea, Seoul (Korea, Republic of)
2015-05-15
The purpose of this research was the statistical analysis for discrimination of the prompt gamma ray peak induced by the 14.1 MeV neutron particles from spectra using Monte Carlo simulation. For the simulation, the information of the eighteen detector materials was used to simulate spectra by the neutron capture reaction. To the best of our knowledge, the results in this study are the first reported data regarding the peak discrimination of high energy prompt gamma ray using the many cases (the eighteen detector materials and the nine prompt gamma ray peaks). The reliable data based on the Monte Carlo method and statistical method with the identical conditions was deducted. Our results are important data in the PGAA study for the peak detection within actual experiments.
International Nuclear Information System (INIS)
The purpose of this research was the statistical analysis for discrimination of the prompt gamma ray peak induced by the 14.1 MeV neutron particles from spectra using Monte Carlo simulation. For the simulation, the information of the eighteen detector materials was used to simulate spectra by the neutron capture reaction. To the best of our knowledge, the results in this study are the first reported data regarding the peak discrimination of high energy prompt gamma ray using the many cases (the eighteen detector materials and the nine prompt gamma ray peaks). The reliable data based on the Monte Carlo method and statistical method with the identical conditions was deducted. Our results are important data in the PGAA study for the peak detection within actual experiments
A clinical study of lung cancer dose calculation accuracy with Monte Carlo simulation
International Nuclear Information System (INIS)
The accuracy of dose calculation is crucial to the quality of treatment planning and, consequently, to the dose delivered to patients undergoing radiation therapy. Current general calculation algorithms such as Pencil Beam Convolution (PBC) and Collapsed Cone Convolution (CCC) have shortcomings in regard to severe inhomogeneities, particularly in those regions where charged particle equilibrium does not hold. The aim of this study was to evaluate the accuracy of the PBC and CCC algorithms in lung cancer radiotherapy using Monte Carlo (MC) technology. Four treatment plans were designed using Oncentra Masterplan TPS for each patient. Two intensity-modulated radiation therapy (IMRT) plans were developed using the PBC and CCC algorithms, and two three-dimensional conformal therapy (3DCRT) plans were developed using the PBC and CCC algorithms. The DICOM-RT files of the treatment plans were exported to the Monte Carlo system to recalculate. The dose distributions of GTV, PTV and ipsilateral lung calculated by the TPS and MC were compared. For 3DCRT and IMRT plans, the mean dose differences for GTV between the CCC and MC increased with decreasing of the GTV volume. For IMRT, the mean dose differences were found to be higher than that of 3DCRT. The CCC algorithm overestimated the GTV mean dose by approximately 3% for IMRT. For 3DCRT plans, when the volume of the GTV was greater than 100 cm3, the mean doses calculated by CCC and MC almost have no difference. PBC shows large deviations from the MC algorithm. For the dose to the ipsilateral lung, the CCC algorithm overestimated the dose to the entire lung, and the PBC algorithm overestimated V20 but underestimated V5; the difference in V10 was not statistically significant. PBC substantially overestimates the dose to the tumour, but the CCC is similar to the MC simulation. It is recommended that the treatment plans for lung cancer be developed using an advanced dose calculation algorithm other than PBC. MC can accurately
International Nuclear Information System (INIS)
Computational Monte Carlo (MC) codes have been used for simulation of nuclear installations mainly for internal monitoring of workers, the well known as Whole Body Counters (WBC). The main goal of this project was the modeling and simulation of the counting efficiency (CE) of a WBC system using three different MC codes: MCNPX, EGSnrc and VMC in-vivo. The simulations were performed for three different groups of analysts. The results shown differences between the three codes, as well as in the results obtained by the same code and modeled by different analysts. Moreover, all the results were also compared to the experimental results obtained in laboratory for meaning of validation and final comparison. In conclusion, it was possible to detect the influence on the results when the system is modeled by different analysts using the same MC code and in which MC code the results were best suited, when comparing to the experimental data result. (author)
The Proton Therapy Nozzles at Samsung Medical Center: A Monte Carlo Simulation Study using TOPAS
Chung, Kwangzoo; Kim, Dae-Hyun; Ahn, Sunghwan; Han, Youngyih
2015-01-01
To expedite the commissioning process of the proton therapy system at Samsung Medical Center (SMC), we have developed a Monte Carlo simulation model of the proton therapy nozzles using TOPAS. At SMC proton therapy center, we have two gantry rooms with different types of nozzles; a multi-purpose nozzle and a dedicated scanning nozzle. Each nozzle has been modeled in detail following the geometry information provided by the manufacturer, Sumitomo Heavy Industries, Ltd. For this purpose, novel features of TOPAS, such as the time feature or the ridge filter class, have been used. And the appropriate physics models for proton nozzle simulation were defined. Dosimetric properties, like percent depth dose curve, spread-out Bragg peak (SOBP), beam spot size, have been simulated and verified against measured beam data. Beyond the Monte Carlo nozzle modeling, we have developed an interface between TOPAS and the treatment planning system (TPS), RayStation. An exported RT plan data from the TPS has been interpreted by th...
Jo, Byung-Du; Lee, Young-Jin; Kim, Dae-Hong; Kim, Hee-Joung
2014-08-01
In conventional digital radiography (DR) using a dual energy subtraction technique, a significant fraction of the detected photons are scattered within the body, making up the scatter component. Scattered radiation can significantly deteriorate image quality in diagnostic X-ray imaging systems. Various methods of scatter correction, including both measurement- and non-measurement-based methods, have been proposed in the past. Both methods can reduce scatter artifacts in images. However, non-measurement-based methods require a homogeneous object and have insufficient scatter component correction. Therefore, we employed a measurement-based method to correct for the scatter component of inhomogeneous objects from dual energy DR (DEDR) images. We performed a simulation study using a Monte Carlo simulation with a primary modulator, which is a measurement-based method for the DEDR system. The primary modulator, which has a checkerboard pattern, was used to modulate the primary radiation. Cylindrical phantoms of variable size were used to quantify the imaging performance. For scatter estimates, we used discrete Fourier transform filtering, e.g., a Gaussian low-high pass filter with a cut-off frequency. The primary modulation method was evaluated using a cylindrical phantom in the DEDR system. The scatter components were accurately removed using a primary modulator. When the results acquired with scatter correction and without scatter correction were compared, the average contrast-to-noise ratio (CNR) with the correction was 1.35 times higher than that obtained without the correction, and the average root mean square error (RMSE) with the correction was 38.00% better than that without the correction. In the subtraction study, the average CNR with the correction was 2.04 (aluminum subtraction) and 1.38 (polymethyl methacrylate (PMMA) subtraction) times higher than that obtained without the correction. The analysis demonstrated the accuracy of the scatter correction and the
Coded aperture optimization using Monte Carlo simulations
International Nuclear Information System (INIS)
Coded apertures using Uniformly Redundant Arrays (URA) have been unsuccessfully evaluated for two-dimensional and three-dimensional imaging in Nuclear Medicine. The images reconstructed from coded projections contain artifacts and suffer from poor spatial resolution in the longitudinal direction. We introduce a Maximum-Likelihood Expectation-Maximization (MLEM) algorithm for three-dimensional coded aperture imaging which uses a projection matrix calculated by Monte Carlo simulations. The aim of the algorithm is to reduce artifacts and improve the three-dimensional spatial resolution in the reconstructed images. Firstly, we present the validation of GATE (Geant4 Application for Emission Tomography) for Monte Carlo simulations of a coded mask installed on a clinical gamma camera. The coded mask modelling was validated by comparison between experimental and simulated data in terms of energy spectra, sensitivity and spatial resolution. In the second part of the study, we use the validated model to calculate the projection matrix with Monte Carlo simulations. A three-dimensional thyroid phantom study was performed to compare the performance of the three-dimensional MLEM reconstruction with conventional correlation method. The results indicate that the artifacts are reduced and three-dimensional spatial resolution is improved with the Monte Carlo-based MLEM reconstruction.
Fast Lattice Monte Carlo Simulations of Polymers
Wang, Qiang; Zhang, Pengfei
2014-03-01
The recently proposed fast lattice Monte Carlo (FLMC) simulations (with multiple occupancy of lattice sites (MOLS) and Kronecker δ-function interactions) give much faster/better sampling of configuration space than both off-lattice molecular simulations (with pair-potential calculations) and conventional lattice Monte Carlo simulations (with self- and mutual-avoiding walk and nearest-neighbor interactions) of polymers.[1] Quantitative coarse-graining of polymeric systems can also be performed using lattice models with MOLS.[2] Here we use several model systems, including polymer melts, solutions, blends, as well as confined and/or grafted polymers, to demonstrate the great advantages of FLMC simulations in the study of equilibrium properties of polymers.
Energy Technology Data Exchange (ETDEWEB)
Chow, James C. L.; Owrangi, Amir M. [Department of Radiation Physics, Princess Margaret Hospital and Department of Radiation Oncology, University of Toronto, Toronto, Ontario M5G 2M9 (Canada); Department of Physics, University of Waterloo, Waterloo, Ontario N2L 3G1 (Canada) and Department of Physics, Ryerson University, Toronto, Ontario M5B 2K3 (Canada); Department of Radiation Physics, Princess Margaret Hospital, Toronto, Ontario M5G 2M9 (Canada)
2009-02-15
This study investigated the depth dependence of electron backscatter from a layer of lead (Pb) for clinical electron beams. The change in the electron backscatter with variation in the water depth above the Pb was determined. Electron energy spectra and relative depth doses as a function of depth in water over the Pb layer were calculated using a Monte Carlo simulation and studied. Phase-space files for 4 and 9 MeV electron beams (10x10 cm{sup 2} applicator and cutout) based on the Varian 21 EX linear accelerator were generated using the EGSnrc-based BEAMNRC code. 3 mm of Pb, at depths of 0.5 and 1 cm in water, was irradiated with electrons. The source-to-surface distance is equal to 100 cm. Electron energy spectra and relative depth doses with and without the presence of the Pb layer at different depths in water were determined using the BEAMNRC code. For the 4 MeV electron energy spectra at a depth of 0.5 cm in water, electron backscatter was found to originate at the Pb-water interface and extend to 0.5 cm above the Pb insert. However, at a depth of 1 cm in water, electron backscatter almost disappeared at 0.5 and 1 cm above th ePb insert. This is due to the increased attenuation of the incident 4 MeV electron beam in a thicker layer of water as well as increased attenuation of the electron backscatter above the Pb. This resulted in a 23% decrease in relative dose at a measurement point of 0.5 cm depth, when the depth of the Pb insert was changed from 1 to 0.5 cm. For the electron energy spectra of the 9 MeV beams with a 0.5 cm depth of water, only a small amount of electron backscatter was observed. However, more electron backscatter was found when the water depth was increased to 1 cm. This is because the electron beam energy was decreased more due to the increase in attenuation from the increased depth of water compared to 0.5 cm. Since the electron energy spectrum and relative depth dose above the Pb layer vary with depth of water on top of the Pb, the
International Nuclear Information System (INIS)
This study investigated the depth dependence of electron backscatter from a layer of lead (Pb) for clinical electron beams. The change in the electron backscatter with variation in the water depth above the Pb was determined. Electron energy spectra and relative depth doses as a function of depth in water over the Pb layer were calculated using a Monte Carlo simulation and studied. Phase-space files for 4 and 9 MeV electron beams (10x10 cm2 applicator and cutout) based on the Varian 21 EX linear accelerator were generated using the EGSnrc-based BEAMNRC code. 3 mm of Pb, at depths of 0.5 and 1 cm in water, was irradiated with electrons. The source-to-surface distance is equal to 100 cm. Electron energy spectra and relative depth doses with and without the presence of the Pb layer at different depths in water were determined using the BEAMNRC code. For the 4 MeV electron energy spectra at a depth of 0.5 cm in water, electron backscatter was found to originate at the Pb-water interface and extend to 0.5 cm above the Pb insert. However, at a depth of 1 cm in water, electron backscatter almost disappeared at 0.5 and 1 cm above th ePb insert. This is due to the increased attenuation of the incident 4 MeV electron beam in a thicker layer of water as well as increased attenuation of the electron backscatter above the Pb. This resulted in a 23% decrease in relative dose at a measurement point of 0.5 cm depth, when the depth of the Pb insert was changed from 1 to 0.5 cm. For the electron energy spectra of the 9 MeV beams with a 0.5 cm depth of water, only a small amount of electron backscatter was observed. However, more electron backscatter was found when the water depth was increased to 1 cm. This is because the electron beam energy was decreased more due to the increase in attenuation from the increased depth of water compared to 0.5 cm. Since the electron energy spectrum and relative depth dose above the Pb layer vary with depth of water on top of the Pb, the electron
Chow, James C L; Owrangi, Amir M
2009-02-01
This study investigated the depth dependence of electron backscatter from a layer of lead (Pb) for clinical electron beams. The change in the electron backscatter with variation in the water depth above the Pb was determined. Electron energy spectra and relative depth doses as a function of depth in water over the Pb layer were calculated using a Monte Carlo simulation and studied. Phase-space files for 4 and 9 MeV electron beams (10 x 10 cm2 applicator and cutout) based on the Varian 21 EX linear accelerator were generated using the EGSnrc-based BEAMNRC code. 3 mm of Pb, at depths of 0.5 and 1 cm in water, was irradiated with electrons. The source-to-surface distance is equal to 100 cm. Electron energy spectra and relative depth doses with and without the presence of the Pb layer at different depths in water were determined using the BEAMNRC code. For the 4 MeV electron energy spectra at a depth of 0.5 cm in water, electron backscatter was found to originate at the Pb-water interface and extend to 0.5 cm above the Pb insert. However, at a depth of 1 cm in water, electron backscatter almost disappeared at 0.5 and 1 cm above th ePb insert. This is due to the increased attenuation of the incident 4 MeV electron beam in a thicker layer of water as well as increased attenuation of the electron backscatter above the Pb. This resulted in a 23% decrease in relative dose at a measurement point of 0.5 cm depth, when the depth of the Pb insert was changed from 1 to 0.5 cm. For the electron energy spectra of the 9 MeV beams with a 0.5 cm depth of water, only a small amount of electron backscatter was observed. However, more electron backscatter was found when the water depth was increased to 1 cm. This is because the electron beam energy was decreased more due to the increase in attenuation from the increased depth of water compared to 0.5 cm. Since the electron energy spectrum and relative depth dose above the Pb layer vary with depth of water on top of the Pb, the electron
International Nuclear Information System (INIS)
Channel capacity of ocean water is limited by propagation distance and optical properties. Previous studies on this problem are based on water-tank experiments with different amounts of Maalox antacid. However, propagation distance is limited by the experimental set-up and the optical properties are different from ocean water. Therefore, the experiment result is not accurate for the physical design of underwater wireless communications links. This letter developed a Monte Carlo model to study channel capacity of underwater optical communications. Moreover, this model can flexibly configure various parameters of transmitter, receiver and channel, and is suitable for physical underwater optical communications links design. (paper)
Monte Carlo simulation for background study of geophysical inspection with cosmic-ray muons
Nishiyama, Ryuichi; Taketa, Akimichi; Miyamoto, Seigo; Kasahara, Katsuaki
2016-08-01
Several attempts have been made to obtain a radiographic image inside volcanoes using cosmic-ray muons (muography). Muography is expected to resolve highly heterogeneous density profiles near the surface of volcanoes. However, several prior works have failed to make clear observations due to contamination by background noise. The background contamination leads to an overestimation of the muon flux and consequently a significant underestimation of the density in the target mountains. To investigate the origin of the background noise, we performed a Monte Carlo simulation. The main components of the background noise in muography are found to be low-energy protons, electrons and muons in case of detectors without particle identification and with energy thresholds below 1 GeV. This result was confirmed by comparisons with actual observations of nuclear emulsions. This result will be useful for detector design in future works, and in addition some previous works of muography should be reviewed from the view point of background contamination.
Dynamic Value at Risk: A Comparative Study Between Heteroscedastic Models and Monte Carlo Simulation
Directory of Open Access Journals (Sweden)
José Lamartine Távora Junior
2006-12-01
Full Text Available The objective of this paper was to analyze the risk management of a portfolio composed by Petrobras PN, Telemar PN and Vale do Rio Doce PNA stocks. It was verified if the modeling of Value-at-Risk (VaR through the place Monte Carlo simulation with volatility of GARCH family is supported by hypothesis of efficient market. The results have shown that the statistic evaluation in inferior to dynamics, evidencing that the dynamic analysis supplies support to the hypothesis of efficient market of the Brazilian share holding market, in opposition of some empirical evidences. Also, it was verified that the GARCH models of volatility is enough to accommodate the variations of the shareholding Brazilian market, since the model is capable to accommodate the great dynamic of the Brazilian market.
International Nuclear Information System (INIS)
Monte-Carlo simulation is one of the most essential computational tools to study the particle transport and interaction of radiation with matter as well as radiation protection and dosimetry. In this paper it was used to calculate percent depth doses in the water phantom for two Co-60 beam irradiation cases with using the MCNP-4C2 code. The simulation results was validated by comparison with those of measurements. Application of the MCNP-4C2 code for dose calculations in Co-60 beam treatment planning was recommended. (author)
Energy Technology Data Exchange (ETDEWEB)
Long, Daniel J.; Lee, Choonsik; Tien, Christopher; Fisher, Ryan; Hoerner, Matthew R.; Hintenlang, David; Bolch, Wesley E. [J Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, Florida 32611-6131 (United States); National Cancer Institute, National Institute of Health, Bethesda, Maryland 20892-1502 (United States); J Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, Florida 32611-6131 (United States); Department of Radiology, University of Florida, Gainesville, Florida 32610-0374 (United States); J Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, Florida 32611-6131 (United States)
2013-01-15
Purpose: To validate the accuracy of a Monte Carlo source model of the Siemens SOMATOM Sensation 16 CT scanner using organ doses measured in physical anthropomorphic phantoms. Methods: The x-ray output of the Siemens SOMATOM Sensation 16 multidetector CT scanner was simulated within the Monte Carlo radiation transport code, MCNPX version 2.6. The resulting source model was able to perform various simulated axial and helical computed tomographic (CT) scans of varying scan parameters, including beam energy, filtration, pitch, and beam collimation. Two custom-built anthropomorphic phantoms were used to take dose measurements on the CT scanner: an adult male and a 9-month-old. The adult male is a physical replica of University of Florida reference adult male hybrid computational phantom, while the 9-month-old is a replica of University of Florida Series B 9-month-old voxel computational phantom. Each phantom underwent a series of axial and helical CT scans, during which organ doses were measured using fiber-optic coupled plastic scintillator dosimeters developed at University of Florida. The physical setup was reproduced and simulated in MCNPX using the CT source model and the computational phantoms upon which the anthropomorphic phantoms were constructed. Average organ doses were then calculated based upon these MCNPX results. Results: For all CT scans, good agreement was seen between measured and simulated organ doses. For the adult male, the percent differences were within 16% for axial scans, and within 18% for helical scans. For the 9-month-old, the percent differences were all within 15% for both the axial and helical scans. These results are comparable to previously published validation studies using GE scanners and commercially available anthropomorphic phantoms. Conclusions: Overall results of this study show that the Monte Carlo source model can be used to accurately and reliably calculate organ doses for patients undergoing a variety of axial or helical CT
International Nuclear Information System (INIS)
Purpose: To validate the accuracy of a Monte Carlo source model of the Siemens SOMATOM Sensation 16 CT scanner using organ doses measured in physical anthropomorphic phantoms. Methods: The x-ray output of the Siemens SOMATOM Sensation 16 multidetector CT scanner was simulated within the Monte Carlo radiation transport code, MCNPX version 2.6. The resulting source model was able to perform various simulated axial and helical computed tomographic (CT) scans of varying scan parameters, including beam energy, filtration, pitch, and beam collimation. Two custom-built anthropomorphic phantoms were used to take dose measurements on the CT scanner: an adult male and a 9-month-old. The adult male is a physical replica of University of Florida reference adult male hybrid computational phantom, while the 9-month-old is a replica of University of Florida Series B 9-month-old voxel computational phantom. Each phantom underwent a series of axial and helical CT scans, during which organ doses were measured using fiber-optic coupled plastic scintillator dosimeters developed at University of Florida. The physical setup was reproduced and simulated in MCNPX using the CT source model and the computational phantoms upon which the anthropomorphic phantoms were constructed. Average organ doses were then calculated based upon these MCNPX results. Results: For all CT scans, good agreement was seen between measured and simulated organ doses. For the adult male, the percent differences were within 16% for axial scans, and within 18% for helical scans. For the 9-month-old, the percent differences were all within 15% for both the axial and helical scans. These results are comparable to previously published validation studies using GE scanners and commercially available anthropomorphic phantoms. Conclusions: Overall results of this study show that the Monte Carlo source model can be used to accurately and reliably calculate organ doses for patients undergoing a variety of axial or helical CT
Monte carlo simulation study of the square lattice S=1/2 quantum heisenberg antiferromagnet
Kim, J K
1999-01-01
For the two dimensional S= 1/2 isotopic quantum Heisenberg antiferromagnet on a square lattice, we report our results of an extensive quantum Monte Carlo simulation for various physical observables such as the correlation length xi, the staggered magnetic susceptibility chi sub S sub T , the structure factor peak value S(Q), the internal energy epsilon, and the uniform susceptibility chi sub u. We find that chi sub S sub T approx chi sup 2 T and S(Q) approx xi sup 2 T sup 2 , in agreement with the predictions of the conventional theory but in disagreement with recent experiments. Our estimate of the spin stiffness constant rho sub s and spin wave velocity c, from the low temperature behavior of the chi sub u is shown to be consistent with the theoretical prediction of the low temperature behavior of the epsilon, and of the xi provided an additional correction up to T sup 2. However, our data are definitely inconsistent with the scenario of the crossover for the xi.
Neutronics studies of solid targets for spallation neutron source using Monte Carlo simulation
Institute of Scientific and Technical Information of China (English)
殷雯; 梁九卿
2003-01-01
Neutronics studies for a solid target have been done with Monte Carlo high-energy particle transport code NMTC/JAM,when the proton beam with high kinetic energy bombards the target.The effect of the main parameters of the target on the neutron flux is discussed to optimize the target,which will be used for the concept design of the target of spallation neutron source.A target with its aspect ratio 1.5:1 or 2:1 gives the highest neutron flux.Tungsten is the most acceptable material from the technical and economical points of view.Beryllium as a moderating reflector can increase the neutron flux effectively.
Monte Carlo simulations of single polymer force-extension relations
International Nuclear Information System (INIS)
We present Monte Carlo simulations for studying the statistical mechanics of arbitrarily long single molecules under stretching. In many cases in which the thermodynamic limit is not satisfied, different statistical ensembles yield different macroscopic force-displacement curves. In this work we provide a description of the Monte Carlo simulations and discuss in details the assumptions adopted.
International Nuclear Information System (INIS)
Application of Monte Carlo method to build spectra library is useful to reduce experiment workload in Prompt Gamma Neutron Activation Analysis (PGNAA). The new Monte Carlo Code MOCA was used to simulate the response spectra of BGO detector for gamma rays from 137Cs, 60Co and neutron induced gamma rays from S and Ti. The results were compared with general code MCNP, show that the agreement of MOCA between simulation and experiment is better than MCNP. This research indicates that building spectra library by Monte Carlo method is feasible. (authors)
Kinetic Monte Carlo simulation of dislocation dynamics
International Nuclear Information System (INIS)
A kinetic Monte Carlo simulation of dislocation motion is introduced. The dislocations are assumed to be composed of pure edge and screw segments confined to a fixed lattice. The stress and temperature dependence of the dislocation velocity is studied, and finite-size effects are discussed. It is argued that surfaces and boundaries may play a significant role in the velocity of dislocations. The simulated dislocations are shown to display kinetic roughening according to the exponents predicted by the Kardar-Parisi-Zhang equation. copyright 1999 The American Physical Society
International Nuclear Information System (INIS)
In radiotherapy, it is essential to have a precise knowledge of the dose delivered in the target volume and the neighbouring critical organs. To be usable clinically, the models of calculation must take into account the exact characteristics of the beams used and the densities of fabrics. Today we can use sophisticated irradiation techniques and get a more precise assessment of the dose and with a better knowledge of its distribution. Thus in this report, will be detailed a simulation of the head of irradiation of accelerator SL-ELEKTA-20 in electrons mode and a dosimetric study of a water phantom. This study is carried out with the code of simulation Monte Carlo GATE adapted for applications of medical physics; the results are compared with the data obtained by the anticancer center 'Jean Perrin' on a similar accelerator. (author)
Energy Technology Data Exchange (ETDEWEB)
Hardiansyah, D.; Haryanto, F. [Nuclear Physics and Biophysics Research Laboratory, Physics Department, Institut Teknologi Bandung (ITB) (Indonesia); Male, S. [Radiotherapy Division, Research Hospital of Hassanudin University (Indonesia)
2014-09-30
Prism is a non-commercial Radiotherapy Treatment Planning System (RTPS) develop by Ira J. Kalet from Washington University. Inhomogeneity factor is included in Prism TPS dose calculation. The aim of this study is to investigate the sensitivity of dose calculation on Prism using Monte Carlo simulation. Phase space source from head linear accelerator (LINAC) for Monte Carlo simulation is implemented. To achieve this aim, Prism dose calculation is compared with EGSnrc Monte Carlo simulation. Percentage depth dose (PDD) and R50 from both calculations are observed. BEAMnrc is simulated electron transport in LINAC head and produced phase space file. This file is used as DOSXYZnrc input to simulated electron transport in phantom. This study is started with commissioning process in water phantom. Commissioning process is adjusted Monte Carlo simulation with Prism RTPS. Commissioning result is used for study of inhomogeneity phantom. Physical parameters of inhomogeneity phantom that varied in this study are: density, location and thickness of tissue. Commissioning result is shown that optimum energy of Monte Carlo simulation for 6 MeV electron beam is 6.8 MeV. This commissioning is used R50 and PDD with Practical length (R{sub p}) as references. From inhomogeneity study, the average deviation for all case on interest region is below 5 %. Based on ICRU recommendations, Prism has good ability to calculate the radiation dose in inhomogeneity tissue.
Hardiansyah, D.; Male, S.; Haryanto, F.
2014-09-01
Prism is a non-commercial Radiotherapy Treatment Planning System (RTPS) develop by Ira J. Kalet from Washington University. Inhomogeneity factor is included in Prism TPS dose calculation. The aim of this study is to investigate the sensitivity of dose calculation on Prism using Monte Carlo simulation. Phase space source from head linear accelerator (LINAC) for Monte Carlo simulation is implemented. To achieve this aim, Prism dose calculation is compared with EGSnrc Monte Carlo simulation. Percentage depth dose (PDD) and R50 from both calculations are observed. BEAMnrc is simulated electron transport in LINAC head and produced phase space file. This file is used as DOSXYZnrc input to simulated electron transport in phantom. This study is started with commissioning process in water phantom. Commissioning process is adjusted Monte Carlo simulation with Prism RTPS. Commissioning result is used for study of inhomogeneity phantom. Physical parameters of inhomogeneity phantom that varied in this study are: density, location and thickness of tissue. Commissioning result is shown that optimum energy of Monte Carlo simulation for 6 MeV electron beam is 6.8 MeV. This commissioning is used R50 and PDD with Practical length (Rp) as references. From inhomogeneity study, the average deviation for all case on interest region is below 5 %. Based on ICRU recommendations, Prism has good ability to calculate the radiation dose in inhomogeneity tissue.
International Nuclear Information System (INIS)
Prism is a non-commercial Radiotherapy Treatment Planning System (RTPS) develop by Ira J. Kalet from Washington University. Inhomogeneity factor is included in Prism TPS dose calculation. The aim of this study is to investigate the sensitivity of dose calculation on Prism using Monte Carlo simulation. Phase space source from head linear accelerator (LINAC) for Monte Carlo simulation is implemented. To achieve this aim, Prism dose calculation is compared with EGSnrc Monte Carlo simulation. Percentage depth dose (PDD) and R50 from both calculations are observed. BEAMnrc is simulated electron transport in LINAC head and produced phase space file. This file is used as DOSXYZnrc input to simulated electron transport in phantom. This study is started with commissioning process in water phantom. Commissioning process is adjusted Monte Carlo simulation with Prism RTPS. Commissioning result is used for study of inhomogeneity phantom. Physical parameters of inhomogeneity phantom that varied in this study are: density, location and thickness of tissue. Commissioning result is shown that optimum energy of Monte Carlo simulation for 6 MeV electron beam is 6.8 MeV. This commissioning is used R50 and PDD with Practical length (Rp) as references. From inhomogeneity study, the average deviation for all case on interest region is below 5 %. Based on ICRU recommendations, Prism has good ability to calculate the radiation dose in inhomogeneity tissue
Mean field simulation for Monte Carlo integration
Del Moral, Pierre
2013-01-01
In the last three decades, there has been a dramatic increase in the use of interacting particle methods as a powerful tool in real-world applications of Monte Carlo simulation in computational physics, population biology, computer sciences, and statistical machine learning. Ideally suited to parallel and distributed computation, these advanced particle algorithms include nonlinear interacting jump diffusions; quantum, diffusion, and resampled Monte Carlo methods; Feynman-Kac particle models; genetic and evolutionary algorithms; sequential Monte Carlo methods; adaptive and interacting Marko
International Nuclear Information System (INIS)
The risk assessment case study presented in this paper evaluates the potential human health risk to residential receptors exposed to benzene, toluene, ethylbenzene, and xylene from a JP-4 fuel spill. The eight residential scenario exposure pathways quantitatively assessed for carcinogenic and non-carcinogenic toxicological effects are: ingestion of groundwater, ingestion of soil, inhalation of volatiles (outdoors), inhalation of fugitive dust, dermal exposure to soil, dermal exposure while showering, inhalation of volatiles while showering, and ingestion of fruits and vegetables. Human health risks were calculated following EPA guidance documents which recommend determining a point estimate for potential risk in a baseline risk assessment (BRA) and a quantified uncertainty in that point estimate by a probabilistic risk assessment (PRA). BRAs typically use conservative estimates for exposure parameters, and consequently, the calculated risk represents an upper-bound or worst scenario that is beyond the reasonable maximum exposure (RME) without an associated quantified uncertainty. PRAs employing Monte Carlo techniques incorporate distributions for exposure parameters into the risk analysis to calculate a distribution for risk with each value in the risk distribution having a corresponding quantified uncertainty. The results of the assessment presented in this paper are examined to show the usefulness of the PRA in quantifying the uncertainty in the BRA
Monte Carlo simulation of block copolymer brushes
International Nuclear Information System (INIS)
We studied a simplified model of a polymer brush formed by linear chains, which were restricted to a simple cubic lattice. The chain macromolecules consisted of a sequence of two kinds of segment, arranged in a specific sequence. The chains were grafted to an impenetrable surface, i.e. they were terminally attached to the surface at one end. The number of chains was varied from low to high grafting density. The model system was studied under different solvent quality, from good to poor solvent. The properties of this model system were studied by means of Monte Carlo simulations. The sampling algorithm was based on local changes of the chain's conformations
Studies of light collection in depolished inorganic scintillators using Monte Carlo Simulations
International Nuclear Information System (INIS)
Scintillators are materials which emit light when energetic particles deposit energy in their volume. It is a quasi-universal requirement that the light detected in scintillator setups be maximised. The following project aims to study how the light collection is affected by surface depolishing using the simulation programs GEANT4 and LITRANI.
Monte Carlo simulation for soot dynamics
Directory of Open Access Journals (Sweden)
Zhou Kun
2012-01-01
Full Text Available A new Monte Carlo method termed Comb-like frame Monte Carlo is developed to simulate the soot dynamics. Detailed stochastic error analysis is provided. Comb-like frame Monte Carlo is coupled with the gas phase solver Chemkin II to simulate soot formation in a 1-D premixed burner stabilized flame. The simulated soot number density, volume fraction, and particle size distribution all agree well with the measurement available in literature. The origin of the bimodal distribution of particle size distribution is revealed with quantitative proof.
Monte carlo simulation for soot dynamics
Zhou, Kun
2012-01-01
A new Monte Carlo method termed Comb-like frame Monte Carlo is developed to simulate the soot dynamics. Detailed stochastic error analysis is provided. Comb-like frame Monte Carlo is coupled with the gas phase solver Chemkin II to simulate soot formation in a 1-D premixed burner stabilized flame. The simulated soot number density, volume fraction, and particle size distribution all agree well with the measurement available in literature. The origin of the bimodal distribution of particle size distribution is revealed with quantitative proof.
International Nuclear Information System (INIS)
In the case of the multi.leaf collimator (MLC), the operation of a moving leaf has been used for field shaping to pass radiation for radiotherapy. The MLC leaf could be positioned by connecting a stepping motor to the leaf's terminal. If the radiation therapy plan data is read as an input to a processing computer, an applied electronic signal can be used to command several leaves to move in a pattern simultaneously. The collimation method for a pixel unit that is used in this research is the method of a grid-type pixel collimator (GTPC). Basically, the grid frame, which is used to hang the attenuation cover, is arranged on a layer. The pixel cover's geometry is determined by using calculations based on Monte Carlo simulations. The basic pixel cover is a flat panel with a square pattern and is composed of a tungsten material to attenuate the radiation gradually. In addition, the attenuation can be controlled electronically by opening and closing the cover. In this study, to determine the possibility of field applications and to evaluate the intrinsic performance of the GTPC, which is different from the MLC, we used Monte Carlo simulation for MLC modeling. The GTPC could simultaneously provide momentary radiation intensity modulation with target guidance, and it was constructed to realize a complex geometry for tumor tracking with pixel unit attenuation
Energy Technology Data Exchange (ETDEWEB)
Shin, Han-Back; Yoon, Do-Kun; Suh, Tae Suk [College of Medicine, Catholic University of Korea, Seoul (Korea, Republic of)
2015-05-15
In the case of the multi.leaf collimator (MLC), the operation of a moving leaf has been used for field shaping to pass radiation for radiotherapy. The MLC leaf could be positioned by connecting a stepping motor to the leaf's terminal. If the radiation therapy plan data is read as an input to a processing computer, an applied electronic signal can be used to command several leaves to move in a pattern simultaneously. The collimation method for a pixel unit that is used in this research is the method of a grid-type pixel collimator (GTPC). Basically, the grid frame, which is used to hang the attenuation cover, is arranged on a layer. The pixel cover's geometry is determined by using calculations based on Monte Carlo simulations. The basic pixel cover is a flat panel with a square pattern and is composed of a tungsten material to attenuate the radiation gradually. In addition, the attenuation can be controlled electronically by opening and closing the cover. In this study, to determine the possibility of field applications and to evaluate the intrinsic performance of the GTPC, which is different from the MLC, we used Monte Carlo simulation for MLC modeling. The GTPC could simultaneously provide momentary radiation intensity modulation with target guidance, and it was constructed to realize a complex geometry for tumor tracking with pixel unit attenuation.
International Nuclear Information System (INIS)
The possibility of using silica-gold nanoshells with 150 nm silica core size and 25 nm thick gold shell as contrasting agents for optical coherence tomography (OCT) is analyzed. Experiments on agar biotissue phantoms showed that the penetration of nanoshells into the phantoms increases the intensity of the optical coherence tomography (OCT) signal and the brightness of the corresponding areas of the OCT image. In vivo experiments on rabbit skin demonstrated that the application of nanoshells onto the skin provides significant contrasting of the borders between the areas containing nanoshells and those without. This effect of nanoshells on skin in vivo is manifested by the increase in intensity of the OCT signal in superficial parts of the skin, boundary contrast between superficial and deep dermis and contrast of hair follicles and glands. The presence of nanoshells in the skin was confirmed by electron microscopy. Monte Carlo simulations of OCT images confirmed the possibility of contrasting skin-layer borders and structures by the application of gold nanoshells. The Monte Carlo simulations were performed for two skin models and exhibit effects of nanoparticles similar to those obtained in the experimental part of the study, thus proving that the effects originate exactly from the presence of nanoparticles
Validation of Compton Scattering Monte Carlo Simulation Models
Weidenspointner, Georg; Hauf, Steffen; Hoff, Gabriela; Kuster, Markus; Pia, Maria Grazia; Saracco, Paolo
2014-01-01
Several models for the Monte Carlo simulation of Compton scattering on electrons are quantitatively evaluated with respect to a large collection of experimental data retrieved from the literature. Some of these models are currently implemented in general purpose Monte Carlo systems; some have been implemented and evaluated for possible use in Monte Carlo particle transport for the first time in this study. Here we present first and preliminary results concerning total and differential Compton scattering cross sections.
Energy Technology Data Exchange (ETDEWEB)
Delis, H; Vlachopoulou, V; Spyrou, G; Costaridou, L; Panayiotakis, G [University of Patras, School of Medicine, Department of Medical Physics, 265 00 Patras (Greece); Tzanakos, G [University of Athens, Department of Physics, 157 71 Athens (Greece)], E-mail: panayiot@upatras.gr
2009-07-15
A Monte Carlo simulation model is utilized to study the influence of mammographic spectra on the SNR of simulated inhomogeneities representing calcifications of various thicknesses, embedded inside a mathematical breast phantom. The phantom is semicylindrical, mimicking a physical phantom for mammography, with background simulating glandular breast tissue. A step wedge arrangement with foils composed of Hydroxyapatite, was embedded. Monte Carlo methods have been used to sample the initial x-ray photon energy and trace the photons inside the breast, taking into account all possible physical processes. For the purposes of this study, only the third dimension (thickness) of calcifications was kept in realistic size, since it is the one related with the influence of the x-ray spectrum on the image, while the calcifications visibility with respect to their projection size is mainly affected by the resolving power of the imaging system. The discrimination of different calcifications thicknesses, described in terms of SNR, strongly depends on all the parameters affecting the x-ray spectrum. Tube voltage strongly affects SNR of small and medium thickness calcifications. The common Mo/Mo spectrum demonstrates improved characteristics, with SNR differences up to 14%, with respect to Rh/Rh for the entire thickness range of calcifications studied. Increase in filter thickness decreases SNR for calcification thicknesses less than 1200 {mu}m, while beyond this point increased filter thickness results in improved SNR. As far as the filter material is concerned, the thicker calcification to be visualized, the higher the k-absorption edge of the filter required, in order to achieve the maximum SNR.
International Nuclear Information System (INIS)
A Monte Carlo simulation model is utilized to study the influence of mammographic spectra on the SNR of simulated inhomogeneities representing calcifications of various thicknesses, embedded inside a mathematical breast phantom. The phantom is semicylindrical, mimicking a physical phantom for mammography, with background simulating glandular breast tissue. A step wedge arrangement with foils composed of Hydroxyapatite, was embedded. Monte Carlo methods have been used to sample the initial x-ray photon energy and trace the photons inside the breast, taking into account all possible physical processes. For the purposes of this study, only the third dimension (thickness) of calcifications was kept in realistic size, since it is the one related with the influence of the x-ray spectrum on the image, while the calcifications visibility with respect to their projection size is mainly affected by the resolving power of the imaging system. The discrimination of different calcifications thicknesses, described in terms of SNR, strongly depends on all the parameters affecting the x-ray spectrum. Tube voltage strongly affects SNR of small and medium thickness calcifications. The common Mo/Mo spectrum demonstrates improved characteristics, with SNR differences up to 14%, with respect to Rh/Rh for the entire thickness range of calcifications studied. Increase in filter thickness decreases SNR for calcification thicknesses less than 1200 μm, while beyond this point increased filter thickness results in improved SNR. As far as the filter material is concerned, the thicker calcification to be visualized, the higher the k-absorption edge of the filter required, in order to achieve the maximum SNR.
Delis, H.; Vlachopoulou, V.; Spyrou, G.; Costaridou, L.; Tzanakos, G.; Panayiotakis, G.
2009-07-01
A Monte Carlo simulation model is utilized to study the influence of mammographic spectra on the SNR of simulated inhomogeneities representing calcifications of various thicknesses, embedded inside a mathematical breast phantom. The phantom is semicylindrical, mimicking a physical phantom for mammography, with background simulating glandular breast tissue. A step wedge arrangement with foils composed of Hydroxyapatite, was embedded. Monte Carlo methods have been used to sample the initial x-ray photon energy and trace the photons inside the breast, taking into account all possible physical processes. For the purposes of this study, only the third dimension (thickness) of calcifications was kept in realistic size, since it is the one related with the influence of the x-ray spectrum on the image, while the calcifications visibility with respect to their projection size is mainly affected by the resolving power of the imaging system. The discrimination of different calcifications thicknesses, described in terms of SNR, strongly depends on all the parameters affecting the x-ray spectrum. Tube voltage strongly affects SNR of small and medium thickness calcifications. The common Mo/Mo spectrum demonstrates improved characteristics, with SNR differences up to 14%, with respect to Rh/Rh for the entire thickness range of calcifications studied. Increase in filter thickness decreases SNR for calcification thicknesses less than 1200 μm, while beyond this point increased filter thickness results in improved SNR. As far as the filter material is concerned, the thicker calcification to be visualized, the higher the k-absorption edge of the filter required, in order to achieve the maximum SNR.
International Nuclear Information System (INIS)
In this work we have developed a simulation tool, based on the PENELOPE code, to study the response of MOSFET devices to irradiation with high-energy photons. The energy deposited in the extremely thin silicon dioxide layer has been calculated. To reduce the statistical uncertainties, an ant colony algorithm has been implemented to drive the application of splitting and Russian roulette as variance reduction techniques. In this way, the uncertainty has been reduced by a factor of ∼5, while the efficiency is increased by a factor of above 20. As an application, we have studied the dependence of the response of the pMOS transistor 3N163, used as a dosimeter, with the incidence angle of the radiation for three common photons sources used in radiotherapy: a 60Co Theratron-780 and the 6 and 18 MV beams produced by a Mevatron KDS LINAC. Experimental and simulated results have been obtained for gantry angles of 0 deg., 15 deg., 30 deg., 45 deg., 60 deg. and 75 deg. The agreement obtained has permitted validation of the simulation tool. We have studied how to reduce the angular dependence of the MOSFET response by using an additional encapsulation made of brass in the case of the two LINAC qualities considered.
Energy Technology Data Exchange (ETDEWEB)
Carvajal, M A; Palma, A J [Departamento de Electronica y Tecnologia de Computadores, Universidad de Granada, E-18071 Granada (Spain); Garcia-Pareja, S [Servicio de Radiofisica Hospitalaria, Hospital Regional Universitario ' Carlos Haya' , Avda Carlos Haya, s/n, E-29010 Malaga (Spain); Guirado, D [Servicio de RadiofIsica, Hospital Universitario ' San Cecilio' , Avda Dr Oloriz, 16, E-18012 Granada (Spain); Vilches, M [Servicio de Fisica y Proteccion Radiologica, Hospital Regional Universitario ' Virgen de las Nieves' , Avda Fuerzas Armadas, 2, E-18014 Granada (Spain); Anguiano, M; Lallena, A M [Departamento de Fisica Atomica, Molecular y Nuclear, Universidad de Granada, E-18071 Granada (Spain)], E-mail: carvajal@ugr.es, E-mail: garciapareja@gmail.com, E-mail: dguirado@ugr.es, E-mail: mvilches@ugr.es, E-mail: mangui@ugr.es, E-mail: ajpalma@ugr.es, E-mail: lallena@ugr.es
2009-10-21
In this work we have developed a simulation tool, based on the PENELOPE code, to study the response of MOSFET devices to irradiation with high-energy photons. The energy deposited in the extremely thin silicon dioxide layer has been calculated. To reduce the statistical uncertainties, an ant colony algorithm has been implemented to drive the application of splitting and Russian roulette as variance reduction techniques. In this way, the uncertainty has been reduced by a factor of {approx}5, while the efficiency is increased by a factor of above 20. As an application, we have studied the dependence of the response of the pMOS transistor 3N163, used as a dosimeter, with the incidence angle of the radiation for three common photons sources used in radiotherapy: a {sup 60}Co Theratron-780 and the 6 and 18 MV beams produced by a Mevatron KDS LINAC. Experimental and simulated results have been obtained for gantry angles of 0 deg., 15 deg., 30 deg., 45 deg., 60 deg. and 75 deg. The agreement obtained has permitted validation of the simulation tool. We have studied how to reduce the angular dependence of the MOSFET response by using an additional encapsulation made of brass in the case of the two LINAC qualities considered.
Carvajal, M A; García-Pareja, S; Guirado, D; Vilches, M; Anguiano, M; Palma, A J; Lallena, A M
2009-10-21
In this work we have developed a simulation tool, based on the PENELOPE code, to study the response of MOSFET devices to irradiation with high-energy photons. The energy deposited in the extremely thin silicon dioxide layer has been calculated. To reduce the statistical uncertainties, an ant colony algorithm has been implemented to drive the application of splitting and Russian roulette as variance reduction techniques. In this way, the uncertainty has been reduced by a factor of approximately 5, while the efficiency is increased by a factor of above 20. As an application, we have studied the dependence of the response of the pMOS transistor 3N163, used as a dosimeter, with the incidence angle of the radiation for three common photons sources used in radiotherapy: a (60)Co Theratron-780 and the 6 and 18 MV beams produced by a Mevatron KDS LINAC. Experimental and simulated results have been obtained for gantry angles of 0 degrees, 15 degrees, 30 degrees, 45 degrees, 60 degrees and 75 degrees. The agreement obtained has permitted validation of the simulation tool. We have studied how to reduce the angular dependence of the MOSFET response by using an additional encapsulation made of brass in the case of the two LINAC qualities considered. PMID:19794247
Monte Carlo simulation of granular fluids
Montanero, J. M.
2003-01-01
An overview of recent work on Monte Carlo simulations of a granular binary mixture is presented. The results are obtained numerically solving the Enskog equation for inelastic hard-spheres by means of an extension of the well-known direct Monte Carlo simulation (DSMC) method. The homogeneous cooling state and the stationary state reached using the Gaussian thermostat are considered. The temperature ratio, the fourth velocity moments and the velocity distribution functions are obtained for bot...
Monte Carlo simulation to study the doses in an accelerator BNCT treatment
International Nuclear Information System (INIS)
In this work the 7Li(p, n)7Be reaction has been studied as a neutron source for accelerator-based BNCT (Boron Neutron Capture Therapy). In order to optimize the design of the neutron production target and the beam shaping assembly, extensive MCNP simulations have been performed. These simulations include a thick Li metal target, a whole-body phantom, a moderator-reflector assembly (Al/AlF3 as moderator and graphite as reflector) and the treatment room. The doses were evaluated for two proton bombarding energies of 1.92 MeV (near to the threshold of the reaction) and 2.3 MeV (near to the resonance of the reaction) and for three Al/ALF3 moderator thicknesses (18, 26 and 34 cm). To assess the doses, a comparison using a Tumor Control Probability (TCP) model was done. In a second instance, the effect of the specific skin radiosensitivity (an RBE of 2.5 for the 10B(n,α)7Li reaction) and a 10B uptake of 17 ppm was considered for the scalp. Finally, the simulations show the advantage of irradiating with near-resonance-energy protons (2.3 MeV) because of the high neutron yield at this energy, leading to the lowest treatment times. Moreover, the 26 cm Al/AlF3 moderator has shown the best performance among the studied cases. (author)
Institute of Scientific and Technical Information of China (English)
PENG,Chang-Jun(彭昌军); LI,Jian-Kang(李健康); LIU,Hong-Lai(刘洪来); HU,Ying(胡英)
2004-01-01
The adsorption of asymmetrical triblock copolymers from a non-selective solvent on solid surface has been studied by using Scheutjens-Fleer mean-field theory and Monte Carlo simulation method on lattice model. The main aim of this paper is to provide detailed computer simulation data, taking As-kB20Ak as a key example, to study the influence of the structure of copolymer on adsorption behavior and make a comparison between MC and SF results. The simulated results show that the size distribution of various configurations and density-profile are dependent on molecular structure and adsorption energy. The molecular structure will lead to diversity of adsorption behavior. This discrepancy between different structures would be enlarged for the surface coverage and adsorption amount with increasing of the adsorption energy. The surface coverage and the adsorption amount as well as the bound fraction will become larger as symmetry of the molecular structure becomes gradually worse. The adsorption layer becomes thicker with increasing of symmetry of the molecule when adsorption energy is smaller but it becomes thinner when adsorption energy is higher. It is shown that SF theory can reproduce the adsorption behavior of asymmetrical triblock copolymers. However, systematic discrepancy between the theory and simulation still exists.The approximations inherited in the mean-filed theory such as random mixing and the allowance of direct back folding may be responsible for those deviations.
Breast tomosynthesis with monochromatic beams: a feasibility study using Monte Carlo simulations
Malliori, A; Bliznakova, K.; Sechopoulos, I; Kamarianakis, Z; Fei, B; Pallikarakis, N
2014-01-01
The aim of the study is to investigate the impact on image quality of using monochromatic beams for lower dose breast tomosynthesis (BT). For this purpose, modeling and simulation of BT and mammography imaging processes have been performed using two x-ray beams: one at 28kVp and a monochromatic at 19keV at different entrance surface air kerma ranging between 0.16 and 5.5 mGy. Two 4cm thick computational breast models in a compressed state were used: one simple homogeneous and one heterogeneou...
Medhat, M. E.
2015-02-01
The main goal of this work is focused on testing the applicability of Geant4 electromagnetic models for studying mass attenuations for different types of composite materials at 59.5, 80, 356, 661.6, 1173.2 and 1332.5 keV photon energies. The simulated results of mass attenuation coefficients were compared with the experimental and theoretical data for the same samples and a good agreement has been observed. The results indicate that this process can be followed to determine the data on the attenuation of gamma-rays with the several energies in different materials.
Energy Technology Data Exchange (ETDEWEB)
Lamia, D., E-mail: debora.lamia@ibfm.cnr.it [Institute of Molecular Bioimaging and Physiology IBFM CNR – LATO, Cefalù (Italy); Russo, G., E-mail: giorgio.russo@ibfm.cnr.it [Institute of Molecular Bioimaging and Physiology IBFM CNR – LATO, Cefalù (Italy); Casarino, C.; Gagliano, L.; Candiano, G.C. [Institute of Molecular Bioimaging and Physiology IBFM CNR – LATO, Cefalù (Italy); Labate, L. [Intense Laser Irradiation Laboratory (ILIL) – National Institute of Optics INO CNR, Pisa (Italy); National Institute for Nuclear Physics INFN, Pisa Section and Frascati National Laboratories LNF (Italy); Baffigi, F.; Fulgentini, L.; Giulietti, A.; Koester, P.; Palla, D. [Intense Laser Irradiation Laboratory (ILIL) – National Institute of Optics INO CNR, Pisa (Italy); Gizzi, L.A. [Intense Laser Irradiation Laboratory (ILIL) – National Institute of Optics INO CNR, Pisa (Italy); National Institute for Nuclear Physics INFN, Pisa Section and Frascati National Laboratories LNF (Italy); Gilardi, M.C. [Institute of Molecular Bioimaging and Physiology IBFM CNR, Segrate (Italy); University of Milano-Bicocca, Milano (Italy)
2015-06-21
We report on the development of a Monte Carlo application, based on the GEANT4 toolkit, for the characterization and optimization of electron beams for clinical applications produced by a laser-driven plasma source. The GEANT4 application is conceived so as to represent in the most general way the physical and geometrical features of a typical laser-driven accelerator. It is designed to provide standard dosimetric figures such as percentage dose depth curves, two-dimensional dose distributions and 3D dose profiles at different positions both inside and outside the interaction chamber. The application was validated by comparing its predictions to experimental measurements carried out on a real laser-driven accelerator. The work is aimed at optimizing the source, by using this novel application, for radiobiological studies and, in perspective, for medical applications. - Highlights: • Development of a Monte Carlo application based on GEANT4 toolkit. • Experimental measurements carried out with a laser-driven acceleration system. • Validation of Geant4 application comparing experimental data with the simulated ones. • Dosimetric characterization of the acceleration system.
International Nuclear Information System (INIS)
We report on the development of a Monte Carlo application, based on the GEANT4 toolkit, for the characterization and optimization of electron beams for clinical applications produced by a laser-driven plasma source. The GEANT4 application is conceived so as to represent in the most general way the physical and geometrical features of a typical laser-driven accelerator. It is designed to provide standard dosimetric figures such as percentage dose depth curves, two-dimensional dose distributions and 3D dose profiles at different positions both inside and outside the interaction chamber. The application was validated by comparing its predictions to experimental measurements carried out on a real laser-driven accelerator. The work is aimed at optimizing the source, by using this novel application, for radiobiological studies and, in perspective, for medical applications. - Highlights: • Development of a Monte Carlo application based on GEANT4 toolkit. • Experimental measurements carried out with a laser-driven acceleration system. • Validation of Geant4 application comparing experimental data with the simulated ones. • Dosimetric characterization of the acceleration system
Chen, Dongsheng; Zeng, Nan; Wang, Yunfei; He, Honghui; Tuchin, Valery V; Ma, Hui
2016-08-01
We conducted Monte Carlo simulations based on anisotropic sclera-mimicking models to examine the polarization features in Mueller matrix polar decomposition (MMPD) parameters during the refractive index matching process, which is one of the major mechanisms of optical clearing. In a preliminary attempt, by changing the parameters of the models, wavelengths, and detection geometries, we demonstrate how the depolarization coefficient and retardance vary during the refractive index matching process and explain the polarization features using the average value and standard deviation of scattering numbers of the detected photons. We also study the depth-resolved polarization features during the gradual progression of the refractive index matching process. The results above indicate that the refractive index matching process increases the depth of polarization measurements and may lead to higher contrast between tissues of different anisotropies in deeper layers. MMPD-derived polarization parameters can characterize the refractive index matching process qualitatively. PMID:27240298
Mondal, Nagendra Nath
2010-01-01
The results of Monte Carlo Simulation (MCS) studies of Most likely position (MLP) and position vector (PV) methods in TOFPET system are presented. MCS based on GEANT3.21 is carried out where the geometry of a real TOFPET system is considered. Results not only manifest resolving powers (RP) of PV and MLP methods ~114% and ~36% but also exhibit shifting of reconstructed images from the original positions ~3% and ~63% respectively. Position conversion factors play a crucial role to reinstate the image position in the PV method and stipulate excellent images. A PV is a position reconstruction method of positron-electron annihilation points developed afresh without iteration and that makes its beauty by saving huge computational time and radiation dose of the patient.
International Nuclear Information System (INIS)
The purpose of this research is a statistical analysis for discrimination of prompt gamma ray peak induced by the 14.1 MeV neutron particles from spectra using Monte Carlo simulation. For the simulation, the information of 18 detector materials was used to simulate spectra by the neutron capture reaction. The discrimination of nine prompt gamma ray peaks from the simulation of each detector material was performed. We presented the several comparison indexes of energy resolution performance depending on the detector material using the simulation and statistics for the prompt gamma activation analysis. (author)
International Nuclear Information System (INIS)
Prostate Brachytherapy is a radiotherapy technique, which consists in inserting a number of radioactive seeds (containing, usually, the following radionuclides 125 l, 241Am or 103Pd ) surrounding or in the vicinity of, prostate tumor tissue . The main objective of this technique is to maximize the radiation dose to the tumor and minimize it in other tissues and organs healthy, in order to reduce its morbidity. The absorbed dose distribution in the prostate, using this technique is usually non-homogeneous and time dependent. Various parameters such as the type of seed, the attenuation interactions between them, their geometrical arrangement within the prostate, the actual geometry of the seeds,and further swelling of the prostate gland after implantation greatly influence the course of absorbed dose in the prostate and surrounding areas. Quantification of these parameters is therefore extremely important for dose optimization and improvement of their plans conventional treatment, which in many cases not fully take into account. The Monte Carlo techniques allow to study these parameters quickly and effectively. In this work, we use the program MCNPX and generic voxel phantom (GOLEM) where simulated different geometric arrangements of seeds containing 125I, Amersham Health model of type 6711 in prostates of different sizes, in order to try to quantify some of the parameters. The computational model was validated using a phantom prostate cubic RW3 type , consisting of tissue equivalent, and thermoluminescent dosimeters. Finally, to have a term of comparison with a treatment real plan it was simulate a treatment plan used in a hospital of Rio de Janeiro, with exactly the same parameters, and our computational model. The results obtained in our study seem to indicate that the parameters described above may be a source of uncertainty in the correct evaluation of the dose required for actual treatment plans. The use of Monte Carlo techniques can serve as a complementary
Kooi, BJ
2006-01-01
An analytical theory has been developed, based on Monte Carlo (MC) simulations, describing the kinetics of isothermal phase transformations proceeding by nucleation and subsequent growth for d-1 dimensional growth in d dimensional space (with d 2 or 3). This type of growth is of interest since it is
Adaptive Multilevel Monte Carlo Simulation
Hoel, H
2011-08-23
This work generalizes a multilevel forward Euler Monte Carlo method introduced in Michael B. Giles. (Michael Giles. Oper. Res. 56(3):607–617, 2008.) for the approximation of expected values depending on the solution to an Itô stochastic differential equation. The work (Michael Giles. Oper. Res. 56(3):607– 617, 2008.) proposed and analyzed a forward Euler multilevelMonte Carlo method based on a hierarchy of uniform time discretizations and control variates to reduce the computational effort required by a standard, single level, Forward Euler Monte Carlo method. This work introduces an adaptive hierarchy of non uniform time discretizations, generated by an adaptive algorithmintroduced in (AnnaDzougoutov et al. Raùl Tempone. Adaptive Monte Carlo algorithms for stopped diffusion. In Multiscale methods in science and engineering, volume 44 of Lect. Notes Comput. Sci. Eng., pages 59–88. Springer, Berlin, 2005; Kyoung-Sook Moon et al. Stoch. Anal. Appl. 23(3):511–558, 2005; Kyoung-Sook Moon et al. An adaptive algorithm for ordinary, stochastic and partial differential equations. In Recent advances in adaptive computation, volume 383 of Contemp. Math., pages 325–343. Amer. Math. Soc., Providence, RI, 2005.). This form of the adaptive algorithm generates stochastic, path dependent, time steps and is based on a posteriori error expansions first developed in (Anders Szepessy et al. Comm. Pure Appl. Math. 54(10):1169– 1214, 2001). Our numerical results for a stopped diffusion problem, exhibit savings in the computational cost to achieve an accuracy of ϑ(TOL),from(TOL−3), from using a single level version of the adaptive algorithm to ϑ(((TOL−1)log(TOL))2).
Kooi, BJ
2006-01-01
An analytical theory has been developed, based on Monte Carlo (MC) simulations, describing the kinetics of isothermal phase transformations proceeding by nucleation and subsequent growth for d-1 dimensional growth in d dimensional space (with d 2 or 3). This type of growth is of interest since it is generally anisotropic, leads to hard impingement, and obtains strong deviations from the traditional Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory. Within the MC simulations 1D growth can occur wit...
Antisite disorder study by Monte Carlo simulation of the double perovskite Sr2CrReO6
El Rhazouani, O.; Benyoussef, A.; Zarhri, Z.; El Kenz, A.
2016-03-01
In the last few years there has been a growing interest in the double perovskite (DP) Sr2CrReO6, as a magnetic material used in spintronics, due to its high Curie temperature (TC=610 K). Antisite disorder is a defect that affects the spin polarization and the Curie temperature of all PDs. We conducted this work by Monte Carlo simulation to study the effect of the antisite disorder on this compound for two cases: Cr-excess expressed by Sr2Cr1+xRe1-xO6 and Re-excess expressed by Sr2Cr1-xRe1+xO6. This simulation has transformed the concept of the antisite conceived as defect, into a tool to explain the role of transition metals, namely Cr and Re, in the stability and the magnetic performance of the compound Sr2CrReO6. This simulation allows positioning the Cr as a key element in determining the high Curie temperature and the ferromagnetic stability. The effect of crystal field of Re in the disordered sublattice regarding the disorder rates was also explored.
Simulation study of GaN n-MOSFETs by two-dimensional full band Monte Carlo approach
International Nuclear Information System (INIS)
Electrical properties of GaN n-MOSFET are presented by simulation study using the two-dimensional full band Monte Carlo approach. The band structure was calculated by the first-principle total-energy pseudopotential method within local-density-functional formalism. The various scatterings, such as polar optical scattering, impurity scattering, acoustic phonon scattering, and intervalley scattering, were included in the simulation. The vertical structure of the GaN n-MOSFET is Au/SiO2 (50 nm)/GaN with the channel of 300 nm length. The simulation results showed that the device is normally off with a threshold voltage of about +3.0 V. IDS is about 4.96 A/cm at VDS=15 V and VGS=5 V. The maximum transconductance is about 0.44 S/cm at VGS=13.75 V and VDS=12 V. The maximum current gain cutoff frequency fT is about 86 GHz at VGS=8.75 V and IDS=2 A/cm.
Monte Carlo simulation of granular fluids
Montanero, J M
2003-01-01
An overview of recent work on Monte Carlo simulations of a granular binary mixture is presented. The results are obtained numerically solving the Enskog equation for inelastic hard-spheres by means of an extension of the well-known direct Monte Carlo simulation (DSMC) method. The homogeneous cooling state and the stationary state reached using the Gaussian thermostat are considered. The temperature ratio, the fourth velocity moments and the velocity distribution functions are obtained for both cases. The shear viscosity characterizing the momentum transport in the thermostatted case is calculated as well. The simulation results are compared with analytical predictions showing an excellent agreement.
Liu, Shitao; Li, Hongdi; Zhang, Yuxuan; Ramirez, Rocio A.; Baghaei, Hossain; An, Shaohui; Wang, Chao; Liu, Jiguo; Wong, Wai-Hoi
2009-01-01
We developed a detailed Monte Carlo simulation method to study the time resolution of detectors for time-of-flight positron emission tomography (TOF PET). The process of gamma ray interaction in detectors, scintillation light emission and transport inside the detectors, the photoelectron generation and anode signal generation in the photomultiplier tube (PMT), and the electronics process of discriminator are simulated. We tested this simulation method using published experimental data, and fo...
Energy Technology Data Exchange (ETDEWEB)
Lee, Seung Kyu; Seo, Hee; Won, Byung Hee; Lee, Hyun Su; Park, Se-Hwan; Kim, Ho-Dong [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)
2014-10-15
The XRF technique compares the measured pulse height of U and Pu peaks which are self-induced characteristic xray emitted from U and Pu to quantify the elemental U and Pu. The measurement of the U and Pu x-ray peak ratio provides information on the relative concentration of U and Pu elements. Photon measurements of spent nuclear fuel using high resolution spectrometers show a large background continuum in the low energy x-ray region in large part from Compton scattering of energetic gamma-rays. The high Compton continuum can make measurements of plutonium x-rays difficult because the relatively small signal to background ratio produced. In pressurized water reactor (PWR) spent fuels with low plutonium contents (-1%), the signal to background ratio may be too low to get an accurate plutonium x-ray measurement. The Compton suppression system has been proposed to reduce the Compton continuum background. In the present study, the feasibility of a Compton suppression system for XRF was evaluated by Monte Carlo simulations and measurements of the radiation source. In this study, the feasibility of a Compton suppression system for XRF was evaluated by MCNP simulations and measurements of the radiation source. Experiments using a standard gamma-ray source showed that the peak-to-total ratios were improved by a factor of three when the Compton suppression system was used.
Cerenkov luminescence imaging of human breast cancer: a Monte Carlo simulations study
Boschi, F.; Pagliazzi, M.; Spinelli, A. E.
2016-03-01
Cerenkov luminescence imaging (CLI) is a novel molecular imaging technique based on the detection of Cerenkov light produced by beta particles traveling through biological tissues. In this paper we simulated using 18F and 90Y the possibility of detecting Cerenkov luminescence in human breast tissues, in order to evaluate the potential of the CLI technique in a clinical setting. A human breast digital phantom was obtained from an 18F-FDG CT-PET scan. The spectral features of the breast surface emission were obtained as well as the simulated images obtainable by a cooled CCD detector. The simulated images revealed a signal to noise ratio equal to 6 for a 300 s of acquisition time. We concluded that a dedicated human Cerenkov imaging detector can be designed in order to offer a valid low cost alternative to diagnostic techniques in nuclear medicine, in particular allowing the detection of beta-minus emitters used in radiotherapy.
Cerenkov luminescence imaging of human breast cancer: a Monte Carlo simulations study
International Nuclear Information System (INIS)
Cerenkov luminescence imaging (CLI) is a novel molecular imaging technique based on the detection of Cerenkov light produced by beta particles traveling through biological tissues. In this paper we simulated using 18F and 90Y the possibility of detecting Cerenkov luminescence in human breast tissues, in order to evaluate the potential of the CLI technique in a clinical setting. A human breast digital phantom was obtained from an 18F-FDG CT-PET scan. The spectral features of the breast surface emission were obtained as well as the simulated images obtainable by a cooled CCD detector. The simulated images revealed a signal to noise ratio equal to 6 for a 300 s of acquisition time. We concluded that a dedicated human Cerenkov imaging detector can be designed in order to offer a valid low cost alternative to diagnostic techniques in nuclear medicine, in particular allowing the detection of beta-minus emitters used in radiotherapy
Boukezzata, M.; Ait-Kaki, A.; Temple-Boyer, P.; Scheid, E.
2003-03-01
This work presents a Monte Carlo simulation study of boron profiles obtained from as-implanted ions into thin films nitrogen doped silicon (NiDoS) thin films. These films are performed by LPCVD technique from Si2H6 and NH3 gas sources, four values deliberately chosen, of the ratio NH3/Si2H6 to obtain samples, differently in situ nitrogen-doped. Taking into account the effect of the codoping case, and the structure specificity of these films, an accurate Monte Carlo model based on binary collisions in a multi-atomic target was performed. Nitrogen atoms present in the target is shown to affect the boron profiles and confirms clearly a reduction penetration effect which becomes more significant at high nitrogen concentrations. Whereas, the fine-grained polysilicon structure, and thus the presence of grains (G) and grain boundaries (GB), is known to enhance the opposite phenomenon by assuming an effective role played by GB's in the scattering calculation process of the incident ions. This role is represented by the change in direction of the incident ion after interaction with GB without corresponding loss in its energy. The results obtained show an enhancement of the stopping parameter when nitrogen concentration increases, while the GB interaction remains very important. This behavior is due to a great number of GB's interactions with boron atoms which gave low deflection angles. So that, the average positions described by the sequences of trajectories took place farther than what expected with channeling effect in crystal silicon materials.
International Nuclear Information System (INIS)
The electron beam X-ray tomographic scanner has been used in industrial and medical field since it was developed two decades ago. However, X-ray electron beam tomography has remained as indoor equipment because of its bulky hardware of X-ray generation devices. By replacing X-ray devices of electron beam CT with a gamma-ray source, a tomographic system can be a portable device. This paper introduces analysis and simulation results on industrial gamma-ray tomographic system with scanning geometry similar to electron beam CT. The gamma-ray tomographic system is introduced through the geometrical layout and analysis on non-uniformly distributed problem. The proposed system adopts clamp-on type device to actualize portable industrial system. MCNPx is used to generate virtual experimental data. Pulse height spectra from F8 tally of MCNPx are obtained for single channel counting data of photo-peak and gross counting. Photo-peak and gross counting data are reconstructed for the cross-sectional image of simulation phantoms by ART, Total Variation algorithm and ML-EM. Image reconstruction results from Monte Carlo simulation show that the proposed tomographic system can provide the image solution for industrial objects. Those results provide the preliminary data for the tomographic scanner, which will be developed in future work. - Highlights: ► We carried out feasibility study on gamma-ray tomography with electron beam CT scanning geometry. ► Gamma ray tomographic system is introduced through geometrical layout and analysis on non-uniformly distributed problem. ► We carried out MCNPx simulation for proposed geometry. ► Results show that this system can be used for transportable tomographic system.
Energy Technology Data Exchange (ETDEWEB)
Rojas C, E.L. [ININ, 52045 Ocoyoacac, Estado de Mexico (Mexico); Al-Dweri, F.M.O.; Lallena R, A.M. [Universidad de Granada, Granada (Spain)]. e-mail: elrc@nuclear.inin.mx
2005-07-01
In this work they are studied, by means of Monte Carlo simulation, the effects that take place in the dose profiles that are obtained with the Leksell Gamma Knife (R), when they are kept in account heterogeneities. The considered heterogeneities simulate the skull and the spaces of air that are in the head, like they can be the nasal breasts or the auditory conduits. The calculations were made using the Monte Carlo Penelope simulation code (v. 2003). The geometry of each one of the 201 sources that this instrument is composed, as well as of the corresponding channels of collimation of the Gamma Knife (R), it was described by means of a simplified model of geometry that has been recently studied. The obtained results when they are kept in mind the heterogeneities they present non worthless differences regarding those obtained when those are not considered. These differences are maximum in the proximities of the interfaces among different materials. (Author)
International Nuclear Information System (INIS)
The use of alternative channel materials to maintain device performance with scaling for CMOS technology is an active area of research, with Germanium offering an extremely attractive possibility for pMOSFETs in CMOS. In this paper we use full band Monte Carlo transport simulations to investigate the impact of substrate orientation and biaxial strain on hole mobility in bulk Germanium helping to establish a preferential substrate channel orientation that can maximize carrier mobility for these devices.
Energy Technology Data Exchange (ETDEWEB)
Riddet, Craig; Watling, Jeremy R; Chan, Kah Hou; Asenov, Asen, E-mail: c.riddet@elec.gla.ac.u [Device Modelling Group, Department of Electronics and Electrical Engineering, University of Glasgow, Glasgow, G12 8LT, Scotland (United Kingdom)
2010-07-01
The use of alternative channel materials to maintain device performance with scaling for CMOS technology is an active area of research, with Germanium offering an extremely attractive possibility for pMOSFETs in CMOS. In this paper we use full band Monte Carlo transport simulations to investigate the impact of substrate orientation and biaxial strain on hole mobility in bulk Germanium helping to establish a preferential substrate channel orientation that can maximize carrier mobility for these devices.
Monte Carlo Simulations of the Photospheric Process
Santana, Rodolfo; Hernandez, Roberto A; Kumar, Pawan
2015-01-01
We present a Monte Carlo (MC) code we wrote to simulate the photospheric process and to study the photospheric spectrum above the peak energy. Our simulations were performed with a photon to electron ratio $N_{\\gamma}/N_{e} = 10^{5}$, as determined by observations of the GRB prompt emission. We searched an exhaustive parameter space to determine if the photospheric process can match the observed high-energy spectrum of the prompt emission. If we do not consider electron re-heating, we determined that the best conditions to produce the observed high-energy spectrum are low photon temperatures and high optical depths. However, for these simulations, the spectrum peaks at an energy below 300 keV by a factor $\\sim 10$. For the cases we consider with higher photon temperatures and lower optical depths, we demonstrate that additional energy in the electrons is required to produce a power-law spectrum above the peak-energy. By considering electron re-heating near the photosphere, the spectrum for these simulations h...
Monte Carlo Simulation for Particle Detectors
Pia, Maria Grazia
2012-01-01
Monte Carlo simulation is an essential component of experimental particle physics in all the phases of its life-cycle: the investigation of the physics reach of detector concepts, the design of facilities and detectors, the development and optimization of data reconstruction software, the data analysis for the production of physics results. This note briefly outlines some research topics related to Monte Carlo simulation, that are relevant to future experimental perspectives in particle physics. The focus is on physics aspects: conceptual progress beyond current particle transport schemes, the incorporation of materials science knowledge relevant to novel detection technologies, functionality to model radiation damage, the capability for multi-scale simulation, quantitative validation and uncertainty quantification to determine the predictive power of simulation. The R&D on simulation for future detectors would profit from cooperation within various components of the particle physics community, and synerg...
Modulated pulse bathymetric lidar Monte Carlo simulation
Luo, Tao; Wang, Yabo; Wang, Rong; Du, Peng; Min, Xia
2015-10-01
A typical modulated pulse bathymetric lidar system is investigated by simulation using a modulated pulse lidar simulation system. In the simulation, the return signal is generated by Monte Carlo method with modulated pulse propagation model and processed by mathematical tools like cross-correlation and digital filter. Computer simulation results incorporating the modulation detection scheme reveal a significant suppression of the water backscattering signal and corresponding target contrast enhancement. More simulation experiments are performed with various modulation and reception variables to investigate the effect of them on the bathymetric system performance.
Izadi, Arman; Kimiagari, Ali Mohammad
2014-05-01
Distribution network design as a strategic decision has long-term effect on tactical and operational supply chain management. In this research, the location-allocation problem is studied under demand uncertainty. The purposes of this study were to specify the optimal number and location of distribution centers and to determine the allocation of customer demands to distribution centers. The main feature of this research is solving the model with unknown demand function which is suitable with the real-world problems. To consider the uncertainty, a set of possible scenarios for customer demands is created based on the Monte Carlo simulation. The coefficient of variation of costs is mentioned as a measure of risk and the most stable structure for firm's distribution network is defined based on the concept of robust optimization. The best structure is identified using genetic algorithms and 14 % reduction in total supply chain costs is the outcome. Moreover, it imposes the least cost variation created by fluctuation in customer demands (such as epidemic diseases outbreak in some areas of the country) to the logistical system. It is noteworthy that this research is done in one of the largest pharmaceutical distribution firms in Iran.
Directory of Open Access Journals (Sweden)
Mondal Nagendra
2009-01-01
Full Text Available This study presents Monte Carlo Simulation (MCS results of detection efficiencies, spatial resolutions and resolving powers of a time-of-flight (TOF PET detector systems. Cerium activated Lutetium Oxyorthosilicate (Lu 2 SiO 5 : Ce in short LSO, Barium Fluoride (BaF 2 and BriLanCe 380 (Cerium doped Lanthanum tri-Bromide, in short LaBr 3 scintillation crystals are studied in view of their good time and energy resolutions and shorter decay times. The results of MCS based on GEANT show that spatial resolution, detection efficiency and resolving power of LSO are better than those of BaF 2 and LaBr 3 , although it possesses inferior time and energy resolutions. Instead of the conventional position reconstruction method, newly established image reconstruction (talked about in the previous work method is applied to produce high-tech images. Validation is a momentous step to ensure that this imaging method fulfills all purposes of motivation discussed by reconstructing images of two tumors in a brain phantom.
Study of the point spread function (PSF) for {sup 123}I SPECT imaging using Monte Carlo simulation
Energy Technology Data Exchange (ETDEWEB)
Cot, A [Departament de FIsica i Enginyeria Nuclear, Universitat Politecnica de Catalunya, Diagonal 647, 08028 Barcelona (Spain); Sempau, J [Institut de Tecniques Energetiques, Universitat Politecnica de Catalunya, Diagonal 647, 08028 Barcelona (Spain); Pareto, D [Unitat de BiofIsica i Bioenginyeria, Universitat de Barcelona, Casanova 143, 08036 Barcelona (Spain); Bullich, S [Unitat de BiofIsica i Bioenginyeria, Universitat de Barcelona, Casanova 143, 08036 Barcelona (Spain); PavIa, J [Servei de Medicina Nuclear, Hospital ClInic i Provincial de Barcelona, Villarroel 170, 08036 Barcelona (Spain); Calvino, F [Departament de FIsica i Enginyeria Nuclear, Universitat Politecnica de Catalunya, Diagonal 647, 08028 Barcelona (Spain); Ros, D [Unitat de BiofIsica i Bioenginyeria, Universitat de Barcelona, Casanova 143, 08036 Barcelona (Spain)
2004-07-21
The iterative reconstruction algorithms employed in brain single-photon emission computed tomography (SPECT) allow some quantitative parameters of the image to be improved. These algorithms require accurate modelling of the so-called point spread function (PSF). Nowadays, most in vivo neurotransmitter SPECT studies employ pharmaceuticals radiolabelled with {sup 123}I. In addition to an intense line at 159 keV, the decay scheme of this radioisotope includes some higher energy gammas which may have a non-negligible contribution to the PSF. The aim of this work is to study this contribution for two low-energy high-resolution collimator configurations, namely, the parallel and the fan beam. The transport of radiation through the material system is simulated with the Monte Carlo code PENELOPE. We have developed a main program that deals with the intricacies associated with tracking photon trajectories through the geometry of the collimator and detection systems. The simulated PSFs are partly validated with a set of experimental measurements that use the 511 keV annihilation photons emitted by a {sup 18}F source. Sensitivity and spatial resolution have been studied, showing that a significant fraction of the detection events in the energy window centred at 159 keV (up to approximately 49% for the parallel collimator) are originated by higher energy gamma rays, which contribute to the spatial profile of the PSF mostly outside the 'geometrical' region dominated by the low-energy photons. Therefore, these high-energy counts are to be considered as noise, a fact that should be taken into account when modelling PSFs for reconstruction algorithms. We also show that the fan beam collimator gives higher signal-to-noise ratios than the parallel collimator for all the source positions analysed.
International Nuclear Information System (INIS)
A spectral computed tomography (CT) system based on an energy-resolved photon-counting Cadmium Zinc Telluride (CZT) detector with a dual energy technique can provide spectral information and can possibly distinguish between two or more materials with a single X-ray exposure using energy thresholds. This work provides the potential for three-material decomposition of vulnerable plaques using two inverse fitting functions. Additionally, there exists the possibility of using gold nanoparticles as a contrast agent for the spectral CT system in conjunction with a CZT photon-counting detector. In this simulation study, we used fan beam CT geometry that consisted of a 90 kVp X-ray spectrum and performed calculations by using the SpekCal program (REAL Software, Inc.) with Monte Carlo simulations. A basic test phantom was imaged with the spectral CT system for the calibration and decomposition process. This phantom contained three different materials, including lipid, iodine and gold nanoparticles, with six holes 3 mm in diameter. In addition to reducing pile-up and charge sharing effect, the photon counting detector was considered an ideal detector. Then, the accuracy of material decomposition techniques with two inverse fitting functions were evaluated between decomposed images and reference images in terms of root mean square error (RMSE). The results showed that decomposed images had a good volumetric fraction for each material, and the RMSE between the measured and true volumes of lipid, iodine and gold nanoparticle fractions varied from 12.51% to 1.29% for inverse fitting functions. The study indicated that spectral CT in conjunction with a CZT photon-counting detector in conjunction with a dual energy technique can be used to identifying materials and may be a promising modality for quantifying material properties of vulnerable plaques
Jo, B. D.; Park, S.-J.; Kim, H. M.; Kim, D. H.; Kim, H.-J.
2016-02-01
A spectral computed tomography (CT) system based on an energy-resolved photon-counting Cadmium Zinc Telluride (CZT) detector with a dual energy technique can provide spectral information and can possibly distinguish between two or more materials with a single X-ray exposure using energy thresholds. This work provides the potential for three-material decomposition of vulnerable plaques using two inverse fitting functions. Additionally, there exists the possibility of using gold nanoparticles as a contrast agent for the spectral CT system in conjunction with a CZT photon-counting detector. In this simulation study, we used fan beam CT geometry that consisted of a 90 kVp X-ray spectrum and performed calculations by using the SpekCal program (REAL Software, Inc.) with Monte Carlo simulations. A basic test phantom was imaged with the spectral CT system for the calibration and decomposition process. This phantom contained three different materials, including lipid, iodine and gold nanoparticles, with six holes 3 mm in diameter. In addition to reducing pile-up and charge sharing effect, the photon counting detector was considered an ideal detector. Then, the accuracy of material decomposition techniques with two inverse fitting functions were evaluated between decomposed images and reference images in terms of root mean square error (RMSE). The results showed that decomposed images had a good volumetric fraction for each material, and the RMSE between the measured and true volumes of lipid, iodine and gold nanoparticle fractions varied from 12.51% to 1.29% for inverse fitting functions. The study indicated that spectral CT in conjunction with a CZT photon-counting detector in conjunction with a dual energy technique can be used to identifying materials and may be a promising modality for quantifying material properties of vulnerable plaques.
Vadapalli, U.; Srivastava, R. P.; Vedanti, N.; Dimri, V. P.
2014-01-01
Permeability of a hydrocarbon reservoir is usually estimated from core samples in the laboratory or from well test data provided by the industry. However, such data is very sparse and as such it takes longer to generate that. Thus, estimation of permeability directly from available porosity logs could be an alternative and far easier approach. In this paper, a method of permeability estimation is proposed for a sandstone reservoir, which considers fractal behavior of pore size distribution and tortuosity of capillary pathways to perform Monte Carlo simulations. In this method, we consider a reservoir to be a mono-dispersed medium to avoid effects of micro-porosity. The method is applied to porosity logs obtained from Ankleshwar oil field, situated in the Cambay basin, India, to calculate permeability distribution in a well. Computed permeability values are in good agreement with the observed permeability obtained from well test data. We also studied variation of permeability with different parameters such as tortuosity fractal dimension (Dt), grain size (r) and minimum particle size (d0), and found that permeability is highly dependent upon the grain size. This method will be extremely useful for permeability estimation, if the average grain size of the reservoir rock is known.
Autocorrelations in hybrid Monte Carlo simulations
International Nuclear Information System (INIS)
Simulations of QCD suffer from severe critical slowing down towards the continuum limit. This problem is known to be prominent in the topological charge, however, all observables are affected to various degree by these slow modes in the Monte Carlo evolution. We investigate the slowing down in high statistics simulations and propose a new error analysis method, which gives a realistic estimate of the contribution of the slow modes to the errors. (orig.)
Simulated Annealing using Hybrid Monte Carlo
Salazar, Rafael; Toral, Raúl
1997-01-01
We propose a variant of the simulated annealing method for optimization in the multivariate analysis of differentiable functions. The method uses global actualizations via the hybrid Monte Carlo algorithm in their generalized version for the proposal of new configurations. We show how this choice can improve upon the performance of simulated annealing methods (mainly when the number of variables is large) by allowing a more effective searching scheme and a faster annealing schedule.
Monte Carlo Simulations of Star Clusters
Giersz, M
2000-01-01
A revision of Stod\\'o{\\l}kiewicz's Monte Carlo code is used to simulate evolution of large star clusters. The survey on the evolution of multi-mass N-body systems influenced by the tidal field of a parent galaxy and by stellar evolution is discussed. For the first time, the simulation on the "star-by-star" bases of evolution of 1,000,000 body star cluster is presented. \\
Topological zero modes in Monte Carlo simulations
International Nuclear Information System (INIS)
We present an improvement of global Metropolis updating steps, the instanton hits, used in a hybrid Monte Carlo simulation of the two-flavor Schwinger model with staggered fermions. These hits are designed to change the topological sector of the gauge field. In order to match these hits to an unquenched simulation with pseudofermions, the approximate zero mode structure of the lattice Dirac operator has to be considered explicitly. (orig.)
Monte Carlo simulation and numerical integration
Geweke, John F.
1995-01-01
This is a survey of simulation methods in economics, with a specific focus on integration problems. It describes acceptance methods, importance sampling procedures, and Markov chain Monte Carlo methods for simulation from univariate and multivariate distributions and their application to the approximation of integrals. The exposition gives emphasis to combinations of different approaches and assessment of the accuracy of numerical approximations to integrals and expectations. The survey illus...
Monte Carlo simulation code modernization
CERN. Geneva
2015-01-01
The continual development of sophisticated transport simulation algorithms allows increasingly accurate description of the effect of the passage of particles through matter. This modelling capability finds applications in a large spectrum of fields from medicine to astrophysics, and of course HEP. These new capabilities however come at the cost of a greater computational intensity of the new models, which has the effect of increasing the demands of computing resources. This is particularly true for HEP, where the demand for more simulation are driven by the need of both more accuracy and more precision, i.e. better models and more events. Usually HEP has relied on the "Moore's law" evolution, but since almost ten years the increase in clock speed has withered and computing capacity comes in the form of hardware architectures of many-core or accelerated processors. To harness these opportunities we need to adapt our code to concurrent programming models taking advantages of both SIMD and SIMT architectures. Th...
Monte Carlo simulations for plasma physics
Energy Technology Data Exchange (ETDEWEB)
Okamoto, M.; Murakami, S.; Nakajima, N.; Wang, W.X. [National Inst. for Fusion Science, Toki, Gifu (Japan)
2000-07-01
Plasma behaviours are very complicated and the analyses are generally difficult. However, when the collisional processes play an important role in the plasma behaviour, the Monte Carlo method is often employed as a useful tool. For examples, in neutral particle injection heating (NBI heating), electron or ion cyclotron heating, and alpha heating, Coulomb collisions slow down high energetic particles and pitch angle scatter them. These processes are often studied by the Monte Carlo technique and good agreements can be obtained with the experimental results. Recently, Monte Carlo Method has been developed to study fast particle transports associated with heating and generating the radial electric field. Further it is applied to investigating the neoclassical transport in the plasma with steep gradients of density and temperatures which is beyong the conventional neoclassical theory. In this report, we briefly summarize the researches done by the present authors utilizing the Monte Carlo method. (author)
Substrate influence on two-dimensional solids and liquids: A Monte Carlo simulation study
DEFF Research Database (Denmark)
Vives, E.; Lindgård, Per-Anker
1991-01-01
solid and liquid phase for all the cases studied. We have in particular investigated the contribution from the two-dimensional liquid to the Bragg peaks corresponding to the substrate structure. Reiter and Moss and their collaborators have demonstrated that this gives valuable information about the...
Shirakawa, Seiji; Tadokoro, Masanori; Hashimoto, Hiroshi; Ushiroda, Tomoya; Toyama, Hiroshi
2015-01-01
In this study, we devised and evaluated a method for attenuation correction of the hot spot in (111)In planar images. By use of the difference in transmittance between two energies (171 and 245 keV), the depth of the hot spot was calculated. Planar images of point sources in a numerical phantom (water) with depths from 0 to 20 cm at 2 cm intervals were prepared by Monte Carlo simulation. From the linear attenuation coefficient of the two energies and the 171/245 keV count ratio-depth relationship, the depth of the point source was calculated, and an attenuation correction was performed. A simulation was made under conditions taking into account both attenuation and scatter (A(+)S(+)) and attenuation alone (A(+)S(-)). The attenuation correction was evaluated with use of corrected and true counts obtained from homogeneous phantoms mimicking attenuation in soft tissue, bone, and the lungs, and heterogeneous phantoms prepared by combining them. In the A(+)S(+) condition, images were affected markedly by scattered photons in all phantoms at depths of 4-8 cm. The errors at depths of 10 cm or greater were within ±10 % in water and within ±6 % in soft tissue. However, the errors were about -30 % in bone and about +70 % in lung, indicating that scatter distributions different from those in water increased the errors. In the A(+)S(-) condition, the errors were within ±5 % in all homogeneous and heterogeneous phantoms, and satisfactory results were obtained. Precise attenuation correction of scatter-corrected planar images was confirmed to be possible with this method. PMID:25149323
A clinical study of lung cancer dose calculation accuracy with Monte Carlo simulation
Zhao, Yanqun; Qi, Guohai; Yin, Gang; Wang, Xianliang; Wang, Pei; Li, Jian; Xiao, Mingyong; Li, Jie; Kang, Shengwei; Liao, Xiongfei
2014-01-01
Background The accuracy of dose calculation is crucial to the quality of treatment planning and, consequently, to the dose delivered to patients undergoing radiation therapy. Current general calculation algorithms such as Pencil Beam Convolution (PBC) and Collapsed Cone Convolution (CCC) have shortcomings in regard to severe inhomogeneities, particularly in those regions where charged particle equilibrium does not hold. The aim of this study was to evaluate the accuracy of the PBC and CCC alg...
International Nuclear Information System (INIS)
International Commission on Radiological Protection (ICRP) reported comprehensive dose conversion coefficients for adult population, which is exposed to external photon sources in the Publication 74. However, those quantities were calculated from so-called stylized (or mathematical) phantoms composed of simplified mathematical surface equations so that the discrepancy between the phantoms and real human anatomy has been investigated by several authors using Caucasian-based voxel phantoms. To address anatomical and racial limitations of the stylized phantoms, several Asian-based voxel phantoms have been developed by Korean and Japanese investigators, independently. In the current study, photon dose conversion coefficients of ICRP 74 were compared with those from a total of five Asian-based male voxel phantoms, whose body dimensions were almost identical. Those of representative radio-sensitive organs (testes, red bone marrow, colon, lungs, and stomach), and effective dose conversion coefficients were obtained for comparison. Even though organ doses for testes, colon and lungs, and effective doses from ICRP 74 agreed well with those from Asian voxel phantoms within 10%, absorbed doses for red bone marrow and stomach showed significant discrepancies up to 30% which was mainly attributed to difference of phantom description between stylized and voxel phantoms. This study showed that the ICRP 74 dosimetry data, which have been reported to be unrealistic compared to those from Caucasian-based voxel phantoms, are also not appropriate for Asian population
Hammermann, M; Brun, N; Klenin, K V; May, R.; Tóth, K; Langowski, J.
1998-01-01
Using small angle neutron scattering we have measured the static form factor of two different superhelical DNAs, p1868 (1868 bp) and pUC18 (2686 bp), in dilute aqueous solution at salt concentrations between 0 and 1.5 M Na+ in 10 mM Tris at 0% and 100% D2O. For both DNA molecules, the theoretical static form factor was also calculated from an ensemble of Monte Carlo configurations generated by a previously described model. Simulated and measured form factors of both DNAs showed the same behav...
Siraleartmukul, Krisana; Siriwong, Khatcharin; Remsungnen, Tawun; Muangsin, Nongnuj; Udomkichdecha, Werasak; Hannongbua, Supot
2004-09-01
The solvation structure of glucosamine in aqueous solution was investigated using Monte Carlo simulation at 298 K. The MCY rigid water model and ab initio glucosamine-water fitted potential were applied. The first hydration shell appears at 4.6 Å from the center of glucosamine with a coordination number of seven water molecules where one water lies in the ligand's plane while two and four of them are about 2-4 Å above and below the plane, respectively. Furthermore, the mobility distribution and orientation of the water molecules around the ligand have been intensively investigated and reported.
International Nuclear Information System (INIS)
This report was aimed at structuring the design of architectures and studying performance measurement of a parallel computing environment using a Monte Carlo simulation for particle therapy using a high performance computing (HPC) instance within a public cloud-computing infrastructure. Performance measurements showed an approximately 28 times faster speed than seen with single-thread architecture, combined with improved stability. A study of methods of optimizing the system operations also indicated lower cost. (author)
Institute of Scientific and Technical Information of China (English)
Wang Yang; Cheng Tianle; Xia Yuanming; Jiang Dazhi
2001-01-01
In this paper, the fracture process of a unidirectional CF/SiC single edge-notched beam (SENB) under three-point bending (TPB) is studied by means of macro/micro-statistical Monte Carlo simulation. The simulated p-△ curves are in agreement with the experimental results before the peaks of curves, and the simulated microevolution patterns are in agreement with the patterns of the crack surfaces, which have verified this method. It is preliminarily demonstrated that the second turning point in the compliance changing rate curve corresponds to the fracture initiation for experiments on SENB under TPB of unidirectional CF/SiC composites.
Chow, James C. L.
2012-10-01
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.
Replica Exchange for Reactive Monte Carlo Simulations
Czech Academy of Sciences Publication Activity Database
Turner, C.H.; Brennan, J.K.; Lísal, Martin
2007-01-01
Roč. 111, č. 43 (2007), s. 15706-15715. ISSN 1932-7447 R&D Projects: GA ČR GA203/05/0725; GA AV ČR 1ET400720409; GA AV ČR 1ET400720507 Institutional research plan: CEZ:AV0Z40720504 Keywords : monte carlo * simulation * reactive system Subject RIV: CF - Physical ; Theoretical Chemistry
Archimedes, the Free Monte Carlo simulator
Sellier, Jean Michel D.
2012-01-01
Archimedes is the GNU package for Monte Carlo simulations of electron transport in semiconductor devices. The first release appeared in 2004 and since then it has been improved with many new features like quantum corrections, magnetic fields, new materials, GUI, etc. This document represents the first attempt to have a complete manual. Many of the Physics models implemented are described and a detailed description is presented to make the user able to write his/her own input deck. Please, fee...
Monte Carlo simulation of electron slowing down in indium
International Nuclear Information System (INIS)
Highlights: • Electron scattering in indium targets. • Modeling of elastic cross-sections. • Monte Carlo simulation of low energy electrons. - Abstract: In the current study, we aim at simulating via a detailed Monte Carlo code, the electron penetration in a semi-infinite indium medium for incident energies ranging from 0.5 to 5 keV. Electron range, backscattering coefficients, mean penetration depths as well as stopping profiles are then reported. The results may be seen as the first predictions for low-energy electron penetration in indium target
Monte Carlo simulation of electron slowing down in indium
Energy Technology Data Exchange (ETDEWEB)
Rouabah, Z.; Hannachi, M. [Materials and Electronic Systems Laboratory (LMSE), University of Bordj Bou Arreridj, Bordj Bou Arreridj (Algeria); Champion, C. [Université de Bordeaux 1, CNRS/IN2P3, Centre d’Etudes Nucléaires de Bordeaux-Gradignan, (CENBG), Gradignan (France); Bouarissa, N., E-mail: n_bouarissa@yahoo.fr [Laboratory of Materials Physics and its Applications, University of M' sila, 28000 M' sila (Algeria)
2015-07-15
Highlights: • Electron scattering in indium targets. • Modeling of elastic cross-sections. • Monte Carlo simulation of low energy electrons. - Abstract: In the current study, we aim at simulating via a detailed Monte Carlo code, the electron penetration in a semi-infinite indium medium for incident energies ranging from 0.5 to 5 keV. Electron range, backscattering coefficients, mean penetration depths as well as stopping profiles are then reported. The results may be seen as the first predictions for low-energy electron penetration in indium target.
Monte Carlo Simulation of Quantum Computation
Cerf, N. J.; Koonin, S. E.
1997-01-01
The many-body dynamics of a quantum computer can be reduced to the time evolution of non-interacting quantum bits in auxiliary fields by use of the Hubbard-Stratonovich representation of two-bit quantum gates in terms of one-bit gates. This makes it possible to perform the stochastic simulation of a quantum algorithm, based on the Monte Carlo evaluation of an integral of dimension polynomial in the number of quantum bits. As an example, the simulation of the quantum circuit for the Fast Fouri...
Monte Carlo Simulation of Critical Casimir Forces
Vasilyev, Oleg A.
2015-03-01
In the vicinity of the second order phase transition point long-range critical fluctuations of the order parameter appear. The second order phase transition in a critical binary mixture in the vicinity of the demixing point belongs to the universality class of the Ising model. The superfluid transition in liquid He belongs to the universality class of the XY model. The confinement of long-range fluctuations causes critical Casimir forces acting on confining surfaces or particles immersed in the critical substance. Last decade critical Casimir forces in binary mixtures and liquid helium were studied experimentally. The critical Casimir force in a film of a given thickness scales as a universal scaling function of the ratio of the film thickness to the bulk correlation length divided over the cube of the film thickness. Using Monte Carlo simulations we can compute critical Casimir forces and their scaling functions for lattice Ising and XY models which correspond to experimental results for the binary mixture and liquid helium, respectively. This chapter provides the description of numerical methods for computation of critical Casimir interactions for lattice models for plane-plane, plane-particle, and particle-particle geometries.
International Nuclear Information System (INIS)
-Small animal PET allows qualitative assessment and quantitative measurement of biochemical processes in vivo, but the accuracy and reproducibility of imaging results can be affected by several parameters. The first aim of this study was to investigate the performance of different CT-based attenuation correction strategies and assess the resulting impact on PET images. The absorbed dose in different tissues caused by scanning procedures was also discussed to minimize biologic damage generated by radiation exposure due to PET/CT scanning. A small animal PET/CT system was modeled based on Monte Carlo simulation to generate imaging results and dose distribution. Three energy mapping methods, including the bilinear scaling method, the dual-energy method and the hybrid method which combines the kVp conversion and the dual-energy method, were investigated comparatively through assessing the accuracy of estimating linear attenuation coefficient at 511 keV and the bias introduced into PET quantification results due to CT-based attenuation correction. Our results showed that the hybrid method outperformed the bilinear scaling method, while the dual-energy method achieved the highest accuracy among the three energy mapping methods. Overall, the accuracy of PET quantification results have similar trend as that for the estimation of linear attenuation coefficients, whereas the differences between the three methods are more obvious in the estimation of linear attenuation coefficients than in the PET quantification results. With regards to radiation exposure from CT, the absorbed dose ranged between 7.29-45.58 mGy for 50-kVp scan and between 6.61-39.28 mGy for 80-kVp scan. For 18F radioactivity concentration of 1.86x105 Bq/ml, the PET absorbed dose was around 24 cGy for tumor with a target-to-background ratio of 8. The radiation levels for CT scans are not lethal to the animal, but concurrent use of PET in longitudinal study can increase the risk of biological effects. The
Guideline for radiation transport simulation with the Monte Carlo method
International Nuclear Information System (INIS)
Today, the photon and neutron transport calculations with the Monte Carlo method have been progressed with advanced Monte Carlo codes and high-speed computers. Monte Carlo simulation is rather suitable expression than the calculation. Once Monte Carlo codes become more friendly and performance of computer progresses, most of the shielding problems will be solved by using the Monte Carlo codes and high-speed computers. As those codes prepare the standard input data for some problems, the essential techniques for solving the Monte Carlo method and variance reduction techniques of the Monte Carlo calculation might lose the interests to the general Monte Carlo users. In this paper, essential techniques of the Monte Carlo method and the variance reduction techniques, such as importance sampling method, selection of estimator, and biasing technique, are described to afford a better understanding of the Monte Carlo method and Monte Carlo code. (author)
Lattice Monte Carlo simulations of polymer melts
Hsu, Hsiao-Ping
2014-12-01
We use Monte Carlo simulations to study polymer melts consisting of fully flexible and moderately stiff chains in the bond fluctuation model at a volume fraction 0.5. In order to reduce the local density fluctuations, we test a pre-packing process for the preparation of the initial configurations of the polymer melts, before the excluded volume interaction is switched on completely. This process leads to a significantly faster decrease of the number of overlapping monomers on the lattice. This is useful for simulating very large systems, where the statistical properties of the model with a marginally incomplete elimination of excluded volume violations are the same as those of the model with strictly excluded volume. We find that the internal mean square end-to-end distance for moderately stiff chains in a melt can be very well described by a freely rotating chain model with a precise estimate of the bond-bond orientational correlation between two successive bond vectors in equilibrium. The plot of the probability distributions of the reduced end-to-end distance of chains of different stiffness also shows that the data collapse is excellent and described very well by the Gaussian distribution for ideal chains. However, while our results confirm the systematic deviations between Gaussian statistics for the chain structure factor Sc(q) [minimum in the Kratky-plot] found by Wittmer et al. [EPL 77, 56003 (2007)] for fully flexible chains in a melt, we show that for the available chain length these deviations are no longer visible, when the chain stiffness is included. The mean square bond length and the compressibility estimated from collective structure factors depend slightly on the stiffness of the chains.
Perspectives for Monte Carlo simulations on the CNN Universal Machine
Ercsey-Ravasz, M.; Roska, T.; Neda, Z.
2006-01-01
Possibilities for performing stochastic simulations on the analog and fully parallelized Cellular Neural Network Universal Machine (CNN-UM) are investigated. By using a chaotic cellular automaton perturbed with the natural noise of the CNN-UM chip, a realistic binary random number generator is built. As a specific example for Monte Carlo type simulations, we use this random number generator and a CNN template to study the classical site-percolation problem on the ACE16K chip. The study reveal...
International Nuclear Information System (INIS)
A mathematical model, based on Monte Carlo simulation, is proposed for deriving absorbed energy and dose distribution in mammography utilizing a mathematical water-like phantom. The model was validated for its accuracy against experimental and published data. The main factor discriminating absorbed energy distribution characteristics among different mammographic techniques was considered the X-ray spectrum. The absorbed energy distribution inside the phantom was investigated via percentage depth dose and isodose curves. The influence of the factors affecting X-ray spectrum (tube voltage, anode material, filter material and thickness) on absorbed energy distribution was examined. The hardness of the beam, due to increase of tube voltage or filtration, was found to be the major factor affecting absorbed energy distribution inside the phantom. In general, Mo and W anode systems demonstrated superior dosimetric characteristics against those of W-Mo or Rh. The model presented can be used for estimating absolute and relative breast dose values and their spatial distributions
Jones, Andrew Osler
There is an increasing interest in the use of inhomogeneity corrections for lung, air, and bone in radiotherapy treatment planning. Traditionally, corrections based on physical density have been used. Modern algorithms use the electron density derived from CT images. Small fields are used in both conformal radiotherapy and IMRT, however their beam characteristics in inhomogeneous media have not been extensively studied. This work compares traditional and modern treatment planning algorithms to Monte Carlo simulations in and near low-density inhomogeneities. Field sizes ranging from 0.5 cm to 5 cm in diameter are projected onto a phantom containing inhomogeneities and depth dose curves are compared. Comparisons of the Dose Perturbation Factors (DPF) are presented as functions of density and field size. Dose Correction Factors (DCF), which scale the algorithms to the Monte Carlo data, are compared for each algorithm. Physical scaling algorithms such as Batho and Equivalent Pathlength (EPL) predict an increase in dose for small fields passing through lung tissue, where Monte Carlo simulations show a sharp dose drop. The physical model-based collapsed cone convolution (CCC) algorithm correctly predicts the dose drop, but does not accurately predict the magnitude. Because the model-based algorithms do not correctly account for the change in backscatter, the dose drop predicted by CCC occurs further downstream compared to that predicted by the Monte Carlo simulations. Beyond the tissue inhomogeneity all of the algorithms studied predict dose distributions in close agreement with Monte Carlo simulations. Dose-volume relationships are important in understanding the effects of radiation to the lung. Dose within the lung is affected by a complex function of beam energy, lung tissue density, and field size. Dose algorithms vary in their abilities to correctly predict the dose to the lung tissue. A thorough analysis of the effects of density, and field size on dose to the lung
Monte Carlo simulation of magnetic nanostructured thin films
Institute of Scientific and Technical Information of China (English)
Guan Zhi-Qiang; Yutaka Abe; Jiang Dong-Hua; Lin Hai; Yoshitake Yamazakia; Wu Chen-Xu
2004-01-01
@@ Using Monte Carlo simulation, we have compared the magnetic properties between nanostructured thin films and two-dimensional crystalline solids. The dependence of nanostructured properties on the interaction between particles that constitute the nanostructured thin films is also studied. The result shows that the parameters in the interaction potential have an important effect on the properties of nanostructured thin films at the transition temperatures.
Quantum Monte Carlo simulation with a black hole
Benić, Sanjin; Yamamoto, Arata
2016-05-01
We perform quantum Monte Carlo simulations in the background of a classical black hole. The lattice discretized path integral is numerically calculated in the Schwarzschild metric and in its approximated metric. We study spontaneous symmetry breaking of a real scalar field theory. We observe inhomogeneous symmetry breaking induced by an inhomogeneous gravitational field.
Accelerated GPU based SPECT Monte Carlo simulations.
Garcia, Marie-Paule; Bert, Julien; Benoit, Didier; Bardiès, Manuel; Visvikis, Dimitris
2016-06-01
Monte Carlo (MC) modelling is widely used in the field of single photon emission computed tomography (SPECT) as it is a reliable technique to simulate very high quality scans. This technique provides very accurate modelling of the radiation transport and particle interactions in a heterogeneous medium. Various MC codes exist for nuclear medicine imaging simulations. Recently, new strategies exploiting the computing capabilities of graphical processing units (GPU) have been proposed. This work aims at evaluating the accuracy of such GPU implementation strategies in comparison to standard MC codes in the context of SPECT imaging. GATE was considered the reference MC toolkit and used to evaluate the performance of newly developed GPU Geant4-based Monte Carlo simulation (GGEMS) modules for SPECT imaging. Radioisotopes with different photon energies were used with these various CPU and GPU Geant4-based MC codes in order to assess the best strategy for each configuration. Three different isotopes were considered: (99m) Tc, (111)In and (131)I, using a low energy high resolution (LEHR) collimator, a medium energy general purpose (MEGP) collimator and a high energy general purpose (HEGP) collimator respectively. Point source, uniform source, cylindrical phantom and anthropomorphic phantom acquisitions were simulated using a model of the GE infinia II 3/8" gamma camera. Both simulation platforms yielded a similar system sensitivity and image statistical quality for the various combinations. The overall acceleration factor between GATE and GGEMS platform derived from the same cylindrical phantom acquisition was between 18 and 27 for the different radioisotopes. Besides, a full MC simulation using an anthropomorphic phantom showed the full potential of the GGEMS platform, with a resulting acceleration factor up to 71. The good agreement with reference codes and the acceleration factors obtained support the use of GPU implementation strategies for improving computational
Accelerated GPU based SPECT Monte Carlo simulations
Garcia, Marie-Paule; Bert, Julien; Benoit, Didier; Bardiès, Manuel; Visvikis, Dimitris
2016-06-01
Monte Carlo (MC) modelling is widely used in the field of single photon emission computed tomography (SPECT) as it is a reliable technique to simulate very high quality scans. This technique provides very accurate modelling of the radiation transport and particle interactions in a heterogeneous medium. Various MC codes exist for nuclear medicine imaging simulations. Recently, new strategies exploiting the computing capabilities of graphical processing units (GPU) have been proposed. This work aims at evaluating the accuracy of such GPU implementation strategies in comparison to standard MC codes in the context of SPECT imaging. GATE was considered the reference MC toolkit and used to evaluate the performance of newly developed GPU Geant4-based Monte Carlo simulation (GGEMS) modules for SPECT imaging. Radioisotopes with different photon energies were used with these various CPU and GPU Geant4-based MC codes in order to assess the best strategy for each configuration. Three different isotopes were considered: 99m Tc, 111In and 131I, using a low energy high resolution (LEHR) collimator, a medium energy general purpose (MEGP) collimator and a high energy general purpose (HEGP) collimator respectively. Point source, uniform source, cylindrical phantom and anthropomorphic phantom acquisitions were simulated using a model of the GE infinia II 3/8" gamma camera. Both simulation platforms yielded a similar system sensitivity and image statistical quality for the various combinations. The overall acceleration factor between GATE and GGEMS platform derived from the same cylindrical phantom acquisition was between 18 and 27 for the different radioisotopes. Besides, a full MC simulation using an anthropomorphic phantom showed the full potential of the GGEMS platform, with a resulting acceleration factor up to 71. The good agreement with reference codes and the acceleration factors obtained support the use of GPU implementation strategies for improving computational efficiency
International Nuclear Information System (INIS)
The solvent effects on the relative free energies of Eu3+ toYb3+ ion mutation in solution have been investigated using a Monte Carlo simulation of statistical perturbation theory (SPT). Our results agree well with available data that were obtained by others. Particularly, the results of water (SPC/E) solvent are almost identical with experimental data. For the present Eu3+ and Yb3+ ions, the relative free energies of solvation vs. Born's function of bulk solvents decrease with increasing Born's function of bulk solvents. There is also good agreement between the calculated structural properties in this study and the published works obtained by computer simulation and experimental work
International Nuclear Information System (INIS)
Radiotherapy computational simulation procedures using Monte Carlo (MC) methods have shown to be increasingly important to the improvement of cancer fighting strategies. One of the biases in this practice is the discretization of the radioactive source in brachytherapy simulations, which often do not match with a real situation. This study had the aim to identify and to measure the influence of radioactive sources discretization in brachytherapy MC simulations when compared to those that do not present discretization, using prostate brachytherapy with Iodine-125 radionuclide as model. Simulations were carried out with 108 events with both types of sources to compare them using EGSnrc code associated to MASH phantom in orthostatic and supine positions with some anatomic adaptations. Significant alterations were found, especially regarding bladder, rectum and the prostate itself. It can be concluded that there is a need to discretized sources in brachytherapy simulations to ensure its representativeness. (author)
International Nuclear Information System (INIS)
This study investigates the radiation shielding design of the treatment room for boron neutron capture therapy at Tsing Hua Open-pool Reactor using 'TORT-coupled MCNP' method. With this method, the computational efficiency is improved significantly by two to three orders of magnitude compared to the analog Monte Carlo MCNP calculation. This makes the calculation feasible using a single CPU in less than 1 day. Further optimization of the photon weight windows leads to additional 50-75% improvement in the overall computational efficiency
Monte Carlo simulation of tomography techniques using the platform Gate
International Nuclear Information System (INIS)
Simulations play a key role in functional imaging, with applications ranging from scanner design, scatter correction, protocol optimisation. GATE (Geant4 for Application Tomography Emission) is a platform for Monte Carlo Simulation. It is based on Geant4 to generate and track particles, to model geometry and physics process. Explicit modelling of time includes detector motion, time of flight, tracer kinetics. Interfaces to voxellised models and image reconstruction packages improve the integration of GATE in the global modelling cycle. In this work Monte Carlo simulations are used to understand and optimise the gamma camera's performances. We study the effect of the distance between source and collimator, the diameter of the holes and the thick of the collimator on the spatial resolution, energy resolution and efficiency of the gamma camera. We also study the reduction of simulation's time and implement a model of left ventricle in GATE. (Author). 7 refs
Monte Carlo Simulation of an American Option
Directory of Open Access Journals (Sweden)
Gikiri Thuo
2007-04-01
Full Text Available We implement gradient estimation techniques for sensitivity analysis of option pricing which can be efficiently employed in Monte Carlo simulation. Using these techniques we can simultaneously obtain an estimate of the option value together with the estimates of sensitivities of the option value to various parameters of the model. After deriving the gradient estimates we incorporate them in an iterative stochastic approximation algorithm for pricing an option with early exercise features. We illustrate the procedure using an example of an American call option with a single dividend that is analytically tractable. In particular we incorporate estimates for the gradient with respect to the early exercise threshold level.
Monte-Carlo simulations: FLUKA vs. MCNPX
Czech Academy of Sciences Publication Activity Database
Oden, M.; Krása, Antonín; Majerle, Mitja; Svoboda, Ondřej; Wagner, Vladimír
Melville : AMER INST PHYSICS, 2007 - (Granja, C.; Leroy, C.; Štekl, I.), s. 219-221 ISBN 978-0-7354-0472-4. ISSN 0094-243X. - (AIP Conference Proceedings. 958). [4th International Summer School on Nuclear Physics Methods and Accelerators in Biology and Medicine . Praha (CZ), 08.07.2007-19.07.2007] R&D Projects: GA MŠk(CZ) LC07050 Institutional research plan: CEZ:AV0Z10480505 Keywords : neutron production * spallation reaction * Monte-Carlo simulation Subject RIV: BG - Nuclear , Atomic and Molecular Physics, Colliders
Monte Carlo simulations for heavy ion dosimetry
Geithner, Oksana
2006-01-01
Water-to-air stopping power ratio ( ) calculations for the ionization chamber dosimetry of clinically relevant ion beams with initial energies from 50 to 450 MeV/u have been performed using the Monte Carlo technique. To simulate the transport of a particle in water the computer code SHIELD-HIT v2 was used which is a substantially modified version of its predecessor SHIELD-HIT v1. The code was partially rewritten, replacing formerly used single precision variables with double precision variabl...
Archimedes, the Free Monte Carlo simulator
Sellier, Jean Michel D
2012-01-01
Archimedes is the GNU package for Monte Carlo simulations of electron transport in semiconductor devices. The first release appeared in 2004 and since then it has been improved with many new features like quantum corrections, magnetic fields, new materials, GUI, etc. This document represents the first attempt to have a complete manual. Many of the Physics models implemented are described and a detailed description is presented to make the user able to write his/her own input deck. Please, feel free to contact the author if you want to contribute to the project.
Monte Carlo simulation of a two-dimensional magnetic foam
International Nuclear Information System (INIS)
A two-dimensional Ising-like model with spin 1 and long-range interactions is studied numerically through a Monte Carlo simulation. The goal of the simulation is to describe pattern formations and critical temperature of two-dimensional magnetic structures. Three sets of parameters are considered, that give rise to stripes, labyrinths or cellular domain structures. We determine for each configuration the transition ordering temperatures, the relaxation of the energy, the hysteresis cycle, and the average size of the domains
Probabilistic fire simulator - Monte Carlo simulation tool for fire scenarios
International Nuclear Information System (INIS)
Risk analysis tool is developed for computing of the distributions of fire model output variables. The tool, called Probabilistic Fire Simulator, combines Monte Carlo simulation and CFAST two-zone fire model. In this work, it is used to calculate failure probability of redundant cables and fire detector activation times in a cable tunnel fire. Sensitivity of the output variables to the input variables is calculated in terms of the rank order correlations. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Rodriguez, Miguel; Sempau, Josep [Institut de Tècniques Energètiques, Universitat Politècnica de Catalunya, Diagonal 647, Barcelona E-08028 (Spain); Brualla, Lorenzo, E-mail: lorenzo.brualla@uni-duisburg-essen.de [NCTeam, Strahlenklinik, Universitätsklinikum Essen, Hufelandstraße 55, Essen D-45122 (Germany)
2015-06-15
Purpose: The Monte Carlo simulation of electron transport in Linac targets using the condensed history technique is known to be problematic owing to a potential dependence of absorbed dose distributions on the electron step length. In the PENELOPE code, the step length is partially determined by the transport parameters C1 and C2. The authors have investigated the effect on the absorbed dose distribution of the values given to these parameters in the target. Methods: A monoenergetic 6.26 MeV electron pencil beam from a point source was simulated impinging normally on a cylindrical tungsten target. Electrons leaving the tungsten were discarded. Radial absorbed dose profiles were obtained at 1.5 cm of depth in a water phantom located at 100 cm for values of C1 and C2 in the target both equal to 0.1, 0.01, or 0.001. A detailed simulation case was also considered and taken as the reference. Additionally, lateral dose profiles were estimated and compared with experimental measurements for a 6 MV photon beam of a Varian Clinac 2100 for the cases of C1 and C2 both set to 0.1 or 0.001 in the target. Results: On the central axis, the dose obtained for the case C1 = C2 = 0.1 shows a deviation of (17.2% ± 1.2%) with respect to the detailed simulation. This difference decreases to (3.7% ± 1.2%) for the case C1 = C2 = 0.01. The case C1 = C2 = 0.001 produces a radial dose profile that is equivalent to that of the detailed simulation within the reached statistical uncertainty of 1%. The effect is also appreciable in the crossline dose profiles estimated for the realistic geometry of the Linac. In another simulation, it was shown that the error made by choosing inappropriate transport parameters can be masked by tuning the energy and focal spot size of the initial beam. Conclusions: The use of large path lengths for the condensed simulation of electrons in a Linac target with PENELOPE conducts to deviations of the dose in the patient or phantom. Based on the results obtained in
Stochastic simulation and Monte-Carlo methods; Simulation stochastique et methodes de Monte-Carlo
Energy Technology Data Exchange (ETDEWEB)
Graham, C. [Centre National de la Recherche Scientifique (CNRS), 91 - Gif-sur-Yvette (France); Ecole Polytechnique, 91 - Palaiseau (France); Talay, D. [Institut National de Recherche en Informatique et en Automatique (INRIA), 78 - Le Chesnay (France); Ecole Polytechnique, 91 - Palaiseau (France)
2011-07-01
This book presents some numerical probabilistic methods of simulation with their convergence speed. It combines mathematical precision and numerical developments, each proposed method belonging to a precise theoretical context developed in a rigorous and self-sufficient manner. After some recalls about the big numbers law and the basics of probabilistic simulation, the authors introduce the martingales and their main properties. Then, they develop a chapter on non-asymptotic estimations of Monte-Carlo method errors. This chapter gives a recall of the central limit theorem and precises its convergence speed. It introduces the Log-Sobolev and concentration inequalities, about which the study has greatly developed during the last years. This chapter ends with some variance reduction techniques. In order to demonstrate in a rigorous way the simulation results of stochastic processes, the authors introduce the basic notions of probabilities and of stochastic calculus, in particular the essential basics of Ito calculus, adapted to each numerical method proposed. They successively study the construction and important properties of the Poisson process, of the jump and deterministic Markov processes (linked to transport equations), and of the solutions of stochastic differential equations. Numerical methods are then developed and the convergence speed results of algorithms are rigorously demonstrated. In passing, the authors describe the probabilistic interpretation basics of the parabolic partial derivative equations. Non-trivial applications to real applied problems are also developed. (J.S.)
The impact of Monte Carlo simulation. A scientometric analysis of scholarly literature
International Nuclear Information System (INIS)
A scientometric analysis of Monte Carlo simulation and Monte Carlo codes has been performed over a set of representative scholarly journals related to radiation physics. The results of this study are reported and discussed. They document and quantitatively appraise the role of Monte Carlo methods and codes in scientific research and engineering applications. (author)
Components of Detector Response Function: Experiment and Monte Carlo Simulation
International Nuclear Information System (INIS)
Components of the response function of an HPGe (high-purity germanium) detector due to full or partial energy deposition by gamma- and X-rays were studied. Experimental response functions for 241Am, Ba and Tb were compared with those obtained from the Monte Carlo simulations. The role of physical mechanisms for each component was investigated by considering escape/absorption of photons, photoelectrons, Auger electrons, recoil electrons and X-rays of the detector material. A detailed comparison of the experimental Compton, photoelectron, detector X-ray escape components and full-energy peaks with those obtained from Monte Carlo program are presented
Atomistic Monte Carlo simulation of lipid membranes
DEFF Research Database (Denmark)
Wüstner, Daniel; Sklenar, Heinz
2014-01-01
molecule, as assessed by calculation of molecular energies and entropies. We also show transition from a crystalline-like to a fluid DPPC bilayer by the CBC local-move MC method, as indicated by the electron density profile, head group orientation, area per lipid, and whole-lipid displacements. We discuss......Biological membranes are complex assemblies of many different molecules of which analysis demands a variety of experimental and computational approaches. In this article, we explain challenges and advantages of atomistic Monte Carlo (MC) simulation of lipid membranes. We provide an introduction...... into the various move sets that are implemented in current MC methods for efficient conformational sampling of lipids and other molecules. In the second part, we demonstrate for a concrete example, how an atomistic local-move set can be implemented for MC simulations of phospholipid monomers and...
Energy Technology Data Exchange (ETDEWEB)
Moradmand Jalali, Hamed; Bashiri, Hadis, E-mail: hbashiri@kashanu.ac.ir; Rasa, Hossein
2015-05-01
In the present study, the mechanism of free radical production by light-reflective agents in sunscreens (TiO{sub 2}, ZnO and ZrO{sub 2}) was obtained by applying kinetic Monte Carlo simulation. The values of the rate constants for each step of the suggested mechanism have been obtained by simulation. The effect of the initial concentration of mineral oxides and uric acid on the rate of uric acid photo-oxidation by irradiation of some sun care agents has been studied. The kinetic Monte Carlo simulation results agree qualitatively with the existing experimental data for the production of free radicals by sun care agents. - Highlights: • The mechanism and kinetics of uric acid photo-oxidation by irradiation of sun care agents has been obtained by simulation. • The mechanism has been used for free radical production of TiO{sub 2} (rutile and anatase), ZnO and ZrO{sub 2}. • The ratios of photo-activity of ZnO to anastase, rutile and ZrO have been obtained. • By doubling the initial concentrations of mineral oxide, the rate of reaction was doubled. • The optimum ratio of initial concentration of mineral oxides to uric acid has been obtained.
International Nuclear Information System (INIS)
In the present study, the mechanism of free radical production by light-reflective agents in sunscreens (TiO2, ZnO and ZrO2) was obtained by applying kinetic Monte Carlo simulation. The values of the rate constants for each step of the suggested mechanism have been obtained by simulation. The effect of the initial concentration of mineral oxides and uric acid on the rate of uric acid photo-oxidation by irradiation of some sun care agents has been studied. The kinetic Monte Carlo simulation results agree qualitatively with the existing experimental data for the production of free radicals by sun care agents. - Highlights: • The mechanism and kinetics of uric acid photo-oxidation by irradiation of sun care agents has been obtained by simulation. • The mechanism has been used for free radical production of TiO2 (rutile and anatase), ZnO and ZrO2. • The ratios of photo-activity of ZnO to anastase, rutile and ZrO have been obtained. • By doubling the initial concentrations of mineral oxide, the rate of reaction was doubled. • The optimum ratio of initial concentration of mineral oxides to uric acid has been obtained
Sunil, C.; Tyagi, Mohit; Biju, K.; Shanbhag, A. A.; Bandyopadhyay, T.
2015-12-01
The scarcity and the high cost of 3He has spurred the use of various detectors for neutron monitoring. A new lithium yttrium borate scintillator developed in BARC has been studied for its use in a neutron rem counter. The scintillator is made of natural lithium and boron, and the yield of reaction products that will generate a signal in a real time detector has been studied by FLUKA Monte Carlo radiation transport code. A 2 cm lead introduced to enhance the gamma rejection shows no appreciable change in the shape of the fluence response or in the yield of reaction products. The fluence response when normalized at the average energy of an Am-Be neutron source shows promise of being used as rem counter.
Monte Carlo simulation of gas Cerenkov detectors
International Nuclear Information System (INIS)
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
Liao, Y.; Su, C. C.; Marschall, R.; Wu, J. S.; Rubin, M.; Lai, I. L.; Ip, W. H.; Keller, H. U.; Knollenberg, J.; Kührt, E.; Skorov, Y. V.; Thomas, N.
2016-03-01
Direct Simulation Monte Carlo (DSMC) is a powerful numerical method to study rarefied gas flows such as cometary comae and has been used by several authors over the past decade to study cometary outflow. However, the investigation of the parameter space in simulations can be time consuming since 3D DSMC is computationally highly intensive. For the target of ESA's Rosetta mission, comet 67P/Churyumov-Gerasimenko, we have identified to what extent modification of several parameters influence the 3D flow and gas temperature fields and have attempted to establish the reliability of inferences about the initial conditions from in situ and remote sensing measurements. A large number of DSMC runs have been completed with varying input parameters. In this work, we present the simulation results and conclude on the sensitivity of solutions to certain inputs. It is found that among cases of water outgassing, the surface production rate distribution is the most influential variable to the flow field.
Energy Technology Data Exchange (ETDEWEB)
Tamulaitis, G.; Kazlauskas, K.; Zukauskas, A. [Institute of Materials Science and Applied Research, Vilnius University (Lithuania); Mickevicius, J.; Shur, M.S. [Department of ECE and CIE, Rensselaer Polytechnic Institute, Troy, NY 12180 (United States); Fareed, R.S.Qhalid; Zhang, J.P.; Gaska, R. [Sensor Electronic Technology, Inc., 1195 Atlas Road, Columbia, SC 29209 (United States)
2006-06-15
Monte Carlo simulation of exciton hopping reveals the features of the potential profile in AlGaN (with Al content of {proportional_to}26%) responsible for S-shaped and W-shaped temperature dependences of photoluminescence band peak position and bandwidth, respectively. One of the samples was grown using the conventional metal-organic chemical vapor deposition (MOCVD), while the second one was grown with the insertion of a buffer layer grown by migration enhanced MOCVD (MEMOCVD trademark) technique. The potential profile is shown to be double-scaled in both Al{sub 0.26}Ga{sub 0.74}N epilayers, and the exciton hopping occurs through random potential fluctuations within isolated low-potential regions with the average energy of the localized states dispersed on the second scale. Both energy fluctuation scales were found to be in the range of 18-20 meV and were independent of the growth technique used. Meanwhile, the carrier lifetime was 30 ps in the sample grown by conventional MOCVD and 190 ps in the sample grown using the MEMOCVD trademark technique. We conclude that the difference in the lifetimes is caused by the density of nonradiative recombination centers rather than by the potential fluctuations affecting the carrier motion. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Parallel Monte Carlo simulation of aerosol dynamics
Zhou, K.
2014-01-01
A highly efficient Monte Carlo (MC) algorithm is developed for the numerical simulation of aerosol dynamics, that is, nucleation, surface growth, and coagulation. Nucleation and surface growth are handled with deterministic means, while coagulation is simulated with a stochastic method (Marcus-Lushnikov stochastic process). Operator splitting techniques are used to synthesize the deterministic and stochastic parts in the algorithm. The algorithm is parallelized using the Message Passing Interface (MPI). The parallel computing efficiency is investigated through numerical examples. Near 60% parallel efficiency is achieved for the maximum testing case with 3.7 million MC particles running on 93 parallel computing nodes. The algorithm is verified through simulating various testing cases and comparing the simulation results with available analytical and/or other numerical solutions. Generally, it is found that only small number (hundreds or thousands) of MC particles is necessary to accurately predict the aerosol particle number density, volume fraction, and so forth, that is, low order moments of the Particle Size Distribution (PSD) function. Accurately predicting the high order moments of the PSD needs to dramatically increase the number of MC particles. 2014 Kun Zhou et al.
Setiani, Tia Dwi; Suprijadi, Haryanto, Freddy
2016-03-01
Monte Carlo (MC) is one of the powerful techniques for simulation in x-ray imaging. MC method can simulate the radiation transport within matter with high accuracy and provides a natural way to simulate radiation transport in complex systems. One of the codes based on MC algorithm that are widely used for radiographic images simulation is MC-GPU, a codes developed by Andrea Basal. This study was aimed to investigate the time computation of x-ray imaging simulation in GPU (Graphics Processing Unit) compared to a standard CPU (Central Processing Unit). Furthermore, the effect of physical parameters to the quality of radiographic images and the comparison of image quality resulted from simulation in the GPU and CPU are evaluated in this paper. The simulations were run in CPU which was simulated in serial condition, and in two GPU with 384 cores and 2304 cores. In simulation using GPU, each cores calculates one photon, so, a large number of photon were calculated simultaneously. Results show that the time simulations on GPU were significantly accelerated compared to CPU. The simulations on the 2304 core of GPU were performed about 64 -114 times faster than on CPU, while the simulation on the 384 core of GPU were performed about 20 - 31 times faster than in a single core of CPU. Another result shows that optimum quality of images from the simulation was gained at the history start from 108 and the energy from 60 Kev to 90 Kev. Analyzed by statistical approach, the quality of GPU and CPU images are relatively the same.
Monte Carlo and detector simulation in OOP
International Nuclear Information System (INIS)
Object-Oriented Programming techniques are explored with an eye towards applications in High Energy Physics codes. Two prototype examples are given: MCOOP (a particle Monte Carlo generator) and GISMO (a detector simulation/analysis package). The OOP programmer does no explicit or detailed memory management nor other bookkeeping chores; hence, the writing, modification, and extension of the code is considerably simplified. Inheritance can be used to simplify the class definitions as well as the instance variables and action methods of each class; thus the work required to add new classes, parameters, or new methods is minimal. The software industry is moving rapidly to OOP since it has been proven to improve programmer productivity, and promises even more for the future by providing truly reusable software. The High Energy Physics community clearly needs to follow this trend
Directory of Open Access Journals (Sweden)
Veres Vincentiu
2013-07-01
Full Text Available Decisions are a result of choices made between several alternatives and will affect all participants in the decision-making process. In this paper we analyze the Monte Carlo simulation as an important management tool in evaluating decisions under risk. The method is particularly useful in simulating decision problems. For example, the profit that could be achieved if a company launches a new product may depend on a number of factors (market share, advertising, production costs, launch costs, the lifetime of the product, etc. The company manager should identify all factors that could affect profit and then to consider the large number of ways in which these factors may interrelate. In such situations it is recommended company manager to divide the problem into smaller parts, asking him to estimate the probability distribution for market share, for advertising, for the cost of launch. Once they were obtained it can be determined their combined effect in order to obtain the probability distribution of profit. Through computer can generate a large number of possible combinations of situations where you choose a particular course of action. Upon completion of the simulation possible combination will be generated mostly while the least possible combination will be generated less frequently. For exemplification we selected a company producing shoes in Cluj market who wants to launch a new model for autumn-winter 2013-2014. In the current period the company has limited production capacity, has a number of additional contracts honored and general economic crisis situation makes money availability to be extremely limited. Accordingly, the company will have to choose a single product to be launched next season. The company will have to decide which of the two new products to be launched on the market: a model of boots for men in business class or a new model of women\\'s boots of the same class business. The company is not sure either production costs or
Monte Carlo simulation of primary recrystallization and annealing twinning
International Nuclear Information System (INIS)
The formation of annealing twins has been studied from the beginning of the 20th century and a variety of mechanisms have been suggested. Molecular dynamics simulations on the atomic scale have also been performed. This paper reports a microscale simulation of primary recrystallization and twinning of a nickel alloy based on the Monte Carlo approach. Different twin morphologies were simulated. A possible dependence of grain growth direction on twin formation during annealing was demonstrated. The formation of incoherent Σ3 and Σ9 boundaries is verified as the indirect outcome after coherent Σ3 formation
Some improvements of BES II TOF Monte Carlo simulation
International Nuclear Information System (INIS)
BES II detector has been upgraded from 1995, the TOF time resolution is about 180 ps for Bhabha events, a big improvement compared with 330 ps of BES I. With the upgrade of the detector, the software including calibration, reconstruction and Monte Carlo (M.C.) simulation needs corresponding improvement, especially for M.C. simulation. Using 50 M J/ψ data taken in the last two years at BES II, the authors studied the TOF resolution carefully, and made some improvements for TOF MC simulation. After such an improvement, the authors compared the TOF resolutions between real data and M.C. data and found they agree with each other
International Nuclear Information System (INIS)
This paper shows a feasibility study on the use of discrete SiPMs to read out monolithic scintillator-based detectors for use in molecular imaging applications. Monte Carlo simulations are carried out in order to evaluate the basic performance of 8 × 8 arrays of discrete SiPMs with different PDE values and compare it to conventional 64 channel multi-anode PMT (MA-PMT) readout. A detailed optical transport model was incorporated into the Monte Carlo simulation and a detector module based on a monolithic scintillator crystal of 50 × 50 × 4 mm3 coupled to a MA-PMT was built for experimental validation. The effect of the SiPM dynamic range was also investigated by including a model of the saturation effects into the optical transport simulation. The results show that a detector module based on an array of 8 × 8 discrete SiPM devices (3 × 3 mm2 and PDE > 32%) is feasible as a replacement of a 64 channel MA-PMT in order to read out large monolithic crystals for MR-compatible gamma cameras.
International Nuclear Information System (INIS)
The purpose of the paper is to present the results of application of stochastic approach based on Monte Carlo (MC) simulation for life cycle inventory (LCI) data of Mittal Steel Poland (MSP) complex in Kraków, Poland. In order to assess the uncertainty, the software CrystalBall® (CB), which is associated with Microsoft® Excel spreadsheet model, is used. The framework of the study was originally carried out for 2005. The total production of steel, coke, pig iron, sinter, slabs from continuous steel casting (CSC), sheets from hot rolling mill (HRM) and blast furnace gas, collected in 2005 from MSP was analyzed and used for MC simulation of the LCI model. In order to describe random nature of all main products used in this study, normal distribution has been applied. The results of the simulation (10,000 trials) performed with the use of CB consist of frequency charts and statistical reports. The results of this study can be used as the first step in performing a full LCA analysis in the steel industry. Further, it is concluded that the stochastic approach is a powerful method for quantifying parameter uncertainty in LCA/LCI studies and it can be applied to any steel industry. The results obtained from this study can help practitioners and decision-makers in the steel production management. - Highlights: • The benefits of Monte Carlo simulation are examined. • The normal probability distribution is studied. • LCI data on Mittal Steel Poland (MSP) complex in Kraków, Poland dates back to 2005. • This is the first assessment of the LCI uncertainties in the Polish steel industry
Energy Technology Data Exchange (ETDEWEB)
Bieda, Bogusław
2014-05-01
The purpose of the paper is to present the results of application of stochastic approach based on Monte Carlo (MC) simulation for life cycle inventory (LCI) data of Mittal Steel Poland (MSP) complex in Kraków, Poland. In order to assess the uncertainty, the software CrystalBall® (CB), which is associated with Microsoft® Excel spreadsheet model, is used. The framework of the study was originally carried out for 2005. The total production of steel, coke, pig iron, sinter, slabs from continuous steel casting (CSC), sheets from hot rolling mill (HRM) and blast furnace gas, collected in 2005 from MSP was analyzed and used for MC simulation of the LCI model. In order to describe random nature of all main products used in this study, normal distribution has been applied. The results of the simulation (10,000 trials) performed with the use of CB consist of frequency charts and statistical reports. The results of this study can be used as the first step in performing a full LCA analysis in the steel industry. Further, it is concluded that the stochastic approach is a powerful method for quantifying parameter uncertainty in LCA/LCI studies and it can be applied to any steel industry. The results obtained from this study can help practitioners and decision-makers in the steel production management. - Highlights: • The benefits of Monte Carlo simulation are examined. • The normal probability distribution is studied. • LCI data on Mittal Steel Poland (MSP) complex in Kraków, Poland dates back to 2005. • This is the first assessment of the LCI uncertainties in the Polish steel industry.
Non-analogue Monte Carlo method, application to neutron simulation
International Nuclear Information System (INIS)
With most of the traditional and contemporary techniques, it is still impossible to solve the transport equation if one takes into account a fully detailed geometry and if one studies precisely the interactions between particles and matters. Nowadays, only the Monte Carlo method offers such possibilities. However with significant attenuation, the natural simulation remains inefficient: it becomes necessary to use biasing techniques where the solution of the adjoint transport equation is essential. The Monte Carlo code Tripoli has been using such techniques successfully for a long time with different approximate adjoint solutions: these methods require from the user to find out some parameters. If this parameters are not optimal or nearly optimal, the biases simulations may bring about small figures of merit. This paper presents a description of the most important biasing techniques of the Monte Carlo code Tripoli ; then we show how to calculate the importance function for general geometry with multigroup cases. We present a completely automatic biasing technique where the parameters of the biased simulation are deduced from the solution of the adjoint transport equation calculated by collision probabilities. In this study we shall estimate the importance function through collision probabilities method and we shall evaluate its possibilities thanks to a Monte Carlo calculation. We compare different biased simulations with the importance function calculated by collision probabilities for one-group and multigroup problems. We have run simulations with new biasing method for one-group transport problems with isotropic shocks and for multigroup problems with anisotropic shocks. The results show that for the one-group and homogeneous geometry transport problems the method is quite optimal without splitting and russian roulette technique but for the multigroup and heterogeneous X-Y geometry ones the figures of merit are higher if we add splitting and russian roulette
Liu, Shitao; Li, Hongdi; Zhang, Yuxuan; Ramirez, Rocio A; Baghaei, Hossain; An, Shaohui; Wang, Chao; Liu, Jiguo; Wong, Wai-Hoi
2009-01-01
We developed a detailed Monte Carlo simulation method to study the time resolution of detectors for time-of-flight positron emission tomography (TOF PET). The process of gamma ray interaction in detectors, scintillation light emission and transport inside the detectors, the photoelectron generation and anode signal generation in the photomultiplier tube (PMT), and the electronics process of discriminator are simulated. We tested this simulation method using published experimental data, and found that it can generate reliable results. Using this method, we simulated the time resolution for a 13 × 13 detector block of 4 × 4 × 20 mm(3) lutetium orthosilicate (LSO) crystals coupled to four 2-inch PMTs using PMT-quadrant-sharing (PQS) technology. We analyzed the effects of several factors, including the number of photoelectrons, light transport, transit time spread (TTS), and the depth of interaction (DOI). The simulation results indicated that system time resolution of 360 ps should be possible with currently available fast PMTs. This simulation method can also be used to simulate the time resolution of other detector design method. PMID:20559457
International Nuclear Information System (INIS)
This work presents a simulation based study by Monte Carlo which uses two adaptive neuro-fuzzy inference systems (ANFIS) for cross talk compensation of simultaneous 99mTc/201Tl dual-radioisotope SPECT imaging. We have compared two neuro-fuzzy systems based on fuzzy c-means (FCM) and subtractive (SUB) clustering. Our approach incorporates eight energy-windows image acquisition from 28 keV to 156 keV and two main photo peaks of 201Tl (77±10% keV) and 99mTc (140±10% keV). The Geant4 application in emission tomography (GATE) is used as a Monte Carlo simulator for three cylindrical and a NURBS Based Cardiac Torso (NCAT) phantom study. Three separate acquisitions including two single-isotopes and one dual isotope were performed in this study. Cross talk and scatter corrected projections are reconstructed by an iterative ordered subsets expectation maximization (OSEM) algorithm which models the non-uniform attenuation in the projection/back-projection. ANFIS-FCM/SUB structures are tuned to create three to sixteen fuzzy rules for modeling the photon cross-talk of the two radioisotopes. Applying seven to nine fuzzy rules leads to a total improvement of the contrast and the bias comparatively. It is found that there is an out performance for the ANFIS-FCM due to its acceleration and accurate results
Heidary, Saeed; Setayeshi, Saeed
2015-01-01
This work presents a simulation based study by Monte Carlo which uses two adaptive neuro-fuzzy inference systems (ANFIS) for cross talk compensation of simultaneous 99mTc/201Tl dual-radioisotope SPECT imaging. We have compared two neuro-fuzzy systems based on fuzzy c-means (FCM) and subtractive (SUB) clustering. Our approach incorporates eight energy-windows image acquisition from 28 keV to 156 keV and two main photo peaks of 201Tl (77±10% keV) and 99mTc (140±10% keV). The Geant4 application in emission tomography (GATE) is used as a Monte Carlo simulator for three cylindrical and a NURBS Based Cardiac Torso (NCAT) phantom study. Three separate acquisitions including two single-isotopes and one dual isotope were performed in this study. Cross talk and scatter corrected projections are reconstructed by an iterative ordered subsets expectation maximization (OSEM) algorithm which models the non-uniform attenuation in the projection/back-projection. ANFIS-FCM/SUB structures are tuned to create three to sixteen fuzzy rules for modeling the photon cross-talk of the two radioisotopes. Applying seven to nine fuzzy rules leads to a total improvement of the contrast and the bias comparatively. It is found that there is an out performance for the ANFIS-FCM due to its acceleration and accurate results.
Energy Technology Data Exchange (ETDEWEB)
Heidary, Saeed, E-mail: saeedheidary@aut.ac.ir; Setayeshi, Saeed, E-mail: setayesh@aut.ac.ir
2015-01-11
This work presents a simulation based study by Monte Carlo which uses two adaptive neuro-fuzzy inference systems (ANFIS) for cross talk compensation of simultaneous {sup 99m}Tc/{sup 201}Tl dual-radioisotope SPECT imaging. We have compared two neuro-fuzzy systems based on fuzzy c-means (FCM) and subtractive (SUB) clustering. Our approach incorporates eight energy-windows image acquisition from 28 keV to 156 keV and two main photo peaks of {sup 201}Tl (77±10% keV) and {sup 99m}Tc (140±10% keV). The Geant4 application in emission tomography (GATE) is used as a Monte Carlo simulator for three cylindrical and a NURBS Based Cardiac Torso (NCAT) phantom study. Three separate acquisitions including two single-isotopes and one dual isotope were performed in this study. Cross talk and scatter corrected projections are reconstructed by an iterative ordered subsets expectation maximization (OSEM) algorithm which models the non-uniform attenuation in the projection/back-projection. ANFIS-FCM/SUB structures are tuned to create three to sixteen fuzzy rules for modeling the photon cross-talk of the two radioisotopes. Applying seven to nine fuzzy rules leads to a total improvement of the contrast and the bias comparatively. It is found that there is an out performance for the ANFIS-FCM due to its acceleration and accurate results.
Monte Carlo Simulations of Novel Scintillator Detectors and Dosimetry Calculations
Lo Meo, Sergio
2009-01-01
Monte Carlo (MC) simulation techniques are becoming very common in the Medical Physicists community. MC can be used for modeling Single Photon Emission Computed Tomography (SPECT) and for dosimetry calculations. 188Re, is a promising candidate for radiotherapeutic production and understanding the mechanisms of the radioresponse of tumor cells "in vitro" is of crucial importance as a first step before "in vivo" studies. The dosimetry of 188Re, used to target different lines of c...
Quantum Monte Carlo Simulations : Algorithms, Limitations and Applications
Raedt, H. De
1992-01-01
A survey is given of Quantum Monte Carlo methods currently used to simulate quantum lattice models. The formalisms employed to construct the simulation algorithms are sketched. The origin of fundamental (minus sign) problems which limit the applicability of the Quantum Monte Carlo approach is shown
Monte Carlo simulations for focusing elliptical guides
Energy Technology Data Exchange (ETDEWEB)
Valicu, Roxana [FRM2 Garching, Muenchen (Germany); Boeni, Peter [E20, TU Muenchen (Germany)
2009-07-01
The aim of the Monte Carlo simulations using McStas Programme was to improve the focusing of the neutron beam existing at PGAA (FRM II) by prolongation of the existing elliptic guide (coated now with supermirrors with m=3) with a new part. First we have tried with an initial length of the additional guide of 7,5cm and coatings for the neutron guide of supermirrors with m=4,5 and 6. The gain (calculated by dividing the intensity in the focal point after adding the guide by the intensity at the focal point with the initial guide) obtained for this coatings indicated that a coating with m=5 would be appropriate for a first trial. The next step was to vary the length of the additional guide for this m value and therefore choosing the appropriate length for the maximal gain. With the m value and the length of the guide fixed we have introduced an aperture 1 cm before the focal point and we have varied the radius of this aperture in order to obtain a focused beam. We have observed a dramatic decrease in the size of the beam in the focal point after introducing this aperture. The simulation results, the gains obtained and the evolution of the beam size will be presented.
Monte Carlo simulation framework for TMT
Vogiatzis, Konstantinos; Angeli, George Z.
2008-07-01
This presentation describes a strategy for assessing the performance of the Thirty Meter Telescope (TMT). A Monte Carlo Simulation Framework has been developed to combine optical modeling with Computational Fluid Dynamics simulations (CFD), Finite Element Analysis (FEA) and controls to model the overall performance of TMT. The framework consists of a two year record of observed environmental parameters such as atmospheric seeing, site wind speed and direction, ambient temperature and local sunset and sunrise times, along with telescope azimuth and elevation with a given sampling rate. The modeled optical, dynamic and thermal seeing aberrations are available in a matrix form for distinct values within the range of influencing parameters. These parameters are either part of the framework parameter set or can be derived from them at each time-step. As time advances, the aberrations are interpolated and combined based on the current value of their parameters. Different scenarios can be generated based on operating parameters such as venting strategy, optical calibration frequency and heat source control. Performance probability distributions are obtained and provide design guidance. The sensitivity of the system to design, operating and environmental parameters can be assessed in order to maximize the % of time the system meets the performance specifications.
Rare event simulation using Monte Carlo methods
Rubino, Gerardo
2009-01-01
In a probabilistic model, a rare event is an event with a very small probability of occurrence. The forecasting of rare events is a formidable task but is important in many areas. For instance a catastrophic failure in a transport system or in a nuclear power plant, the failure of an information processing system in a bank, or in the communication network of a group of banks, leading to financial losses. Being able to evaluate the probability of rare events is therefore a critical issue. Monte Carlo Methods, the simulation of corresponding models, are used to analyze rare events. This book sets out to present the mathematical tools available for the efficient simulation of rare events. Importance sampling and splitting are presented along with an exposition of how to apply these tools to a variety of fields ranging from performance and dependability evaluation of complex systems, typically in computer science or in telecommunications, to chemical reaction analysis in biology or particle transport in physics. ...
International Nuclear Information System (INIS)
This study evaluated the use of Compton imaging technology to monitor prompt gamma rays emitted by 10B in boron neutron capture therapy (BNCT) applied to a computerized human phantom. The Monte Carlo method, including particle-tracking techniques, was used for simulation. The distribution of prompt gamma rays emitted by the phantom during irradiation with neutron beams is closely associated with the distribution of the boron in the phantom. Maximum likelihood expectation maximization (MLEM) method was applied to the information obtained from the detected prompt gamma rays to reconstruct the distribution of the tumor including the boron uptake regions (BURs). The reconstructed Compton images of the prompt gamma rays were combined with the cross-sectional images of the human phantom. Quantitative analysis of the intensity curves showed that all combined images matched the predetermined conditions of the simulation. The tumors including the BURs were distinguishable if they were more than 2 cm apart
Energy Technology Data Exchange (ETDEWEB)
Lee, Taewoong; Lee, Hyounggun; Lee, Wonho, E-mail: wonhol@korea.ac.kr
2015-10-21
This study evaluated the use of Compton imaging technology to monitor prompt gamma rays emitted by {sup 10}B in boron neutron capture therapy (BNCT) applied to a computerized human phantom. The Monte Carlo method, including particle-tracking techniques, was used for simulation. The distribution of prompt gamma rays emitted by the phantom during irradiation with neutron beams is closely associated with the distribution of the boron in the phantom. Maximum likelihood expectation maximization (MLEM) method was applied to the information obtained from the detected prompt gamma rays to reconstruct the distribution of the tumor including the boron uptake regions (BURs). The reconstructed Compton images of the prompt gamma rays were combined with the cross-sectional images of the human phantom. Quantitative analysis of the intensity curves showed that all combined images matched the predetermined conditions of the simulation. The tumors including the BURs were distinguishable if they were more than 2 cm apart.
Monte Carlo simulations in small animal PET imaging
International Nuclear Information System (INIS)
This work is based on the use of an implemented Positron Emission Tomography (PET) simulation system dedicated for small animal PET imaging. Geant4 Application for Tomographic Emission (GATE), a Monte Carlo simulation platform based on the Geant4 libraries, is well suited for modeling the microPET FOCUS system and to implement realistic phantoms, such as the MOBY phantom, and data maps from real examinations. The use of a microPET FOCUS simulation model with GATE has been validated for spatial resolution, counting rates performances, imaging contrast recovery and quantitative analysis. Results from realistic studies of the mouse body using -F and [18F]FDG imaging protocols are presented. These simulations include the injection of realistic doses into the animal and realistic time framing. The results have shown that it is possible to simulate small animal PET acquisitions under realistic conditions, and are expected to be useful to improve the quantitative analysis in PET mouse body studies
Monte Carlo simulations in small animal PET imaging
Energy Technology Data Exchange (ETDEWEB)
Branco, Susana [Universidade de Lisboa, Faculdade de Ciencias, Instituto de Biofisica e Engenharia Biomedica, Lisbon (Portugal)], E-mail: susana.silva@fc.ul.pt; Jan, Sebastien [Service Hospitalier Frederic Joliot, CEA/DSV/DRM, Orsay (France); Almeida, Pedro [Universidade de Lisboa, Faculdade de Ciencias, Instituto de Biofisica e Engenharia Biomedica, Lisbon (Portugal)
2007-10-01
This work is based on the use of an implemented Positron Emission Tomography (PET) simulation system dedicated for small animal PET imaging. Geant4 Application for Tomographic Emission (GATE), a Monte Carlo simulation platform based on the Geant4 libraries, is well suited for modeling the microPET FOCUS system and to implement realistic phantoms, such as the MOBY phantom, and data maps from real examinations. The use of a microPET FOCUS simulation model with GATE has been validated for spatial resolution, counting rates performances, imaging contrast recovery and quantitative analysis. Results from realistic studies of the mouse body using {sup -}F and [{sup 18}F]FDG imaging protocols are presented. These simulations include the injection of realistic doses into the animal and realistic time framing. The results have shown that it is possible to simulate small animal PET acquisitions under realistic conditions, and are expected to be useful to improve the quantitative analysis in PET mouse body studies.
Leroch, Sabine; Wendland, Martin
2013-10-01
Adhesion forces between nanoparticles strongly depend on the amount of adsorbed condensed water from ambient atmosphere. Liquid water forms bridges in the cavities separating the particles, giving rise to the so-called capillary forces which in most cases dominate the van der Waals and long-range electrostatic interactions. Capillary forces promote the undesirable agglomeration of particles to large clusters, thereby hindering the flowability of dry powders in process containers. In process engineering macroscopic theories based on the Laplace pressures are used to estimate the strength of the capillary forces. However, especially for low relative humidity and when the wetting of rough or small nanoparticles is studied, those theories can fail. Molecular dynamic simulations can help to give better insight into the water-particle interface. The simulated force versus distance curve as well as adhesion forces and the adsorption isotherm for silica nanoparticles at varying relative humidity will be discussed in comparison to experiments, theories, and simulations. PMID:24015790
International Nuclear Information System (INIS)
Duplex stainless steels used in primary circuit of 2. generation nuclear power plant endure thermal ageing at service temperatures (285 C-323 C). This leads to an increase of their hardness and to a decrease of their Charpy toughness. The evolution of these properties is due to the phase transformations which occur in ferrite. Even if it is well known that the steel composition plays a role on the mechanical properties evolution (steels with low Ni and Mo contents are less sensitive to thermal ageing), the origin of this difference of behaviour has not been clearly identified yet. In this study, the kinetics of the phase transformations in the ferrite of a duplex stainless steel with low Ni and Mo contents and duplex model alloys with specific compositions have been studied by atom probe tomography.This work showed that: i) G phase precipitation is less intense and the kinetic of the spinodal decomposition is slower for this steel than for steels with higher Ni and Mo contents, ii) the synergy between spinodal decomposition and G phase precipitation is also observed in this steel, iii) the Mo does not affect the early stages of the G phase precipitation, iv) the formation mechanism of G phase precipitates is at least a two steps mechanism, v) when the number density of G phase precipitates is low, hardening is mainly controlled by the amplitude and the mean wavelength of the spinodal decomposition, vi) when the number density of G phase precipitates is high, the hardening due to G phase precipitates may not be negligible. A kinetic Monte Carlo model has been developed to explain the synergy observed experimentally between the spinodal decomposition and the G phase precipitation. This model allowed us to show that the coarsening of G phase precipitates is driven by a diffusion mechanism along a/a' interfaces, and not by a bulk diffusion mechanism. (author)
Zagorska, A.; Bliznakova, K.; Buchakliev, Z.
2015-09-01
In 2012, the International Commission on Radiological Protection has recommended a reduction of the dose limits to the eye lens for occupational exposure. Recent studies showed that in interventional rooms is possible to reach these limits especially without using protective equipment. The aim of this study was to calculate the scattered energy spectra distribution at the level of the operator's head. For this purpose, an in-house developed Monte Carlo-based computer application was used to design computational phantoms (patient and operator), the acquisition geometry as well as to simulate the photon transport through the designed system. The initial spectra from 70 kV tube voltage and 8 different filtrations were calculated according to the IPEM Report 78. An experimental study was carried out to verify the results from the simulations. The calculated scattered radiation distributions were compared to the initial incident on the patient spectra. Results showed that there is no large difference between the effective energies of the scattered spectra registered in front of the operator's head obtained from simulations of all 8 incident spectra. The results from the experimental study agreed well to simulations as well.
Monte Carlo simulations of neoclassical transport in toroidal plasmas
International Nuclear Information System (INIS)
FORTEC-3D code, which solves the drift-kinetic equation for torus plasmas and radial electric field using the δf Monte Carlo method, has developed to study the variety of issues relating to neoclassical transport phenomena in magnetic confinement plasmas. Here the numerical techniques used in FORTEC-3D are reviewed, and resent progress in the simulation method to simulate GAM oscillation is also explained. A band-limited white noise term is introduced in the equation of time evolution of radial electric field to excite GAM oscillation, which enables us to analyze GAM frequency using FORTEC-3D even in the case the collisionless GAM damping is fast. (author)
Energy Technology Data Exchange (ETDEWEB)
Silva, Laura E. da; Nicolucci, Patricia, E-mail: laura.emilia.fm@gmail.com [Universidade de Sao Paulo (USP), Ribeirao Preto, SP (Brazil). Faculdade de Filosofia, Ciencias e Letras
2014-04-15
The development of nanotechnology has boosted the use of nanoparticles in radiation therapy in order to achieve greater therapeutic ratio between tumor and healthy tissues. Gold has been shown to be most suitable to this task due to the high biocompatibility and high atomic number, which contributes to a better in vivo distribution and for the local energy deposition. As a result, this study proposes to study, nanoparticle in the tumor cell. At a range of 11 nm from the nanoparticle surface, results have shown an absorbed dose 141 times higher for the medium with the gold nanoparticle compared to the water for an incident energy spectrum with maximum photon energy of 50 keV. It was also noted that when only scattered radiation is interacting with the gold nanoparticles, the dose was 134 times higher compared to enhanced local dose that remained significant even for scattered radiation. (author)
Monte Carlo simulations for heavy ion dosimetry
Energy Technology Data Exchange (ETDEWEB)
Geithner, O.
2006-07-26
Water-to-air stopping power ratio (s{sub w,air}) calculations for the ionization chamber dosimetry of clinically relevant ion beams with initial energies from 50 to 450 MeV/u have been performed using the Monte Carlo technique. To simulate the transport of a particle in water the computer code SHIELD-HIT v2 was used which is a substantially modified version of its predecessor SHIELD-HIT v1. The code was partially rewritten, replacing formerly used single precision variables with double precision variables. The lowest particle transport specific energy was decreased from 1 MeV/u down to 10 keV/u by modifying the Bethe- Bloch formula, thus widening its range for medical dosimetry applications. Optional MSTAR and ICRU-73 stopping power data were included. The fragmentation model was verified using all available experimental data and some parameters were adjusted. The present code version shows excellent agreement with experimental data. Additional to the calculations of stopping power ratios, s{sub w,air}, the influence of fragments and I-values on s{sub w,air} for carbon ion beams was investigated. The value of s{sub w,air} deviates as much as 2.3% at the Bragg peak from the recommended by TRS-398 constant value of 1.130 for an energy of 50 MeV/u. (orig.)
Monte Carlo simulations for heavy ion dosimetry
International Nuclear Information System (INIS)
Water-to-air stopping power ratio (sw,air) calculations for the ionization chamber dosimetry of clinically relevant ion beams with initial energies from 50 to 450 MeV/u have been performed using the Monte Carlo technique. To simulate the transport of a particle in water the computer code SHIELD-HIT v2 was used which is a substantially modified version of its predecessor SHIELD-HIT v1. The code was partially rewritten, replacing formerly used single precision variables with double precision variables. The lowest particle transport specific energy was decreased from 1 MeV/u down to 10 keV/u by modifying the Bethe- Bloch formula, thus widening its range for medical dosimetry applications. Optional MSTAR and ICRU-73 stopping power data were included. The fragmentation model was verified using all available experimental data and some parameters were adjusted. The present code version shows excellent agreement with experimental data. Additional to the calculations of stopping power ratios, sw,air, the influence of fragments and I-values on sw,air for carbon ion beams was investigated. The value of sw,air deviates as much as 2.3% at the Bragg peak from the recommended by TRS-398 constant value of 1.130 for an energy of 50 MeV/u. (orig.)
Sarstedt, Marko
2006-01-01
As mixture regression models increasingly receive attention from both theory and practice, the question of selecting the correct number of segments gains urgency. A misspecification can lead to an under- or oversegmentation, thus resulting in flawed management decisions on customer targeting or product positioning. This paper presents the results of an extensive simulation study that examines the performance of commonly used information criteria in a mixture regression context with normal dat...
Monte Carlo study of real time dynamics
Alexandru, Andrei; Bedaque, Paulo F; Vartak, Sohan; Warrington, Neill C
2016-01-01
Monte Carlo studies involving real time dynamics are severely restricted by the sign problem that emerges from highly oscillatory phase of the path integral. In this letter, we present a new method to compute real time quantities on the lattice using the Schwinger-Keldysh formalism via Monte Carlo simulations. The key idea is to deform the path integration domain to a complex manifold where the phase oscillations are mild and the sign problem is manageable. We use the previously introduced "contraction algorithm" to create a Markov chain on this alternative manifold. We substantiate our approach by analyzing the quantum mechanical anharmonic oscillator. Our results are in agreement with the exact ones obtained by diagonalization of the Hamiltonian. The method we introduce is generic and in principle applicable to quantum field theory albeit very slow. We discuss some possible improvements that should speed up the algorithm.
International Nuclear Information System (INIS)
This study was conducted to analyze the radiological impact in the experimental area of the Hard X-Ray beamline at Canadian Light Source under beam loss scenario during Top-up injection. The radiation doses were calculated using Monte Carlo code: FLUKA. The physical size, location, and material of the beamline components were adopted from the technical drawings and were incorporated in the FLUKA model. Three (03) beam loss scenarios were simulated: (i) Beam was miss-steered in the storage ring (ii) Beam hit misaligned components inside the ring and (iii) Beam was lost inside the primary optical enclosure (POE). Total ambient dose was calculated at several observation points for each scenario considering the injected beam as the primary source. The results and impacts were discussed. - Highlights: • Monte Carlo method was used to calculate radiation dose for a beamline at Canadian Light Source. • Three possible beam loss scenarios were studied. • The predicted worst dose was found below the regulatory dose limit
Bieda, Bogusław
2014-05-15
The purpose of the paper is to present the results of application of stochastic approach based on Monte Carlo (MC) simulation for life cycle inventory (LCI) data of Mittal Steel Poland (MSP) complex in Kraków, Poland. In order to assess the uncertainty, the software CrystalBall® (CB), which is associated with Microsoft® Excel spreadsheet model, is used. The framework of the study was originally carried out for 2005. The total production of steel, coke, pig iron, sinter, slabs from continuous steel casting (CSC), sheets from hot rolling mill (HRM) and blast furnace gas, collected in 2005 from MSP was analyzed and used for MC simulation of the LCI model. In order to describe random nature of all main products used in this study, normal distribution has been applied. The results of the simulation (10,000 trials) performed with the use of CB consist of frequency charts and statistical reports. The results of this study can be used as the first step in performing a full LCA analysis in the steel industry. Further, it is concluded that the stochastic approach is a powerful method for quantifying parameter uncertainty in LCA/LCI studies and it can be applied to any steel industry. The results obtained from this study can help practitioners and decision-makers in the steel production management. PMID:24290145
Identification of Logical Errors through Monte-Carlo Simulation
Emmett, Hilary L
2010-01-01
The primary focus of Monte Carlo simulation is to identify and quantify risk related to uncertainty and variability in spreadsheet model inputs. The stress of Monte Carlo simulation often reveals logical errors in the underlying spreadsheet model that might be overlooked during day-to-day use or traditional "what-if" testing. This secondary benefit of simulation requires a trained eye to recognize warning signs of poor model construction.
Monte Carlo simulation on kinetics of batch and semi-batch free radical polymerization
Shao, Jing
2015-10-27
Based on Monte Carlo simulation technology, we proposed a hybrid routine which combines reaction mechanism together with coarse-grained molecular simulation to study the kinetics of free radical polymerization. By comparing with previous experimental and simulation studies, we showed the capability of our Monte Carlo scheme on representing polymerization kinetics in batch and semi-batch processes. Various kinetics information, such as instant monomer conversion, molecular weight, and polydispersity etc. are readily calculated from Monte Carlo simulation. The kinetic constants such as polymerization rate k p is determined in the simulation without of “steady-state” hypothesis. We explored the mechanism for the variation of polymerization kinetics those observed in previous studies, as well as polymerization-induced phase separation. Our Monte Carlo simulation scheme is versatile on studying polymerization kinetics in batch and semi-batch processes.
Kurudirek, Murat
2015-09-01
Some gel dosimeters, water, human tissues and water phantoms were investigated with respect to their radiological properties in the energy region 10 keV-10 MeV. The effective atomic numbers (Zeff) and electron densities (Ne) for some heavy charged particles such as protons, He ions, B ions and C ions have been calculated for the first time for Fricke, MAGIC, MAGAT, PAGAT, PRESAGE, water, adipose tissue, muscle skeletal (ICRP), muscle striated (ICRU), plastic water, WT1 and RW3 using mass stopping powers from SRIM Monte Carlo software. The ranges and straggling were also calculated for the given materials. Two different set of mass stopping powers were used to calculate Zeff for comparison. The water equivalence of the given materials was also determined based on the results obtained. The Monte Carlo simulation of the charged particle transport was also done using SRIM code. The heavy ion distribution along with its parameters were shown for the given materials for different heavy ions. Also the energy loss and damage events in water when irradiated with 100 keV heavy ions were studied in detail.
Simulation and the Monte Carlo Method, Student Solutions Manual
Rubinstein, Reuven Y
2012-01-01
This accessible new edition explores the major topics in Monte Carlo simulation Simulation and the Monte Carlo Method, Second Edition reflects the latest developments in the field and presents a fully updated and comprehensive account of the major topics that have emerged in Monte Carlo simulation since the publication of the classic First Edition over twenty-five years ago. While maintaining its accessible and intuitive approach, this revised edition features a wealth of up-to-date information that facilitates a deeper understanding of problem solving across a wide array of subject areas, suc
On Monte Carlo Simulation and Analysis of Electricity Markets
International Nuclear Information System (INIS)
This dissertation is about how Monte Carlo simulation can be used to analyse electricity markets. There are a wide range of applications for simulation; for example, players in the electricity market can use simulation to decide whether or not an investment can be expected to be profitable, and authorities can by means of simulation find out which consequences a certain market design can be expected to have on electricity prices, environmental impact, etc. In the first part of the dissertation, the focus is which electricity market models are suitable for Monte Carlo simulation. The starting point is a definition of an ideal electricity market. Such an electricity market is partly practical from a mathematical point of view (it is simple to formulate and does not require too complex calculations) and partly it is a representation of the best possible resource utilisation. The definition of the ideal electricity market is followed by analysis how the reality differs from the ideal model, what consequences the differences have on the rules of the electricity market and the strategies of the players, as well as how non-ideal properties can be included in a mathematical model. Particularly, questions about environmental impact, forecast uncertainty and grid costs are studied. The second part of the dissertation treats the Monte Carlo technique itself. To reduce the number of samples necessary to obtain accurate results, variance reduction techniques can be used. Here, six different variance reduction techniques are studied and possible applications are pointed out. The conclusions of these studies are turned into a method for efficient simulation of basic electricity markets. The method is applied to some test systems and the results show that the chosen variance reduction techniques can produce equal or better results using 99% fewer samples compared to when the same system is simulated without any variance reduction technique. More complex electricity market models
Monte Carlo simulations of particle acceleration at oblique shocks
Baring, Matthew G.; Ellison, Donald C.; Jones, Frank C.
1994-02-01
The Fermi shock acceleration mechanism may be responsible for the production of high-energy cosmic rays in a wide variety of environments. Modeling of this phenomenon has largely focused on plane-parallel shocks, and one of the most promising techniques for its study is the Monte Carlo simulation of particle transport in shocked fluid flows. One of the principal problems in shock acceleration theory is the mechanism and efficiency of injection of particles from the thermal gas into the accelerated population. The Monte Carlo technique is ideally suited to addressing the injection problem directly, and previous applications of it to the quasi-parallel Earth bow shock led to very successful modeling of proton and heavy ion spectra, as well as other observed quantities. Recently this technique has been extended to oblique shock geometries, in which the upstream magnetic field makes a significant angle ThetaB1 to the shock normal. Spectral resutls from test particle Monte Carlo simulations of cosmic-ray acceleration at oblique, nonrelativistic shocks are presented. The results show that low Mach number shocks have injection efficiencies that are relatively insensitive to (though not independent of) the shock obliquity, but that there is a dramatic drop in efficiency for shocks of Mach number 30 or more as the obliquity increases above 15 deg. Cosmic-ray distributions just upstream of the shock reveal prominent bumps at energies below the thermal peak; these disappear far upstream but might be observable features close to astrophysical shocks.
Monte Carlo simulation of transition radiation and δ electrons
International Nuclear Information System (INIS)
This paper employs Monte Carlo simulations of the performance of a transition radiation detector (TRD). The program has been written for the TRD in the ZEUS spectrometer, which separates electrons from hadrons in the momentum range between 1 GeV/c and 30 GeV/c. Both, total charge method and cluster counting method were simulated taking into account various experimental parameters. In particular, it was found that the cluster counting method relies on a quantitative understanding of the background originating from the production of δ-electrons by charged particles. The results of the Monte Carlo calculations are in agreement with experimental data obtained with prototypes within a systematic uncertainty of 20%. We applied our Monte Carlo program to studies in order to find an optimum layout for the TRD within available space in the ZEUS spectrometer. In this context, the performance of TRD layouts with different geometries and materials has been evaluated comprehensively. The geometry found by optimization promises an improvement on hadron suppression by a factor of about two for both methods compared with present results from test measurements. Applying algorithms for a detailed analysis of the energy and space distributions of the clusters in the TRD, hadrons in the momentum range from 1 to 30 GeV/c can be suppressed to a level of less than 2%. This method of cluster analysing improves the suppression of hadrons by a factor of about two compared to the total charge method. (orig.)
International Nuclear Information System (INIS)
The investigation of some effects of the bombardment of material surfaces by keV ions has been carried out using a Monte Carlo computer simulation. This code models the target as an amorphous semi-infinite solid. Up to three elements may be used in the solid. The target's composition change during bombardment is simulated. Of the many phenomena taking place during the bombardment the simulation program will be used to study the dose dependence of the sputtering yield and ion-induced Auger electron emission. The study concludes that implanted Ar beam atoms do not alter the kinematics of the target by the amount necessary to cause the experimentally observed increase in the sputtering yield of Si. The computer study also suggests that for Ar bombardment of Al and Si the Auger electrons are predominantly from sputtered atoms. A novel technique for cleaning the surface of a liquid is described. This method has been used to obtain a highly clean surface on a liquid Ga drop. The surface flow generated by the ion bombardment is discussed. The circuit and structure of a quartz crystal third overtone resonator is presented. The resonator is designed for use in making dose dependent sputtering yield measurements. This apparatus can detect the removal of a fraction of a monolayer from a thin film that has been evaporated on its surface
International Nuclear Information System (INIS)
To examine information which may be obtained by the simultaneous observation of gamma-ray families and accompanying air showers, a Monte-Carlo simulation is carried out under various assumptions for primary cosmic rays and nuclear interactions. It is shown that only proton primary can produce those families that have energy greater than ΣEsub(γ) approximately=100 TeV with air shower size less than 105; other heavy primaries such as alpha, carbon etc always generate larger sizes than 105 for families ΣEsub(γ)>=100 TeV. Therefore we will be able to select families generated by proton primaries and discuss the character of nuclear interaction at very high energies without suffering from the problem of imitations of various new characters (large Pt, large multiplicity etc) by heavy primaries. Moreover, it is shown that the chemical composition of the primaries at >=1015 eV region is possibly studied through ΣEsub(γ)-size correlation
'Odontologic dosimetric card' experiments and simulations using Monte Carlo methods
International Nuclear Information System (INIS)
The techniques for data processing, combined with the development of fast and more powerful computers, makes the Monte Carlo methods one of the most widely used tools in the radiation transport simulation. For applications in diagnostic radiology, this method generally uses anthropomorphic phantoms to evaluate the absorbed dose to patients during exposure. In this paper, some Monte Carlo techniques were used to simulation of a testing device designed for intra-oral X-ray equipment performance evaluation called Odontologic Dosimetric Card (CDO of 'Cartao Dosimetrico Odontologico' in Portuguese) for different thermoluminescent detectors. This paper used two computational models of exposition RXD/EGS4 and CDO/EGS4. In the first model, the simulation results are compared with experimental data obtained in the similar conditions. The second model, it presents the same characteristics of the testing device studied (CDO). For the irradiations, the X-ray spectra were generated by the IPEM report number 78, spectrum processor. The attenuated spectrum was obtained for IEC 61267 qualities and various additional filters for a Pantak 320 X-ray industrial equipment. The results obtained for the study of the copper filters used in the determination of the kVp were compared with experimental data, validating the model proposed for the characterization of the CDO. The results shower of the CDO will be utilized in quality assurance programs in order to guarantee that the equipment fulfill the requirements of the Norm SVS No. 453/98 MS (Brazil) 'Directives of Radiation Protection in Medical and Dental Radiodiagnostic'. We conclude that the EGS4 is a suitable code Monte Carlo to simulate thermoluminescent dosimeters and experimental procedures employed in the routine of the quality control laboratory in diagnostic radiology. (author)
Optimization of a high-resolution collimator for a CdTe detector: Monte Carlo simulation studies
International Nuclear Information System (INIS)
Photon counting detectors using cadmium zinc telluride (CZT) or cadmium telluride (CdTe) have benefits compared to conventional scintillation detectors, and CZT and CdTe have advantageous physical characteristics for nuclear medicine imaging. Recently, many studies have been conducted using these materials to improve the sensitivity and the spatial resolution of the photon counting detector. By using a pixelated parallel-hole collimator, we may be able to improve the sensitivity and the spatial resolution. The purpose of this study was to optimize the design of a collimator to achieve excellent resolution and high sensitivity for a gamma camera system based on the CdTe detector. In this study we simulated a gamma camera system with a photon counting detector based on CdTe and evaluated the system's performance. We performed a simulation study of the PID 350 (Ajat Oy Ltd., Finland) CdTe detector by using a Geant4 Application for Tomographic Emission (GATE) simulation. This detector consists of small pixels (0.35 x 0.35 mm2). We designed two parallel-hole collimators with different shapes and verified their usefulness. One was the proposed pixelated parallel-hole collimator in which the hole size and the pixel size are the same, and the other was the hexagonal parallel-hole collimator, which had a hole size similar to that of the pixelated parallel-hole collimator. We evaluated the sensitivity, spatial resolution, and contrast resolution to determine which parallel-hole collimator was best for the PID 350 CdTe detector. The average sensitivity was 22.65% higher for the pixelated parallel-hole collimator than for the hexagonal parallel-hole collimator. Also, the pixelated parallel-hole collimator provided 10.7% better spatial resolution than the hexagonal parallel-hole collimator, and the contrast resolution was improved by 8.93%. These results reflect an improvement in sensitivity and spatial resolution, and indicate that the imaging performance of the pixelated
International Nuclear Information System (INIS)
A Monte Carlo study of the energy response of an aluminium oxide (Al2O3) detector in kilo-voltage and mega-voltage photon beams relative to 60Co gamma rays has been performed using EGSnrc Monte Carlo simulations. The sensitive volume of the Al2O3 detector was simulated as a disc of diameter 2.85 mm and thickness 1 mm. The phantom material was water and the irradiation depth chosen was 2.0 cm in kilo-voltage photon beams and 5.0 cm in mega-voltage photon beams. The results show that the energy response of the Al2O3 detector is constant within 3% for photon beam energies in the energy range of 60 Co gamma rays to 25 MV X-rays. However, the Al2O3 detector shows an enhanced energy response for kilo-voltage photon beams, which in the case of 50 kV X-rays is 3.2 times higher than that for 60Co gamma rays. There is essentially no difference in the energy responses of LiF and Al2O3 detectors irradiated in mega-voltage photon beams when these Al2O3 results are compared with literature data for LiF thermoluminescence detectors. However, the Al2O3 detector has a much higher enhanced response compared with LiF detectors in kilo-voltage X-ray beams, more than twice as much for the case of 50 kV X-rays. (authors)
International Nuclear Information System (INIS)
In conventional PET systems,the parallax error degrades image resolution and causes image distortion. To remedy this, a PET ring diameter has to be much larger than the required size of field of view (FOV), and therefore the cost goes up. Measurement of depth-of-interaction (DOI) information is effective to reduce the parallax error and improve the image quality. This study is aimed at developing a practical method to incorporate DOI information in PET sonogram generation and image reconstruction processes and evaluate its efficacy through Monte Carlo simulation. An animal PET system with 30-mm long LSO crystals and 2-mm DOI measurement accuracy was simulated and list-mode PET data were collected. A sonogram generation method was proposed to bin each coincidence event to the correct LOR location according to both incident crystal indices and DOI positions of the two annihilation photons. The sonograms were reconstructed with an iterative OSMAPEM (ordered subset maximum a posteriori expectation maximization) algorithm. Two phantoms (a rod source phantom and a Derenzo phantom) were simulated, and the benefits of DOI were investigated in terms of reconstructed source diameter (FWHM) and source positioning accuracy. The results demonstrate that the proposed method works well to incorporate DOI information in data processing, which not only overcomes the image distortion problem but also significantly improves image resolution and resolution uniformity and results in satisfactory image quality. (authors)
Public Infrastructure for Monte Carlo Simulation: publicMC@BATAN
Waskita, A A; Akbar, Z; Handoko, L T; 10.1063/1.3462759
2010-01-01
The first cluster-based public computing for Monte Carlo simulation in Indonesia is introduced. The system has been developed to enable public to perform Monte Carlo simulation on a parallel computer through an integrated and user friendly dynamic web interface. The beta version, so called publicMC@BATAN, has been released and implemented for internal users at the National Nuclear Energy Agency (BATAN). In this paper the concept and architecture of publicMC@BATAN are presented.
International Nuclear Information System (INIS)
There have been many efforts to advance the technology of X-ray digital mammography in order to enhance the early detection of breast pathology. The purpose of this study was to evaluate image quality and the radiation dose after magnifying X-ray digital mammography using the Geant4 Application for Tomographic Emission (GATE). In this study, we simulated a Monte Carlo model of an X-ray digital mammographic system, and we present a technique for magnification and discuss how it affects the image quality. The simulated X-ray digital mammographic system with GATE consists of an X-ray source, a compression paddle, a supporting plate, and an imaging plate (IP) of computed radiography (CR). The degree of magnification ranged from 1.0 to 2.0. We designed a semi-cylindrical phantom with a thickness of 45-mm and a radius of 50-mm in order to evaluate the image quality after magnification. The phantom was made of poly methyl methacrylate (PMMA) and contained four spherical specks with diameters of 750, 500, 250, and 100-μm to simulate microcalcifications. The simulation studies were performed with an X-ray energy spectrum calculated using the spectrum processor SRS-78. A combination of a molybdenum anode and a molybdenum filter (Mo/Mo) was used for the mammographic X-ray tubes. The effects of the degree of magnification were investigated in terms of both the contrast-to-noise ratio (CNR) and the average glandular dose (AGD). The results show that the CNR increased as the degree of magnification increased and decreased as breast glandularity increased. The AGD showed only a minor increase with magnification. Based on the results, magnification of mammographic images can be used to obtain high image quality with an increased CNR. Our X-ray digital mammographic system model with GATE may be used as a basis for future studies on X-ray imaging characteristics.
Monte-Carlo Simulation on Neutron Instruments at CARR
Institute of Scientific and Technical Information of China (English)
2001-01-01
The design of high resolution neutron powder diffractometer(HRPD) and two cold neutron guides(CNGs) to be built at China advanced research reactor(CARR) are studied by Monte-Carlo simulation technique.The HRPD instrument is desiged to have a minimum resolution of 0.2% and neutron fluence rate of greater than 106 cm-2 ·s-1 at sample position. The resolution curves, neutron fluence rate and effective neutron beam size at sample position are given. Differences in resolutions and intensity between the
Monte Carlo simulations of charge transport in heterogeneous organic semiconductors
Aung, Pyie Phyo; Khanal, Kiran; Luettmer-Strathmann, Jutta
2015-03-01
The efficiency of organic solar cells depends on the morphology and electronic properties of the active layer. Research teams have been experimenting with different conducting materials to achieve more efficient solar panels. In this work, we perform Monte Carlo simulations to study charge transport in heterogeneous materials. We have developed a coarse-grained lattice model of polymeric photovoltaics and use it to generate active layers with ordered and disordered regions. We determine carrier mobilities for a range of conditions to investigate the effect of the morphology on charge transport.
Monte Carlo simulation of neutron scattering instruments
International Nuclear Information System (INIS)
A library of Monte Carlo subroutines has been developed for the purpose of design of neutron scattering instruments. Using small-angle scattering as an example, the philosophy and structure of the library are described and the programs are used to compare instruments at continuous wave (CW) and long-pulse spallation source (LPSS) neutron facilities. The Monte Carlo results give a count-rate gain of a factor between 2 and 4 using time-of-flight analysis. This is comparable to scaling arguments based on the ratio of wavelength bandwidth to resolution width
A comparison of Monte Carlo and cellular automata approaches for semiconductor device simulation
Energy Technology Data Exchange (ETDEWEB)
Zandler, G.; Di Carlo, A.; Kometer, K.; Lugli, P.; Vogl, P.; Gornik, E. (Technische Univ. Muenchen (Germany))
1993-02-01
The authors present a detailed comparison of Monte Carlo and cellular automata approaches as applied to the study of nonequilibrium transport and semiconductor device simulation. They show that the novel cellular automata (CA) technique enjoys all benefits of the more traditional Monte Carlo (MC) method, while at the same time allowing considerably higher performances.
Monte Carlo Simulation Tool Installation and Operation Guide
Energy Technology Data Exchange (ETDEWEB)
Aguayo Navarrete, Estanislao; Ankney, Austin S.; Berguson, Timothy J.; Kouzes, Richard T.; Orrell, John L.; Troy, Meredith D.; Wiseman, Clinton G.
2013-09-02
This document provides information on software and procedures for Monte Carlo simulations based on the Geant4 toolkit, the ROOT data analysis software and the CRY cosmic ray library. These tools have been chosen for its application to shield design and activation studies as part of the simulation task for the Majorana Collaboration. This document includes instructions for installation, operation and modification of the simulation code in a high cyber-security computing environment, such as the Pacific Northwest National Laboratory network. It is intended as a living document, and will be periodically updated. It is a starting point for information collection by an experimenter, and is not the definitive source. Users should consult with one of the authors for guidance on how to find the most current information for their needs.
International Nuclear Information System (INIS)
Methods for Monte Carlo procedure in radiation measurement by SPECT (single photon emission computed tomography) and 3-D PET (3-dimensional positron emission tomography) are described together with its application to develop and optimize the scattering correction method in 201Tl-SPECT. In the medical technology, the Monte Carlo simulation makes it possible to quantify the behavior of a photon like scattering and absorption, and which can be performed by the use of EGS4 simulation code consisting from Step A - E. With the method, data collection procedures of the diagnostic equipments for nuclear medicine and application to develop the transmission radiation source for SPECT are described. Precision of the scattering correction method is also evaluated in the SPECT by the Monte Carlo simulation. The simulation is a useful tool for evaluating the behavior of radiation in the human body which can not be actually measured. (K.H.)
Application of Monte Carlo simulation for three-dimensional flows
Scheurlen, M.; Noll, B.; Wittig, S.
1992-02-01
A Monte Carlo technique is outlined for the simulation of the transport of a joint scalar probability density function (PDF). The discretization of the partial differential equations is based on a finite volume approximation. The problem of frozen solutions is addressed if the number of stochastic elements is limited. Non-adiabatic boundary conditions are discussed if the energy equation is solved by a Monte Carlo simulation. The Monte Carlo simulation is compared with deterministic calculations and with an experiment in a three dimensional non-isothermal non-reacting jet mixing flow. The results of the simulation agree very well with the experiment and the deterministic calculations. However, the computer time and storage requirements for a three dimensional simulation of the transport of a single scalar PDF increases dramatically in comparison to deterministic calculations. The results also indicate the need for a simulation procedure that is free of numerical diffusion.
International Nuclear Information System (INIS)
It is recommended that a pixelated parallel-hole collimator in which the hole and pixel sizes are equal be used to improve the sensitivity and spatial resolution when using a small pixel size and a single-photon emission computed tomography (SPECT) system with pixelated semiconductor detector materials (e.g., CdTe and CZT). However, some significant problems arise in the manufacturing of a pixelated parallel-hole collimator. Therefore, we sought to simulate a pixelated semiconductor SPECT system with various collimator geometric designs. The purpose of this study was to compare the quality of images generated with a pixelated semiconductor SPECT system simulated with pixelated parallel-hole collimators of various geometric designs. The sensitivity and spatial resolution of the various collimator geometric designs with varying septal heights and hole sizes were measured. Moreover, to evaluate the overall performance of the imaging system, a hot-rod phantom was designed using a Monte Carlo simulation. According to the results, the average sensitivity using a 15 mm septal height was 1.80, 2.87, and 4.16 times higher than that obtained with septal heights of 20, 25, and 30 mm, respectively. Also, the average spatial resolution using the 30 mm septal height was 44.33, 22.08, and 9.26% better than that attained with 15, 20, and 25 mm septal heights, respectively. When the results acquired with 0.3 and 0.6 mm hole sizes were compared, the average sensitivity with the 0.6 mm hole size was 3.97 times higher than that obtained with the 0.3 mm hole size, and the average spatial resolution with the 0.3 mm hole size was 45.76% better than that with the 0.6 mm hole size. We have presented the pixelated parallel-hole collimators of various collimator geometric designs and evaluations. Our results showed that the effect of various collimator geometric designs can be investigated by Monte Carlo simulation so as to evaluate the feasibility of a high resolution parallel
Lee, Y.-J.; Park, S.-J.; Lee, S.-W.; Kim, D.-H.; Kim, Y.-S.; Jo, B.-D.; Kim, H.-J.
2013-03-01
It is recommended that a pixelated parallel-hole collimator in which the hole and pixel sizes are equal be used to improve the sensitivity and spatial resolution when using a small pixel size and a single-photon emission computed tomography (SPECT) system with pixelated semiconductor detector materials (e.g., CdTe and CZT). However, some significant problems arise in the manufacturing of a pixelated parallel-hole collimator. Therefore, we sought to simulate a pixelated semiconductor SPECT system with various collimator geometric designs. The purpose of this study was to compare the quality of images generated with a pixelated semiconductor SPECT system simulated with pixelated parallel-hole collimators of various geometric designs. The sensitivity and spatial resolution of the various collimator geometric designs with varying septal heights and hole sizes were measured. Moreover, to evaluate the overall performance of the imaging system, a hot-rod phantom was designed using a Monte Carlo simulation. According to the results, the average sensitivity using a 15 mm septal height was 1.80, 2.87, and 4.16 times higher than that obtained with septal heights of 20, 25, and 30 mm, respectively. Also, the average spatial resolution using the 30 mm septal height was 44.33, 22.08, and 9.26% better than that attained with 15, 20, and 25 mm septal heights, respectively. When the results acquired with 0.3 and 0.6 mm hole sizes were compared, the average sensitivity with the 0.6 mm hole size was 3.97 times higher than that obtained with the 0.3 mm hole size, and the average spatial resolution with the 0.3 mm hole size was 45.76% better than that with the 0.6 mm hole size. We have presented the pixelated parallel-hole collimators of various collimator geometric designs and evaluations. Our results showed that the effect of various collimator geometric designs can be investigated by Monte Carlo simulation so as to evaluate the feasibility of a high resolution parallel
Monte Carlo simulation experiments on box-type radon dosimeter
Jamil, Khalid; Kamran, Muhammad; Illahi, Ahsan; Manzoor, Shahid
2014-11-01
Epidemiological studies show that inhalation of radon gas (222Rn) may be carcinogenic especially to mine workers, people living in closed indoor energy conserved environments and underground dwellers. It is, therefore, of paramount importance to measure the 222Rn concentrations (Bq/m3) in indoors environments. For this purpose, box-type passive radon dosimeters employing ion track detector like CR-39 are widely used. Fraction of the number of radon alphas emitted in the volume of the box type dosimeter resulting in latent track formation on CR-39 is the latent track registration efficiency. Latent track registration efficiency is ultimately required to evaluate the radon concentration which consequently determines the effective dose and the radiological hazards. In this research, Monte Carlo simulation experiments were carried out to study the alpha latent track registration efficiency for box type radon dosimeter as a function of dosimeter's dimensions and range of alpha particles in air. Two different self developed Monte Carlo simulation techniques were employed namely: (a) Surface ratio (SURA) method and (b) Ray hitting (RAHI) method. Monte Carlo simulation experiments revealed that there are two types of efficiencies i.e. intrinsic efficiency (ηint) and alpha hit efficiency (ηhit). The ηint depends upon only on the dimensions of the dosimeter and ηhit depends both upon dimensions of the dosimeter and range of the alpha particles. The total latent track registration efficiency is the product of both intrinsic and hit efficiencies. It has been concluded that if diagonal length of box type dosimeter is kept smaller than the range of alpha particle then hit efficiency is achieved as 100%. Nevertheless the intrinsic efficiency keeps playing its role. The Monte Carlo simulation experimental results have been found helpful to understand the intricate track registration mechanisms in the box type dosimeter. This paper explains that how radon concentration from the
Monte Carlo simulation experiments on box-type radon dosimeter
Energy Technology Data Exchange (ETDEWEB)
Jamil, Khalid, E-mail: kjamil@comsats.edu.pk; Kamran, Muhammad; Illahi, Ahsan; Manzoor, Shahid
2014-11-11
Epidemiological studies show that inhalation of radon gas ({sup 222}Rn) may be carcinogenic especially to mine workers, people living in closed indoor energy conserved environments and underground dwellers. It is, therefore, of paramount importance to measure the {sup 222}Rn concentrations (Bq/m{sup 3}) in indoors environments. For this purpose, box-type passive radon dosimeters employing ion track detector like CR-39 are widely used. Fraction of the number of radon alphas emitted in the volume of the box type dosimeter resulting in latent track formation on CR-39 is the latent track registration efficiency. Latent track registration efficiency is ultimately required to evaluate the radon concentration which consequently determines the effective dose and the radiological hazards. In this research, Monte Carlo simulation experiments were carried out to study the alpha latent track registration efficiency for box type radon dosimeter as a function of dosimeter’s dimensions and range of alpha particles in air. Two different self developed Monte Carlo simulation techniques were employed namely: (a) Surface ratio (SURA) method and (b) Ray hitting (RAHI) method. Monte Carlo simulation experiments revealed that there are two types of efficiencies i.e. intrinsic efficiency (η{sub int}) and alpha hit efficiency (η{sub hit}). The η{sub int} depends upon only on the dimensions of the dosimeter and η{sub hit} depends both upon dimensions of the dosimeter and range of the alpha particles. The total latent track registration efficiency is the product of both intrinsic and hit efficiencies. It has been concluded that if diagonal length of box type dosimeter is kept smaller than the range of alpha particle then hit efficiency is achieved as 100%. Nevertheless the intrinsic efficiency keeps playing its role. The Monte Carlo simulation experimental results have been found helpful to understand the intricate track registration mechanisms in the box type dosimeter. This paper
International Nuclear Information System (INIS)
Grand canonical Monte Carlo (GCMC) simulation combined with ab initio quantum mechanics calculations were employed to study methane storage in homogeneous armchair open-ended single-walled silicon nanotubes (SWSiNTs), single-walled carbon nanotubes (SWCNTs), and single-walled silicon carbide nanotubes (SWSiCNTs) in triangular arrays. Two different groups of nanotubes were studied: the first were (12,12) SiNTs, (19,19) CNTs, and (15,15) SiCNTs and the second were (7,7) SiNTs, (11,11) CNTs, and (9,9) SiCNTs with the diameters of 26 and 15 Å for the first and second groups, respectively. The simulations were carried out at different thermodynamic states. The potential energy functions were calculated using ab initio quantum mechanics and then fitted with (12,6) Lennard–Jones potential model as a bridge between first-principles calculations and GCMC simulations. The absolute, excess, and delivery adsorption isotherms of methane were calculated for two groups of nanotubes. The specific surface area and the isosteric heat of adsorption were computed. The radial distribution functions for the adsorbed molecules on different nanotubes were also calculated. Different isotherm models were fitted with the simulation adsorption data. According to the results, the excess uptake value of methane adsorption in (11,11) CNT array exceeded the US Department of Energy target (180 V/V at 298 K and 35 bar). The results also indicate that SiNTs and SiCNTs are not desirable materials compared with corresponding CNTs for natural gas storage.
Energy Technology Data Exchange (ETDEWEB)
Mahdizadeh, Sayyed Jalil, E-mail: saja.mahdizadeh@gmail.com; Goharshadi, Elaheh K. [Ferdowsi University of Mashhad, Department of Chemistry (Iran, Islamic Republic of)
2013-01-15
Grand canonical Monte Carlo (GCMC) simulation combined with ab initio quantum mechanics calculations were employed to study methane storage in homogeneous armchair open-ended single-walled silicon nanotubes (SWSiNTs), single-walled carbon nanotubes (SWCNTs), and single-walled silicon carbide nanotubes (SWSiCNTs) in triangular arrays. Two different groups of nanotubes were studied: the first were (12,12) SiNTs, (19,19) CNTs, and (15,15) SiCNTs and the second were (7,7) SiNTs, (11,11) CNTs, and (9,9) SiCNTs with the diameters of 26 and 15 A for the first and second groups, respectively. The simulations were carried out at different thermodynamic states. The potential energy functions were calculated using ab initio quantum mechanics and then fitted with (12,6) Lennard-Jones potential model as a bridge between first-principles calculations and GCMC simulations. The absolute, excess, and delivery adsorption isotherms of methane were calculated for two groups of nanotubes. The specific surface area and the isosteric heat of adsorption were computed. The radial distribution functions for the adsorbed molecules on different nanotubes were also calculated. Different isotherm models were fitted with the simulation adsorption data. According to the results, the excess uptake value of methane adsorption in (11,11) CNT array exceeded the US Department of Energy target (180 V/V at 298 K and 35 bar). The results also indicate that SiNTs and SiCNTs are not desirable materials compared with corresponding CNTs for natural gas storage.
Lattice Monte Carlo simulation of Galilei variant anomalous diffusion
International Nuclear Information System (INIS)
The observation of an increasing number of anomalous diffusion phenomena motivates the study to reveal the actual reason for such stochastic processes. When it is difficult to get analytical solutions or necessary to track the trajectory of particles, lattice Monte Carlo (LMC) simulation has been shown to be particularly useful. To develop such an LMC simulation algorithm for the Galilei variant anomalous diffusion, we derive explicit solutions for the conditional and unconditional first passage time (FPT) distributions with double absorbing barriers. According to the theory of random walks on lattices and the FPT distributions, we propose an LMC simulation algorithm and prove that such LMC simulation can reproduce both the mean and the mean square displacement exactly in the long-time limit. However, the error introduced in the second moment of the displacement diverges according to a power law as the simulation time progresses. We give an explicit criterion for choosing a small enough lattice step to limit the error within the specified tolerance. We further validate the LMC simulation algorithm and confirm the theoretical error analysis through numerical simulations. The numerical results agree with our theoretical predictions very well
Lattice Monte Carlo simulation of Galilei variant anomalous diffusion
Energy Technology Data Exchange (ETDEWEB)
Guo, Gang, E-mail: hndzgg@aliyun.com [School of Information System and Management, National University of Defense Technology, Changsha, 410073 (China); Institute of Computer Science, University of Rostock, Albert Einstein Str. 22, Rostock, 18059 (Germany); Bittig, Arne, E-mail: arne.bittig@uni-rostock.de [Institute of Computer Science, University of Rostock, Albert Einstein Str. 22, Rostock, 18059 (Germany); Uhrmacher, Adelinde, E-mail: lin@informatik.uni-rostock.de [Institute of Computer Science, University of Rostock, Albert Einstein Str. 22, Rostock, 18059 (Germany)
2015-05-01
The observation of an increasing number of anomalous diffusion phenomena motivates the study to reveal the actual reason for such stochastic processes. When it is difficult to get analytical solutions or necessary to track the trajectory of particles, lattice Monte Carlo (LMC) simulation has been shown to be particularly useful. To develop such an LMC simulation algorithm for the Galilei variant anomalous diffusion, we derive explicit solutions for the conditional and unconditional first passage time (FPT) distributions with double absorbing barriers. According to the theory of random walks on lattices and the FPT distributions, we propose an LMC simulation algorithm and prove that such LMC simulation can reproduce both the mean and the mean square displacement exactly in the long-time limit. However, the error introduced in the second moment of the displacement diverges according to a power law as the simulation time progresses. We give an explicit criterion for choosing a small enough lattice step to limit the error within the specified tolerance. We further validate the LMC simulation algorithm and confirm the theoretical error analysis through numerical simulations. The numerical results agree with our theoretical predictions very well.
Monte Carlo simulation of the energy spectrum for CdZnTe Frisch grid detector
Xu, Zhaoli; Wang, Linjun; Min, Jiahua; Teng, Jianyong; Qin, Kaifeng; Hu, Dongni; Zhang, Jijun; Huang, Jian; Xia, Yiben
2009-07-01
In this paper, we use the Monte-Carlo method to study the reaction of the electron-hole pairs produced to randomicity and the statistics rule, according to the principal of the detector and the gamma ray track in the CdZnTe detector. The EGSnrc software based on Monte-Carlo method is used to simulate the process of carriers' transportation. The statistics rule greatly reflects the result in Monte Carlo simulation. Firstly, we use Ansys software to create a model of the object for Monte-Carlo simulation, which is the basis for our further Monte-Carlo research. During Ansys simulation, a columniform block is created, where the electrical and thermal properties of the materials for simulation use are established. Then, the charge collection efficiency through the statistical approach was calculated using the EGSnrc software. Furthermore, by considering the interaction mechanism of CdZnTe with gamma ray, several modules in the software are added into Monte Carlo simulation. Finally, the pulse height spectra with the response to gamma ray, are available from the simulation. The comparison between the simulation and the measurement result is indicated, which shows that the simulation experiment is reliable. The Frisch grid detector can get the responses more efficiently than other structure devices.
Monte Carlo simulation in statistical physics an introduction
Binder, Kurt
1992-01-01
The Monte Carlo method is a computer simulation method which uses random numbers to simulate statistical fluctuations The method is used to model complex systems with many degrees of freedom Probability distributions for these systems are generated numerically and the method then yields numerically exact information on the models Such simulations may be used tosee how well a model system approximates a real one or to see how valid the assumptions are in an analyical theory A short and systematic theoretical introduction to the method forms the first part of this book The second part is a practical guide with plenty of examples and exercises for the student Problems treated by simple sampling (random and self-avoiding walks, percolation clusters, etc) are included, along with such topics as finite-size effects and guidelines for the analysis of Monte Carlo simulations The two parts together provide an excellent introduction to the theory and practice of Monte Carlo simulations
International Nuclear Information System (INIS)
Carbon nanotubes (CNTs) are outstanding novel materials that have great potential for a variety of chemical and biomedical applications. However, the mechanism of their interactions with biomaterials is still not fully understood, and more insightful research work is needed. In this work, we use the 2D hydrophobic-polar lattice model and the Monte Carlo simulation method to study the interactions between model peptides and CNTs. The energy parameters of the coarse-grained lattice model are qualitatively determined based on experimental data and molecular dynamics simulation results. Our model is capable of reproducing the essential phenomena of peptides folding in bulk water and binding to CNTs, as well as providing new insights into the thermodynamics and conformational properties of peptides interacting with nanotubes. The results suggest that both the internal energy and the peptide conformational entropy contribute to the binding process. Upon binding to the CNTs, peptides generally unfold into their denatured structures before they reach the lowest-accessible energy states of the system. Temperature has a significant influence on the adsorption process
International Nuclear Information System (INIS)
We studied the performance of a dual-panel positron emission tomography (PET) camera dedicated to breast cancer imaging using Monte Carlo simulation. The PET camera under development has two 10x15 cm2 plates that are constructed from arrays of 1x1x3 mm3 LSO crystals coupled to novel ultra-thin (3 intrinsic spatial resolution, 3, 2x2x10 mm3, 3x3x30 mm3, and 4x4x20 mm3 LSO crystal resolutions and different panel separations. Images were reconstructed by focal plane tomography with attenuation and normalization corrections applied. Simulation results indicate that with an activity concentration ratio of tumor:breast:heart:torso of 10:1:10:1 and 30 s of acquisition time, only the dual-plate PET camera comprising 1x1x3 mm3 crystals could resolve 2.5 mm diameter spheres with an average peak-to-valley ratio of 1.3
International Nuclear Information System (INIS)
Based on the recently constructed Ni-Zr-Al n-body potential, Monte Carlo simulations are performed to study the glass formation and associated structural evolutions in the system. The micro-chemical inhomogeneity (MCI) parameter and Honeycutt and Anderson (HA) pair analysis are employed to investigate both the chemical short-range orders and topological short-range orders for the ternary Ni-Zr-Al metallic glasses. Results reveal that remarkable chemical short-range orders (CSROs) exist in the ternary Ni-Zr-Al metallic glasses and are strongly influenced by the chemical interactions among the constituent elements. Moreover, topological short-range orders are clearly formed in the ternary Ni-Zr-Al metallic glasses, with the most remarkable characteristic being the icosahedral local packing. Similarly to CSRO, the extent of icosahedral short-range orders formed in the Ni-Zr-Al system varies distinctly with the chemical composition. In addition, simulation results reveal that chemical short-range orders and topological short-range orders turn out to be influenced by different factors. Unlike CSRO, both chemical interactions and geometrical constraints play important roles in forming the topological short-range orders.
Energy Technology Data Exchange (ETDEWEB)
Papadimitroulas, P; Kostou, T; Kagadis, G [University of Patras, Rion, Ahaia (Greece); Loudos, G [Technological Educational Institute of Athens, Egaleo, Attika (Greece)
2015-06-15
Purpose: The purpose of the present study was to quantify, evaluate the impact of cardiac and respiratory motion on clinical nuclear imaging protocols. Common SPECT and scintigraphic scans are studied using Monte Carlo (MC) simulations, comparing the resulted images with and without motion. Methods: Realistic simulations were executed using the GATE toolkit and the XCAT anthropomorphic phantom as a reference model for human anatomy. Three different radiopharmaceuticals based on 99mTc were studied, namely 99mTc-MDP, 99mTc—N—DBODC and 99mTc—DTPA-aerosol for bone, myocardium and lung scanning respectively. The resolution of the phantom was set to 3.5 mm{sup 3}. The impact of the motion on spatial resolution was quantified using a sphere with 3.5 mm diameter and 10 separate time frames, in the ECAM modeled SPECT scanner. Finally, respiratory motion impact on resolution and imaging of lung lesions was investigated. The MLEM algorithm was used for data reconstruction, while the literature derived biodistributions of the pharmaceuticals were used as activity maps in the simulations. Results: FWHM was extracted for a static and a moving sphere which was ∼23 cm away from the entrance of the SPECT head. The difference in the FWHM was 20% between the two simulations. Profiles in thorax were compared in the case of bone scintigraphy, showing displacement and blurring of the bones when respiratory motion was inserted in the simulation. Large discrepancies were noticed in the case of myocardium imaging when cardiac motion was incorporated during the SPECT acquisition. Finally the borders of the lungs are blurred when respiratory motion is included resulting to a dislocation of ∼2.5 cm. Conclusion: As we move to individualized imaging and therapy procedures, quantitative and qualitative imaging is of high importance in nuclear diagnosis. MC simulations combined with anthropomorphic digital phantoms can provide an accurate tool for applications like motion correction
International Nuclear Information System (INIS)
Purpose: The purpose of the present study was to quantify, evaluate the impact of cardiac and respiratory motion on clinical nuclear imaging protocols. Common SPECT and scintigraphic scans are studied using Monte Carlo (MC) simulations, comparing the resulted images with and without motion. Methods: Realistic simulations were executed using the GATE toolkit and the XCAT anthropomorphic phantom as a reference model for human anatomy. Three different radiopharmaceuticals based on 99mTc were studied, namely 99mTc-MDP, 99mTc—N—DBODC and 99mTc—DTPA-aerosol for bone, myocardium and lung scanning respectively. The resolution of the phantom was set to 3.5 mm3. The impact of the motion on spatial resolution was quantified using a sphere with 3.5 mm diameter and 10 separate time frames, in the ECAM modeled SPECT scanner. Finally, respiratory motion impact on resolution and imaging of lung lesions was investigated. The MLEM algorithm was used for data reconstruction, while the literature derived biodistributions of the pharmaceuticals were used as activity maps in the simulations. Results: FWHM was extracted for a static and a moving sphere which was ∼23 cm away from the entrance of the SPECT head. The difference in the FWHM was 20% between the two simulations. Profiles in thorax were compared in the case of bone scintigraphy, showing displacement and blurring of the bones when respiratory motion was inserted in the simulation. Large discrepancies were noticed in the case of myocardium imaging when cardiac motion was incorporated during the SPECT acquisition. Finally the borders of the lungs are blurred when respiratory motion is included resulting to a dislocation of ∼2.5 cm. Conclusion: As we move to individualized imaging and therapy procedures, quantitative and qualitative imaging is of high importance in nuclear diagnosis. MC simulations combined with anthropomorphic digital phantoms can provide an accurate tool for applications like motion correction
International Nuclear Information System (INIS)
The catalytic oxidation of CO has already been studied over a square surface through Monte Carlo simulation via a model based on the Langmuir-Hinshelwood (LH) mechanism in which the dissociated adsorption of the O2 molecule is considered on a pair of vacancies found in the nearest neighbourhood. The results of this study are well known. Here, this reaction system has been studied on the basis of the precursor mechanism, which involves the motion of two oxygen precursors into the first and the third nearest neighbourhood. This study shows that contrary to the dimer-dimer model, the mobility of precursors into the third nearest neighbourhood has no significant effect on the phase diagram of the system. If the reaction of a precursor with chemisorbed oxygen atoms is allowed, the situation changes significantly. In this case, the mobility of precursors has the same effect as observed in the dimer-dimer model. We also have explored the effect of an experimentally observed hot atom adsorption mechanism on the phase diagram of the reaction system. When two oxygen precursors are adsorbed with an average distance of two lattice constants, the second-order phase transition is eliminated. The moment yCO departs from zero, the continuous production of CO2 starts and the phase diagram closely resembles the experimental one qualitatively
Monte Carlo simulation of medical linear accelerator using primo code
International Nuclear Information System (INIS)
The use of monte Carlo simulation has become very important in the medical field and especially in calculation in radiotherapy. Various Monte Carlo codes were developed simulating interactions of particles and photons with matter. One of these codes is PRIMO that performs simulation of radiation transport from the primary electron source of a linac to estimate the absorbed dose in a water phantom or computerized tomography (CT). PRIMO is based on Penelope Monte Carlo code. Measurements of 6 MV photon beam PDD and profile were done for Elekta precise linear accelerator at Radiation and Isotopes Center Khartoum using computerized Blue water phantom and CC13 Ionization Chamber. accept Software was used to control the phantom to measure and verify dose distribution. Elektalinac from the list of available linacs in PRIMO was tuned to model Elekta precise linear accelerator. Beam parameter of 6.0 MeV initial electron energy, 0.20 MeV FWHM, and 0.20 cm focal spot FWHM were used, and an error of 4% between calculated and measured curves was found. The buildup region Z max was 1.40 cm and homogenous profile in cross line and in line were acquired. A number of studies were done to verily the model usability one of them is the effect of the number of histories on accuracy of the simulation and the resulted profile for the same beam parameters. The effect was noticeable and inaccuracies in the profile were reduced by increasing the number of histories. Another study was the effect of Side-step errors on the calculated dose which was compared with the measured dose for the same setting.It was in range of 2% for 5 cm shift, but it was higher in the calculated dose because of the small difference between the tuned model and measured dose curves. Future developments include simulating asymmetrical fields, calculating the dose distribution in computerized tomographic (CT) volume, studying the effect of beam modifiers on beam profile for both electron and photon beams.(Author)
Energy Technology Data Exchange (ETDEWEB)
Fonseca, T.C.F.; Bastos, F.M.; Figueiredo, M.T.T.; Souza, L.S.; Guimaraes, M.C.; Silva, C.R.E.; Mello, O.A.; Castelo e Silva, L.A.; Paixao, L., E-mail: tcff01@gmail.com [Centro de Desenvolvimento da Tecnologia Nuclear (CDTN/CNEN-MG), Belo Horizonte, MG (Brazil); Benavente, J.A.; Paiva, F.G. [Universidade Federal de Minas Gerais (PCTN/UFMG), Belo Horizonte, MG (Brazil). Curso de Pos-Graduacao em Ciencias e Tecnicas Nucleares
2015-07-01
Computational Monte Carlo (MC) codes have been used for simulation of nuclear installations mainly for internal monitoring of workers, the well known as Whole Body Counters (WBC). The main goal of this project was the modeling and simulation of the counting efficiency (CE) of a WBC system using three different MC codes: MCNPX, EGSnrc and VMC in-vivo. The simulations were performed for three different groups of analysts. The results shown differences between the three codes, as well as in the results obtained by the same code and modeled by different analysts. Moreover, all the results were also compared to the experimental results obtained in laboratory for meaning of validation and final comparison. In conclusion, it was possible to detect the influence on the results when the system is modeled by different analysts using the same MC code and in which MC code the results were best suited, when comparing to the experimental data result. (author)
Methods for variance reduction in Monte Carlo simulations
Bixler, Joel N.; Hokr, Brett H.; Winblad, Aidan; Elpers, Gabriel; Zollars, Byron; Thomas, Robert J.
2016-03-01
Monte Carlo simulations are widely considered to be the gold standard for studying the propagation of light in turbid media. However, due to the probabilistic nature of these simulations, large numbers of photons are often required in order to generate relevant results. Here, we present methods for reduction in the variance of dose distribution in a computational volume. Dose distribution is computed via tracing of a large number of rays, and tracking the absorption and scattering of the rays within discrete voxels that comprise the volume. Variance reduction is shown here using quasi-random sampling, interaction forcing for weakly scattering media, and dose smoothing via bi-lateral filtering. These methods, along with the corresponding performance enhancements are detailed here.
Adjoint Monte Carlo simulation of fixed-energy secondary radiation
International Nuclear Information System (INIS)
Fixed energy secondary generation for adjoint Monte Carlo methods constitutes certain difficulties because of zero probability of reaching fixed value from continuous distribution. This paper proposes a possible approach to adjoint Monte Carlo simulation with fixed energy secondary radiation which does not contain any simplifying restriction. This approach uses the introduced before generalized particle concept developed for description of mixed-type radiation transport and allows adjoint Monte Carlo simulation of such processes. It treats particle type as additional discrete coordinate and always considers only one particle even for the interactions with many particles outgoing from the collision. The adjoint fixed energy secondary radiation simulation is performed as local energy estimator through the intermediate state with fixed energy. The proposed algorithm is tested on the example of coupled gamma/electron/positron transport with generation of annihilation radiation. Forward and adjoint simulation according to generalized particle concept show statistically similar results. (orig.)
Monte Carlo simulation techniques : The development of a general framework
Nilsson, Emma
2009-01-01
Algorithmica Research AB develops software application for the financial markets. One of their products is Quantlab that is a tool for quantitative analyses. An effective method to value several financial instruments is Monte Carlo simulation. Since it is a common method Algorithmica is interesting in investigating if it is possible to create a Monte Carlo framework. A requirement from Algorithmica is that the framework is general and this is the main problem to solve. It is difficult to gene...
International Nuclear Information System (INIS)
We have investigated the solvent effects on Δlog Ks (the difference of stability constant of binding) and the relative free energies of binding of La3+ to Nd3+ ions to 18-crown-6 by a Monte Carlo simulation of statistical perturbation theory (SPT) in diverse solvents. We compared relative binding Gibbs free energies and the differences in stability constant (Δlog Ks) of binding of La3+ and Nd3+ ions to 18-crown-6 in CH3OH in this study with the experimental. There is a good agreement between our study and the experimental. We noted that Borns function of the solvents,the electron pair donor properties of the solvent, the radii of host and guest and the differences in solvation dominate the differences in the stability constant (Δlog Ks) as well as the relative free energies of binding of La3+ to Nd3+ ions to 18-crown-6. The results of this study appear promising for providing the association properties of crown ethers with alkaline earth metals among polar solvents and the less polar or non-polar solvents
Virtual detector characterisation with Monte-Carlo simulations
Sukowski, F.; Yaneu Yaneu, J. F.; Salamon, M.; Ebert, S.; Uhlmann, N.
2009-08-01
In the field of X-ray imaging flat-panel detectors which convert X-rays into electrical signals, are widely used. For different applications, detectors differ in several specific parameters that can be used for characterizing the detector. At the Development Center X-ray Technology EZRT we studied the question how well these characteristics can be determined by only knowing the layer composition of a detector. In order to determine the required parameters, the Monte-Carlo (MC) simulation program ROSI [J. Giersch et al., Nucl. Instr. and Meth. A 509 (2003) 151] was used while taking into account all primary and secondary particle interactions as well as the focal spot size of the X-ray tube. For the study, the Hamamatsu C9311DK [Technical Datasheet Hamamatsu C9311DK flat panel sensor, Hamamatsu Photonics, ( www.hamamatsu.com)], a scintillator-based detector, and the Ajat DIC 100TL [Technical description of Ajat DIC 100TL, Ajat Oy Ltd., ( www.ajat.fi)], a direct converting semiconductor detector, were used. The layer compositions of the two detectors were implemented into the MC simulation program. The following characteristics were measured [N. Uhlmann et al., Nucl. Instr. and Meth. A 591 (2008) 46] and compared to simulation results: The basic spatial resolution (BSR), the modulation transfer function (MTF), the contrast sensitivity (CS) and the specific material thickness range (SMTR). To take scattering of optical photons into account DETECT2000 [C. Moisan et al., DETECT2000—A Program for Modeling Optical Properties of Scintillators, Department of Electrical and Computer Engineering, Laval University, Quebec City, 2000], another Monte-Carlo simulation was used.
Energy Technology Data Exchange (ETDEWEB)
Han, Eun Young [Department of Radiation Oncology, University of Arkansas Medical Sciences, Little Rock, Arkansas 72205 (United States); Lee, Choonsik [Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institute of Health, Bethesda, Maryland 20852 (United States); Mcguire, Lynn; Brown, Tracy L. Y. [Department of Radiology, Division of Nuclear Medicine, University of Arkansas Medical Sciences, Little Rock, Arkansas 72205 (United States); Bolch, Wesley E. [J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, Florida 32611 (United States)
2013-08-15
the newborn and 1-yr-old phantoms for a hyperthyroid-patient source are higher than values for a DTC-patient source.Conclusions: The authors performed realistic assessments of {sup 131}I organ S values and effective dose per time-integrated activity from adult patients treated for hyperthyroidism and DTC to family members. In addition, the authors’ studies consider Monte Carlo simulated “mother and baby/child” exposure scenarios for the first time. Based on these results, the authors reconfirm the strong conservatism underlying the point source method recommended by the US NRC. The authors recommend that various factors such as the type of the patient's disease, the age of family members, and the distance/posture between the patient and family members must be carefully considered to provide realistic dose estimates for patient-to-family exposures.
International Nuclear Information System (INIS)
newborn and 1-yr-old phantoms for a hyperthyroid-patient source are higher than values for a DTC-patient source.Conclusions: The authors performed realistic assessments of 131I organ S values and effective dose per time-integrated activity from adult patients treated for hyperthyroidism and DTC to family members. In addition, the authors’ studies consider Monte Carlo simulated “mother and baby/child” exposure scenarios for the first time. Based on these results, the authors reconfirm the strong conservatism underlying the point source method recommended by the US NRC. The authors recommend that various factors such as the type of the patient's disease, the age of family members, and the distance/posture between the patient and family members must be carefully considered to provide realistic dose estimates for patient-to-family exposures
Monte Carlo simulations of hydrogen storage in carbon nanotubes
International Nuclear Information System (INIS)
The storage capacities of porous materials made up of carbon nanotubes are estimated by Monte Carlo simulations for the specific case of hydrogen in the pressure domain from 0.1 to 20 MPa at temperatures of 293, 150 and 77 K. The use of these materials in devices for hydrogen storage is discussed on the basis of the simulation results. (author)
Research of Monte Carlo Simulation in Commercial Bank Risk Management
Institute of Scientific and Technical Information of China (English)
BeimingXiao
2004-01-01
Simulation method is an important-tool in financial risk management. It can simulate financial variable or economic wriable and deal with non-linear or non-nominal issue. This paper analyzes the usage of "Monte Carlo" approach in commercial bank risk management.
Monte Carlo simulation of virtual compton scattering at MAMI
International Nuclear Information System (INIS)
The Monte Carlo simulation developed specially for the VCS experiments taking place at MAMI in fully described. This simulation can generate events according to the Bethe-Heitler + Born cross section behaviour and takes into account resolution deteriorating effects. It is used to determine solid angles for the various experimental settings. (authors)
Energy Technology Data Exchange (ETDEWEB)
Masrour, R., E-mail: rachidmasrour@hotmail.com [Laboratory of Materials, Processes, Environment and Quality, Cady Ayyed University, National School of Applied Sciences, PB 63, 46000 Safi (Morocco); Laboratoire de Magnétisme et Physique des Hautes Energies LMPHE-URAC 12, Université Mohammed V, Faculté des Sciences, B.P. 1014, Rabat (Morocco); Jabar, A. [Laboratoire de Magnétisme et Physique des Hautes Energies LMPHE-URAC 12, Université Mohammed V, Faculté des Sciences, B.P. 1014, Rabat (Morocco); Benyoussef, A. [Laboratoire de Magnétisme et Physique des Hautes Energies LMPHE-URAC 12, Université Mohammed V, Faculté des Sciences, B.P. 1014, Rabat (Morocco); Institute of Nanomaterials and Nanotechnologies, MAScIR, Rabat (Morocco); Hassan II Academy of Science and Technology, Rabat (Morocco); Hamedoun, M. [Institute of Nanomaterials and Nanotechnologies, MAScIR, Rabat (Morocco)
2015-12-01
The magnetic properties of Fe- and FeO-modified Graphene-nano-ribbon: C{sub 32}H{sub 2}Fe{sub 2} and C{sub 32}H{sub 2}Fe{sub 2}O{sub 2} are studied using Monte Carlo simulations. The thermal magnetization and magnetic susceptibility with different values of exchange interactions, zero crystal field and zero magnetic field are established. The transition temperature is deduced for different values of exchange interactions. The internal energy, magnetization with a fixed value of exchange interactions, zero crystal field and external magnetic field are given. The magnetization versus the exchange interaction with different values of temperature, different values of crystal field and external magnetic field of are obtained. The magnetic hysteresis cycles have been deduced. - Highlights: • The magnetic properties of C{sub 32}H{sub 2}Fe{sub 2} and C{sub 32}H{sub 2}Fe{sub 2}O{sub 2} are studied by MCS. • The transition temperature of C{sub 32}H{sub 2}Fe{sub 2} and C{sub 32}H{sub 2}Fe{sub 2}O{sub 2} is deduced. • The magnetic hysteresis cycles are deduced for two graphene nano-ribbon.
Monte Carlo Simulation in Statistical Physics An Introduction
Binder, Kurt
2010-01-01
Monte Carlo Simulation in Statistical Physics deals with the computer simulation of many-body systems in condensed-matter physics and related fields of physics, chemistry and beyond, to traffic flows, stock market fluctuations, etc.). Using random numbers generated by a computer, probability distributions are calculated, allowing the estimation of the thermodynamic properties of various systems. This book describes the theoretical background to several variants of these Monte Carlo methods and gives a systematic presentation from which newcomers can learn to perform such simulations and to analyze their results. The fifth edition covers Classical as well as Quantum Monte Carlo methods. Furthermore a new chapter on the sampling of free-energy landscapes has been added. To help students in their work a special web server has been installed to host programs and discussion groups (http://wwwcp.tphys.uni-heidelberg.de). Prof. Binder was awarded the Berni J. Alder CECAM Award for Computational Physics 2001 as well ...
Energy Technology Data Exchange (ETDEWEB)
Crespo, Cristina; Aguiar, Pablo [Universitat de Barcelona - IDIBAPS, Unitat de Biofisica i Bioenginyeria, Departament de Ciencies Fisiologiques I, Facultat de Medicina, Barcelona (Spain); Gallego, Judith [Universitat Politecnica de Catalunya, Institut de Tecniques Energetiques, Barcelona (Spain); Institut de Bioenginyeria de Catalunya, Barcelona (Spain); Cot, Albert [Universitat de Barcelona - IDIBAPS, Unitat de Biofisica i Bioenginyeria, Departament de Ciencies Fisiologiques I, Facultat de Medicina, Barcelona (Spain); Universitat Politecnica de Catalunya, Seccio d' Enginyeria Nuclear, Departament de Fisica i Enginyeria Nuclear, Barcelona (Spain); Falcon, Carles; Ros, Domenec [Universitat de Barcelona - IDIBAPS, Unitat de Biofisica i Bioenginyeria, Departament de Ciencies Fisiologiques I, Facultat de Medicina, Barcelona (Spain); CIBER en Bioingenieria, Biomateriales y Nanomedicina (CIBER-BBN), Barcelona (Spain); Bullich, Santiago [Hospital del Mar, Center for Imaging in Psychiatry, CRC-MAR, Barcelona (Spain); Pareto, Deborah [CIBER en Bioingenieria, Biomateriales y Nanomedicina (CIBER-BBN), Barcelona (Spain); PRBB, Institut d' Alta Tecnologia, Barcelona (Spain); Sempau, Josep [Universitat Politecnica de Catalunya, Institut de Tecniques Energetiques, Barcelona (Spain); CIBER en Bioingenieria, Biomateriales y Nanomedicina (CIBER-BBN), Barcelona (Spain); Lomena, Francisco [IDIBAPS, Servei de Medicina Nuclear, Hospital Clinic, Barcelona (Spain); Calvino, Francisco [Universitat Politecnica de Catalunya, Institut de Tecniques Energetiques, Barcelona (Spain); Universitat Politecnica de Catalunya, Seccio d' Enginyeria Nuclear, Departament de Fisica i Enginyeria Nuclear, Barcelona (Spain); Pavia, Javier [CIBER en Bioingenieria, Biomateriales y Nanomedicina (CIBER-BBN), Barcelona (Spain); IDIBAPS, Servei de Medicina Nuclear, Hospital Clinic, Barcelona (Spain)
2008-07-15
{sup 123}I-labelled radioligands are commonly used for single-photon emission computed tomography (SPECT) imaging of the dopaminergic system to study the dopamine transporter binding. The aim of this work was to compare the quantitative capabilities of two different SPECT systems through Monte Carlo (MC) simulation. The SimSET MC code was employed to generate simulated projections of a numerical phantom for two gamma cameras equipped with a parallel and a fan-beam collimator, respectively. A fully 3D iterative reconstruction algorithm was used to compensate for attenuation, the spatially variant point spread function (PSF) and scatter. A post-reconstruction partial volume effect (PVE) compensation was also developed. For both systems, the correction for all degradations and PVE compensation resulted in recovery factors of the theoretical specific uptake ratio (SUR) close to 100%. For a SUR value of 4, the recovered SUR for the parallel imaging system was 33% for a reconstruction without corrections (OSEM), 45% for a reconstruction with attenuation correction (OSEM-A), 56% for a 3D reconstruction with attenuation and PSF corrections (OSEM-AP), 68% for OSEM-AP with scatter correction (OSEM-APS) and 97% for OSEM-APS plus PVE compensation (OSEM-APSV). For the fan-beam imaging system, the recovered SUR was 41% without corrections, 55% for OSEM-A, 65% for OSEM-AP, 75% for OSEM-APS and 102% for OSEM-APSV. Our findings indicate that the correction for degradations increases the quantification accuracy, with PVE compensation playing a major role in the SUR quantification. The proposed methodology allows us to reach similar SUR values for different SPECT systems, thereby allowing a reliable standardisation in multicentric studies. (orig.)
International Nuclear Information System (INIS)
The mass attenuation coefficients, μ/ρ, the linear attenuation coefficients, μ and the mean free path, MFP of normal and heavy concretes; ordinary, hematite-serpentine, ilmenite-limonite, basalt-magnetite, ilmenite, steel-scrap and steel-magnetite have been investigated using Geant4 Monte Carlo method at photon energies 1.5, 2, 3, 4, 5 and 6 MeV. The mass attenuation coefficients, the linear attenuation coefficient and the mean free path for the concretes were found dependent upon chemical compositions, density and the photon energy. The linear attenuation coefficient values for the selected concretes increase with the density and decrease with the energy. The mean free path thickness for the all the concretes decrease with increase in iron content and increase with increase the photon energy. The Geant4 Monte Carlo simulation method results have been compared with experimental and theoretical XCOM data, and showed a very good agreement. Our investigation validates the utilization of the Geant4 Monte Carlo simulation method for high energy photon interactions. (author)
Brunetti, Antonio; Fabian, Julio; La Torre, Carlos Wester; Schiavon, Nick
2016-06-01
An innovative methodological approach based on XRF measurements using a polychromatic X-ray beam combined with simulation tests based on an ultra-fast custom-made Monte Carlo code has been used to characterize the bulk chemical composition of restored (i.e., cleaned) and unrestored multilayered Peruvian metallic artifacts belonging to the twelfth- and thirteenth-century AD funerary complex of Chornancap-Chotuna in northern Peru. The multilayered structure was represented by a metal substrate covered by surface corrosion patinas and/or a layer from past protective treatments. The aim of the study was to assess whether this new approach could be used to overcome some of the limitations highlighted in previous research performed using monochromatic X-ray beam on patina-free and protective treatment-free metal artifacts in obtaining reliable data both on the composition on the bulk metals and on surface layers thickness. Results from the analytical campaign have led to a reformulation of previous hypotheses about the structure and composition of the metal used to create the Peruvian artifacts under investigation.
Li, Junli; Li, Chunyan; Qiu, Rui; Yan, Congchong; Xie, Wenzhang; Wu, Zhen; Zeng, Zhi; Tung, Chuanjong
2015-09-01
The method of Monte Carlo simulation is a powerful tool to investigate the details of radiation biological damage at the molecular level. In this paper, a Monte Carlo code called NASIC (Nanodosimetry Monte Carlo Simulation Code) was developed. It includes physical module, pre-chemical module, chemical module, geometric module and DNA damage module. The physical module can simulate physical tracks of low-energy electrons in the liquid water event-by-event. More than one set of inelastic cross sections were calculated by applying the dielectric function method of Emfietzoglou's optical-data treatments, with different optical data sets and dispersion models. In the pre-chemical module, the ionised and excited water molecules undergo dissociation processes. In the chemical module, the produced radiolytic chemical species diffuse and react. In the geometric module, an atomic model of 46 chromatin fibres in a spherical nucleus of human lymphocyte was established. In the DNA damage module, the direct damages induced by the energy depositions of the electrons and the indirect damages induced by the radiolytic chemical species were calculated. The parameters should be adjusted to make the simulation results be agreed with the experimental results. In this paper, the influence study of the inelastic cross sections and vibrational excitation reaction on the parameters and the DNA strand break yields were studied. Further work of NASIC is underway. PMID:25883312
International Nuclear Information System (INIS)
The method of Monte Carlo simulation is a powerful tool to investigate the details of radiation biological damage at the molecular level. In this paper, a Monte Carlo code called NASIC (Nanodosimetry Monte Carlo Simulation Code) was developed. It includes physical module, pre-chemical module, chemical module, geometric module and DNA damage module. The physical module can simulate physical tracks of low-energy electrons in the liquid water event-by-event. More than one set of inelastic cross sections were calculated by applying the dielectric function method of Emfietzoglou's optical-data treatments, with different optical data sets and dispersion models. In the pre-chemical module, the ionised and excited water molecules undergo dissociation processes. In the chemical module, the produced radiolytic chemical species diffuse and react. In the geometric module, an atomic model of 46 chromatin fibres in a spherical nucleus of human lymphocyte was established. In the DNA damage module, the direct damages induced by the energy depositions of the electrons and the indirect damages induced by the radiolytic chemical species were calculated. The parameters should be adjusted to make the simulation results be agreed with the experimental results. In this paper, the influence study of the inelastic cross sections and vibrational excitation reaction on the parameters and the DNA strand break yields were studied. Further work of NASIC is underway (authors)
Suppression of the initial transient in Monte Carlo criticality simulations
International Nuclear Information System (INIS)
Criticality Monte Carlo calculations aim at estimating the effective multiplication factor (k-effective) for a fissile system through iterations simulating neutrons propagation (making a Markov chain). Arbitrary initialization of the neutron population can deeply bias the k-effective estimation, defined as the mean of the k-effective computed at each iteration. A simplified model of this cycle k-effective sequence is built, based on characteristics of industrial criticality Monte Carlo calculations. Statistical tests, inspired by Brownian bridge properties, are designed to discriminate stationarity of the cycle k-effective sequence. The initial detected transient is, then, suppressed in order to improve the estimation of the system k-effective. The different versions of this methodology are detailed and compared, firstly on a plan of numerical tests fitted on criticality Monte Carlo calculations, and, secondly on real criticality calculations. Eventually, the best methodologies observed in these tests are selected and allow to improve industrial Monte Carlo criticality calculations. (author)
Simulate the progress of PGNAA with Monte Carlo
International Nuclear Information System (INIS)
A kind of model to simulate bulk coal PGNAA process was set up, and some problems in PGNAA experiments was solved using the MOCA -Monte Carlo software. Analysis of the relationship between the thermal neutron field and the source distance, and the relationship curve with MOCA was obtained, and can be used to design measurement object bucket; simulated bulk coal PGNAA process, and analyzed activated γ spectrum. Through simulating PGNAA process, provide a theoretical basis for a bulk coal PGNAA experiments. (authors)
Two Approaches to Accelerated Monte Carlo Simulation of Coulomb Collisions
Ricketson, Lee
2014-01-01
In plasma physics, the direct simulation of inter-particle Coulomb collisions is often necessary to capture the relevant physics, but presents a computational bottleneck because of the complexity of the process. In this thesis, we derive, test and discuss two methods for accelerating the simulation of collisions in plasmas in certain scenarios. The first is a hybrid fluid-Monte Carlo scheme that reduces the number of collisions that must be simulated. Coupling between the fluid and particl...
Monte-Carlo Simulation for an Aerogel Cherenkov Counter
al, Ryuji Suda et
1997-01-01
We have developed a Monte-Carlo simulation code for an aerogel \\v Cerenkov Counter which is operated under a strong magnetic field such as 1.5T. This code consists of two parts: photon transportation inside aerogel tiles, and one-dimensional amplification in a fine-mesh photomultiplier tube. It simulates the output photoelectron yields as accurately as 5% with only a single free parameter. This code is applied to simulations for a B-Factory particle-identification system.
MONTE-CARLO SIMULATION OF ROAD TRANSPORT EMISSION
Directory of Open Access Journals (Sweden)
Adam Torok
2015-09-01
Full Text Available There are microscopic, mezoscopic and macroscopic models in road traffic analysis and forecasting. From microscopic models one can calculate the macroscopic data by aggregation. The following paper describes the disaggregation method of macroscopic state, which could lead to microscopic properties of traffic. In order to ensure the transform between macroscopic and microscopic states Monte-Carlo simulation was used. MS Excel macro environment was built to run Monte-Carlo simulation. With this method the macroscopic data can be disaggregated to macroscopic data and as a byproduct mezoscopic, regional data can be gained. These mezoscopic data can be used further on regional environmental or transport policy assessment.
Monte Carlo simulation of PET images for injection dose optimization
Czech Academy of Sciences Publication Activity Database
Boldyš, Jiří; Dvořák, Jiří; Bělohlávek, O.; Skopalová, M.
London : Taylor and Francis, 2011 - (Manuel, J.; Tavares, R.; Jorge, N.), s. 1-6 ISBN 978-0-415-68395-1. [VipIMAGE 2011 - third ECCOMAS thematic conference on computational vision and medical image processing. Olhao, Algarve (PT), 12.10.2011-14.10.2011] R&D Projects: GA MŠk(CZ) 1M0572 Institutional research plan: CEZ:AV0Z10750506 Keywords : positron emission tomography * Monte Carlo simulation * biological system modeling * image quality Subject RIV: BD - Theory of Information http://library.utia.cas.cz/separaty/2012/ZOI/boldys-monte carlo simulation of pet images for injection dose optimization.pdf
International Nuclear Information System (INIS)
Xenon gas proportional-scintillation counters (GPSC) have many applications in the detection of soft x rays where their energy resolution, R, is comparable to solid-state detectors when large window areas are required. However, R is known to deteriorate for energies Exr below 2 - 3 keV due to electron loss to the entrance window. Since the addition of a lighter noble gas increases the absorption depth, we have investigated the use of Xe - Ne gas mixtures at atmospheric pressure as detector fillings. The results of a Monte Carlo simulation study of the Fano factor, F, the w value, and the intrinsic energy resolution, R=2.36(Fw/Exr)1/2, are presented for Xe - Ne mixtures and pure Xe and Ne. The results show that the addition of Ne to Xe reduces the intrinsic energy resolution R but this never compensates for the reduction in scintillation yield in GPSC applications, implying that the instrumental energy resolution R will only improve with the addition of Ne when electron loss to the window in pure Xe is significant. The simulation reproduces the photoionization process of the Xe and Ne atoms, the vacancy cascade decay of the residual ions, and the elastic and inelastic scattering of electrons by the gas atoms. The contribution of energy and charge transfer mechanisms such as Penning, associative, and transfer ionization is discussed in detail. It is shown that Penning and associative ionization are the crucial indirect ionization processes which determine the behavior of F and w at low concentrations of Xe. The importance of the nonmetastable Ne states is also assessed. [copyright] 2001 American Institute of Physics
Validation of the Monte Carlo simulator GATE for indium-111 imaging.
Assié, K; Gardin, I; Véra, P; Buvat, I
2005-07-01
Monte Carlo simulations are useful for optimizing and assessing single photon emission computed tomography (SPECT) protocols, especially when aiming at measuring quantitative parameters from SPECT images. Before Monte Carlo simulated data can be trusted, the simulation model must be validated. The purpose of this work was to validate the use of GATE, a new Monte Carlo simulation platform based on GEANT4, for modelling indium-111 SPECT data, the quantification of which is of foremost importance for dosimetric studies. To that end, acquisitions of (111)In line sources in air and in water and of a cylindrical phantom were performed, together with the corresponding simulations. The simulation model included Monte Carlo modelling of the camera collimator and of a back-compartment accounting for photomultiplier tubes and associated electronics. Energy spectra, spatial resolution, sensitivity values, images and count profiles obtained for experimental and simulated data were compared. An excellent agreement was found between experimental and simulated energy spectra. For source-to-collimator distances varying from 0 to 20 cm, simulated and experimental spatial resolution differed by less than 2% in air, while the simulated sensitivity values were within 4% of the experimental values. The simulation of the cylindrical phantom closely reproduced the experimental data. These results suggest that GATE enables accurate simulation of (111)In SPECT acquisitions. PMID:15972984
Directory of Open Access Journals (Sweden)
Ambrish Singh
2015-08-01
Full Text Available The inhibition of the corrosion of N80 steel in 3.5 wt. % NaCl solution saturated with CO2 by four porphyrins, namely 5,10,15,20-tetrakis(4-hydroxyphenyl-21H,23H-porphyrin (HPTB, 5,10,15,20-tetra(4-pyridyl-21H,23H-porphyrin (T4PP, 4,4′,4″,4‴-(porphyrin-5,10,15,20-tetrayltetrakis(benzoic acid (THP and 5,10,15,20-tetraphenyl-21H,23H-porphyrin (TPP was studied using electrochemical impedance spectroscopy (EIS, potentiodynamic polarization, scanning electrochemical microscopy (SECM and scanning electron microscopy (SEM techniques. The results showed that the inhibition efficiency, η% increases with increasing concentration of the inhibitors. The EIS results revealed that the N80 steel surface with adsorbed porphyrins exhibited non-ideal capacitive behaviour with reduced charge transfer activity. Potentiodynamic polarization measurements indicated that the studied porphyrins acted as mixed type inhibitors. The SECM results confirmed the adsorption of the porphyrins on N80 steel thereby forming a relatively insulated surface. The SEM also confirmed the formation of protective films of the porphyrins on N80 steel surface thereby protecting the surface from direct acid attack. Quantum chemical calculations, quantitative structure activity relationship (QSAR were also carried out on the studied porphyrins and the results showed that the corrosion inhibition performances of the porphyrins could be related to their EHOMO, ELUMO, ω, and μ values. Monte Carlo simulation studies showed that THP has the highest adsorption energy, while T4PP has the least adsorption energy in agreement with the values of σ from quantum chemical calculations.
Singh, Ambrish; Lin, Yuanhua; Quraishi, Mumtaz A; Olasunkanmi, Lukman O; Fayemi, Omolola E; Sasikumar, Yesudass; Ramaganthan, Baskar; Bahadur, Indra; Obot, Ime B; Adekunle, Abolanle S; Kabanda, Mwadham M; Ebenso, Eno E
2015-01-01
The inhibition of the corrosion of N80 steel in 3.5 wt. % NaCl solution saturated with CO2 by four porphyrins, namely 5,10,15,20-tetrakis(4-hydroxyphenyl)-21H,23H-porphyrin (HPTB), 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphyrin (T4PP), 4,4',4″,4‴-(porphyrin-5,10,15,20-tetrayl)tetrakis(benzoic acid) (THP) and 5,10,15,20-tetraphenyl-21H,23H-porphyrin (TPP) was studied using electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, scanning electrochemical microscopy (SECM) and scanning electron microscopy (SEM) techniques. The results showed that the inhibition efficiency, η% increases with increasing concentration of the inhibitors. The EIS results revealed that the N80 steel surface with adsorbed porphyrins exhibited non-ideal capacitive behaviour with reduced charge transfer activity. Potentiodynamic polarization measurements indicated that the studied porphyrins acted as mixed type inhibitors. The SECM results confirmed the adsorption of the porphyrins on N80 steel thereby forming a relatively insulated surface. The SEM also confirmed the formation of protective films of the porphyrins on N80 steel surface thereby protecting the surface from direct acid attack. Quantum chemical calculations, quantitative structure activity relationship (QSAR) were also carried out on the studied porphyrins and the results showed that the corrosion inhibition performances of the porphyrins could be related to their EHOMO, ELUMO, ω, and μ values. Monte Carlo simulation studies showed that THP has the highest adsorption energy, while T4PP has the least adsorption energy in agreement with the values of σ from quantum chemical calculations. PMID:26295223
Accuracy of Monte Carlo simulations compared to in-vivo MDCT dosimetry
Energy Technology Data Exchange (ETDEWEB)
Bostani, Maryam, E-mail: mbostani@mednet.ucla.edu; McMillan, Kyle; Cagnon, Chris H.; McNitt-Gray, Michael F. [Departments of Biomedical Physics and Radiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California 90024 (United States); Mueller, Jonathon W. [United States Air Force, Keesler Air Force Base, Biloxi, Mississippi 39534 (United States); Cody, Dianna D. [University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030 (United States); DeMarco, John J. [Departments of Biomedical Physics and Radiation Oncology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California 90024 (United States)
2015-02-15
Purpose: The purpose of this study was to assess the accuracy of a Monte Carlo simulation-based method for estimating radiation dose from multidetector computed tomography (MDCT) by comparing simulated doses in ten patients to in-vivo dose measurements. Methods: MD Anderson Cancer Center Institutional Review Board approved the acquisition of in-vivo rectal dose measurements in a pilot study of ten patients undergoing virtual colonoscopy. The dose measurements were obtained by affixing TLD capsules to the inner lumen of rectal catheters. Voxelized patient models were generated from the MDCT images of the ten patients, and the dose to the TLD for all exposures was estimated using Monte Carlo based simulations. The Monte Carlo simulation results were compared to the in-vivo dose measurements to determine accuracy. Results: The calculated mean percent difference between TLD measurements and Monte Carlo simulations was −4.9% with standard deviation of 8.7% and a range of −22.7% to 5.7%. Conclusions: The results of this study demonstrate very good agreement between simulated and measured doses in-vivo. Taken together with previous validation efforts, this work demonstrates that the Monte Carlo simulation methods can provide accurate estimates of radiation dose in patients undergoing CT examinations.
Radiotherapy Monte Carlo simulation using cloud computing technology
International Nuclear Information System (INIS)
Cloud computing allows for vast computational resources to be leveraged quickly and easily in bursts as and when required. Here we describe a technique that allows for Monte Carlo radiotherapy dose calculations to be performed using GEANT4 and executed in the cloud, with relative simulation cost and completion time evaluated as a function of machine count. As expected, simulation completion time decreases as 1/n for n parallel machines, and relative simulation cost is found to be optimal where n is a factor of the total simulation time in hours. Using the technique, we demonstrate the potential usefulness of cloud computing as a solution for rapid Monte Carlo simulation for radiotherapy dose calculation without the need for dedicated local computer hardware as a proof of principal.
Hajizadeh-Safar, M; Ghorbani, M; Khoshkharam, S; Ashrafi, Z
2014-07-01
Gamma camera is an important apparatus in nuclear medicine imaging. Its detection part is consists of a scintillation detector with a heavy collimator. Substitution of semiconductor detectors instead of scintillator in these cameras has been effectively studied. In this study, it is aimed to introduce a new design of P-N semiconductor detector array for nuclear medicine imaging. A P-N semiconductor detector composed of N-SnO2 :F, and P-NiO:Li, has been introduced through simulating with MCNPX monte carlo codes. Its sensitivity with different factors such as thickness, dimension, and direction of emission photons were investigated. It is then used to configure a new design of an array in one-dimension and study its spatial resolution for nuclear medicine imaging. One-dimension array with 39 detectors was simulated to measure a predefined linear distribution of Tc(99_m) activity and its spatial resolution. The activity distribution was calculated from detector responses through mathematical linear optimization using LINPROG code on MATLAB software. Three different configurations of one-dimension detector array, horizontal, vertical one sided, and vertical double-sided were simulated. In all of these configurations, the energy windows of the photopeak were ± 1%. The results show that the detector response increases with an increase of dimension and thickness of the detector with the highest sensitivity for emission photons 15-30° above the surface. Horizontal configuration array of detectors is not suitable for imaging of line activity sources. The measured activity distribution with vertical configuration array, double-side detectors, has no similarity with emission sources and hence is not suitable for imaging purposes. Measured activity distribution using vertical configuration array, single side detectors has a good similarity with sources. Therefore, it could be introduced as a suitable configuration for nuclear medicine imaging. It has been shown that using
Guideline of Monte Carlo calculation. Neutron/gamma ray transport simulation by Monte Carlo method
2002-01-01
This report condenses basic theories and advanced applications of neutron/gamma ray transport calculations in many fields of nuclear energy research. Chapters 1 through 5 treat historical progress of Monte Carlo methods, general issues of variance reduction technique, cross section libraries used in continuous energy Monte Carlo codes. In chapter 6, the following issues are discussed: fusion benchmark experiments, design of ITER, experiment analyses of fast critical assembly, core analyses of JMTR, simulation of pulsed neutron experiment, core analyses of HTTR, duct streaming calculations, bulk shielding calculations, neutron/gamma ray transport calculations of the Hiroshima atomic bomb. Chapters 8 and 9 treat function enhancements of MCNP and MVP codes, and a parallel processing of Monte Carlo calculation, respectively. An important references are attached at the end of this report.
Monte Carlo simulation with the Gate software using grid computing
International Nuclear Information System (INIS)
Monte Carlo simulations are widely used in emission tomography, for protocol optimization, design of processing or data analysis methods, tomographic reconstruction, or tomograph design optimization. Monte Carlo simulations needing many replicates to obtain good statistical results can be easily executed in parallel using the 'Multiple Replications In Parallel' approach. However, several precautions have to be taken in the generation of the parallel streams of pseudo-random numbers. In this paper, we present the distribution of Monte Carlo simulations performed with the GATE software using local clusters and grid computing. We obtained very convincing results with this large medical application, thanks to the EGEE Grid (Enabling Grid for E-science), achieving in one week computations that could have taken more than 3 years of processing on a single computer. This work has been achieved thanks to a generic object-oriented toolbox called DistMe which we designed to automate this kind of parallelization for Monte Carlo simulations. This toolbox, written in Java is freely available on SourceForge and helped to ensure a rigorous distribution of pseudo-random number streams. It is based on the use of a documented XML format for random numbers generators statuses. (authors)
Monte Carlo Simulation Optimizing Design of Grid Ionization Chamber
Institute of Scientific and Technical Information of China (English)
ZHENG; Yu-lai; WANG; Qiang; YANG; Lu
2013-01-01
The grid ionization chamber detector is often used for measuring charged particles.Based on Monte Carlo simulation method,the energy loss distribution and electron ion pairs of alpha particle with different energy have been calculated to determine suitable filling gas in the ionization chamber filled with
Simulating Strongly Correlated Electron Systems with Hybrid Monte Carlo
Institute of Scientific and Technical Information of China (English)
LIU Chuan
2000-01-01
Using the path integral representation, the Hubbard and the periodic Anderson model on D-dimensional cubic lattice are transformed into field theories of fermions in D + 1 dimensions. These theories at half-filling possess a positive definite real symmetry fermion matrix and can be simulated using the hybrid Monte Carlo method.
Monte Carlo Simulations of Impact Ionization Feedback in MOSFET Structures
Bude, Jeff D.
1998-01-01
Although impact ionization feedback is recognized as an important current multiplication mechanism, its importance as a carrier heating mechanism has been largely overlooked. This work emphasizes the inclusion of impact ionization feedback in Monte Carlo device simulations, and its implications for carrier heating in sub-micron CMOS and EEPROM technologies.
Radio emission from cosmic ray air showers : Monte Carlo simulations
Huege, T.; Falcke, H.D.E.
2005-01-01
We present time-domain Monte Carlo simulations of radio emission from cosmic ray air showers in the scheme of coherent geosynchrotron radiation. Our model takes into account the important air shower characteristics such as the lateral and longitudinal particle distributions, the particle track lengt
Microbial contamination in poultry chillers estimated by Monte Carlo simulations
The risk of microbial contamination during poultry processing may be reduced by the operating characteristics of the chiller. The performance of air chillers and immersion chillers were compared in terms of pre-chill and post-chill contamination using Monte Carlo simulations. Three parameters were u...
Monte Carlo simulations of plutonium gamma-ray spectra
International Nuclear Information System (INIS)
Monte Carlo calculations were investigated as a means of simulating the gamma-ray spectra of Pu. These simulated spectra will be used to develop and evaluate gamma-ray analysis techniques for various nondestructive measurements. Simulated spectra of calculational standards can be used for code intercomparisons, to understand systematic biases and to estimate minimum detection levels of existing and proposed nondestructive analysis instruments. The capability to simulate gamma-ray spectra from HPGe detectors could significantly reduce the costs of preparing large numbers of real reference materials. MCNP was used for the Monte Carlo transport of the photons. Results from the MCNP calculations were folded in with a detector response function for a realistic spectrum. Plutonium spectrum peaks were produced with Lorentzian shapes, for the x-rays, and Gaussian distributions. The MGA code determined the Pu isotopes and specific power of this calculated spectrum and compared it to a similar analysis on a measured spectrum
Monte Carlo simulation of ICRF discharge initiation in ITER
Tripský, M.; Wauters, T.; Lyssoivan, A.; Křivská, A.; Louche, F.; Van Schoor, M.; Noterdaeme, J.-M.
2015-12-01
Discharges produced and sustained by ion cyclotron range of frequency (ICRF) waves in absence of plasma current will be used on ITER for (ion cyclotron-) wall conditioning (ICWC). The here presented simulations aim at ensuring that the ITER ICRH&CD system can be safely employed for ICWC and at finding optimal parameters to initiate the plasma. The 1D Monte Carlo code RFdinity1D3V was developed to simulate ICRF discharge initiation. The code traces the electron motion along one toroidal magnetic field line, accelerated by the RF field in front of the ICRF antenna. Electron collisions in the calculations are handled by a Monte Carlo procedure taking into account their energies and the related electron collision cross sections for collisions with H2, H2+ and H+. The code also includes Coulomb collisions between electrons and ions (e - e, e - H2+ , e - H+). We study the electron multiplication rate as a function of the RF discharge parameters (i) antenna input power (0.1-5MW), and (ii) the neutral pressure (H2) for two antenna phasing (monopole [0000]-phasing and small dipole [0π0π]-phasing). Furthermore, we investigate the electron multiplication rate dependency on the distance from the antenna straps. This radial dependency results from the decreasing electric amplitude and field smoothening with increasing distance from the antenna straps. The numerical plasma breakdown definition used in the code corresponds to the moment when a critical electron density nec for the low hybrid resonance (ω = ωLHR) is reached. This numerical definition was previously found in qualitative agreement with experimental breakdown times obtained from the literature and from experiments on the ASDEX Upgrade and TEXTOR.
Energy Technology Data Exchange (ETDEWEB)
Thiam, Ch. O
2003-06-01
In radiotherapy, it is essential to have a precise knowledge of the dose delivered in the target volume and the neighbouring critical organs. To be usable clinically, the models of calculation must take into account the exact characteristics of the beams used and the densities of fabrics. Today we can use sophisticated irradiation techniques and get a more precise assessment of the dose and with a better knowledge of its distribution. Thus in this report, will be detailed a simulation of the head of irradiation of accelerator SL-ELEKTA-20 in electrons mode and a dosimetric study of a water phantom. This study is carried out with the code of simulation Monte Carlo GATE adapted for applications of medical physics; the results are compared with the data obtained by the anticancer center 'Jean Perrin' on a similar accelerator. (author)
Assessing Excel VBA Suitability for Monte Carlo Simulation
Botchkarev, Alexei
2015-01-01
Monte Carlo (MC) simulation includes a wide range of stochastic techniques used to quantitatively evaluate the behavior of complex systems or processes. Microsoft Excel spreadsheets with Visual Basic for Applications (VBA) software is, arguably, the most commonly employed general purpose tool for MC simulation. Despite the popularity of the Excel in many industries and educational institutions, it has been repeatedly criticized for its flaws and often described as questionable, if not complet...
Monte Carlo simulation of photon migration path in turbid media
Institute of Scientific and Technical Information of China (English)
无
2008-01-01
A new method of Monte Carlo simulation is developed to simulate the photon migration path in a scattering medium after an ultrashort-pulse laser beam comes into the medium.The most probable trajectory of photons at an instant can be obtained with this method.How the photon migration paths are affected by the optical parameters of the scattering medium is analyzed.It is also concluded that the absorption coefficient has no effect on the most probable trajectory of photons.
Monte Carlo simulation of virtual Compton scattering below pion threshold
International Nuclear Information System (INIS)
This paper describes the Monte Carlo simulation developed specifically for the Virtual Compton Scattering (VCS) experiments below pion threshold that have been performed at MAMI and JLab. This simulation generates events according to the (Bethe-Heitler + Born) cross-section behaviour and takes into account all relevant resolution-deteriorating effects. It determines the 'effective' solid angle for the various experimental settings which are used for the precise determination of the photon electroproduction absolute cross-section
Multipurpose Monte Carlo simulator for photon transport in turbid media
Guerra, Pedro; Aguirre, Juan; Ortuño, Juan E.; María J Ledesma-Carbayo; Vaquero, Juan José; Desco, Manuel; Santos, Andrés
2009-01-01
Monte Carlo methods provide a flexible and rigorous solution to the problem of light transport in turbid media, which enable approaching complex geometries for a closed analytical solution is not feasible. The simulator implements local rules of propagation in the form of probability density functions that depend on the local optical properties of the tissue. This work presents a flexible simulator that can be applied in multiple applications related to optical tomography. In particular...
Saraiva, A; Oliveira, C; Reis, M; Portugal, L; Paiva, I; Cruz, C
2016-07-01
A model of an n-type ORTEC GMX45 HPGe detector was created using the MCNPX and the MCNP-CP codes. In order to validate the model, experimental efficiency was compared with the Monte Carlo simulations results. The reference source is a NIST traceable multi-gamma volume source in a water-equivalent epoxy resin matrix (1.15gcm(-3) density) containing several radionuclides: (210)Pb, (241)Am, (137)Cs and (60)Co in a cylinder shape container. Two distances of source bottom to end cap front surface of the detector have been considered. The efficiency for the nearest distance is higher than for longer distance. The relative difference between the measured and the simulated full-energy peak efficiency is less than 4.0% except for the 46.5keV energy peak of (210)Pb for the longer distance (6.5%) allowing to consider the model validated. In the absence of adequate standard calibration sources, efficiency and efficiency transfer factors for geometry deviations and matrix effects can be accurately computed by using Monte Carlo methods even if true coincidence could occur as is the case when the (60)Co radioisotope is present in the source. PMID:27131096
Grain-boundary melting: A Monte Carlo study
DEFF Research Database (Denmark)
Besold, Gerhard; Mouritsen, Ole G.
1994-01-01
Grain-boundary melting in a lattice-gas model of a bicrystal is studied by Monte Carlo simulation using the grand canonical ensemble. Well below the bulk melting temperature T(m), a disordered liquidlike layer gradually emerges at the grain boundary. Complete interfacial wetting can be observed...
Comparing statistical data to Monte Carlo simulation - parameter fitting and unfolding
International Nuclear Information System (INIS)
The author presents an introduction to the statistical analysis of experimental data by means of Monte Carlo simulations. After a description of the χ2 test of a hypothesis the least-square and maximum-likelihood fits to Monte Carlo distributions are described. Then unfolding is described. Finally confidence intervals are studied, and the computation of upper and lower limits is discussed from a Bayesian point of view. (HSI)
Genetic algorithms and Monte Carlo simulation for optimal plant design
International Nuclear Information System (INIS)
We present an approach to the optimal plant design (choice of system layout and components) under conflicting safety and economic constraints, based upon the coupling of a Monte Carlo evaluation of plant operation with a Genetic Algorithms-maximization procedure. The Monte Carlo simulation model provides a flexible tool, which enables one to describe relevant aspects of plant design and operation, such as standby modes and deteriorating repairs, not easily captured by analytical models. The effects of deteriorating repairs are described by means of a modified Brown-Proschan model of imperfect repair which accounts for the possibility of an increased proneness to failure of a component after a repair. The transitions of a component from standby to active, and vice versa, are simulated using a multiplicative correlation model. The genetic algorithms procedure is demanded to optimize a profit function which accounts for the plant safety and economic performance and which is evaluated, for each possible design, by the above Monte Carlo simulation. In order to avoid an overwhelming use of computer time, for each potential solution proposed by the genetic algorithm, we perform only few hundreds Monte Carlo histories and, then, exploit the fact that during the genetic algorithm population evolution, the fit chromosomes appear repeatedly many times, so that the results for the solutions of interest (i.e. the best ones) attain statistical significance
Martini - Monte Carlo Simulation of Jet Evolution
International Nuclear Information System (INIS)
We present the Modular Algorithm for Relativistic Treatment of heavy IoN Interactions (MARTINI), an event generator for the hard and penetrating probes in high energy nucleus-nucleus collisions. The simulation consists of a time evolution model for the soft background, such as hydrodynamics, PYTHIA 8.1 to generate and hadronize the hard partons after the medium evolution, which is based on the McGill-AMY formalism and includes both radiative and elastic processes. MARTINI allows for the generation of full event configurations in the high pT region. We present results for the neutral pion and photon nuclear modification factor in Au + Au collisions at RHIC. (authors)
Baräo, Fernando; Nakagawa, Masayuki; Távora, Luis; Vaz, Pedro
2001-01-01
This book focusses on the state of the art of Monte Carlo methods in radiation physics and particle transport simulation and applications, the latter involving in particular, the use and development of electron--gamma, neutron--gamma and hadronic codes. Besides the basic theory and the methods employed, special attention is paid to algorithm development for modeling, and the analysis of experiments and measurements in a variety of fields ranging from particle to medical physics.
Parallelization of a Monte Carlo particle transport simulation code
Hadjidoukas, P.; Bousis, C.; Emfietzoglou, D.
2010-05-01
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.
Meaningful timescales from Monte Carlo simulations of molecular systems
Costa, Liborio I
2016-01-01
A new Markov Chain Monte Carlo method for simulating the dynamics of molecular systems with atomistic detail is introduced. In contrast to traditional Kinetic Monte Carlo approaches, where the state of the system is associated with minima in the energy landscape, in the proposed method, the state of the system is associated with the set of paths traveled by the atoms and the transition probabilities for an atom to be displaced are proportional to the corresponding velocities. In this way, the number of possible state-to-state transitions is reduced to a discrete set, and a direct link between the Monte Carlo time step and true physical time is naturally established. The resulting rejection-free algorithm is validated against event-driven molecular dynamics: the equilibrium and non-equilibrium dynamics of hard disks converge to the exact results with decreasing displacement size.
Research on ionization and secondary reaction coupled Monte Carlo simulation and its application
International Nuclear Information System (INIS)
Coupled simulation of deuteron or triton ionization and secondary fusion reaction was studied with a Monte Carlo tool named RSMC (Reaction Sequence Monte Carlo). The detail history and condensed history methods were employed for ionization simulation. Fusion cross sections of deuteron and triton were adopted from ENDF or TENDL. The 'forced particle production' variance reduction technique was also employed to improve the simulation efficiency. As a validation, three types of examples were introduced, including neutron depth profiling, accelerator based mono-energy neutron source, and thermal-to-fusion neutron converter. (authors)
Lee, Seung-Wan; Choi, Yu-Na; Cho, Hyo-Min; Lee, Young-Jin; Ryu, Hyun-Ju; Kim, Hee-Joung
2012-08-01
The energy-resolved photon counting detector provides the spectral information that can be used to generate images. The novel imaging methods, including the K-edge imaging, projection-based energy weighting imaging and image-based energy weighting imaging, are based on the energy-resolved photon counting detector and can be realized by using various energy windows or energy bins. The location and width of the energy windows or energy bins are important because these techniques generate an image using the spectral information defined by the energy windows or energy bins. In this study, the reconstructed images acquired with K-edge imaging, projection-based energy weighting imaging and image-based energy weighting imaging were simulated using the Monte Carlo simulation. The effect of energy windows or energy bins was investigated with respect to the contrast, coefficient-of-variation (COV) and contrast-to-noise ratio (CNR). The three images were compared with respect to the CNR. We modeled the x-ray computed tomography system based on the CdTe energy-resolved photon counting detector and polymethylmethacrylate phantom, which have iodine, gadolinium and blood. To acquire K-edge images, the lower energy thresholds were fixed at K-edge absorption energy of iodine and gadolinium and the energy window widths were increased from 1 to 25 bins. The energy weighting factors optimized for iodine, gadolinium and blood were calculated from 5, 10, 15, 19 and 33 energy bins. We assigned the calculated energy weighting factors to the images acquired at each energy bin. In K-edge images, the contrast and COV decreased, when the energy window width was increased. The CNR increased as a function of the energy window width and decreased above the specific energy window width. When the number of energy bins was increased from 5 to 15, the contrast increased in the projection-based energy weighting images. There is a little difference in the contrast, when the number of energy bin is
Lee, Youngjin; Lee, Amy Candy; Kim, Hee-Joung
2016-09-01
Recently, significant effort has been spent on the development of photons counting detector (PCD) based on a CdTe for applications in X-ray imaging system. The motivation of developing PCDs is higher image quality. Especially, the K-edge subtraction (KES) imaging technique using a PCD is able to improve image quality and useful for increasing the contrast resolution of a target material by utilizing contrast agent. Based on above-mentioned technique, we presented an idea for an improved K-edge log-subtraction (KELS) imaging technique. The KELS imaging technique based on the PCDs can be realized by using different subtraction energy width of the energy window. In this study, the effects of the KELS imaging technique and subtraction energy width of the energy window was investigated with respect to the contrast, standard deviation, and CNR with a Monte Carlo simulation. We simulated the PCD X-ray imaging system based on a CdTe and polymethylmethacrylate (PMMA) phantom which consists of the various iodine contrast agents. To acquired KELS images, images of the phantom using above and below the iodine contrast agent K-edge absorption energy (33.2 keV) have been acquired at different energy range. According to the results, the contrast and standard deviation were decreased, when subtraction energy width of the energy window is increased. Also, the CNR using a KELS imaging technique is higher than that of the images acquired by using whole energy range. Especially, the maximum differences of CNR between whole energy range and KELS images using a 1, 2, and 3 mm diameter iodine contrast agent were acquired 11.33, 8.73, and 8.29 times, respectively. Additionally, the optimum subtraction energy width of the energy window can be acquired at 5, 4, and 3 keV for the 1, 2, and 3 mm diameter iodine contrast agent, respectively. In conclusion, we successfully established an improved KELS imaging technique and optimized subtraction energy width of the energy window, and based on
Monte Carlo simulations of neutron oil well logging tools
International Nuclear Information System (INIS)
Monte Carlo simulations of simple neutron oil well logging tools into typical geological formations are presented. The simulated tools consist of both 14 MeV pulsed and continuous Am-Be neutron sources with time gated and continuous gamma ray detectors respectively. The geological formation consists of pure limestone with 15% absolute porosity in a wide range of oil saturation. The particle transport was performed with the Monte Carlo N-Particle Transport Code System, MCNP-4B. Several gamma ray spectra were obtained at the detector position that allow to perform composition analysis of the formation. In particular, the ratio C/O was analyzed as an indicator of oil saturation. Further calculations are proposed to simulate actual detector responses in order to contribute to understand the relation between the detector response with the formation composition. (author)
Monte Carlo simulation of quantum Zeno effect in the brain
Georgiev, Danko
2014-01-01
Environmental decoherence appears to be the biggest obstacle for successful construction of quantum mind theories. Nevertheless, the quantum physicist Henry Stapp promoted the view that the mind could utilize quantum Zeno effect to influence brain dynamics and that the efficacy of such mental efforts would not be undermined by environmental decoherence of the brain. To address the physical plausibility of Stapp's claim, we modeled the brain using quantum tunneling of an electron in a multiple-well structure such as the voltage sensor in neuronal ion channels and performed Monte Carlo simulations of quantum Zeno effect exerted by the mind upon the brain in the presence or absence of environmental decoherence. The simulations unambiguously showed that the quantum Zeno effect breaks down for timescales greater than the brain decoherence time. To generalize the Monte Carlo simulation results for any n-level quantum system, we further analyzed the change of brain entropy due to the mind probing actions and proved ...
Monte Carlo Simulations of Neutron Oil well Logging Tools
International Nuclear Information System (INIS)
Monte Carlo simulations of simple neutron oil well logging tools into typical geological formations are presented.The simulated tools consist of both 14 MeV pulsed and continuous Am-Be neutron sources with time gated and continuous gamma ray detectors respectively.The geological formation consists of pure limestone with 15% absolute porosity in a wide range of oil saturation.The particle transport was performed with the Monte Carlo N-Particle Transport Code System, MCNP-4B.Several gamma ray spectra were obtained at the detector position that allow to perform composition analysis of the formation.In particular, the ratio C/O was analyzed as an indicator of oil saturation.Further calculations are proposed to simulate actual detector responses in order to contribute to understand the relation between the detector response with the formation composition
Monte Carlo Simulations of Neutron Oil well Logging Tools
Azcurra, M
2002-01-01
Monte Carlo simulations of simple neutron oil well logging tools into typical geological formations are presented.The simulated tools consist of both 14 MeV pulsed and continuous Am-Be neutron sources with time gated and continuous gamma ray detectors respectively.The geological formation consists of pure limestone with 15% absolute porosity in a wide range of oil saturation.The particle transport was performed with the Monte Carlo N-Particle Transport Code System, MCNP-4B.Several gamma ray spectra were obtained at the detector position that allow to perform composition analysis of the formation.In particular, the ratio C/O was analyzed as an indicator of oil saturation.Further calculations are proposed to simulate actual detector responses in order to contribute to understand the relation between the detector response with the formation composition
A new lattice Monte Carlo method for simulating dielectric inhomogeneity
Duan, Xiaozheng; Wang, Zhen-Gang; Nakamura, Issei
We present a new lattice Monte Carlo method for simulating systems involving dielectric contrast between different species by modifying an algorithm originally proposed by Maggs et al. The original algorithm is known to generate attractive interactions between particles that have different dielectric constant than the solvent. Here we show that such attractive force is spurious, arising from incorrectly biased statistical weight caused by the particle motion during the Monte Carlo moves. We propose a new, simple algorithm to resolve this erroneous sampling. We demonstrate the application of our algorithm by simulating an uncharged polymer in a solvent with different dielectric constant. Further, we show that the electrostatic fields in ionic crystals obtained from our simulations with a relatively small simulation box correspond well with results from the analytical solution. Thus, our Monte Carlo method avoids the need for the Ewald summation in conventional simulation methods for charged systems. This work was supported by the National Natural Science Foundation of China (21474112 and 21404103). We are grateful to Computing Center of Jilin Province for essential support.
Monte Carlo Simulations of Necrotic Cell Targeted Alpha Therapy
International Nuclear Information System (INIS)
Full text: Hypoxic tumour cells are radioresistant and are significant contributors to the locoregional recurrences and distant metastases that mark treatment failure. Due to restricted circulatory supply, hypoxic tumor cells frequently become necrotic and thus necrotic areas often lie near hypoxic tumour areas. In this study we investigate the feasibility of binding an alpha-emitting conjugate to necrotic cells located in the proximity of hypoxic, viable tumour cells. Monte Carlo radiation transport simulations were performed to investigate the dose distribution resulting from the thorium 227 (Th227) decay chain in a representative tumour geometry. The Geant4 software toolkit was used to simulate the decay and interactions of the Th227 decay chain. The distribution of Th227 was based on a study by Thomlinson and Gray of human lung cancer histological samples (Thomlinson RH, Gray LH. Br J Cancer 1955; 9:539). The normalized dose distribution obtained with Geant4 from a cylindrical Th227 source in water is illustrated in Fig. I. The relative contribution of the different decay channels is displayed, together with a profile through the centre of the accumulated dose map. The results support the hypothesis that significant α-particle doses will be deposited in the hypoxic tumor tissue immediately surrounding the necrotic core (where the majority of Th227 will be located). As an internal a-particle generator, the Th227-radioimmunoconjugate shows potential as an efficient hypoxic tumour sterilizer.
Monte Carlo simulations of lattice models for single polymer systems
Energy Technology Data Exchange (ETDEWEB)
Hsu, Hsiao-Ping, E-mail: hsu@mpip-mainz.mpg.de [Max-Planck-Institut für Polymerforschung, Ackermannweg 10, D-55128 Mainz (Germany)
2014-10-28
Single linear polymer chains in dilute solutions under good solvent conditions are studied by Monte Carlo simulations with the pruned-enriched Rosenbluth method up to the chain length N∼O(10{sup 4}). Based on the standard simple cubic lattice model (SCLM) with fixed bond length and the bond fluctuation model (BFM) with bond lengths in a range between 2 and √(10), we investigate the conformations of polymer chains described by self-avoiding walks on the simple cubic lattice, and by random walks and non-reversible random walks in the absence of excluded volume interactions. In addition to flexible chains, we also extend our study to semiflexible chains for different stiffness controlled by a bending potential. The persistence lengths of chains extracted from the orientational correlations are estimated for all cases. We show that chains based on the BFM are more flexible than those based on the SCLM for a fixed bending energy. The microscopic differences between these two lattice models are discussed and the theoretical predictions of scaling laws given in the literature are checked and verified. Our simulations clarify that a different mapping ratio between the coarse-grained models and the atomistically realistic description of polymers is required in a coarse-graining approach due to the different crossovers to the asymptotic behavior.
Energy Technology Data Exchange (ETDEWEB)
Ahmad, I.; Back, B.B.; Betts, R.R. [and others
1995-08-01
An essential component in the assessment of the significance of the results from APEX is a demonstrated understanding of the acceptance and response of the apparatus. This requires detailed simulations which can be compared to the results of various source and in-beam measurements. These simulations were carried out using the computer codes EGS and GEANT, both specifically designed for this purpose. As far as is possible, all details of the geometry of APEX were included. We compared the results of these simulations with measurements using electron conversion sources, positron sources and pair sources. The overall agreement is quite acceptable and some of the details are still being worked on. The simulation codes were also used to compare the results of measurements of in-beam positron and conversion electrons with expectations based on known physics or other methods. Again, satisfactory agreement is achieved. We are currently working on the simulation of various pair-producing scenarios such as the decay of a neutral object in the mass range 1.5-2.0 MeV and also the emission of internal pairs from nuclear transitions in the colliding ions. These results are essential input to the final results from APEX on cross section limits for various, previously proposed, sharp-line producing scenarios.
International Nuclear Information System (INIS)
Digital zenith camera systems (DZCS) are dedicated astronomical-geodetic measurement systems for the observation of the direction of the plumb line. A DZCS key component is a pair of tilt meters for the determination of the instrumental tilt with respect to the plumb line. Highest accuracy (i.e., 0.1 arc-seconds or better) is achieved in practice through observation with precision tilt meters in opposite faces (180° instrumental rotation), and application of rigorous tilt reduction models. A novel concept proposes the development of a hexapod (Stewart platform)-based DZCS. However, hexapod-based total rotations are limited to about 30°–60° in azimuth (equivalent to ±15° to ±30° yaw rotation), which raises the question of the impact of the rotation angle between the two faces on the accuracy of the tilt measurement. The goal of the present study is the investigation of the expected accuracy of tilt measurements to be carried out on future hexapod-based DZCS, with special focus placed on the role of the limited rotation angle. A Monte-Carlo simulation study is carried out in order to derive accuracy estimates for the tilt determination as a function of several input parameters, and the results are validated against analytical error propagation. As the main result of the study, limitation of the instrumental rotation to 60° (30°) deteriorates the tilt accuracy by a factor of about 2 (4) compared to a 180° rotation between the faces. Nonetheless, a tilt accuracy at the 0.1 arc-second level is expected when the rotation is at least 45°, and 0.05 arc-second (about 0.25 microradian) accurate tilt meters are deployed. As such, a hexapod-based DZCS can be expected to allow sufficiently accurate determination of the instrumental tilt. This provides supporting evidence for the feasibility of such a novel instrumentation. The outcomes of our study are not only relevant to the field of DZCS, but also to all other types of instruments where the instrumental tilt
Hirt, Christian; Papp, Gábor; Pál, András; Benedek, Judit; Szũcs, Eszter
2014-08-01
Digital zenith camera systems (DZCS) are dedicated astronomical-geodetic measurement systems for the observation of the direction of the plumb line. A DZCS key component is a pair of tilt meters for the determination of the instrumental tilt with respect to the plumb line. Highest accuracy (i.e., 0.1 arc-seconds or better) is achieved in practice through observation with precision tilt meters in opposite faces (180° instrumental rotation), and application of rigorous tilt reduction models. A novel concept proposes the development of a hexapod (Stewart platform)-based DZCS. However, hexapod-based total rotations are limited to about 30°-60° in azimuth (equivalent to ±15° to ±30° yaw rotation), which raises the question of the impact of the rotation angle between the two faces on the accuracy of the tilt measurement. The goal of the present study is the investigation of the expected accuracy of tilt measurements to be carried out on future hexapod-based DZCS, with special focus placed on the role of the limited rotation angle. A Monte-Carlo simulation study is carried out in order to derive accuracy estimates for the tilt determination as a function of several input parameters, and the results are validated against analytical error propagation. As the main result of the study, limitation of the instrumental rotation to 60° (30°) deteriorates the tilt accuracy by a factor of about 2 (4) compared to a 180° rotation between the faces. Nonetheless, a tilt accuracy at the 0.1 arc-second level is expected when the rotation is at least 45°, and 0.05 arc-second (about 0.25 microradian) accurate tilt meters are deployed. As such, a hexapod-based DZCS can be expected to allow sufficiently accurate determination of the instrumental tilt. This provides supporting evidence for the feasibility of such a novel instrumentation. The outcomes of our study are not only relevant to the field of DZCS, but also to all other types of instruments where the instrumental tilt
Monte Carlo Simulation of HERD Calorimeter
Xu, M; Dong, Y W; Lu, J G; Quan, Z; Wang, L; Wang, Z G; Wu, B B; Zhang, S N
2014-01-01
The High Energy cosmic-Radiation Detection (HERD) facility onboard China's Space Station is planned for operation starting around 2020 for about 10 years. It is designed as a next generation space facility focused on indirect dark matter search, precise cosmic ray spectrum and composition measurements up to the knee energy, and high energy gamma-ray monitoring and survey. The calorimeter plays an essential role in the main scientific objectives of HERD. A 3-D cubic calorimeter filled with high granularity crystals as active material is a very promising choice for the calorimeter. HERD is mainly composed of a 3-D calorimeter (CALO) surrounded by silicon trackers (TK) from all five sides except the bottom. CALO is made of 9261 cubes of LYSO crystals, corresponding to about 55 radiation lengths and 3 nuclear interaction lengths, respectively. Here the simulation results of the performance of CALO with GEANT4 and FLUKA are presented: 1) the total absorption CALO and its absorption depth for precise energy measure...
Monte Carlo simulation for dual head gamma camera
International Nuclear Information System (INIS)
Monte Carlo (MC) simulation technique was used widely in medical physics applications. In nuclear medicine MC was used to design new medical imaging devices such as positron emission tomography (PET), gamma camera and single photon emission computed tomography (SPECT). Also it can be used to study the factors affecting image quality and internal dosimetry, Gate is on of monte Carlo code that has a number of advantages for simulation of SPECT and PET. There is a limit accessibilities in machines which are used in clinics because of the work load of machines. This makes it hard to evaluate some factors effecting machine performance which must be evaluated routinely. Also because of difficulties of carrying out scientific research and training of students, MC model can be optimum solution for the problem. The aim of this study was to use gate monte Carlo code to model Nucline spirit, medico dual head gamma camera hosted in radiation and isotopes center of Khartoum which is equipped with low energy general purpose LEGP collimators. This was used model to evaluate spatial resolution and sensitivity which is important factor affecting image quality and to demonstrate the validity of gate by comparing experimental results with simulation results on spatial resolution. The gate model of Nuclide spirit, medico dual head gamma camera was developed by applying manufacturer specifications. Then simulation was run. In evaluation of spatial resolution the FWHM was calculated from image profile of line source of Tc 99m gammas emitter of energy 140 KeV at different distances from modeled camera head at 5,10,15,20,22,27,32,37 cm and for these distances the spatial resolution was founded to be 5.76, 7.73, 10.7, 13.8, 14.01,16.91, 19.75 and 21.9 mm, respectively. These results showed a decrement of spatial resolution with increase of the distance between object (line source) and collimator in linear manner. FWHM calculated at 10 cm was compared with experimental results. The
Monte Carlo study of nanowire magnetic properties
Institute of Scientific and Technical Information of China (English)
R.Masrour; L.Bahmad; A.Benyoussef
2013-01-01
In this work,we use Monte Carlo simulations to study the magnetic properties of a nanowire system based on a honeycomb lattice,in the absence as well as in the presence of both an external magnetic field and crystal field.The system is formed with NL layers having spins that can take the values σ =+1/2 and S =+1,0.The blocking temperature is deduced,for each spin configuration,depending on the crystal field A.The effect of the exchange interaction coupling Jp between the spin configurations σ and S is studied for different values of temperature at fixed crystal field.The established ground-state phase diagram,in the plane (Jp,A),shows that the only stable configurations are:(1/2,0),(1/2,+1),and (1/2,-1).The thermal magnetization and susceptibility are investigated for the two spin configurations,in the absence as well as in the presence of a crystal field.Finally,we establish the hysteresis cycle for different temperature values,showing that there is almost no remaining magnetization in the absence of the external magnetic field,and that the studied system exhibits a super-paramagnetic behavior.
Computed radiography simulation using the Monte Carlo code MCNPX
International Nuclear Information System (INIS)
Simulating x-ray images has been of great interest in recent years as it makes possible an analysis of how x-ray images are affected owing to relevant operating parameters. In this paper, a procedure for simulating computed radiographic images using the Monte Carlo code MCNPX is proposed. The sensitivity curve of the BaFBr image plate detector as well as the characteristic noise of a 16-bit computed radiography system were considered during the methodology's development. The results obtained confirm that the proposed procedure for simulating computed radiographic images is satisfactory, as it allows obtaining results comparable with experimental data. (author)
Monte Carlo simulation of a prototype photodetector used in radiotherapy
Kausch, C; Albers, D; Schmidt, R; Schreiber, B
2000-01-01
The imaging performance of prototype electronic portal imaging devices (EPID) has been investigated. Monte Carlo simulations have been applied to calculate the modulation transfer function (MTF( f )), the noise power spectrum (NPS( f )) and the detective quantum efficiency (DQE( f )) for different new type of EPIDs, which consist of a detector combination of metal or polyethylene (PE), a phosphor layer of Gd sub 2 O sub 2 S and a flat array of photodiodes. The simulated results agree well with measurements. Based on simulated results, possible optimization of these devices is discussed.
Modifications to the TRIM Monte Carlo simulation program
Energy Technology Data Exchange (ETDEWEB)
Macrander, A. T.
1979-04-01
Extensive modifications were made to the TRIM (TRansport of Ions in Matter) Monte Carlo computer code which simulates the ion irradiation of amorphous solids. The original FORTRAN code was translated into BASIC for use on minicomputers with 32 K words of memory. Versions have been written to simulate very low-energy irradiations and the irradiation of binary alloys. Furthermore, a version was written which added the capability of following a lateral direction, in addition to the penetration depth of an ion. Subsequently, a version was written to simulate the production of collision cascades. Details of these modifications were discussed and examples of their use were given.
Monte Carlo simulations of (e,2e) experiments on solids
Energy Technology Data Exchange (ETDEWEB)
Vos, M. [Flinders Univ. of South Australia, Adelaide, SA (Australia). Electronic Structure of Materials Centre; Bottema, M. [Flinders Univ. of South Australia, Adelaide, SA (Australia). Dept. of Mathematics and Statistics]|[Centre for Sensor Signal and Information Processing, Technology Park, SA (Australia)
1995-12-01
The aim of this work was to simulate the multiple scattering effects occuring in a real (e,2e) experiment for a free-electron solid. Realistic cross sections for elastic and inelastic scattering events were used for all electrons involved. The Monte Carlo simulation was successfully applied to investigate how multiple scattering parameters used affect the relation between the electronic structure of solid and actually measured intensity. Good agreement was found, on a semiquantitative level, between the simulation and the actual experiments. 24 refs., 1 tab., 10 figs.
Monte Carlo simulations of (e,2e) experiments on solids
International Nuclear Information System (INIS)
The aim of this work was to simulate the multiple scattering effects occuring in a real (e,2e) experiment for a free-electron solid. Realistic cross sections for elastic and inelastic scattering events were used for all electrons involved. The Monte Carlo simulation was successfully applied to investigate how multiple scattering parameters used affect the relation between the electronic structure of solid and actually measured intensity. Good agreement was found, on a semiquantitative level, between the simulation and the actual experiments. 24 refs., 1 tab., 10 figs
Monte Carlo simulation of the Neutrino-4 experiment
Serebrov, A. P.; Fomin, A. K.; Onegin, M. S.; Ivochkin, V. G.; Matrosov, L. N.
2015-12-01
Monte Carlo simulation of the two-section reactor antineutrino detector of the Neutrino-4 experiment is carried out. The scintillation-type detector is based on the inverse beta-decay reaction. The antineutrino is recorded by two successive signals from the positron and the neutron. The simulation of the detector sections and the active shielding is performed. As a result of the simulation, the distributions of photomultiplier signals from the positron and the neutron are obtained. The efficiency of the detector depending on the signal recording thresholds is calculated.
Monte Carlo simulation of the Neutrino-4 experiment
Energy Technology Data Exchange (ETDEWEB)
Serebrov, A. P., E-mail: serebrov@pnpi.spb.ru; Fomin, A. K.; Onegin, M. S.; Ivochkin, V. G.; Matrosov, L. N. [National Research Center Kurchatov Institute, Petersburg Nuclear Physics Institute (Russian Federation)
2015-12-15
Monte Carlo simulation of the two-section reactor antineutrino detector of the Neutrino-4 experiment is carried out. The scintillation-type detector is based on the inverse beta-decay reaction. The antineutrino is recorded by two successive signals from the positron and the neutron. The simulation of the detector sections and the active shielding is performed. As a result of the simulation, the distributions of photomultiplier signals from the positron and the neutron are obtained. The efficiency of the detector depending on the signal recording thresholds is calculated.
Direct Simulation Monte Carlo Investigation of Noncontinuum Couette Flow
Torczynski, J. R.; Gallis, M. A.
2009-11-01
The Direct Simulation Monte Carlo (DSMC) method of molecular gas dynamics is used to study noncontinuum effects in Couette flow. The walls have equal temperatures and equal accommodation coefficients but unequal tangential velocities. Simulations are performed for near-free-molecular to near-continuum gas pressures with accommodation coefficients of 0.25, 0.5, and 1. Ten gases are examined: argon, helium, nitrogen, sea-level air, and six Inverse-Power-Law (IPL) gases with viscosity temperature exponents of 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0, as represented by the Variable Soft Sphere (VSS) interaction. In all cases, the wall shear stress is proportional to the slip velocity. The momentum transfer coefficient relating these two quantities can be accurately correlated in terms of the Knudsen number based on the wall separation. The two dimensionless parameters in the correlation are similar for all gases examined. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
Monte Carlo simulation of electron swarms in H2
International Nuclear Information System (INIS)
A Monte-Carlo simulation of the motion of an electron swarm in molecular hydrogen was studied in the range E/N = 1.4-170 Td (1 Td = 10-17V/cms2). The simulation was performed for 400-600 electrons at several values of E/N for two different sets of inelastic collision cross sections at high values of E/N. The longitudinal diffusion coefficient Dsub(L), lateral diffusion coefficient D, swarm drift velocity W, average swarm energy epsilon, and the ionization and excitation production coefficients were obtained and compared with experimental results where these are available. It was found that the results obtained differ significantly from the experimental values and this is attributed to the isotopic scattering model used in this work. However, the results lend support to the experimental technique reported by Blevin et al used to determine these transport parameters, and in particular confirm their result that Dsub(L) > D at high values of E/N. (author)
Monte Carlo Simulation of Callisto's Exosphere
Vorburger, Audrey; Wurz, Peter; Galli, André; Mousis, Olivier; Barabash, Stas; Lammer, Helmut
2014-05-01
to the surface the sublimated particles dominate the day-side exosphere, however, their density profiles (with the exception of H and H2) decrease much more rapidly with altitude than those of the sputtered particles, thus, the latter particles start to dominate at altitudes above ~1000 km. Since the JUICE flybys are as low as 200 km above Callisto's surface, NIM is expected to register both the sublimated as well as sputtered particle populations. Our simulations show that NIM's sensitivity is high enough to allow the detection of particles sputtered from the icy as well as the mineral surfaces, and to distinguish between the different composition models.
Directory of Open Access Journals (Sweden)
Biniam Tesfamicael
2016-03-01
Full Text Available Purpose: The main purpose of this study was to monitor the secondary dose distribution originating from a water phantom during proton therapy of prostate cancer using scintillating fibers.Methods: The Geant4 Monte Carlo toolkit version 9.6.p02 was used to simulate a proton therapy of prostate cancer. Two cases were studied. In the first case, 8 × 8 = 64 equally spaced fibers inside three 4 × 4 × 2.54 cm3 Delrin® blocks were used to monitor the emission of secondary particles in the transverse (left and right and distal regions relative to the beam direction. In the second case, a scintillating block with a thickness of 2.54 cm and equal vertical and longitudinal dimensions as the water phantom was used. Geometrical cuts were implemented to extract the energy deposited in each fiber and inside the scintillating block.Results: The transverse dose distributions from the detected secondary particles in both cases are symmetric and agree to within <3.6%. The energy deposited gradually increases as one moves from the peripheral row of fibers towards the center of the block (aligned with the center of the prostate by a factor of approximately 5. The energy deposited was also observed to decrease as one goes from the frontal to distal region of the block. The ratio of the energy deposited in the prostate to the energy deposited in the middle two rows of fibers showed a linear relationship with a slope of (-3.55±2.26 × 10-5 MeV per treatment Gy delivered. The distal detectors recorded a negligible amount of energy deposited due to higher attenuation of the secondary particles by the water in that direction.Conclusion: With a good calibration and with the ability to define a good correlation between the radiation flux recorded by the external fibers and the dose delivered to the prostate, such fibers can be used for real time dose verification to the target. The system was also observed to respond to the series of Bragg Peaks used to generate the
Study on random number generator in Monte Carlo code
International Nuclear Information System (INIS)
The Monte Carlo code uses a sequence of pseudo-random numbers with a random number generator (RNG) to simulate particle histories. A pseudo-random number has its own period depending on its generation method and the period is desired to be long enough not to exceed the period during one Monte Carlo calculation to ensure the correctness especially for a standard deviation of results. The linear congruential generator (LCG) is widely used as Monte Carlo RNG and the period of LCG is not so long by considering the increasing rate of simulation histories in a Monte Carlo calculation according to the remarkable enhancement of computer performance. Recently, many kinds of RNG have been developed and some of their features are better than those of LCG. In this study, we investigate the appropriate RNG in a Monte Carlo code as an alternative to LCG especially for the case of enormous histories. It is found that xorshift has desirable features compared with LCG, and xorshift has a larger period, a comparable speed to generate random numbers, a better randomness, and good applicability to parallel calculation. (author)
Nonlinear Condition Tolerancing Using Monte Carlo Simulation
Directory of Open Access Journals (Sweden)
JOUILEL Naima
2016-05-01
Full Text Available To ensure accuracy and performance of the products, designers tend to hug the tolerances. While, manufacturers prefer to increase them in order to reduce costs and ensure competition. The analysis and synthesis of tolerances aim on studying their influence on conformity with functional requirements. This study may be conducted in the case of the most unfavorable configurations with the "worst case" method, or "in all cases" using the statistical approach. However, having a nonlinear condition make it difficult to analyse the influence of parameters on the functional condition. In this work, we are interested in the tolerance analysis of a mechanism presenting a nonlinear functional condition (slider crank mechanism. To do this we'll develop an approach of tolerances analysis combining the worst case and the statistical methods.
Monte Carlo simulation in systems biology
Schellenberger, Jan
2010-01-01
Constraint Based Reconstruction and Analysis (COBRA) is a framework within the field of Systems Biology which aims to understand cellular metabolism through the analysis of large scale metabolic models. These models are based on meticulously curated reconstructions of all chemical reactions in an organism. Instead of attempting to predict the exact state of the biological system, COBRA describes the physiological constraints that the system must satisfy and studies the range of solutions sati...
International Nuclear Information System (INIS)
The computer simulation has been widely used in physical researches by both the viability of the codes and the growth of the power of computers in the last decades. The Monte Carlo simulation program, EGS4 code is a simulation program used in the area of radiation transport. The simulators, surrogate tissues, phantoms are objects used to perform studies on dosimetric quantities and quality testing of images. The simulators have characteristics of scattering and absorption of radiation similar to tissues that make up the body. The aim of this work is to translate the effects of radiation interactions in a real healthy breast tissues, sick and on simulators using the EGS4 Monte Carlo simulation code
International Nuclear Information System (INIS)
Radon alpha-activities per unit volume have been measured inside and outside different building material samples by using CR-39 and LR-115 type II solid state nuclear track detectors (SSNTD). Radon emanation coefficients of the studied building materials have been evaluated. The porosities of the building material samples studied have been determined by using a Monte Carlo calculational method adapted to the experimental conditions and compared with data obtained by the Archimedes's method. The influence of the building material porosity on the radon emanation coefficient has been investigated
Monte Carlo studies of domain growth in two dimensions
International Nuclear Information System (INIS)
Monte Carlo simulations have been carried out to study the effect of temperature on the kinetics of domain growth. The concept of ''spatial entropy'' is introduced. It is shown that ''spatial entropy'' of the domain can be used to give a measure of the roughening of the domain. Most of the roughening is achieved during the initial time (t< or approx. 10 Monte Carlo cycles), the rate of roughening being greater for higher temperatures. For later times the roughening of the domain for different temperatures proceeds at essentially the same rate. (author)
Monte Carlo simulations on a 9-node PC cluster
International Nuclear Information System (INIS)
Monte Carlo simulation methods are frequently used in the fields of medical physics, dosimetry and metrology of ionising radiation. Nevertheless, the main drawback of this technique is to be computationally slow, because the statistical uncertainty of the result improves only as the square root of the computational time. We present a method, which allows to reduce by a factor 10 to 20 the used effective running time. In practice, the aim was to reduce the calculation time in the LNHB metrological applications from several weeks to a few days. This approach includes the use of a PC-cluster, under Linux operating system and PVM parallel library (version 3.4). The Monte Carlo codes EGS4, MCNP and PENELOPE have been implemented on this platform and for the two last ones adapted for running under the PVM environment. The maximum observed speedup is ranging from a factor 13 to 18 according to the codes and the problems to be simulated. (orig.)
Application of Monte Carlo Simulations to Improve Basketball Shooting Strategy
Min, Byeong June
2016-01-01
The underlying physics of basketball shooting seems to be a straightforward example of the Newtonian mechanics that can easily be traced by numerical methods. However, a human basketball player does not make use of all the possible basketball trajectories. Instead, a basketball player will build up a database of successful shots and select the trajectory that has the greatest tolerance to small variations of the real world. We simulate the basketball player's shooting training as a Monte Carlo sequence to build optimal shooting strategies, such as the launch speed and angle of the basketball, and whether to take a direct shot or a bank shot, as a function of the player's court positions and height. The phase space volume that belongs to the successful launch velocities generated by Monte Carlo simulations are then used as the criterion to optimize a shooting strategy that incorporates not only mechanical, but human factors as well.
International Nuclear Information System (INIS)
The two alloy systems: namely, Ni-Mo-based alloys and Al-Ti alloys, share some common features in that the ordered structures and the ordering processes in these two systems can be described in terms of three types of superlattice tiles: squares and fat or lean rhombi. In Ni- Mo-based alloys these represent one-molecule clusters of three fcc superlattice structures: Ni4Mo (D1a), Ni3Mo (D022) and Ni2Mo (Pt2Mo-type), while in Al-Ti these represent two dimensional Ti4AI, Ti3Al and Ti2Al derivatives on Ti-rich (002) planes of the off stoichiometric TiAl (L10) phase. Evolution of short range order (SRO): 11/20 special point SRO in the case of Ni-Mo and the incommensurate SRO in the case of the Al-rich TiAl intermetallic alloys and evolution of LRO phases from these have been followed using both conventional and high resolution TEM. Corroborative evidence from Monte Carlo simulations will also be presented in order to explain the observed experimental results. Occurrence of antiphase boundaries (APBs) and their energies, as we will see, play an important role in these transformations. Predominantly two types of APBs occur in the Al5Ti3 phase in Al-rich TiAl. Monte Carlo Simulations and the experimental observations reveal both of these. These play a synergistic role in the formation of Al5Ti3 antiphase domains
Conceptual design and Monte Carlo simulations of the AGATA array
Energy Technology Data Exchange (ETDEWEB)
Farnea, E., E-mail: Enrico.Farnea@pd.infn.i [Istituto Nazionale di Fisica Nucleare, Sezione di Padova, Padova (Italy); Recchia, F.; Bazzacco, D. [Istituto Nazionale di Fisica Nucleare, Sezione di Padova, Padova (Italy); Kroell, Th. [Institut fuer Kernphysik, Technische Universitaet Darmstadt, Darmstadt (Germany); Podolyak, Zs. [Department of Physics, University of Surrey, Guildford (United Kingdom); Quintana, B. [Departamento de Fisica Fundamental, Universidad de Salamanca, Salamanca (Spain); Gadea, A. [Instituto de Fisica Corpuscular, CSIC-Universidad de Valencia, Valencia (Spain)
2010-09-21
The aim of the Advanced GAmma Tracking Array (AGATA) project is the construction of an array based on the novel concepts of pulse shape analysis and {gamma}-ray tracking with highly segmented Ge semiconductor detectors. The conceptual design of AGATA and its performance evaluation under different experimental conditions has required the development of a suitable Monte Carlo code. In this article, the description of the code as well as simulation results relevant for AGATA, are presented.
Calculating Variable Annuity Liability 'Greeks' Using Monte Carlo Simulation
Cathcart, Mark J.; Steven Morrison; McNeil, Alexander J.
2011-01-01
Hedging methods to mitigate the exposure of variable annuity products to market risks require the calculation of market risk sensitivities (or "Greeks"). The complex, path-dependent nature of these products means these sensitivities typically must be estimated by Monte Carlo simulation. Standard market practice is to measure such sensitivities using a "bump and revalue" method. As well as requiring multiple valuations, such approaches can be unreliable for higher order Greeks, e.g., gamma. In...
Monte Carlo simulation of PET images for injection doseoptimization
Czech Academy of Sciences Publication Activity Database
Boldyš, Jiří; Dvořák, Jiří; Skopalová, M.; Bělohlávek, O.
2013-01-01
Roč. 29, č. 9 (2013), s. 988-999. ISSN 2040-7939 R&D Projects: GA MŠk 1M0572 Institutional support: RVO:67985556 Keywords : positron emission tomography * Monte Carlo simulation * biological system modeling * image quality Subject RIV: FD - Oncology ; Hematology Impact factor: 1.542, year: 2013 http://library.utia.cas.cz/separaty/2013/ZOI/boldys-0397175.pdf
Modular Monte Carlo Simulation Including Secondary Electron Raytracing
Czech Academy of Sciences Publication Activity Database
Gnieser, D.; Frase, C. G.; Bosse, H.; Konvalina, Ivo; Müllerová, Ilona
Brno: Institute of Scientific Instruments AS CR, v.v.i, 2008 - (Mika, F.), s. 31-32 ISBN 978-80-254-0905-3. [International Seminar on Recent Trends in Charged Particle Optics and Surface Physics Instrumentation /11./. Skalský dvůr (CZ), 14.07.2008-18.07.2008] Institutional research plan: CEZ:AV0Z20650511 Keywords : Monte Carlo simulation * SEM Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering
Image reconstruction using Monte Carlo simulation and artificial neural networks
International Nuclear Information System (INIS)
PET data sets are subject to two types of distortions during acquisition: the imperfect response of the scanner and attenuation and scattering in the active distribution. In addition, the reconstruction of voxel images from the line projections composing a data set can introduce artifacts. Monte Carlo simulation provides a means for modeling the distortions and artificial neural networks a method for correcting for them as well as minimizing artifacts. (author) figs., tab., refs
Monte Carlo simulation of particle acceleration at astrophysical shocks
Campbell, Roy K.
1989-09-01
A Monte Carlo code was developed for the simulation of particle acceleration at astrophysical shocks. The code is implemented in Turbo Pascal on a PC. It is modularized and structured in such a way that modification and maintenance are relatively painless. Monte Carlo simulations of particle acceleration at shocks follow the trajectories of individual particles as they scatter repeatedly across the shock front, gaining energy with each crossing. The particles are assumed to scatter from magnetohydrodynamic (MHD) turbulence on both sides of the shock. A scattering law is used which is related to the assumed form of the turbulence, and the particle and shock parameters. High energy cosmic ray spectra derived from Monte Carlo simulations have observed power law behavior just as the spectra derived from analytic calculations based on a diffusion equation. This high energy behavior is not sensitive to the scattering law used. In contrast with Monte Carlo calculations diffusive calculations rely on the initial injection of supra-thermal particles into the shock environment. Monte Carlo simulations are the only known way to describe the extraction of particles directly from the thermal pool. This was the triumph of the Monte Carlo approach. The question of acceleration efficiency is an important one in the shock acceleration game. The efficiency of shock waves efficient to account for the observed flux of high energy galactic cosmic rays was examined. The efficiency of the acceleration process depends on the thermal particle pick-up and hence the low energy scattering in detail. One of the goals is the self-consistent derivation of the accelerated particle spectra and the MHD turbulence spectra. Presumably the upstream turbulence, which scatters the particles so they can be accelerated, is excited by the streaming accelerated particles and the needed downstream turbulence is convected from the upstream region. The present code is to be modified to include a better
A Monte Carlo simulation technique to determine the optimal portfolio
Directory of Open Access Journals (Sweden)
Hassan Ghodrati
2014-03-01
Full Text Available During the past few years, there have been several studies for portfolio management. One of the primary concerns on any stock market is to detect the risk associated with various assets. One of the recognized methods in order to measure, to forecast, and to manage the existing risk is associated with Value at Risk (VaR, which draws much attention by financial institutions in recent years. VaR is a method for recognizing and evaluating of risk, which uses the standard statistical techniques and the method has been used in other fields, increasingly. The present study has measured the value at risk of 26 companies from chemical industry in Tehran Stock Exchange over the period 2009-2011 using the simulation technique of Monte Carlo with 95% confidence level. The used variability in the present study has been the daily return resulted from the stock daily price change. Moreover, the weight of optimal investment has been determined using a hybrid model called Markowitz and Winker model in each determined stocks. The results showed that the maximum loss would not exceed from 1259432 Rials at 95% confidence level in future day.
A Monte Carlo simulation approach for flood risk assessment
Agili, Hachem; Chokmani, Karem; Oubennaceur, Khalid; Poulin, Jimmy; Marceau, Pascal
2016-04-01
Floods are the most frequent natural disaster and the most damaging in Canada. The issue of assessing and managing the risk related to this disaster has become increasingly crucial for both local and national authorities. Brigham, a municipality located in southern Quebec Province, is one of the heavily affected regions by this disaster because of frequent overflows of the Yamaska River reaching two to three times per year. Since Irene Hurricane which hit the region in 2011 causing considerable socio-economic damage, the implementation of mitigation measures has become a major priority for this municipality. To do this, a preliminary study to evaluate the risk to which this region is exposed is essential. Conventionally, approaches only based on the characterization of the hazard (e.g. floodplains extensive, flood depth) are generally adopted to study the risk of flooding. In order to improve the knowledge of this risk, a Monte Carlo simulation approach combining information on the hazard with vulnerability-related aspects of buildings has been developed. This approach integrates three main components namely hydrological modeling through flow-probability functions, hydraulic modeling using flow-submersion height functions and the study of buildings damage based on damage functions adapted to the Quebec habitat. The application of this approach allows estimating the annual average cost of damage caused by floods on buildings. The obtained results will be useful for local authorities to support their decisions on risk management and prevention against this disaster.
In silico radiobiology: Have we reached the limit of Monte Carlo simulations?
International Nuclear Information System (INIS)
Monte Carlo radiation transport models are increasingly being used to simulate biological damage. However, such radiation biophysics simulations require realistic molecular models for water, whereas existing Monte Carlo models are limited by their use of atomic cross-sections, which become inadequate for accurately modelling interactions of the very low-energy electrons that are responsible for biological damage. In this study, we borrow theoretical methods commonly employed in molecular dynamics simulations to model the molecular wavefunction of the water molecule as the first step towards deriving new molecular cross-sections. We calculate electron charge distributions for molecular water and find non-negligible differences between the vapor and liquid phases that can be attributed to intermolecular bonding in the condensed phase. We propose that a hybrid Monte Carlo – Molecular Dynamics (MC-MD) approach to modelling radiation biophysics will provide new insights into radiation damage and new opportunities to develop targeted molecular therapy strategies.
Confidence interval procedures for Monte Carlo transport simulations
International Nuclear Information System (INIS)
The problem of obtaining valid confidence intervals based on estimates from sampled distributions using Monte Carlo particle transport simulation codes such as MCNP is examined. Such intervals can cover the true parameter of interest at a lower than nominal rate if the sampled distribution is extremely right-skewed by large tallies. Modifications to the standard theory of confidence intervals are discussed and compared with some existing heuristics, including batched means normality tests. Two new types of diagnostics are introduced to assess whether the conditions of central limit theorem-type results are satisfied: the relative variance of the variance determines whether the sample size is sufficiently large, and estimators of the slope of the right tail of the distribution are used to indicate the number of moments that exist. A simulation study is conducted to quantify the relationship between various diagnostics and coverage rates and to find sample-based quantities useful in indicating when intervals are expected to be valid. Simulated tally distributions are chosen to emulate behavior seen in difficult particle transport problems. Measures of variation in the sample variance s2 are found to be much more effective than existing methods in predicting when coverage will be near nominal rates. Batched means tests are found to be overly conservative in this regard. A simple but pathological MCNP problem is presented as an example of false convergence using existing heuristics. The new methods readily detect the false convergence and show that the results of the problem, which are a factor of 4 too small, should not be used. Recommendations are made for applying these techniques in practice, using the statistical output currently produced by MCNP
Monte Carlo simulation of AB-copolymers with saturating bonds
Chertovich, A V; Khokhlov, A R; Bohr, J
2003-01-01
Structural transitions in a single AB-copolymer chain where saturating bonds can be formed between A-and B-units are studied by means of Monte Carlo computer simulations using the bond fluctuation model. Three transitions are found, coil-globule, coil-hairpin and globule-hairpin, depending on the nature of a particular AB-sequence: statistical random sequence, diblock sequence and 'random-complementary' sequence (one-half of such an AB-sequence is random with Bernoulli statistics while the other half is complementary to the first one). The properties of random-complementary sequences are closer to those of diblock sequences than to the properties of random sequences. The model (although quite rough) is expected to represent some basic features of real RNA molecules, i.e. the formation of secondary structure of RNA due to hydrogen bonding of corresponding bases and stacking interactions of the base pairs in helixes. We introduce the notation of RNA-like copolymers and discuss in what sense the sequences studie...
Multi-Level Monte Carlo Simulations with Importance Sampling
Przemyslaw S. Stilger and Ser-Huang Poon
2013-01-01
We present an application of importance sampling to multi-asset options under the Heston and the Bates models as well as to the Heston-Hull-White and the Heston-Cox-Ingersoll-Ross models. Moreover, we provide an efficient importance sampling scheme in a Multi-Level Monte Carlo simulation. In all cases, we explain how the Greeks can be computed in the different simulation schemes using the Likelihood Ratio Method, and how combining it with importance sampling leads to a significant variance re...
Monte Carlo simulation of gamma ray shielding parameters of concretes
International Nuclear Information System (INIS)
Highlights: • MCNP simulation of photon interaction parameters of concretes at 1.5, 2, 3, 4, 5 and 6 MeV. • Compared MCNP, experiment and XCOM photon cross-section database. • μ and TVL of the concretes were found dependent upon chemical composition, density and photon energy. • TVL values of the concretes decrease with increase Fe content and increase with increase in photon energy. - Abstract: The mass attenuation coefficients, linear attenuation coefficients and tenth value layer of seven types of concretes having density (2.3–5.11 g cm−3) have been simulated by Monte Carlo simulation techniques at photon energies 1.5, 2, 3, 4, 5 and 6 MeV. Numerical simulation results have been compared with experimental and XCOM photon cross section database and showed a good agreement. Linear attenuation coefficient and tenth value layer of the concretes were found chemical composition, density and photon energy dependent. The tenth value layer of the concretes decrease with increase iron content and increase with increase in photon energy. The linear attenuation coefficients values of the concretes increase with density and decrease with photon energy. Monte Carlo simulation, calculated and experimental results show that the ordinary concrete having lowest iron content (0.63%) have minimum linear attenuation coefficient
Hashikin, N. A. A.; Yeong, C. H.; Guatelli, S.; Abdullah, B. J. J.; Ng, K. H.; Malaroda, A.; Rosenfeld, A. B.; Perkins, A. C.
2016-03-01
90Y-radioembolization is a palliative treatment for liver cancer. 90Y decays via beta emission, making imaging difficult due to absence of gamma radiation. Since post-procedure imaging is crucial, several theranostic radionuclides have been explored as alternatives. However, exposures to gamma radiation throughout the treatment caused concern for the organs near the liver. Geant4 Monte Carlo simulation using MIRD Pamphlet 5 reference phantom was carried out. A spherical tumour with 4.3cm radius was modelled within the liver. 1.82GBq of 90Y sources were isotropically distributed within the tumour, with no extrahepatic shunting. The simulation was repeated with 153Sm, 166Ho and 177Lu. The estimated tumour doses for all radionuclides were 262.9Gy. Tumour dose equivalent to 1.82GBq 90Y can be achieved with 8.32, 5.83, and 4.44GBq for 153Sm, 166Ho and 177Lu, respectively. Normal liver doses by the other radionuclides were lower than 90Y, hence beneficial for normal tissue sparing. The organ doses from 153Sm and 177Lu were relatively higher due to higher gamma energy, but were still well below 1Gy. 166Ho, 177Lu and 153Sm offer useful gamma emission for post-procedure imaging. They show potential as 90Y substitutes, delivering comparable tumour doses, lower normal liver doses and other organs doses far below the tolerance limit.
Jung, Joo-Young; Lu, Bo; Yoon, Do-Kun; Hong, Key Jo; Jang, HongSeok; Liu, Chihray; Suh, Tae Suk
2016-04-01
We confirmed the feasibility of using our proposed system to extract two different kinds of functional images from a positron emission tomography (PET) module by using an insertable collimator during boron neutron capture therapy (BNCT). Coincidence events from a tumor region that included boron particles were identified by a PET scanner before BNCT; subsequently, the prompt gamma ray events from the same tumor region were collected after exposure to an external neutron beam through an insertable collimator on the PET detector. Five tumor regions that contained boron particles and were located in the water phantom and in the BNCT system with the PET module were simulated with Monte Carlo simulation code. The acquired images were quantitatively analyzed. Based on the receiver operating characteristic (ROC) curves in the five boron regions, A, B, C, D, and E, the PET and single-photon images were 10.2%, 11.7%, 8.2% (center region), 12.6%, and 10.5%, respectively. We were able to acquire simultaneously PET and single prompt photon images for tumor regions monitoring by using an insertable collimator without any additional isotopes. PMID:26970679
Monte Carlo computer simulation of sedimentation of charged hard spherocylinders
International Nuclear Information System (INIS)
In this article we present a NVT Monte Carlo computer simulation study of sedimentation of an electroneutral mixture of oppositely charged hard spherocylinders (CHSC) with aspect ratio L/σ = 5, where L and σ are the length and diameter of the cylinder and hemispherical caps, respectively, for each particle. This system is an extension of the restricted primitive model for spherical particles, where L/σ = 0, and it is assumed that the ions are immersed in an structureless solvent, i.e., a continuum with dielectric constant D. The system consisted of N = 2000 particles and the Wolf method was implemented to handle the coulombic interactions of the inhomogeneous system. Results are presented for different values of the strength ratio between the gravitational and electrostatic interactions, Γ = (mgσ)/(e2/Dσ), where m is the mass per particle, e is the electron's charge and g is the gravitational acceleration value. A semi-infinite simulation cell was used with dimensions Lx ≈ Ly and Lz = 5Lx, where Lx, Ly, and Lz are the box dimensions in Cartesian coordinates, and the gravitational force acts along the z-direction. Sedimentation effects were studied by looking at every layer formed by the CHSC along the gravitational field. By increasing Γ, particles tend to get more packed at each layer and to arrange in local domains with an orientational ordering along two perpendicular axis, a feature not observed in the uncharged system with the same hard-body geometry. This type of arrangement, known as tetratic phase, has been observed in two-dimensional systems of hard-rectangles and rounded hard-squares. In this way, the coupling of gravitational and electric interactions in the CHSC system induces the arrangement of particles in layers, with the formation of quasi-two dimensional tetratic phases near the surface
Monte Carlo computer simulation of sedimentation of charged hard spherocylinders.
Viveros-Méndez, P X; Gil-Villegas, Alejandro; Aranda-Espinoza, S
2014-07-28
In this article we present a NVT Monte Carlo computer simulation study of sedimentation of an electroneutral mixture of oppositely charged hard spherocylinders (CHSC) with aspect ratio L/σ = 5, where L and σ are the length and diameter of the cylinder and hemispherical caps, respectively, for each particle. This system is an extension of the restricted primitive model for spherical particles, where L/σ = 0, and it is assumed that the ions are immersed in an structureless solvent, i.e., a continuum with dielectric constant D. The system consisted of N = 2000 particles and the Wolf method was implemented to handle the coulombic interactions of the inhomogeneous system. Results are presented for different values of the strength ratio between the gravitational and electrostatic interactions, Γ = (mgσ)/(e(2)/Dσ), where m is the mass per particle, e is the electron's charge and g is the gravitational acceleration value. A semi-infinite simulation cell was used with dimensions Lx ≈ Ly and Lz = 5Lx, where Lx, Ly, and Lz are the box dimensions in Cartesian coordinates, and the gravitational force acts along the z-direction. Sedimentation effects were studied by looking at every layer formed by the CHSC along the gravitational field. By increasing Γ, particles tend to get more packed at each layer and to arrange in local domains with an orientational ordering along two perpendicular axis, a feature not observed in the uncharged system with the same hard-body geometry. This type of arrangement, known as tetratic phase, has been observed in two-dimensional systems of hard-rectangles and rounded hard-squares. In this way, the coupling of gravitational and electric interactions in the CHSC system induces the arrangement of particles in layers, with the formation of quasi-two dimensional tetratic phases near the surface. PMID:25084954
Energy Technology Data Exchange (ETDEWEB)
Barbosa, Antonio Konrado de Santana; Vieira, Jose Wilson [Instituto Federal de Educacao, Ciencia e Tecnologia (IFPE), Recife, PE (Brazil); Costa, Kleber Souza Silva [Faculdade Integrada de Pernambuco (FACIPE), Recife, PE (Brazil); Lima, Fernando Roberto de Andrade, E-mail: falima@cnen.gov.b [Centro Regional de Ciencias Nucleares do Nordeste (CRCN-NE/CNEN-PE), Recife, PE (Brazil)
2011-07-01
Radiotherapy computational simulation procedures using Monte Carlo (MC) methods have shown to be increasingly important to the improvement of cancer fighting strategies. One of the biases in this practice is the discretization of the radioactive source in brachytherapy simulations, which often do not match with a real situation. This study had the aim to identify and to measure the influence of radioactive sources discretization in brachytherapy MC simulations when compared to those that do not present discretization, using prostate brachytherapy with Iodine-125 radionuclide as model. Simulations were carried out with 108 events with both types of sources to compare them using EGSnrc code associated to MASH phantom in orthostatic and supine positions with some anatomic adaptations. Significant alterations were found, especially regarding bladder, rectum and the prostate itself. It can be concluded that there is a need to discretized sources in brachytherapy simulations to ensure its representativeness. (author)
Pattern Recognition for a Flight Dynamics Monte Carlo Simulation
Restrepo, Carolina; Hurtado, John E.
2011-01-01
The design, analysis, and verification and validation of a spacecraft relies heavily on Monte Carlo simulations. Modern computational techniques are able to generate large amounts of Monte Carlo data but flight dynamics engineers lack the time and resources to analyze it all. The growing amounts of data combined with the diminished available time of engineers motivates the need to automate the analysis process. Pattern recognition algorithms are an innovative way of analyzing flight dynamics data efficiently. They can search large data sets for specific patterns and highlight critical variables so analysts can focus their analysis efforts. This work combines a few tractable pattern recognition algorithms with basic flight dynamics concepts to build a practical analysis tool for Monte Carlo simulations. Current results show that this tool can quickly and automatically identify individual design parameters, and most importantly, specific combinations of parameters that should be avoided in order to prevent specific system failures. The current version uses a kernel density estimation algorithm and a sequential feature selection algorithm combined with a k-nearest neighbor classifier to find and rank important design parameters. This provides an increased level of confidence in the analysis and saves a significant amount of time.
Monte-Carlo Simulations of Star Clusters; 1, First Results
Giersz, M
1998-01-01
A revision of Stodolkiewicz's Monte-Carlo code is used to simulate evolution of star clusters. The new method treats each superstar as a single star and follows the evolution and motion of all individual stellar objects. The first calculations for isolated, equal-mass N-body systems with three-body energy generation according to Spitzer's formulae show good agreement with direct N-body calculations for N=2000, 4096 and 10000 particles. The density, velocity, mass distributions, energy generation, number of binaries etc. follow the N-body results. Only the number of escapers is slightly too high compared to N-body results and there is no level off anisotropy for advanced post-collapse evolution of Monte-Carlo models as is seen in N-body simulations for N 10000 gravothermal oscillations are clearly visible. The calculations of N=2000, 4096, 10000, 32000 and 100000 models take about 2, 6, 20, 130 and 2500 hours, respectively. The Monte-Carlo code is at least 10^5 times faster than the N-body one for N=32768 wit...
Monte Carlo simulation for statistical decay of compound nucleus
International Nuclear Information System (INIS)
We perform Monte Carlo simulations for particle and γ-ray emissions from a compound nucleus based on the Hauser-Feshbach statistical theory; the Monte Carlo Hauser-Feshbach (MCHF) method. The MCHF calculation, which gives us correlated information between emitted particles and γ-rays, will be a powerful tool in many applications, because we are able to probe nuclear reactions in more microscopic way. For example, the MCHF code can be used as an event generator in a radiation transport code. Having the correlated neutron and γ-ray emission process in the transport calculations, energy conservation is satisfied automatically event-by-event. In addition, the correlations amongst particles and γ-ray can be a signature of a particular nuclear reaction occurred in a nuclear system. We have been developing the MCHF code, CGM, which solves the Hauser-Feshbach equation with the Monte Carlo method. The code includes all the common models that emerge in a standard Hauser-Feshbach code, namely the particle transmission generator, the level density module, interface to the discrete level database, and so on. The code allows to emit multiple neutrons, as long as the excitation energy of the compound nucleus is larger than the neutron separation energy. The γ-ray competition is always included at each compound decay stage, and the angular momentum conservation holds too. In this paper, we discuss our technique to calculate the particle and γ-ray correlations in the statistical model framework, and some simulation examples are shown
Monte Carlo Simulation for the Adsorption of Symmetric Triblock Copolymers
Institute of Scientific and Technical Information of China (English)
彭昌军; 李健康; 刘洪来; 胡英
2004-01-01
The adsorption behavior of symmetric triblock copolymers, Am/2BnAm/2, from a nonselective solvent at solid-liquid interface has been studied by Monte Carlo simulations on a simple lattice model. Either segment A or segment B is attractive, while the other is non-attractive to the surface. Influences of the adsorption energy,bulk concentration, chain composition and chain length on the microstructure of adsorbed layers are presented.The results show that the total surface coverage and the adsorption amount increases monotonically as the bulk concentration increases. The larger the adsorption energy and the higher the fraction of adsorbing segments, the higher the total surface coverage is exhibited. The product of surface coverage and the proportion of non-attractive segments are nearly independent of the chain length, and the logarithm of the adsorption amount is a linear function of the reciprocal of the reduced temperature. When the adsorption energy is larger, the adsorption amount exhibits a maximum as the fraction of adsorbing segment increases. The adsorption isotherms of copolymers with different length of non-attractive segments can be mapped onto a single curve under given adsorption energy. The adsorption layer thickness decreases as the adsorption energy and the fraction of adsorbing segments increases, but it increhses as the length of non-attractive segments increases. The tails mainly govern the adsorption layer thickness.
Optimization of reconstruction algorithms using Monte Carlo simulation
International Nuclear Information System (INIS)
A method for optimizing reconstruction algorithms is presented that is based on how well a specified task can be performed using the reconstructed images. Task performance is numerically assessed by a Monte Carlo simulation of the complete imaging process including the generation of scenes appropriate to the desired application, subsequent data taking, reconstruction, and performance of the stated task based on the final image. The use of this method is demonstrated through the optimization of the Algebraic Reconstruction Technique (ART), which reconstructs images from their projections by a iterative procedure. The optimization is accomplished by varying the relaxation factor employed in the updating procedure. In some of the imaging situations studied, it is found that the optimization of constrained ART, in which a nonnegativity constraint is invoked, can vastly increase the detectability of objects. There is little improvement attained for unconstrained ART. The general method presented may be applied to the problem of designing neutron-diffraction spectrometers. 11 refs., 6 figs., 2 tabs
Performance of three-photon PET imaging: Monte Carlo simulations
Kacperski, K; Kacperski, Krzysztof; Spyrou, Nicholas M.
2005-01-01
We have recently introduced the idea of making use of three-photon positron annihilations in positron emission tomography. In this paper the basic characteristics of the three-gamma imaging in PET are studied by means of Monte Carlo simulations and analytical computations. Two typical configurations of human and small animal scanners are considered. Three-photon imaging requires high energy resolution detectors. Parameters currently attainable by CdZnTe semiconductor detectors, the technology of choice for the future development of radiation imaging, are assumed. Spatial resolution is calculated as a function of detector energy resolution and size, position in the field of view, scanner size, and the energies of the three gamma annihilation photons. Possible ways to improve the spatial resolution obtained for nominal parameters: 1.5 cm and 3.2 mm FWHM for human and small animal scanners, respectively, are indicated. Counting rates of true and random three-photon events for typical human and small animal scann...
Performance of three-photon PET imaging: Monte Carlo simulations
Kacperski, Krzysztof; Spyrou, Nicholas M.
2005-12-01
We have recently introduced the idea of making use of three-photon positron annihilations in positron emission tomography. In this paper, the basic characteristics of the three-gamma imaging in PET are studied by means of Monte Carlo simulations and analytical computations. Two typical configurations of human and small animal scanners are considered. Three-photon imaging requires high-energy resolution detectors. Parameters currently attainable by CdZnTe semiconductor detectors, the technology of choice for the future development of radiation imaging, are assumed. Spatial resolution is calculated as a function of detector energy resolution and size, position in the field of view, scanner size and the energies of the three-gamma annihilation photons. Possible ways to improve the spatial resolution obtained for nominal parameters, 1.5 cm and 3.2 mm FWHM for human and small animal scanners, respectively, are indicated. Counting rates of true and random three-photon events for typical human and small animal scanning configurations are assessed. A simple formula for minimum size of lesions detectable in the three-gamma based images is derived. Depending on the contrast and total number of registered counts, lesions of a few mm size for human and sub mm for small animal scanners can be detected.
CloudMC: a cloud computing application for Monte Carlo simulation
Miras, H.; Jiménez, R.; Miras, C.; Gomà, C.
2013-04-01
This work presents CloudMC, a cloud computing application—developed in Windows Azure®, the platform of the Microsoft® cloud—for the parallelization of Monte Carlo simulations in a dynamic virtual cluster. CloudMC is a web application designed to be independent of the Monte Carlo code in which the simulations are based—the simulations just need to be of the form: input files → executable → output files. To study the performance of CloudMC in Windows Azure®, Monte Carlo simulations with penelope were performed on different instance (virtual machine) sizes, and for different number of instances. The instance size was found to have no effect on the simulation runtime. It was also found that the decrease in time with the number of instances followed Amdahl's law, with a slight deviation due to the increase in the fraction of non-parallelizable time with increasing number of instances. A simulation that would have required 30 h of CPU on a single instance was completed in 48.6 min when executed on 64 instances in parallel (speedup of 37 ×). Furthermore, the use of cloud computing for parallel computing offers some advantages over conventional clusters: high accessibility, scalability and pay per usage. Therefore, it is strongly believed that cloud computing will play an important role in making Monte Carlo dose calculation a reality in future clinical practice.
CloudMC: a cloud computing application for Monte Carlo simulation
International Nuclear Information System (INIS)
This work presents CloudMC, a cloud computing application—developed in Windows Azure®, the platform of the Microsoft® cloud—for the parallelization of Monte Carlo simulations in a dynamic virtual cluster. CloudMC is a web application designed to be independent of the Monte Carlo code in which the simulations are based—the simulations just need to be of the form: input files → executable → output files. To study the performance of CloudMC in Windows Azure®, Monte Carlo simulations with penelope were performed on different instance (virtual machine) sizes, and for different number of instances. The instance size was found to have no effect on the simulation runtime. It was also found that the decrease in time with the number of instances followed Amdahl's law, with a slight deviation due to the increase in the fraction of non-parallelizable time with increasing number of instances. A simulation that would have required 30 h of CPU on a single instance was completed in 48.6 min when executed on 64 instances in parallel (speedup of 37 ×). Furthermore, the use of cloud computing for parallel computing offers some advantages over conventional clusters: high accessibility, scalability and pay per usage. Therefore, it is strongly believed that cloud computing will play an important role in making Monte Carlo dose calculation a reality in future clinical practice. (note)
Monte Carlo simulation of positronium thermalization in gases
Directory of Open Access Journals (Sweden)
Marjanović Srđan D.
2010-01-01
Full Text Available In this paper we present the results of Monte Carlo simulations of positronium (Ps swarm thermalization in helium (He and water vapour. We have investigated the temporal evolution of energy and spatial parameters of the swarm and their sensitivity to the shape of the cross-section and the initial energy distribution. Positron anihilation spectroscopy (PAS and positron emission tomography (PET are techniques that depend on anihilation of positronium in materials and tissue. The results obtained point that the Monte Carlo technique shows good agreement with experimental results and is capable of accurately describing the behaviour of Ps particles including the energy, particle lifetime and the moment and location of the anihilation.
Fast Monte Carlo-assisted simulation of cloudy Earth backgrounds
Adler-Golden, Steven; Richtsmeier, Steven C.; Berk, Alexander; Duff, James W.
2012-11-01
A calculation method has been developed for rapidly synthesizing radiometrically accurate ultraviolet through longwavelengthinfrared spectral imagery of the Earth for arbitrary locations and cloud fields. The method combines cloudfree surface reflectance imagery with cloud radiance images calculated from a first-principles 3-D radiation transport model. The MCScene Monte Carlo code [1-4] is used to build a cloud image library; a data fusion method is incorporated to speed convergence. The surface and cloud images are combined with an upper atmospheric description with the aid of solar and thermal radiation transport equations that account for atmospheric inhomogeneity. The method enables a wide variety of sensor and sun locations, cloud fields, and surfaces to be combined on-the-fly, and provides hyperspectral wavelength resolution with minimal computational effort. The simulations agree very well with much more time-consuming direct Monte Carlo calculations of the same scene.
The MCLIB library: Monte Carlo simulation of neutron scattering instruments
International Nuclear Information System (INIS)
Monte Carlo is a method to integrate over a large number of variables. Random numbers are used to select a value for each variable, and the integrand is evaluated. The process is repeated a large number of times and the resulting values are averaged. For a neutron transport problem, first select a neutron from the source distribution, and project it through the instrument using either deterministic or probabilistic algorithms to describe its interaction whenever it hits something, and then (if it hits the detector) tally it in a histogram representing where and when it was detected. This is intended to simulate the process of running an actual experiment (but it is much slower). This report describes the philosophy and structure of MCLIB, a Fortran library of Monte Carlo subroutines which has been developed for design of neutron scattering instruments. A pair of programs (LQDGEOM and MC RUN) which use the library are shown as an example
Atomistic Kinetic Monte Carlo Simulations of Polycrystalline Copper Electrodeposition
Treeratanaphitak, Tanyakarn; Abukhdeir, Nasser Mohieddin
2014-01-01
A high-fidelity kinetic Monte Carlo (KMC) simulation method (T. Treeratanaphitak, M. Pritzker, N. M. Abukhdeir, Electrochim. Acta 121 (2014) 407--414) using the semi-empirical multi-body embedded-atom method (EAM) potential has been extended to model polycrystalline metal electrodeposition. The presented KMC-EAM method enables true three-dimensional atomistic simulations of electrodeposition over experimentally relevant timescales. Simulations using KMC-EAM are performed over a range of overpotentials to predict the effect on deposit texture evolution. Results show strong agreement with past experimental results both with respect to deposition rates on various copper surfaces and roughness-time power law behaviour. It is found that roughness scales with time $\\propto t^\\beta$ where $\\beta=0.62 \\pm 0.12$, which is in good agreement with past experimental results. Furthermore, the simulations provide insights into sub-surface deposit morphologies which are not directly accessible from experimental measurements.
Monte carlo simulation for designing an explosive-inspection system
International Nuclear Information System (INIS)
In order to optimize the design of γ-ray detectors and data analysis of the system for inspection of explosive with associated alpha particle technique, Monte Carlo code EGSnrc was used to simulated detection efficiency and response function of inorganic scintillator detector for γ-rays, aimed at choosing the right type detector. Pulse height spectra of γ-rays of φ5' x 8' NaI(Tl) from graphite, water, ammonium nitrate and simulated explosive induced by 14 MeV neutron were simulated. The calculated results were analyzed and compared with experiments results, demonstrating that simulation method is reliable and it can be used to obtain the database of response function for explosive inspection. (authors)
Research on Monte Carlo simulation method of industry CT system
International Nuclear Information System (INIS)
There are a series of radiation physical problems in the design and production of industry CT system (ICTS), including limit quality index analysis; the effect of scattering, efficiency of detectors and crosstalk to the system. Usually the Monte Carlo (MC) Method is applied to resolve these problems. Most of them are of little probability, so direct simulation is very difficult, and existing MC methods and programs can't meet the needs. To resolve these difficulties, particle flux point auto-important sampling (PFPAIS) is given on the basis of auto-important sampling. Then, on the basis of PFPAIS, a particular ICTS simulation method: MCCT is realized. Compared with existing MC methods, MCCT is proved to be able to simulate the ICTS more exactly and effectively. Furthermore, the effects of all kinds of disturbances of ICTS are simulated and analyzed by MCCT. To some extent, MCCT can guide the research of the radiation physical problems in ICTS. (author)
Accelerating particle-in-cell simulations using multilevel Monte Carlo
Ricketson, Lee
2015-11-01
Particle-in-cell (PIC) simulations have been an important tool in understanding plasmas since the dawn of the digital computer. Much more recently, the multilevel Monte Carlo (MLMC) method has accelerated particle-based simulations of a variety of systems described by stochastic differential equations (SDEs), from financial portfolios to porous media flow. The fundamental idea of MLMC is to perform correlated particle simulations using a hierarchy of different time steps, and to use these correlations for variance reduction on the fine-step result. This framework is directly applicable to the Langevin formulation of Coulomb collisions, as demonstrated in previous work, but in order to apply to PIC simulations of realistic scenarios, MLMC must be generalized to incorporate self-consistent evolution of the electromagnetic fields. We present such a generalization, with rigorous results concerning its accuracy and efficiency. We present examples of the method in the collisionless, electrostatic context, and discuss applications and extensions for the future.
Monte Carlo Simulation Of Emission Tomography And Other Medical Imaging Techniques
Harrison, Robert L.
2010-01-01
An introduction to Monte Carlo simulation of emission tomography. This paper reviews the history and principles of Monte Carlo simulation, then applies these principles to emission tomography using the public domain simulation package SimSET (a Simulation System for Emission Tomography) as an example. Finally, the paper discusses how the methods are modified for X-ray computed tomography and radiotherapy simulations.
Review of neutron noise analysis theory by Monte Carlo simulation
International Nuclear Information System (INIS)
Some debates on the theory of neutron noise analysis for reactor kinetic parameter measurement were found before 1970 but a report firmly clearing these debates has not been found, and a question was raised when neutron noise experiments for the TRIGA and HANARO reactors in Korea were performed. In order to clarify this question, the neutron noise experiment is simulated by the Monte Carlo method. This simulation confirms that the widely used equation is approximately valid and that the confusion was caused from the explanation on the derivation of the equation. Rossi-α technique is one of the representative methods of noise analyses for the reactor kinetic parameter measurement, but different opinions were raised for the chain reaction related term in the equation. The equation originally derived at the Los Alamos National Laboratory (LANL) has been widely accepted. However, the others were supported by strict mathematics and experiments as well, and the reason of discrepancy has not been clarified. Since it is the problem of basic concept before the effect of neutron energy or geometry is included, the Monte Carlo simulation for the simplest reactor model could clarify it. For this purpose, the experiment measuring the neutron noise is simulated, and it results that the original equation is approximately valid. However, it is judged that the explanation on the equation by the authors derived it for the first time is not so correct, but Orndoff who made the first experiment by the Ross-α technique explained it rather correctly
Modeling and Computer Simulation: Molecular Dynamics and Kinetic Monte Carlo
Energy Technology Data Exchange (ETDEWEB)
Wirth, B.D.; Caturla, M.J.; Diaz de la Rubia, T.
2000-10-10
Recent years have witnessed tremendous advances in the realistic multiscale simulation of complex physical phenomena, such as irradiation and aging effects of materials, made possible by the enormous progress achieved in computational physics for calculating reliable, yet tractable interatomic potentials and the vast improvements in computational power and parallel computing. As a result, computational materials science is emerging as an important complement to theory and experiment to provide fundamental materials science insight. This article describes the atomistic modeling techniques of molecular dynamics (MD) and kinetic Monte Carlo (KMC), and an example of their application to radiation damage production and accumulation in metals. It is important to note at the outset that the primary objective of atomistic computer simulation should be obtaining physical insight into atomic-level processes. Classical molecular dynamics is a powerful method for obtaining insight about the dynamics of physical processes that occur on relatively short time scales. Current computational capability allows treatment of atomic systems containing as many as 10{sup 9} atoms for times on the order of 100 ns (10{sup -7}s). The main limitation of classical MD simulation is the relatively short times accessible. Kinetic Monte Carlo provides the ability to reach macroscopic times by modeling diffusional processes and time-scales rather than individual atomic vibrations. Coupling MD and KMC has developed into a powerful, multiscale tool for the simulation of radiation damage in metals.
Energy Technology Data Exchange (ETDEWEB)
Park, M; Jung, H; Kim, G; Ji, Y; Kim, K; Park, S [Korea Institute of Radiological and Medical Sciences, Seoul, Nowon-gu (Korea, Republic of)
2014-06-01
Purpose: To estimate the three dimensional dose distributions in a polymer gel and a radiochromic gel by comparing with the virtual water phantom exposed to proton beams by applying Monte Carlo simulation. Methods: The polymer gel dosimeter is the compositeness material of gelatin, methacrylic acid, hydroquinone, tetrakis, and distilled water. The radiochromic gel is PRESAGE product. The densities of polymer and radiochromic gel were 1.040 and 1.0005 g/cm3, respectively. The shape of water phantom was a hexahedron with the size of 13 × 13 × 15 cm3. The proton beam energies of 72 and 116 MeV were used in the simulation. Proton beam was directed to the top of the phantom with Z-axis and the shape of beam was quadrangle with 10 × 10 cm2 dimension. The Percent depth dose and the dose distribution were evaluated for estimating the dose distribution of proton particle in two gel dosimeters, and compared with the virtual water phantom. Results: The Bragg-peak for proton particles in two gel dosimeters was similar to the virtual water phantom. Bragg-peak regions of polymer gel, radiochromic gel, and virtual water phantom were represented in the identical region (4.3 cm) for 72 MeV proton beam. For 116 MeV proton beam, the Bragg-peak regions of polymer gel, radiochromic gel, and virtual water phantom were represented in 9.9, 9.9 and 9.7 cm, respectively. The dose distribution of proton particles in polymer gel, radiochromic gel, and virtual water phantom was approximately identical in the case of 72 and 116 MeV energies. The errors for the simulation were under 10%. Conclusion: This work indicates the evaluation of three dimensional dose distributions by exposing proton particles to polymer and radiochromic gel dosimeter by comparing with the water phantom. The polymer gel and the radiochromic gel dosimeter show similar dose distributions for the proton beams.
Monte Carlo study of microdosimetric diamond detectors
International Nuclear Information System (INIS)
Ion-beam therapy provides a high dose conformity and increased radiobiological effectiveness with respect to conventional radiation-therapy. Strict constraints on the maximum uncertainty on the biological weighted dose and consequently on the biological weighting factor require the determination of the radiation quality, defined as the types and energy spectra of the radiation at a specific point. However the experimental determination of radiation quality, in particular for an internal target, is not simple and the features of ion interactions and treatment delivery require dedicated and optimized detectors. Recently chemical vapor deposition (CVD) diamond detectors have been suggested as ion-beam therapy microdosimeters. Diamond detectors can be manufactured with small cross sections and thin shapes, ideal to cope with the high fluence rate. However the sensitive volume of solid state detectors significantly deviates from conventional microdosimeters, with a diameter that can be up to 1000 times the height. This difference requires a redefinition of the concept of sensitive thickness and a deep study of the secondary to primary radiation, of the wall effects and of the impact of the orientation of the detector with respect to the radiation field. The present work intends to study through Monte Carlo simulations the impact of the detector geometry on the determination of radiation quality quantities, in particular on the relative contribution of primary and secondary radiation. The dependence of microdosimetric quantities such as the unrestricted linear energy L and the lineal energy y are investigated for different detector cross sections, by varying the particle type (carbon ions and protons) and its energy. (paper)
Numerical thermalization in particle-in-cell simulations with Monte-Carlo collisions
International Nuclear Information System (INIS)
Numerical thermalization in collisional one-dimensional (1D) electrostatic (ES) particle-in-cell (PIC) simulations was investigated. Two collision models, the pitch-angle scattering of electrons by the stationary ion background and large-angle collisions between the electrons and the neutral background, were included in the PIC simulation using Monte-Carlo methods. The numerical results show that the thermalization times in both models were considerably reduced by the additional Monte-Carlo collisions as demonstrated by comparisons with Turner's previous simulation results based on a head-on collision model [M. M. Turner, Phys. Plasmas 13, 033506 (2006)]. However, the breakdown of Dawson's scaling law in the collisional 1D ES PIC simulation is more complicated than that was observed by Turner, and the revised scaling law of the numerical thermalization time with numerical parameters are derived on the basis of the simulation results obtained in this study
Quantum Monte Carlo Simulations of Adulteration Effect on Bond Alternating Spin=1/2 Chain
Zhang, Peng; Xu, Zhaoxin; Ying, Heping; Dai, Jianhui; Crompton, Peter
The S=1/2 Heisenberg chain with bond alternation and randomness of antiferromagnetic (AFM) and ferromagnetic (FM) interactions is investigated by quantum Monte Carlo simulations of loop/cluster algorithm. Our results have shown interesting finite temperature magnetic properties of this model. The relevance of our study to former investigation results is discussed.
Performance analysis based on a Monte Carlo simulation of a liquid xenon PET detector
International Nuclear Information System (INIS)
Liquid xenon is a very attractive medium for position-sensitive gamma-ray detectors for a very wide range of applications, namely, in medical radionuclide imaging. Recently, the authors have proposed a liquid xenon detector for positron emission tomography (PET). In this paper, some aspects of the performance of a liquid xenon PET detector prototype were studied by means of Monte Carlo simulation
Blom, H.A.P.; Krystul, J.; Bakker, G.J.
2006-01-01
We study the problem of estimating small reachability probabilities for large scale stochastic hybrid processes through Sequential Monte Carlo (SMC) simulation. Recently, [Cerou et al., 2002, 2005] developed an SMC approach for diffusion processes, and referred to the resulting SMC algorithm as an I
Monte Carlo Simulation for Moderator of Compact D-T Neutron Generator
Institute of Scientific and Technical Information of China (English)
无
2011-01-01
In order to study the neutron moderation of D-T neutron generator, moderators with diffident materials and structures are predicted by Monte Carlo simulations. Neutron generator is simplified as the diameter 20 cm, length 25 cm cylinder. The target is very
Monte Carlo particle simulation and finite-element techniques for tandem mirror transport
International Nuclear Information System (INIS)
A description is given of numerical methods used in the study of axial transport in tandem mirrors owing to Coulomb collisions and rf diffusion. The methods are Monte Carlo particle simulations and direct solution to the Fokker-Planck equations by finite-element expansion. (author)
A Monte Carlo simulation model for stationary non-Gaussian processes
DEFF Research Database (Denmark)
Grigoriu, M.; Ditlevsen, Ove Dalager; Arwade, S. R.
2003-01-01
includes translation processes and is useful for both Monte Carlo simulation and analytical studies. As for translation processes, the mixture of translation processes can have a wide range of marginal distributions and correlation functions. Moreover, these processes can match a broader range of second...... athe proposed Monte Carlo algorithm and compare features of translation processes and mixture of translation processes. Keywords: Monte Carlo simulation, non-Gaussian processes, sampling theorem, stochastic processes, translation processes......A class of stationary non-Gaussian processes, referred to as the class of mixtures of translation processes, is defined by their finite dimensional distributions consisting of mixtures of finite dimensional distributions of translation processes. The class of mixtures of translation processes...
Monte Carlo Simulation Program from the World Petroleum Assessment 2000, DDS-60 (Emc2.xls).
U.S. Geological Survey, Department of the Interior — Monte Carlo programs described in chapter MC, Monte Carlo Simulation Method. Emc2.xls was the program used to calculate the estimates of undiscovered resources for...
Monte Carlo Simulation Program from the World Petroleum Assessment 2000, DDS-60 (Emc2.xls)
U.S. Geological Survey, Department of the Interior — Monte Carlo programs described in chapter MC, Monte Carlo Simulation Method. Emc2.xls was the program used to calculate the estimates of undiscovered resources for...
Mont Carlo Simulation Program from the World Petroleum Assessment 2000, DDS-60 (emcee.xls).xml
U.S. Geological Survey, Department of the Interior — Monte Carlo programs described in chapter MC, Monte Carlo Simulation Method. Emc2.xls was the program used to calculate the estimates of undiscovered resources for...
Mont Carlo Simulation Program from the World Petroleum Assessment 2000, DDS-60 (emcee.xls)
U.S. Geological Survey, Department of the Interior — Monte Carlo programs described in chapter MC, Monte Carlo Simulation Method. Emc2.xls was the program used to calculate the estimates of undiscovered resources for...
Vilches, M.; García-Pareja, S.; Guerrero, R.; Anguiano, M.; Lallena, A. M.
2007-09-01
When a therapeutic electron linear accelerator is simulated using a Monte Carlo (MC) code, the tuning of the initial spectra and the renormalization of dose (e.g., to maximum axial dose) constitute a common practice. As a result, very similar depth dose curves are obtained for different MC codes. However, if renormalization is turned off, the results obtained with the various codes disagree noticeably. The aim of this work is to investigate in detail the reasons of this disagreement. We have found that the observed differences are due to non-negligible differences in the angular scattering of the electron beam in very thin slabs of dense material (primary foil) and thick slabs of very low density material (air). To gain insight, the effects of the angular scattering models considered in various MC codes on the dose distribution in a water phantom are discussed using very simple geometrical configurations for the LINAC. The MC codes PENELOPE 2003, PENELOPE 2005, GEANT4, GEANT3, EGSnrc and MCNPX have been used.
International Nuclear Information System (INIS)
This paper presents results of the application Monte Carlo method to analyze data from the interaction of deuteron beams with metallic targets saturated with deuterium. The SRIM software was used to generate energy spectrum of ions passing the target. These spectra were used to calculate the neutron yields from dd reactions in energy range 7–12 keV of incident deuteron beams. The calculated outputs were compared with the experimental data for the determination of the electron screening potential for dd reactions. The calculations were performed using two different values of the beam energy spread (FWHM) equal 1% and 16%. It was shown that plasma beams with a relatively high spread (16%) were almost as good a tool as the traditional accelerator with mono-energy beam related to the study of the reaction within an ultra-low energy region. (author)
Bian, Liang; Shu, Yuan-Jie; Wang, Xin-Feng
2012-07-01
Amorphous and crystalline poly (chloro-p-xylylene) (PPX C) membranes are constructed by using a novel computational technique, that is, a combined method of NVT+NPT-molecular dynamics (MD) and gradually reducing the size (GRS) methods. The related free volumes are defined as homology clusters. Then the sorption and the permeation of gases in PPX C polymers are studied using grand canonical Monte Carlo (GCMC) and NVT-MD methods. The results show that the crystalline PPX C membranes provide smaller free volumes for absorbing or transferring gases relative to the amorphous PPX C area. The gas sorption in PPX C membranes mainly belongs to the physical one, and H bonds can appear obviously in the amorphous area. By cluster analyzing on the mean square displacement of gases, we find that gases walk along the x axis in the crystalline area and walk randomly in the amorphous area. The calculated permeability coefficients are close to the experimental data.
Monte Carlo simulations for design of the KFUPM PGNAA facility
Naqvi, A A; Maslehuddin, M; Kidwai, S
2003-01-01
Monte Carlo simulations were carried out to design a 2.8 MeV neutron-based prompt gamma ray neutron activation analysis (PGNAA) setup for elemental analysis of cement samples. The elemental analysis was carried out using prompt gamma rays produced through capture of thermal neutrons in sample nuclei. The basic design of the PGNAA setup consists of a cylindrical cement sample enclosed in a cylindrical high-density polyethylene moderator placed between a neutron source and a gamma ray detector. In these simulations the predominant geometrical parameters of the PGNAA setup were optimized, including moderator size, sample size and shielding of the detector. Using the results of the simulations, an experimental PGNAA setup was then fabricated at the 350 kV Accelerator Laboratory of this University. The design calculations were checked experimentally through thermal neutron flux measurements inside the PGNAA moderator. A test prompt gamma ray spectrum of the PGNAA setup was also acquired from a Portland cement samp...
Lanczos and Recursion Techniques for Multiscale Kinetic Monte Carlo Simulations
Energy Technology Data Exchange (ETDEWEB)
Rudd, R E; Mason, D R; Sutton, A P
2006-03-13
We review an approach to the simulation of the class of microstructural and morphological evolution involving both relatively short-ranged chemical and interfacial interactions and long-ranged elastic interactions. The calculation of the anharmonic elastic energy is facilitated with Lanczos recursion. The elastic energy changes affect the rate of vacancy hopping, and hence the rate of microstructural evolution due to vacancy mediated diffusion. The elastically informed hopping rates are used to construct the event catalog for kinetic Monte Carlo simulation. The simulation is accelerated using a second order residence time algorithm. The effect of elasticity on the microstructural development has been assessed. This article is related to a talk given in honor of David Pettifor at the DGP60 Workshop in Oxford.
Monte Carlo Simulation for Statistical Decay of Compound Nucleus
Directory of Open Access Journals (Sweden)
Chadwick M.B.
2012-02-01
Full Text Available We perform Monte Carlo simulations for neutron and γ-ray emissions from a compound nucleus based on the Hauser-Feshbach statistical theory. This Monte Carlo Hauser-Feshbach (MCHF method calculation, which gives us correlated information between emitted particles and γ-rays. It will be a powerful tool in many applications, as nuclear reactions can be probed in a more microscopic way. We have been developing the MCHF code, CGM, which solves the Hauser-Feshbach theory with the Monte Carlo method. The code includes all the standard models that used in a standard Hauser-Feshbach code, namely the particle transmission generator, the level density module, interface to the discrete level database, and so on. CGM can emit multiple neutrons, as long as the excitation energy of the compound nucleus is larger than the neutron separation energy. The γ-ray competition is always included at each compound decay stage, and the angular momentum and parity are conserved. Some calculations for a fission fragment 140Xe are shown as examples of the MCHF method, and the correlation between the neutron and γ-ray is discussed.
Monte Carlo simulation of quantum Zeno effect in the brain
Georgiev, Danko
2015-12-01
Environmental decoherence appears to be the biggest obstacle for successful construction of quantum mind theories. Nevertheless, the quantum physicist Henry Stapp promoted the view that the mind could utilize quantum Zeno effect to influence brain dynamics and that the efficacy of such mental efforts would not be undermined by environmental decoherence of the brain. To address the physical plausibility of Stapp's claim, we modeled the brain using quantum tunneling of an electron in a multiple-well structure such as the voltage sensor in neuronal ion channels and performed Monte Carlo simulations of quantum Zeno effect exerted by the mind upon the brain in the presence or absence of environmental decoherence. The simulations unambiguously showed that the quantum Zeno effect breaks down for timescales greater than the brain decoherence time. To generalize the Monte Carlo simulation results for any n-level quantum system, we further analyzed the change of brain entropy due to the mind probing actions and proved a theorem according to which local projections cannot decrease the von Neumann entropy of the unconditional brain density matrix. The latter theorem establishes that Stapp's model is physically implausible but leaves a door open for future development of quantum mind theories provided the brain has a decoherence-free subspace.
Monte Carlo simulation for simultaneous particle coagulation and deposition
Institute of Scientific and Technical Information of China (English)
ZHAO; Haibo; ZHENG; Chuguang
2006-01-01
The process of dynamic evolution in dispersed systems due to simultaneous particle coagulation and deposition is described mathematically by general dynamic equation (GDE). Monte Carlo (MC) method is an important approach of numerical solutions of GDE. However, constant-volume MC method exhibits the contradictory of low computation cost and high computation precision owing to the fluctuation of the number of simulation particles; constant-number MC method can hardly be applied to engineering application and general scientific quantitative analysis due to the continual contraction or expansion of computation domain. In addition, the two MC methods depend closely on the "subsystem" hypothesis, which constraints their expansibility and the scope of application. A new multi-Monte Carlo (MMC) method is promoted to take account of GDE for simultaneous particle coagulation and deposition. MMC method introduces the concept of "weighted fictitious particle" and is based on the "time-driven" technique. Furthermore MMC method maintains synchronously the computational domain and the total number of fictitious particles, which results in the latent expansibility of simulation for boundary condition, the space evolution of particle size distribution and even particle dynamics. The simulation results of MMC method for two special cases in which analytical solutions exist agree with analytical solutions well, which proves that MMC method has high and stable computational precision and low computation cost because of the constant and limited number of fictitious particles. Lastly the source of numerical error and the relative error of MMC method are analyzed, respectively.
Monte Carlo simulations of the Galileo energetic particle detector
International Nuclear Information System (INIS)
Monte Carlo radiation transport studies have been performed for the Galileo spacecraft energetic particle detector (EPD) in order to study its response to energetic electrons and protons. Three-dimensional Monte Carlo radiation transport codes, MCNP version 4B (for electrons) and MCNPX version 2.2.3 (for protons), were used throughout the study. The results are presented in the form of 'geometric factors' for the high-energy channels studied in this paper: B1, DC2, and DC3 for electrons and B0, DC0, and DC1 for protons. The geometric factor is the energy-dependent detector response function that relates the incident particle fluxes to instrument count rates. The trend of actual data measured by the EPD was successfully reproduced using the geometric factors obtained in this study
Anisotropic flows from colour strings: Monte-Carlo simulations
Braun, M A; Vechernin, V V
2012-01-01
By direct Monte-Carlo simulations it is shown that the anisotropic flows can be successfully described in the colour string picture with fusion and percolation provided anisotropy of particle emission from the fused string is taken into account. Quenching of produced particles in the strong colour field of the string is the basic mechanism for this anisotropy. The concrete realization of this mechanism is borrowed from the QED. Due to dependence of this mechanism on the external field strength the found flows grow with energy, with values for $v_2$ at LHC energies greater by ~15% than at RHIC energies.
Proceedings of the first symposium on Monte Carlo simulation
International Nuclear Information System (INIS)
The first symposium on Monte Carlo simulation was held at Mitsubishi Research Institute, Otemachi, Tokyo, on 10th and 11st of September, 1998. This symposium was organized by Nuclear Code Research Committee at Japan Atomic Energy Research Institute. In the sessions, were presented orally 21 papers on code development, parallel calculation, reactor physics, burn-up, criticality, shielding safety, dose evaluation, nuclear fusion reactor, thermonuclear fusion plasma, nuclear transmutation, electromagnetic cascade, fuel cycle facility. Those presented papers are compiled in this proceedings. The 21 of the presented papers are indexed individually. (J.P.N.)
Proceedings of the first symposium on Monte Carlo simulation
Energy Technology Data Exchange (ETDEWEB)
NONE
2001-01-01
The first symposium on Monte Carlo simulation was held at Mitsubishi Research Institute, Otemachi, Tokyo, on 10th and 11st of September, 1998. This symposium was organized by Nuclear Code Research Committee at Japan Atomic Energy Research Institute. In the sessions, were presented orally 21 papers on code development, parallel calculation, reactor physics, burn-up, criticality, shielding safety, dose evaluation, nuclear fusion reactor, thermonuclear fusion plasma, nuclear transmutation, electromagnetic cascade, fuel cycle facility. Those presented papers are compiled in this proceedings. The 21 of the presented papers are indexed individually. (J.P.N.)
Implict Monte Carlo Radiation Transport Simulations of Four Test Problems
Energy Technology Data Exchange (ETDEWEB)
Gentile, N
2007-08-01
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.
Monte Carlo simulation of the Tien-Shan effect
International Nuclear Information System (INIS)
Monte Carlo simulation of the Tien-Shan effect is carried out. Interaction between hadrons with the energy above 10 TeV and the nuclei of lead atoms with the cross sections ∼ 40% of inelastic interaction is shown to result in production of decaying (unstable) particles (Λc-baryon and D-meson), extracting the main share of interacting hadron energy. These particles production results in irregular energy dependence of the mean-free path for absorption of energy flux of hadron component of a wide atmosphere shower (Tien-Shan effect)
Monte Carlo simulation on backward steps of single kinesin molecule
Institute of Scientific and Technical Information of China (English)
Wang Hong; Zhang Yong; Dou Shuo-Xing; Wang Peng-Ye
2008-01-01
Kinesin is a stepping molecular motor travelling along the microtubule. It moves primarily in the plus end direction of the microtubule and occasionally in the minus-end, backward, direction. Recently, the backward steps of kinesin under different loads and temperatures start to attract interests, and the relations among them are revealed. This paper aims to theoretically understand these relations observed in experiments. After introducing a backward pathway into the previous model of the ATPase cycle of kinesin movement, the dependence of the backward movement on the load and the temperature is explored through Monte Carlo simulation. Our results agree well with previous experiments.
New electron multiple scattering distributions for Monte Carlo transport simulation
Energy Technology Data Exchange (ETDEWEB)
Chibani, Omar (Haut Commissariat a la Recherche (C.R.S.), 2 Boulevard Franz Fanon, Alger B.P. 1017, Alger-Gare (Algeria)); Patau, Jean Paul (Laboratoire de Biophysique et Biomathematiques, Faculte des Sciences Pharmaceutiques, Universite Paul Sabatier, 35 Chemin des Maraichers, 31062 Toulouse cedex (France))
1994-10-01
New forms of electron (positron) multiple scattering distributions are proposed. The first is intended for use in the conditions of validity of the Moliere theory. The second distribution takes place when the electron path is so short that only few elastic collisions occur. These distributions are adjustable formulas. The introduction of some parameters allows impositions of the correct value of the first moment. Only positive and analytic functions were used in constructing the present expressions. This makes sampling procedures easier. Systematic tests are presented and some Monte Carlo simulations, as benchmarks, are carried out. ((orig.))
Detention Pond Sediment Accumulation Prediction using Monte Carlo Simulation
Directory of Open Access Journals (Sweden)
Supiah Shamsudin
2012-01-01
Full Text Available Problem statement: A study in Malaysia had been carried out to predict the sediment accumulation in urban detention ponds. Suspended sediment is pollutant of primary concern to the river that results in adverse environmental effect. Detention pond becomes a practical approach to this problem. Suspended sediment that settled in stormwater detention pond, can bring effect to the detention pond functions. Questions were raised on how certain were the observed and predicted values of sediment depth and load accumulation estimations. Secondly the question was what the sediment accumulation be in the next 100 years. The uncertainties of sediments estimation vary greatly due to the hydrological variability and rainfall random nature obtain the relationship between flow discharge and suspended sediment rate using on-site data collection at UTM and Ledang Heights, Nusajaya. Predict accumulated sediment loads and depth from MUSLE over 10-100 years. Analyze the uncertainties of sediment loads and depth using Monte Carlo Simulation (MCS combining normal distribution. Obtain the maximum probability of occurrence of sediment loads and depth in the detention pond. Approach: Modified Universal Soil Loss Equation (MUSLE and Trap Efficiency (TE Method was applied to predict sediment accumulation. This uncertainty of sediment loads and depth was carried out using Monte Carlo Simulation (MCS Method. The water samples were collected for suspended solids data and other water quality parameters at Ledang Heights, Nusajaya, Johor and University Technology Malaysia (UTM, Johor. Sampling station were randomly selected at the inlet and outlet of the detention pond. The hydrological parameters such as flow and velocity were also collected. Results: The simulation results showed the maximum probability of occurrence value for observed sediment loads and sediment depth from Ledang Heights were 0.0062 tons (16.5% and 0.0005 mm (17.5% respectively. The maximum probability of
Monte Carlo simulation of a single detector unit for the neutron detector array NEDA
Jaworski, G.; Palacz, M.; Nyberg, Johan; De Angelis, G.; de France, G; Nitto, A. Di; Egea, J.; Erduran, M. N.; Ertürk, S.; Farnea, E.; Gadea, A.; V González; Gottardo, A.(Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Legnaro, Legnaro, I-35020, Italy); Hüyük, T.; Kownacki, J.
2012-01-01
A study of the dimensions and performance of a single detector of the future neutron detector array NEDA was performed by means of Monte Carlo simulations, using GEANT4. Two different liquid scintillators were evaluated: the hydrogen based BC501A and the deuterated BC537. The efficiency and the probability that one neutron will trigger a signal in more than one detector were investigated as a function of the detector size. The simulations were validated comparing the results to experimental m...
Monte Carlo simulation of the properties of an electromagnetic streamer tube calorimeter
Energy Technology Data Exchange (ETDEWEB)
Baumgart, R.; Grupen, C.; Meyer, H.J.; Schaefer, U.
1988-06-20
Saturation effects in an electromagnetic calorimeter with streamer tube readout have been studied by Monte Carlo simulations. Streamers produce temporary dead zones which remain insensitive to other particles within one event. The observed longitudinal shower profiles can be fitted by the results of simulations yielding a value for the width of the dead zone of delta = 1 mm. We attribute this relatively low value to the use of small sampling cells and a pure isobutane gas filling.
Monte Carlo simulation of the properties of an electromagnetic streamer tube calorimeter
International Nuclear Information System (INIS)
Saturation effects in an electromagnetic calorimeter with streamer tube readout have been studied by Monte Carlo simulations. Streamers produce temporary dead zones which remain insensitive to other particles within one event. The observed longitudinal shower profiles can be fitted by the results of simulations yielding a value for the width of the dead zone of δ = 1 mm. We attribute this relatively low value to the use of small sampling cells and a pure isobutane gas filling. (orig.)
International Nuclear Information System (INIS)
In this paper we present an optimization approach based on the combination of a Genetic Algorithms maximization procedure with a Monte Carlo simulation. The approach is applied within the context of plant logistic management for what concerns the choice of maintenance and repair strategies. A stochastic model of plant operation is developed from the standpoint of its reliability/availability behavior, i.e. of the failure/repair/maintenance processes of its components. The model is evaluated by Monte Carlo simulation in terms of economic costs and revenues of operation. The flexibility of the Monte Carlo method allows us to include several practical aspects such as stand-by operation modes, deteriorating repairs, aging, sequences of periodic maintenances, number of repair teams available for different kinds of repair interventions (mechanical, electronic, hydraulic, etc.), components priority rankings. A genetic algorithm is then utilized to optimize the components maintenance periods and number of repair teams. The fitness function object of the optimization is a profit function which inherently accounts for the safety and economic performance of the plant and whose value is computed by the above Monte Carlo simulation model. For an efficient combination of Genetic Algorithms and Monte Carlo simulation, only few hundreds Monte Carlo histories are performed for each potential solution proposed by the genetic algorithm. Statistical significance of the results of the solutions of interest (i.e. the best ones) is then attained exploiting the fact that during the population evolution the fit chromosomes appear repeatedly many times. The proposed optimization approach is applied on two case studies of increasing complexity
Benchmarking of proton transport in Super Monte Carlo simulation program
International Nuclear Information System (INIS)
Full text of the publication follows. The Monte Carlo (MC) method has been traditionally applied in nuclear design and analysis due to its capability of dealing with complicated geometries and multi-dimensional physics problems as well as obtaining accurate results. The Super Monte Carlo Simulation Program (SuperMC) is developed by FDS Team in China for fusion, fission, and other nuclear applications. The simulations of radiation transport, isotope burn-up, material activation, radiation dose, and biology damage could be performed using SuperMC. Complicated geometries and the whole physical process of various types of particles in broad energy scale can be well handled. Bi-directional automatic conversion between general CAD models and full-formed input files of SuperMC is supported by MCAM, which is a CAD/image-based automatic modeling program for neutronics and radiation transport simulation. Mixed visualization of dynamical 3D dataset and geometry model is supported by RVIS, which is a nuclear radiation virtual simulation and assessment system. Continuous-energy cross section data from hybrid evaluated nuclear data library HENDL are utilized to support simulation. Neutronic fixed source and critical design parameters calculates for reactors of complex geometry and material distribution based on the transport of neutron and photon have been achieved in our former version of SuperMC. Recently, the proton transport has also been integrated in SuperMC in the energy region up to 10 GeV. The physical processes considered for proton transport include electromagnetic processes and hadronic processes. The electromagnetic processes include ionization, multiple scattering, Bremsstrahlung, and pair production processes. Public evaluated data from HENDL are used in some electromagnetic processes. In hadronic physics, the Bertini intra-nuclear cascade model with excitons, preequilibrium model, nucleus explosion model, fission model, and evaporation model are incorporated to
Landry, Guillaume; Granton, Patrick V.; Reniers, Brigitte; Öllers, Michel C.; Beaulieu, Luc; Wildberger, Joachim E.; Verhaegen, Frank
2011-10-01
This work compares Monte Carlo (MC) dose calculations for 125I and 103Pd low-dose rate (LDR) brachytherapy sources performed in virtual phantoms containing a series of human soft tissues of interest for brachytherapy. The geometries are segmented (tissue type and density assignment) based on simulated single energy computed tomography (SECT) and dual energy (DECT) images, as well as the all-water TG-43 approach. Accuracy is evaluated by comparison to a reference MC dose calculation performed in the same phantoms, where each voxel's material properties are assigned with exactly known values. The objective is to assess potential dose calculation accuracy gains from DECT. A CT imaging simulation package, ImaSim, is used to generate CT images of calibration and dose calculation phantoms at 80, 120, and 140 kVp. From the high and low energy images electron density ρe and atomic number Z are obtained using a DECT algorithm. Following a correction derived from scans of the calibration phantom, accuracy on Z and ρe of ±1% is obtained for all soft tissues with atomic number Z in [6,8] except lung. GEANT4 MC dose calculations based on DECT segmentation agreed with the reference within ±4% for 103Pd, the most sensitive source to tissue misassignments. SECT segmentation with three tissue bins as well as the TG-43 approach showed inferior accuracy with errors of up to 20%. Using seven tissue bins in our SECT segmentation brought errors within ±10% for 103Pd. In general 125I dose calculations showed higher accuracy than 103Pd. Simulated image noise was found to decrease DECT accuracy by 3-4%. Our findings suggest that DECT-based segmentation yields improved accuracy when compared to SECT segmentation with seven tissue bins in LDR brachytherapy dose calculation for the specific case of our non-anthropomorphic phantom. The validity of our conclusions for clinical geometry as well as the importance of image noise in the tissue segmentation procedure deserves further
A Monte Carlo simulation of ion transport at finite temperatures
International Nuclear Information System (INIS)
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. (paper)
Quantifying the Effect of Undersampling in Monte Carlo Simulations Using SCALE
Energy Technology Data Exchange (ETDEWEB)
Perfetti, Christopher M [ORNL; Rearden, Bradley T [ORNL
2014-01-01
This study explores the effect of undersampling in Monte Carlo calculations on tally estimates and tally variance estimates for burnup credit applications. Steady-state Monte Carlo simulations were performed for models of several critical systems with varying degrees of spatial and isotopic complexity and the impact of undersampling on eigenvalue and flux estimates was examined. Using an inadequate number of particle histories in each generation was found to produce an approximately 100 pcm bias in the eigenvalue estimates, and biases that exceeded 10% in fuel pin flux estimates.
Monte Carlo computer simulation of sedimentation of charged hard spherocylinders
Energy Technology Data Exchange (ETDEWEB)
Viveros-Méndez, P. X., E-mail: xviveros@fisica.uaz.edu.mx; Aranda-Espinoza, S. [Unidad Académica de Física, Universidad Autónoma de Zacatecas, Calzada Solidaridad esq. Paseo, La Bufa s/n, 98060 Zacatecas, Zacatecas, México (Mexico); Gil-Villegas, Alejandro [Departamento de Ingeniería Física, División de Ciencias e Ingenierías, Campus León, Universidad de Guanajuato, Loma del Bosque 103, Lomas del Campestre, 37150 León, Guanajuato, México (Mexico)
2014-07-28
In this article we present a NVT Monte Carlo computer simulation study of sedimentation of an electroneutral mixture of oppositely charged hard spherocylinders (CHSC) with aspect ratio L/σ = 5, where L and σ are the length and diameter of the cylinder and hemispherical caps, respectively, for each particle. This system is an extension of the restricted primitive model for spherical particles, where L/σ = 0, and it is assumed that the ions are immersed in an structureless solvent, i.e., a continuum with dielectric constant D. The system consisted of N = 2000 particles and the Wolf method was implemented to handle the coulombic interactions of the inhomogeneous system. Results are presented for different values of the strength ratio between the gravitational and electrostatic interactions, Γ = (mgσ)/(e{sup 2}/Dσ), where m is the mass per particle, e is the electron's charge and g is the gravitational acceleration value. A semi-infinite simulation cell was used with dimensions L{sub x} ≈ L{sub y} and L{sub z} = 5L{sub x}, where L{sub x}, L{sub y}, and L{sub z} are the box dimensions in Cartesian coordinates, and the gravitational force acts along the z-direction. Sedimentation effects were studied by looking at every layer formed by the CHSC along the gravitational field. By increasing Γ, particles tend to get more packed at each layer and to arrange in local domains with an orientational ordering along two perpendicular axis, a feature not observed in the uncharged system with the same hard-body geometry. This type of arrangement, known as tetratic phase, has been observed in two-dimensional systems of hard-rectangles and rounded hard-squares. In this way, the coupling of gravitational and electric interactions in the CHSC system induces the arrangement of particles in layers, with the formation of quasi-two dimensional tetratic phases near the surface.
CORPORATE VALUATION USING TWO-DIMENSIONAL MONTE CARLO SIMULATION
Directory of Open Access Journals (Sweden)
Toth Reka
2010-12-01
Full Text Available In this paper, we have presented a corporate valuation model. The model combine several valuation methods in order to get more accurate results. To determine the corporate asset value we have used the Gordon-like two-stage asset valuation model based on the calculation of the free cash flow to the firm. We have used the free cash flow to the firm to determine the corporate market value, which was calculated with use of the Black-Scholes option pricing model in frame of the two-dimensional Monte Carlo simulation method. The combined model and the use of the two-dimensional simulation model provides a better opportunity for the corporate value estimation.
A Transport Condensed History Algorithm for Electron Monte Carlo Simulations
International Nuclear Information System (INIS)
An advanced multiple scattering algorithm for the Monte Carlo simulation of electron transport problems is developed. Unlike established multiple scattering algorithms, this new method, called transport condensed history (TCH), is a true transport process - it simulates a transport equation that approximates the exact Boltzmann transport process. In addition to having a larger mean free path and a more isotropic scattering operator than the Boltzmann equation, the approximate transport equation also preserves the zeroth- and first-order angular moments of the exact equation. These features enable TCH to accurately predict electron position as a function of energy (path length) and to move particles across material boundaries and interfaces with acceptable accuracy and efficiency. Numerical results and dose calculations are shown to reveal the advantages of TCH over conventional condensed history schemes
Treatment planning in radiosurgery: parallel Monte Carlo simulation software
Energy Technology Data Exchange (ETDEWEB)
Scielzo, G. [Galliera Hospitals, Genova (Italy). Dept. of Hospital Physics; Grillo Ruggieri, F. [Galliera Hospitals, Genova (Italy) Dept. for Radiation Therapy; Modesti, M.; Felici, R. [Electronic Data System, Rome (Italy); Surridge, M. [University of South Hampton (United Kingdom). Parallel Apllication Centre
1995-12-01
The main objective of this research was to evaluate the possibility of direct Monte Carlo simulation for accurate dosimetry with short computation time. We made us of: graphics workstation, linear accelerator, water, PMMA and anthropomorphic phantoms, for validation purposes; ionometric, film and thermo-luminescent techniques, for dosimetry; treatment planning system for comparison. Benchmarking results suggest that short computing times can be obtained with use of the parallel version of EGS4 that was developed. Parallelism was obtained assigning simulation incident photons to separate processors, and the development of a parallel random number generator was necessary. Validation consisted in: phantom irradiation, comparison of predicted and measured values good agreement in PDD and dose profiles. Experiments on anthropomorphic phantoms (with inhomogeneities) were carried out, and these values are being compared with results obtained with the conventional treatment planning system.
Monte Carlo simulation of electrical corona discharge in air
Energy Technology Data Exchange (ETDEWEB)
Settaouti, A.; Settaouti, L. [Electrotechnic Department, University of Sciences and Technology, P.O. Box 1505, El-M' naouar, Oran (Algeria)
2011-01-15
Electrical discharges play a key role in technologies; there are many industrial applications where the corona discharge is used. Air as insulator is probably the best compromise solution for many applications. All of this reflects on the great importance of the evaluation of the corona performance characteristics. Numerical simulation of the corona discharge helps to better understand the involved phenomena and optimize the corona devices. This paper is aimed at calculating the corona discharge in negative point-plane air gaps. To describe the non-equilibrium behavior of the electronic avalanches and to simulate the development of corona discharge the method of Monte Carlo has been used. This model provides the spatial-temporal local field and particles charged densities variations as well as the ionization front velocity. (author)
Treatment planning in radiosurgery: parallel Monte Carlo simulation software
International Nuclear Information System (INIS)
The main objective of this research was to evaluate the possibility of direct Monte Carlo simulation for accurate dosimetry with short computation time. We made us of: graphics workstation, linear accelerator, water, PMMA and anthropomorphic phantoms, for validation purposes; ionometric, film and thermo-luminescent techniques, for dosimetry; treatment planning system for comparison. Benchmarking results suggest that short computing times can be obtained with use of the parallel version of EGS4 that was developed. Parallelism was obtained assigning simulation incident photons to separate processors, and the development of a parallel random number generator was necessary. Validation consisted in: phantom irradiation, comparison of predicted and measured values good agreement in PDD and dose profiles. Experiments on anthropomorphic phantoms (with inhomogeneities) were carried out, and these values are being compared with results obtained with the conventional treatment planning system
Neutronic analysis of the PULSTAR reactor using Monte Carlo simulations
International Nuclear Information System (INIS)
Neutronic analysis of the PULSTAR nuclear reactor was performed in support of its utilization and power upgrade from 1-MWth to 2-MWth. The PULSTAR is an open pool research reactor that is currently fueled with UO2 enriched to 4% in U-235. Detailed models were constructed of its core using the MCNP6 Monte Carlo code and its standard nuclear data libraries. The models covered all eight variations of the core starting with the first critical core in 1972 to the current core that was configured in 2011. Three dimensional heterogeneous models were constructed that faithfully reflected the geometry of the core and its surroundings using the original as-built engineering drawings. The Monte Carlo simulations benefited extensively from measurements that were performed upon the loading of each core and its subsequent operation. This includes power distribution and peaking measurements, depletion measurements (reflecting a core's excess reactivity), and measurements of reactivity feedback coefficients. Furthermore, to support the PULSTAR's fuel needs, the simulations explored the utilization of locally existing inventory of fresh UO2 fuel that is enriched to 6% in U-235. The analysis shows reasonable agreement between the results of the MCNP6 simulations and the available measured data. In general, most discrepancies between simulations and measurements may be attributed to the limited knowledge of the exact conditions of the historical measurements and the procedures used to analyze the measured data. Nonetheless, the results indicate the ability of the constructed models to support safety analysis and licensing action in relation to the on-going upgrades of the PULSTAR reactor. (author)
Neutron-induced semiconductor soft error simulation using the PHITS Monte Carlo simulator
International Nuclear Information System (INIS)
We have performed a neutron-induced soft error simulation using the PHITS Monte Carlo simulator. We validated our technique by comparing the MBGR (Modified Burst Generation Rate) values estimated by our simulation and a well known MBGR table by Fujitsu Laboratories, Ltd. We also evaluated a neutron-induced soft error rate of a SRAM cell as a function of the critical charge as well as a representation using a generally used unit, FIT rate [error/109 hour/device]. (author)
Three-Dimensional Electron Microscopy Simulation with the CASINO Monte Carlo Software
Demers, Hendrix; Poirier-Demers, Nicolas; Couture, Alexandre Réal; Joly, Dany; Guilmain, Marc; de Jonge, Niels; Drouin, Dominique
2011-01-01
Monte Carlo softwares are widely used to understand the capabilities of electron microscopes. To study more realistic applications with complex samples, 3D Monte Carlo softwares are needed. In this paper, the development of the 3D version of CASINO is presented. The software feature a graphical user interface, an efficient (in relation to simulation time and memory use) 3D simulation model, accurate physic models for electron microscopy applications, and it is available freely to the scientific community at this website: www.gel.usherbrooke.ca/casino/index.html. It can be used to model backscattered, secondary, and transmitted electron signals as well as absorbed energy. The software features like scan points and shot noise allow the simulation and study of realistic experimental conditions. This software has an improved energy range for scanning electron microscopy and scanning transmission electron microscopy applications. PMID:21769885
Monte Carlo simulation of gamma ray tomography for image reconstruction
International Nuclear Information System (INIS)
The Monte Carlo simulations of known density and shape object was validate with Gamma Ray Tomography in static experiments. An aluminum half-moon piece placed inside a steel pipe was the MC simulation test object that was also measured by means of gamma ray transmission. Wall effect of the steel pipe due to irradiation geometry in a single pair source-detector tomography was evaluated by comparison with theoretical data. MCNPX code requires a defined geometry to each photon trajectory which practically prevents this usage for tomography reconstruction simulation. The solution was found by writing a program in Delphi language to create input files automation code. Simulations of tomography data by automated MNCPX code were carried out and validated by experimental data. Working in this sequence the produced data needed a databank to be stored. Experimental setup used a Cesium-137 isotopic radioactive source (7.4 × 109 Bq), and NaI(Tl) scintillation detector of (51 × 51) × 10−3 m crystal size coupled to a multichannel analyzer. A stainless steel tubes of 0,154 m internal diameter, 0.014 m thickness wall. The results show that the MCNPX simulation code adapted to automated input file is useful for generating a matrix data M(θ,t), of a computerized gamma ray tomography for any known density and regular shape object. Experimental validation used RMSE from gamma ray paths and from attenuation coefficient data. (author)
Monte Carlo simulation of x-ray spectra in mammography
International Nuclear Information System (INIS)
A model for generating x-ray spectra in mammography is presented. This model used the ITS version 3 Monte Carlo code for simulating the radiation transport. Various target/filter combinations such as tungsten/aluminium, molybdenum/molybdenum, molybdenum/rhodium and rhodium/rhodium were used in the simulation. Both bremsstrahlung and characteristic x-ray production were included in the model. The simulated x-ray emission spectra were compared with two sets of spectra, those of Boone et al (1997 Med. Phys. 24 1863-74) and IPEM report 78. The χ2 test was used for the overall goodness of fit of the spectral data. There is good agreement between the simulated x-ray spectra and the comparison spectra as the test yielded a probability value of nearly 1. When the transmitted x-ray spectra for specific target/filter combinations were generated and compared with a measured molybdenum/rhodium spectrum and spectra generated in IPEM report 78, close agreement is also observed. This was demonstrated by the probability value for the χ2 test being almost 1 for all the cases. However, minor differences between the simulated spectra and the 'standard' ones are observed. (author)
Monte Carlo simulation of x-ray spectra in mammography
Energy Technology Data Exchange (ETDEWEB)
Ng, K.P. [Department of Optometry and Radiography, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong (China). E-mail: benngkp at netvigator.com; Kwok, C.S.; Ng, K.P.; Tang, F.H. [Department of Optometry and Radiography, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong (China)
2000-05-01
A model for generating x-ray spectra in mammography is presented. This model used the ITS version 3 Monte Carlo code for simulating the radiation transport. Various target/filter combinations such as tungsten/aluminium, molybdenum/molybdenum, molybdenum/rhodium and rhodium/rhodium were used in the simulation. Both bremsstrahlung and characteristic x-ray production were included in the model. The simulated x-ray emission spectra were compared with two sets of spectra, those of Boone et al (1997 Med. Phys. 24 1863-74) and IPEM report 78. The {chi}{sup 2} test was used for the overall goodness of fit of the spectral data. There is good agreement between the simulated x-ray spectra and the comparison spectra as the test yielded a probability value of nearly 1. When the transmitted x-ray spectra for specific target/filter combinations were generated and compared with a measured molybdenum/rhodium spectrum and spectra generated in IPEM report 78, close agreement is also observed. This was demonstrated by the probability value for the {chi}{sup 2} test being almost 1 for all the cases. However, minor differences between the simulated spectra and the 'standard' ones are observed. (author)
Monte Carlo simulation of gamma ray tomography for image reconstruction
Energy Technology Data Exchange (ETDEWEB)
Guedes, Karlos A.N.; Moura, Alex; Dantas, Carlos; Melo, Silvio; Lima, Emerson, E-mail: karlosguedes@hotmail.com [Universidade Federal de Pernambuco (UFPE), Recife, PE (Brazil); Meric, Ilker [University of Bergen (Norway)
2015-07-01
The Monte Carlo simulations of known density and shape object was validate with Gamma Ray Tomography in static experiments. An aluminum half-moon piece placed inside a steel pipe was the MC simulation test object that was also measured by means of gamma ray transmission. Wall effect of the steel pipe due to irradiation geometry in a single pair source-detector tomography was evaluated by comparison with theoretical data. MCNPX code requires a defined geometry to each photon trajectory which practically prevents this usage for tomography reconstruction simulation. The solution was found by writing a program in Delphi language to create input files automation code. Simulations of tomography data by automated MNCPX code were carried out and validated by experimental data. Working in this sequence the produced data needed a databank to be stored. Experimental setup used a Cesium-137 isotopic radioactive source (7.4 × 109 Bq), and NaI(Tl) scintillation detector of (51 × 51) × 10−3 m crystal size coupled to a multichannel analyzer. A stainless steel tubes of 0,154 m internal diameter, 0.014 m thickness wall. The results show that the MCNPX simulation code adapted to automated input file is useful for generating a matrix data M(θ,t), of a computerized gamma ray tomography for any known density and regular shape object. Experimental validation used RMSE from gamma ray paths and from attenuation coefficient data. (author)
Energy Technology Data Exchange (ETDEWEB)
Menezes, Claudio J.M.; Lima, Ricardo de A.; Peixoto, Joao E. [Centro Regional de Ciencias Nucleares (CRCN/CNEN-PE), Recife, PE (Brazil)]. E-mails: cjmm@cnen.gov.br; ralima@cnen.gov.br; joao.e.peixoto@uol.com.br; Vieira, Jose W. [Centro Federal de Educacao Tecnologica de Pernambuco (CEFETPE), Recife, PE (Brazil)]. E-mail: jwvieira@br.inter.net
2007-07-01
The development of fast and more powerful computers, combined with techniques for data processing, makes the Monte Carlo methods one of the most widely used tools in the radiation transport area. For applications in radiodiagnostic, these methods generally use anthropomorphic phantoms for to evaluate the absorbed dose to patients during exposure. This work used an exposure computational model CDO/EGS4 for a testing device designed for intra-oral X-ray equipment performance evaluation. The developed model was utilized for studying the positioning, dimensions and materials used in the manufacture of the testing device. The Odontologic Dosimetric Card (CDO) will be utilized in quality assurance programs in order to guarantee that the equipment fulfill the requirements of the Norm SVS no. 453/98 MS 'Diretrizes de Protecao Radiologica em Radiodiagnostico Medico e Odontologico'. The results obtained for the study of the absorbing medium and copper filters dimension used in the determination of the kVp did not they show significant differences. (author)
A Fast Monte Carlo Simulation for the International Linear Collider Detector
International Nuclear Information System (INIS)
The following paper contains details concerning the motivation for, implementation and performance of a Java-based fast Monte Carlo simulation for a detector designed to be used in the International Linear Collider. This simulation, presently included in the SLAC ILC group's org.lcsim package, reads in standard model or SUSY events in STDHEP file format, stochastically simulates the blurring in physics measurements caused by intrinsic detector error, and writes out an LCIO format file containing a set of final particles statistically similar to those that would have found by a full Monte Carlo simulation. In addition to the reconstructed particles themselves, descriptions of the calorimeter hit clusters and tracks that these particles would have produced are also included in the LCIO output. These output files can then be put through various analysis codes in order to characterize the effectiveness of a hypothetical detector at extracting relevant physical information about an event. Such a tool is extremely useful in preliminary detector research and development, as full simulations are extremely cumbersome and taxing on processor resources; a fast, efficient Monte Carlo can facilitate and even make possible detector physics studies that would be very impractical with the full simulation by sacrificing what is in many cases inappropriate attention to detail for valuable gains in time required for results
Monte Carlo Molecular Simulation with Isobaric-Isothermal and Gibbs-NPT Ensembles
Du, Shouhong
2012-05-01
This thesis presents Monte Carlo methods for simulations of phase behaviors of Lennard-Jones fluids. The isobaric-isothermal (NPT) ensemble and Gibbs-NPT ensemble are introduced in detail. NPT ensemble is employed to determine the phase diagram of pure component. The reduced simulation results are verified by comparison with the equation of state by by Johnson et al. and results with L-J parameters of methane agree considerably with the experiment measurements. We adopt the blocking method for variance estimation and error analysis of the simulation results. The relationship between variance and number of Monte Carlo cycles, error propagation and Random Number Generator performance are also investigated. We review the Gibbs-NPT ensemble employed for phase equilibrium of binary mixture. The phase equilibrium is achieved by performing three types of trial move: particle displacement, volume rearrangement and particle transfer. The simulation models and the simulation details are introduced. The simulation results of phase coexistence for methane and ethane are reported with comparison of the experimental data. Good agreement is found for a wide range of pressures. The contribution of this thesis work lies in the study of the error analysis with respect to the Monte Carlo cycles and number of particles in some interesting aspects.
International Nuclear Information System (INIS)
with a lower MDL than that of for example liquid scintillation method with a number of advantages. The results are presented and discussed. - Highlights: ► A new passive detection method is introduced for efficient radon measurements in water. ► Method is based on alpha tracks of radon/progeny in CR-39 in a non-polar medium above water. ► Sensitivity was enhanced (>80 times) relative to water by radon/progeny detected in hexane. ► Monte Carlo simulation was applied to determine CR-39 sensitivity to radon/progeny in water. ► The method has a number of advantages with MDL lower than alternative wide-scale methods
PhyloSim - Monte Carlo simulation of sequence evolution in the R statistical computing environment
Directory of Open Access Journals (Sweden)
Massingham Tim
2011-04-01
Full Text Available Abstract Background The Monte Carlo simulation of sequence evolution is routinely used to assess the performance of phylogenetic inference methods and sequence alignment algorithms. Progress in the field of molecular evolution fuels the need for more realistic and hence more complex simulations, adapted to particular situations, yet current software makes unreasonable assumptions such as homogeneous substitution dynamics or a uniform distribution of indels across the simulated sequences. This calls for an extensible simulation framework written in a high-level functional language, offering new functionality and making it easy to incorporate further complexity. Results PhyloSim is an extensible framework for the Monte Carlo simulation of sequence evolution, written in R, using the Gillespie algorithm to integrate the actions of many concurrent processes such as substitutions, insertions and deletions. Uniquely among sequence simulation tools, PhyloSim can simulate arbitrarily complex patterns of rate variation and multiple indel processes, and allows for the incorporation of selective constraints on indel events. User-defined complex patterns of mutation and selection can be easily integrated into simulations, allowing PhyloSim to be adapted to specific needs. Conclusions Close integration with R and the wide range of features implemented offer unmatched flexibility, making it possible to simulate sequence evolution under a wide range of realistic settings. We believe that PhyloSim will be useful to future studies involving simulated alignments.
International Nuclear Information System (INIS)
Amorphous and crystalline poly (chloro-p-xylylene) (PPX C) membranes are constructed by using a novel computational technique, that is, a combined method of NVT+NPT-molecular dynamics (MD) and gradually reducing the size (GRS) methods. The related free volumes are defined as homology clusters. Then the sorption and the permeation of gases in PPX C polymers are studied using grand canonical Monte Carlo (GCMC) and NVT-MD methods. The results show that the crystalline PPX C membranes provide smaller free volumes for absorbing or transferring gases relative to the amorphous PPX C area. The gas sorption in PPX C membranes mainly belongs to the physical one, and H bonds can appear obviously in the amorphous area. By cluster analyzing on the mean square displacement of gases, we find that gases walk along the x axis in the crystalline area and walk randomly in the amorphous area. The calculated permeability coefficients are close to the experimental data. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)
Construction of the quantitative analysis environment using Monte Carlo simulation
International Nuclear Information System (INIS)
The thoracic phantom image was acquisitioned of the axial section to construct maps of the source and density with Monte Carlo (MC) simulation. The phantom was Heart/Liver Type HL (Kyoto Kagaku Co., Ltd.) single photon emission CT (SPECT)/CT machine was Symbia T6 (Siemence) with the collimator LMEGP (low-medium energy general purpose). Maps were constructed from CT images with an in-house software using Visual studio C Sharp (Microsoft). The code simulation of imaging nuclear detectors (SIMIND) was used for MC simulation, Prominence processor (Nihon Medi-Physics) for filter processing and image reconstruction, and the environment DELL Precision T7400 for all image processes. For the actual experiment, the phantom was given 15 MBq of 99mTc assuming the uptake 2% at the dose of 740 MBq in its myocardial portion and SPECT image was acquisitioned and reconstructed with Butter-worth filter and filter back projection method. CT images were similarly obtained in 0.3 mm thick slices, which were filed in one formatted with digital imaging and communication in medicine (DICOM), and then processed for application to SIMIND for mapping the source and density. Physical and mensuration factors were examined in ideal images by sequential exclusion and simulation of those factors as attenuation, scattering, spatial resolution deterioration and statistical fluctuation. Gamma energy spectrum, SPECT projection and reconstructed images given by the simulation were found to well agree with the actual data, and the precision of MC simulation was confirmed. Physical and mensuration factors were found to be evaluable individually, suggesting the usefulness of the simulation for assessing the precision of their correction. (T.T.)
Monte Carlo simulation of the TRIGA mark 2 criticality experiment
International Nuclear Information System (INIS)
The criticality analysis of the TRIGA-2 bench-mark experiment at the Musashi Institute of Technology Research Reactor (MuITR, 100 kW) was performed by the three-dimensional continuous-energy Monte Carlo code (MCNP4A). To minimize errors due to an inexact geometry model, all fresh fuel and control rods as well as vicinity of the core were precisely modeled. Core multiplication factors (Keff) in the initial core critical experiment and in the excess reactivity adjustment for the several fuel-loading patterns as well as the fuel element reactivity worth distributions were used in the validation process of the physical model and neutron cross section data from the ENDF/B-V evaluation. The calculated Keff overestimated the experimental data by 1.0% for both the initial core and the several fuel-loading arrangements (fuel or graphite element was added only to the outer-ring), but the discrepancy increased to 1.8% for the some fuel-loading patterns (graphite element was positioned in the inner-ring). The comparison result of the fuel element worth distribution showed above tendency. Al in all, the agreement between the MCNP predictions and the experimentally determined values is good, which indicates that the Monte Carlo model is enough to simulate criticality of the TRIGA-2 reactor. (author)
Monte Carlo simulation of the spear reflectometer at LANSCE
International Nuclear Information System (INIS)
The Monte Carlo instrument simulation code, MCLIB, contains elements to represent several components found in neutron spectrometers including slits, choppers, detectors, sources and various samples. Using these elements to represent the components of a neutron scattering instrument, one can simulate, for example, an inelastic spectrometer, a small angle scattering machine, or a reflectometer. In order to benchmark the code, we chose to compare simulated data from the MCLIB code with an actual experiment performed on the SPEAR reflectometer at LANSCE. This was done by first fitting an actual SPEAR data set to obtain the model scattering-length-density profile, Β(z), for the sample and the substrate. Then these parameters were used as input values for the sample scattering function. A simplified model of SPEAR was chosen which contained all of the essential components of the instrument. A code containing the MCLIB subroutines was then written to simulate this simplified instrument. The resulting data was then fit and compared to the actual data set in terms of the statistics, resolution and accuracy
Learning About Ares I from Monte Carlo Simulation
Hanson, John M.; Hall, Charlie E.
2008-01-01
This paper addresses Monte Carlo simulation analyses that are being conducted to understand the behavior of the Ares I launch vehicle, and to assist with its design. After describing the simulation and modeling of Ares I, the paper addresses the process used to determine what simulations are necessary, and the parameters that are varied in order to understand how the Ares I vehicle will behave in flight. Outputs of these simulations furnish a significant group of design customers with data needed for the development of Ares I and of the Orion spacecraft that will ride atop Ares I. After listing the customers, examples of many of the outputs are described. Products discussed in this paper include those that support structural loads analysis, aerothermal analysis, flight control design, failure/abort analysis, determination of flight performance reserve, examination of orbit insertion accuracy, determination of the Upper Stage impact footprint, analysis of stage separation, analysis of launch probability, analysis of first stage recovery, thrust vector control and reaction control system design, liftoff drift analysis, communications analysis, umbilical release, acoustics, and design of jettison systems.
Modelling laser light propagation in thermoplastics using Monte Carlo simulations
Parkinson, Alexander
Laser welding has great potential as a fast, non-contact joining method for thermoplastic parts. In the laser transmission welding of thermoplastics, light passes through a semi-transparent part to reach the weld interface. There, it is absorbed as heat, which causes melting and subsequent welding. The distribution and quantity of light reaching the interface are important for predicting the quality of a weld, but are experimentally difficult to estimate. A model for simulating the path of this laser light through these light-scattering plastic parts has been developed. The technique uses a Monte-Carlo approach to generate photon paths through the material, accounting for absorption, scattering and reflection between boundaries in the transparent polymer. It was assumed that any light escaping the bottom surface contributed to welding. The photon paths are then scaled according to the input beam profile in order to simulate non-Gaussian beam profiles. A method for determining the 3 independent optical parameters to accurately predict transmission and beam power distribution at the interface was established using experimental data for polycarbonate at 4 different glass fibre concentrations and polyamide-6 reinforced with 20% long glass fibres. Exit beam profiles and transmissions predicted by the simulation were found to be in generally good agreement (R2>0.90) with experimental measurements. The simulations allowed the prediction of transmission and power distributions at other thicknesses as well as information on reflection, energy absorption and power distributions at other thicknesses for these materials.
Monte Carlo simulations of luminescence processes under quasi-equilibrium (QE) conditions
International Nuclear Information System (INIS)
Previous researchers have carried out Monte Carlo simulations of thermoluminescence (TL) phenomena by considering the allowed transitions of charge carriers between the conduction band, electron traps and recombination centers. Such simulations have demonstrated successfully the effect of trap clustering on the kinetics of charge carriers in a solid, and showed that trap clustering can significantly change the observed luminescence properties. While such Monte Carlo simulations have been carried out for TL, there has been no such trap clustering studies for optically stimulated luminescence phenomena (OSL). This paper presents a simplified method of carrying out Monte Carlo simulations for TL and linearly modulated optically stimulated luminescence (LM-OSL) phenomena, based on the General One Trap (GOT) model, which is a special case of the one trap one recombination center model (OTOR) when quasi-equilibrium conditions (QE) hold. The simulated results show that the presence of small clusters consisting of a few traps in a solid can lead to multiple peaks in both the TL and LM-OSL signals. The effects of retrapping and degree of trap filling are simulated for such multi-peak luminescence signals, and insight is obtained into the mechanism producing these peaks. The method presented in this paper can be easily generalized for other types of luminescence solids in which the recombination probability varies with time. - Highlights: • A simplified Monte Carlo method for TL and OSL is presented. • Method is based on General One Trap model, and quasi-equilibrium conditions. • Small clusters of a few traps can lead to multiple peaks in TL and LM-OSL signals. • Effects of retrapping and degree of trap filling are simulated
Measurement and Monte Carlo simulation of 6 MV X-rays for small radiation fields
International Nuclear Information System (INIS)
In order to obtain basic data for treatment plan in radiosurgery, we measured small fields of 6 MV X-rays and compared the measured data with our Monte Carlo simulations for the small fields. The small fields of 1.0, 2.0 and 3.0 cm in diameter were used in this study. Percentage depth dose (PDD) and beam profiles of those fields were measured and calculated. A small semiconductor detector, water phantoms, and a remote control system were used for the measurement. Monte Carlo simulations were performed using the EGS4 code with the input data prepared for the energy distribution of 6MV X-rays, beam divergence, circular fields and the geometry of the water phantoms. In the case of PDD values, the calculated values were lower than the measured values for all fields and depths, with the differences being 0.3 to 5.7% at the depths of 2.0 to 20.0 cm and 0.0 to 8.9% at the surface regions. As a result of the analysis of beam profiles for all field sizes at a depth of 10cm in water phantom, the measured 90% dose widths were in good agreement with the calculated values, however, the calculated penumbra radii were 0.1cm shorter than measured values. The measured PDDs and beam profiles agreement with the Monte Carlo calculations approximately. However, it is different when it comes to calculations in the area of phantom surface and penumbra because the Monte Carlo calculations were performed under the simplified geometries. Therefore, we have to study how to include the actual geometries and more precise data for the field area in Monte Carlo calculations. The Monte Carlo calculations will be used as a useful tool for the very complicated conditions in measurement and verification
OPTIMIZATION OF THE HYSPEC DESIGN USING MONTE CARLO SIMULATIONS.
Energy Technology Data Exchange (ETDEWEB)
GHOSH, V.J.; HAGEN, M.E.; LEONHARDT, W.J.; ZALIZNYAK, I.; SHAPIRO, S.M.; PASSELL, L.
2005-04-25
HYSPEC is a direct geometry spectrometer to be installed at the SNS [1] on beamline 14B where it will view a cryogenic coupled hydrogen moderator, The ''hybrid'' design combines time-of-flight spectroscopy with focusing Bragg optics to provide a high monochromatic flux on small single crystal samples, with a very low background at an extended detector bank. The instrument is optimized for an incident energy range of 3-90meV. It will have a medium energy resolution (2-10%) and will provide a flux on sample of the order of 10{sup 6}-10{sup 7} neutrons/s-cm{sup 2}. The spectrometer will be located in a satellite building outside the SNS experimental hall at the end of a 35m curved supermirror guide. A straight-slotted Fermi chopper will be used to monochromate the neutron beam and to determine the burst width. The 15cm high, 4cm wide beam will be focused onto a 2cm by 2cm area at the sample position using Bragg reflection from one of two crystal arrays. For unpolarized neutron studies these will be Highly Oriented Pyrolitic graphite crystals while for polarized neutron studies these will be replaced with Heusler alloy crystals. These focusing crystal arrays will be placed in a drum shield similar to those used for triple axis spectrometers. Hyspec will have a movable detector bank housing 160 position sensitive detectors. This detector bank will pivot about the sample axis. It will have a radius of 4.5m, a horizontal range of 60{sup o}, and a vertical range of {+-} 7.5{sup o}. In order to reduce background at the detector bank both a curved guide and a T0 chopper will be used. A bank of 20 supermirror bender polarization analyzers [2] will be used to spatially separate the polarized neutrons in the scattered beam so that both scattered neutron spin states can be measured simultaneously. The results of Monte Carlo simulations performed to optimize the instrument design will be discussed.
International Nuclear Information System (INIS)
Highlights: • The subdivision combines both advantages of uniform and non-uniform schemes. • The grid models were proved to be more efficient than traditional CSG models. • Monte Carlo simulation performance was enhanced by Optimal Spatial Subdivision. • Efficiency gains were obtained for realistic whole reactor core models. - Abstract: Geometry navigation is one of the key aspects of dominating Monte Carlo particle transport simulation performance for large-scale whole reactor models. In such cases, spatial subdivision is an easily-established and high-potential method to improve the run-time performance. In this study, a dedicated method, named Optimal Spatial Subdivision, is proposed for generating numerically optimal spatial grid models, which are demonstrated to be more efficient for geometry navigation than traditional Constructive Solid Geometry (CSG) models. The method uses a recursive subdivision algorithm to subdivide a CSG model into non-overlapping grids, which are labeled as totally or partially occupied, or not occupied at all, by CSG objects. The most important point is that, at each stage of subdivision, a conception of quality factor based on a cost estimation function is derived to evaluate the qualities of the subdivision schemes. Only the scheme with optimal quality factor will be chosen as the final subdivision strategy for generating the grid model. Eventually, the model built with the optimal quality factor will be efficient for Monte Carlo particle transport simulation. The method has been implemented and integrated into the Super Monte Carlo program SuperMC developed by FDS Team. Testing cases were used to highlight the performance gains that could be achieved. Results showed that Monte Carlo simulation runtime could be reduced significantly when using the new method, even as cases reached whole reactor core model sizes
Stochastic resonance phenomenon in Monte Carlo simulations of silver adsorbed on gold
Gimenez, María Cecilia
2016-03-01
The possibility of observing the stochastic resonance phenomenon was analyzed by means of Monte Carlo simulations of silver adsorbed on 100 gold surfaces. The coverage degree was studied as a function of the periodical variation of the chemical potential. The signal-noise relationship was studied as a function of the amplitude and frequency of chemical potential and temperature. When this value is plotted as a function of temperature, a maximum is found, indicating the possible presence of stochastic resonance.
Quantum Monte Carlo study of the protonated water dimer
Dagrada, Mario; Saitta, Antonino M; Sorella, Sandro; Mauri, Francesco
2013-01-01
We report an extensive theoretical study of the protonated water dimer (Zundel ion) by means of the highly correlated variational Monte Carlo and lattice regularized Monte Carlo approaches. This system represents the simplest model for proton transfer (PT) and a correct description of its properties is essential in order to understand the PT mechanism in more complex acqueous systems. Our Jastrow correlated AGP wave function ensures an accurate treatment of electron correlations. Exploiting the advantages of contracting the primitive basis set over atomic hybrid orbitals, we are able to limit dramatically the number of variational parameters with a systematic control on the numerical precision, crucial in order to simulate larger systems. We investigate energetics and geometrical properties of the Zundel ion as a function of the oxygen-oxygen distance, taken as reaction coordinate. In both cases, our QMC results are found in excellent agreement with coupled cluster CCSD(T) technique, the quantum chemistry "go...
Residual entropy of ice III from Monte Carlo simulation.
Kolafa, Jiří
2016-03-28
We calculated the residual entropy of ice III as a function of the occupation probabilities of hydrogen positions α and β assuming equal energies of all configurations. To do this, a discrete ice model with Bjerrum defect energy penalty and harmonic terms to constrain the occupation probabilities was simulated by the Metropolis Monte Carlo method for a range of temperatures and sizes followed by thermodynamic integration and extrapolation to N = ∞. Similarly as for other ices, the residual entropies are slightly higher than the mean-field (no-loop) approximation. However, the corrections caused by fluctuation of energies of ice samples calculated using molecular models of water are too large for accurate determination of the chemical potential and phase equilibria. PMID:27036463
Monte Carlo simulations of medium-scale CMB anisotropy
Kogut, A J
1996-01-01
Recent detections of cosmic microwave background (CMB) anisotropy at half-degree angular scales show considerable scatter in the reported amplitude even at similar angular resolution. We use Monte Carlo techniques to simulate the current set of medium-scale CMB observations, including all relevant aspects of sky coverage and measurement technique. The scatter in the reported amplitudes is well within the range expected for the standard cold dark matter (CDM) cosmological model, and results primarily from the restricted sky coverage of each experiment. Within the context of standard CDM current observations of CMB anisotropy support the detection of a ``Doppler peak'' in the CMB power spectrum consistent with baryon density 0.01 < Omega_b < 0.13 (95% confidence) for Hubble constant H_0 = 50 km/s/Mpc. The uncertainties are approximately evenly divided between instrument noise and cosmic variance arising from the limited sky coverage.
Monte Carlo simulations of air showers in atmospheric electric fields
Buitink, S; Falcke, H; Heck, D; Kuijpers, J
2009-01-01
The development of cosmic ray air showers can be influenced by atmospheric electric fields. Under fair weather conditions these fields are small, but the strong fields inside thunderstorms can have a significant effect on the electromagnetic component of a shower. Understanding this effect is particularly important for radio detection of air showers, since the radio emission is produced by the shower electrons and positrons. We perform Monte Carlo simulations to calculate the effects of different electric field configurations on the shower development. We find that the electric field becomes important for values of the order of 1 kV/cm. Not only can the energy distribution of electrons and positrons change significantly for such field strengths, it is also possible that runaway electron breakdown occurs at high altitudes, which is an important effect in lightning initiation.
Monte Carlo simulations of landmine detection using neutron backscattering imaging
Energy Technology Data Exchange (ETDEWEB)
Datema, Cor P. E-mail: c.datema@iri.tudelft.nl; Bom, Victor R.; Eijk, Carel W.E. van
2003-11-01
Neutron backscattering is a technique that has successfully been applied to the detection of non-metallic landmines. Most of the effort in this field has concentrated on single detectors that are scanned across the soil. Here, two new approaches are presented in which a two-dimensional image of the hydrogen distribution in the soil is made. The first method uses an array of position-sensitive {sup 3}He-tubes that is placed in close proximity of the soil. The second method is based on coded aperture imaging. Here, thermal neutrons from the soil are projected onto a detector which is typically placed one to several meters above the soil. Both methods use a pulsed D/D neutron source. The Monte Carlo simulation package GEANT 4 was used to investigate the performance of both imaging systems.
Monte Carlo simulations of gases adsorbed within nanopores
Trasca, Raluca A.; Mercedes Calbi, M.; Cole, Milton W.
2003-03-01
Condensation of gases within nanopores is different from bulk condensation because of the role of confinement including reduced dimensionality. For a typical range of nanotube radii, the adsorption may take place on two different sites (corresponding to different interaction energies with the nanopore), which we call shell and axial sites. Thus, we model the shell and axial adatoms as interacting species, and employ both a lattice gas model and Monte Carlo simulations to find their corresponding adsorption isotherms and specific heat. We compare these results with exact results at T=0 and with mean field results at finite T, obtained in a previous paper (1,*). 1. Raluca A. Trasca, M. Mercedes Calbi and Milton W. Cole, PRE 65, 061607 (2002) * This research is supported by the Petroleum Research of the American Chemical Society.
Monte Carlo simulations of random non-commutative geometries
Barrett, John W.; Glaser, Lisa
2016-06-01
Random non-commutative geometries are introduced by integrating over the space of Dirac operators that form a spectral triple with a fixed algebra and Hilbert space. The cases with the simplest types of Clifford algebra are investigated using Monte Carlo simulations to compute the integrals. Various qualitatively different types of behaviour of these random Dirac operators are exhibited. Some features are explained in terms of the theory of random matrices but other phenomena remain mysterious. Some of the models with a quartic action of symmetry-breaking type display a phase transition. Close to the phase transition the spectrum of a typical Dirac operator shows manifold-like behaviour for the eigenvalues below a cut-off scale.
Monte Carlo simulations of random non-commutative geometries
Barrett, John W
2015-01-01
Random non-commutative geometries are introduced by integrating over the space of Dirac operators that form a spectral triple with a fixed algebra and Hilbert space. The cases with the simplest types of Clifford algebra are investigated using Monte Carlo simulations to compute the integrals. Various qualitatively different types of behaviour of these random Dirac operators are exhibited. Some features are explained in terms of the theory of random matrices but other phenomena remain mysterious. Some of the models with a quartic action of symmetry-breaking type display a phase transition. Close to the phase transition the spectrum of a typical Dirac operator shows manifold-like behaviour for the eigenvalues below a cut-off scale.
Optimization of Monte Carlo transport simulations in stochastic media
International Nuclear Information System (INIS)
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)
The Monte Carlo simulation of the absorbed dose in quartz
Energy Technology Data Exchange (ETDEWEB)
Chen Shaowen [School of Physics Science and Engineering, Sun Yat-Sen University, Guangzhou, Guangdong 510275 (China) and Electron Engineering Department, Dongguan University of Technology, Dongguan 523808 (China)], E-mail: siumon@163.com; Liu Xiaowei; Zhang Chunxiang; Tang Qiang [School of Physics Science and Engineering, Sun Yat-Sen University, Guangzhou, Guangdong 510275 (China)
2009-05-15
Regeneration irradiation is a necessary procedure in TL or OSL dating protocol. The accuracy of measuring the absorbed dose is one of the important factors in dating. Since a beta source is often used in the regeneration irradiation process, the size of the quartz sample, pressure of nitrogen gas and the material of the sample holder may cause significant uncertainties in delivering the absorbed dose. In this work, the effects of the size of the quartz sample, the pressure of nitrogen gas and the material of the sample holder are simulated using the Monte Carlo method, and the uncertainties are discussed in these cases. The results show that they need to be considered in the dating.
Monte Carlo simulations for optimization of neutron shielding concrete
Piotrowski, Tomasz; Tefelski, Dariusz; Polański, Aleksander; Skubalski, Janusz
2012-06-01
Concrete is one of the main materials used for gamma and neutron shielding. While in case of gamma rays an increase in density is usually efficient enough, protection against neutrons is more complex. The aim of this paper is to show the possibility of using the Monte Carlo codes for evaluation and optimization of concrete mix to reach better neutron shielding. Two codes (MCNPX and SPOT — written by authors) were used to simulate neutron transport through a wall made of different concretes. It is showed that concrete of higher compressive strength attenuates neutrons more effectively. The advantage of heavyweight concrete (with barite aggregate), usually used for gamma shielding, over the ordinary concrete was not so clear. Neutron shielding depends on many factors e.g. neutron energy, barrier thickness and atomic composition. All this makes a proper design of concrete as a very important issue for nuclear power plant safety assurance.
Characterization of parallel-hole collimator using Monte Carlo Simulation
International Nuclear Information System (INIS)
Accuracy of in vivo activity quantification improves after the correction of penetrated and scattered photons. However, accurate assessment is not possible with physical experiment. We have used Monte Carlo Simulation to accurately assess the contribution of penetrated and scattered photons in the photopeak window. Simulations were performed with Simulation of Imaging Nuclear Detectors Monte Carlo Code. The simulations were set up in such a way that it provides geometric, penetration, and scatter components after each simulation and writes binary images to a data file. These components were analyzed graphically using Microsoft Excel (Microsoft Corporation, USA). Each binary image was imported in software (ImageJ) and logarithmic transformation was applied for visual assessment of image quality, plotting profile across the center of the images and calculating full width at half maximum (FWHM) in horizontal and vertical directions. The geometric, penetration, and scatter at 140 keV for low-energy general-purpose were 93.20%, 4.13%, 2.67% respectively. Similarly, geometric, penetration, and scatter at 140 keV for low-energy high-resolution (LEHR), medium-energy general-purpose (MEGP), and high-energy general-purpose (HEGP) collimator were (94.06%, 3.39%, 2.55%), (96.42%, 1.52%, 2.06%), and (96.70%, 1.45%, 1.85%), respectively. For MEGP collimator at 245 keV photon and for HEGP collimator at 364 keV were 89.10%, 7.08%, 3.82% and 67.78%, 18.63%, 13.59%, respectively. Low-energy general-purpose and LEHR collimator is best to image 140 keV photon. HEGP can be used for 245 keV and 364 keV; however, correction for penetration and scatter must be applied if one is interested to quantify the in vivo activity of energy 364 keV. Due to heavy penetration and scattering, 511 keV photons should not be imaged with HEGP collimator
Monte Carlo simulation of MOSFET dosimeter for electron backscatter using the GEANT4 code.
Chow, James C L; Leung, Michael K K
2008-06-01
The aim of this study is to investigate the influence of the body of the metal-oxide-semiconductor field effect transistor (MOSFET) dosimeter in measuring the electron backscatter from lead. The electron backscatter factor (EBF), which is defined as the ratio of dose at the tissue-lead interface to the dose at the same point without the presence of backscatter, was calculated by the Monte Carlo simulation using the GEANT4 code. Electron beams with energies of 4, 6, 9, and 12 MeV were used in the simulation. It was found that in the presence of the MOSFET body, the EBFs were underestimated by about 2%-0.9% for electron beam energies of 4-12 MeV, respectively. The trend of the decrease of EBF with an increase of electron energy can be explained by the small MOSFET dosimeter, mainly made of epoxy and silicon, not only attenuated the electron fluence of the electron beam from upstream, but also the electron backscatter generated by the lead underneath the dosimeter. However, this variation of the EBF underestimation is within the same order of the statistical uncertainties as the Monte Carlo simulations, which ranged from 1.3% to 0.8% for the electron energies of 4-12 MeV, due to the small dosimetric volume. Such small EBF deviation is therefore insignificant when the uncertainty of the Monte Carlo simulation is taken into account. Corresponding measurements were carried out and uncertainties compared to Monte Carlo results were within +/- 2%. Spectra of energy deposited by the backscattered electrons in dosimetric volumes with and without the lead and MOSFET were determined by Monte Carlo simulations. It was found that in both cases, when the MOSFET body is either present or absent in the simulation, deviations of electron energy spectra with and without the lead decrease with an increase of the electron beam energy. Moreover, the softer spectrum of the backscattered electron when lead is present can result in a reduction of the MOSFET response due to stronger
Monte Carlo simulation of photon way in clinical laser therapy
Ionita, Iulian; Voitcu, Gabriel
2011-07-01
The multiple scattering of light can increase efficiency of laser therapy of inflammatory diseases enlarging the treated area. The light absorption is essential for treatment while scattering dominates. Multiple scattering effects must be introduced using the Monte Carlo method for modeling light transport in tissue and finally to calculate the optical parameters. Diffuse reflectance measurements were made on high concentrated live leukocyte suspensions in similar conditions as in-vivo measurements. The results were compared with the values determined by MC calculations, and the latter have been adjusted to match the specified values of diffuse reflectance. The principal idea of MC simulations applied to absorption and scattering phenomena is to follow the optical path of a photon through the turbid medium. The concentrated live cell solution is a compromise between homogeneous layer as in MC model and light-live cell interaction as in-vivo experiments. In this way MC simulation allow us to compute the absorption coefficient. The values of optical parameters, derived from simulation by best fitting of measured reflectance, were used to determine the effective cross section. Thus we can compute the absorbed radiation dose at cellular level.
Monte Carlo simulations for design of the KFUPM PGNAA facility
Energy Technology Data Exchange (ETDEWEB)
Naqvi, A.A. E-mail: aanaqvi@kfupm.edu.sa; Nagadi, M.M.; Khateeb-ur-Rehman; Maslehuddin, M.; Kidwai, S
2003-02-01
Monte Carlo simulations were carried out to design a 2.8 MeV neutron-based prompt gamma ray neutron activation analysis (PGNAA) setup for elemental analysis of cement samples. The elemental analysis was carried out using prompt gamma rays produced through capture of thermal neutrons in sample nuclei. The basic design of the PGNAA setup consists of a cylindrical cement sample enclosed in a cylindrical high-density polyethylene moderator placed between a neutron source and a gamma ray detector. In these simulations the predominant geometrical parameters of the PGNAA setup were optimized, including moderator size, sample size and shielding of the detector. Using the results of the simulations, an experimental PGNAA setup was then fabricated at the 350 kV Accelerator Laboratory of this University. The design calculations were checked experimentally through thermal neutron flux measurements inside the PGNAA moderator. A test prompt gamma ray spectrum of the PGNAA setup was also acquired from a Portland cement sample, using a pulsed beam of 2.8 MeV neutrons. Prompt gamma ray peaks due to the calcium, silicon and iron content of the Portland cement were detected.
Monte Carlo simulations for design of the KFUPM PGNAA facility
International Nuclear Information System (INIS)
Monte Carlo simulations were carried out to design a 2.8 MeV neutron-based prompt gamma ray neutron activation analysis (PGNAA) setup for elemental analysis of cement samples. The elemental analysis was carried out using prompt gamma rays produced through capture of thermal neutrons in sample nuclei. The basic design of the PGNAA setup consists of a cylindrical cement sample enclosed in a cylindrical high-density polyethylene moderator placed between a neutron source and a gamma ray detector. In these simulations the predominant geometrical parameters of the PGNAA setup were optimized, including moderator size, sample size and shielding of the detector. Using the results of the simulations, an experimental PGNAA setup was then fabricated at the 350 kV Accelerator Laboratory of this University. The design calculations were checked experimentally through thermal neutron flux measurements inside the PGNAA moderator. A test prompt gamma ray spectrum of the PGNAA setup was also acquired from a Portland cement sample, using a pulsed beam of 2.8 MeV neutrons. Prompt gamma ray peaks due to the calcium, silicon and iron content of the Portland cement were detected
Monte Carlo simulation of transport from an electrothermal vaporizer
International Nuclear Information System (INIS)
Monte Carlo simulations were developed to elucidate the time and spatial distribution of analyte during the transport process from an electrothermal vaporizer to an inductively coupled plasma. A time-of-flight mass spectrometer was employed to collect experimental data that was compared with the simulated transient signals. Consideration was given to analyte transport as gaseous species as well as aerosol particles. In the case of aerosols, the simulation assumed formation of 5 nm particles and used the Einstein-Stokes equation to estimate the aerosol's diffusion coefficient, which was ca. 1% of the value for free atom diffusion. Desorption conditions for Cu that had been previously elucidated for electrothermal atomic absorption spectrometry were employed for the release processes from the electrothermal vaporizer. The primary distinguishing feature in the output signal to differentiate between gas and aerosol transport was a pronounced, long lived signal after the transient peak if aerosols were transported. Time and spatial distributions of particles within the transport system are presented. This characteristic was supported by independent atomic absorption measurements using a heated (or unheated) quartz T-tube with electrothermal vaporizer introduction
Improving computational efficiency of Monte Carlo simulations with variance reduction
International Nuclear Information System (INIS)
CCFE perform Monte-Carlo transport simulations on large and complex tokamak models such as ITER. Such simulations are challenging since streaming and deep penetration effects are equally important. In order to make such simulations tractable, both variance reduction (VR) techniques and parallel computing are used. It has been found that the application of VR techniques in such models significantly reduces the efficiency of parallel computation due to 'long histories'. VR in MCNP can be accomplished using energy-dependent weight windows. The weight window represents an 'average behaviour' of particles, and large deviations in the arriving weight of a particle give rise to extreme amounts of splitting being performed and a long history. When running on parallel clusters, a long history can have a detrimental effect on the parallel efficiency - if one process is computing the long history, the other CPUs complete their batch of histories and wait idle. Furthermore some long histories have been found to be effectively intractable. To combat this effect, CCFE has developed an adaptation of MCNP which dynamically adjusts the WW where a large weight deviation is encountered. The method effectively 'de-optimises' the WW, reducing the VR performance but this is offset by a significant increase in parallel efficiency. Testing with a simple geometry has shown the method does not bias the result. This 'long history method' has enabled CCFE to significantly improve the performance of MCNP calculations for ITER on parallel clusters, and will be beneficial for any geometry combining streaming and deep penetration effects. (authors)
Scalable Metropolis Monte Carlo for simulation of hard shapes
Anderson, Joshua A.; Eric Irrgang, M.; Glotzer, Sharon C.
2016-07-01
We design and implement a scalable hard particle Monte Carlo simulation toolkit (HPMC), and release it open source as part of HOOMD-blue. HPMC runs in parallel on many CPUs and many GPUs using domain decomposition. We employ BVH trees instead of cell lists on the CPU for fast performance, especially with large particle size disparity, and optimize inner loops with SIMD vector intrinsics on the CPU. Our GPU kernel proposes many trial moves in parallel on a checkerboard and uses a block-level queue to redistribute work among threads and avoid divergence. HPMC supports a wide variety of shape classes, including spheres/disks, unions of spheres, convex polygons, convex spheropolygons, concave polygons, ellipsoids/ellipses, convex polyhedra, convex spheropolyhedra, spheres cut by planes, and concave polyhedra. NVT and NPT ensembles can be run in 2D or 3D triclinic boxes. Additional integration schemes permit Frenkel-Ladd free energy computations and implicit depletant simulations. In a benchmark system of a fluid of 4096 pentagons, HPMC performs 10 million sweeps in 10 min on 96 CPU cores on XSEDE Comet. The same simulation would take 7.6 h in serial. HPMC also scales to large system sizes, and the same benchmark with 16.8 million particles runs in 1.4 h on 2048 GPUs on OLCF Titan.
Monte Carlo simulation of transport from an electrothermal vaporizer
Energy Technology Data Exchange (ETDEWEB)
Holcombe, James A. [Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, TX 78712 (United States)]. E-mail: holcombe@mail.utexas.edu; Ertas, Gulay [Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, TX 78712 (United States)
2006-06-15
Monte Carlo simulations were developed to elucidate the time and spatial distribution of analyte during the transport process from an electrothermal vaporizer to an inductively coupled plasma. A time-of-flight mass spectrometer was employed to collect experimental data that was compared with the simulated transient signals. Consideration was given to analyte transport as gaseous species as well as aerosol particles. In the case of aerosols, the simulation assumed formation of 5 nm particles and used the Einstein-Stokes equation to estimate the aerosol's diffusion coefficient, which was ca. 1% of the value for free atom diffusion. Desorption conditions for Cu that had been previously elucidated for electrothermal atomic absorption spectrometry were employed for the release processes from the electrothermal vaporizer. The primary distinguishing feature in the output signal to differentiate between gas and aerosol transport was a pronounced, long lived signal after the transient peak if aerosols were transported. Time and spatial distributions of particles within the transport system are presented. This characteristic was supported by independent atomic absorption measurements using a heated (or unheated) quartz T-tube with electrothermal vaporizer introduction.
Monte Carlo simulations of intensity profiles for energetic particle propagation
Tautz, R. C.; Bolte, J.; Shalchi, A.
2016-02-01
Aims: Numerical test-particle simulations are a reliable and frequently used tool for testing analytical transport theories and predicting mean-free paths. The comparison between solutions of the diffusion equation and the particle flux is used to critically judge the applicability of diffusion to the stochastic transport of energetic particles in magnetized turbulence. Methods: A Monte Carlo simulation code is extended to allow for the generation of intensity profiles and anisotropy-time profiles. Because of the relatively low number density of computational particles, a kernel function has to be used to describe the spatial extent of each particle. Results: The obtained intensity profiles are interpreted as solutions of the diffusion equation by inserting the diffusion coefficients that have been directly determined from the mean-square displacements. The comparison shows that the time dependence of the diffusion coefficients needs to be considered, in particular the initial ballistic phase and the often subdiffusive perpendicular coefficient. Conclusions: It is argued that the perpendicular component of the distribution function is essential if agreement between the diffusion solution and the simulated flux is to be obtained. In addition, time-dependent diffusion can provide a better description than the classic diffusion equation only after the initial ballistic phase.
Maria Grazia PiaINFN Sezione di Genova; Marcia BegalliState University Rio de Janeiro; Anton LechnerVienna University of Technology; Lina QuintieriINFN Laboratori Nazionali di Frascati; Paolo SaraccoINFN Sezione di Genova
2014-01-01
The issue of how epistemic uncertainties affect the outcome of Monte Carlo simulation is discussed by means of a concrete use case: the simulation of the longitudinal energy deposition profile of low energy protons. A variety of electromagnetic and hadronic physics models is investigated, and their effects are analyzed. Possible systematic effects are highlighted. The results identify requirements for experimental measurements capable of reducing epistemic uncertainties in the physics models.
Pia, Maria Grazia; Lechner, Anton; Quintieri, Lina; Saracco, Paolo
2010-01-01
The issue of how epistemic uncertainties affect the outcome of Monte Carlo simulation is discussed by means of a concrete use case: the simulation of the longitudinal energy deposition profile of low energy protons. A variety of electromagnetic and hadronic physics models is investigated, and their effects are analyzed. Possible systematic effects are highlighted. The results identify requirements for experimental measurements capable of reducing epistemic uncertainties in the physics models.
High multiplicity trigger in ALICE and Monte Carlo studies
Rauchegger, Christoph
2015-01-01
The ALICE experiment has an extensive program for the measurement of high multiplicity events in pp collisions. As a summer student, I was involved in different tasks for the preparation of the high multiplicity data taking and Monte Carlo studies. Several ALICE sub-detectors are part of the trigger system and can be used to set up a high multiplicity trigger. Moreover, the high multiplicity triggers have to be harmonized with the other goals of the experiment, limiting the bandwidth which can be dedicated to these triggers. In this project we discuss the optimization of the trigger strategy and some initial studies for the simulation of high multiplicity events.
Complete Monte Carlo Simulation of Neutron Scattering Experiments
International Nuclear Information System (INIS)
The majority of experiments investigating the elastic scattering of fast neutrons were done some 30 years ago. At that time it was not possible to obtain valid corrections for the finite geometry and the finite sample size of the experimental set up, not even having the main frame computers of the Los Alamos National Laboratory at one’s disposal. The reason was not only the limited calculation capacity of those ancient computers but also, to an even higher degree, the lack of powerful Monte Carlo codes and the very limited data base for the isotope in question. The computing power of a present day PC is about ten thousand times that of a super computer of the1970ies. Moreover, most PCs are idle over-night so that using a powerful Monte Carlo program, like MCNPX from Los Alamos, corrections of important scattering experiments can be determined reliably at practically no computer cost. Surely one of the most important experiments is neutron scattering from liquid helium-3, especially considering the expensive and complicated cryogenic target. A complete documentation of such an experiment as performed in the year 1971 at the Los Alamos National Laboratory is available. Therefore it is now possible to perform a thorough simulation of the experiment: starting from the production of mono-energetic neutrons in a gas target, followed by the interaction in the ambient air, and the interaction with the cryostat structure, and finally the scattering medium itself. Another simulation deals with the scattering from hydrogen as a reference measurement. As two thirds of all available differential scattering cross sections of that reaction depend on these measurements the newly arrived at corrections prove to be highly significant because they are smaller by a factor of five. Moreover, it was necessary to simulate another experiment on this reaction, using a white neutron source. This way it was possible to convert the corresponding relative yield excitation functions to
Monte Carlo study for γ+N→π+N at a new compound target
Institute of Scientific and Technical Information of China (English)
无
2008-01-01
An inbuilt compound target composed of carbon and tungsten is designed,and optimized by realistic GEANT4 Monte Carlo simulation.Also,we do a Monte Carlo study for single-pion photoproduction at the target.The results are presented from the simulation of pion yield,angular distribution and spectrum (at θ1ab,θcm=41°).These efforts are important to the coming measurement of the differential cross section for γ+N→π+N.
Monte Carlo study for γ + N→π+N at a new compound target
International Nuclear Information System (INIS)
An inbuilt compound target composed of carbon and tungsten is designed, and optimized by realistic GEANT4 Monte Carlo simulation. Also, we do a Monte Carlo study for single-pion photoproduction at the target. The results are presented from the simulation of pion yield, angular distribution and spectrum (at θlab, θcm=41 degree). These efforts are important to the coming measurement of the differential cross section for γ + N→π+N. (authors)
Gold nanoparticle DNA damage in radiotherapy: A Monte Carlo study
Directory of Open Access Journals (Sweden)
Chun He
2016-07-01
Full Text Available This study investigated the DNA damage due to the dose enhancement of using gold nanoparticles (GNPs as a radiation sensitizer in radiotherapy. Nanodosimetry of a photon irradiated GNP was performed with Monte Carlo simulations using Geant4-DNA (ver. 10.2 in the nanometer scale. In the simulation model, GNP spheres (with diameters of 30, 50, and 100 nm and a DNA model were placed in a water cube (1 µm3. The GNPs were irradiated by photon beams with varying energies (50, 100, and 150 keV, which produced secondary electrons, enhancing the dose to the DNA. To investigate the dose enhancement effect at the DNA level, energy deposition to the DNA with and without the GNP were determined in simulations for calculation of the dose enhancement ratio (DER. The distance between the GNP and the DNA molecule was varied to determine its effect on the DER. Monte Carlo results were collected for three variables; GNP size, distances between the GNP and DNA molecule, and the photon beam energy. The DER was found to increase with the size of GNP and decrease with the distance between the GNP and DNA molecule. The largest DER was found to be 3.7 when a GNP (100 nm diameter was irradiated by a 150 keV photon beam set at 30 nm from the DNA molecule. We conclude that there is significant dependency of the DER on GNP size, distance to the DNA and photon energy and have simulated those relationships.
PRIMO: A graphical environment for the Monte Carlo simulation of Varian and Elekta linacs
Rodriguez, Manuel Jairo; Sempau Roma, Josep; Brualla, Lorenzo
2013-01-01
Background: The accurate Monte Carlo simulation of a linac requires a detailed description of its geometry and the application of elaborate variance-reduction techniques for radiation transport. Both tasks entail a substantial coding effort and demand advanced knowledge of the intricacies of the Monte Carlo system being used. Methods: PRIMO, a new Monte Carlo system that allows the effortless simulation of most Varian and Elekta linacs, including their multileaf collimators and electron appli...
Nagata, H; Žukovič, M.; Idogaki, T.
2013-01-01
The three-dimensional XY model with bilinear-biquadratic exchange interactions $J$ and $J'$, respectively, has been studied by Monte Carlo simulations. From the detailed analysis of the thermal variation of various physical quantities, as well as the order parameter and energy histogram analysis, the phase diagram including two different ordered phases has been determined. There is a single phase boundary from a paramagnetic to a dipole-quadrupole ordered phase, which is of second order in a ...
Risk analysis and Monte Carlo simulation applied to the generation of drilling AFE estimates
International Nuclear Information System (INIS)
This paper presents a method for developing an authorization-for-expenditure (AFE)-generating model and illustrates the technique with a specific offshore field development case study. The model combines Monte Carlo simulation and statistical analysis of historical drilling data to generate more accurate, risked, AFE estimates. In addition to the general method, two examples of making AFE time estimates for North Sea wells with the presented techniques are given
The use of Monte Carlo simulations for seismic hazard assessment in the U.K.
R. M. W. Musson
2000-01-01
The input required for a seismic hazard study using conventional Probabilistic Seismic Hazard assessment (PSHA) methods can also be used for probabilistic analysis of hazard using Monte Carlo simulation methods. This technique is very flexible, and seems to be under-represented in the literature. It is very easy to modify the form of the seismicity model used, for example, to introduce non-Poissonian behaviour, without extensive reprogramming. Uncertainty in input parameters can also be model...
REX: A Monte Carlo simulation of thick gas target resonant scattering reactions
Energy Technology Data Exchange (ETDEWEB)
Curtis, N., E-mail: n.curtis@bham.ac.uk; Walshe, J.
2015-10-11
A Monte Carlo code has been developed to simulate resonant scattering reactions using the thick gas target technique in inverse kinematics. Results are presented for the {sup 4}He({sup 20}Ne,α){sup 20}Ne reaction at 70 MeV, and compared to an experimental measurement which utilised an array of segmented silicon strip detectors. In the case studied, angular straggling in the chamber window is found to dominate the excitation energy resolution.
Risk Analysis of Tilapia Recirculating Aquaculture Systems: A Monte Carlo Simulation Approach
Kodra, Bledar
2007-01-01
Risk Analysis of Tilapia Recirculating Aquaculture Systems: A Monte Carlo Simulation Approach Bledar Kodra (ABSTRACT) The purpose of this study is to modify an existing static analytical model developed for a Re-circulating Aquaculture Systems through incorporation of risk considerations to evaluate the economic viability of the system. In addition the objective of this analysis is to provide a well documented risk based analytical system so that individuals (investors/lenders) c...
International Nuclear Information System (INIS)
In recent decades, cancer has been one of the main ever increasing causes of death in developed countries. In order to fulfill the aforementioned considerations different techniques have been used, one of which is Monte Carlo simulation technique. High accuracy of the Monte Carlo simulation has been one of the main reason for its wide spread application. In this study, MCNP-4C code was employed to simulate electron mode of the Neptun 10 PC Linac, dosimetric quantities for conventional fields have also been both measured and calculated. Although Neptun 10 PC Linac is no longer licensed for installation in European and some other countries but regrettably nearly 10 of them have been installed in different centers around the country and are in operation. Therefore, in this circumstance, to improve the accuracy of treatment planning, Monte Carlo simulation for Neptun 10 PC was recognized as a necessity. Simulated and measured values of depth dose curves, off axis dose distributions for 6 , 8 and 10 MeV electrons applied for four different size fields, 6 x 6 cm2, 10 x 10 cm2, 15 x 15 cm2 and 20 x 20 cm2 were obtained. The measurements were carried out by a Welhofer-Scanditronix dose scanning system, Semiconductor Detector and Ionization Chamber. The results of this study have revealed that the values of two main dosimetric quantities depth dose curves and off axis dose distributions, acquired by MCNP-4C simulation and the corresponding values achieved by direct measurements are in a very good agreement (within 1% to 2% difference). In general, very good consistency of simulated and measured results, is a good proof that the goal of this work has been accomplished. In other word where measurements of some parameters are not practically achievable, MCNP-4C simulation can be implemented confidently. (author)
Finsy, Vincent; Calero, Sofia; García-Pérez, Elena; Merkling, Patrick J; Vedts, Gill; De Vos, Dirk E; Baron, Gino V; Denayer, Joeri F M
2009-05-14
Low-coverage adsorption properties of the metal-organic framework MIL-47 were determined by a combined experimental and simulation study. Henry constants and low coverage adsorption enthalpies of C5-C8 linear and branched alkanes, cyclohexane and benzene were measured from 120 to 240 degrees C using pulse gas chromatography. An adapted force field for linear and branched alkanes in MIL-47 was used to compute the adsorption properties of those molecules. A new set of charges was developed for simulations with benzene in MIL-47. The adsorption enthalpy of linear alkanes increases with about 7.6 kJ mol(-1) per additional -CH2- group. Henry adsorption constants of iso-alkanes are slightly lower than those of the linear chains but the MIL-47 framework is not imposing steric constraints on the branched chains. Benzene and cyclohexane are adsorbed less strongly than n-hexane as they have less hydrogen atoms. For the studied non-polar molecules, the adsorption energies are dominated by van der Waals interactions and benzene adsorption is additionally influenced by Coulombic interactions. The simulated tendencies are in good agreement with the experiments. PMID:19421556
Hajizadeh-Safar, M.; Ghorbani, M.; Khoshkharam, S.; Ashrafi, Z.
2014-01-01
Gamma camera is an important apparatus in nuclear medicine imaging. Its detection part is consists of a scintillation detector with a heavy collimator. Substitution of semiconductor detectors instead of scintillator in these cameras has been effectively studied. In this study, it is aimed to introduce a new design of P-N semiconductor detector array for nuclear medicine imaging. A P-N semiconductor detector composed of N-SnO2 :F, and P-NiO:Li, has been introduced through simulating with MCNPX...
Hybrid Monte Carlo studies of high temperature superconductors
International Nuclear Information System (INIS)
In this thesis we have developed a Hybrid Monte Carlo simulation of the vortex state in layered high-temperature superconductors. A set of potentials that govern vortex behaviour are derived from the Lawrence-Doniach free-energy functional which incorporate (i) intra-layer coupling (ii) inter-layer Josephson and electromagnetic interactions. We develop an extensive set of system observables that enable detailed studies of the structural properties of the vortex state. Naive truncation of the long-range intra-layer potential is shown to cause incorrect physical behaviour. We present two methods to overcome the problem. The first smoothes the potential and the second performs an in-plane infinite lattice summation for the intra-layer interactions, which provides a minimum 20,000 speed-up over previous methods. We present results of the numerical B-T phase diagram in the pure and pinned system and obtain good agreement with available experimental and theoretical results. Significant hysteresis is observed in the melting properties of the system and we implement the Hybrid Monte Carlo (HMC) method for the first time in such a system to overcome this. The correlation time in the system and the rate of transitions between solid and liquid states are both shown to improve by a factor of 5 over the Monte Carlo (MC) method. We perform HMC simulations on a simple, well-studied model (Ryu, 1996b) and show that the HMC method accurately simulates the system. Finally we investigate the effects of a phenomenological pinning surface upon the melting properties of this system, and demonstrate that the effects of introducing disorder into the system are consistent with experimental and other numerical studies. (author)
Czech Academy of Sciences Publication Activity Database
Tarasenko, Alexander; Jastrabík, Lubomír
Berlin Heidelberg : Springer-Verlag, 2012 - (Delgado, J.; Barbosa de Lima, A.; Vázquez da Silva, M.), s. 63-83 ISBN 978-3-642-30531-3. - (Advanced Structured Materials. 27) R&D Projects: GA TA ČR TA01010517; GA ČR GAP108/12/1941 Institutional research plan: CEZ:AV0Z10100522 Keywords : zeolites * lattice-gas model * Monte Carlo Subject RIV: BM - Solid Matter Physics ; Magnetism
Schierz, Philipp; Zierenberg, Johannes; Janke, Wolfhard
2015-10-01
Molecular Dynamics (MD) and Monte Carlo (MC) simulations are the most popular simulation techniques for many-particle systems. Although they are often applied to similar systems, it is unclear to which extent one has to expect quantitative agreement of the two simulation techniques. In this work, we present a quantitative comparison of MD and MC simulations in the microcanonical ensemble. For three test examples, we study first- and second-order phase transitions with a focus on liquid-gas like transitions. We present MD analysis techniques to compensate for conservation law effects due to linear and angular momentum conservation. Additionally, we apply the weighted histogram analysis method to microcanonical histograms reweighted from MD simulations. By this means, we are able to estimate the density of states from many microcanonical simulations at various total energies. This further allows us to compute estimates of canonical expectation values.
Schierz, Philipp; Zierenberg, Johannes; Janke, Wolfhard
2015-10-01
Molecular Dynamics (MD) and Monte Carlo (MC) simulations are the most popular simulation techniques for many-particle systems. Although they are often applied to similar systems, it is unclear to which extent one has to expect quantitative agreement of the two simulation techniques. In this work, we present a quantitative comparison of MD and MC simulations in the microcanonical ensemble. For three test examples, we study first- and second-order phase transitions with a focus on liquid-gas like transitions. We present MD analysis techniques to compensate for conservation law effects due to linear and angular momentum conservation. Additionally, we apply the weighted histogram analysis method to microcanonical histograms reweighted from MD simulations. By this means, we are able to estimate the density of states from many microcanonical simulations at various total energies. This further allows us to compute estimates of canonical expectation values. PMID:26450299
Monte Carlo Simulation and Experimental Characterization of a Dual Head Gamma Camera
Rodrigues, S; Abreu, M C; Santos, N; Rato-Mendes, P; Peralta, L
2007-01-01
The GEANT4 Monte Carlo simulation and experimental characterization of the Siemens E.Cam Dual Head gamma camera hosted in the Particular Hospital of Algarve have been done. Imaging tests of thyroid and other phantoms have been made "in situ" and compared with the results obtained with the Monte Carlo simulation.
On the inclusion of macroscopic theory in Monte Carlo simulation using game theory
International Nuclear Information System (INIS)
This paper presents the inclusion of macroscopic damage theory into Monte Carlo particle-range simulation using game theory. A new computer code called RADDI was developed on the basis of this inclusion. Results of Monte Carlo damage simulation after 6.3 MeV proton bombardment of silicon are compared with experimental data of Bulgakov et al. (orig.)
Mechanical properties of carbon nanostructures investigated by Monte Carlo simulations
International Nuclear Information System (INIS)
Full text: Carbon nanostructures are a fascinating class of materials combining high stiffness with low weight and exceptional toughness that makes carbon a promising candidate for applications in structural mechanics. Understanding the mechanical behavior of carbon structures also on atomistic length scales is inevitable in describing the mechanical performance and stability of large, hierarchical structures like carbon onions and fibers. In the presented work ab initio calculations were used to extract classical potentials describing stretching, bending and torsion deformations of carbon bonds that were used in subsequent Monte Carlo simulations to perform computational mechanical tests on graphene, carbon nanotubes and fullerenes. These tests included the application of hydrostatic pressure, the application of a ring load and the deformation of a fullerene between two plates. We analyzed the elastic response, as well as the stability limits and post buckling behavior of the structures for different sizes. The simulation results were compared to the predictions of nite element methods to evaluate macroscopic parameters like elastic modulus or Poisson ratio of the investigated structures. In fullerenes special attention was paid to the influence of pentagons that are inherently present in these structures. It was observed that the pentagons deform less than the atomic bonds in hexagonal geometry. (author)
On the use of tally servers in Monte Carlo simulations of light-water reactors
International Nuclear Information System (INIS)
An algorithm for decomposing tally data in Monte Carlo simulations using servers has recently been proposed and analyzed. In the present work, we make a number of refinements to a theoretical performance model of the tally server algorithm to better predict the performance of a realistic reactor simulation using Monte Carlo. The impact of subdividing fuel into annular segments on parameters of the performance model is evaluated and shown to result in a predicted overhead of less than 20% for a PWR benchmark on the Mira Blue Gene/Q supercomputer. Additionally, a parameter space study is performed comparing tally server implementations using blocking and non-blocking communication. Non-blocking communication is shown to reduce the communication overhead relative to blocking communication, in some cases resulting in negative overhead. (authors)
MONTE CARLO SIMULATION OF SPIN-POLARIZED SECONDARY ELECTRONS FROM IRON
Institute of Scientific and Technical Information of China (English)
X. Sun; Z.J. Ding; H.M Li; K. Salma; Z.M. Zhang; W.S. Tan
2005-01-01
A Monte Carlo model considering the electron spin direction and spin asymmetry has been developed. The energy distribution of the secondary electron polarization and the primary energy dependence of the polarization from Fe are studied. The simulation results show that:(1) the intensity of the spin-up secondary electrons is larger thanvthat of thevspin-down secondary electrons, suggesting the secondary electrons are spin polarized; (2) the spin polarization of secondary electrons with nearly zero kinetic energy is higher than the average valance spin polarization, Pb=27% for Fe. With increasing kinetic energy, the spin polarization of the secondary electrons decreases to the value of Pb remaining constant at higher kinetic energies;(3) the spin polarization increases with an increase in the primary energy and reaches a saturation value at higher primary energy in both the Monte Carlo simulation and experimental results.
International Nuclear Information System (INIS)
When a compound is maintained in far for equilibrium configurations by nuclear collisions under irradiation, the steady-state properties of the system can no longer be predicted from equilibrium thermodynamics. Here the authors propose Monte Carlo simulations for addressing the question of phase stability under irradiation. They are based on a kinetic model with two dynamics acting in parallel: thermally activated jumps of vacancies and ballistic events induced by nuclear collisions. Two transformations are studied: the A2-B2 order-disorder transition and the precipitation of copper in iron. In the former case a shift from second to first order of the A2-B2 transition, predicted by the model, has been experimentally checked by 1 MeV electron irradiations of a FeAl alloy. In the latter case, the precipitation kinetics are determined by Monte Carlo simulations and are found to be in very good agreement with available experimental data
Thermal conductivity of nanofluids and size distribution of nanoparticles by Monte Carlo simulations
International Nuclear Information System (INIS)
Nanofluids, a class of solid-liquid suspensions, have received an increasing attention and studied intensively because of their anomalously high thermal conductivites at low nanoparticle concentration. Based on the fractal character of nanoparticles in nanofluids, the probability model for nanoparticle's sizes and the effective thermal conductivity model are derived, in which the effect of the microconvection due to the Brownian motion of nanoparticles in the fluids is taken into account. The proposed model is expressed as a function of the thermal conductivities of the base fluid and the nanoparticles, the volume fraction, fractal dimension for particles, the size of nanoparticles, and the temperature, as well as random number. This model has the characters of both analytical and numerical solutions. The Monte Carlo simulations combined with the fractal geometry theory are performed. The predictions by the present Monte Carlo simulations are shown in good accord with the existing experimental data.
Energy Technology Data Exchange (ETDEWEB)
Strigari, L.; D' Andrea, M.; Benassi, M. [Regina Elena Cancer Institute, Laboratory of Medical Physics and Expert Systems, Rome (Italy); Sciuto, R.; Pasqualoni, R.; Maini, C.L. [Regina Elena Cancer Institute, Nuclear Medicine Department, Rome (Italy)
2007-07-15
The aim of the paper is to calculate the dose to bone surface and bone volume using a Monte Carlo particle transport model and to give quantitative arguments for activity prescription. This study simulates the dose delivery process to skeletal metastases by bone surface- and bone volume-seeking radiopharmaceuticals. Dose distributions for three radiopharmaceuticals, {sup 186}Re-HEDP, {sup 153}Sm-EDTMP and {sup 89}SrCl{sub 2}, frequently used for pain palliation therapies, were calculated using the EGSnrc Monte Carlo code. The model simulates a cylindrical geometry with regions of different constant density compositions and radioactivity distribution consistent with known biodistribution features of the three radiopharmaceuticals: superficial for phosphonates ({sup 186}Re-HEDP and {sup 153}Sm-EDTMP) and volumetric for {sup 89}SrCl{sub 2}. After 3D dose distribution calculation, dose-volume histogram reduction was carried out using the ''preferred Lyman'' method, which yields effective uniform dose (D{sub eff}) equivalent to the inhomogeneous dose distributions to the reference region (volume and surface). Our simulations showed that to obtain a delivered dose to bone surface equivalent to that obtained from {sup 89}SrCl{sub 2}, the administered activities of {sup 153}Sm-EDTMP and {sup 186}Re-HEDP should be increased by 37% and 48%, respectively, in comparison with those usually administered. These results prove theoretically the empirical results from clinical observations and show that improvement in bone pain palliation by means of radiopharmaceutical therapy should be expected for dose-guided prescription. (orig.)
International Nuclear Information System (INIS)
The activity of environmental samples is usually measured by high resolution HPGe gamma spectrometers. In this work a set-up with a 9 in.x9 in. NaI well-detector with 3 in. thickness and a 3 in.×3 in. plug detector in a 15-cm-thick lead shielding is considered as an alternative (Hansman, 2014). In spite of its much poorer resolution, it requires shorter measurement times and may possibly give better detection limits. In order to determine the U-238, Th-232, and K-40 content in the samples by this NaI(Tl) detector, the corresponding photopeak efficiencies must be known. These efficiencies can be found for certain source matrix and geometry by Geant4 simulation. We found discrepancy between simulated and experimental efficiencies of 5–50%, which can be mainly due to effects of light collection within the detector volume, an effect which was not taken into account by simulations. The influence of random coincidence summing on detection efficiency for radionuclide activities in the range 130–4000 Bq, was negligible. This paper describes also, how the efficiency in the detector depends on the position of the radioactive point source. To avoid large dead time, relatively weak Mn-54, Co-60 and Na-22 point sources of a few kBq were used. Results for single gamma lines and also for coincidence summing gamma lines are presented. - Highlights: • 9 in.x9 in. NaI well detector and 3 in.x3 in. plug detector studied. • Peak efficiency simulated with Geant4. • Result shows discrepancy with measurements. • High efficiency useful for environmental samples
A Monte Carlo simulation of neutron activation analysis of bulk objects
Energy Technology Data Exchange (ETDEWEB)
Fantidis, J.G. [Faculty of Engineering, Department of Electrical and Computer Engineering, Laboratory of Nuclear Technology, Democritus University of Thrace, Vas. Sofias 12, 67100 Xanthi (Greece); Nicolaou, G. [Faculty of Engineering, Department of Electrical and Computer Engineering, Laboratory of Nuclear Technology, Democritus University of Thrace, Vas. Sofias 12, 67100 Xanthi (Greece)], E-mail: nicolaou@ee.duth.gr; Tsagas, N.F. [Faculty of Engineering, Department of Electrical and Computer Engineering, Laboratory of Nuclear Technology, Democritus University of Thrace, Vas. Sofias 12, 67100 Xanthi (Greece)
2009-03-15
A PGNAA facility comprising an isotopic neutron source has been simulated using the Monte Carlo code MCNPX. The facility is envisaged for elemental composition studies of biomedical, environmental and industrial bulk objects. The study carried out, aimed to improve the detection sensitivity of prompt gamma-rays emitted by a bulk object, measured in the presence of higher energy ones. An appropriate collimator, a filter between the neutron source and the object and an optimisation of the positioning of the neutron beam and the detector relative to the object analysed were means to improve the desired sensitivity. The simulation is demonstrated for the in-vivo PGNAA of boron in the human liver.