Calculation Of Energy Deposition Research Articles

Calculation of electron trajectory and energy deposition in no screening region

The probability density function (PDF) of energy for inelastic collision is obtained by solving the integro-differential form of the quantity equation with the Bhabha differential cross section for particles with spin 1/2. Hence, the total PDF in no screening region is determined by folding theory with the following two assumptions: (1) the electron loses energy by collision and radiation and (2) the electron velocity does not change with a thin absorber. Therefore, a set of coupled stochastic differential equations based on the deviation and energy loss PDFs for electron is presented to obtain the electron trajectory inside the target. The energy PDFs for an electron beam with incident energy of 15.7MeV inside aluminum and copper are calculated. Besides, the dose distributions for an electron beam with incident energies of 20, 10.2, 6, and 0.5MeV in water are obtained. The results are in excellent agreement with the experimental data reported in the literature.

N2 state population in Titan’s atmosphere

We present a detailed model for the vibrational population of all non pre-dissociating excited electronic states of N2, as well as for the ground and ionic states, in Titan’s atmosphere. Our model includes the detailed energy deposition calculations presented in the past (Lavvas, P. et al. [2011]. Icarus 213(1), 233–251) as well as the more recent developments in the high resolution N2 photo-absorption cross sections that allow us to calculate photo-excitation rates for different vibrational levels of singlet nitrogen states, and provide information for their pre-dissociation yields. In addition, we consider the effect of collisions and chemical reactions in the population of the different states. Our results demonstrate that above 600km altitude, collisional processes are efficient only for a small sub-set of the excited states limited to the A and W(ν=0) triplet states, and to a smaller degree to the a′ singlet state. In addition, we find that a significant population of vibrationally excited ground state N2 survives in Titan’s upper atmosphere. Our calculations demonstrate that this hot N2 population can improve the agreement between models and observations for the emission of the c4′ state that is significantly affected by resonant scattering. Moreover we discuss the potential implications of the vibrationally excited population on the ionospheric densities.

Contribution of proton and electron precipitation to the observed electron concentration in October–November 2003 and September 2005

Abstract. Understanding the altitude distribution of particle precipitation forcing is vital for the assessment of its atmospheric and climate impacts. However, the proportion of electron and proton forcing around the mesopause region during solar proton events is not always clear due to uncertainties in satellite-based flux observations. Here we use electron concentration observations of the European Incoherent Scatter Scientific Association (EISCAT) incoherent scatter radars located at Tromsø (69.58° N, 19.23° E) to investigate the contribution of proton and electron precipitation to the changes taking place during two solar proton events. The EISCAT measurements are compared to the results from the Sodankylä Ion and Neutral Chemistry Model (SIC). The proton ionization rates are calculated by two different methods – a simple energy deposition calculation and the Atmospheric Ionization Model Osnabrück (AIMOS v1.2), the latter providing also the electron ionization rates. Our results show that in general the combination of AIMOS and SIC is able to reproduce the observed electron concentration within ± 50% when both electron and proton forcing is included. Electron contribution is dominant above 90 km, and can contribute significantly also in the upper mesosphere especially during low or moderate proton forcing. In the case of strong proton forcing, the AIMOS electron ionization rates seem to suffer from proton contamination of satellite-based flux data. This leads to overestimation of modelled electron concentrations by up to 90% between 75–90 km and up to 100–150% at 70–75 km. Above 90 km, the model bias varies significantly between the events. Although we cannot completely rule out EISCAT data issues, the difference is most likely a result of the spatio-temporal fine structure of electron precipitation during individual events that cannot be fully captured by sparse in situ flux (point) measurements, nor by the statistical AIMOS model which is based upon these observations.

Simulated ablation of carbon wall by alpha particles for a laser fusion reactor

Thermal reactions of materials heated by charged particles may lead to serious damage in a laser fusion reactor. When charged particles irradiate and heat the wall material with high intensity like at above 109W/cm2, the material can be ablated. Once the wall is ablated, expanding gas or plasma can disturb the propagation of laser light irradiating the fuel target if it stagnates long enough for next laser shot. In order to understand the ablation dynamics in detail, we have performed 1-D hydro simulation to evaluate this ablation. As a new feature, we introduce the calculation of energy deposition by charged particles focusing on the interaction between ablated material and charged particles.

GAMMA-400 Space Gamma-telescope Mathematical Model with Engineering Elements Included

Mathematical model creation is a necessary stage in scientific apparatus development. The mathematical model of gamma-ray telescope GAMMA-400 is used to emulate transport of various elementary particles through the apparatus. The new iteration of the model is based on precise technical drawings and includes all the elements of the real gamma-telescope. It is created in Geant4 environment. This model allows calculation of energy deposition not only in detectors, but in any part of the apparatus, including construction elements. Moreover, it supports creation of virtual sensitive volumes, allowing determination of the number and properties of particles passing through an arbitrary part of the construction.Software for automated creation of Geant4 model based on technical drawings in STEP 3D Model format was developed. This software is capable of making models of other apparatus based particularly on scintillation and strip detectors.

Monte Carlo calculation of energy deposition in ionization chambers for tritium measurements

Energy deposition in ionization chambers for tritium measurements has been theoretically studied using Monte Carlo code MCNP 5. The influence of many factors, including carrier gas, chamber size, wall materials and gas pressure, has been evaluated in the simulations. It is found that β rays emitted by tritium deposit much more energy into chambers flowing through with argon than with deuterium in them, as much as 2.7times higher at pressure 100Pa. As chamber size gets smaller, energy deposition decreases sharply. For an ionization chamber of 1mL, β rays deposit less than 1% of their energy at pressure 100Pa and only 84% even if gas pressure is as high as 100kPa. It also indicates that gold plated ionization chamber results in the highest deposition ratio while aluminum one leads to the lowest. In addition, simulations were validated by comparison with experimental data. Results show that simulations agree well with experimental data.

SU‐E‐CAMPUS‐I‐02: Estimation of the Dosimetric Error Caused by the Voxelization of Hybrid Computational Phantoms Using Triangle Mesh‐Based Monte Carlo Transport

Purpose:Computational voxel phantom provides realistic anatomy but the voxel structure may result in dosimetric error compared to real anatomy composed of perfect surface. We analyzed the dosimetric error caused from the voxel structure in hybrid computational phantoms by comparing the voxel‐based doses at different resolutions with triangle mesh‐based doses.Methods:We incorporated the existing adult male UF/NCI hybrid phantom in mesh format into a Monte Carlo transport code, penMesh that supports triangle meshes. We calculated energy deposition to selected organs of interest for parallel photon beams with three mono energies (0.1, 1, and 10 MeV) in antero‐posterior geometry. We also calculated organ energy deposition using three voxel phantoms with different voxel resolutions (1, 5, and 10 mm) using MCNPX2.7.Results:Comparison of organ energy deposition between the two methods showed that agreement overall improved for higher voxel resolution, but for many organs the differences were small. Difference in the energy deposition for 1 MeV, for example, decreased from 11.5% to 1.7% in muscle but only from 0.6% to 0.3% in liver as voxel resolution increased from 10 mm to 1 mm. The differences were smaller at higher energies. The number of photon histories processed per second in voxels were 6.4×104, 3.3×104, and 1.3×104, for 10, 5, and 1 mm resolutions at 10 MeV, respectively, while meshes ran at 4.0×104 histories/sec.Conclusion:The combination of hybrid mesh phantom and penMesh was proved to be accurate and of similar speed compared to the voxel phantom and MCNPX. The lowest voxel resolution caused a maximum dosimetric error of 12.6% at 0.1 MeV and 6.8% at 10 MeV but the error was insignificant in some organs. We will apply the tool to calculate dose to very thin layer tissues (e.g., radiosensitive layer in gastro intestines) which cannot be modeled by voxel phantoms.

A non-conforming multi-element DGTD method for the simulation of human exposure to electromagnetic waves

The great majority of numerical calculations of electric energy deposition in human tissues exposed to microwaves are performed using the finite-difference time-domain FDTD method and voxel-based geometrical models of the tissues. The straightforward implementation of the method and its computational efficiency are among the main reasons for FDTD being currently the leading method for numerical assessment of human exposure to electromagnetic waves. However, the rather difficult departure from the commonly used Cartesian grid and cell size limitations regarding the discretization of very detailed structures of human tissues are often recognized as the main weaknesses of the FDTD method in this application context. In particular, interfaces between tissues where sharp gradients of the electromagnetic field may occur are hardly modeled rigorously in these studies this is generally referred as the staircasing effect. We present here an alternative numerical dosimetry methodology that is based on a DGTD method designed to work with non-conforming cubic-tetrahedral meshes for more flexibility in the discretization process of complex propagation scenes. For example, in the context of head tissues exposure to mobile phone radiation, the computation domain is divided in two regions: an unstructured tetrahedral mesh-based heterogeneous model of head tissues and an orthogonal cartesian mesh of the vacuum part of the propagation domain. We present numerical results comparing this approach with strategies based on fully Cartesian and fully tetrahedral meshes of the whole computational domain. Copyright © 2013 John Wiley & Sons, Ltd.

Calculation of Cross Section for Ion-Induced SEU Through Direct Ionization in Nanometric Silicon Devices With Small Critical Energy

The cross section (CS) for energy deposition by ions in 50 nm cubic volume in silicon, which represents the size of sensitive volumes in nanometric devices, was calculated using a fast Monte Carlo code. The results are used to estimate SEU CS in modern devices with small critical energy. It is shown that, for precise evaluation of SEU rate, detailed energy deposition calculations are needed for each ion. The average track structure can be used only for estimating the energy deposition by relatively high LET ions. It is found that the ion-LET is a good parameter for the SEU CS. However, a better metric is the ion inverse-mean-free-path or a reduced LET which is proportional to this value.

Assessment of doses caused by electrons in thin layers of tissue-equivalent materials, using MCNP

Absorbed doses caused by electron irradiation were calculated with Monte Carlo N-Particle transport code (MCNP) for thin layers of tissue-equivalent materials. The layers were so thin that the calculation of energy deposition was on the border of the scope of MCNP. Therefore, in this article application of three different methods of calculation of energy deposition is discussed. This was done by means of two scenarios: in the first one, electrons were emitted from the centre of a sphere of water and also recorded in that sphere; and in the second, an irradiation with the PTB Secondary Standard BSS2 was modelled, where electrons were emitted from an (90)Sr/(90)Y area source and recorded inside a cuboid phantom made of tissue-equivalent material. The speed and accuracy of the different methods were of interest. While a significant difference in accuracy was visible for one method in the first scenario, the difference in accuracy of the three methods was insignificant for the second one. Considerable differences in speed were found for both scenarios. In order to demonstrate the need for calculating the dose in thin small zones, a third scenario was constructed and simulated as well. The third scenario was nearly equal to the second one, but a pike of lead was assumed to be inside the phantom in addition. A dose enhancement (caused by the pike of lead) of ∼113 % was recorded for a thin hollow cylinder at a depth of 0.007 cm, which the basal-skin layer is referred to in particular. Dose enhancements between 68 and 88 % were found for a slab with a radius of 0.09 cm for all depths. All dose enhancements were hardly noticeable for a slab with a cross-sectional area of 1 cm(2), which is usually applied to operational radiation protection.

Development of collimator for in-situ measurement of 90Sr specific activity by β-ray survey meter and Monte Carlo calculation

For the in-situ measurement of 90Sr contamination, the collimators to be combined with the β-ray survey meter were designed with MCNP-4C calculations. The designed collimators were manufactured and its characteristics were measured in accordance with the calculations. The calculated energy deposition in the survey meter agreed within 27% to its counting rate measured in terms of their dependencies on the collimator dimension. This supports the usability of the manufactured collimators and numerical correction of the sensitivity of the survey meter depending on the geometry.

On the energy deposition by electrons in air and the accurate determination of the air-fluorescence yield

The uncertainty in the absolute value of the air-fluorescence yield still puts a severe limit on the accuracy in the primary energy of ultra-high-energy cosmic rays. The precise measurement of this parameter in laboratory is in turn conditioned by a careful evaluation of the energy deposited in the experimental collision chamber. In this work we discuss on the calculation of the energy deposition and its accuracy. Results from an upgraded Monte Carlo algorithm that we have developed are compared with those obtained using Geant4, showing excellent agreement. These updated calculations of energy deposition are used to apply some corrections to the available measurements of the absolute fluorescence yield, allowing us to obtain a reliable world average of this important parameter.

Three-Dimensional Electron Energy Deposition Modeling of Cathodoluminescence Emission near Threading Dislocations in GaN and Electron-Beam Lithography Exposure Parameters for a PMMA Resist

The Monte Carlo software CASINO has been expanded with new modules for the simulation of complex beam scanning patterns, for the simulation of cathodoluminescence (CL), and for the calculation of electron energy deposition in subregions of a three-dimensional (3D) volume. Two examples are presented of the application of these new capabilities of CASINO. First, the CL emission near threading dislocations in gallium nitride (GaN) was modeled. The CL emission simulation of threading dislocations in GaN demonstrated that a better signal-to-noise ratio was obtained with lower incident electron energy than with higher energy. Second, the capability to simulate the distribution of the deposited energy in 3D was used to determine exposure parameters for polymethylmethacrylate resist using electron-beam lithography (EBL). The energy deposition dose in the resist was compared for two different multibeam EBL schemes by changing the incident electron energy.

Energy deposition of multi-MeV protons in compressed targets of fast-ignition inertial confinement fusion

The energy loss and penetration of multi-megelectronvolt protons into a uniform deuterium-tritium (DT) plasma has been calculated. The effects of nuclear elastic scattering and Coulomb interactions are treated from a unified point of view. In general, multiple scattering enhances the proton linear-energy transfer along the initial proton direction, thus the energy deposition increases near the end of its range. The net effect of multiple scattering is to reduce the penetration from 1.20 to 1.02 g cm-2 for 12 MeV protons in a ρ=500 g cm-3 plasma at T=5 keV. These results should have relevance to proton fast ignition, specifically to energy deposition calculations that critically assess quantitative ignition requirements.

The numerical simulation of the electronic energy deposition and temperature variation in post-hole convolute of magnetically insulated transmission lines

In this paper, we introduce the numerical simulation theory and method to achieve the energy deposition and temperature variation produced by the high-energy electron bombarding the anode surface. A simple beam launch model is developed. The accuracy of the numerical calculation of the anode surface electronic energy deposition is primarily validated. Then, selecting the magnetically insulated transmission line in post-hole convolute as a model, the energy deposition and the temperature variation in the anode produced in the process are simulated. Also by comparing the simulation results with the results given in the literature, the simulation accuracy is further proved. Finally, the simulation results are analyzed and the physical mechanism produced by the simulation results is also discussed.

A probability-conserving cross-section biasing mechanism for variance reduction in Monte Carlo particle transport calculations

In Monte Carlo particle transport codes, it is often important to adjust reaction cross-sections to reduce the variance of calculations of relatively rare events, in a technique known as non-analog Monte Carlo. We present the theory and sample code for a Geant4 process which allows the cross-section of a G4VDiscreteProcess to be scaled, while adjusting track weights so as to mitigate the effects of altered primary beam depletion induced by the cross-section change. This makes it possible to increase the cross-section of nuclear reactions by factors exceeding 10 4 (in appropriate cases), without distorting the results of energy deposition calculations or coincidence rates. The procedure is also valid for bias factors less than unity, which is useful in problems that involve the computation of particle penetration deep into a target (e.g. atmospheric showers or shielding studies).

A Heterogeneous Coarse Mesh Method for Coupled Photon Electron Transport Problems

A hybrid Monte Carlo/deterministic coarse mesh transport method (COMET-PE) has been developed for pure photon or coupled photon and electron transport in heterogeneous problems. The accuracy of the method was evaluated in two highly stylized 2D benchmark problems: (1) a homogeneous rectangular water phantom and (2) a heterogeneous problem that is typical of a 2D vertical slice of lung. It was found that the method produces results that are very close to those of direct Monte Carlo with significantly higher computational efficiency (2–3 orders of magnitude). In both test problems, the maximum and the average energy deposition differences between COMET-PE and the reference Monte Carlo solutions for the pure photon transport case ranged from 2.0%–2.4% and 1.0%–1.2%, respectively. The corresponding differences for the coupled photon and electron transport case ranged from 1.1%–2.2% and 0.5%–0.9%, respectively. The COMET-PE computation time was more than 200 and 700 times shorter than EGSnrc in the homogeneous and the heterogeneous problems, respectively. Therefore, it is concluded that the new incident flux response expansion method is highly accurate and efficient for energy deposition calculation in heterogeneous tissues.

3D visualisation of the stochastic patterns of the radial dose in nano-volumes by a Monte Carlo simulation of HZE ion track structure

The description of energy deposition by high charge and energy (HZE) nuclei is of importance for space radiation risk assessment and due to their use in hadrontherapy. Such ions deposit a large fraction of their energy within the so-called core of the track and a smaller proportion in the penumbra (or track periphery). We study the stochastic patterns of the radial dependence of energy deposition using Monte Carlo track structure codes RITRACKS and RETRACKS, that were used to simulate HZE tracks and calculate energy deposition in voxels of 40 nm. The simulation of a (56)Fe(26+) ion of 1 GeV u(-1) revealed zones of high-energy deposition which maybe found as far as a few millimetres away from the track core in some simulations. The calculation also showed that ∼43 % of the energy was deposited in the penumbra. These 3D stochastic simulations combined with a visualisation interface are a powerful tool for biophysicists which may be used to study radiation-induced biological effects such as double strand breaks and oxidative damage and the subsequent cellular and tissue damage processing and signalling.

Calculation of energy deposition, photon and neutron production in proton therapy of thyroid gland using MCNPX

In this study, the MCNPX code has been used to simulate a proton therapy in thyroid gland, in order to calculate the proton energy deposition in the target region. As well as, we have calculated the photon and neutron production spectra due to proton interactions with the tissue. We have considered all the layers of tissue, from the skin to the thyroid gland, and an incident high energy pencil proton beam. The results of the simulation show that the best proton energy interval, to cover completely the thyroid tissue, is from 42 to 54 MeV, assuming that the thyroid gland has a 14 mm thickness and is located 11.2mm under the skin surface. The most percentage of deposited energy (78%) is related to the 54 MeV proton energy beam. Total photon and neutron production are linear and polynomial second order functions of the proton energy, respectively.

SU-GG-T-403: A Coarse Mesh Transport Method for the Calculation of Photon Energy Deposition in Tissue

Purpose: To develop and test a novel, transport‐based method for calculating the energy deposition of a photon beam in tissue. Method and Materials: The new method is based on a hybrid Monte Carlo‐Deterministic Coarse Mesh Transport Method COMET.COMET is a method for solving the linear Boltzmann Transport Equation based on an incident angular current expansion. It has been shown to perform well for 2D coupled photon‐electron transport calculations aimed at determining the energy deposition of a photon beam. The COMET method uses pre‐computed Monte Carlo‐based response expansion coefficients to achieve accuracy comparable to Monte Carlo methods in a fraction of the time. The current work extends the photon transport capability of the COMET method to handle 3D geometry and to simulate realistic photon sources. The method is tested with a simple benchmark problem consisting of a 20×20×20cm water phantom irradiated by a collimated, polyenergetic photon source at a source‐to‐surface distance (SSD) of 80cm. Although the COMET mesh size is arbitrary, the phantom is divided into 1×1×1cm voxels for convenience. The accuracy of the method is evaluated by comparison to a reference calculation performed with EGSnrc. Results: The distribution of energy deposition was examined voxel by voxel. The largest error for any voxel is found to be less than 3.3% of the maximum energy deposition value from the reference solution. The relative standard error for each voxel in the reference solution is less than 0.5%. The COMETsolution took 0.27 core‐hours to compute compared with 84 core‐hours for the reference solution.Conclusion: The work indicates that the COMET method holds promise for fast and accurate 3D photon and electron dose calculations. Furthermore, sources of error are identified and suggestions are made to improve the accuracy of the new method during future development.