اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدA Comparative Study on Monte Carlo Simulations of Electron Emission from Liquid Water
279
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Liquid water has been proved to be an excellent medium for specimen structure imaging by a scanning electron microscope. Knowledge of electron-water interaction physics and particularly the secondary electron yield is essential to the interpretation of the imaging contrast. However, very little is known up to now experimentally on the low energy electron interaction with liquid water because of certain practical limitations. It is then important to gain some useful information about electron emission from water by a Monte Carlo (MC) simulation technique that can numerically model electron transport trajectories in water. In this study, we have performed MC simulations of electron emission from liquid water in the primary energy range of 50 eV-30 keV by using two different codes, i.e. a classical MC (CMC) code developed in our laboratory and the Geant4-DNA (G4DNA) code. The calculated secondary electron yield and electron backscattering coefficient are compared with experimental results wherever applicable to verify the validity of physical models for the electron-water interaction. The secondary electron yield vs. primary energy curves calculated by the two codes present the same generic curve shape as that of metals but in rather different absolute values. G4DNA yields the underestimated absolute values due to the application of one step thermalization model by setting a cutoff energy at 7.4 eV so that the low energy losses due to phonon excitations are omitted. Our CMC calculation of secondary electron yield is closer to the experimental data and the energy distribution is reasonable. It is concluded that a full dielectric function data at low energy loss values below 7.4 eV shall be employed in G4DNA model for the modeling of low energy electrons.
قيم البحث
اقرأ أيضاً
The Monte Carlo simulation of the electron transport through thin slabs is studied with five general purpose codes: PENELOPE, GEANT3, GEANT4, EGSnrc and MCNPX. The different material foils analyzed in the old experiments of Kulchitsky and Latyshev [P
hys. Rev. 61 (1942) 254-266] and Hanson et al. [Phys. Rev. 84 (1951) 634-637] are used to perform the comparison between the Monte Carlo codes. Non-negligible differences are observed in the angular distributions of the transmitted electrons obtained with the some of the codes. The experimental data are reasonably well described by EGSnrc, PENELOPE (v. 2005) and GEANT4. A general good agreement is found for EGSnrc and GEANT4 in all the cases analyzed.
We present density-functional theory (DFT) and quantum Monte Carlo (QMC) calculations designed to resolve experimental and theoretical controversies over the optical properties of H-terminated C nanoparticles (diamondoids). The QMC results follow the
trends of well-converged plane-wave DFT calculations for the size dependence of the optical gap, but they predict gaps that are 1-2 eV higher. They confirm that quantum confinement effects disappear in diamondoids larger than 1 nm, which have gaps below that of bulk diamond. Our QMC calculations predict a small exciton binding energy and a negative electron affinity (NEA) for diamondoids up to 1 nm, resulting from the delocalized nature of the lowest unoccupied molecular orbital. The NEA suggests a range of possible applications of diamondoids as low-voltage electron emitters.
In this paper we investigate, with a detailed Monte-Carlo simulation based on Geant4, the novel approach [Nucl. Instrum. Methods A588 (2008) 457] to 3D imaging with photon scattering. A monochromatic and well collimated gamma beam is used to illumina
te the object to be imaged and the photons Compton scattered are detected by means of a surrounding germanium strip detector. The impact position and the energy of the photons are measured with high precision and the scattering position along the beam axis is calculated. We study as an application of this technique the case of brain imaging but the results can be applied as well to situations where a lighter object, with localized variations of density, is embedded in a denser container. We report here the attainable sensitivity in the detection of density variations as a function of the beam energy, the depth inside the object and size and density of the inclusions. Using a 600 keV gamma beam, for an inclusion with a density increase of 30% with respect to the sorrounding tissue and thickness along the beam of 5 mm, we obtain at midbrain position a resolution of about 2 mm and a contrast of 12%. In addition the simulation indicates that for the same gamma beam energy a complete brain scan would result in an effective dose of about 1 mSv.
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 longitudina
l particle distributions, the particle track length and energy distributions, a realistic magnetic field geometry and the shower evolution as a whole. The Monte Carlo approach allows us to retain the full polarisation information and to carry out the calculations without the need for any far-field approximations. We demonstrate the strategies developed to tackle the computational effort associated with the simulation of a huge number of particles for a great number of observer bins and illustrate the robustness and accuracy of these techniques. We predict the emission pattern, the radial and the spectral dependence of the radiation from a prototypical 10^17 eV vertical air shower and find good agreement with our analytical results (Huege & Falcke 2003) and the available historical data. Track-length effects in combination with magnetic field effects surprisingly wash out any significant asymmetry in the total field strength emission pattern in spite of the magnetic field geometry. While statistics of total field strengths alone can therefore not prove the geomagnetic origin, the predicted high degree of polarisation in the direction perpendicular to the shower and magnetic field axes allows a direct test of the geomagnetic emission mechanism with polarisation-sensitive experiments such as LOPES. Our code provides a robust, yet flexible basis for detailed studies of the dependence of the radio emission on specific shower parameters and for the inclusion of additional radiation mechanism in the future.
A classical description of electron emission differential ionization cross sections for highly-charged high-velocity ions ($sim$ 10 a.u.) impinging on water molecules is presented. We investigate the validity of the classical statistical mechanics de
scription of ionization ($hbar=0$ limit of quantum mechanics) in different ranges of electron emission energy and solid angle, where mechanisms such as soft and binary collisions are expected to contribute. The classical-trajectory Monte Carlo method is employed to calculate doubly and singly differential cross sections for C$^{6+}$, O$^{8+}$ and Si$^{13+}$ projectiles, and comparisons with Continuum Distorted Wave Eikonal Initial State theoretical results and with experimental data are presented. We implement a time-dependent screening effect in our model, in the spirit of mean-field theory to investigate its effect for highly charged projectiles. We also focus on the role of an accurate description of the molecular target by means of a three-center potential to show its effect on differential cross sections. Very good agreement with experiments is found at medium to high electron emission energies.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
