Features of the scattering of protons and relativistic electrons intersecting a thin planar target at a small angle to its surface

The processes of scattering of protons and relativistic electrons incident on a planar target at a small angle to its surface have been simulated by the Monte Carlo method. The spatial and energy distributions of the beams of particles both passed through the target and reflected from it have been calculated. The dependence of the characteristics of beams on the initial energy and direction of injection of particles, as well as on the material and thickness of the target, has been considered. The transmission, reflection, and absorption coefficients for electrons in the target have been calculated. The initial energy in the calculations is varied in the range of 7–100 MeV and the angle between the trajectory of particles and the surface of the target is in the range of 1°–45°. The thickness of the target varies from 0.2 to 3 mm. Aluminum, iron, and copper targets have been considered. It has been shown that the intersection of targets at small angles not only increases the transverse dimensions of a beam, but also changes the direction of its motion. The results of the reported calculations of the scattering of relativistic electrons intersecting a foil at small angles to its surface are in qualitative agreement with experimental data.     

光子与相对论麦克斯韦分布电子散射的能谱角度谱研究

光子与相对论麦克斯韦分布电子散射的描述及能谱角度谱计算非常复杂且费时.本文提出了一种光子与相对论麦克斯韦速度分布电子散射的蒙特卡罗(MC)模拟方法,该方法能够细致模拟高温等离子体中任意能量光子与任意温度电子的Compton和逆Compton散射问题.对于散射后光子的能谱和角度谱参数,可以根据电子温度抽样若干不同状态的电子,分别模拟其与光子发生散射,可以得到各次散射后的光子能量和偏转角度,取统计平均后的结果即可获得该光子与该温度电子散射的能谱和角度谱分布.根据该方法编写了光子与相对论电子散射MC模拟程序,开展了高温全电离等离子体中光子与相对论电子散射的能谱角度谱计算和分析,分析结果显示:热运动电子将展宽出射光子能谱,且低能光子与高温电子散射后的蓝移现象明显;出射光子的角度谱很复杂,其决定于入射光子能量、出射光子能量及电子温度.基于该方法计算并以数表形式给出的光子-相对论电子散射能谱角度谱数据,可以供辐射输运数值模拟程序使用.     

Monte Carlo方法计算低能电子作用下固体背散射电子发射及空间分布

应用Monte Carlo方法,对能量E₀≤5keV低能电子作用下固体Al、Cu、Ag、Au的背散射电子发射及表面空间分布作了计算.模型应用Mott散射截面及修正的Bethe方程分别描述低能电子在固体中的弹性和非弹性散射.计算了背散射电子能量分布、表面空间分布、深度分布和角分布规律及特征,还计算分析了背散射电子角分布与深度分布、表面空间分布及能量分布之间的关系,系统地描述了背散射电子的发射及分布规律.     

Spin dependent 2D electron scattering by nanomagnets

The 2D scattering problem of an electron by a magnetized nanoparticle is solved in the Born approximation with account of the dipole-dipole interaction of the magnetic moments of electron and nanomagnet. The scattering amplitudes in this problem are the two-component spinors. They are obtained as functions of the electron spin orientation, the electron energy and show anisotropy in scattering angle. The initially polarized beam of electrons scattered by the nanomagnet consists of electrons with no spin flipped and spin flipped. The majority of electrons with no spin flipped are scattered by small angles. The majority electrons with spin flipped are scattered in the vicinity of the scattering angles π/2 and 3π/2. This can be used as one more method of controlling the spin currents.     

Koinzidenzexperimente zum Elementarprozeß der Bremsstrahlungserzeugung

By using a coincidence method, the angular distribution of bremsstrahlung has been measured for definite energy loss and definite angle of the outgoing electron. The incident electron energy was 300 keV. With a magnetic spectrometer, outgoing electrons with an energy of 170 keV and scattering angles of 0°, 5° and 10° were selected. The electrons and photons were both detected in scintillation counters. A gold foil of 250 Å thickness served as the target. The experimental results are compared with theoretical calculations.     

Temperaturabhängigkeit des Streuuntergrundes im Elektroneninterferenzdiagramm polykristalliner Silberschichten

The filtered and unfiltered intensities of electrons (30 to 50 kev) scattered in thin polycrystalline silver foils (300 to 1400 Å) were measured by means of a retarding field apparatus in the temperature range from 170 to 380 °K. Further the absorption coefficients due to the inelastic and the different elastic scattering processes were determined. It is shown, that the diffuse elastic scattering intensity increases with temperature for all values of thickness and electron energy. From the measured absorption coefficients the contributions of the different elastic scattering processes to the total background intensity are calculated. It turns out, that the main contribution is due to multiple scattering processes including both Bragg reflections and thermal diffuse scattering. Furthermore it is shown, that in contrary to the filtered diagram the background intensity of the unfiltered diagram increases with temperature only for larger scattering angles. In the small angle region a reversed temperature behaviour is observed. This effect is caused by that part of inelastically scattered electrons at low angles coming directly from the primary beam and from the low order diffraction rings.     

He-O_2转动激发截面的理论计算

用公认精确的密耦 (Close Coupling)方法、采用两种不同的相互作用势计算了He -O2 碰撞的态 态转动激发截面 (E =2 6.8meV) ,通过系统研究和计算发现 :低能散射时 ,He -O2 碰撞的弹性散射主要发生在小角部分 ,而非弹性转动激发主要发生在大角部分。研究表明 :转动激发截面对势能表面的方向性和散射角都非常敏感。     

Longitudinal magnetoresistance of platinum: The influence of lattice vacancies

The longitudinal magnetoresistance of polycrystalline platinum wires has been measured in magnetic fields up to 45 kOe at liquid helium temperatures. The deviations from Kohler's rule found depend on the concentration of quenched-in vacancies, and are interpreted as due to the contribution of single vacancies in platinum to the small angle scattering of electrons. The small-angle scattering may also be responsible for the linear magnetoresistance of platinum in high magnetic fields.     

The elastic scattering of low energy electrons from Xenon

Calculations are presented of angular distributions for electrons elastically scattered from xenon in the energy range 5.5 to 10 eV. The potential describing the xenon atom is determined by the X_α-approximation. The relative dependence with energy of the differential cross section at 30° scattering angle has been calculated in the range 30 to 200 eV. The theoretical results are in very good agreement with experimental data.     

The scattering of low energy electrons by electric field fluctuations near crystal surfaces

We present a discussion of the interaction of low energy electrons with surface lattice vibrations, with emphasis on the role played in this interaction by electric field fluctuations set up outside the crystal by the lattice vibration. We review briefly the experimental data presently available, along with theoretical interpretations that have been offered. We also examine in a manner more general than earlier discussions the contribution to the small angle scattering cross section from scattering by electric field fluctuations. After certain assumptions are introduced, we find that this contribution to the cross section is proportional to Im $\text{[1 + ?(Ω)]}{}^{\mathrm{?1}}$, where ?(Ω) is the frequency dependent dielectric constant of the material. We also exhibit an expression for the cross section for scattering from electric field fluctuations set up by particle—hole excitations.     

Elastic scattering of electrons from tetrahydrofuran molecule

Absolute differential cross-sections (DCSs) for elastic scattering of electrons from the DNA backbone sugarlike analogue tetrahydrofuran (THF) molecule were determined using a crossed beam measurements for incident energies from 20 eV to 300 eV and scattering angles from 10^o to 110^o. Using the relative-flow technique, elastic DCSs for THF relative to nitrogen have been obtained at incident energies of 20, 30, 40, 50 and 60 eV. In the energy region above 30 eV, the DCSs were measured independently as a function of both incident electron energy and scattering angle. Therefore, this set of relative DCSs has been calibrated to the absolute scale via normalization to a single point in the overlapping region. Additionally, both vibrational and electronic energy loss spectra for THF are presented and influence of energy resolution to the obtained DCSs is discussed.     

Streuung von 25 keV-Elektronen an Gasen

The angular distribution of 25 kev electrons scattered elastically and inelastically by molecular hydrogen has been measured in the angular range 7·10^?4≦?≦4,3·10^?2. By the separation of the inelastically scattered electrons observation of deviations from the Debye Ehrenfest theory of the electron diffraction by molecules at small angles is possible. These deviations are due to the alteration of the electron density distribution of the hydrogen atoms induced by the bonding. The energy loss spectra at different scattering angles (energy resolution ≈1 ev) shows a strong peak atΔE=12,6 ev. At larger angles forΔE>15 ev a continuum appears. That part of the inelastic processes which leads to ionization of the molecule is raising with increasing scattering angle. Normalization of the experimental values to the theoretical elastic differential cross section enables comparison of the angular distribution of the 12,6 ev energy loss with the distribution calculated byRoscoe. The shape of the experimental curve is in fairly good agreement with the calculated one but the experimental values at small angles are 20–30% higher. For zero angle the energy loss spectrum is taken with better resolution (≈0,04 ev). It shows vibrational states of the Lyman and Werner band and higher terms. The probability of the excitation of some vibrational states of the Werner band (square of the overlapp integral) calculated here is inspite of the required approximations in excellent agreement with the measurement, while Hutchisson's result fails for the Lyman band.     

Effects of dislocations on small signal high frequency hot electron mobility in n-GaN at low and high temperatures under high magnetic fields including hot phonon effect

The small signal high-frequency ac mobility of hot electrons in n-GaN in the extreme quantum limit at low- and high-temperatures has been calculated considering the non-equilibrium phonon distribution as well as the thermal phonon distributions. The energy loss rate has been calculated considering the dominance of the piezo electric coupling scattering and the polar optical phonon scattering while the momentum loss rate has been calculated considering the acoustic phonon scattering via deformation potential and the piezo electric coupling and the dislocation scattering.     

Einzelstreuung mittelschneller Elektronen an schweren Atomkernen

The Mott theory of the Coulomb-scattering of electrons and some experimental results (for example those ofKinzinger andBothe) do not agree. Therefore a new experimental method was used to investigate this problem: The 150-kev electrons were not scattered by foils but by gases of low pressure; to get enough scattering events in spite of the small number of scattering centres an annular counter was used, which integrated with respect to the azimuth angle. Scattering by a gaseous target had the important advantage that corrections for multiple scattering were negligible. The main experimental difficulty was the complete suppression of the electrons having been backscattered from the chamber walls. Relative cross sections were determined for 60, 90, 120 and 135 degrees for the atomic numbers 36, 54, and 80. The data are in agreement with the Mott theory within the experimental error of ± 5 %.     

Laser induced electronic acceleration process in nano dot

A physical model of the laser induced electron transport in dielectric with small size is discussed. The model assumes that free electrons are originally existent or produced by impact detrapping. The free electrons transporting in low dimensional dielectrics interact with phonons and surface. When the laser electric field strength is high enough, the inelastic electron scattering such as impact ionization and cascade processes will play important roles. A small size effect has been found in electron absorbing laser energy under the conditions that the laser wavelength is in near infrared zone and the material has size in nanometer level. This is a very significative effect to enlighten us on preparing ultrahigh threshold laser films with new nano-structure.     

Monte Carlo calculation of electron spectra produced in water phantoms by 20 keV-1 GeV photons

Abstract

A Monte Carlo calculation for the energy spectra of electrons and positrons produced in infinite and semiinfinite water phantoms by photons ranging in energies from 20 keV to 1 GeV are presented. The dominant processes considered are the photoelectric effect, Auger effect, Compton effect, pair, and triplet production. Bremsstrahlung produced by electrons and positrons with energies greater than 1 MeV is also included. The effect of multiple Compton scattering, not considered in the earlier calculation, for the infinite phantom for photon energies higher than 2 MeV has been incorporated. For a semi-infinite phantom, multiple Compton scattering and backscattering through the top are considered. The results are compared with the earlier calculations for the first-collision spectrum. It is found that the inclusion of multiple Compton scattering significantly increases the average number of electrons/cm³ per photon/cm² at all energies considered whereas bremsstrahlung reduces the number of high energy electrons and produces more low energy electrons in the spectrum.     

Possible evidence for heavy-ion-induced collective electron emission from solids

A peak has been observed for the first time in the angular distributions of low energy electrons (E_c<5 eV) emitted under heavy-ion bombardment of solids. The peak energy and angle coincide with the peak energy and angle predicted recently for collective electron emission in heavy-ion-solid collisions.     

电子与锂和铍原子碰撞角分布的理论研究

用模型势方法研究电子与锂和铍原子弹性散射，计算了能量从０．１到１．０ｅＶ散射电子的角分布（微分散射截面），从理论计算中，看到在０．１－１．０ｅＶ能区内，随入射电子能量增加，电子被Ｌｉ和Ｂｅ原子散射的微分截面有相似变化，即小角微分散射截面越来越大     

Backscattering of Relativistic Electrons Incident on a Planar Foil at a Small Angle to Its Surface

Photographs of cross sections of an electron beam backscattered from a thin tungsten target have been obtained on a dosimetric film. The procession of images makes it possible to obtain the spatial distribution of backscattered particles. The angles of back reflection θ_br of electron beams from foils have been measured. A 7.4-MeV microtron has been used as a source of electrons. The experiments have been performed with a tungsten foil 386 mg/cm² (200 μm) thick and a tantalum foil 1328 mg/cm² (800 μm) thick. Particles have been injected at an angle of α = 10° to the foil surface. The Monte Carlo simulation of the scattering of relativistic electrons incident on a planar target at small angles to its surface has been performed. The spatial and energy distributions of backscattered particle fluxes both transmitted through the target and reflected from it have been calculated. The dependences of fluxes on the direction of injection of particles and on the material and thickness of the target have been considered.     

Investigation of movement of average solute concentration under irradiation environment

Abstract

The movement of an average concentration of Zn inside and outside the matrix in a room temperature aged A1, Zn alloy under irradiation environment has been studied, using small angle neutron scattering (SANS). The samples of A1–11.8 at % Zn alloy were irradiated with 2Mev electrons with a flux of 10¹⁴ electrons/cm²-s for different periods of time. It is observed that at low doses the average Zn concentration in the precipitates decreases and consequently it moves into the matrix. On further doses of irradiation some of the Zn atoms from the matrix return to the remaining precipitate, resulting in an increase of Zn concentration in the precipitates, but never attaining the original value.