Orbital angular momentum of channeling radiation from relativistic electrons in thin Si crystal

We propose to use channeling radiation (CR) from relativistic electrons as a source of high energy twisted photons in the MeV range. We calculate numerically the orbital angular momentum (OAM) of radiation produced by electrons with the energies $155÷2500$ MeV for the axial and planar channeling in the thin Si crystal. We obtain that the average OAM of CR in this case is approximately $1÷6?$ per photon with the photon energies about $1÷2$ MeV.     

Asymmetry of the angular distribution of radiation of channeled relativistic electrons in optically transparent crystals

It has been shown that optical and ultraviolet radiation from relativistic electrons at planar channeling in optically transparent crystals is characterized by an unusual dependence on the polar and azimuth angles. A fraction of radiation with the frequency ω near which the derivative of the refractive index is nonzero, n'(ω) = dn(ω)/dω ≠ 0, should be observed at an angle close to π/2 with respect to the electron beam. For normal dispersion (n'(ω) > 0), this angle is smaller than π/2, whereas for anomalous dispersion (n'(ω) < 0), it is larger than π/2 (“backward” radiation). A pronounced dependence of the radiation intensity on the azimuth angle φ, i.e., azimuthal asymmetry, appears beyond the region of normal and anomalous dispersion at a fixed polar angle θ. In particular, the ratio of radiation intensities at angles φ = 0 and π/2 at θ = π/2 reaches a maximum value of about the square of the refractive index.     

Electromagnetic radiation of MeV electrons in thick aligned single crystals

Abstract

Earlier published theoretical models for MeV electrons are generalized in this paper. Different theoretical predictions for planar channeling and accompanying electromagnetic radiation in thick crystals are presented. A comparative analysis of theoretical and experimental spectra of photon radiation is given. Thickness dependences of channeling quantum state populations, radiation line broadening and photon flux intensities are obtained. The existence of planar electron channeling at 54 MeV in a silicon single crystal with a thickness of several millimetres is shown.     

等离子体中相对论电子的同步曲率辐射特性研究

根据同步曲率辐射理论推导了在等离子体环境中,不同磁场条件下的相对论性电子的吸收系数和发射系数表达式，计算了电子的发射强度，并且在此基础上研究了同步曲率辐射机制的脉泽效应.研究了两种磁场位型，第一种是强度均匀但弯曲的磁场，第二种是偶极磁场，结果发现了一些偶极磁场下特有的辐射特性.考虑到在天体的环境下电子具有的不同的能谱分布，分别选用了三种典型的能谱分布(幂率分布，高斯分布，热分布)进行了研究，通过计算负吸收和脉泽放大效应在发射强度上的表现后， 发现在某些天体物理环境中，同步曲率辐射在等离子体中的确存在脉泽放大效应.这些研究结果对太阳系中行星外层辐射的研究和宇宙中的射电高亮温度等问题的研究可能提供有益的帮助. 关键词： 同步曲率辐射 负吸收 脉泽效应     

A comparison of ionizing radiation damage in CMOS devices from 60Co gamma rays, electrons and protons

Radiation hardened CC4007RH and non-radiation hardened CC4011 devices were irradiated using 80Co gamma rays, 1 MeV electrons and 1--9 MeV protons to compare the ionizing radiation damage of the gamma rays with the charged particles. For all devices examined, with experimental uncertainty, the radiation induced threshold voltage shifts (△Vth) generated by 60Co gamma rays are equal to that of 1 MeV electron and 1-7 MeV proton radiation under 0 gate bias condition. Under 5 V gate bias condition, the distinction of threshold voltage shifts (△Vth) generated by 60Co gamma rays and 1 MeV electrons irradiation are not large, and the radiation damage for protons below 9 MeV is always less than that of 60Co gamma rays. The lower energy the proton has, the less serious the radiation damage becomes.     

A comparison of ionizing radiation damage in CMOS devices from ^60Co gamma rays,electrons and protons

Radiation hardened CC4007RH and non-radiation hardened CC4011 devices were irradiated using ^60Co gamma rays, 1 MeV electrons and 1-9 MeV protons to compare the ionizing radiation damage of the gamma rays with the charged particles. For all devices examined, with experimental uncertainty, the radiation induced threshold voltage shifts （△Vth） generated by ^60Co gamma rays are equal to that of 1 MeV electron and 1-7 MeV proton radiation under 0 gate bias condition. Under 5 V gate bias condition, the distinction of threshold voltage shifts （△Vth） generated by ^60Co gamma rays and 1 MeV electrons irradiation are not large, and the radiation damage for protons energy the proton has, the less serious below 9 MeV is always less than the radiation damage becomes. that of ^60Co gamma rays. The lower     

CMOS器件60Co γ射线、电子和质子电离辐射损伤比较

利用TRIM95蒙特卡罗软件计算了质子在二氧化硅中的质量阻止本领和能量沉积，比较了质子在二氧化硅中的电离阻止本领与核阻止本领，分析了质子在材料的表面吸收剂量与灵敏区实际吸收剂量的关系.利用⁶⁰Co γ射线、1MeV电子和2—9 MeV质子对CC4007RH和CC4011器件进行辐照实验，比较⁶⁰Co γ射线和带电粒子的电离辐射损伤情况.实验结果表明，⁶⁰Co γ射线、1MeV 电子和2—7MeV质子辐照损伤效应中，在0V栅压下可以相互等效； 关键词： γ射线 电子 质子 辐射损伤     

超热电子的产生与输运背向辐射的实验研究

报道了在100TW fs激光器上采用电子磁谱仪和光学CCD积分成像相机分别对激光-固体靶相互作用在靶背方向产生的超热电子能谱及其光学渡越辐射进行的测量.能谱测量结果显示:超热电子能谱呈单温类-麦克斯韦分布,拟合的温度为107 keV;光学渡越辐射(OTR)测量结果显示:OTR是由于超热电子输运穿越固体靶所致,而辐射区域呈圆盘状、有发散角、有光强分布;如果考虑超热电子的产生和加热机制,则占主导地位的加热机制是共振吸收对电子的加热.     

电子在激光驻波场中运动产生的太赫兹及X射线辐射研究

采用单电子模型和经典辐射理论分别对低能和高能电子在线偏振激光驻波场中的运动和辐射过程进行了研究. 结果表明: 垂直于激光电场方向入射的低速电子在激光驻波场中随着光强的增大, 逐渐从一维近周期运动演变为二维折叠运动, 并产生强的微米量级波长的太赫兹辐射; 高能电子垂直或者平行于激光电场方向入射到激光驻波场中, 都会产生波长在几个纳米的高频辐射; 低能电子与激光驻波场作用中, 激光强度影响着电子的运动形式、辐射频率以及辐射强度; 高能电子入射时, 激光强度影响了电子高频辐射的强度, 电子初始能量影响着辐射的频率; 电子能量越高, 产生的辐射频率越大. 研究表明可以由激光加速电子的方式得到不同能量的电子束, 并利用电子束在激光驻波场的辐射使之成为太赫兹和X射线波段的小型辐射源. 研究结果可以为实验研究和利用激光驻波场中的电子辐射提供依据.     

Quasielastic electron scattering in relativistic mean-field theory

The density-dependent relativistic hadron (DDRH) field theory proposed recently is extended to investigate the longitudinal response function and the Coulomb sum rule in quasielastic electron scattering in the relativistic random phase approximation (RPA). The results in the DDRH model are compared with those in other models systematically. It is found that meson effective masses induced by the nonlinear terms in the nonlinear Walecka model should be used to obtain the meson Greens functions when the longitudinal response function and the Coulomb sum rule are calculated. The effects of the and mesons are clearly shown in quasielastic electron scattering, and the isospin-dependent attractive potential between nucleons due to the exchange of the -meson cancels the isospin-dependent repulsive contribution of the -meson to a certain extent. The obtained results in the DDRH model are in good agreement with experimental data except for the Coulomb sum rule in ²⁰⁸Pb.     

Shape evolution for Sm isotopes in relativistic mean-field theory

The evolution of shape from the spherical to the axially deformed shapes in the Sm isotopes is investigated microscopically in relativistic mean-field theory. The microscopic and self-consistent quadrupole deformation constrained relativistic mean-field calculations show a clear shape change for the even-even Sm isotopes with N = 82-96. The potential surfaces for ¹⁴⁸Sm, ¹⁵⁰Sm and ¹⁵²Sm are found to be relatively flat, which may be the possible critical-point nuclei. By examining the single-particle spectra and nearest-neighbor spacing distribution of the single-particle levels, one finds that the single-particle levels in ¹⁴⁸Sm , ¹⁵⁰Sm, and ¹⁵²Sm distribute more uniformly.     

Determining the divergence of an ultra-relativistic electron beam from the diffracted transition radiation in a single-crystal target

We have studied the possibilities of using diffracted transition radiation excited by a relativistic electron beam in a single-crystal target to determine the beam divergence. For this purpose, we investigated the expressions we had previously derived that describe the angular density of diffracted transition radiation excited by a relativistic electron beam crossing a thin single-crystal plate. In our calculations, we used the two-parameter model distribution function to represent the angular distribution of ultra-relativistic electrons in the beam. For determining the beam divergence parameters, the methods of two-dimensional objective function minimization were used. The model calculations we performed confirm the efficiency of the above-mentioned methods for determining the divergence of a relativistic electron beam.     

Scattering of electrons from gas-phase N2O(1Σ): Computed cross-sections and angular distributions in comparison with experiments

Ab initio calculations are reported for the quantum scattering of electrons from N₂O molecules in the gas phase and for energies which range from near threshold up to about 100 eV. Elastic integral cross-sections and angular distributions are examined in detail and an extensive comparison is made with existing experiments. The agreement found with the latter data is fairly good and results are further discussed to explain the physical mechanisms at work for this polar target.     

Effects of temperature and impurities on electron radiation damage in the high voltage microscope

This paper describes the results of irradiation of specimens of copper and copper containing up to 2 at % beryllium in the high-voltage electron microscope. The results of irradiation at temperatures ranging from 20–500 K are described and discussed in the light of recently proposed theories of defect nucleation. Although the results are difficult to interpret because of the many diverse factors which influence the nucleation and growth of the damage it was found that the values for the volume density of defects were in general agreement with the predictions, if the effects of the foil surfaces were taken into account.

The corrected densities were used to derive values for the activation energy for motion of an interstitial in copper, E_m , and the binding energy between an interstitial and a beryllium atom, E_b . The results obtained were 0.12±0.03 eV for E_m and 0.29±0.07 eV for E_b .     

云和降水扰动对黄土高原半干旱草地辐射收支及能量分配的影响

地表辐射收支和能量分配对陆-气系统的反馈是气候模式中最重要的物理过程之一. 认识半干旱地区云和降水的扰动对辐射收支和能量分配的影响规律, 是提高数值模式中评估地表辐射收支和能量平衡参数化效果的关键环节. 利用兰州大学半干旱气候与环境观测站2008年的观测资料, 研究了云和降水的扰动对辐射收支各分量的削弱作用及对地表能量平衡的影响规律. 年平均结果表明, 多云状况可以作为年平均的气候背景; 云和降水对短波辐射削弱最强, 大气向下长波辐射随天空云量的增加而增强, 地表向上长波辐射随着云量的增加而减小, 净辐射占总辐射的比率受云和降水的影响较小. 季节平均结果显示, 短波辐射日积分量在生长季和非生长季均随云量的增加而降低, 生长季云和降水对短波辐射的削弱作用明显强于非生长季. 生长季, 晴天、少云和多云时向上长波辐射差异不大, 阴天时向下和向上长波辐射明显减小. 非生长季, 地表向上长波辐射受云和降水的影响较小, 日积分量变化不大, 向下长波辐射随云量的增多而增强. 地表反照率具有明显的日变化和季节变化, 冬季大, 秋季小; 地表反照率日变化呈不对称的“V”形分布. 生长季, 感热通量和土壤热通量随云量增多而减小; 潜热通量在晴天、少云和多云状况下随云量增多而增大; 阴天时受降水影响, 净辐射的严重削弱导致了潜热通量大大降低. 非生长季, 少云时净辐射日积分量最大, 晴天时的净辐射与多云和阴天状况接近; 感热和潜热通量随云量的增多而减小, 土壤热通量日平均积分值在非生长季为负. 生长季, 多云状况的能量闭合度最好, 能量不平衡差额占净辐射的3.9%; 阴天时最差, 不平衡差额占净辐射的16.8%; 晴天和少云状况不平衡差额约占净辐射量的7%. 非生长季受积雪影响, 能量不闭合差额明显大于生长季. 关键词： 半干旱草地 云和降水的扰动 辐射收支 能量平衡     

Energy loss of 18 keV electrons in gaseous T and quench condensed D films

Measurements of the energy loss of fast electrons at an energy of 18 keV have been performed on molecules of hydrogen isotopes, gaseous T ₂ and frozen D ₂ . Whereas in the case of gaseous T ₂ the values of total inelastic cross-section ( cm² for E = 18.6 keV), average energy loss ( eV) and peak position of the energy loss spectra ( eV) agree well with the expectations, the corresponding values for quench condensed D ₂ differ significantly from the ones for gaseous T ₂ . We observe a significant lower total inelastic cross-section ( cm², for E = 18.6 keV) larger average energy loss ( eV) and higher peak position ( eV). These differences may be interpreted in terms of changes of the final state spectrum. A CI calculation for a D ₂ cluster shows indeed a clear shift of the excited states in agreement with the observation. Received 24 August 1999     

Spontaneous emission from a ladder three-level atom in anisotropic photonic crystals

We investigate the spontaneous radiation from a ladder three-level atom embedded in a three-dimensional anisotropic photonic crystal with an external driving field. The properties of the spontaneous emission are dependent strongly on the relative position of the middle level from the band edge. Due to the Autler-Townes splitting by the action of the driving field, the external driving field can also affect the properties of the spontaneous emission. The population exchanged between the upper and the middle levels decreases as the detuning of the external driving field frequency from the corresponding transition frequency increases. The properties of the emission field can be changed or so much as controlled by choosing suitable intensity of the external driving field. The emission spectrum is more complex, and dependent on the location of the observer in this case.     

Pulsed laser ablation of zinc selenide in nitrogen ambience: Formation of zinc nitride films

Zinc nitride (Zn₃N₂) thin films are prepared using pulsed laser deposition (PLD) from zinc selenide (ZnSe) target at different nitrogen ambient pressures viz. 1, 3, 5, 7 and 10 Pa. The films prepared with nitrogen pressures 1 and 3 Pa are amorphous in nature, whereas the films prepared at 5, 7 and 10 Pa exhibit the presence of cubic bixbyite Zn₃N₂ structure with lattice parameter very close to bulk of Zn₃N₂. The particle size calculated by Debye Scherrer's formula is in the nano regime. Surface morphology of the films is studied by SEM and AFM analysis. Optical parameters such as band gap, refractive index and porosity of the films are calculated. Moreover, the present study confers an outlook about how do various factors such as substrate temperature, reactive supplementing gas and laser-target interaction influence the film developing process during pulsed lased deposition.     

Do we understand the electric quadrupole strength distributions in magic nuclei?

A comparison between the electric quadrupole (E2) strength distributions in ^{40, 48}Ca with new results from ⁵²Cr is presented. The deduced E2 strength distributions and the exhaustion of the isoscalar energy-weighted E2 sum rule are very different. Microscopic approaches fail to reproduce these differences. A survey of the available data shows that the exhaustion of the energy-weighted isoscalar E2 sum rule in doubly magic nuclei below the isoscalar giant quadrupole resonance is typically more than two times larger than in semi-magic nuclei. On the other hand, the E2 strength in this energy region exhausts about 50% of the total E2 strength, independent from shell closures.