Quantum effects on polarization bremsstrahlung from electron-atom collisions in partially ionized dense hydrogen plasmas

The quantum effects on the polarization bremsstrahlung emission due to the low-energy electron-atom collisions are investigated in partially ionized dense hydrogen plasmas. The impact parameter analysis is employed to describe the motion of the projectile electron in order to investigate the variation of the bremsstrahlung emission spectrum as a function of the impact parameter, de Broglie wave length, Debye length, and radiation photon energy. The results show that the quantum effects strongly suppress the polarization bremsstarhlung emission. It is also found that the polarization bremsstarhlung emission cross section shows the maximum value at the position of the Bohr radius. It is interesting to note that the quantum effects are found to be more important than the screening effects in the polarization bremsstarhlung emission.     

Nonuniform charge distribution effects on bremsstrahlung emission in drifting dusty plasmas

The effect of the nonuniform charge distribution due to the ion flow on the ion–dust grain bremsstrahlung process is investigated in dusty plasmas. The impact-parameter analysis is applied to the motion of the projectile ion in order to investigate the variation of the bremsstrahlung radiation cross section as a function of the impact parameter, Debye length, Mach number, radiation photon energy, and projectile energy. The result shows that the nonuniform charge distribution effect strongly enhances the bremsstrahlung cross section. It is also found that the bremsstrahlung radiation cross section decreases with increasing the Debye length.     

A relativistic description of the polarization mechanism of elastic bremsstrahlung

A completely relativistic mechanism for describing polarization bremsstrahlung caused by an elastic collision of a charged particle with a many-electron target was suggested. Multipole expansions for the amplitude and cross section of the process taking into account radiation lag effects were obtained. Including higher order multipoles was shown to result in substantial asymmetry of the angular distribution of emitted photons compared with the dipole case and in a noticeable change in the spectral characteristics of polarization radiation. The cross section of polarization bremsstrahlung was found to increase logarithmically as the energy of incident particles grew.     

Dynamic plasma screening effects on low-energy bremsstrahlung emission in nonideal plasmas

The dynamic screening effects on the low-energy electron–ion bremsstrahlung process are investigated for both the soft and hard photon radiations in nonideal plasmas. The impact-parameter analysis is employed to obtain the bremsstrahlung radiation cross section as a function of the impact parameter, projectile energy, radiation photon energy, thermal energy, and Debye length. The results show that the dynamic screening effect on the bremsstrahlung radiation is found to be more significant for distant encounters. In addition, the dynamic screening effect is found to be more important for the soft photon radiation and decreases with increasing the radiation photon energy.     

Bremsstrahlung shielding parameters in polymer concretes

Concretes are used for shielding in nuclear power plants. Beta radiation is emitted during the nuclear reactions. This beta radiation interacts with the concrete and results in secondary radiation such as bremsstrahlung. Shielding parameters of beta-induced bremsstrahlung in concretes are important in the field of radiation protection. We have evaluated the cross section, yield, intensity and dose rate of beta-induced bremsstrahlung by pure beta nuclides of end point energy ranges from 0.4 to 5?MeV in some polymer-based concretes such as sulfur polymer concrete, barium polymer concrete, calcium polymer concrete, fluorine polymer concrete, chlorine polymer concrete and germanium polymer concrete. We have compared the shielding properties among the studied polymer concretes. The efficiency, intensity and dose rate of bremsstrahlung increases with a maximum energy of beta nuclide and modified atomic number of the concrete. From the detailed study, it is clear that the barium polymer concrete is having large bremsstrahlung dose rate and specific bremsstrahlung constant values than the other studied polymer concretes. This means barium polymer concrete is a good absorber of bremsstrahlung radiation than the other studied polymer concretes.     

Effects of magnetic field and temperature on the nonrelativistic bremsstrahlung process in magnetized anisotropic plasmas

The magnetic field and thermal effects on the nonrelativistic electron-ion bremsstrahlung process are investigated in magnetized anisotropic plasmas. The effective electron-ion interaction potential is obtained in the presence of an external magnetic field. Using the Born approximation for the initial and final states of the projectile electron, the bremsstrahlung radiation cross section and bremsstrahlung emission rate are obtained as functions of the electron energy, radiation photon energy, magnetic field strength, plasma temperature, and Debye length. It is shown that the effects of the magnetic field enhance the bremsstrahlung radiation cross section for low plasma temperatures and, however, suppress the bremsstrahlung cross section for high plasma temperatures. It is also shown that the magnetic field effects diminish the bremsstrahlung emission rate in magnetized high temperature plasmas.     

The role of the polarization mechanism for emission of radiation by atoms over a broad photon frequency range

This paper develops an effective method for calculating the bremsstrahlung cross section with allowance for the polarization mechanism. We calculate the cross section of bremsstrahlung produced in the scattering of electrons and positrons by H and Kr atoms. We also demonstrate the important role of polarization bremsstrahlung in the formation of the total emission spectrum over the entire frequency range. Zh. éksp. Teor. Fiz. 114, 458–473 (August 1998)     

Effect of electron and γ polarization on two-photon bremsstrahlung of electrons in a nuclear field

The cross section for two-photon bremsstrahlung is integrated over the electron scattering angle and the (common) emission angle of the bremsstrahlung photons. Equations are found for the energetic, angular, and polarization distributions of the cross section. The cross section for two-photon bremsstrahlung for the case in which the momenta of the bremsstrahlung photons are parallel can be larger than the corresponding Bethe-Heitler cross section. The probabilities for certain polarization states of the electrons are also analyzed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 13–18, July, 1972.     

Contribution of the second-order born approximation to the coherent bremsstrahlung cross section by relativistic electrons and positrons in crystals

Equations for the cross section and polarization of the coherent bremsstrahlung emitted by relativistic electrons and positrons in crystals are obtained taking into account the contribution from the second-order Born approximation. The radiation cross section and polarization in the field of the atomic plane is considered as a function of the charge sign of the particle.     

Dose estimation and shielding calculation for X-ray hazard at high intensity laser facilities

An ionizing radiation hazard produced from the interaction between high intensity lasers and solid targets has been observed. Laser-plasma interactions create "hot" electrons, which generate bremsstrahlung X-rays when they interact with ions in the target. However, up to now only limited studies have been conducted on this laser-induced radiological protection issue. In this paper, the physical process and characteristics of the interaction between high intensity lasers and solid targets are analyzed. The parameters of the radiation sources are discussed, including the energy conversion efficiency from laser to hot electrons, hot electron energy spectrum and electron temperature, and the bremsstrahlung X-ray energy spectrum produced by hot electrons. Based on this information, the X-ray dose generated with high-Z targets for laser intensities between 10¹⁴ and 10²⁰ W/cm² is estimated. The shielding effects of common shielding items such as the glass view port, aluminum chamber wall and concrete wall are also studied using the FLUKA Monte Carlo code. This study provides a reference for the dose estimation and the shielding design of high intensity laser facilities.     

Nonperturbative gluon radiation and energy dependence of elastic scattering

The energy dependence of the total hadronic cross sections is caused by gluon bremsstrahlung which we treat nonperturbatively. It is located at small transverse distances about 0.3 fm from the valence quarks. The cross section of gluon radiation is predicted to exponentiate and rise with energy as s(delta) with delta = 0.17+/-0. 01. The total cross section also includes a large energy independent Born term which corresponds to no gluon radiation. The calculated total cross section and the slope of elastic scattering are in good agreement with the data.     

偏振分辨激光诱导击穿光谱的铝铁合金信背比改善效果研究

偏振分辨激光诱导击穿光谱(PRLIBS)以其低成本压制背景的特点在LIBS降低检测限上有着重要意义,但是理论上的争议和信背比改善效果不稳定限制了其应用前景。为深入分析等离子体产生偏振特性的原理和PRLIBS信背比的改善效果,采用1 064 nm纳秒脉冲激光器和光纤光谱仪对铝铁合金样品进行了偏振分辨LIBS的信背比改善效果及偏振原理的探索性实验。通过对辐射能量的估算,大胆地推测轫致辐射在背景辐射中的占比是由大变小的,并据此解释了背景辐射强度在时间上的变化。通过改变能量密度、检偏角度、探测角、延时时间、积分时间等因素,采集光谱强度和波长数据、计算偏振度和信背比,观察到铝铁合金的等离子体光谱中背景谱和分立谱均有偏振且存在偏振度和偏振方向的差异,发现偏振LIBS改善信背比的效果与实验参数包括能量密度、延时时间、检偏角度以及波长有关。PRLIBS信背比关于能量密度的变化与一般LIBS类似,在能量较大时会趋于饱和。检偏角度会影响信背比大小,与光谱的偏振方向和偏振度有关,推导了信背比改善效果关于偏振度、检偏角度、偏振方向夹角的公式。在波长上连续谱偏振度趋势较为稳定而分立谱偏振度随光谱强度增大而减小。随延时时间增加,偏振度变化不明显,原因是相比于积分时间延时的改变量很小,而信背比的变化趋势与无偏振LIBS一致。总结了国内外对PRLIBS机理具有代表性的解释并进行了讨论,排除了激光光场、菲涅尔反射、各向异性电子速度分布等因素对等离子体偏振特性的决定性作用。研究结论是在ns-LIBS实验中,复合辐射在可见光和紫外光范围内占背景辐射的大部分,其偏振特性主要源于等离子体复合阶段产生的各向异性复合过程,原子谱偏振特性可能源于该过程中受激原子的磁性支能级间数量的不平衡,而背景谱与原子谱的偏振度及偏振方向的差异主要取决于偏振特性产生机理的不同。研究发现, PRLIBS并不总能提升元素的信背比,尤其对弱光谱信号改善效果有限,要获得较好的压制背景的效果,可以对PRLIBS的能量密度、检偏角度、延时与积分时间等条件加以控制,在能量密度20 J·cm-2积分时间30μs检偏角度20°下FeⅠ407.12 nm处的信背比由4.86提升至12.97。偏振度与探测角相关性较小,原因可能是导体的菲涅尔反射效应很弱。研究结果对PRLIBS的原理研究和应用提供了有效的理论基础。     

Hydrostatic pressure,impurity position and electric and magnetic field effects on the binding energy and photo-ionization cross section of a hydrogenic donor impurity in an InAs Pöschl-Teller quantum ring

Using the variational method and the effective mass and parabolic band approximations, the behaviour of the binding energy and photo-ionization cross section of a hydrogenic-like donor impurity in an InAs quantum ring, with Pöschl-Teller confinement potential along the axial direction, has been studied. In the investigation, the combined effects of hydrostatic pressure and electric and magnetic fields applied in the direction of growth have been taken into account. Parallel polarization of the incident radiation and several values of the applied electric and magnetic fields, hydrostatic pressure, and parameters of the Pöschl-Teller confinement potential were considered. The results obtained can be summarised as follows: (1) the influence of the applied electric and magnetic fields and the asymmetry degree of the Pöschl-Teller confinement potential on the donor binding energy is strongly dependent on the impurity position along the growth and radial directions of the quantum ring, (2) the binding energy is an increasing function of hydrostatic pressure and (3) the decrease (increase) in the binding energy with the electric and magnetic fields and parameters of the confinement potential (hydrostatic pressure) leads to a red shift (blue shift) of the maximum of the photo-ionization cross section spectrum of the on-centre impurity.     

New phenomena in laser-assisted scattering of an electron by a muon

The scattering of an electron by a muon in the presence of a linearly polarized laser field is investigated in the first Born approximation. The theoretical results reveal the following: i) At medium and large scattering angles, many multiphoton processes occur during scattering, and these nonlinear phenomena may predict the resonant state of the electron and the muon formed in the collision process. ii) The photoabsorption (inverse bremsstrahlung) dominates the photoemission (bremsstrahlung), causing the cross section to increase. iii) When the laser polarization deviates from the incident direction, the lasermodified total cross section depends considerably on the azimuthal angle of the scattered electron. The dependence of the cross section on the field strength, polarization direction, and electron-impact energy are studied.     

Classical and quantum theories of the polarization bremsstrahlung in the local electron density model

Classical and quantum theories of polarization bremsstrahlung in a statistical (Thomas-Fermi) potential of complex atoms and ions are developed. The basic assumptions of the theories correspond to the approximations employed earlier in classical and quantum calculations of ordinary bremsstrahlung in a static potential. This makes it possible to study on a unified basis the contribution of both channels in the radiation taking account of their interference. The classical model makes it possible to obtain simple universal formulas for the spectral characteristics of the radiation. The theory is applied to electrons with moderate energies, which are characteristic for plasma applications, specifically, radiation from electrons on the argon-like ion KII at frequencies close to its ionization potential. The computational results show the importance of taking account of the polarization channel of the radiation for plasma with heavy ions.     

Oscillatory screening and quantum interference effects on electron collisions in quantum plasmas

The oscillatory screening and collision-induced quantum interference effects on electron-electron collisions are investigated in dense quantum plasmas. The modified Debye-Hückel potential with the total spin states of the system is considered to obtain the differential electron-electron scattering cross section in quantum plasmas. It is shown that the electron-electron scattering cross section decreases with an increase of the quantum wave number. In addition, the minimum position of the cross section has been appeared with increasing the collision energy at the scattering angle θL=π/4. It is also found that the oscillatory screening effects strongly suppress the cross section near θL=π/4. In addition, it is found that the quantum interference effects suppress the cross section, especially, for the forward and backward scattering cases.     

Angular asymmetries ofe + e − annihilation to three jets

We discuss the angular asymmetries of 3-jet events ine ⁺ e ^? annihilation, originating from hard gluon bremsstrahlung off quarks. Lepton beam polarization helps to disentangle the various helicity components of the bremsstrahlung cross section. They are sensitive to the spin of the radiated quantum but are otherwise parameter-free.     

The refractive properties of the gluon plasma in SU(2) gauge theory

New representations of the total probability of radiation and of the radiative energy loss for charged particle moving in an arbitrary extenal field are obtained in the frame of the quasiclassical operator approach in the quantum electrodynamics. From general results new representations of the total probability and the total intensity of the magnetic bremsstrahlung are derived. The polarization of the radiation, radiation of polarized electrons and radiative polarization have been considered as well.     

The scattering of partially polarized light by oriented atoms

A compact expression is derived for the cross section of scattering of arbitrarily polarized light by oriented atomic systems, in which the dependence on the geometric parameters and on the Stokes parameters preassigning the state of partial polarization of incident radiation is explicitly separated. It is found that the cross section of any photoprocess accompanied by photon absorption (stimulated emission) contains the sum of the products of the circular and linear dichroisms of the process by the respective Stokes parameters. The effect of the atomic orientation and of the dissipation of light energy on the polarization singularities and angular distribution of scattered light is investigated. In particular, it is demonstrated that, in the case of an open dissipation channel, the angular distribution remains dependent on the atomic orientation even in the case of zero degree of circular polarization of scattered radiation.     

Spontaneous interference bremsstrahlung effect in the scattering of a relativistic electron by a nucleus in the field of two light waves

This paper presents, for the general relativistic case, a theoretical study of nonresonance spontaneous bremsstrahlung by an electron scattered by a nucleus in the field of two elliptically polarized light waves propagating in the same direction. We show that there are two significantly different kinematic regions: the noninterference region where the main multiphoton parameters are the Bunkin-Fedorov quantum parameters γ _1,2, and the interference region where interference effects play an important role and where the quantum interference parameters α(±) act as multiphoton parameters. We encounter the spontaneous interference bremsstrahlung effect in two cases: in the special case of the same linear polarization of both waves, and in the general case of elliptical polarization of the waves. The effect manifests itself in the interference region and is due to stimulated, correlated emission and absorption of photons of both waves. For moderately strong fields, we find the cross sections of spontaneous bremsstrahlung by an electron scattered by a nucleus in the given kinematic regions. Finally, we show that the differential cross section in the interference region with correlated emission (absorption) of equal numbers of photons of both waves can be much greater than the corresponding cross section in any other geometry. Zh. éksp. Teor. Fiz. 116, 1210–1240 (October 1999)