Polarization bremsstrahlung process in quantum plasmas including electron-exchange and shielding effects

The electron-exchange and quantum shielding effects on the polarization bremsstrahlung spectrum due to the electron-shielding sphere encounters are investigated in quantum plasmas. From this work, it is found that the electron-exchange effect strongly suppresses the polarization bremsstrahlung radiation cross section. Additionally, it is found that the polarization bremsstrahlung radiation cross section increases with increasing plasmon energy and, however, decreases with increasing Fermi energy. The variation of the influence of electron-exchange and quantum shielding on the polarization bremsstrahlung spectrum is also discussed.     

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.     

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.     

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)     

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.     

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.     

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.     

Statistical Models in Theory of Polarization Bremsstrahlung

Universal relations have been derived to describe the spectral-angular dependence of the polarization bremsstrahlung of a fast charged particle, based on a statistical model for the electron skeleton of the target. Three statistical atomic models are considered in terms of which the target characteristics that determine the cross section for polarization bremsstrahlung are calculated and analyzed.     

Absolute differential bremsstrahlung cross section for the scattering of 0.6-keV electrons by xenon atoms

The spectral distribution of the absolute differential cross section for total bremsstrahlung, including ordinary and polarization, for the scattering of 0.6-keV electrons from free xenon atoms has been measured. The bremsstrahlung photons have been detected at an angle of 97° with respect to the electron motion direction. The investigations have been carried out in the ultrasoft x-ray spectral region 60–240 eV. The results are compared with the total cross sections for bremsstrahlung calculated in several approximations for the scattering of 5-and 25-keV electrons by Xe atoms. Both the value and the spectral distribution of the experimental absolute cross sections are most satisfactorily reproduced by the calculations in the distorted partial wave approximation.     

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.     

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.     

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.     

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.     

Eine Koinzidenzmessung zum Elementarprozeß der Elektron-Elektron-Bremsstrahlung bei 300 keV

The absolute cross section of electron-electron bremsstrahlung which is differential in all the free kinematical variables was measured by using an electron-photon coincidence technique. An electron beam of 300 keV was used, incident on a carbon target. Within the experimental errors we found agreement with recent theoretical calculations. Simultaneously with the electron-electron bremsstrahlung the absolute cross section of electron-nucleus bremsstrahlung of carbon was measured.     

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.     

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)     

Z dependance of bremsstrahlung of electrons between 2.5 and 4.0 MeV

TheZ-dependance of the high frequency part of the bremsstrahlung spektrum in the forward direction is investigated with a 4.3 MeV electron linear accelerator for electron kinetic energies ranging from 2.5 to 4.0 MeV. We used thin beryllium, carbon, aluminium, titanium, copper, zirconium, silver and gold foils as targets. The relative photon yields are measured by counting the number of neutrons from the Be⁹ (γ, n) Be⁸ reaction, the neutrons being detected by a long counter. An adequate correction factor to the bremsstrahlung yield for multiple scattering of the electrons before radiating is presented and checked at 3.5 MeV with a number of Al foils ranging in thickness from 0.27×10^?3 to 1.61×10^?3 radiation lenghts. The results are compared with five different theoretical expressions for the bremsstrahlung cross section. The presence of electron-electron bremsstrahlung is very clear. For each used theoretical cross section the amount of photons due to this effect was determined supposing the theoretical nuclear cross section be exact for lowZ elements. It is found that theoretical yields obtained with the Elwert corrected Born approximation formulas agree with experiment for all used elements except for gold. The experimental results for gold as compared with the Born approximation formulas are in agreement with the curves given byKoch andMotz.     

Bremsstrahlung of nonrelativistic electrons in metals with allowance made for the polarization channel

We theoretically investigate the bremsstrahlung that appears when nonrelativistic electrons are scattered in a metal target with allowance made for the polarization contribution. We take into account the interference of ordinary and polarization bremsstrahlung, the absorption of radiation in the target material, the energy losses and elastic scattering of an electron by atoms of the medium, and the coherent effects when the radiating electron interacts with the target. We analyze the influence of the target thickness on the process and the contribution of polarization bremsstrahlung to the total yield of bremsstrahlung photons as a function of the problem parameters.     

Polarization bremsstrahlung at collisions of fast ions with multiatomic targets

The processes of polarization bremsstrahlung at collisions of fast ions with linear chains consisting of isolated atoms have been considered. The intensities and angular distributions of radiation spectra have been obtained for an arbitrary number of atoms in a chain. It has been shown that the interference of the photon emission amplitudes leads to a noticeable change in the spectral angular distributions of polarization bremsstrahlung as compared to the distributions at collisions with an isolated atom. The results allow standard generalization to the cases of polarization bremsstrahlung at channeling of fast ions over surfaces and in solid lattices.