Polarization transfer in relativistic electron-nucleus bremsstrahlung

The emission of circularly polarized photons during the scattering of fast spin-polarized electrons from heavy nuclei is studied within the Dirac-Sommerfeld-Maue approach. Predictions are made for the dependence of the polarization correlations C₃₂ and C₁₂ on collision energy, photon energy and nuclear charge. A comparison with pilot measurements of the transmission asymmetry, sensitive to C₃₂, for 3.5 MeV e + Pb verifies that the polarization transfer increases with photon energy for small emission angles.     

Features of bremsstrahlung from relativistic electrons in solid targets

It has been shown that the classical Bethe-Heitler result can be inapplicable for describing the bremsstrahlung spectrum of relativistic electrons in real solid targets.     

Coherent bremsstrahlung of relativistic electrons in antiferromagnets

The coherent bremssstrahlung (CB) of relativistic electrons in antiferromagnetic crystals is studied theoretically. It is shown that the internal magnetic field of an antiferromagnet has a negligible effect on CB. The complete CB spectrum is calculated for hematite, -Fe₂O₃.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 57–61, February, 1988.     

Experimental study of polarization bremsstrahlung from small-grained polycrystals

The spectrum of polarization Bremsstrahlung is measured in backscattering geometry for 7-MeV electrons and a polycrystalline Ni foil without texture. The average size of grains in the foil is 300 nm. The results show the possibility of using a new method in the diagnostics of the atomic structure of polycrystalline materials with nanosized grains. The method is based on measuring the coherent component of polarization Bremsstrahlung.     

Asymmetry of bremsstrahlung by moderately relativistic polarized electrons

The asymmetry of bremsstrahlung by transversely polarized electrons using Sommerfeld–Maue wave functions has been calculated. In order to simplify the final formula the relativistic approximation has been used. The results obtained show a linear dependence of the asymmetry on the atomic number Z for the range 4≤Z≤26. It is shown that the approach developed gives the zeroth asymmetry for ultrarelativistic energies as expected but for initial electron energies ～5 MeV the asymmetry may achieve a magnitude ～8% (for Z=26). Polarimetry of electrons with energy higher than 1 MeV (where conventional Mott polarimeters have large experimental difficulties) may be carried out using the bremsstrahlung process providing a reasonable asymmetry and high cross section.     

Measurement of the polarization bremsstrahlung of relativistic electrons in polycrystalline targets

The spectra of the collimated polarization bremsstrahlung of 7-MeV electrons intersecting Al, Cu, and Ni polycrystalline films have been measured. Detailed quantitative comparison of the experimental data with theoretical predictions has been performed. It has been shown that the model of a polycrystal as an ensemble of randomly oriented single crystals adequately describes the experimental results. This makes it possible to expect the development of a new method of diagnostics of the atomic structure of partially ordered solids.     

Coherent bremsstrahlung from relativistic channelled positrons

Poor beam collimation leads to overcompensation of suppression of coherent bremsstrahlung in the axial channelling case. This fact has been used to study the effect of beam divergence on the radiation emitted by relativistic (axially) channelled positrons. It has been found that due to beam divergence in the experiment of Alguard and co-workers in which radiation of 56 MeV positrons channelling along 〈110〉 rows of a silicon crystal is observed, coherent bremsstrahlung becomes an important contributing factor to the high frequency part of the observed spectrum.     

Generation of circularly polarized photons by relativistic electrons moving in a crystal

The relativistic-electron (relativistic-positron) acceleration arising in its scattering on the potential of a crystal atomic string is highly anisotropic, which causes polarization of accompanying radiation. The possibility of developing an efficient source of circularly polarized photons by using electrons or positrons of energies attainable at many operating accelerators is demonstrated and analyzed.     

Diagnostics of nanodisperse polycrystals based on the polarization bremsstrahlung of relativistic electrons

The spectra of polarization bremsstrahlung are measured in the backscattering geometry during the interaction of 7-MeV electrons with a polycrystalline Ni foil. Measurement is conducted under conditions such that the size of the region of coherent X-ray radiation scattering in a target is on the order of 10 nm. The obtained results make it possible to suggest that using polarization bremsstrahlung as a new method for the diagnostics of the atomic structures of nanodisperse polycrystals is effective.     

Interference effects in X-ray radiation from relativistic electrons moving at a small angle to an atomic plane

X-ray radiation of relativistic electrons interacting with a set of parallel atomic planes is considered. The anomalous behavior of the radiation due to the interplay of parametric and coherent bremsstrahlung emission mechanisms, which simultaneously occur under specific conditions, is studied.     

Photon bremsstrahlung from an extreme relativistic hydrogen plasma

The effect of the electron-positron pair creation on the intensity of radiation by an extreme relativistic plasma is studied. The degeneracy of the electron and positron gases is taken into account. It is found that the pair creation is of considerable importance for both the quantity and temperature dependence of the radiation intensity.Dedicated to Professor V. Votruba on his sixtieth birthday.     

Quantum beats from channeling relativistic electrons

Possibility has been explored of periodic time variation of intensity (quanturn beats) of radiation emitted from relativistic electrons channeling along the 〈110〉 axis of a crystal of f.c.c. (diamond) lattice structure.     

Polarization and angular distribution of the radiation of electrons moving in a focusing magnetic field

The angular distribution of the linear-polarization components is found for the radiation of an electron moving in a nonuniform weak-focusing magnetic field. The distribution shape is studied as a function of the amplitudes of the axial and radial betatron oscillations. It is shown that the minimum intensity of the component of the radiation does not vanish, in contrast with the case of a uniform field.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 3, pp. 52–58, March, 1971.The authors thank A. A. Sokolov for suggesting the topic and for fruitful discussions.     

Properties of coherent bremsstrahlung from electrons in thick single crystals

A technique for calculating the frequency and polarization of the coherent bremsstrahlung from relativistic electrons in single crystals of arbitrary thickness is proposed and implemented. It accurately includes multiple scattering of the emitting particles and the angular distribution and collimation of the radiation. The spectral properties of the collimated beam of radiation from electrons with energies of 900 MeV in thick (0.1 r.l.) single crystals of diamond, silicon, and tungsten are compared with the calculations. When the radiation is tightly collimated the dependence of the frequency and polarization properties of the radiation on the multiple scattering of the emitting particles in the crystals becomes weaker.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 21–43, June, 1991.     

Polarization bremsstrahlung of heavy charged particles in a polycrystal

Polarization bremsstrahlung (PBS) of a fast ion scattered in a polycrystalline medium is calculated and analyzed with allowance for the contributions from the coherent and incoherent channels of the process. It is shown that scattering of a projectile from the crystal lattice of the target is responsible for typical features of the PBS spectrum. For example, PBS is suppressed (as compared to radiation emitted by a single atom) in the low-frequency part of the spectrum, where coherent PBS dominates. In the intermediate spectral region, a step structure is formed as a result of “elimination” of the contribution from the reciprocal lattice vector with a preset magnitude to the coherent component of the process. Finally, incoherent PBS dominates in the high-frequency part of the spectrum and the process occurs as in the case of a single atom. These spectral peculiarities of PBS are determined by the structure of the target and depend on the velocity of the projectile and the emission angle, and can be observed in experiments dealing with radiation emitted by fast charged particles in thin polycrystalline films.     

Polarization bremsstrahlung of a hydrogen-like ion in a single crystal

Polarization bremsstrahlung (PB) that arises when a fast hydrogen-like ion is scattered in a single crystal is investigated theoretically. Four types of the process are analyzed that are caused by virtual excitation of electrons of the target and of the incident particle (IP), as well as by a coherent and incoherent interaction between the IP and the single crystal. The spectral, angular, and velocity (of the IP) characteristics of PB are calculated with regard to the spectral function of a photodetector. Optimal observation conditions and regions in which different types of PB are dominant are determined, and the dependence of these regions on the charge of the IP nucleus and of the target atoms is revealed.     

On relativistic electron bremsstrahlung in thin targets

The simple model of relativistic electron bremsstrahlung in a thin target is presented for conditions when its thickness less then a photon formation length. Results of our calculations obtained with account of an influence of target dielectric properties are in agreement with data at 25 GeV electron bremsstrahlung in thin layers of different media.