<title>Multiple scattering effect on angular distribution and polarization of radiation by relativistic electrons in a thin crystal</title>

Abstract

The multiple scattering of ultra relativistic electrons in an amorphous matter leads to the suppression of the soft part of radiation spectrum (the Landau-Pomeranchuk-Migdal effect), and also can change essentially the angular distribution of the emitted photons. A similar effect must take place in a crystal for the coherent radiation of relativistic electron. The results of the theoretical investigation of angular distributions and polarization of radiation by a relativistic electron passing through a thin (in comparison with a coherence length) crystal at a small angle to the crystal axis are presented. The electron trajectories in crystal were simulated using the binary collision model which takes into account both coherent and incoherent effects at scattering. The angular distribution of radiation and polarization were calculated as a sum of radiation from each electron. It is shown that there are nontrivial angular distributions of the emitted photons and their polarization that are connected to the superposition of the coherent scattering of electrons by atomic rows ("doughnut scattering" effect) and the suppression of radiation (similar to the Landau-Pomeranchuk-Migdal effect in an amorphous matter). It is also shown that circular polarization of radiation in the considered case is identically zero.

Radiation of a relativistic electron with non-equilibrium own Coulomb field

“…As it was shown in [23] the non-dipole regime of radiation changes essentially not only spectrum of emitted gamma quanta, but also their angular distribution. In [24] it was proposed to use special features of angular characteristics of non-dipole coherent radiation in a thin crystal for production of the intensive photon beams with high degree of linear polarization.…”

“…On the basis of the theoretical approach explained in details in [24] we have carried out the calculations of the angular distributions and polarization of radiation by 3.5 GeV electrons incident on a tungsten crystal at the angle ψ = ψ L to the axis <111> (where ψ L is the Lindhard angle [27]). In this case θ ms ≈ ψ L = 0.6 µrad and the parameter of non-dipolity is γθ ms ≈ 4.…”

“…In this case θ ms ≈ ψ L = 0.6 µrad and the parameter of non-dipolity is γθ ms ≈ 4. The results of the computer (using binary collision model [24]) for 3.5 GeV electron scattering by the 10 µm tungsten crystal when the electron beam falls at the angle ψ = ψ L to the crystal axis <111> are presented in Fig. 3.…”

“…We also propose to carry out a new experiment to study the special features of the angular distribution of radiation at the TSF effect conditions, which were theoretically described in [23]. These features can give a new opportunity for obtaining a high degree of linear polarization of gamma-quanta that was proposed in [24].…”