Contribution of incoherent effects to the orientation dependence of bremsstrahlung from rapid electrons in crystal

Abstract

The bremsstrahlung cross section for relativistic electrons in a crystal is split into the sum of coherent and incoherent parts (the last is due to a thermal motion of atoms in the crystal). Although the spectrum of incoherent radiation in crystal is similar to one in amorphous medium, the incoherent radiation intensity could demonstrate substantial dependence on the crystal orientation due to the electrons' flux redistribution in the crystal. In the present paper we apply our method of the incoherent bremsstrahlung simulation developed earlier to interpretation of some recent experimental results obtained at the Mainz Microtron MAMI.

Incoherent bremsstrahlung in flat and bent crystals

“…Although the spectrum of incoherent radiation in crystal is similar to one in amorphous medium, the incoherent radiation intensity can demonstrate substantial dependence on the crystal orientation due to the electrons' flux redistribution in the crystal (channeling etc.). The simulation based on the semiclassical description of the radiation process [4,5,6] confirms that viewpoint. The results of simulation are in a good agreement with the corresponding early [7] and recent [8] experimental data.…”

“…The spectral density of the incoherent radiation from the individual electron moving on the given trajectory is described by the formula [5,6]…”

“…It is convenient to compare the incoherent radiation intensity of the uniform electron beam in the crystal to the corresponding intensity in the amorphous medium (described by Bethe-Heitler formula). The ratio of these two values is equal to [5,6]…”

Incoherent radiation of fast electrons in a bent crystal

“…Thus, it becomes possible to study the influence of incoherent electron scattering on the intensity of incoherent radiation for various crystal orientations relative to the beam, "switching on and off" the influence of thermal vibra tions of atoms on the electron trajectory in a crystal. The procedure is described in detail elsewhere [9][10][11][12][13]. [3].…”

“…The spectrum of incoherent radia tion is similar to the spectrum of radiation in an amor phous medium; however, its intensity is proportional to the number of close electron-atom collisions and, therefore, reflects the pattern of electron motion in a crystal (channeling or above barrier motion). In [9][10][11][12][13] a procedure was developed for simulating the incoher ent radiation of fast electrons in a crystal based on the quasiclassic description of bremsstrahlung. The results of the simulation are in good agreement with the data of previous [14] and recent [15] experiments.…”