Investigation of the Electromagnetic Radiation Emitted by Sub-GeV Electrons in a Bent Crystal

Abstract

The radiation emitted by 855 MeV electrons via planar channeling and volume reflection in a 30.5-μm-thick bent Si crystal has been investigated at the MAMI (Mainzer Mikrotron) accelerator. The spectral intensity was much more intense than for an equivalent amorphous material, and peaked in the MeV range in the case of channeling radiation. Differently from a straight crystal, also for an incidence angle larger than the Lindhard angle, the spectral intensity remains nearly as high as for channeling. This is due to volume reflection, for which the intensity remains high at a large incidence angle over the whole angular acceptance, which is equal to the bending angle of the crystal. Monte Carlo simulations demonstrated that incoherent scattering significantly influences both the radiation spectrum and intensity, either for channeling or volume reflection. In the latter case, it has been shown that incoherent scattering increases the radiation intensity due to the contribution of volume-captured particles. As a consequence, the experimental spectrum becomes a mixture of channeling and pure volume reflection radiations. These results allow a better understanding of the radiation emitted by electrons subjected to coherent interactions in bent crystals within a still-unexplored energy range, which is relevant for possible applications for innovative and compact x-ray or γ-ray sources

Steering of Sub-GeV electrons by ultrashort Si and Ge bent crystals

“…Over the years, positive particle beam steering has been well investigated in a wide range of energies, from few MeV up to the recent result at LHC with 6.5 TeV protons. Conversely, the negatively charged particle case has been poorly investigated and only recently, thanks to the realization of very short bent Si crystals, it has become possible to steer negatively charged particles beams [11,12,13,14,15,16,17,18,19,20,21]. However, the possibility to steer electron beams is promising for applications in electron-positron collider collimation systems [13,22,23,24,25] as well as innovative high-intensity X-or γ-radiation sources [11,12,13,14,26].…”

Strong Reduction of the Effective Radiation Length in an Axially Oriented Scintillator Crystal

“…Since part of the radiated energy by the primary electrons was converted in pairs and not collected at the calorimeter, a proper estimation of the X 0 ef f reduction factor can be done only through Monte Carlo simulation. We recently developed a method of direct integration of the Baier Katkov (BK) formula [19,22] and tested it vs. experimental results with Si crystals [19,21,23]. The BK quasiclassical method is used to compute the e.m. radia-tion emission by ultrarelativistic particles in an external field taking into account quantum recoil and is commonly used to treat the strong field effects in crystals [24].…”

Broad angular anisotropy of multiple scattering in a Si crystal

“…(10), take into consideration the residual coherent effects, such as the influence of the string potential on incoherent scattering and an additional angular spread arising at both the entrance and exit of a particle in/out of a crystal. All these effects have been fully taken into consideration by using the CRYSTAL code [24,25], a program for Monte Carlo simulations of charged particle trajectories in the potential of a crystalline medium with simulation of incoherent scattering, tested in different experiments [26,27,28]. The results of simulations are shown in Fig.…”