The impact of ionising collisions on channeling and radiation emission for high-energy electrons and positrons

TL;DR

This work quantifies how inelastic ionising collisions with lattice atoms affect channeling and the resulting radiation of high-energy electrons and positrons in oriented diamond and silicon crystals. Using relativistic molecular dynamics with MBN Explorer, the authors simulate 10 GeV particles in (110) and (111) planes, comparing scenarios with and without ionising collisions. They find electrons are only weakly affected, with changes under ~10% in channelling fractions and spectra, while positrons show strong dechannelling, especially in diamond, and the impact on radiation strongly depends on the radiation-collection cone. The results provide concrete guidance for simulation strategies and crystal-source designs, highlighting when ionising collisions can be neglected and when they must be included to accurately predict peak radiation intensities and spectral features.

Abstract

This paper presents a quantitative analysis of the impact of inelastic collisions with atoms in a crystalline environment on the channeling efficiency and intensity of the channeling radiation for high-energy electrons and positrons passing through oriented crystalline targets. This analysis is based on numerical simulations of the channeling process, which were performed using the MBN Explorer software package. Ionising collisions are considered random, fast and local events, and are incorporated into the classical relativistic molecular dynamics framework according to the previously described algorithm. The case studies presented refer to 10 GeV electrons and positrons incident on single crystals of diamond and silicon, oriented along the (110) and (111) planes, with thicknesses of up to 1 mm for electrons and 6 mm for positrons. To elucidate the role of ionising collisions, simulations were performed with and without accounting for them. It is shown that, for electrons, both approaches lead to similar results with regard to both the channelling efficiency and the radiation intensity. In practical terms, this means that numerical simulations can be carried out without accounting for ionising collisions, which are much faster yet produce similar results. For positrons, the ionising collisions reduce significantly the channeling efficiency. However, their impact on the radiation intensity strongly depends on the opening angle of the cone within which the radiation emission is collected. A quantitative analysis of this feature is presented in the paper.

Figures (10)

• Figure 1: Channeling fractions $f_{{\rm ch}, 0}$ (solid lines) and $f_{\rm ch}$ (dashed lines) versus penetration distance $z$ for 10 GeV electrons in oriented diamond (left column) and silicon (right column) crystals. The upper row corresponds to the crystal orientation along the (110) plane, the lower row - along the (111) plane. Curves with filled symbols (circles and squares) show the results obtained with account for ionising collisions. Curves with the open symbols represent the dependencies calculated without ionising collisions (labelled 'without').
• Figure 2: Spectral distribution of radiation emitted by 10 GeV electrons channeled in the diamond crystal oriented along the (110) and (111) planes (left and right columns, respectively). The upper and lower rows correspond to the emission cones $\theta_0=25$ and 150 $\mu$rad, respectively. The solid and dashed curves show the results obtained with and without the ionising collisions being accounted for. The spectra shown refer to the crystal thicknesses of 100, 200, 400 and 600 microns, as indicated in the right-bottom graph. In graph (b), labels 1-4 mark the features discussed in the text.
• Figure 3: Same as in Fig. \ref{['Figure02.fig']} but for oriented silicon crystal.
• Figure 4: Same as in Fig. \ref{['Figure01.fig']} but for 10 GeV positrons.
• Figure 5: Spectral distribution of radiation emitted by 10 GeV positrons channeled in the diamond crystal oriented along the (110) and (111) planes (left and right columns, respectively). The upper and lower rows correspond to the emission cones $\theta_0=25$ and 150 $\mu$rad, respectively. The solid and dashed curves show the results obtained with and without the ionising collisions being accounted for. The spectra shown refer to the crystal thicknesses of 1 and 6 millimeters, as indicated in the right-bottom graph.