K-shell ionization and characteristic x-ray radiation by high-energy electrons and positrons in oriented silicon crystals

TL;DR

The study addresses K-shell ionization and characteristic x-ray radiation (CXR) produced by high-energy electrons and positrons in oriented silicon crystals. It advances a trajectory-based computer simulation that combines a lattice-aware near-field treatment inside a boundary radius $ρ_0$ with an equivalent-photon description outside, incorporating transition-radiation driven density effects and a separate close-collision component. By computing the angular density $dN/do$ of CXR from the upstream surface for axial <100> and planar (100) and (110) orientations over energies from $1\,GeV$ to $1\,TeV$, the work reveals a non-monotonic evolution of CXR yields with crystal orientation and energy. Key findings show that electron dechanneling strongly shapes the orientation dependence (enhancing yields in axial channels for electrons but suppressing them for positrons), while positron yields tend to approach those of an amorphous target with increasing energy. These results enable using CXR as a diagnostic for crystal orientation and dechanneling, with potential extensions to Ge crystals for stronger CXR sources.

Abstract

K-shell ionization and characteristic x-ray radiation (CXR) by high-energy electrons and positrons in oriented silicon crystals are studied using computer simulation. A method for this simulation has been developed and is described in detail. The evolution of the angular distribution of CXR from the upstream surface of the crystal with changes in the angle between the incident particle momentum and the crystal <100> axis or (100) plane, as well as with changes in particle energy over a wide range (1-1000 GeV), is investigated. It is shown that in most cases this evolution is non-monotonic. The physical mechanisms underlying this behavior are discussed. In particular, the impact of the dechanneling process on CXR produced by electrons is analyzed.

Figures (7)

• Figure 1: Arrangement of atomic strings (black dots) in the plane perpendicular to $\langle100\rangle$ axis of a silicon crystal. The particle moves at a small angle with respect to $\langle100\rangle$ axis, which is parallel to the $z$ axis.
• Figure 2: Dependence of the second term in the braces of (\ref{['N_d']}) on the distance from the surface of a silicon target for two electron (positron) momentum values.
• Figure 3: Dependence of $N_t=N_d + N_c$ on the particle path length in the crystal for different crystal orientations.
• Figure 4: Dependence of angular density of the number of CXR photons emitted from the upstream surface of the crystal on the angle between the observation direction and the direction opposite to the $z$ axis.
• Figure 5: Dependence of the angular density of the number of CXR photons emitted from the upstream surface of the crystal on the angle between the atomic axis/plane and the momentum of the particles incident on the crystal. The particle energy is 1 GeV.