The `quasi-mosaic' effect in crystals and its applications in modern physics

Abstract

`Quasi‐mosaicity' is an effect of anisotropy in crystals that permits one to obtain a curvature of internal crystallographic planes that would be flat otherwise. The term `quasi‐mosaicity' was introduced by O. Sumbaev in 1957. The concept of `quasi‐mosaicity' was then retrieved about ten years ago and was applied to steering of charged‐particle beams at the Super Proton Synchrotron at CERN. Beams were deviated by exploiting channeling and volume reflection phenomena in curved crystals that show the `quasi‐mosaic' effect. More recently, a crystal of this kind was installed in the Large Hadron Collider at CERN for beam collimation by the UA9 collaboration. Since 2011, another important application involving the `quasi‐mosaic' effect has been the focalization of hard X‐rays and soft γ‐rays. In particular, the possibility of obtaining both high diffraction efficiency and the focalization of a diffracted beam has been proved, which cannot be obtained using traditional diffracting crystals. A comprehensive survey of the physical properties of `quasi‐mosaicity' is reported here. Finally, experimental demonstrations for adjustable values of the `quasi‐mosaic' curvature are provided.

Innovative remotely-controlled bending device for thin silicon and germanium crystals

“…The sample of the photo has a visible primary curvature along the main surface, which is parallel to the (211) planes, with a radius of 2.8 mm. A secondary bending of 10 mm of the (111) inner planes due to the quasi-mosaic effect [14,21] is exploited for channeling.…”

Channeling, volume reflection, and volume capture study of electrons in a bent silicon crystal

“…The silicon (Si) crystal used in this experiment was fabricated [30] at the Sensors and Semiconductor Laboratory at the University of Ferrara with crystallographic orientation chosen to produce quasimosaic bending of the (111) plane [31]. Its thickness was measured interferometrically to be 60 AE 1 μm.…”

Observation of Quasichanneling Oscillations

“…It is a silicon (Si) crystal with a thickness of l cr = 60 ± 1 µm. The crystal bending exploits the quasi-mosaic effect [12] to provide (111) bent planes at a radius R = 15 ± 0.42 cm. The bending angle of the crystal is θ b = 402 ± 9 µrad.…”