Experimental and theoretical study of diffraction properties of various crystals for the realization of a soft gamma-ray Laue lens

TL;DR

This paper combines theoretical calculations and experimental measurements to evaluate various crystals for use in a high-sensitivity space gamma-ray Laue lens, identifying promising materials with high reflectivity and low mosaicity.

Contribution

It provides a comprehensive analysis of candidate crystals' diffraction properties, including new experimental data on SiGe, Cu, and Au crystals for gamma-ray lens applications.

Findings

Crystals can achieve over 30% reflectivity across the energy range

SiGe crystals show up to 60% reflectivity at 300 keV

Cu crystals exhibit mosaicity as low as 15 arcsec

Abstract

Crystals are the elementary constituents of Laue lenses, an emerging technology which could allow the realization of a space borne telescope 10 to 100 times more sensitive than existing ones in the 100 keV - 1.5 MeV energy range. This study addresses the current endeavor to the development of efficient crystals for the realization of a Laue lens. In the theoretical part 35 candidate-crystals both pure and two-components are considered. Their peak reflectivity at 100 keV, 500 keV and 1 MeV is calculated assuming they are mosaic crystals. It results that a careful selection of crystals can allow a reflectivity above 30% over the whole energy range, and even reaching 40% in its lower part. Experimentally, we concentrated on three different materials (Si_{1-x}Ge_x with gradient of composition, mosaic Cu and Au) that have been measured both at ESRF and ILL using highly-monochromatic beams ranging from 300 keV up to 816 keV. The aim was to check their homogeneity, quality and angular spread (mosaicity). These crystals have shown outstanding performance such as reflectivity up to 31% at ~600 keV (Au) or 60% at 300 keV (SiGe) and angular spread as low as 15 arcsec for Cu, fulfilling very well the requirements for a Laue lens application. Unexpectedly, we also noticed important discrepancies with Darwin's model when a crystal is measured using various energies.