Physics of Reflective Optics for the Soft Gamma-Ray Photon Energy Range

Abstract

Traditional multilayer reflective optics that have been used in the past for imaging at x-ray photon energies as high as 200 keV are governed by classical wave phenomena. However, their behavior at higher energies is unknown, because of the increasing effect of incoherent scattering and the disagreement between experimental and theoretical optical properties of materials in the hard x-ray and gamma-ray regimes. Here, we demonstrate that multilayer reflective optics can operate efficiently and according to classical wave physics up to photon energies of at least 384 keV. We also use particle transport simulations to quantitatively determine that incoherent scattering takes place in the mirrors but it does not affect the performance at the Bragg angles of operation. Our results open up new possibilities of reflective optical designs in a spectral range where only diffractive optics (crystals and lenses) and crystal monochromators have been available until now.

Demonstration of multilayer reflective optics at photon energies above 06 MeV

“…With a range of multilayer periods present, Bragg's law is fulfilled at additional angles of incidence thereby broadening the response. The feature did not present itself in previous X-ray campaigns at lower photon energies, on account of the relatively small beam footprints (10 mm, [20]) along the direction of the beam. The reduced grazing incidence angle and increased beam vertical size in use above 0.5 MeV results in an order of magnitude longer footprint.…”

“…Recent research has shown that multilayer coatings can reflect X-rays efficiently at 0.38 MeV [20] where incoherent scattering effects become non-negligible. With the present work, we have nearly doubled the proven range of operation to 0.65 MeV an improvement that may enable new applications, e.g.…”

Gamma-ray mirrors for direct measurement of spent nuclear fuel

“…Details of this work have been published in 2013 in two refereed papers [20,21] and are briefly summarized below.…”

Quasi-mosaicity of (311) planes in silicon and its use in a Laue lens with high-focusing power

“…Another solution to concentrate hard X-rays consists of multilayer optics, which was recently proved to focus photons of up to hundreds of keV with high-efficiency and according to classical-wave physics [3,4]. However, these new reflective optics work at very low grazing incidence angles, below 0.1 • , thus featuring a very low acceptance area for the incident photons.…”

“…The legend describes the diffracting plane employed. The crystals are 10×30×5 mm3 Si and Ge tiles. The disposition of the tiles is optimized with a specifically written code, named LaueGen…”