We perform a study on Rayleigh scattering of highly linearly polarized hard x rays on a thin Au foil target. In the study the angular distribution of the scattered radiation is analyzed in a relativistic regime both within and out of the plane of polarization of the incident beam. Within this experiment we scatter a synchrotron beam with a photon energy of 175 keV on a high-$Z$ target foil, namely, gold. Our findings correlate well with state-of-the-art calculations of the scattering process performed in the framework of quantum electrodynamics and may have considerable impact on future experiments regarding a polarization-resolved analysis of Delbrück scattering. Furthermore, we show that the angular distribution of Rayleigh scattering can be used for a highly sensitive determination of the degree and orientation of the linear polarization of the incident hard-x-ray beam, if we rely on the theoretical framework.

For photon energies from several 10 keV up to a few MeV Compton polarimetry is an indispensable tool to gain insight into subtle details of fundamental atomic radiative processes. Within the SPARC collaboration several segmented semiconductor detectors are developed that are well suited for application as efficient Compton polarimeters. In this report, these recent developments are reviewed and it is discussed how Compton polarimetry can be employed at the upcoming Gamma Factory.

We present a theoretical investigation of the elastic Rayleigh scattering of X-rays by atomic targets. Special attention is paid to the question of how the polarization of the scattered photons is affected if the incident light is itself polarized. In particular, we found that the circular polarization of the incoming X-rays may lead to a remarkable modification of the linear polarization of the scattered photons. Based on this ’circular-to-linear-polarization-transfer’ and on the fact that the linear polarization of X-rays can be conveniently observed by solid-state Compton detectors, we argue that Rayleigh scattering may be used as a tool for circular polarimetry of hard X-rays. To illustrate our proposal, we performed detailed calculations of 145 and 500 keV circularly polarized photons scattered by lead atoms. Based on these calculations, we found that the photon scattering under large angles with respect to the incident beam direction is most favorable for the circular polarimetry of hard X-rays. In particular, for 500 keV photon energy and scattering angles around 70 deg we found a remarkable modification of the linear polarization of scattered light for the case when the incident radiation is circularly polarized.

We perform a study on the Compton scattering of a photon beam off atomic targets. The main focus of this study is the influence of the momentum distribution of the target electrons on the polarization transfer in Compton scattering from the incident to the scattered photons. For this purpose we developed a Monte Carlo simulation of the Compton scattering process based on the relativistic impulse approximation. This simulation provides information on the double differential scattering cross section as well as the linear polarization of the scattered radiation over the entire energy range of the Compton peak for arbitrary incident linear polarization characteristics. Furthermore, we compare the predictions yielded by the simulation to data obtained in an experiment where a highly linearly polarized hard x-ray beam with a photon energy of 175 keV was scattered off a thin gold foil target. Both the simulation as well as the experimental results suggest a deviation of the linear polarization of the scattered radiation at the center of the Compton peak compared to scattering off a free electron at rest and a change of the polarization over the Compton peak due to the influence of the initial electron momentum.

We present a theoretical study of elastic photon scattering by atomic targets. This process is of special interest since various channels from atomic and nuclear physics as well as quantum elctrodynamics contribute to it. In this work, we focus on Delbrück scattering which proceeds via production of virtual $e^{+}{e}^{-}$ pairs. In particular, we explore whether and how the Delbrück channel can be “seen” in present synchrotron experiments which employ strongly linearly polarized light in the energy range of a few hundred keV. In order to answer this question, detailed calculations have been performed for the scattering of 300- and 889.2-keV photons off helium-like tin ions. Based on these calculations, we argue that the Delbrück scattering for the energies below the threshold for $e^{+}{e}^{-}$ pair creation leads to a shift in the angular distribution and the polarization of the scattered photons which can be observed by state-of-the-art solid-state detectors.

We present an experimental study of the Rayleigh scattering of highly linearly polarized hard x rays. For this study, photons produced by a synchrotron source with an energy of 175 k e V are scattered by a thin gold foil target. While the linear polarization in terms of degree of polarization and its orientation of the incident photon beam are well known, the outgoing scattered photons are analyzed by means of Compton polarimetry. For this, a polarimeter detector is positioned at different observation angles with respect to the incident photon beam. For the first time the polarization of elastically scattered photons outside of the polarization plane of the incident radiation is investigated, enabling novel access to a so-far untested component of the polarization transfer. The experimental findings are compared to predictions of two theoretical models. It is found that, when leaving the polarization plane of the incident photon beam, a strong deviation from the form factor approximation is evident, while calculations of the Rayleigh scattering in the S -matrix approach agree with the experimental results. Furthermore, this study is a foundation for future experiments dedicated to a polarization-resolved analysis of Delbrück scattering.