Abstract
AbstractFor 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.
Highlights
Photon polarimetry is an indispensable fundamental atomic radiative processes
Moving to higher photon energies, in the soft to medium X-ray regime polarimetry techniques based on Bragg diffraction[9] are commonly used
A much more sensitive test could be performed using a linear polarized photon beam as stated in Ref. [31] since for a scattering angle of 90◦ nuclear Thomson scattering and giant dipole resonance vanish. In their recent paper Koga and Hayakawa presented a more in depth analysis of a possible experimental scenario using a polarized γ-ray beam and measuring the differential scattering cross section for scattering within the polarization plane of the incident beam.[32]. They show that the scattering cross section regarding the part of the scattered radiation being polarized in the scattering plane will be highly dominated by Delbrück scattering for certain polar scattering angles θ while the other scattering constituents are strongly suppressed
Summary
Compton scattering, being the inelastic scattering of a photon on a free (or quasi–free) electron, can be described by the Klein– Nishina formula which gives the angular differential cross section of the process dσ dΩ. The detector crystal (Figure 1b) has a thickness of 9 mm and an active area of 32 mm×32 mm which is segmented on front and back side into 32 strips of 1 mm width each with the strips on front and backside being oriented perpendicular to each other This segmentation of the crystal, leading to an array of 1024 pseudo-pixels, makes it into a high-resolution position-sensitive detector. Each of these strips has its own readout electronics with a cooled preamplification stage leading to an energy resolution of less than 1 keV at a photon energy of 60 keV.[14] The detector crystal serves as Compton scatterer and detector for the scattered photons at the same time. From this reconstruction of the scattering events the azimuthal scattering profile, as shown in Figure 1d can be received in order to extract the degree of linear polarization and the orientation of the polarization vector.[18]
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