出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：A gamma-ray telescope mission concept (GRI: Gamma Ray Imager) based on Laue
focusing techniques has been proposed in reply to the European Space Agency call for mission
ideas (Cosmic Vision 2015-2025). In order to aid the design optimization of its main instrument,
a series of experiments based on CdZnTe pixelized detector prototypes was carried out at the
European Synchrotron Radiation Facility where a ~ 99% polarized high energy beam is
available. The main purpose of these experiments, denominated as POLCA (POlarimtery with
Cadmium Telluride Arrays), was to assess the performance of a CdZnTe pixel detector as a
polarimeter in the gamma-ray band. The spectroscopic, imaging and timing performances were
studied and in particular its potential as a polarimeter was evaluated. The prototype detectors
tested were CdTe and CdZnTe arrays up to 7 mm thick. They were irradiated with a
monochromatic linearly polarized beam with a spot diameter of about 0.5 mm over an energy
range up to 750 keV. Polarimetric Q factors of 0.35 were obtained. Further measurements were
performed with a copper Laue monochromator crystal placed between the beam and the detector
prototype. In this configuration we have demonstrated that a polarized beam does not change its
polarization level and direction after undergoing a small angle (<1º) Laue diffraction inside a
crystal. Upon rotating this crystal by 360º with 22.5º steps no systematic effects were noticed in
the detected polarization after the Laue diffraction process.
