Polarimetric performance of a Laue lens gamma-ray CdZnTe focal plane prototype

Abstract

A gamma-ray telescope mission concept [gamma ray imager (GRI)] based on Laue focusing techniques has been proposed in reply to the European Space Agency call for mission ideas within the framework of the next decade planning (Cosmic Vision 2015–2025). In order to optimize the design of a focal plane for this satellite mission, a CdZnTe detector prototype has been tested at the European Synchrotron Radiation Facility under an ∼100% polarized gamma-ray beam. The spectroscopic, imaging, and timing performances were studied and in particular its potential as a polarimeter was evaluated. Polarization has been recognized as being a very important observational parameter in high energy astrophysics (>100 keV) and therefore this capability has been specifically included as part of the GRI mission proposal. The prototype detector tested was a 5 mm thick CdZnTe array with an 11×11 active pixel matrix (pixel area of 2.5×2.5 mm2). The detector was irradiated by a monochromatic linearly polarized beam with a spot diameter of about 0.5 mm over the energy range between 150 and 750 keV. Polarimetric Q factors of 0.35 and double event relative detection efficiency of 20% 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 (<1°) Laue diffraction inside a crystal.

Hard X-ray polarimetry with Caliste, a high performance CdTe based imaging spectrometer

“…These results illustrate the advantage of the fine energy resolution of Caliste-256 to maximize the figure of merit, admitting the efficiency is affected. When compared with other CdTe-based single layer and planar polarimeters, we obtain a higher Q factor (Curado da Silva et al 2008). This is explained by Caliste-256 prototypes fine pitch, which allows better modulation resolution (Lei et al 1997, Caroli et al 2005, and the excellent energy resolution, which allows an optimal angular selection of Compton double events.…”

“…In the hard X-ray / soft gamma-ray domain, the use of high Z material is mandatory, and in order to optimize a focal plane instrument for the different missions envisioned, CdZnTe polarimeters prototypes have already been tested in a series of experiments (Curado da Silva et al 2004Silva et al , 2008Silva et al , 2012, which allowed the evaluation of their polarimetric performance and the study of possible sources of errors and factors limiting the achievable performance.…”

Development of a 3D CZT detector prototype for Laue Lens telescope

“…Meanwhile we intend to submit a proposal to ESRF in Grenoble (France) to perform measurements with a high energy (50-700 keV) polarised photon beam at the line ID15A. The features of this beam line will allow us to characterise, over a wide energy range, with different beam size and as function of the photon incidence angles, our prototype in imaging capabilities, spectroscopic performance and effectiveness as scattering polarimeter 15 .…”

Hard X ray polarimetry with wide band Laue lens telescopes

“…This CZT pixel sensor was readout by a custom designed front end electronics based on 8 32 channels ASICS (eV Products) and acquired trough a multi-parametric electronics with coincidence logic able to handle up 128 channels (see Figure 3). Using this detection system three more experiments have been performed at the ESRF facility devoted to study different aspects and parameters affecting the performance as scattering polarimeter of a CZT pixel spectrometer ( Figure 3) [8].…”