Polarimetry with a Laue Lens and CZT pixel detector

A new generation of high sensitivity telescopes based on the use of Laue lenses coupled with high efficiency solid state focal plane detectors has been identified as a possibility for hard X and soft gamma ray astronomy. For this kind of space mission, polarimetry is recognized as a very important observational parameter and therefore this capability should be included as one of the primary scientific requirements. In this framework our group has realized a small experiment to demonstrate that the combination of a Laue Lens, built using Cu mosaic crystals, with a CZT pixel detector is capable of measuring the polarization of hard X ray sources contemporaneously with spectroscopy and imaging. This experiment was performed at the beginning of March 2008 using the ID15B beam line at ESRF (Grenoble). The experiment was based on a pixel CZT detector (5 mm thick array with 11×11 pixels of 2.5×2.5 mm²) with a sensitive area of 3×3 cm² in conjunction with a mosaic Cu crystal (15×15 mm², 4 mm thick) used in the Laue diffraction configuration. During the tests the Cu crystal was rotated so as to simulate a Laue lens ring, and the detector was moved in order to have the diffracted beam always impinging on the same pixel. The beam at the ID15B have allow us to test the response of this system, with almost 100% linearly polarized photon at ∼90, 270, 350 keV. In this paper we describe the experimental setup and we report on the preliminary results, with particular emphasis on the evaluation of possible systematic effect introduced in the detected polarization of the impinging photon by the Laue diffraction process.