Compact array of CdTe spectrometers for a prototype balloon flight

Abstract

The CACTµS (Compact Array of Cadmium Telluride Micro Spectrometers) instrument was constructed as a prototype detection plane for the Coded Imager and Polarimeter for High Energy Radiation (CIPHER) telescope. The instrument, flown as a 'piggy-back' experiment on a stratospheric balloon as part of the Summer 2002 trans-mediterranean flight campaign from the Milo Italian balloon base in Sicily, was constructed in order to verify the feasibility of using this kind of position sensitive detector for hard X and soft gamma ray polarimetry and imaging, with the objective of studying the instrumental background at stratospheric balloon altitudes over the 20-1000 keV energy range. Of particular interest is the spectrum and distribution of Compton scattered events that trigger two pixel (double) events, the recognition of which is essential for providing a high sensitivity to linear polarisation. It was also used to evaluate the efficiency and the reliability of an off-line numerical algorithm to be applied to the CdTe flight data for signal compensation, which uses the amplitudes obtained by readout electronics with a double shaping filter stage.

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

“…For each event we obtained information about the number of hits, the triggered pixels, and the energy deposited in each hit. 11 The recorded data are analyzed offline by an Interactive Data Language s/w custom tool, which allows the selection of single, double, and multiple events ͑photons undergoing at least three interactions in the detection plane͒. 12 Using an 11ϫ 11 array, the irradiation of a central pixel of the detector and the measurement of the double event distribution generated around it by the polarized beam would only allow distributions out to the fifth order pixels to be studied.…”