Performance of the InFOCμS pixellated CdZnTe detector

Abstract

InFOCμS is a new generation balloon-borne hard X-ray telescope with focusing optics and spectroscopy in a collaboration between NASA's GSFC and Nagoya University. We had a successful 22.5-hour flight from Fort Sumner, NM on September 16-17, 2004. The InFOCμS hard X-ray telescope consists of a depth-graded platinum-carbon multilayer mirror and a CdZnTe detector, which is a pixellated solid-state device capable of imaging spectroscopy. In this paper, we present the performance of the InFOCμS CdZnTe detector. The detector is configured with a 12 × 12 segmented array of detector pixels. The pixels are 2 mm square, and are placed on 2.1 mm centers. The averaged energy resolution is 4.4 keV at 60 keV and its standard deviation is 0.36 keV over 128 pixels. It has a 241 Am tagged source to monitor the energy gain of each detector pixel during the flight. The gain was stable within a few percent during observations. The detector is also surrounded by a 3-cm thick CsI anti-coincidence shield to reduce background from particles and photons not incident along the mirror focal direction. Owing to the active shield, 97.3% of the background was rejected as vetoed events. The observed background rate is 2.9 × 10 -4 cts sec -1 cm -2 keV -1 (20-50 keV). We achieved sensitivity as great as 5 × 10-6 cts sec -1 cm -2 keV -1 with 8-hour observations (in 20-50 keV and three sigma detection) in this flight. We also present our plan for the future InFOCμS flights as well as their sensitivity we would expect.