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Proceedings Paper

Cathode depth sensing in CZT detectors
Author(s): JaeSub Hong; Eric C. Bellm; Jonathan E. Grindlay; Tomohiko Narita
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Paper Abstract

Measuring the depth of interaction in thick Cadmium-Zinc-Telluride (CZT) detectors allows improved imaging and spectroscopy for hard X-ray imaging above 100 keV. The Energetic X-ray Imaging Survey Telescope (EXIST) will employ relatively thick (5 - 10 mm) CZT detectors, which are required to perform the broad energy-band sky survey. Interaction depth information is needed to correct events to the detector "focal plane" for correct imaging and can be used to improve the energy resolution of the detector at high energies by allowing event-based corrections for incomplete charge collection. Background rejection is also improved by allowing low energy events from the rear and sides of the detector to be rejected. We present experimental results of intereaction depth sensing in a 5 mm thick pixellated Au-contact IMARAD CZT detector. The depth sensing was done by making simultaneous measurements of cathode and anode signals, where the interaction depth at a given energy is proportional to the ratio of cathode/anode signals. We demonstrate how a simple empirical formula describing the event distributions in the cathode/anode signal space can dramatically improve the energy resolution. We also estimate the energy and depth resolution of the detector as a function of the energy and the interaction depth. We also show a depth-sensing prototype system currently under development for EXIST in which cathode signals from 8, 16 or 32 crystals can be read-out by a small multi-channel ASIC board that is vertically edge-mounted on the cathode electrode along every second CZT crystal boundary. This allows CZT crystals to be tiled contiguously with minimum impact on throughput of incoming photons. The robust packaging is crucial in EXIST, which will employ very large area imaging CZT detector arrays.

Paper Details

Date Published: 3 February 2004
PDF: 9 pages
Proc. SPIE 5165, X-Ray and Gamma-Ray Instrumentation for Astronomy XIII, (3 February 2004); doi: 10.1117/12.506216
Show Author Affiliations
JaeSub Hong, Harvard-Smithsonian Ctr. for Astrophysics (United States)
Eric C. Bellm, Harvard-Smithsonian Ctr. for Astrophysics (United States)
Jonathan E. Grindlay, Harvard-Smithsonian Ctr. for Astrophysics (United States)
Tomohiko Narita, College of the Holy Cross (United States)

Published in SPIE Proceedings Vol. 5165:
X-Ray and Gamma-Ray Instrumentation for Astronomy XIII
Kathryn A. Flanagan; Oswald H. W. Siegmund, Editor(s)

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