Study of Thick CZT Detectors for X-ray and Gamma-Ray Astronomy

TL;DR

This study systematically tests thick CZT detectors for X-ray and gamma-ray astronomy, achieving some of the best energy resolutions for detectors of this thickness, and explores how resolution depends on detector properties.

Contribution

It provides new data on thick CZT detectors' performance and investigates the factors affecting energy resolution without depth correction.

Findings

Achieved world-best energy resolutions for thick CZT detectors at 59 keV and 122 keV.

Found no clear trend between detector thickness, pixel pitch, and energy resolution.

Demonstrated sub-1% energy resolution at 662 keV without depth correction.

Abstract

CdZnTe (CZT) is a wide bandgap II-VI semiconductor developed for the spectroscopic detection of X-rays and {\gamma}-rays at room temperature. The Swift Burst Alert Telescope is using an 5240 cm2 array of 2 mm thick CZT detectors for the detection of 15-150 keV X-rays from Gamma-Ray Bursts. We report on the systematic tests of thicker (\geq 0.5 cm) CZT detectors with volumes between 2 cm3 and 4 cm3 which are potential detector choices for a number of future X-ray telescopes that operate in the 10 keV to a few MeV energy range. The detectors contacted in our laboratory achieve Full Width Half Maximum energy resolutions of 2.7 keV (4.5%) at 59 keV, 3 keV (2.5%) at 122 keV and 4 keV (0.6%) at 662 keV. The 59 keV and 122 keV energy resolutions are among the world-best results for \geq 0.5 cm thick CZT detectors. We use the data set to study trends of how the energy resolution depends on the detector thickness and on the pixel pitch. Unfortunately, we do not find clear trends, indicating that even for the extremely good energy resolutions reported here, the achievable energy resolutions are largely determined by the properties of individual crystals. Somewhat surprisingly, we achieve the reported results without applying a correction of the anode signals for the depth of the interaction. Measuring the interaction depths thus does not seem to be a pre-requisite for achieving sub-1% energy resolutions at 662 keV.