Development of the Next Generation High-Sensitivity CdZnTe Imaging Gamma-Ray Spectrometer for Planetary Science Applications.

Abstract

The Probing In situ with Neutrons and Gamma-rays (PING) instrument, developed at NASA Goddard Space Flight Center (GSFC) by the neutron/gamma-ray group, is a technology used to determine the subsurface elemental composition of a planet. It uses a pulsed neutron generator to excite the solid materials of a planet and measures the resulting neutron and gamma-ray emissions with its detector system. A key objective of NASA is to develop instruments with reduced mass, volume and power consumption. The NASA GSFC neutron/gamma-ray group is currently developing the Imaging Gamma-Ray Spectrometer (IGS), the next generation light and compact high resolution and sensitivity instrument on PING. The spectroscopic and imaging performance of pixelated CdZnTe detectors as the innovative technology for IGS were investigated. This work has shown that pixelated CdZnTe detectors have the advantages of high-resolution spectroscopic performance, room-temperature operation thus eliminating the need for a cryogenic cooler, and Compton imaging capabilities to reject secondary gamma rays originating from the spacecraft or environment. The spectroscopic performance of a large volume single crystal pixelated CdZnTe detector showed a single pixel energy resolution of 1.4% FWHM at 662 keV. Imaging methods were developed in this study to reject gamma rays from a source placed above the detectors using Compton imaging techniques: the full-energy Compton rejection method and the imaging ratio method. Simulations have demonstrated that with the imaging ratio method, it is possible to reject a significant fraction of the gamma rays coming from a point source above the detectors thus increasing the sensitivity of the measurement to the planet surface below.