Up down gamma discrimination using the imaging ratio method with CZT Gamma-ray detectors for In situ and remote sensing operations

The neutron/gamma-ray group at NASA GSFC is currently developing the Imaging Gamma-ray Spectrometer (IGS), a next generation compact high-resolution high sensitivity gamma-ray imaging spectrometer. The innovative technology for IGS is the pixelated room-temperature semiconductor Cadmium Zinc Telluride (CZT) detector. This technology gives IGS the advantages of low mass and low power imaging over a large field of view and high spectroscopic resolution (1% FWHM at 662 keV). The imaging capabilities of pixelated CZT detectors can be used to determine the incoming directions of gamma rays. Therefore, it is possible to improve the sensitivity of the IGS to a planet below it by discriminating the gamma rays originating from above the IGS such as from the activation of the spacecraft. In this paper, the imaging ratio method is used to demonstrate that the gamma rays coming from a point source placed above the detectors can be eliminated from the energy spectrum thus improving the sensitivity of the detector to the gamma rays originating from below.