State of the art X-ray Detectors
NuSTAR has two detector units, one at the focus of each of the two co-aligned NuSTAR optics units. One detector unit or focal plane, is comprised of four Cadmium-Zinc-Telluride (CdZnTe, or CZT) detectors manufactured by eV Products. Each detector is rectangular crystal of dimension 20mmx20mm and thickness 2mm that have been gridded into 32×32 pixels. The detectors have an energy resolution of 0.4 keV.
CZT detectors are state-of-the-art room temperature semiconductors that are very efficient at turning high energy photons into electrons. The electrons are then digitally recorded using custom Application Specific Integrated Circuits (ASICs) designed by the NuSTAR Caltech Focal Plane Team.
The focal planes are shielded by Cesium-Iodide (CsI) crystals that surround the detector housings. The crystal shields, grown by Saint-Gobain, register high energy photons and cosmic rays which cross the focal plane from directions other than the along the NuSTAR optical axis. Such events are the primary background for NuSTAR and must be properly identified and subtracted in order to identify high energy photons from cosmic sources. The NuSTAR active shielding ensures that any CZT detector event coincident with an active shield event is ignored.