Instrumentation: State-of-the-art detectors
NuSTAR has two detector units, each at the focus of one of the two co-aligned NuSTAR optics units. The optical units observe the same area of sky, and the two images are combined on the ground. The focal planes are each comprised of four 32×32 pixel Cadmium-Zinc-Tellurium (CdZnTe, or CZT) detectors manufactured by eV Products. 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-Iodine (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.