Evaluation of a cadmium–zinc–telluride focal plane detector for hard X-ray astronomy

Abstract

Because the Earth has a protective atmosphere that is opaque to many wavelengths, X-ray astronomy cannot be performed from the ground. It was not until the 1960s that astronomers had the technological capability to put their experiments at high enough altitudes to directly observe cosmic X-rays (Giacconi et al., 1962). Since that time a multitude of high-altitude balloons, rockets, and satellites have been launched to study the Universe in this wavelength region. Of the 108 missions flown, the majority of them concentrate on studying the Universe below 20 keV (Slavis, 2001). As a result, the hard X-ray region (20–100 keV) is still relatively unexplored. One instrument that will study the Universe in the hard X-ray region is the high energy replicated optics (HERO) balloon borne telescope being developed at Marshall Space Flight Center and the National Space Science and Technology Center. The HERO telescope consists of nested grazing incidence optics and several focal plane detectors. The full balloon payload will consist of 16 mirror modules each containing 15 nested shells (Ramsey et al., 2004). Each focal plane detector must exhibit a high photopeak quantum efficiency, good energy resolution, and good spatial resolution (B200mm). To sample the full mirror response the focal plane detector must have 128 128 pixels (Ramsey, 2001), although the sensitive portion of the mirrors’ response can be covered by 64 64 pixels. These focal plane requirements can be optimally met with a many-pixel cadmium–zinc–telluride (CdZnTe) array.