High-resolution CCD x-ray detector for microdiffraction and tomography applications

Abstract

This paper reports on the charge-coupled device (CCD) x-ray detector development for imaging and diffraction applications at CHESS, the Cornell High Energy Sychrotron Source. The detector currently under test is based on the Kodak KAF-0400 chip, featuring 512 X 768 pixels at 9 micrometers square pixel size. The final version of the device will use the KAF- 1600, which has four times the active area at the same pixel size. Different x-ray detection schemes are planes to adapt the detector most efficiently to the application. For imaging at high spatial resolution the x-rays are converted to visible light by phosphors, i.e. Gd<SUB>2</SUB>O<SUB>3</SUB>S:Tb screens or CdWO<SUB>4</SUB> single-crystals. An optical lens system focuses the phosphor image onto the CCD. Typical magnification factors for the optics are 3 to 1 to 1 to 1. This detector has been designed for radiography in materials science and biology. First tests on the performance of the device showed a good spatial resolution at a dynamic range of approximately 10 bits. To comply with the needs in diffraction experiments, e.g. microbeam and surface diffraction experiments, a second type of detector will be built. The front end of this device will consist of a scintillator coupled to a fiberoptic taper. The output of the demagnifying taper is focused onto the CCD. This concept allows a very compact design, necessary for a detector to be used routinely by users of the CHESS facility.