X-ray Imaging Detector Technology
For its imaging activities ANKA needs a pool of powerful pixel array detectors. In order to achieve this ANKA has established a small group, mainly by third party funding, working within international collaborations like SCINTAX, UFO, EDAS, Galapad, the HGF detector initiative, and the Medipix3 collaboration. This group works on the developement and optimization of direct converting and indirect converting detector systems.
Indirect imaging detectors are based on the conversion of X-rays to light by a scintillator. The luminescence image is projected via visible light optics onto a digital camera chip. The quality of such detector systems is mainly influenced by the scintillating screen, the visible light optics and the read out quality of the camera. ANKA has been coordinating the ScinTax collaboration funded by the European Commission (STRP 033 427, FP6) in the development of scintillating materials and benefits from a fruitful collaboration with ESRF in the CCD-based camera development. Within the German-Russian UFO project, the group is pushing “The ultra fast X-ray imaging of scientific processes with on-line assessment and data-driven process control”.
Direct converting hybrid pixel array detectors consist of semiconductor sensor material interconnected with a pixelated CMOS (Complementary Metal-Oxide Semiconductor) read-out chip.
This allows high sensitivity for hard X-rays. Moreover the single photon counting capability of the Medipix chips is extremely useful when weak signals have to be detected. ANKA and the University of Karlsruhe together with the university of Freiburg are currently involved in the EDAS project (Efficient Pixel array Detectors for Application in the Synchrotron) together with the University of Freiburg. The project's target is the development of a fast 2D-detector (selection times<10 μs) for the detection of X-rays in highly brilliant synchrotron sources of high photon energy, spanning from 20 keV to approximately 150 keV. Additionally, a pixel size of 55 μm will guarantee a sufficiently good spatial resolution. Within the Galapad project and the Medipix3 collaboration a direct converting X-ray camera will be developed based on a Hybrid Pixel Array Detector with a GaAs sensor. This combination guarantees a high efficiency of the sensor to X-ray radiation up to 60 keV. In addition, sensors from CdZnTe and corroded 3D structures on silicon will be examined in order to investigate other possibilities of raising the sensor's efficiency.
The Detectorlab established at ANKA is dedicated to R&D of imaging detectors. In this lab, detectors can be characterized, calibrated and tested “off-line”, completely independent of the synchrotron storage ring status and/or user operation. Two experimental stations are available in the lab: An X-ray setup to implement standardized procedures which allow qualitative and quantitative detector testing and a complementary optical setup to characterize the visible light components of indirect converting X-ray detectors.