The work presented in this Tesi di Laurea arises from a collaboration between the IPL (Image Processing Laboratory) of the Dipartimento di Elettrotecnica, Elettronica ed Informatica (DEEI) at the University of Trieste and the Instrumentation and Dete
ctor Laboratory belonging to the ELETTRA Synchrotron Light Source of Trieste. Under the European Contract ERBFMGECT 980104 a project was active at ELETTRA with the objective to improve facilities for time resolved small angle X-ray scattering (SAXS) experiments within Europe. Partners of the project were, together with ELETTRA, other large scale facilities like the HASYLAB (Hamburger Synchrotron, Germany), the CCLRC (Daresbury Laboratory, UK), the ESRF (European Synchrotron Radiation Facility in Grenoble, France) and the University of Siegen (Germany). In particular the latest half of the time spent working on this project was based in the Arbeitsgruppe Detektorphysik und Elektronik belonging to the Faculty of Physics at the University of Siegen.
In this work a combination of an ionization chamber with one-dimensional spatial resolution and a MicroCAT structure will be presented. The combination between gas gain operations and integrating front-end electronics yields a dynamic range as high a
s eight to nine orders of magnitude. Therefore this device is well suitable for medical imaging or applications such as small angle x-ray scattering, where the requirements on the dynamic of the detector are exceptional high. Basically the described detector is an ionization chamber adapted to fan beam geometry with an active area of 192 cm and a pitch of the anode strips of 150 micrometer. In the vertical direction beams as high as 10 mm can be accepted. Every read-out strip is connected to an analogue integrating electronics channel realized in a custom made VLSI chip. A MicroCAT structure utilized as a shielding grid enables frame rates as high as 10kHz. The high dynamic range observed stems from the fact that the MicroCAT enables active electron amplification in the gas. Thus a single photon resolution can be obtained for low photon fluxes even with the integrating electronics. The specialty of this device is that for each photon flux the gas amplification can be adjusted in such a fashion that the maximum DQE value is achieved.
An X-ray detector will be presented that is the combination of a segmented ionization chamber featuring one-dimensional spatial resolution integrated with an intelligent ADC front-end, multi DSP processing and embedded PC platform. This detector is o
ptimized to fan beam geometry with an active area of 192 mm (horizontal) and a vertical acceptance of 6 mm. Spatial resolution is obtained by subdividing the anode into readout strips, having pitch of 150 micrometers, which are connected to 20 custom made integrating VLSI chips (each capable of 64-channel read-out and multiplexing) and read out by 14 bits 10 MHz ADCs and fast adaptive PGAs into DSP boards. A bandwidth reaching 3.2Gbit/s of raw data, generated from the real time sampling of the 1280 micro strips, is cascaded processed with FPGA and DSP to allow data compression resulting in several days of uninterrupted acquisition capability. Fast acquisition rates reaching 10 kHz are allowed due to the MicroCAT structure utilized not only as a shielding grid in ionization chamber mode but also to provide active electron amplification in the gas.
