Seminars Archive

Development of XRF instrumentation based on Silicon Drift Detectors and Development of a Fast Readout CCD system to be used as a

Abstract


Friday, December 17, 2004, 15:30
Seminar Room, ground floor, Building "T"
Sincrotrone Trieste, Basovizza
Development of XRF instrumentation based on Silicon Drift Detectors and Development of a Fast Readout CCD system to be used as a Configurable Detector in Scanning Transmission X-ray Microscopy (STXM)


Alessandra Gianoncelli

(King’s College London, UK)
Abstract
The seminar will talk about the activity developed during the PhD at the Electronics Department of the Politecnico di Milano (Milano, Italy) and the current research at the Physics Department of the King’s College, University of London (London, UK). A part of my PhD activity was the development of an innovative XRF instrumentation based on a new kind of detector: a ring-shaped monolithic array of 12 Silicon Drift Detectors. As an excitation source, an X-ray tube with policapillary lenses was used. The radiation is directed on the sample through the central hole done on the detector chip: this configuration allows to collect a big solid angle of the XRF radiation emitted by the sample. Thanks to the high spatial and energy resolution, this instrument is especially suitable for elemental mapping and microanalysis of materials. A first experiment of elemental mapping will be shown during the talk. Moreover several XRF analyses, both qualitative and quantitative, were carried out on different kinds of samples (works of art, metallic samples...) by using a portable and compact instrument based on a single Silicon Drift Detector. Some of the results of these analyses will be presented during the seminar. The current activity is part of the EC RT&D project "Twinmic" (HPRI-2001-RTD-50024). King’s College is involved in the development of a fast Readout CCD system to be used as a configurable detector in the Scanning Transmission Mode of the Microscope. The system is based around a fast-readout electron-multiplying CCD (EMCCD) camera from Andor Technology. The detector has 128_128 pixels and it can be read out at more than 110 frames per second. The CCD is a back-face imaging device, thermoelectrically-cooled, with high sensitivity and low noise performance. It is not used in direct x-ray detection mode, to avoid the possibility of radiation damage to the detector. Instead a visible-light coupling system is currently in development, which allows also the x-ray pattern on a phosphor screen to be matched to the active area of the CCD. By using a CCD detector, a full frame is collected from every pixel in the raster scan of the scanning microscope. In this way it is possible to use a flexible range of configurable detector response functions and produce different imaging modes of the sample (brightfield, darkfield, absorption and phase contrast methods). In principle, the phase contrast method also allows quantitative measurements of the complex refractive index, and some examples of the analysis required to achieve this are presented.