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Detector development for time resolved small angle scattering and fluorescence holography


The main subject will be detector development for small angle scattering and fluorescence holography using synchrotron radiation. - - _ Small angle scattering requires essentially linear position sensitive detectors for x-rays in the energy range of 5..20keV with a position resolution of the order of 0.1 mm. The specialty of advanced measurements requires in addition a time resolution of 0 01 . 1 ms for time dependent measurements. For repetitive measurements proportional counters are used successfully.
However, these detectors are not useful for non repetitive measurements where a large flux in a single position cell has to be recorded in order to obtain a reasonable precision. Here a multi cell position sensitive ionization chamber is proposed as used already in the project of the non invasive coronary angiography at HASYLAB, DESY, Hamburg. In order to apply it to small angle scattering three major improvements have to be developed:
- position resolution of 0.1 mm instead of 0.3 mm
- higher sensitivity ( lower noise of the read out electronics) - higher dynamic range
For the first two improvements some work has already carried out using a finer structured read out anode and for the electronics by using a low noise front end. The third point will be important to record the direct beam as well in order to improve the small angle region by avoiding an absorber for the central part and the associated scattering. First calculations for the saturation behavior of the ionization chamber based on the measurements obtained at DESY together with a new simulation program show that the direct beam up to 1012 photons/mm2 can be measured. For time resolved diffraction work an acquisition electronics based on new analog sampling and storage VLSI circuits as used in the particle physics ( e.g. at the ZEUSS caloriemeter) has to be adapted.
For the measurements of fluorescence holography the spectra of scattered radiation from the sample has to be recorded and the | intensity of the selected fluorescence radiation as well as the intensity has to be recorded as function of the rotation angle of D | the sample. For this purpose up to now semiconductors as well as proportional counters are used. Recently a multi cell
Semiconductor detector based on the drift diode principle has been used for the first time for EXAFS application at the ESRF showing excellent energy resolution ( ca 200 eV) at potentially high rates up to several MHz per detector. This would reduce the acquisition time of the spectra and improve the precision at the same time such that improved 3D images of atomic structures should be possible. The development of the drift detectors involves the development of a multi channel acquisition electronics and the optimization of the high rate behavior. For both projects a high intensity beam line would be essential and the collaboration with research groups in the application mentioned. Both requirements seem to me to be ideally fulfilled at the Sincrotrone Trieste.


Sincrotrone Trieste ScpA
Padriciano 99
34012 Trieste

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