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Collective excitation in the ionization of atoms, in semiconductors and biological tissues (Collexcit)
Start date: 01 Jun 2008, End date: 31 May 2012 PROJECT  FINISHED 

Experimental determination of ionization and decay parameters of x-ray transitions, used in analytical applications, and basic physics research. Measurements are designed to establish the size of the many-body interactions in the excitation and decay processes. In this sub-field mainly single particle approaches have been used. The experimental data contradict basic conservation laws and arithmetic. Therefore, new methodological approaches are necessary. Improved detection techniques and quality assurance capable signal processors have emerged which allow new approaches to measuring these parameters. Energetic charged particles in x-ray and gamma ray solid state detectors lose their energy mainly by plasmon creation. Plasmons are collective excitations. Using a high energy electron spectrometer we will determine the plasmon creation probability in the energy range of 200 eV to 10 keV by a high energy photoelectron spectrometer. We will develop a deconvolution method, to analyze the photoelectron spectra. We intend to study semiconductor x-ray and gamma ray detectors’ response function as a function of the band gap and plasmon energy. We plan to develop a new signal processing approach based on the obtained information. We will study various surface modification of detectors, to reduce the surface plasmon creation probability. Collective excitations are also important in biological tissues. Many radioactive materials are used in medical imaging. Delocalized plasmons excited in biological tissue by energetic particles could be transferred to nearby molecules like DNA causing radiation damage. As a pilot study, we want to study what type of plasmon excitation is possible, measure the plasmon energy and the plasmon creation efficiency.
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