Optimization and application of a time-of-flight spectrometer with pseudo-statistical chopper

At the research reactor in Garching a time-of-flight spectrometer for quasie-elastic neutron scattering was erected, which works according to the pseudo-statistical measuring method. In the framework of this installation the optimization and the extension of the instrument were performed. It comprehends besides numerous constructive improvements the equipment of the spectrometer with modern data acquisition and guiding electronics. The correlation calculation required in the pseudo-statistical measuring method can now be performed on-line and allows by this a continuous monitoring of the experiment during the running time. For the evaluation of the measurement data by means of least-square fit a new procedure especially fitted to the requirement of the pseudo-statistical spectrometer was developed. The practical usefulness of instrument and evaluation system proves an experiment, which studies a highly compressed H2-Ar mixture as sample. It is considered as good realization of the Lorentz model of molecular dynamics. Statements of some approaches proposed in latest time for its description can be confirmed by means of the measurement data. Considerations on the further development of the pseudo-statistical measuring method in form of a double-statistical spectrometer conclude the thesis. Thereby a concept for the realization of such a spectrometer is presented and discussed by means of results from computer simulations on an especially constructed parallel-computer system. (orig./HSI)