THz dynamics in glasses studied by means of Inelastic Neutron Scattering

The THz dynamics of two different glasses has been studied by means of Inelastic Neutron Scattering: the germanium diselenide (v-GeSe2) [1], an amorphous glass belonging to the family of continuous random network forming glasses and the glucose (C6H12O6). In both cases two well-defined peaks are resolved in the dynamic structure factor in a broad Q region, below and above the position of the first sharp diffraction peak in the static structure factor. Their common characteristics and possible differences will be discussed during the talk. The presence of two pseudo-‘branches’ in glasses seems to be quite general, but their nature is not completely understood, mainly due to the lack of theoretical models able to provide a complete description of this intriguing features[3]. Acknowledgment: All the authors of the reference paper [1] are acknowledged for their participation in the work: L. Orsingher, G. Baldi, A. Fontana, L. E. Bove, T. Unruh, A. Orecchini, C. Petrillo and F. Sacchetti [1] L. Orsingher, G. Baldi, A. Fontana, L. E. Bove, T. Unruh, A. Orecchini, C. Petrillo, N. Violini and F. Sacchetti Phys. Rev. B 82, 115201 (2010). [2] N. Violini and F. Sacchetti, paper in preparation (unpublished).[3] N. Violini, PhD Thesis (2011)

Compact chopper spectrometers for pulsed sources

We report on the opportunities for direct geometry chopper spectrometers (DGCS) by polychromatic illumination of the sample. At pulsed sources the use of multiple initial neutron energies appears naturally, if the repetition rate of chopper in front of the sample is larger than the repetition rate of the source. As a consequence, a large part of the spectrum is measured redundantly with variable energy and momentum transfer resolution. This can be used to optimize a chopper instrument for deep inelastic scattering, relaxing the requirements on the pulse length, by which the sample is illuminated, and on the secondary flight path, while the width of the spectral distribution must be narrowed down. This can open the path to new types of compact direct geometry chopper spectrometers, which need comparably small areas of detector coverage and allow very high repetition rates to provide a high intensity even if sample size and divergence distributions are limited