Scattering-geometry experiments

Obviously, experiments designed to measure cross-sections as a function of energy are needed. At present, tandem experiments are not capable of high precision at low energies because one must assume details of collision mechanics and because it is difficult to estimate collection efficiencies in forward scattering geometry (15). The extension of all known techniques to lower energy (64, 65) and the further development of pulse methods (58) offer the possibility for advances in this area. 

Fig. 17 Temperature dependencies of the mode observed in ST016 closed circles), STO 18-23 closed squares), and STO 18-32 closed triangles) observed in the scattering geometry x yy)-x. Crosses indicate the results for STO 16 obtained by the hyper-Raman scattering experiment. The corresponding open symbols denotes the half-width at half maximum of the soft u mode spectrum of each specimen [27]...

Figure 3-3 Detail of the scattering geometry in laser Raman DAC experiment. Figure not drawn to scale. (Reproduced with permission from Ref. 7.)...

The 90-degree scattering geometry is frequently used in the macromode work, whereas back scattering geometry is usually the choice for microprobe experiments. Specimen sampling needs are somewhat different for these two types of geometries. 

J/cm. That corresponded to the melting threshold of crystalline Si [4]. Number of pulses was 1 or 10. Spectra of Raman scattering (RS) excited by Ar laser radiation (514.5 nm) were registered at room temperature in the back scattering geometry. Other details of experiments and calculations were described elsewhere [5]. 

A comment should be added on the rotational viscosity of the sample in the experiment. It can easily be shown that in the case of azimuthal anchoring measurements, the viscosity entering the analysis equals the rotational viscosity 71. When measuring the zenithal anchoring coefficient, the effective viscosity has to be corrected according to the scattering geometry. However, in first approximation the pure splay mode viscosity is sufficient. 

We assume that the energy resolution available in the experiment does not allow us to discriminate between states with different A/-values. In this instance, the matrix elements quoted are averaged over M, just as in the calculation of the elastic cross-section. Assembling the results, the cross-section for a near-forward scattering geometry in which an ion is excited between states J and / = 7 -I-1 separated by an energy A is... 

Figure 3-7. Raman spectra in polarized light of stretch-oriented high density polyethylene. Experiments were taken in different scattering geometries. Porto s notation is used in the definition of the scattering geometries. Space group symmetry species are indicated (from f63]i.

A standard six-circle diffractometer for diffraction experiments in horizontal and vertical scattering geometries at ambient conditions is operational in the first experimental hutch (EH I). In addition, it can accommodate a furnace (300-1200K) and continuous flow cryostat (10-300K) allowing for NRS experiments in a large temperature range. 

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