Quasi-elastic neutron scattering spectra

Trantham, E. C., Rorschach, H. E., Clegg, J. S., Hazlewood, C. F., Nicklow, R. M., Wakabayashi, N. (1984). Diffusive properties of water in Anemia cysts as determined from quasi-elastic neutron scattering spectra. Biophys J. 45,927-938. 

Figure 11. Incoherent quasi-elastic neutron scattering spectrum obtained with a 220 C dehydrated acid Nafion sample = 0.59 A )...

Furthermore, in the picture of this chapter also, the appearance of more than one Lorentzian curve in the spectrum of the quasi-elastic neutron scattering (a result which has been recendy confirmed by Teixeira et al. ) is related to the H-bond dynamics, whereas Teixeira et al. ascribe this effect to the orientational part of the intermediate scattering function. We believe that both physical causes can contribute to this effect. 

Viscoelastic spectrum Quasi-elastic neutron scattering... 

Mossbauer spectroscopy of the iron salt showed two different iron environments one having a high water content and the other with almost no assodated water molecules. Quasi-elastic neutron scattering revealed that there were two types of water molecule, each with different diffusion coefficients, which were observed in the quasi-elastic spectrum as peaks having different widths. To explain these observations the authors presented a structure containing three phases microcrystallites, ionic clusters, and an intermediate ionic phase with a lower ionic concentration. The relative proportions of the last two phases depended on the... 

Interesting results have been obtained by a combination of NMR and quasi-elastic incoherent neutron scattering. The presence of one single line in an NMR spectrum, for all the water concentrations, can be interpreted in two ways either we have only one kind of water molecule with a very well defined environment or we have different kinds subject to a fast chemical exchange (t < 10 3 sec.). Two regimes of absorption have been demonstrated and two different motions have been characterized both by NMR spin lattice relation time measurements and quasi-elastic incoherent neutron scattering. From these results and from results obtained on the Nafion salts W a structural model will be proposed (9). 

Fig. 29. Inelastic neutron spectrum measured at T= 10 K on a CePdj single crystal. The solid line is fit to the data which is the sum of a constant background, a Gaussian for elastic scattering and phonon scattering (15.5 meV), a narrow quasi-elastic Lorentzian of 3 meV width, and an inelastic Lorentzian at lOmeV and 15mcV wide. The excess background at high energies on account of changes in counting times was subtracted (Shapiro et al. 1989).

There are two broad classes of neutron scattering measurement. In diffraction measurements, the energy of the scattered radiation is not analyzed, so only the intensity versus Q is determined. Such measurements determine the structure of the sample. In a second class, the scattered energy is analyzed, so the intensity versus Q and h(0 is determined. This type of measurement is able to give structural and dynamic information about the sample, and is often called an inelastic measurement. In the special case where there are diffusive motions in the sample, which broaden the sharp incident spectrum, the term quasi-elastic is used. Neutron scattering instruments are optimized for one or the other of these types of measurement. 

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