Cross-polarisation theory

The total cross-section in any direction is independent of polarisation, but the individual line cross-sections are not. A typical oriented crystal Mossbauer spectrum of FeCOa is shown in Fig. 6.15. One of the consequences of the modified theory is that the theoretical area ratio is comparatively insensitive to the recoil-free fraction and that it is unrealistic to determine it by an area ratio method. The presence of impurities and imperfections in the mineral specimens was held to explain some of the experimental deviations from prediction. No direct evidence for anisotropy of the recoil-free fraction was obtained, a conclusion since verified by Goldanskii [50], who made new polarisation measurements using single crystals of FeCOa as polariser and analyser. 

Although this model may be considered to be a significant contribution to the theory of concentration polarisation and limiting flux behaviour in ultrafiltraiion, some drawbacks should be mentioned. In literature data have indicated that the gel concentration Cg is not a constant but depends on the bulk concentration and the cross flow velocity [16], In... 

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