Contrast and deuterium labeling

3 Contrast and deuterium labeling 7.3.1 High-concentration labeling 

The quantity (od - an) is related to the difference in scattering power between labeled and unlabeled chains and is called the contrast factor. In general, radiation 

Polymer or solvent Density ,/o (gem (atr 23°C) Neutron-scattering-length density, p (10 cm ) 

The values of SLD are calculated at the indicated densities (p), which vary slightly with temperature, tacticity (e.g. for PMMA), degree of crystallinity (e.g. for polyethylene), etc. For different densities, the SLD is proportional to p and may be scaled from the values shown. For deuterated materials, it is assumed that the number of monomers per unit volume is independent of deuteration to a good approximation. 

The contrast-variation methods which have found wide application in structural biology can sometimes be used to remove a component of the scattering by matching its scattering power with that of the medium in which it is dispersed, and thus 

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