Читать книгу Encyclopedia of Glass Science, Technology, History, and Culture - Группа авторов - Страница 190

As already stated, this technique takes advantage of the dependence of the neutron diffraction on the number of neutrons contained in the atoms undergoing diffraction. By making isotopic substitutions in the sample, it becomes possible to eliminate some PSF in the TSF. This makes determining the various pair‐correlation functions simpler and can lead to unambiguous assignment of features in the total correlation function to specific atom interactions. Basically, two experiments are performed on a sample in which one of the elements is in two different isotopic states. The two TSF can then be subtracted and their difference enables extraction of the PSF involving the element in the different isotopic states. To extract three PSF from a binary system, one requires diffraction experiments on three samples that are identical in every respect, except for the isotopic compositions of one or both of the chemical species.

The difference function is essentially similar to X‐ray absorption spectroscopy (XAS) but the accuracy of the diffraction data can be improved to higher distances and providing more accurate CN of the element of interest. One should note, however, that the structural role of the two isotopes should be identical, which may not necessarily be the case as observed for light elements such as deuterium and hydrogen. The technique is similar to anomalous wide angle X‐ray scattering (AWAXS) or diffraction anomalous X‐ray scattering (DAXS).