Theory and computation of Atomic Form Factors

Edges of low-Z atoms can be used to test predictions of scattering, attenuation and diffraction processes in matter, in the soft X-ray regime. Here Cherenkov radiation studies agree with recent theory but disagree with numerous other theoretical predictions and tabulations.

Form factors (see the top of the X-ray optics home page) are used to determine the diffraction, scatttering and attenuation processes of light through matter. Within the X-ray regime it is an excellent approximation to talk about 'Atomic form factors' (neglecting chemical bonding and structure) and 'independent particle approximations' (treating each excitation as localized for a single electron). A result of this theory can make detailed and accurate predictions in physically interesting regimes of particular elements, such as the carbon K-edge illustrated here.

However, current comprehensive theories within these assumptions differ by many times their quoted 1% uncertainties in central X-ray regimes. A number of studies have supported the current theoretical results of C. Chantler at U. Melbourne, but more work is needed to investigate the theoretical and experimental dilemmas more closely. The theory is maintained as an extensive database available for general users: NIST - Maintained Reference Database FFAST, Author C.T. Chantler

[It is also available as NIST Database 66: Form Factor Attenuation scattering Tables, and in J. Phys.Chem Ref. Dat. 24, pp71-643.]

This topic is closely linked to the experimental investigations of diffraction and attenuation.