X-ray natural circular dichroism
  This paper discusses a theory of natural circular dichroism in the x-ray region. Integrated spectra are interpreted in terms of microscopic effective operators, which are derived in the framework of a localised (atomic) model. It is shown that the generators of a de Sitter group, such as that introduced by Goshen and Lipkin for nuclear structure, are suitable for describing electronic properties of non-centrosymmetric crystals. 
Paolo Carra and Robert Benoist (ESRF)