Similarities and differences between the IXS and INS cross section are summarised below:

  1. Q - E limitation for INS
  2. Small beam size for IXS
  3. X-rays couple to the electrons of the system with a cross-section proportional to the square of the classical electron radius, ro=2.82.10-13cm, i.e. with a strength comparable to the neutron-nucleus scattering cross-section b.
  4. The IXS cross section is proportional to fj(Q)2. In the limit Q→0, the form factor is equal to the number of electrons in the scattering atom, Z; for increasing values of Q, the form factor decays with decay constants of the order of the inverse of the atomic wavefunction dimensions of the electrons in the atom.
  5. The total absorption cross-section of X-rays above 10 keV energy is limited in almost all cases (Z>4) by the photoelectric absorption process, and not by the Thomson scattering process. The photoelectric absorption, whose cross-section is roughly proportional to Z4, determines therefore the actual sample size along the scattering path. Consequently the Thomson scattering channel is not very efficient for system with high Z in spite of the Z2 dependence of its cross-section.
  6. As a consequence of the above point  multiple scattering processes can in general be neglected
  7. The magnetic cross section is negligible for IXS, whereas it is comparable to the nuclear cross section for neutrons.
  8. The IXS cross section is highly coherent
  9. The shape of the IXS instrumental energy resolution is not Gaussian as it is for a neutron triple-axis spectrometer, but Lorentzian.