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

Q  E limitation for INS

Small beam size for IXS
 Xrays couple to the electrons of the system with a crosssection proportional to the square of the classical electron radius, r_{o}=2.82.10^{13}cm, i.e. with a strength comparable to the neutronnucleus scattering crosssection b.
 The IXS cross section is proportional to f_{j}(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.
 The total absorption crosssection of Xrays 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 crosssection is roughly proportional to Z^{4}, 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 Z^{2} dependence of its crosssection.
 As a consequence of the above point multiple scattering processes can in general be neglected
 The magnetic cross section is negligible for IXS, whereas it is comparable to the nuclear cross section for neutrons.
 The IXS cross section is highly coherent
 The shape of the IXS instrumental energy resolution is not Gaussian as it is for a neutron tripleaxis spectrometer, but Lorentzian.