Resonant neutron scattering lengths

Unlike most of the periodic table, many rare-earth elements display considerable resonant scattering for thermal neutrons. Although this property is accompanied by strong neutron absorption, modern high-intensity neutron sources make diffraction experiments possible with these elements. Computation of scattering intensities is accomplished by fitting the variation in resonant scattering lengths (b, b′ and b″) to a semi-empirical Breit-Wigner formalism, which can be evaluated over the range of neutron energies useful for diffraction, typically E = 10-600 meV; λ = 0.4-2.8 Å (with good extrapolation to longer wavelengths).