Why use neutrons for condensed matter studies?
Neutrons scatter from materials by interacting with the nucleus of an atom rather than the electron cloud. This means that the scattering power (cross-section) of an atom is not strongly related to its atomic number (the number of positive protons in the atom, and therefore number of negative electrons, since the atom must remain neutral), unlike X-rays and electrons where the scattering power increases in proportion to the number of electrons in the atom. This has three advantages: i. it is easier to sense light atoms, such as hydrogen, in the presence of heavier ones ii. neighbouring elements in the periodic table generally have substantially different scattering cross sections and can be distinguished iii. the nuclear dependence of scattering allows isotopes of the same element to have substantially different scattering lengths for neutrons. Isotopic substitution can be used to label different parts of the molecules making up a material. The interaction of a neutron with the nucleus
