The measurement of atomic momentum distributions in condensed matter systems by high energy neutron scattering is analogous to the measurement of electron momentum distributions by Compton scattering and the measurement of nucleon momenta by Deep Inelastic Scattering (1). The technique is known as Neutron Compton Scattering (NCS) or Deep Inelastic Neutron Scattering (DINS) by analogy with these older techniques. The principle is the same in each case; the momentum distribution of target particles (electrons, components of nuclei or atoms, respectively) is measured by inelastic scattering of high energy incident particles (photons, electrons or neutrons). The Impulse Approximation (IA), which is exact only in the limit of infinite momentum transfer (2,3), is used in the interpretation of NCS measurements and large incident energies are required to keep deviations from the IA small.