Fundamental aspects of neutron optics

Abstract

The microscopic theory of the neutron optical field is reviewed with particular emphasis on the derivation of an expression for the neutron refractive index that describes correctly both the local field effects and the attenuation of the coherent wave in the medium due to diffuse s scattering and absorption. The latter requirement guarantees that the "optical theorem" of scattering theory is obeyed. It is pointed out that the definition of coherence that is employed in optics (absolute coherence) differs from that which is used in other branches of neutron physics (relative coherence) and the difference between the two is discussed. The extinction theorem for neutrons is derived. Finally, numerical values for the local field correction are given for a number of simple liquids for which accurate pair correlation functions are available. © 1982.