Table of contents

The theory is developed in terms of monatomic systems in order to demonstrate the relationships between the momentum and energy profiles of the scattered neutrons and the properties of the scattering nuclei. An indication is then given of how this framework may be expanded to deal with molecular systems. A brief discussion of the more commonly used experimental methods is included. Because of difficulties of interpretation and the lower resolution compared to other spectroscopic techniques, neutron scattering methods have been most successfully applied to certain well defined problems in molecular spectroscopy. A detailed discussion of low energy neutron scattering in the energy range of molecular translation and hindered rotation demonstrates both the difficulties involved and several instances where this technique has shed new light on the problem of molecular motions. The review concludes with a survey of neutron scattering of the dynamics of macromolecules.

During the past decade there has been considerable progress in the study of the structure and elementary excitations of liquid helium. This has largely arisen from the development and refinement of neutron, X-ray and light scattering techniques and also from more detailed ultrasonic measurements. A large part of this review is concerned with describing the results of these experiments and their implications for theories of liquid helium. During the last few years there has also been considerable progress made in the theory of the excitations in liquid helium. These developments are briefly reviewed and the most promising lines of development indicated.