Theory of inelastic scattering of cold neutrons from liquid helium (original) (raw)
Published July 1, 1957 | public
Journal Article Open
Abstract
A measurement of the energy losses of monoenergetic neutrons scattered from liquid He II would permit a determination of the energy-versus-momentum relation for the elementary excitations (phonons and rotons) in the liquid. A major part of the scattering at a fixed angle arises from production or annihilation of a single excitation and appears as sharp lines in the energy spectrum. From the position of these lines the energy-versus-momentum relation of the excitations can be inferred. Other processes, such as production or annihilation of multiple excitations, contribute a continuous background, and occur at a negligible rate if the incident neutrons are slow (λ~>4A) and the helium cold (T<2°K). The total cross-section data can be accounted for by production of single excitations; the theoretical cross section, computed from a wave function previously proposed to represent excitations, agrees with experiment over the entire energy range, within 30%. Line widths in the discrete spectrum are negligible at 1°K because of the long lifetime of phonons and rotons.
Additional Information
©1957 The American Physical Society. Received 25 March 1957. We wish to thank P. J. Bendt, M. Gell-Mann, W. J. Karzas, and H. Palevsky for valuable discussions.