1957/07/01 by Michael J. Cohen, Richard P. Feynman · 1 citation
Physics and Astronomy · Earth and Planetary Sciences · #Quantum, superfluid, helium dynamics #Atomic and Subatomic Physics Research #High-pressure geophysics and materials
paper · doi:10.1103/physrev.107.13
openalex publication_date 1957/07/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/06/26
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 (\ensuremathλ\ensuremath\gtrsim4A) and the helium cold (T<2\ifmmode^∘\else\textdegree\fiK). 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\ifmmode^∘\else\textdegree\fiK because of the long lifetime of phonons and rotons.