[en] The experimental investigation for ⁴He⁴He elastic scattering at energy 49.9 MeV has been carried out. The experimental technique and results were listed. The phase analysis of ⁴He⁴He elastic scattering at 49.9 MeV and other energies has been performed. (author)

No abstract available

No abstract available

[en] A new interpretation is given to experiments on double-atom excitation in He-He collisions that were focused on the relative population and coherence of atomic substate combinations. It is shown that a proposed two-state propensity rule may describe basic characteristics of the measurements. More generally by choosing the quantization axis perpendicular to the beam axis it can be understood why the two-state propensity model is successful. It also turns out that the diagonal elements of the new density matrix are independent of the kinetic energy. From experimental excitation parameters the angular part of the atomic charge density for double-atom excitatiin is viewed by fixing the direction of one of the excited electrons and showing the angular charge distribution of the other. The shape of the atoms changes dramatically with the collision energy, especially if the direction of the first electron is 'frozen' in the direction of the initial relative velocity. (author)

[en] When an atom is evaporated from or added to a free liquid surface there is a density perturbation of the surface. We have detected this surface spoiling rising a ⁴He atomic beam at glancing angles to the surface. With a perfect free liquid surface some of the atoms reflect specularly and some condense. We find that the specular reflection coefficient decreases as the surface is spoiled by another beam of ⁴He atoms. The degree of spoiling as measured by the decrease in reflectivity, is initially proportional to the spoiling beam flux, but at higher fluxes the spoiling saturates. A phenomenological model is developed to describe this behaviour

[en] The scattering of free helium atoms at the surface of liquid ⁴He at zero temperature is discussed in terms of the Feynman variational method. If the scattered atom is distinguishable from those in the liquid target, as is true for the scattering of ³He, the problem reduces to the motion of a single particle in an effective potential. Above the surface the effective potential is the same as the real van der Waals potential and, in the surface and below, it is related to the density and kinetic-energy distribution in the liquid ground state. If the theory is applied to the scattering of ⁴He, neglecting the indistinguishability of the scattered atom, an excellent fit to the experimental reflection coefficient is obtained. When the trial wave function is fully symmetrized to calculate the reflection coefficient for ⁴He more realistically, the theory describes the production of a single excitation (phonon) from each absorbed atom. The resulting reflection coefficient disagrees with experiment, predicting total reflection at certain critical angles. Even when multiple production of low-energy phonons is considered, total reflection will still occur. It follows that the multiple production of some other type of excitation, in particular low-energy ripplons, must be a dominant process in agreement with the calculations of Echenique and Pendry. It seems that the simple unsymmetrized theory fits the data because the reflection coefficent is mainly determined by the static Van der Waals potential outside the liquid where the effects of symmetry, inelastic scattering, etc., are negligible. An atom which penetrates below this region is then effectively lost as far as the original beam is concerned because it begins to produce low-energy ripplons and is incoherently scattered. The problem of determining the density profile at the liquid surface from the experimental scattering data is briefly considered

[en] In this letter is described a new approximate and relatively simple version of the Glauber formula for nucleus nucleus scattering

[en] We determine the Coulomb sum for ⁴He using world data on ⁴He(e, e') and compare the results to calculations based on realistic interactions and including two-body components in the nuclear charge operator. We find good agreement between theory and experiment using free-nucleon form factors. The apparent reduction of the in-medium G_ep implied by IA-interpretation of the L/T-ratios measured in ⁴He(e,e'p) and ⁴He([vec]e, e'p) is not confirmed

[en] A partial-wave analysis of elastic ⁴He⁴He scattering is performed in the energy range 40–50 MeV.

[en] The authors compare the properties of vacancies in ⁴He implied by X-ray, NMR, and acoustic measurements with specific heat, pressure, and melting curve data. Taken together, these different measurements indicate that the model of vacancies as occupying a narrow band of states cannot be correct. Better agreement can be obtained by assuming that vacancies occupy a wide band but inconsistencies remain. An unambiguous determination of the properties of vacancies requires additional experimental and theoretical work