No abstract available

[en] What follows is an account of neutron scattering studies on liquid helium done at Oak Ridge over the last 15 or so years. As time progressed, the measurement techniques improved considerably, but more important was our improved understanding of the measurements. In particular, a better understanding was gained of the difficulty of obtaining a condensate fraction from measurements of S(Q,ω)of liquid ⁴He. This paper discusses these neutron scattering techniques further. 11 refs., 11 figs

[en] In one aspect, the invention is an improved pulsed-neutron monochromator of the vibrated-crystal type. The monochromator is designed to provide neutron pulses which are characterized both by short duration and high density. A row of neutron-reflecting crystals is disposed in a neutron beam to reflect neutrous onto a common target. The crystals in the row define progressively larger neutron-scattering angles and are vibrated sequentially in descending order with respect to the size of their scattering angles, thus generating neutron pulses which arrive simultaneously at the target. Transducers are coupled to one end of the crystals to vibrate them in an essentially non-resonant mode. The transducers propagate transverse waves in the crystal which progress longitudinally therein. The wave are absorbed at the undriven ends of the crystals by damping material mounted thereon. In another aspect, the invention is a method for generating neutron pulses characterized by high intensity and short duration

[en] We present a new method of designing supermirrors, based on considering the contribution of each bilayer to the extinction in a given stack of bilayers, and derive and solve the discrete equations governing the choice of layer thicknesses. In the limit of zero layer thickness, the usual continuum result is recovered. The design, which can produce essentially perfect reflectivity over the entire supermirror range, also provides an objective physical mechanism for trading reflectivity to gain angular range. 17 refs., 3 figs

No abstract available

No abstract available

[en] Inelastic neutron scattering measurements have been made on sputter-deposited amorphous Tb₀.₃₃Fe₀.₆₇ using time-of-flight spectrometers at Argonne and at Oak Ridge. At 433⁰K (above T/sub c/) the magnetic scattering function S(Q, ω) exhibited an approximately Gaussian dependence on energy transfer characteristic of a paramagnet. Below T/sub c/, at 299⁰K, a broad distribution of magnetic inelastic scattering is present, centered approximately at ΔE = 11 meV. As expected, this distribution was significantly broadened and was shifted to a lower energy than the equivalent polycrystalline compound TbFe₂ which showed a single inelastic peak near 18 MeV. Polarized beam time-of-flight data taken at Oak Ridge showed evidence for discrete spin wave excitations for Q approximately less than 1.0 A^-1 in the amorphous sample

[en] Neutron-inelastic-scattering techniques have been used to study the spin dynamics of EuO. High-quality single crystals were used so that temperature-dependent line shapes could be obtained at all momentum values. It was found that the magnetic excitations above T/sub c/ changed from Lorentzian-like peaks centered at zero energy near the zone center to rather well defined spin-wave-like excitations at the zone boundary

[en] The neutron total cross sections of several single crystals (Si, Cu, sapphire), several polycrystalline samples (Cu, Fe, Be, C, Bi, Ta), and a fine-powder copper sample have been measured from 0.002 to 5 eV. The Cu powder and polycrystalline Fe, Be and C data exhibit the expected abrupt changes in cross section. The cross section of the single crystal of Si is smooth with only small broad fluctuations. The data on two single Cu crystals, the sapphire crystal, cast Bi, and rolled samples of Ta and Cu have many narrow peaks approx. 10^-3 eV wide. High resolution (0.3%) transmission measurements were made on the 1.057-eV resonance in ²⁴⁰Pu and the 0.433-eV resonance in ¹⁸⁰Ta, both at room and low temperatures to study the effects of crystal binding. Although the changes in Doppler broadening with temperature were apparent, no asymmetries due to a recoilless contribution were observed

[en] The magnetic moment of neutrons makes them an excellent probe of magnetic phenomena and very direct information is obtainable with neutrons. In fact the generalized susceptibility is directly given by a neutron scattering experiment, and this quantity tells all there is to know about a magnetic system. This paper serves as an introduction to a series of papers on magnetic excitations. The necessary neutron scattering formalism is established and various types of magnetic systems are briefly discussed