Search results for "SMALL-ANGLE NEUTRON"

Some comments on fluctuating-elasticity and local oscillator models for anomalous vibrational excitations in glasses

2011

Abstract An overview is given on the present status of the theoretical description of vibrational spectra of glasses, as seen by inelastic neutron, X-ray and light (Raman) scattering. Using the language of Green's/response functions the merits and shortcomings of a local oscillator and a generalized elasticity-theory point of view are discussed. It is pointed out that in both cases the interaction of phonons with disorder-induced irregularities leads to Rayleigh scattering (mean free path l ∝ ω − 4 ) at low enough frequencies and temperatures. In disordered solids at ambient temperature the Rayleigh scattering is usually masqued by Akhiezer-like anharmonic scattering l ∝ ω − 2 , but it can …

Elastic electron scattering from the multipole moment distributions ofMg25

1977

4He+Ni elastic scattering near the Coulomb barrier and optical model parameters

2002

Cross sections for the elastic scattering system of 4He+Ni have been investigated. Natural nickel was bombarded by 4He ions in the laboratory energy range of 3.0–14.3 MeV and the intensity of helium backscattering through laboratory angles of 96°, 117°, and 137° was observed. From measured yield data, the cross sections were extracted for the direct Ni(4He,4He)Ni scattering process as well as for the inverse recoil scattering process 4He(58Ni,4He)58Ni by calculating the kinematical reversal of the reaction. The experimental helium scattering angles convert to helium recoil angles of 20°, 30°, and 40°, and the incident helium ion energies to 43.5–207 MeV for incident 58Ni ions in the reverse…

SANS polarization analysis at V4 SANS instrument of HMI Berlin

2008

The V4 instrument has recently been upgraded with a 3He spin filter cell, placed directly in the homogeneous field B of the sample magnet, to enhance the SANSPOL option for polarization analysis. The prototype setup was still affected by: (a) a quick relaxation of the 3He nuclear polarization in the cell with a time constant of only ?130 min which significantly changes the spin filter transmissions T+ and T? for neutrons polarized parallel I+ and anti-parallel I? to B, and (b) the absence of a flipping aid behind the sample. The usual polarization analysis procedure, expecting virtually time-independent transmissions and a second flipping device, is therefore not applicable. We present an a…

Neutron polarizability and the n-e scattering length

1972

Abstract It is shown that the neutron polarizability contribution to the n-e scattering length is within the present level of precision. The experimental result on this interaction is consistent with a value of the neutron polarizability similar to the proton one.

A Ramsey apparatus for the measurement of the incoherent neutron scattering length of the deuteron

2008

Abstract A Ramsey apparatus for cold, polarised neutrons is described, which enables us to measure neutron precession angles with an absolute accuracy of about 1 ∘ . This is necessary to perform a planned high-accuracy measurement of the incoherent neutron scattering length b i , d of the deuteron. The performance of the apparatus is demonstrated in systematic stability measurements as well as in two selected examples using samples containing polarised nuclear spins.

Angular and polarization dependence of Compton scattering from in the Δ-resonance region

1998

Abstract Using linearly polarized tagged photons from coherent bremsstrahlung, differential cross sections and beam asymmetries for Compton scattering by 4 He have been measured at MAMI in the energy interval between 150 MeV and 500 MeV for scattering angles of θ γ lab =37°, 93° and 137°, thus largely increasing the available data base. Improved calculations in terms of the Δ -hole model completely fail to describe the data at large scattering angles. The same proved to be true for a schematic model, even after taking into account properties of nuclear photo-absorption in very detail.

Comment on “Comparison of Polarization Observables in Electron Scattering from the Proton and Deuteron”

1998

Small Angle Neutron Scattering from Systems of Interacting Particles. Modelling High Density Micellar Fluids

1992

The need for analytical solutions of the scattering equation for complex situations (polydisperse samples, scattering from non centrosymmetrical particles, etc.) has somehow escaped the attention of the workers in the Small Angle Scattering field, although it is clear that, at the level of sophistication today available for the experiments, a more rigorous approach is necessary. For quite a few years our group has been actively engaged in SANS research and has occasionally devoted its attention to develop alternative ways of data analysis based on more rigorous solutions of the scattering equation.

Inelastic neutron scattering by coupled rotational and translational modes in KCN

1980

The TA [100] phonon branch of the molecular crystal KCN was studied by inelastic neutron scattering in the cubic phase. In addition the distribution of the quasielastic scattered neutrons was investigated. The results are analysed by assuming a coupling of the phonon modes to the rotational degrees of freedom of the CN-dumb-bells which are regarded as a system of interacting quadrupoles. A good description of the present results and also of the existing ultrasonic and Brillouin data is achieved by a simple model which uses a single collective rotational mode of finite excitation energy and line width.