Quark scattering amplitudes with quasi-elastic unitarity

We consider quark-quark scattering at high energies and fixed momentum transfer. In a model where in the s and u channel intermediate states only gluons with sufficiently small transverse momenta are emitted, the scattering amplitudes are expressed in terms of the S-matrix elements for exactly soluble two-dimensional field theories.     

Recoil effect in quasi-elastic hadron-deuteron scattering

The problem of hadron-deuteron quasi-elastic scattering is considered for large momentum transfers. The longitudinal part of the momentum transfer is included in the single and double scattering. It is shown that a simple enhancement factor relates the double scattering contribution to the differential cross section to the same quantity in Glauber theory.     

Quark exchange in quasi-elastic electron-nucleus scattering

In this paper the consequences of the Pauli principle applied at the quark level are investigated for nuclear structure functions in electron-nucleus scattering in the quasi-elastic scattering region. The effect of quark exchange contributions is studied for both inclusive and exclusive electron-nucleus scattering and is shown to give rise to nonnegligible corrections to the impulse approximation picture. Examples are given for light nuclei using gaussian wave functions.     

A simple model of resonance-dominated quasi-elastic scattering

We examine a highly simplified model of projectile-nucleus scattering in which the elementary interactions are resonance dominated. The essential element introduced into the nuclear dynamics is a shift of spectral strength to an energy comparable with or greater than the resonance half-width. The interplay of the energy dependences yields strong sensitivity to the underlying dynamics. Phenomenological treatments based on simplified nuclear dynamics, such as the -hole model, are seen to reproduce inclusive observables. They do less well on more exclusive observables and can be misleading in their implications for the underlying physics.Communicated by F. Lenz     

Bound water fractions from quasi-elastic neutron scattering

Quasi-elastic neutron scattering measurements of AlCl₃ aqueous solution are analysed to derived the ratio of bound to solvent water molecules. We find that the ratio depends on the nature of the binding of the water molecules in the hydration shell and in the solvent. If the details of the binding are not known it is shown that such measurements must be carried out at small neutron wavevector transfers to obtain quantitative results.     

Effects of nuclear deformation in quasi-elastic electron scattering

We discuss effects due to nuclear deformation that can be observed in quasi-elastic electron scattering from deformed nuclei. To simplify the discussion we restrict ourselves to the plane wave impulse approximation (PWIA) and compare the form of the spectral function for axially symmetric deformed nuclei with that for spherical nuclei in the independent particle model. We point out that a strong dependence on deformation can be expected for momentum distributions measured in narrow missing energy ranges. This is illustrated taking ²⁸Si as an example.     

Experimental study of quasi-elastic scattering of ultracold neutrons

Ultracold neutrons (UCN) are lost from traps if they are quasi-elastically scattered from the wall with an energy gain sufficient to exceed the Fermi potential for the wall. Possible mechanisms of a quasi-elastic energy transfer are, for instance, scattering from hydrogen diffusing in an impurity surface layer or on surface waves at a liquid wall. Using two different experimental methods at the UCN source of the Institut Laue-Langevin we have investigated both the energy-gain and the energy-loss side of quasi-elastic UCN scattering on Fomblin grease coated walls. For Fomblin oil and similar new types of oil we report up-scattering data as a function of temperature and energy transfer. These low-temperature oils may be used in an improved measurement of the neutron lifetime, which requires extremely low wall reflection losses. Received 13 March 2002 Published online 31 July 2002     

Integrated quasi-elastic neutron scattering intensity of hydrogen in niobium

The integrated quasi-elastic neutron scattering intensity of NbH_0.13 has been measured at 235°C over a large momentum transfer range $\text{(0.6 < K < 7}\text{A}\text{?}{}^{-1}\text{)}$. In the high temperaturephase a deviation from a simple Debye-Waller factor governed intensity dependence has been observed.     

Algebraic solution of RPA equationsfor CC quasi-elastic neutrino-nucleus scattering

An algebraic solution of the RPA equations for nucleon re-interactions in the case of quasi-elastic charged-current neutrino-nucleus scattering is presented. The Abelian algebra of the matrices allows us to extract four independent corrections to the cross section separately. The results of numerical computations are shown.Received: 25 March 2003, Revised: 26 August 2003, Published online: 10 October 2003     

Eikonal analysis of Coulomb distortion in quasi-elastic electron scattering

An eikonal expansion is used to provide systematic corrections to the eikonal approximation through order 1/k ², where k is the wave number. Electron wave functions are obtained for the Dirac equation with a Coulomb potential. They are used to investigate distorted-wave matrix elements for quasi-elastic electron scattering from a nucleus. A form of effective-momentum approximation is obtained using trajectory-dependent eikonal phases and focusing factors. Fixing the Coulomb distortion effects at the center of the nucleus, the often-used ema approximation is recovered. Comparisons of these approximations are made with full calculations using the electron eikonal wave functions. The ema results are found to agree well with the full calculations.     

Neutron scattering from FeSi

The inelastic neutron scattering from the unusual paramagnet FeSi has been measured at temperatures of up to 700 K in order to investigate the possible existence of a local magnetic moment at high temperatures. The estimated intensities of the central peaks around $\text{h}\text{?}\text{ω = 0}$ and the nearly constant backgrounds ($\text{h}\text{?}\text{ω ? 16 meV}$) indicate that the paramagnetic state above 600 K in FeSi cannot be interpreted in terms of a simple localized spin model with $\text{S ～}\text{1}\text{2}$.     

Neutron scattering in intermetallics

Inelastic and elastic neutron scattering as a probe of long range and disordered magnetism is discussed for example cases in rare earth intermetallic crystalline compounds and amorphous analogues. The determination of the sublattice site magnetizations is illustrated for RFe₂ and Y₆(Mn_xFe_1−x)₂₃ compounds. The latter are shown to exhibit strong exchange disorder effects for intermediate compositions, as manifested by the development of short range antiferromagnetic clusters. The effect of randomization of the crystal field interaction in destroying long range order is illustrated in amorphous rare earth compounds and in rare earth compound hydrides. Results of inelastic scattering measurements on Laves phase Fe, Co, and Al compounds are summarized which yield exchange and crystal field parameters.     

Generalized diffusion and quasi-elastic scattering widths in two-dimensional systems

The paper presents approximate calculations of dimensionality and lattice symmetry effects in the wave vector and frequency dependent diffusional response of disordered lattices. Numerical results are given and comparatively discussed for the tracer diffusion correlation function and the quasi-elastic incoherent scattering width in triangular, simple square and simple cubic lattices, only the restriction of double occupancy avoidance being taken into account. The quasi-elastic coherent scattering width is estimated for a triangular system possessing liquid-like structural disorder by means of the simple inclusion of a spread in jump lengths around a preferred set of jumps. Qualitative contact is made with recent neutron scattering experiments on alkali-metal graphite intercalation compounds.     

Neutron scattering from PEEK

An alkali‐soluble polysaccharide, GM5‐1, from the mycelium of Ganoderma tsugae, was fractionated by the nonsolvent addition method. The weight‐average molecular mass (M _w) and intrinsic viscosity ([η]) of fractions were studied by laser light scattering and viscometry with dimethylsulfoxide (DMSO) containing 0.25M LiCl (0.25M LiCl/DMSO) as the solvent at 30°C. The dependences of [η] and the radius of gyration (?S ²?_z ^1/2) on M _w were found to be [η]=9.8×10^?2 M _w ^0.57 (cm³g^?1) and ?S ²?_z ^1/2=1.65×10^?2 M _w ^0.58 (nm) in the M _w range from 8.6×10⁵ to 2.6×10⁶. The analysis based on current theories for a wormlike chain showed that the chain conformational parameters of GM5‐1 were 4.2 nm for persistence length (q) and 833 nm^?1 for linear mass density (M_L) with an obvious excluded volume effect. The results suggested the alkali‐soluble polysaccharide behaves like a semiflexible chain in 0.25M LiCl/DMSO at 30°C.     

High-resolution study of quasi-elastic electron scattering from a two-layer system

In large-angle elastic scattering events of keV electrons a significant amount of momentum is transferred from the electron to a nucleus in the target. As a consequence kinetic energy is transferred from the energetic electron to the nucleus, and hence these processes can be referred to as ‘quasi-elastic’. How much energy is transferred depends on the mass of the nucleus. In this paper, we present measurements from a two-layer system (a germanium layer and a carbon layer), and at high energies the quasi-elastic peaks of Ge and C are clearly resolved. It is demonstrated that the sample geometry has a huge effect on the observed relative intensities. It is shown that the intensities are influenced by the elastic scattering cross-section of the atoms in the film, film composition and selective attenuation, due to varying amount of inelastic scattering for layers of the film. However truly quantitative agreement is not obtained.     

Microscopic properties of liquid gallium from quasi-elastic neutron scattering experiments

The results of the neutron diffraction study of liquid gallium on the DIN-2PI spectrometer (IBR-2 reactor, JINR, Dubna) have been discussed. The analysis of the experimental data has provided temperature dependences of diffusion and relaxation characteristics of liquid gallium in the temperature range of 313–793 K. It has been found that an increase in the temperature is accompanied by the gradual deviation of the temperature dependence of the self-diffusion coefficient from the known dependences obtained from the data on viscosity. Such a behavior is explained by the beginning clustering of liquid gallium induced by the prevailing covalent character of interatomic bonds.     

Neutron scattering of iron-based superconductors

Low-energy spin excitations have been studied on polycrystalline LaFeAsO_1?xF_x samples by inelastic neutron scattering. The Q-integrated dynamical spin susceptibility χ″(ω) of the superconducting samples is found to be comparable to that of the magnetically ordered parent sample. On the other hand, χ″(ω) almost vanishes at x = 0.158, where the superconducting transition temperature T_c is suppressed to 7 K. In addition, χ″(ω) in optimally doped LaFeAsO_0.918F_0.082 with T_c = 29 K exhibits a spin resonance mode. The peak energy, E_res, when scaled by k_BT_c is similar to the value of about 4.7 reported in other high-T_c iron-based superconductors. This result suggests that there is intimate relationship between the dynamical spin susceptibility and high-T_c superconductivity in iron-based superconductors, and is consistent with a nesting condition between Fermi surfaces at the Γ and M points.     

Neutron scattering of lanthanide materials

A selected review of recent neutron scattering results on lanthanide materials is presented. Topics covered include the magnetic structures of the elemental metals, magnetic superlattices, enhanced nuclear magnetism, magnetic excitations and critical scattering.     

Structural phase transitions III. Critical dynamics and quasi-elastic scattering

The dynamical behaviour of systems exhibiting structural phase transitions is reviewed, with particular emphasis on the problems posed by the simultaneous existence of quasi-elastic and phonon features in the dynamic response of the soft coordinates. The results of scattering experiments revealing this phenomenon are surveyed in detail, and are used in an assessment of current theories, subdivided into three categories: those which seek to describe the phenomenon within an extended phonon-based theory; those which attempt to trace the effect to the formation of long-lived clusters of precursor order; and those which associate the quasi-elastic scattering with crystal imperfections.     

Neutron scattering from natural silicon

Differential cross sections for elastic and inelastic scattering of neutrons from natural silicon were measured in the energy region between 4.00 and 5.75 MeV, in steps of about 250 keV in the primary neutron energy. The results are presented in form of coefficients of Legendre polynomial expansions.