Magnetic scattering of neutrons in magnetic superconductors

The magnetic dipolar interaction responsible for the neutron scattering due to magnetic moments in a crystal is affected by the persistent current in the superconducting state. From this effect, the small angle scattering of neutrons is strongly depressed, and the intensity maximum of the critical scattering appears at a finite scattering wave number even in ferromagnetic superconductors.     

A method for the rapid evaluation of critical multiple scattering

Simple analytic formulas are derived for the double scattering to single scattering ratio near the critical point of a fluid. They are valid even close to the critical temperature, where turbidity is important, and concern right-angle scattering from a roughly cubic sample. New experimental results for the binary mixture nitrobenzene-n-hexane, as well as previously published results for 4 critical fluids are in good agreement (±20%) with our theoretical predictions. The order of magnitude for the ratio of spectral intensities is also estimated.     

Dynamic fluctuations and static speckle in critical X-ray scattering from SrTiO3

We report a study of critical x-ray scattering from SrTiO3 near the antiferrodistortive structural phase transition at T(C) approximately 105 K. A line shape analysis of the thermal diffuse scattering results in the most precise experimental determination to date of the critical exponent gamma. The microscopic mechanism behind the anomalous "central peak" critical scattering component is clarified here by the first-ever observation of a static coherent diffraction pattern (speckle pattern) within the anomalous critical scattering of SrTiO3. This observation allows us to directly attribute the origins of the central peak to Bragg diffraction from remnant static disorder above T(C).     

X-ray scattering from a randomly rough surface

Abstract

On the basis of the method of reduced Rayleigh equations we present a simple and reciprocal theory of the coherent and incoherent scattering of x-rays from one- and two-dimensional randomly rough surfaces, that appears to be free from the limitations of earlier theories of such scattering based on the Born and distorted-wave Born approximations. In our approach, the reduced Rayleigh equation for the scattering amplitude(s) is solved perturbatively, with the small parameter of the theory η(ω) = 1 - ε(ω), where ε(ω) is the dielectric function of the scattering medium. The magnitude of η(ω) for x-rays is in the range from 10^?6 to 10^?3, depending on the wavelength of the x-rays. The contributions to the mean differential reflection coefficient from the coherent and incoherent components of the scattered x-rays are calculated through terms of second order in η(ω). The resulting expressions are valid to all orders in the surface profile function. The results for the incoherent scattering display a Yoneda peak when the scattering angle equals the critical angle for total internal reflection from the vacuum-scattering medium interface for a fixed angle of incidence, and when the angle of incidence equals the critical angle for total internal reflection for a fixed scattering angle. The approach used here may also be useful in theoretical studies of the scattering of electromagnetic waves from randomly rough dielectric-dielectric interfaces, when the difference between the dielectric constants on the two sides of the interface is small.     

The critical position for elastic electron scattering in neon

A measurement of the electron energy and scattering angle where the differential cross section for elastic electron scattering by neon atoms reaches its smallest value is reported. This is compared with our derivations of the critical position from seven theoretical models and from two sets of phase shifts obtained by analysis of experimental data. The latter show poor agreement with our value. The theoretical critical positions tend to lie at a lower energy and angle than our measurement, but theR-matrix calculations of Blum and Burke yield a critical position closest to it.     

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.     

Interference in light scattering from slightly rough dielectric layers

The scattering of light from a slightly rough surface overlying a reflecting surface is investigated. It is shown that the long-scale component of the roughness spectrum plays a critical role in the scattering patterns obtained. The scattered interference patterns are critically dependent on small variation of the rms height of the long-scale component of the roughness. Conventional perturbation theory is found to be invalid in cases in which interference phenomena in the scattering are of importance. A model is proposed that quantitatively describes the measured angular intensity distributions.     

Critical hyper-Raman scattering in ferroelectrics

It is shown, that the critical hyper Raman scattering (CHRS) due to the polarization fluctuations in ferroelectrics must increase sharply in the vicinity of the phase transition point T_c. The spectral intensity of the CHRS is expressed explicitely in terms of the imaginary part of low-frequency dielectric permeability ε(ω, T) which permits to use the CHRS for investigations of the critical dynamics near T_c, in particular, in centrosymmetric phase, where the ordinary Raman scattering (of the first order) is forbidden. The calculated CHRS intensity in the BaTiO₃ type crystals is found to be larger by 4–5 orders of magnitude than that in the media investigated earlier.     

Dynamics at the air-water interface revealed by evanescent wave light scattering

A new tool to study surface phenomena by evanescent wave light scattering is employed for an investigation of an aqueous surface through the water phase. When the angle of incidence passes the critical angle of total internal reflection, a high and narrow scattering peak is observed. It is discussed as an enhancement of scattering at critical angle illumination. Peak width and height are affected by the interfacial profile and the focusing of the beam. In addition, the propagation of capillary waves was studied at the surface of pure water and in the presence of latex particles and amphiphilic diblock copolymers. The range of the scattering vectors where propagating surface waves were detected is by far wider than standard surface quasi-elastic light scattering (SQELS) and comparable with those of X-ray photon correlation spectroscopy (XPCS).     

Molecular light scattering of multiplicity 1.5

The “interference” contributions from compact groups of scattering centers to the total intensity of molecular scattering in a liquid are analyzed. The result of the algebra of fluctuating quantities has been restored for the case of long-range correlations between the groups. The role of short-range correlations is most significant for moderate deviations (10^?3?10^?2) of the dimensionless temperature from its critical value. Estimates of the relative value and temperature peculiarities of the contributions of multiplicity 1.5 proportional to the third-order moment of the density fluctuations and an analysis of experimental data indicate that they can be partially observed under conditions deviating from the critical isochore.     

散射中子对超瞬发临界系统动态行为的影响北大核心CSCD

在点反应堆理论的基础上,建立了研究散射中子影响超瞬发临界系统动态行为的模拟计算方法,利用CFBR-Ⅱ堆的脉冲实验验证了该方法的正确性。通过分析计算表明,在超瞬发临界状态,散射中子的影响包括增加反应性、使脉冲波形后沿展宽和增加脉冲裂变产额。建立的模拟计算方法为预测脉冲堆外各种物体产生的散射中子的动力学效应提供了途径,对提高脉冲堆的核安全有应用价值。     

Anomalous scattering in supercooled ST2 water

ABSTRACT

Large-scale molecular dynamics (MD) simulations of systems containing up to 256,000 molecules were performed to investigate the scattering behaviour of the ST2 water model at deeply supercooled conditions. The simulations reveal that ST2 exhibits anomalous scattering, reminiscent of that observed in experiment, which is characterised by an increase in the static structure factor at low wavenumbers. This unusual behaviour in ST2 is linked with coupled fluctuations in density and local tetrahedral order in the liquid. The Ornstein–Zernike correlation length estimated from the anomalous scattering component exhibits power-law growth upon cooling, consistent with the existence of a liquid–liquid critical point (LLCP) in the ST2 model at ca. 245 K. Further, spontaneous liquid–liquid phase separation is observed upon thermally quenching a large system with 256,000 water molecules below the predicted critical temperature into the two-phase region. The large-scale MD simulations therefore confirm the existence of a metastable liquid–liquid phase transition in ST2 and support findings from previous computational studies performed using smaller systems containing only a few hundred molecules. We anticipate that our analysis may prove useful in interpreting recent scattering experiments that have been performed to search for an LLCP in deeply supercooled water.     

产生切连科夫辐射的康普顿电子在介质中的临界散射角

讨论了γ光子在同一种介质中连续产生康普顿散射和切连科夫辐射的条件。这一条件可用产生切连科夫辐射的康普顿电子在介质中的临界散射角的大小来表示。     

Laser light scattering in micellar solutions

Summary The laser light scattering apparatus used for both total intensity and quasi-elastic light scattering experiments on micellar solutions is described in detail. The absolute calibration of the scattered intensity is obtained by exploiting the existence of a lower critical consolution point in a low-concentration aqueous solution of a nonionic amphiphile (C₁₂E₈). The obtained results suggest that micellar solutions may represent a very convenient light scattering standard for both static and dynamic experiments. Paper presented at the “Meeting on Lyotropics and Related Fields”, held in Rende, Cosenza, September 13—18, 1982.     

Temperature shift of the maximum of neutron critical scattering as a result of scattering of neutrons on spin waves in a paramagnetic phase

A new physical mechanism which causes the temperature shift of the maximum of neutron critical scattering has been proposed. It has been assumed that a dominant role is played by the scattering of neutrons on spin-wave-like excitations of magnetization fluctuations in the paramagnetic phase. The relationships between the temperature shift and a scattering vector (or observation angle) have been obtained. The theoretical results obtained are in agreement with the experimental data.     

Depolarized light scattering in a 2.6-lutidine-water solution near the critical point

The spectra of depolarized Rayleigh light scattering, i.e., the Rayleigh line wing (RLW), and Raman scattering in a solution with the lower critical point in the phase separation diagram is experimentally studied. The Rayleigh line wing is studied to 30 cm^?1 from the exciting light frequency; the Raman scattering line (RSL) is studied in the near profile region. In the vicinity of the lower critical point, as well as in solutions with the upper critical point, strong narrowing of the RLW and RSL is observed. In this case, the conditions arise for the manifestation of the profile in the Rayleigh line spectrum, which is caused by the interaction of concentration and anisotropy fluctuations. Previously, this spectral line was theoretically predicted by I. A. Chaban in [1].     

Resonance Raman scattering at the saddle points of semiconductors

An approximate theory is formulated to describe resonance Raman scattering near the critical points of semiconductors using a model density of states. Large resonance enhancements and absolute scattering cross sections are predicted near the saddle points.     

Fermi systems with strong forward scattering

We review the theory of interacting Fermi systems whose low-energy physics is dominated by forward scattering, that is scattering processes generated by effective interactions with small momentum transfers. These systems include Fermi liquids as well as several important non-Fermi-liquid phases: one-dimensional Luttinger liquids, systems with long-range interactions, and fermions coupled to a gauge field. We report results for the critical dimensions separating different 'universality classes' and discuss the behaviour of physical quantities such as the momentum distribution function, the single-particle propagator and low-energy response functions in each class. The renormalization group for Fermi systems will be reviewed and applied as a link between microscopic models and effective lowenergy theories. Particular attention is paid to conservation laws, which constrain any effective low-energy theory of interacting Fermi systems. In scattering processes with small momentum transfers the velocity of each scattering particle is (almost) conserved. This asymptotic conservation law leads to non-trivial cancellations of Feynman diagrams and other simplifications, making thus possible a non-perturbative treatment of forward scattering via Ward identities or bosonization techniques.     

Specific features of depolarized and polarized light scattering in a solution with a layering isolated region

Intensities of depolarized and polarized light scattering in guaiacol-glycerin solutions with layering isolated regions are measured. It is shown that (a) the depolarized scattering intensity is the same above the higher critical point (HCP) and below the lower critical point (LCP), and (b) the polarized scattering intensity below LCP is higher, the higher the HCP. An empirical formula is offered to describe the polarized scattered light intensity. No increase in the single depolarized scattering intensity is found approaching LCP and HCP.