Anisotropic Neutron Research Articles

Microstructural characterization of yttria-stabilized zirconia plasma-sprayed deposits using multiple small-angle neutron scattering

Density, electron microscopy, elastic modulus, and small-angle neutron scattering studies are used to characterize the microstructures of yttria-stabilized zirconia plasma-sprayed deposits as a function of both feedstock morphology and annealing. In particular, anisotropic multiple small-angle neutron scattering data are combined with anisotropic Porod scattering results to quantify each of the three main porous components in these thermal barrier coating materials: intrasplat cracks, intersplat lamellar pores and globular pores. An inverse correlation between the volume of porosity and its surface area is confirmed for the as-sprayed deposits, as is a preferential annealing of intrasplat cracks at elevated temperatures. The average elastic modulus is correlated with the total void surface area while the elastic anisotropy is related more closely to the intersplat porosity. However, depending on the feedstock morphology, globular pores are also shown to play a surprisingly significant role in post-anneal deposit microstructures and properties.

Directional distribution of radiation around an accident at a uranium fuel factory in Tokai-mura, 1999.

A beta-ray survey was carried out on concrete walls of the boundary and buildings after a criticality accident at a factory of JCO Co. Ltd. at Tokai-mura. A remarkable distribution of beta counts was observed on the walls depending on the complex internal and external structures of buildings surrounding a precipitation vessel containing uranium 23 days after the accident. The directional distribution function, based on the beta counts on the walls, was consistent with data concerning the neutron dose rate measured in several directions during the accident, suggesting an anisotropic neutron distribution to the residential area.

Evaluation procedure for anisotropic SANS

A brief description of an improvement of a special evaluation procedure for treatment of data from anisotropic Small-Angle Neutron Scattering (SANS) is presented. A spatial orientation distribution of particles, the improved calculation of a size distribution, the option to fit a data from a sample containing two types of particles as well as the raw-data treatment are the main extensions. The application of the procedure is demonstrated on data taken from investigation of precipitation in single-crystal nickel-base superalloys.

Three-dimensional small-angle neutron scattering (3D-SANS) and its application

Three-dimensional small-angle neutron scattering (3D-SANS) analysis is derived. This analysis using neutrons, which can penetrate matter easily, is a powerful technique to investigate the anisotropic nanoscale structures in single crystal bulk materials, although it takes a long time to get a complete data set. This technique is applied to the analysis of the anisotropic neutron scattering from a superconductor CeRu2. It suggests that planar defects correlate well with the lattice symmetry of the crystal and influence superconducting properties as pinning centers. It is also shown by simulation that the 3D-SANS analysis is useful even at intense short pulse spallation sources that give a wider band width of neutron wavelength, if the SANS profile is highly anisotropic.

Effect of anisotropic D–D fusion neutron emission on counter calibration using activation techniques

Detailed plasma and neutron transport simulation is needed for accurate measurements of the total neutron emission by means of foil activation during deuterium neutral beam injection into toroidal fusion plasmas. Results from a dedicated package of computer codes for simulation of neutron production and neutron transport are presented. The simulation procedure comprises spatially resolved Fokker–Planck calculations of the deuteron velocity distribution, the calculation of absolute neutron spectra as functions of the direction of emission and, finally, a detailed Monte Carlo neutron transport simulation. The simulation procedure is used to calculate the influence of anisotropic neutron emission on activation foil measurements for neutral-beam-heated toroidal fusion plasmas due to the variation of the differential D–D neutron production with angle of emission. Theoretical results predict effects in the order of a few percent. This is consistent with experimental results which show that the total neutron yield is underestimated by about 5% if effects of anisotropic emission are being neglected.

Melting of columnar hexagonal DNA liquid crystals

The persistence length DNA hexagonal-cholesteric phase transition upon dilution and/or in- crease in solvent ionic strength is investigated with polarized light microscopy. The ionic strength depen- dence of the transition follows Lindemann criterion CL =0 :098 0:003, i.e., the hexagonal lattice melts when the root-mean-square fluctuations in transverse order exceed 10% of the interaxial spacing. The spacings are derived from density and the fluctuations are estimated with a theory of undulation enhanced electrostatic interactions. Additional support for this theory is given by the DNA equation of state and anisotropic neutron radiation scattering from magnetically aligned cholesteric samples just below the phase transition.

Interplay between heavy fermions and crystal-field excitation in Kondo lattices: Low-temperature thermodynamics and inelastic neutron scattering spectra of CeNiSn

The microscopic theory of interaction between the heavy fermions and the crystal field excitations in Kondo lattices is presented. It is shown that the heavy-fermion spectrum scaled by the Kondo temperature $T_K$ can be modified by the crystal field excitations with the energy $\Delta_{CF}$ provided the inequality $\Delta_{CF}<T_K$ is realized. On the base of general description of excitation spectrum the detailed qualitative and quantitative explanation of anisotropic inelastic neutron scattering spectra and low-temperature specific heat of orthorhombic CeNiSn is given. The theory resolves the apparent contradiction between the metallic conductivity and the gap-wise behavior of thermodynamic properties and spin response of CeNiSn at low temperatures.

Anisotropic Neutron Critical Scattering in DKDP Originating from the Ice Rule by Six-States Rotator Model

A theoretical origin of the anisotropic neutron critical scattering observed in DKDP is studied on the basis of the H 2 PO 4 dipole order-disorder model and the ice rule constraint in KDP type ferroelectrics. A radical D 2 PO 4 is assumed to take six Slater configurations described by a six states rotator. The diffused scattering intensity is given in terms of neutron scattering structure factors for respective six configurations and correlation functions among six states rotators. The scattering intensity contour in the reciprocal lattice space is numerically computed and shown to be similar to the experimental results even if the rigid ice constraint is released to some extent. Discussions are made on the controversy between the proton tunneling model and the H 2 PO 4 dipole order-disorder model from these results.

Experimental Verification and Analysis of Neutron Streaming Effect through Void Holes for Control Rod Insertion in HTTR

Control rod columns of the High Temperature Engineering Test Reactor (HTTR) core have each three cylindrical void holes for insertion of the control rods. The reactivity worths of the simulated void holes were measured in the Very High Temperature Reactor Critical Assembly (VHTRC) by the pulsed neutron method with the purpose of evaluating the neutron streaming effect on the reactivity worths of the void holes. The reactivity worths were determined using the revised King-Simmons' formula. The measured results are compared with the calculated ones based on the nuclear data of ENDFIB-IV, using the Benoist's anisotropic neutron diffusion coefficients. It is concluded that the reactivity worths are enlarged up to about twice as large as that obtained using the conventional isotropic neutron diffusion coefficients, and it is also found that the neutron streaming effect that is defined as the relative fraction components exceeding the reactivity worths obtained by the conventional isotropic neutron diffusion coefficients are likely overestimated about 11 and 32% with the void holes being in the core and reflector regions, respectively. Then, the reactivity decrease due to the neutron streaming effect is able to be evaluated around 1%Δk for the initial critical core of the HTTR.

Anisotropic Small Angle Light and Neutron Scattering from a Lyotropic Lamellar Phase under Shear

The influence of shear on the lamellar phase of a semi-dilute solution (36% (w/w)) of tetra ethylenglycol dodecylether (CH 3 [CH 2 ] 11 [OCH 2 CH 2 ) 4 OH, C 12 E 4 ) in water was investigated by Small Angle Light Scattering (SALS), Small Angle Neutron Scattering (SANS) and rheology. A plateau modulus was determined by low amplitude oscillatory shear experiments. A strong scattering peak perpendicular to the flow direction and a small peak along the flow direction were observed in rheo-SANS. The rheo-SALS patterns were also anisotropic. At low shear rates, a four lobe pattern was found in depolarized light scattering (H v ) and scattering perpendicular to the flow direction was observed in polarized scattering (H H ). A butterfly pattern was found in light scattering at high shear rates. The butterfly pattern was stable after cessation of shear, but it was changed by slow shear flow. The scattering data can be explained by a shear induced formation of deformed vesicles and the butterfly pattern might be correlated with an assembly of vesicles disordered in the direction of shear.

Non-affine deformation and spatial fluctuations of the modulus observed in heterogeneous networks and nanocomposites

The anisotropic small-angle neutron scattering from two different materials is considered. One is a polymer network permeated by free, uncross-linked, deuteriated chains. These free chains behave as mobile species. The other is made up of two networks, one being deuteriated, grown interwoven with each other. They are made of two different polymers which are immiscible, one being in a soft, rubbery state, the other in a hard, glassy state.The scattering of the two systems displays an unusual dependence upon the direction with respect to the stretching axis. The scattered intensity recorded along any direction which corresponds to an increase in the dimensions increases strongly with the elongation ratio. The isointensity patterns, so-called butterflies, have the shape of 8s, oriented along the stretching axis.We propose a general explanation: in both cases this increase is due to the separation between some hard, weakly deformed regions inside a softer matrix.This implies, for the network permeated by free chains, that a scattering contrast is created between hard and soft regions: the free chains migrate into the soft regions. The increase of the correlation length, ξ, along any extended direction of the sample (such as the one parallel to the stretching) reveals an intermediate regime at lower and lower values of the scattering vector, q. In this q range, the intensity, I(q), is superimposed on a limit curve, characteristic of each sample. The perpendicular scattering is essentially unaffected. Different continuous-medium elasticity theories have tried to explain such an anisotropy of the spatial fluctuations of concentration. Rather accurate measurements allow us to detect disagreements between these theories and experiment. In our opinion, this confirms our more direct picture: the progressive unscreening of the structure of the spatial distribution of the modulus.

Neutron spectroscopy and anisotropy of the magnetic properties of UOS: interpretation in a crystal-field and molecular-field model

Uranium oxysulphide is an ionic compound whose magnetic and thermodynamic properties have been extensively studied in the past. UOS becomes antiferromagnetic below T N = 55 K with an ordered moment μ ord ≅ 2 μ B. A previous neutron crystal field (CF) spectroscopy experiment was performed to observe the splitting of the J = 4 ground manifold. Two possible CF level schemes were proposed in order to interpret the results, differing essentially for the presence of the intense Г (1) t5 → Г t4 transition at low energy (<10 meV). One of the aims of this work was to look for a peak in this range of energy, which was not accessible at the time of the first experiment. Another goal was to test the CF model against a careful study of the anisotropic magnetic susceptibility of high-quality single crystals. The results of these new measurements are presented and discussed in the frame of a self-consistent molecular field model taking into account the exchange anisotropy.

Neutron spectroscopy and anisotropy of the magnetic properties of UOS: Interpretation in a crystal-field and molecular-field model

Uranium oxysulphide is an ionic compound whose magnetic and thermodynamic properties have been extensively studied in the past. UOS becomes antiferromagnetic below TN = 55 K with an ordered moment μord ≅ 2μB. A previous neutron crystal field (CF) spectroscopy experiment was performed to observe the splitting of the J = 4 ground manifold. Two possible CF level schemes were proposed in order to interpret the results, differing essentially for the presence of the intense Г(1)t5 → Гt4 transition at low energy (<10 meV). One of the aims of this work was to look for a peak in this range of energy, which was not accessible at the time of the first experiment. Another goal was to test the CF model against a careful study of the anisotropic magnetic susceptibility of high-quality single crystals. The results of these new measurements are presented and discussed in the frame of a self-consistent molecular field model taking into account the exchange anisotropy.

Maximum azimuthal anisotropy of neutrons from Nb-Nb collisions at 400A MeV and the nuclear equation of state.

We measured the first azimuthal distributions of triple--differential cross sections of neutrons emitted in heavy-ion collisions, and compared their maximum azimuthal anisotropy ratios with Boltzmann--Uehling--Uhlenbeck (BUU) calculations with a momentum-dependent interaction. The BUU calculations agree with the triple- and double-differential cross sections for positive rapidity neutrons emitted at polar angles from 7 to 27 degrees; however, the maximum azimuthal anisotropy ratio for these free neutrons is insensitive to the size of the nuclear incompressibility modulus K characterizing the nuclear matter equation of state.

Structure of RecA-DNA complexes studied by combination of linear dichroism and small-angle neutron scattering measurements on flow-oriented samples

By combining anisotropy of small-angle neutron scattering (SANS) and optical anisotropy (linear dichroism, l.d.) on flow-oriented RecA-DNA complexes, the average DNA-base orientation has been determined in RecA complexes with double-stranded (ds) as well as single-stranded (ss) DNA. From the anisotropy of the two-dimensional SANS intensity representation, the second moment orientation function S is obtained. Knowledge of S is crucial for the interpretation of l.d. spectra in terms of orientation of the DNA bases and the aromatic amino acid residues. The DNA-base planes are essentially perpendicular to the fibre axis of the complex between RecA and dsDNA in the presence of cofactor ATP gamma S. A somewhat tilted base geometry is found for the RecA-ATP gamma S complexes with single-stranded poly(dT) and poly(d epsilon A). This behaviour contrasts the RecA-ssDNA complex formed without cofactor which displays a poor orientation of the bases. Well-ordered bases in the ssDNA-RecA complex is possibly reflecting the role of RecA in preparing a nucleotide strand for base-pairing in the search-for-homology process. While the central SANS intensity is essentially independent of the pitch of the helical complex, a secondary intensity maximum, which becomes focused upon flow orientation, is found to be a sensitive measure of the pitch. The pitch values for the complexes compare well with cryo-electron microscopy results but are slightly larger than those seen for uranyl-stained samples.

Shear Induced Phase Transition and Transient Small Angle Neutron Scattering Experiments on Micellar Solutions

Abstract Time dependent anisotropic small-angle neutron scattering (SANS) patterns of micellar solutions are presented and discussed. Alignements of the anisotropic micelles in a shear gradient, in a magnetic and in an electric field are explored. Typical time constants for relaxation range from 150 ms to hours.

Transient SANS Studies on p‐Tetrafluorethylen (p‐TFE)

AbstractTime dependent anisotropic small‐angle neutron scattering (SANS) patterns of p‐TFE fibrilles are presented. In the experiment the fibrilles were exposed to a parallel AC‐electric field in which the on and off cycle time had been adjusted to the orientation time of the fibrilles. The time resolution of the experiment was 40 ms. By an analysis of the time evolution of the SANS pattern relaxation times for alignment τ1 and randomisation τ2 were deduced. Both times, being equal within the error bars, are around 150 ns. The scattering curve for the fibrilles could only be fitted with the assumption of considerable polydispersity of their diameter.

Anisotropic small-angle neutron scattering from oxide precipitates in silicon single crystals

Anisotropic small-angle neutron scattering has been observed from Czochralski-grown silicon single crystals annealed for different times at 750 degrees C. This scattering has been attributed to oxide platelet precipitates lying on the (100) planes. The precipitate size, number density and oxygen concentration in the matrix are obtained from the analysis of this scattering. The oxygen diffusion coefficient has been calculated from the increase in the size of the precipitates with anneal time and it is found to be in agreement with the value obtained from mass transport experiments. The loss of solute oxygen from the matrix follows the equation derived by Ham (1958).

Transient SANS studies of rodlike micelles on a time scale of 100 ms

Time-dependent anisotropic small-angle neutron scattering (SANS) patterns of rodlike micelles in a shear gradient F, suddenly changing its value from zero to a constant value, are presented. The time resolution of the experiment was 100 ms. By an analysis of the steady-state pattern a rotational diffusion coefficient D of ,~ 2 s- 1 is deduced. Furthermore it is shown that in a well aligned sample the SANS pattern is sensitive to the rod length distribution in spite of correlation peaks which are caused by repulsive inter-micellar interaction.

A coordinate transform method for one-speed neutron transport in composite slabs

The optical path transformation is applied to reduce the one-speed neutron transport equation for a class of composite subcritical slabs to single-region problems. The class idealises, within the uncertainty of the one-speed model, a variety of practical situations such as U-D2O-C-Zr-Pb or Pu-U-Na-Fe symmetric reactor assemblies; which may possibly contain a symmetrically anisotropic neutron source. A closed form double series solution, which turns out to be quite convenient for design and optimisation purposes, has been obtained, in terms of discontinuous functions for the multi-regional angular flux by application of a double finite Legendre transform. The double transform blends the conventional PN method with the spatial polynomial expansion method. Disadvantage factor evaluations for a U-C lattice cell resulting from a low-order P0P1 approximation of this method are found to be in full agreement with hybrid diffusion-transport estimates.