Showing papers by "Chalk River Laboratories published in 2009"
TL;DR: In this paper, the authors present recent Canadian advances in nuclear-based production of hydrogen by electrolysis and the thermochemical copper-chlorine (Cu-Cl) cycle, including individual process and reactor developments within the Cu-Cl cycle, thermochemical properties, advanced materials, controls, safety, reliability, economic analysis of electrolysis at off peak hours, and integrating hydrogen plants with Canada's nuclear power plants.
217 citations
TL;DR: Comparison of the experimental and simulated form factors shows that Alm helices are inserted transmembrane at high humidity and high concentrations, in agreement with earlier results.
100 citations
TL;DR: High-resolution x-ray scattering data were analyzed in conjunction with contrast-varied neutron scattering data to show that the manner by which bilayer thickness increases with increasing n in monounsaturated diacylphosphatidylcholines is dependent on the double bond's position.
96 citations
TL;DR: In this paper, the stability properties of pyrochlore and fluorite solid solutions were studied using neutron powder diffraction and electron microscopy to determine the stability fields of the compounds.
90 citations
TL;DR: This PEG-based thermoresponsive surface exhibited good protein adsorption resistance, and extended and collapsed brushes showed the same level of protein repulsion, something that was not expected.
Abstract: The thermoresponsive PEG-based copolymer poly[2-(2-methoxyethoxy)ethyl methacrylate-co-oligo(ethylene glycol) methacrylate) (P(MEO2MA-co-OEGMA)] was grafted onto a silicon wafer, and its chain conformation in aqueous solution was studied by neutron reflectometry. The effects of temperature and salt concentration on the polymer’s conformation were evaluated. With increasing temperature, it was found that the polymer brushes underwent a transition from an extended state to a compressed state, and eventually a collapsed state above the lower critical solution temperature. The presence of salt significantly affected the well-extended brushes but had little effect on compressed and collapsed brushes. This PEG-based thermoresponsive surface exhibited good protein adsorption resistance. Interestingly, extended and collapsed brushes showed the same level of protein repulsion, something that was not expected.
82 citations
TL;DR: In this article, the authors investigated the magnetic and structural phase transitions in a high quality single crystalline sample of the undoped, iron pnictide compound BaFe and characterized the phase transitions via neutron diffraction measurements.
Abstract: We present the results of an investigation of both the magnetic and structural phase transitions in a high quality single crystalline sample of the undoped, iron pnictide compound BaFe$_2$As$_2$. Both phase transitions are characterized via neutron diffraction measurements which reveal simultaneous, continuous magnetic and structural orderings with no evidence of hysteresis, consistent with a single second order phase transition. The onset of long-range antiferromagnetic order can be described by a simple power law dependence $\phi(T)^2\propto(1-\frac{T}{T_N})^{2\beta}$ with $\beta=0.103\pm0.018$; a value near the $\beta=0.125$ expected for a two-dimensional Ising system. Biquadratic coupling between the structural and magnetic order parameters is also inferred along with evidence of three-dimensional critical scattering in this system.
70 citations
TL;DR: In this article, two sites ordered double perovskites were investigated as part of a systematic study of geometric magnetic frustration in this class of oxide materials and the results from dc susceptibility, neutron-diffraction, heat-capacity, and magnetic-susceptibility (Fisher's heat capacity) data were presented.
Abstract: Two $B$-site ordered double perovskites, ${\text{Ba}}_{2}{\text{YRuO}}_{6}$ and ${\text{La}}_{2}{\text{LiRuO}}_{6}$, have been reinvestigated as part of a systematic study of geometric magnetic frustration in this class of oxide materials. Both involve ${\text{Ru}}^{5+}(4{d}^{3},S=3/2)$ as the magnetic ion residing on a face-centered-cubic lattice---one of the canonical frustrated lattices. Results from dc susceptibility, neutron-diffraction, heat-capacity, $^{7}\text{L}\text{i}$ and $^{89}\text{Y}$ NMR studies are presented. ${\text{La}}_{2}{\text{LiRuO}}_{6}$ $(P{2}_{1}/n)$ shows long-range antiferromagnetic order below 24 K from $^{7}\text{L}\text{i}$ NMR, heat-capacity and magnetic-susceptibility (Fisher's heat-capacity) data which is well below the susceptibility maximum at 30 K. Analysis of the entropy loss and the $^{7}\text{L}\text{i}$ data indicates the importance of short-range spin correlations at higher temperatures, consistent with a frustrated system. ${\text{Ba}}_{2}{\text{YRuO}}_{6}$ retains $Fm3m$ symmetry found at room temperature down to 2.8 K with cell constants, $a=8.33559(9)$ and $a=8.3239(5)\text{ }\text{\AA{}}$, respectively. However, $^{89}\text{Y}$ magic-angle-spinning NMR detects a very low $\ensuremath{\sim}1%$ site mixing between Y and Ru ions. Magnetic-susceptibility data are more complex than reported previously with two broad peaks around 37 and 47 K. The transition temperature is 36 K from heat capacity and variable-temperature neutron-diffraction data. The Weiss temperatures and frustration indices, $|\ensuremath{\theta}|/{T}_{\text{N}}$, for ${\text{Ba}}_{2}{\text{YRuO}}_{6}$ are $\ensuremath{-}522$ K and 16 while much smaller values are observed for ${\text{La}}_{2}{\text{LiRuO}}_{6}$, $\ensuremath{-}184$ K and 8, which can be attributed to the monoclinic structural distortion in the latter which weakens the superexchange interactions.
67 citations
TL;DR: In this paper, the extent to which the martensite-start temperature of the weld filler metal can be adjusted to engineer the residual stress distribution in a bainitic-martensitic steel weld was investigated.
Abstract: Residual stress in the vicinity of a weld can have a large influence on structural integrity. Here the extent to which the martensite-start temperature of the weld filler metal can be adjusted to engineer the residual stress distribution in a bainitic-martensitic steel weld was investigated. Three single-pass groove welds were deposited by manual-metal-arc welding on 12 mm thick steel plates using filler metals designed to have different martensite-start temperatures. Their longitudinal, transverse, and normal residual stress distributions were then characterized across the weld cross section by neutron diffraction. It was found that tensile stresses along the welding direction can be reduced or even replaced with compressive stresses if the transformation temperature is lowered sufficiently. The results are interpreted in the context of designing better welding consumables.
56 citations
TL;DR: The crystal and magnetic structures of the brownmillerite material were investigated using powder X-ray and neutron diffraction methods, the latter from 3.8 to 700 K as discussed by the authors.
53 citations
TL;DR: The thickening of bilayers was rationalized in terms of cholesterol's ordering effect on the lipid's acyl chains, which dominates over the other option of rectifying the hydrophobic mismatch, surprisingly even in the case of diC22:1PC and cholesterol.
Abstract: Membrane thickness is thought to play a key role in protein function. Thus understanding the cell's ability to modulate the thickness of its membranes is essential in elucidating the structure/function relationship in biological membranes. We have investigated the influence of cholesterol on the structure of "thin" (diC14:1PC) and "thick" (diC22:1PC) phospholipid bilayers using oriented multibilayers and small angle neutron diffraction. Neutron contrast variation was used to determine the structure factors and the distribution of water across the bilayers. We found that in response to cholesterol, bilayer thickness changed in a similar fashion in both systems. The thickening of bilayers was rationalized in terms of cholesterol's ordering effect on the lipid's acyl chains, which dominates over the other option of rectifying the hydrophobic mismatch, surprisingly even in the case of diC22:1PC and cholesterol.
50 citations
TL;DR: In this paper, the constrained moduli of the Ni superalloy CMSX-4 have been determined using in situ neutron diffraction, and the elastic moduli were found to be E [ 100 ] = 103 GPa in the γ and 134 GPa at room temperature, while at 900°C they are 96 and 90 GPa.
TL;DR: In this paper, high-cycle fatigue tests were conducted on specimens machined from 50 sequentially cast instrument panels made from high-pressure die-cast (HPDC) AM60B magnesium alloy.
15 Feb 2009-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, both in situ tension and compression tests have been carried out on textured Zr-2.5Nb plate material at room temperature and the evolution of interphase and intergranular strain was determined by the relative phase properties, crystal properties and texture distribution.
Abstract: Both in situ tension and compression tests have been carried out on textured Zr–2.5Nb plate material at room temperature. Deformation along all the three principle plate directions has been studied and the evolution of interphase and intergranular strains along the loading and the principle Poisson's directions has been investigated by neutron diffraction. The evolution of interphase and intergranular strain was determined by the relative phase properties, crystal properties and texture distribution. The average phase behaviors are similar during tension and compression, where the β-phase in this material is stronger than the α-phase. The asymmetric yielding of the α-{0 0 0 2} grain family results in a relatively large intergranular strain in the loading direction during compression and different dependence of strength during tension and compression on texture. The combination of the thermal residual stress and the asymmetric CRSS in the 〈 c 〉 axis gives the {0 0 0 2} grain family a higher strength in compression than in tension.
TL;DR: The morphology of these ULVs has mainly been characterized using small angle neutron scattering (SANS), a technique highly suited for the study of hydrogenous materials and show great promise as imaging and therapeutic carriers.
Abstract: Mixtures of long- and short-chain phospholipids can spontaneously form uniform unilamellar vesicles (ULVs) with diameters 50 nm (polydispersities of <0.3) or less. The morphology of these ULVs has mainly been characterized using small angle neutron scattering (SANS), a technique highly suited for the study of hydrogenous materials. Once formed, these ULVs have turned out to be highly stable and show great promise as imaging and therapeutic carriers.
TL;DR: In this paper, a model for the atomic displacements associated with these phonon modes that is based on a combination of structure factors and group theoretical analysis was proposed, which suggests that the scattering is not from tilt modes rotational modes of oxygen octahedra, but from zone-boundary optic modes associated with the displacement of Pb 2+ and O 2� ions.
Abstract: which is similar to the onset temperature of the zone-center diffuse scattering, indicating a competition between ferroelectric and antiferroelectric distortions. We propose a model for the atomic displacements associated with these phonon modes that is based on a combination of structure factors and group theoretical analysis. This analysis suggests that the scattering is not from tilt modes rotational modes of oxygen octahedra, but from zone-boundary optic modes that are associated with the displacement of Pb 2+ and O 2� ions. Whereas similar columns of scattering have been reported in metallic and less commonly molecular systems, they are unusual in insulating materials, particularly in ferroelectrics; therefore, the physical origin of this inelastic feature in PMN is unknown. We speculate that the underlying disorder contributes to this unique anomaly.
TL;DR: Experimental evidence for a long-range protein-protein interaction in purple membrane (PM) is presented and the effective spring constant for the interaction between neighboring protein trimers is determined to be k = 53 N/m.
Abstract: We present experimental evidence for a long-range protein-protein interaction in purple membrane (PM). The interprotein dynamics were quantified by measuring the spectrum of the acoustic phonons in the 2D bacteriorhodopsin (BR) protein lattice using inelastic neutron scattering. Phonon energies of about 1 meV were determined. The data are compared to an analytical model, and the effective spring constant for the interaction between neighboring protein trimers are determined to be k ¼ 53 N=m. Additional, optical-like excitations at 0.45 meV were found and assigned to intraprotein dynamics between neighboring BR monomers.
TL;DR: In this paper, the solid solubility of Nb in α-Zr is an important parameter that has a potential impact on the corrosion properties of Zr-Nb alloys at reactor operating temperatures, i.e. below the monotectoid temperature.
TL;DR: The results from the third round of the powder diffractometry round robin were discussed in this article, and it was concluded that solving a structure from powder data remains a challenge, at least one order of magnitude more difficult than solving a problem with similar complexity from single-crystal data.
Abstract: The results from a third structure determination by powder diffractometry (SDPD) round robin are discussed. From the 175 potential participants having downloaded the powder data, nine sent a total of 12 solutions (8 and 4 for samples 1 and 2, respectively, a tetrahydrated calcium tartrate and a lanthanum tungstate). Participants used seven different computer programs for structure solution (ESPOIR, EXPO, FOX, PSSP, SHELXS, SUPERFLIP, and TOPAS), applying Patterson, direct methods, direct space methods, and charge flipping approach. It is concluded that solving a structure from powder data remains a challenge, at least one order of magnitude more difficult than solving a problem with similar complexity from single-crystal data. Nevertheless, a few more steps in the direction of increasing the SDPD rate of success were accomplished since the two previous round robins: this time, not only the computer program developers were successful but also some users. No result was obtained from crystal structure prediction experts.
11 Sep 2009-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: Development and performance of image reconstruction algorithms for the TMI are discussed, as well as a hybrid imaging algorithm wherein CA and CI information is fused to generate a higher fidelity reconstruction.
Abstract: The trimodal imager (TMI) images gamma-ray sources from a mobile platform using both coded aperture (CA) and Compton imaging (CI) modalities. In this paper we will discuss development and performance of image reconstruction algorithms for the TMI. In order to develop algorithms in parallel with detector hardware we are using a GEANT4 [J. Allison, K. Amako, J. Apostolakis, H. Araujo, P.A. Dubois, M. Asai, G. Barrand, R. Capra, S. Chauvie, R. Chytracek, G. Cirrone, G. Cooperman, G. Cosmo, G. Cuttone, G. Daquino, et al., IEEE Trans. Nucl. Sci. NS-53 (1) (2006) 270] based simulation package to produce realistic data sets for code development. The simulation code incorporates detailed detector modeling, contributions from natural background radiation, and validation of simulation results against measured data. Maximum likelihood algorithms for both imaging methods are discussed, as well as a hybrid imaging algorithm wherein CA and CI information is fused to generate a higher fidelity reconstruction.
TL;DR: An asymmetric distribution of lipid densities across certain bilayers is detected from small-angle X-ray scattering experiments, potentially of relevance to biological membranes made up of different types of lipids and whose local curvature may be dictated by lipid composition.
Abstract: We have studied the effect of cholesterol on curved bilayers using 600 A unilamellar vesicles made of monounsaturated lipids. From small-angle X-ray scattering experiments we were able to detect an asymmetric distribution of lipid densities across certain bilayers. We discovered that, with the exception of diC24:1PC bilayers, monounsaturated diacylphosphatidylcholine lipids (diCn:1PC, n = 14, 16, 18, 20, and 22) form symmetric bilayers. However, the addition of 44 mol % cholesterol resulted in some of these bilayers (i.e., n = 14, 16, and 18) to become asymmetric, where cholesterol was found to distribute unequally between the bilayer’s two leaflets. This finding is potentially of relevance to biological membranes made up of different types of lipids and whose local curvature may be dictated by lipid composition.
TL;DR: In this paper, the evolution of the crystal structure of Mg 6 Pd alloy, synthesized by ball milling, was investigated by simultaneous Rietveld refinement of neutron and X-ray powder diffraction.
TL;DR: Mechanistic insights into the oxidative formation of ScVO(4) via the defect structure are presented and the fully oxidized zircon structure ScVO (4) is compared with the fully dehydrated zir Con structure using powder X-ray diffracted, neutron diffraction, and bulk magnetic susceptibility data.
Abstract: We report the formation pathway of ScVO(4) zircon from ScVO(3) bixbyite with emphasis on the synthesis and stability of the novel intermediate defect zircon phase ScVO(4-x) (0.0 < x
TL;DR: The optimization of instruments and preparation techniques, as well as the new possibilities offered by protein deuteration, have opened up new avenues for the study of lipid/protein interactions that were not previously possible.
Abstract: Membranes that surround cells and separate their contents from the external environment are ubiquitous in biological systems. These membranes are organized assemblies consisting mainly of lipids and proteins, and are highly selective permeability barriers which control the flow of information between cells and their environment. It is accepted that the lipid bilayer is the underlying structure of most, if not all, biomembranes. As such, over the years scientists have exerted much effort in studying lipid bilayers and their biological relevance in hopes of understanding the functional mechanisms taking place at membrane interfaces. Neutron and X-ray scattering techniques are powerful tools for the characterization of the structure and dynamics of biomimetic systems as they provide unique access to microscopic structure and dynamics at length scales ranging from microns to intermolecular and/or atomic distances. The optimization of instruments and preparation techniques, as well as the new possibilities offered by protein deuteration, have opened up new avenues for the study of lipid/protein interactions that were not previously possible. One can now look at the insertion of biomolecules into membranes and accurately determine the structure as well as the dynamics of the interaction. To illustrate the usefulness of diffraction and scattering techniques with regard to biologically relevant systems, we review some of the leading edge studies that have taken place over the last couple of years in which these scattering techniques have played a central role.
TL;DR: In this paper, a complete magnetic phase diagram of the Tb and Er subsystems is presented to find that two straight lines of the ordering of the two subsystems are persistently seen, which intersect at a tetracritical point.
Abstract: We have studied ${\text{Tb}}_{x}{\text{Er}}_{1\ensuremath{-}x}{\text{Ni}}_{5}$ ($x=0$, 0.1, 0.2, 0.3, 0.4, 0.6, 0.8, 0.925, and 1.0) compounds by using several experimental techniques such as ac-susceptibility, heat-capacity, and neutron-diffraction measurements. All the compounds are found to crystallize in the ${\text{CaCu}}_{5}$-type structure with space group $P6/mmm$. The $a$ axis shows a linear increase with Tb concentration, whereas the $c$ axis remains almost unchanged over the whole doping range. Our neutron-diffraction studies revealed that samples for $0\ensuremath{\le}x\ensuremath{\le}0.8$ have a commensurate magnetic structure with $\mathbf{k}=0$, whereas the two samples on the Tb-rich phase ($x=0.925$ and 1.0) have an incommensurate structure. Of particular interest is that individual Tb and Er moments keep their mutually orthogonal arrangement seen at the end-member compositions over the whole doping range, due to very strong magnetic anisotropy of single-ion nature. We have established a complete magnetic $x\text{\ensuremath{-}}T$ phase diagram of ${\text{Tb}}_{x}{\text{Er}}_{1\ensuremath{-}x}{\text{Ni}}_{5}$ to find that two straight lines of the ordering of the Tb and Er subsystems are persistently seen, which intersect at a tetracritical point.
TL;DR: In this paper, the transport and thermodynamic properties of stoichiometric single crystals of the hexagonal iron-pnictide FeCrAs were investigated and the in-plane resistivity showed an unusual "non-metallic" dependence on temperature T, rising continuously with decreasing T from ~800 K to below 100 mK.
Abstract: We report transport and thermodynamic properties of stoichiometric single crystals of the hexagonal iron-pnictide FeCrAs. The in-plane resistivity shows an unusual "non-metallic" dependence on temperature T, rising continuously with decreasing T from ~800 K to below 100 mK. The c-axis resistivity is similar, except for a sharp drop upon entry into an antiferromagnetic state at TN~125 K. Below 10 K the resistivity follows a non–Fermi-liquid power law, ρ(T)=ρ0-ATx with x<1, while the specific heat shows Fermi-liquid behaviour with a large Sommerfeld coefficient, γ~30 mJ/mol K2. The high-temperature properties are reminiscent of those of the parent compounds of the new layered iron-pnictide superconductors, however the T→0 K properties suggest a new class of non-Fermi liquid.
TL;DR: A spherical phantom and space bubble detectors were used on board the International Space Station to characterise the neutron radiation field in order to establish the relationship between the neutron dose measured externally to the body and the dose received internally.
Abstract: As part of the Matroshka-R experiments, a spherical phantom and space bubble detectors (SBDs) were used on board the International Space Station to characterise the neutron radiation field. Seven experimental sessions with SBDs were carried out during expeditions ISS-13, ISS-14 and ISS-15. The detectors were positioned at various places throughout the Space Station, in order to determine dose variations with location and on/in the phantom in order to establish the relationship between the neutron dose measured externally to the body and the dose received internally. Experimental data on/in the phantom and at different locations are presented.
TL;DR: In this article, the authors measured the rate of delayed hydride cracking in Zircaloy-4 fuel cladding using the Pin-Loading Tension technique and found that the fracture surface consisted of flat fracture with no striations.
TL;DR: In this paper, a more advanced Bayesian probabilistic approach is presented to estimate the degradation free lifetime distribution of Alloy 800 tubing, which is used to quantify the probability of degradation during the service life and to evaluate the impact of potential occurrences of degradation on reliability of SG tubing.
TL;DR: Evidence is presented that the itinerant excitations, like those in chromium, are due to Fermi surface nesting of hole and electron pockets; hence the hidden order phase probably originates from a Fermani surface instability.
Abstract: By means of neutron scattering we show that the high temperature precursor to the hidden order state of the heavy fermion superconductor URu2Si2 exhibits heavily damped incommensurate paramagnons whose strong energy dispersion is very similar to that of the long-lived longitudinal f spin excitations that appear below T0. This suggests that there is a strongly hybridized character to the itinerant excitations observed previously above the hidden order transition. Here we present evidence that the itinerant excitations, like those in chromium, are due to Fermi surface nesting of hole and electron pockets; hence the hidden order phase probably originates from a Fermi surface instability. We identify wavevectors that span nested regions of a f–d hybridized band calculation and that match the neutron spin crossover from incommensurate to commensurate on approach to the hidden order phase.
21 Feb 2009-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this article, the structural changes of thin Pd-capped Mg 0.7 Al 0.4 alloy films after hydrogen absorption and during hydrogen desorption were studied.
Abstract: We used neutron reflectometry (NR) to study the structural changes of thin Pd-capped Mg 0.7 Al 0.3 and Mg 0.6 Al 0.4 alloy films after hydrogen absorption and during hydrogen desorption. NR enabled us to determine the hydrogen content and hydrogen distribution in these thin MgAl alloy films along with the structural changes associated with the desorption process. The thin films expand by about 20% during the hydrogen absorption and the hydrogen is stored only in the MgAl layer with no hydrogen content in the Pd layer. The Mg 0.7 Al 0.3 films are fully desorbed at 448 K, whereas for the Mg 0.6 Al 0.4 films a temperature of 473 K is needed to fully desorb the hydrogen. Our NR measurements show that the higher annealing temperature needed to desorb the hydrogen from the Mg 0.6 Al 0.4 films led to an interdiffusion of the Pd layer into the MgAl layer. This Pd interdiffusion was also observed in a Mg 0.7 Al 0.3 film after a 9 h annealing at 473 K. So, the Pd interdiffusion into a MgAl film that has been charged with hydrogen is a common feature of the Pd/Mg 0.7 Al 0.3 and Pd/Mg 0.6 Al 0.4 alloy system. In contrast, for the as-prepared hydrogen-free Pd/Mg 0.7 Al 0.3 film the Pd layer stays intact and only a small interdiffusion zone occurs at the Pd/MgAl interface.