Showing papers by "Chalk River Laboratories published in 2008"
TL;DR: An improved method for determining lipid areas helps to reconcile long-standing differences in the values of lipid areas obtained from stand-alone x-ray and neutron scattering experiments and poses new challenges for molecular dynamics simulations.
538 citations
TL;DR: X-ray diffuse scattering was measured from oriented stacks and unilamellar vesicles of dioleoylphosphatidylcholine lipid bilayers to obtain the temperature dependence of the structure and of the material properties, and interactions between bilayers were found to be nearly independent of temperature.
335 citations
TL;DR: It is shown that the addition of 40 mol % cholesterol results in a nearly identical increase in the thickness of the two different bilayers, and that the diC14:1PC bilayer is significantly more permeable to water.
147 citations
TL;DR: In this paper, the synthesis and basic characterization of LaFeAsO was reported and basic properties of the parent phase were analyzed for several values of $x, and it was shown that Co is an effective dopant to induce superconductivity.
Abstract: Here we report the synthesis and basic characterization of ${\text{LaFe}}_{1\ensuremath{-}x}{\text{Co}}_{x}\text{AsO}$ for several values of $x$. The parent phase LaFeAsO orders antiferromagnetically $({T}_{N}\ensuremath{\approx}145\text{ }\text{K})$. Replacing Fe with Co is expected both to electron dope and introduce disorder in the FeAs layer. For $x=0.05$ antiferromagnetic order is destroyed and superconductivity is observed at ${T}_{c}^{\text{onset}}=11.2\text{ }\text{K}$. For $x=0.11$ superconductivity is observed at ${T}_{c}^{\text{onset}}=14.3\text{ }\text{K}$ and for $x=0.15$ it is observed at ${T}_{c}^{\text{onset}}=6.0\text{ }\text{K}$. For $x=1$, and the material appears to be ferromagnetic as judged by magnetization measurements. We conclude that Co is an effective dopant to induce superconductivity. Somewhat surprisingly, the system appears to tolerate considerable disorder in the FeAs planes.
126 citations
TL;DR: It is shown that the magnetic interactions in LuFe(2)O(4) are three-dimensional in character, and the magnetic structure is refined as a ferrimagnetic spin configuration below the 240 K transition.
Abstract: We present single crystal neutron diffraction measurements on multiferroic LuFe{sub 2}O{sub 4}. Magnetic reflections are observed below transitions at 240 and 175 K indicating that the magnetic interactions in LuFe{sub 2}O{sub 4} are three-dimensional in character. The magnetic structure is refined as a ferrimagnetic spin configuration below the 240 K transition. Below 175 K a significant broadening of the magnetic peaks is observed along with the buildup of a diffuse component to the magnetic scattering.
107 citations
TL;DR: Small-angle neutron scattering (SANS) curves of unilamellar dipalmitoylphosphatidylcholine (DPPC) vesicles in 1-60mM CaCl2 were analyzed using a strip-function model of the phospholipid bilayer to determine the fraction of Ca2+ ions bound in the DPPC polar head group region.
87 citations
TL;DR: Comparing the whole-organism activity concentrations predicted by eight models participating within the IAEA Environmental Modelling for Radiation Safety programme for a range of radionuclides to terrestrial and freshwater organisms demonstrates that the largest contribution to variability between model predictions is the parameterisation of their transfer components.
Abstract: A number of models have recently been, or are currently being, developed to enable the assessment of radiation doses from ionising radiation to non-human species. A key component of these models is the ability to predict whole-organism activity concentrations in a wide range of wildlife. In this paper, we compare the whole-organism activity concentrations predicted by eight models participating within the IAEA Environmental Modelling for Radiation Safety programme for a range of radionuclides to terrestrial and freshwater organisms. In many instances, there was considerable variation, ranging over orders of magnitude, between the predictions of the different models. Reasons for this variability (including methodology, data source and data availability) are identified and discussed. The active participation of groups responsible for the development of key models within this exercise is a useful step forward in providing the transparency in methodology and data provenance required for models which are either currently being used for regulatory purposes or which may be used in the future. The work reported in this paper, and supported by other findings, demonstrates that the largest contribution to variability between model predictions is the parameterisation of their transfer components. There is a clear need to focus efforts and provide authoritative compilations of those data which are available.
78 citations
15 Aug 2008-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the authors used neutron diffraction to track the development of internal strains in three dimensions in samples cut from a rolled Zircaloy-2 slab and the samples were subjected to room temperature compression or tension in situ in the neutron diffractometer with loading along each of the three principal directions of the slab.
Abstract: Internal strains can greatly affect the mechanical performance of Zircaloy-2 and the study of their development provides insight into the operating deformation mechanisms. In this study, neutron diffraction was used to track the development of internal strains in three dimensions in samples cut from a rolled Zircaloy-2 slab. The samples were subjected to room temperature compression or tension in situ in the neutron diffractometer with loading along each of the three principal directions of the slab. The recorded intensity changes for the different crystallographic planes also provided information on the grain reorientations during deformation. Strong evidence was found for tensile twinning in tensile tests in the plate normal direction and in compression tests in the transverse and rolling directions. This provides an extensive data set with which to develop and test models for plastic deformation and texture development in polycrystalline Zircaloy-2.
66 citations
TL;DR: The Rietveld refinement of the structure of monohydrocalcite showed significant changes in the orientation of water molecules and a major change in orientation of a carbonate group with respect to the currently accepted structure.
Abstract: Samples of beachrock from Lakes Butler and Fellmongery, near Robe, South Australia, were examined by neutron and X-ray powder diffraction. Considerable variation in phase composition was observed, although all samples possessed monohydrocalcite, calcite, aragonite, and magnesiancalcite. The Rietveld refinement of the structure of monohydrocalcite showed significant changes in the orientation of water molecules and a major change in the orientation of a carbonate group with respect to the currently accepted structure. The current refinement shows that the hydrogen-bonding structure consists of three distinct networks, with each of the three carbonate groups being bonded to a single water molecule via one linear and one bifurcated hydrogen bond.
63 citations
15 Mar 2008
TL;DR: Small angle neutron scattering (SANS) was employed to investigate the size and morphology of rhamnolipid aggregates and micelle structure in the presence of heavy metals Cu, Zn, and Ni, and the results indicate the importance of the pH of the system in the morphology of the aggregates in the rhamNolipids solution.
Abstract: Pollution of soils and sediments by heavy metals is an environmental concern. Among the remedial techniques, soil washing is proving to be reliable. Biosurfactant rhamnolipid has shown its potential as a washing agent. In this research, small angle neutron scattering (SANS) was employed to investigate the size and morphology of rhamnolipid aggregates and micelle structure in the presence of heavy metals Cu, Zn, and Ni. The results indicate the importance of the pH of the system in the morphology of the aggregates in the rhamnolipid solution. Creation of a basic condition by addition of 1% NaOH led to the formation of large aggregates (>2000 A) + micelles with R G ∼ 17 A while in the acidic environment with 1% NaCl, large polydisperse vesicles with a radius about 550–600 A were formed. The size of the aggregates in both acidic and basic condition is fine enough to ease the flow of the rhamnolipid solution through the porous media with the pore sizes as small as 200 nm.
61 citations
TL;DR: In this article, a probabilistic model of wall thinning due to flow-accelerated corrosion (FAC) is presented and calibrated with a set of feeder wall thickness measurements obtained from a CANDU plant.
TL;DR: In this article, a new structural model was proposed to fit the SANS data in the q range covering 0.005-0.4 A -1, which combines a form factor of flexible wormlike aggregates with an ellipsoidal cross section and a structure factor of hard-disk interaction accounting for the low-q scattering as well as the Teubner-Strey model for the high-q "ionomer peak".
Abstract: Highly fluorinated comb-shaped ionomer membranes made by solution casting have shown high proton conductivity coupled with low dimensional swelling upon hydration, which demonstrates their potential as materials for proton exchange membranes (PEM) for fuel cells (FC). Small-angle neutron scattering (SANS) and neutron diffraction studies on the copolymers have been conducted to resolve the morphological structures. Two peaks were found in the SANS curves: the low-q peak is assigned to the strong interaction among the self-aggregating hydrophilic and hydrophobic domains, whereas the high-q peak is attributed to the "ionomer peak". We propose a new structural model to fit the SANS data in the q range covering 0.005-0.4 A -1 . This model combines a form factor of flexible wormlike aggregates with an ellipsoidal cross section and a structure factor of hard-disk interaction accounting for the low-q scattering as well as the Teubner-Strey model for the high-q "ionomer peak". Water uptakes can be derived from the best-fitting results of the current model and are consistent with the measured values. The neutron diffraction data indicate that there is little long-range orientation, if any, of the hydrophilic or hydrophobic domains.
TL;DR: It was found that 33 mol% of both sterols increased the thickness of diCn:1PC bilayers with n=18-22 similarly, and the structural difference in the side chain between cholesterol and beta-sitosterol plays a negligible role in influencing the structural parameters of bilayers studied.
TL;DR: In this article, the authors present a work package (WP) of the SARNET Source Term topic, which includes reactor-scenariostudies that can be used to define the conditions of new experiments.
TL;DR: In this paper, a flat-plate sample holder with silicon single-crystal windows was used to place a thin layer of material in a neutron beam and obtain Rietveld refinement quality diffraction data in a modest time.
Abstract: The extreme absorption cross section of natural gadolinium has so far precluded routine neutron diffraction work on its alloys and compounds. However, it is shown here that an easily constructed flat-plate sample holder with silicon single-crystal windows can be used to place a thin layer of material in a neutron beam and obtain Rietveld refinement quality diffraction data in a modest time. The flat-plate geometry uses a large area to compensate for the necessarily thin sample. Demonstration data are presented on two intermetallic compounds, Sm3Ag4Sn4 and Gd3Ag4Sn4, and it is shown that both structural and magnetic information can be derived from the diffraction patterns. By working at a wavelength of 2.37 A, it is possible to observe the low-Q diffraction peaks associated with magnetic ordering. This simple methodology should now enable routine measurements on even the most highly absorbing materials.
TL;DR: In this paper, the authors determined the magnetic structure and fluctuations in the superconducting phase of the YBCO superconductor and showed that the long-range ordered collinear spins of the insulating antiferromagnet are replaced by a commensurate central mode arising from slow, isotropically polarized, short-range spin correlations extending over four planar unit cells.
Abstract: From neutron inelastic and elastic scattering we have determined the magnetic structure and fluctuations in the $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6.35}$ (YBCO) superconductor $({T}_{c}=18\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ near the boundary of the superconducting phase. The long-range ordered collinear spins of the insulating antiferromagnet are replaced by a commensurate central mode arising from slow, isotropically polarized, short-range spin correlations extending over four planar unit cells. The inelastic spectrum up to $30\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ is also broad in wave vector and commensurate. In contrast to the resonance peak of higher-${T}_{c}$ superconductors, the spins exhibit a single overdamped spectrum whose rate of relaxation $\ensuremath{\Gamma}$ decreases on cooling and saturates at $2\ensuremath{\Gamma}=5\ifmmode\pm\else\textpm\fi{}1\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ below $\ensuremath{\sim}50\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. As the relaxation rate saturates, the quasistatic spin correlations grow and become resolution limited in energy. The spin susceptibility above $\ensuremath{\sim}50\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ follows the same $\ensuremath{\omega}∕T$ scaling relation found for the monolayer ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}\mathrm{Cu}{\mathrm{O}}_{4}$ system, indicating that the dominant energy scale is set by the temperature. Below $50\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ the scale length is geometric and not linked by velocity to dynamic widths. Despite the large differences from an antiferromagnet, we show that integrated intensity conserves the total moment sum rule, and that on cooling the spectral weight transfers from the inelastic spin relaxation to the elastic central peak. There is no observable suppression of the spin fluctuations or central mode upon the onset of superconductivity. The spins respond not to coherent charge pairs but to hole doping, allowing coexistence of glassy short-range spin order with superconductivity. Since the physics of the weakly superconducting system ${\mathrm{YBCO}}_{6.35}$ must connect continuously with that in more strongly superconducting ${\mathrm{YBCO}}_{6.5}$, we find that neither incommensurate stripe-like spin modulations nor a well-defined neutron spin resonance are essential for the onset with doping of pairing in a high-temperature cuprate superconductor.
TL;DR: Small-angle neutron scattering (SANS) is used to examine the influence of membrane curvature on the formation of membrane domains and it is found that, although vesicle size and polydispersity are not significantly altered by the formationof membrane domains, the area fraction occupied by domains depends on the overall vesicles size.
Abstract: An interdependence between local curvature and domain formation has been observed in both cell and model membranes. An implication of this observation is that domain formation in model membranes may be modulated by membrane curvature. In this paper, small-angle neutron scattering (SANS) is used to examine the influence of membrane curvature (i.e., vesicle size) on the formation of membrane domains. It is found that, although vesicle size and polydispersity are not significantly altered by the formation of membrane domains, the area fraction occupied by domains depends on the overall vesicle size. In particular, increasing membrane curvature (i.e., decreasing vesicle size) results in increased area fractions of membrane domains.
TL;DR: In this paper, the micro-mechanisms of fatigue crack nucleation and subsequent propagation in a commercial high pressure die-cast (HPDC) AM60B alloy were studied and it was found that the majority of fatigue cracks were initiated due to the compressive residual stresses at the locations of large casting pores underneath the machined surfaces.
TL;DR: In this article, the authors studied the spin ordering and low energy spin dynamics of cuprate superconductors with a single crystal underdoped with a high temperature of 29 K and a low temperature of 0.095.
Abstract: By using neutron scattering techniques, we have studied the incommensurate spin ordering as well as the low energy spin dynamics in single crystal underdoped ${\text{La}}_{2\ensuremath{-}x}{\text{Ba}}_{x}{\text{CuO}}_{4}$ with $x\ensuremath{\sim}0.095$ and 0.08, which are high temperature superconductors with ${T}_{C}\ensuremath{\sim}27$ and 29 K, respectively. Static two dimensional incommensurate magnetic order appears below ${T}_{N}=39.5\ifmmode\pm\else\textpm\fi{}0.3\text{ }\text{K}$ in ${\text{La}}_{2\ensuremath{-}x}{\text{Ba}}_{x}{\text{CuO}}_{4}$ $(x=0.095)$ and a similar temperature for $x=0.08$ within the low temperature tetragonal phase. The spin order is unaffected by either the onset of superconductivity or the application of magnetic fields of up to 7 T applied along the $c$ axis in the $x=0.095$ sample. Such a magnetic field independent behavior is in marked contrast to the field induced enhancement of the staggered magnetization observed in the related ${\text{La}}_{2\ensuremath{-}x}{\text{Sr}}_{x}{\text{CuO}}_{4}$ system, which indicates that this phenomenon is not a universal property of cuprate superconductors. Surprisingly, we find that the incommensurability $\ensuremath{\delta}$ is only weakly dependent on doping relative to ${\text{La}}_{2\ensuremath{-}x}{\text{Sr}}_{x}{\text{CuO}}_{4}$. Dispersive excitations in ${\text{La}}_{2\ensuremath{-}x}{\text{Ba}}_{x}{\text{CuO}}_{4}$ $(x=0.095)$ at the same incommensurate wave vector persist up to at least 60 K. The dynamical spin susceptibility of the low energy spin excitations saturates below ${T}_{C}$ in a similar manner to that seen in the superconducting state of ${\text{La}}_{2}{\text{CuO}}_{4+y}$.
TL;DR: In this article, the lattice strains in AL6XN stainless steel specimens subjected to in situ biaxial stress states have been measured by neutron diffraction and the results revealed the role of the stress state in the differences in average lattice strain between various crystallographic fibers.
TL;DR: Spontaneously forming small unilamellar vesicles (SULVs) are easy to prepare and show great promise for use in delivering therapeutic payloads and are capable of entrapping, and subsequently releasing, hydrophilic molecules in a controlled fashion over two different temperature ranges.
TL;DR: In this paper, the morphology, crystal structure and hydrogen absorption-desorption kinetics of ball-milled Mg-TiV 1.1 Mn 0.9 composites were investigated.
TL;DR: Li3Mg2RuO6 was synthesized in polycrystalline form by a solid-state method and the crystal structure was refined from powder neutron diffraction data in the orthorhombic Fddd space group as discussed by the authors.
Abstract: The new ruthenate, Li3Mg2RuO6, was synthesized in polycrystalline form by a solid-state method. The crystal structure of Li3Mg2RuO6 was refined from powder neutron diffraction data in the orthorhombic Fddd space group in an ordered NaCl structure type with a = 5.8759 (2) A, b = 8.4206 (1) A, and c = 17.6455 (5) A. The Ru5+ (S = 3/2) sublattice shows a unique topology, which consists of chains of edge-sharing triangles interconnected by corner sharing and thus there exists the potential for geometric magnetic frustration. This is the first time that magnetic behavior of a material with such sublattice has been investigated. The isostructural, nonmagnetic Li3Mg2NbO6 was prepared as the lattice match for the heat capacity analysis. The temperature-dependent magnetic susceptibility, heat capacity, and neutron diffraction data reveal that the system undergoes a long-range AFM ordering below 17 K but also provide evidence for short-range spin correlations well above TN. The magnetic frustration index, f ≈ 109/1...
TL;DR: In this paper, the microstructure of the non-modulated martensite in a Ni-Mn-Ga alloy has been characterized in detail by conventional transmission electron microscopy.
TL;DR: In this paper, the authors used hierarchical clustering and Kohonen's self-organising neural network map to process the data from acoustic emission and to develop a relationship in terms of the deformation modes.
Abstract: The mechanical behaviour of extruded AZ31B magnesium alloy with two different textures was studied. Acoustic emission (AE) was used to record the signals to detect the various deformation processes occurring during the mechanical test. Hierarchical clustering and Kohonen's self-organising neural network map were used to process the data from AE and to develop a relationship in terms of the deformation modes. The signals produced from the two different deformation mechanisms (i.e. slip and twinning) were successfully identified. The developed method could be efficiently used for the classification of AE data.
TL;DR: Tritiated water (HTO) and organically bound tritium (OBT) concentrations in the non-human biota inhabiting Duke Swamp were measured during the 2005 growing season.
Abstract: Tritiated water (HTO) and organically bound tritium (OBT) concentrations in the non-human biota inhabiting Duke Swamp were measured during the 2005 growing season Samples of surface water, soil, p
TL;DR: The major corrosion degradation operating experience of various out-of-core materials in-service in currently operating CANDU reactors is summarized and the materials and R&D needs beyond the immediate future are discussed.
TL;DR: This review will highlight some of the major breakthroughs in model membrane research that have taken place as a result of substrate supported samples.
Abstract: Highly aligned, substrate supported membranes have made it possible for physical techniques to extract unambiguous structural information previously not accessible from commonly available membrane dispersions, or so-called powder samples. This review will highlight some of the major breakthroughs in model membrane research that have taken place as a result of substrate supported samples.
TL;DR: The performance of zirconium alloys in BWR, PWR, and PHWR nuclear reactors is dependent on the microstructure as discussed by the authors, and the characterization of the micro-structure is an integral part of any study conducted to develop models for in-reactor performance.
Abstract: The performance of zirconium alloys in BWR, PWR, and PHWR nuclear reactors is dependent on the microstructure. Accordingly, the characterization of the microstructure is an integral part of any study conducted to develop models for in-reactor performance. Although the as-fabricated microstructure (texture, grain size, dislocation density, and phase or precipitate distribution) determines the basic physical properties of a given component, there are changes that occur during irradiation that can have a significant effect on these properties. Microstructures that illustrate specific features of the radiation damage that forms in Zr alloys will be illustrated and discussed in terms of the dose, dose rate, and impurity factors that are applicable.
TL;DR: In this work, three ICP-MS methods were compared with one TIMS method and two alpha spectrometry methods for the measurement of 239Pu and 240Pu in human urine samples spiked at different concentration levels.
Abstract: Following a radiological or nuclear emergency, medical intervention requires rapid assessment of the exposure of people usually through determination of internal dose. For the plutonium urine bioassay, besides thermal ionization mass spectrometry (TIMS) and alpha spectrometry methods, inductively coupled plasma mass spectrometry (ICP-MS) methods have been recently developed, which can provide much higher sample throughput. In this work, three ICP-MS methods were compared with one TIMS method and two alpha spectrometry methods for the measurement of 239Pu and 240Pu in human urine samples spiked at different concentration levels. The sample throughputs for all three ICP-MS methods are similar: each instrument measures about 80 samples in the first 24 hours and 200 samples in the first 48 hours following the emergency event, if the samples arrive at the laboratory 8 hours after the event occurs. Method accuracy and precision were determined using ANSI N13.30. Method detection limits and minimum detectable amounts (MDA) were determined to evaluate method sensitivities. The sensitivities of the three ICP-MS methods were also compared with the derived urine action level (24 h urine, 500 mSv committed effective dose equivalent, inhalation exposure, maximum dose conversion factor) to evaluate their applicability to exposure situations.