Chalk River Laboratories

About: Chalk River Laboratories is a based out in . It is known for research contribution in the topics: Neutron diffraction & Neutron scattering. The organization has 2297 authors who have published 2700 publications receiving 73287 citations.

Magnetic properties of the S = 3 2 geometrically frustrated double perovskites La 2 LiRuO 6 and Ba 2 YRuO 6

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.

Development of internal strains in textured Zircaloy-2 during uni-axial deformation

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.

Effect of particle distribution on deformation and damage of two-phase alloys

Abstract: The effect of an inhomogeneous distribution of second phase particles on strength and damage has been studied here using a model system based on rapidly solidified Al–Cu alloys which result in Al–CuAl2 composites, Materials with both a homogeneous and bimodal distribution of the CuAl2 particles have been produced. When tested in compression (i.e. little or no damage) the clustered materials are significantly stronger than homogeneous alloys containing the same overall CuAl2 volume fraction. These results are consistent with a previously published self-consistent model.

Anharmonic Interactions in Alkali Halides. I

Abstract: Calculations of the Griineisen parameters of individual modes of vibration, of the average Griineisen parameter, and of the temperature dependence of the elastic constants, of sodium iodide and potassium bromide have given reasonable agreement with experiment. The model used was a shell model, obtained from experimental measurements of the dispersion curves, extended in a simple way to include the anharmonicity. Calculations have also been made of the spectral functions of some of the normal modes propagating in the [111] direction. These show qualitative agreement with experiment in that the longitudinal optic modes are particularly temperature dependent. The results are used to discuss the validity and usefulness of a quasi-harmonic approximation in which the frequencies are those measured experimentally. The optical constants and the reflectivity of the crystals have also been calculated and are compared with experiment.

Neutron polarization with a polarized 3He spin filter

Abstract: We report the first use of a polarized 3 He spin filter to polarize epithermal neutrons. The 3 He was polarized to 70% by spin exchange with optically pumped Rb vapor and had a cross sectional area of 0.65 cm 2 and a thickness of 3 × 10 20 atoms cm −2 of 3 He. Neutron polarization up to 20% at 0.734 eV was produced in an epithermal neutron beam at the Los Alamos Neutron Scattering Center and measured by observing the change in neutron transmission produced by the 3 He polarization and also the helicity dependent transmission for a parity-nonconserving resonance in 139 La.