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.

Temperature Dependence of g Values for Aqueous Solutions Irradiated with 23 MeV 2H+ and 157 MeV 7Li3+ Ion Beams

Abstract: The temperature (T) dependence of the g values for the radiolysis of water with 23 MeV 2H+ and 157 MeV 7Li3+ ion beams is reported. The results indicate that as the linear energy transfer characteristics of the radiation increase, (i) d(g(eaq-))/dT decreases, (ii) d(g(H2))/dT increases, (iii) d(g(OH))/dT remains constant, and (iv) d(g(H2O2))/dT is approximately constant. These observations are qualitatively consistent with the kinetic−diffusion model of the spur/track. The g values for 2 MeV fission neutrons have been estimated from these ion beam results for the temperature range 25−300 °C.

Bias in genetic variance estimates due to spatial autocorrelation.

Abstract: A central problem in the analysis of genetic field trials is the dichotomy of “genetic” and “environmental” effects because one cannot be defined without the other. Results from 768,000 simulated family trials in complete randomized block designs demonstrated a serious upward bias in estimates of family variance components from multi-unit plot designs when the phenotypic observations were compatible with a first-order autoregressive (AR1) process. The inflation of family variances and, thus, additive genetic variance and narrow sense individual heritabilities progressed exponentially with an increase in the nearest neighbor correlation (ϱ) in the AR1 process. Significant differences in inflation rates persisted among various plot configurations. At ϱ = 0.2 the inflation of family variances reached 48–73%. Inflation rates were independent of the level of heritability. Modified Papadakis nearest neighbor (NN) adjustment procedures were tested for their ability to remove the bias in family variances. A NN-adjustment based on Mead's coefficient of interplant interaction and one derived from Bartlett's simultaneous autoregressive scheme removed up to 97% of the bias introduced by the phenotypic correlations. NN-adjusted estimates had slightly (5–8%) higher relative errors than did unadjusted estimates.

The Anomalous Skin Effect in Single Crystal Relaxor Ferroelectric PZN-xPT and PMN-xPT

Abstract: X-ray and neutron scattering studies of the lead-based family of perovskite relaxors Pb(Zn1/3Nb2/3)O3–xPbTiO3 (PZN-xPT) and Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PMN-xPT) have documented a highly unusual situation in which the near-surface region of a single crystal can exhibit a structure that is different from that of the bulk when cooled to low temperatures. The near-surface region, or “skin” can also display critical behavior that is absent in the crystal interior, as well as a significantly different lattice spacing. By varying the incident photon energy, and thus the effective penetration depth, X-ray measurements indicate a skin thickness of order 10–50 µm for PZN-xPT samples with 0 ≤ x ≤ 8%. Neutron residual stress measurements on a large PMN single crystal reveal a uniform lattice spacing within the bulk, but an increased strain near the surface. The presence of this skin effect has led to incorrect phase diagrams for both the PZN-xPT and PMN-xPT systems and erroneous characterizations of the nature of the r...

Liquidlike correlations in single-crystalline Y 2 Mo 2 O 7 : An unconventional spin glass

Abstract: The spin-glass behavior of Y${}_{2}$Mo${}_{2}$O${}_{7}$ has remained a puzzle for nearly three decades Free of bulk disorder within the resolution of powder diffraction methods, it is thought that this material is a rare realization of a spin glass resulting from weak disorder such as bond disorder or local lattice distortions Here we report on the single-crystal growth of Y${}_{2}$Mo${}_{2}$O${}_{7}$ Using neutron scattering, we present isotropic magnetic diffuse scattering occurring below the spin-glass transition Our attempts to model the diffuse scattering using a computationally exhaustive search of a class of simple spin Hamiltonians show no agreement with the experimentally observed energy-integrated (diffuse) neutron scattering This suggests that spin degrees of freedom are insufficient to describe this system Indeed, a ${T}^{2}$ temperature dependence in the heat capacity and density functional theory calculations hint at the presence of a significant frozen degeneracy in both the spin and orbital degrees of freedom resulting from spin-orbital coupling (Kugel-Khomskii type) and random fluctuations in the Mo environment at the local level