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.

Accelerated Irradiation Growth of Zirconium Alloys

Abstract: Sponge zirconium and Zr-2.5 wt% Nb, Zircaloy, or Excel alloys all exhibit accelerated irradiation growth compared with high-purity crystal-bar zirconium for irradiation temperatures between 550 to 710 K and fluences between 0.1 to 10 x 10 2 5 n . m - 2 (E > 1 MeV). There is generally an incubation period or fluence before the onset of accelerated or "breakaway" growth, which is dependent on the particular material being irradiated, its metallurgical condition before irradiation, and the irradiation temperature. Transmission electron microscopy has shown that there is a correlation between accelerated irradiation growth and the appearance of c-component vacancy loops on basal planes. Measurements in some specimens indicate that a significant fraction of the strain can be directly attributed to the loops themselves. There is considerable evidence to show that their formation is dependent both on the specimen purity and on the irradiation temperature. Materials that have a high interstitial-solute content contain c-component loops and exhibit high growth rates even at low fluences ( 1 MeV). For sponge zirconium and the Zircaloys, c-component loop formation and the associated acceleration of growth (breakaway) during irradiation occurs because the intrinsic interstitial solute (mainly, oxygen, carbon and nitrogen) in the zirconium matrix is supplemented by interstitial iron, chromium, and nickel from the radiation-induced dissolution of precipitates; iron is the most important element. Zr-2.5 wt% Nb and Excel alloys exhibit accelerated growth which has similar characteristics.

Tb x Er 1 − x Ni 5 compounds: An ideal model system for competing Ising- X Y anisotropy energies

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.

Estimation of mating system parameters in plant populations using the EM algorithm

Abstract: An EM algorithm procedure is presented for the maximum-likelihood estimation of mating system parameters of mixed mating system models for both angiosperms and gymnosperms. One advantage of the procedure is the ability to accommodate any number of alleles in the mature population and pollen pool. Estimates of the outcrossing rate ( $$\hat t$$ ) derived from the model are bounded strictly within the natural biological range (i.e., 0 ≦ $$\hat t$$ ≦1).