Atomic Energy of Canada Limited

About: Atomic Energy of Canada Limited is a company organization based out in Ottawa, Ontario, Canada. It is known for research contribution in the topics: Neutron & Zirconium alloy. The organization has 4845 authors who have published 4826 publications receiving 102951 citations.

The Hydrogeochemistry Of Fractured Plutonic Rocks In The Canadian Shield

Abstract: The composition of groundwater has been determined in selected granitic, gabbroic and gneissic plutons in the Canadian Shield as part of the Canadian Nuclear Fuel Waste Management Program. A similar geochemical evolution of the groundwater is seen with increasing depth or with flow along the hydraulic gradient, irrespective of rock type. This pattern is comparable to that seen in mine groundwaters from throughout the Canadian Shield. Near-surface groundwaters are typically dilute, slightly alkaline and Ca-(Na)-HCO3 in composition. They evolve to higher pH, Na-(Ca)-HCO3 compositions along the flow path because of interaction with plagioclase, calcite precipitation and ion exchange on clay minerals. At greater depths (>≈200 m), groundwater salinity increases as a result of the dissolution of Cl-rich salts in the rock matrix and, in certain areas, mixing with Na-Cl brines from seawater or basinal formation water. Stable and radioactive isotopic data for the groundwaters help to interpret these characteristics and indicate high residence times for the deeper, saline groundwater.

Distribution of Polypyrimidine · Polypurine Segments in DNA from Diverse Organisms

Abstract: Polypyrimidine . polypurine segments are regions of duplex DNA which contain a highly asymmetric distribution of pyrimidine and purine nucleotides. A polypyrimidine in single-stranded DNA can be detected by its ability to form a complex and poly(A, G) which will bind to hydroxyapatite. We tested DNA from a variety of organisms and found that most contained polypyrimidines. From the shape of the curve relating DNA size to percentage bound to hydroxyapatite, we conclude that polypyrimidine . polypurine segments occur widely in DNA from higher organisms, at intervals of 6000--8000 base pairs throughout the majority of the genome. Lower levels occur in DNA from yeast and Drosophila.

An atom size effect in tracer diffusion

Abstract: Published diffusion data permit an extensive comparison to be made between tracer diffusion coefficients, D, in Pb and in alpha -Zr, at 0.6 Tm, where Tm(K) is the melting temperature of the host metal. For these metals, a striking correlation is found between D and the metallic radius, r, of the corresponding tracer element; except for the smallest r values, the correlation may be expressed in the general form lg D=A+exp(-br+c) where A, b and c are individual constants for each host metal. There is, for tracer diffusion in Pb, sufficient experimental data to permit the evaluation of an additional relationship, of the type proposed by Zener, between the preexponential factor, D0, and the activation enthalpy, Delta H, in the usual expressions D=D0exp(- Delta H/RT) describing the temperature dependence of D. A combination of these relationships allows the evaluation of expressions for D0 and Delta H in which r is the only variable. In order to compare tracer diffusion in these 'open' metals (i.e. metals with a relatively large metallic/ionic radius ratio) with tracer diffusion in a 'full' metal, values of D at 0.6 Tm have been calculated from published data for diffusion in Cu.

"Molecular" States Formed by Two Carbon Nuclei

Abstract: The existence of " molecular" states of two C/sup 12/ nuclei is discussed, based on its physical origin and its implications for nuclear structure. The experimental data are the cross sections for carbon and oxygen bombardment by C/sup 12/ and O/sup 16/ ions at energies to 15 Mev. The width and spacing of the observed C/sup 12/ + C/sup 12/ resonance levels cannot be attributed to the compound nucleus Mg/sup 24/. The spacing is that of a well much larger than the usual Mg/sup 24/ nucleus. The observed resonances are attributed to almost pure single-particle states of two C/sup 12/ nuclei. A qualitative illustration is given of the potentials connected with the motion of two C/sup 12/ nuclei as a function of their separation. (B.O.G.)