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.

Character of Excitations in Substitutionally Disordered Antiferromagnets

Abstract: Magnetic excitations in several single crystals of the systems K(Co,Mn)${\mathrm{F}}_{3}$ and (Co, Mn)${\mathrm{F}}_{2}$ have been studied by neutron inelastic scattering. It is found that two branches of well-defined magnetic excitatios, both of which exhibit propagating character, occur at certain compositions. The dispersion relation for two branches of propagating excitations cannot be adequately described by current theories, but an extension of Anderson's criterion for localization in disordered alloys gives approximate agreement with the observed character.

Radiation damage and xenon release in quartz and fused silica following ion bombardment

Abstract: Single-crystalline quartz and fused silica were bombarded with 40 keV xenon ions to give integrated ion doses of up to 2 × 1016 ions/cm2. At low dose (8 × 1010 ions/cm2) diffusional release processes dominated with activation enthalpies of 58 and 61 kcal/mol for quartz (diffusion along and perpendicular to the c-axis respectively) and 72 kcal/mol for fused silica. Diffusion in the amorphous phase was markedly slower than diffusion in the crystalline phase. At doses ≧ 4 × 1013 ions/cm2 radiation damage in the form of a phase change to a quasi-amorphous state occurred in quartz, as revealed by reflection electron diffraction. The annealing of this structural damage coincided with enhanced thermally activated gas release at temperatures below those of volume diffusion. Fused silica showed a similar enhanced release at high bombardment dose. Thus, the quasi-amorphous phase produced by ion bombardment is different from that of fused silica. The present results indicate further, in agreement with the literature on neutron irradiated quartz and fused silica, that both materials approach a common state at a high level of radiation damage. Quarzeinkristalle und Quarzglasproben werden mit 40 keV Xenonionen bis zu Gesamtionendosen von 2 × 1016 Ionen/cm2 beschossen. Bei niedriger Dosis (8 × 1010 Ionen/cm2) liegt Gasabgabe durch Diffusionsprozesse vor, mit Aktivierungsenthalpien von 58 und 61 kcal/Mol fur Quarz (Diffusion parallel und senkrecht zur c-Achse) und 72 kcal/Mol fur Quarzglas. Die Diffusion in der amorphen Phase verlauft wesentlich langsamer als die Diffusion in der kristallinen Phase. Durch Elektronenbeugung in Reflexion wird gezeigt, das bei Dosen ≧ 4 × 1013 Ionen/cm2 in Quarzkristallen Strahlenschaden in Form einer Phasen-umwandlung zu einer quasi-amorphen Phase auftreten. Das Ausheilen dieser strukturellen Strahlenschaden fallt mit thermisch aktivierter Gasabgabe zusammen und findet bei Temperaturen statt, die unterhalb derjenigen fur Gitterdiffusion liegen. Quarzglas zeigt eine ahnlich gesteigerte Gasabgabe bei hoher Beschusdosis. Folglich ist die quasi-amorphe Phase, die durch Ionenbeschus erzeugt wird, von der des normalen Quarzglases verschieden. In Ubereinstimmung mit der Literatur uber neutronenbestrahlten kristallinen Quarz und Quarzglas deuten die vorliegenden Ergebnisse ferner darauf hin, das bei einem hohen Grad von Strahlenschaden beide Materialien einen gemeinsamen Zustand erreichen.

Shell-model calculations of interaction energies between point defects and dislocations in ionic crystals

Abstract: A general method for atomistic calculations of interactions between point-defects and dislocations in cubic ionic crystals is presented. Our lattice model has ions of integer charge interacting by Coulomb and short range, central potentials; the electric potential for the dislocated lattice is computed using the original Madelung method of summing contributions from strings of equivalent ions. The simplest calculations with unpolarizable ions have then been extended to include a proper description of ionic polarization using the shell model. We review methods used to compute the lattice distortion about the dislocation and emphasize the advantage of using flexible boundary regions surrounding the dislocation core; the dislocation thus becomes the appropriate reference configuration for the calculation of the additional relaxation when a vacancy, impurity ion, or interstitial is introduced into the core. This substantial calculation is again reduced by using a harmonic boundary region in which the...