Showing papers by "Atomic Energy of Canada Limited published in 1977"
TL;DR: In this paper, photoelectron spectroscopic studies of Ni(111), Ni(100) and Ni(110) surfaces were conducted to investigate the oxidation process of NiO.
292 citations
TL;DR: In this article, a quantitative model for hydrogen cracking in Zr-2.5 pct Nb is presented and compared with available experimental data, showing that the process occurs in an intermittent fashion; hydride clusters accumulate at the crack tip followed by unstable crack advance and subsequent crack arrest in repeated cycles.
Abstract: Mechanisms which have been formulated to describe delayed hydrogen cracking in hydride-forming metals are reviewed and discussed. Particular emphasis is placed on the commercial alloy Zr-2.5 pct Nb (Cb) which is extensively used in nuclear reactor core components. A quantitative model for hydrogen cracking in this material is presented and compared with available experimental data. The kinetics of crack propagation are controlled by the growth of hydrides at the stressed crack tip by the diffusive ingress of hydrogen into this region. The driving force for the diffusion flux is provided by the local stress gradient which interacts with both hydrogen atoms in solution and hydrogen atoms being dissolved and reprecipitated at the crack tip. The model is developed using concepts of elastoplastic fracture mechanics. Stage I crack growth is controlled by hydrides growing in the elastic stress gradient, while Stage II is controlled by hydride growth in the plastic zone at the crack tip. Recent experimental observations are presented which indicate that the process occurs in an intermittent fashion; hydride clusters accumulate at the crack tip followed by unstable crack advance and subsequent crack arrest in repeated cycles.
204 citations
TL;DR: Radical scavenging experiments indicate that hydroxyl radical attack initiates the oxidative damage, and Dimethyl sulphoxide is exceptional in that it does not protect, but sensitizes, linoleic acid to radiation induced peroxidation.
Abstract: Cellular membranes have been suggested as possible loci for the development of the oxygen effect in radiobiology. Unsaturated lipids from membranes are subject to very efficient radiation-induced peroxidation, and the deleterious effects generally associated with lipid autoxidation could be initiated by ionizing radiation. Oxidative damage in lipids is characterized not only by high yields but also by a profound dose-rate effect. At dose-rates of X-irradiation below 100 rad/min, a very sharp rise occurs in oxidative damage. This damage has been quantified spectrophotometrically in terms of diene conjugation (O.D. 234 mm) and chromatographically in terms of specific 9- and 13-hydroperoxide formation in linoleic acid micelles. Radical scavenging experiments indicate that hydroxyl radical attack initiates the oxidative damage. Dimethyl sulphoxide is exceptional in that it does not protect, but sensitizes, linoleic acid to radiation induced peroxidation. The yields of hydroperoxides are substantial (G=10--40) and can be related to biological changes known to be effected by autoxidizing lipids.
124 citations
TL;DR: The sensitizers, metronidazole, Ro 7-0582, and Ro7-0741, at 5 mM concentration were effective in reducing the OER's of the beams studied by ∼ 55%, ∼ 75% and ∼ 85%, respectively, and such drugs appear to have a potential benefit in radiotherapy planned with heavy ions.
Abstract: Homogeneous populations of stationary phase and G 1-phase Chinese hamster cells were irradiated in stirred suspensions placed in the plateau regions and the extended Bragg peaks of particle beams from the 184 in. cyclotron and Bevalac at Berkeley. Cell inactivation data were best-fitted to the linear quadratic expression. SSo=exp (− αD − βD2). The increase in RBE observed with increasing LET up to 100–150 keV/μ resulted predominantly from an increase in the single-hit mechanism (a). The double-hit mechanism (√β) increased by ∼ 10% over the same range of LET for these energetic particle beams. The ratio, RBE (spread peak)/RBE (plateau), is an important factor to maximize for therapeutic considerations. The ratio is greater than 1.0 and increases with particle Z -value up to carbon for beams whose Bragg peaks had been spread to 4 cm. Its value decreases for Ne and becomes less than 1.0 for Ar. Chemical radiosensitizers have been studied in combination with He and beavy-lon beams. OER's were measured for hamster cells irradiated in the plateaus and spread peaks and found to decrease with increasing LET. The sensitizers, metronidazole, Ro 7-0582, and Ro 7-0741, at 5 mM concentration were effective in reducing the OER's of the beams studied by ∼ 55%, ∼ 75% and ∼ 85%, respectively. Such drugs appear to have a potential benefit in radiotherapy planned with heavy ions.
103 citations
TL;DR: In this article, a compilation and an analysis of data relating to oxygen diffusion in alpha-zirconium is presented, which spans the temperature range 290 to 1500°C and fourteen orders of magnitude in the diffusion coefficient.
101 citations
TL;DR: In this paper, the stability of the ordered phase of Zr3Al when subjected to Ar+ ion bombardment was explored using transmission electron microscopy, showing that at low ion fluences (up to 1012 ions/cm2) individual damaged regions were observed.
96 citations
TL;DR: In this paper, neutron yields and spectral distributions of neutrons produced by bombarding thick 7Li and 9Be targets with protons and deuterons of energies 14.8, 18 and 23 MeV were measured at five angles between 0° and 40°.
93 citations
TL;DR: In this paper, the change in the Fermi matrix element due to deviations from perfect analogue symmetry has been estimated in a single-particle model with both harmonic oscillator and Saxon-Woods radial wave functions.
88 citations
87 citations
TL;DR: Girard-T reagent (trimethylaminoacetohydrazide chloride) under mild acid or alkaline conditions, reacts with aldehydes and ketones containing α-dicarbonyl functional groups to produce addition compounds which strongly absorb ultraviolet light.
65 citations
TL;DR: Concrete canisters for interim dry storage of spent, irradiated Canadian Deuterium Uranium (CANDU) fuel are being developed by Atomic Energy of Canada Limited as mentioned in this paper.
Abstract: Concrete canisters for interim dry storage of spent, irradiated Canadian Deuterium Uranium (CANDU) fuel are being developed by Atomic Energy of Canada Limited. The canisters are designed to contain...
TL;DR: In this article, the influence of test section orientation on boiling crisis occurring in a tube has been studied experimentally, and the same tube was tested with both water and Freon-12 to determine the effects of fluid properties and the applicability of vertical fluid-to-fluid modelling criteria to horizontal flow.
TL;DR: In this paper, a broadening of a (p, γ) resonance yield curve was used to measure the concentration distributions of 13C, 23Na, 26Mg, 27 Al, and 34S ions implanted in tantalum and of 29Si ion implanted in aluminum.
Abstract: Concentration distributions of 13C, 23Na, 26Mg, 27 Al, and 34S ions implanted in tantalum and of 29Si ions implanted in aluminum have been measured in the energy range 20-100 keV by means of the broadening of a (p, γ) resonance yield curve. Proton energy straggling is included in the analysis in an improved manner. Mean ranges in these polycrystalline targets were found to be larger than those predicted by the Lindhard—Scharff-SchiOtt theory valid for amorphous targets. Range profiles of 27Al in Ta2O5 and of 29Si ions in Al2O3, both amorphous materials, were found to agree well with theory. Relevance to nuclear Doppler-shift attenuation measurements, which are done in polycrystalline targets, is discussed. It is necessary in comparing theory and experiment to take account of the fraction of reflections; the calculated reflection coefficients are given.
01 Jan 1977
TL;DR: It is led to conclude that DNA damage can lead to congenital malformations; thus, enzymatic DNA repair processes play a vital role in normal neonatal development.
Abstract: A unique feature of ataxia telangiectasia (AT), a hereditary multisystem disease, is extreme sensitivity to ionizing radiation, observed both clinically and in cell culture. Hence, we have measured the DNA repair capabilities of ten diploid fibroblast strains derived from unrelated AT donors, following anoxic 60Co γ-irradiation. Compared to two control strains, six of the ten mutant strains are markedly deficient in γ-induced repair replication. Two defective strains were defined further. While capable of rejoining single-strand breaks normally, both are impaired in the initial incision step in excision repair of base defects, assayed as γ-modified sites sensitive to a Micrococcus luteus endonuclease activity. Cell fusion studies assign three repair-deficient strains to two complementation groups; this result, coupled with a normal repair-replication ability in four of the ten AT strains, indicates genetic heterogeneity in the disease. AT strains appear otherwise normal, including their ability to repair UV damage. Aside from providing molecular insight into this complex disorder, our findings characterize AT as a γ-ray analogue of the UV-sensitive skin disease, xeroderma pigmentosum. Moreover, since AT patients are cancer-prone, faulty DNA repair is implicated in neoplastic transformation. Finally, given that (i) impaired embryonic differentiation best explains the clinical features of AT and (ii) defective DNA repair is of etiological relevance, we are led to conclude that DNA damage can lead to congenital malformations; thus, enzymatic DNA repair processes play a vital role in normal neonatal development.
TL;DR: UV-irradiated human fibroblasts in tissue culture were exposed to photoreactivating light in an attempt to demonstrate a light-dependent loss of thymine dimers from the acid-insoluble fraction of the DNA.
Abstract: UV-irradiated human fibroblasts in tissue culture were exposed to photoreactivating light in an attempt to demonstrate a light-dependent loss of thymine dimers from the acid-insoluble fraction of the DNA. The only experimental conditions in which this phenomenon was observed was if the cells were grown for at least 10 days in Dulbecco's modified Eagle's minimum essential medium. Such cells lost a maximum of between 10–30% of the thymine dimers from their DNA during illumination for 1 h. When cells were grown in a variety of other media the phenomenon was not observed. The present experiments do not discriminate between true enzymatic photoreactivation and a medium-dependent photosensitization phenomenon that is not enzymatic in nature.
TL;DR: In this paper, core polarisation calculations taken beyond first order perturbation theory provide a mechanism to explain the breakdown in the additivity rule for magnetic moments in high spin isomers of configuration.
TL;DR: In this article, a semi-analytical method is presented for calculating the energy straggling in a beam of fast charged particles in the presence of charge-changing processes, showing the development of the beam toward charge-state equilibrium.
TL;DR: In this paper, a review outlines progress in the development of SEM electron channelling pattern techniques since Coates first observed patterns and Bookeret et al. explained their origin ten years ago.
Abstract: This review outlines progress in the development of SEM electron channelling pattern techniques since Coates first observed patterns and Bookeret al. explained their origin ten years ago. Discussions are included on the mechanism of electron channelling in crystals, electron optical and specimen conditions for generating patterns, pattern indexing, selected-area analysis, and applications. Progress in revealing crystal defects is also discussed.
TL;DR: In this article, normal, phosphoric and nitrate films were classified into three classes: normal, normal, and normal anodically formed on Zr-2, and they were found to fall into three categories: normal films were cubic ZrO 2 containing 3.5 nm diameter micropores and 50 nm diameter crystallites.
TL;DR: A linear transformation method of modelling equal-time displacement correlations in computer simulations of ion-lattice interactions is presented and test examples for the one-dimensional atomic string and three-dimensional lattice cases are discussed.
TL;DR: In this paper, the g-factors of the 3.4 μs 17 2 − state in 91Nb, the 9.3 ns 11− state in 92Mo, the 10.1 µm 17 2 in 93Tc, the 65.5 ns 6+ state and the 68 μs 8 + state in 94Ru were measured for the first time.
TL;DR: In this paper, a flexible boundary method based on linear elasticity theory and recently developed by Hoagland, Hirth and Gehlen was used to provide a more accurate determination of the boundary between the atomistic and the elasto-atomic regions.
Abstract: A study was undertaken to improve upon a previous rigid boundary atomistic calculation of the core properties of a/2〈110〉{110} edge dislocations in MgO. A flexible boundary method (Flex-II) based on linear elasticity theory and recently developed by Hoagland, Hirth and Gehlen (1976) was used to provide a more accurate determination of the boundary between the atomistic and the elasto-atomic regions. A central-force breathing shell model due to Sangster (1973) was used to take account of many-body effects in the interaction between ions. This marks the first application of the breathing shell model to the calculation of dislocation core configurations in ionic crystals. Within this model two potentials were used. One is due to Sangster (1973), the other is our previously developed Model 1 potential. The results obtained using the above potentials are analysed in terms of the stability of the dislocation symmetry type, the core displacement field, the volume of expansion and the total strain energy...
TL;DR: In this article, X-ray photoelectron spectroscopy (XPS) was used to study coal-associated pyrites, oxidized for various time intervals at low temperatures with humid air or oxygen.
TL;DR: In this paper, a general method for atomistic calculations of interactions between point-defects and dislocations in cubic ionic crystals is presented, where the lattice model has ions of integer charge interacting by Coulomb and short range, central potentials.
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...
TL;DR: In this article, the authors measured the γ-ray lineshapes in time coincidence with backscattered ions and were analyzed with a computer program incorporating tabulated electronic stopping powers.
TL;DR: Using 59Fe3+ and 32PO43− as tracers, the uptake and transport of iron and phosphate from a water environment by roots and shoots of the vascular aquatic plant Vallisneria spiralis L. were studied.
TL;DR: In this article, a group theoretical analysis of lattice vibrations in GaS and neutron inelastic scattering measurements of acoustic phonons propagating along the Delta, Sigma and T directions is presented.
Abstract: The group theoretical analysis of lattice vibrations in GaS and neutron inelastic scattering measurements of acoustic phonons propagating along the Delta , Sigma and T directions are presented. The elastic constants C11, C33, and C44 are derived and the results for the Delta direction are analysed to determine interlayer force constants. The frequencies of the B1 modes along Sigma and T show a weak quadratic dependence on wavevector. A simple interatomic force model is fitted to the phonon frequencies, and the frequency distribution function is calculated. The temperature dependence of the lattice specific heat and of the corresponding Debye temperature is calculated; over a small temperature range the variation of the specific heat is characteristic of a pseudo-two-dimensional solid.
TL;DR: In this article, a strategy for flow-boiling analysis for the equal velocity and equal temperature model is presented, with particular emphasis on the role of benchmark solutio in the analysis.
Abstract: A strategy for flow-boiling analysis development is illustrated through application to the equal-velocity and equal-temperature model Particular emphasis is placed on the role of benchmark solutio