Showing papers by "Atomic Energy of Canada Limited published in 1978"
TL;DR: In this article, the authors measured reaction kinetics and the rate of growth of the combined (ZrO2 + α-Zr) layer for Zircaloy-2 and Zirconoy-4 oxidation in steam over the temperature range 1050 −1850°C.
215 citations
TL;DR: In this article, a mechanism for the precipitation of γ-zirconium hydride in zircimium is presented, which does not require the diffusion of zircanium, and the transformation is completed by shears caused by 1 3 〈1010〉 Shockley partial dislocations on alternate zircalium basal planes.
107 citations
TL;DR: In this article, a bundle of polypropylene tubes contained inside a polyvinyl chloride (PVC) pipe that is installed in the aquifer is used as a point water sampler and piezometer.
Abstract: A simple inexpensive device for sample collection and for monitoring of ground-water potential at many levels from a single borehole installation has been developed. The device consists of a bundle of polypropylene tubes contained inside a polyvinyl chloride (PVC) pipe that is installed in the aquifer. Each tube protrudes through the wall of the pipe at a different elevation where it serves as a point water sampler and piezometer. The tip of each tube is encased in fine-meshed stainless-steel screening. The device is best suited for use in cohesionless deposits and where the piezometric levels are close enough to ground surface to enable samples to be obtained by suction methods. It can be conveniently installed using a hollow-stem auger, driven casing or wash-boring methods. The usefulness of this multilevel sampling device has been demonstrated in detailed monitoring of a leachate plume from a sanitary landfill.
102 citations
TL;DR: Although 1O2 dominates as the inactivating species, the possibility of additional (∼15%) minor mechanisms involving free radicals exists, however, O‐2 does not appear to be the damaging species, since superoxide dismutase does not provide any protection.
Abstract: — The skin photosensitizing furocoumarins, 8-methoxypsoralen (MOP) and 4,5′,8-trimethylpsoralen (TMP), inactivate E. coli ribosomes in vitro, on UV irradiation at 313 nm. Purging the solutions with N2 protects the ribosomes considerably against photoinactivation (75% with MOP and 80% with TMP). In air, the ribosome photoinactivation is mainly due to singlet oxygen (1O2), since the presence of NaN3 and other 1O2 quenchers protects the system and the inactivation is enhanced in D2O. Although 1O2 dominates as the inactivating species, the possibility of additional (∼15%) minor mechanisms involving free radicals exists. However, O-2 does not appear to be the damaging species, since superoxide dismutase does not provide any protection.
Photosensitization of the partially purified enzyme, phe-tRNA-synthetase with MOP or TMP shows inactivation and protection curves similar to those seen with the ribosomes. On the other hand, unfrac-tionated tRNAphc is not photosensitized under similar conditions, although it shows self-photosensitization. It is likely that in the furocoumarin-sensitized ribosomes, the primary events of photoinactivation are associated with the proteins.
90 citations
TL;DR: In this paper, the authors detected yrast isomers with spins Ω(n) √ 4n √ 6, √ 3, ∦ (n + 1), √ (n), 1, 2, 3, 4, 5, 6, 7, and 7.
Abstract: We have identified yrast states of $^{152}\mathrm{Dy}$ to spin \ensuremath{\sim}37, with unusually strong population of high-spin states in the ($^{32}\mathrm{S}$, $4n\ensuremath{\gamma}$) reaction. Yrast isomers with spins \ensuremath{\sim}17, 21, 27, and 31 were detected. For $Ig~14$ the yrast states scatter about a straight line on an $E$ vs $I(I+1)$ plot, consistent with predictions for aligned-particle configurations. The slope of the line yields an effective moment of inertia 18% larger than the rigid-sphere value. This and other arguments suggest possible oblate deformation at high spin.
90 citations
TL;DR: The chapter presents the substrate specificity—types of lesions detected— of all known enzymes potentially suitable for incorporation into the assays and highlights the strengths and weaknesses of the conventional assays largely responsible for their elucidation.
Abstract: Publisher Summary This chapter focuses on a recent methodological advance, namely, the exploitation of the unique properties of purified lesion-recognizing enzymes as the basis of assays that monitor with superb sensitivity and specificity the repair of DNA lesions in vivo . The chapter describes the assays, presents a comparison of their assets and liabilities and those of conventional assays, and discusses new findings emerging from their use. The chapter presents the substrate specificity—types of lesions detected—of all known enzymes potentially suitable for incorporation into the assays. The chapter also describes the basic enzymatic mechanisms mediating the repair of DNA and highlights the strengths and weaknesses of the conventional assays largely responsible for their elucidation.
88 citations
01 Jan 1978
TL;DR: In this paper, the authors discuss the Doppler shift attenuation method (DSAM) and the recoil distance plunger method (RDM) for lifetime measurements of nuclear levels.
Abstract: The importance of lifetime measurements of nuclear levels has been recognized for a long time. The techniques employed to measure lifetimes, or absolute transition probabilities, are very simple conceptually but are ingeniously adapted to obtain sensitivity to the decay products and to cover an enormous time scale from 10−20 sec to many years. In this chapter, the techniques we discuss cover only a small fraction of this time scale, namely, ∼10−15−∼10−9 sec. Radiative lifetimes of excited nuclear levels in this range can be measured with some sensitivity and accuracy by the Doppler-shift methods, the recoil distance plunger method (RDM) and the Doppler-shift attenuation method (DSAM). It is an important range, particularly for obtaining information about the collective excitation modes of nuclei throughout the periodic table.
86 citations
TL;DR: Protection of X‐irradiated mice by bovine superoxide dismutase is enhanced when the enzyme is given intravenously both before and after the exposure, in a dose range where hematological damage is an important contributor to animal lethality.
Abstract: Abstract— Protection of X‐irradiated mice by bovine superoxide dismutase is enhanced when the enzyme is given intravenously both before and after the exposure. With the combined treatment, the LD50(30) dose is increased from 734 ± 8 to 1144 ± 15rad for a dose reduction factor of 1.56 ± 0.04. This protection occurs in a dose range where hematological damage is an important contributor to animal lethality. The proliferative capacity of bone marrow stem cells, X‐irradiated in air, is protected by exogenous superoxide dismutase. The enzyme increased the D0 from 105 ± 6 to 290 ± 34rad, an increase that represents 83% of the oxygen enhancement ratio of 3.3. In N2 and N2O, the D0 of the stem cells is 348 ± 50 and 327 ± 55 rad, respectively, and the enzyme does not significantly change these values.
84 citations
TL;DR: A new method of detecting and handling discontinuities in arbitrary functions which form part of an ordinary differential equation set that applies to any predictor corrector integration algorithm with Nordsieck step size control.
82 citations
TL;DR: Singlet oxygen, superoxide anion, hydroxyl radicals and peroxy radicals are the major transient species formed on exposure of biological systems to high energy radiations; the minor species formed include hydrogen peroxide as discussed by the authors.
Abstract: Singlet oxygen, superoxide anion, and hydrogen peroxide are known to be formed in normal biological processes. Superoxide anion, hydroxyl radicals and peroxy radicals are the major transient species formed on exposure of biological systems to high energy radiations; the minor species formed include hydrogen peroxide. singlet oxygen, oxygen atoms, ozone and triplet excited oxygen. Many of these species are also formed on exposure of biological systems to light. All of these species should always be present in small amounts in biological systems, formed by exposure to sunlight and to the earth’s natural background of high energy radiations. Recently, there has been growing awareness of the possibility of interconversion of many of these species into each other (a-c).
79 citations
TL;DR: A thorough flow-induced vibration analysis of nuclear components such as heat exchangers and steam generators is essential at the design stage to ensure good performance and reliability as mentioned in this paper. But this analysis is limited to two-phase systems.
TL;DR: In this article, the effect of 1 MeV electron radiation on the L12 ordered intermetallic compound, Zr3Al, has been studied over the temperature range 130-775 K, using a high voltage electron microscope.
TL;DR: In this article, high speed cinematography was used to measure the lifetimes of thin aqueous films formed between nitrogen bubbles in dilute solutions of ammonium bromide, tetramethylammonium and tetra-n -propylammmonium-bromide.
TL;DR: In this paper, the dissolution of zirconium hydride has been examined using a hot stage in a high voltage electron microscope, and it was found that a significant proportion of the dislocations generated by the sydride needles during growth were not annihilated when dissolution occurred on heating to well above the solvus temperature.
TL;DR: In this paper, the authors compared 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.
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.
TL;DR: In this article, channeling measurements have shown that self-interstitial atoms in Al and Cu are trapped strongly by small solute atoms and weakly by large solutes atoms, and the strong trapping configuration is the mixed dumbbell, in which the solute atom is displaced from its lattice site by 0.1-0.14 nm in a 〈100〉 direction.
TL;DR: The exogenous enzyme shortens the delay in recovery of the white blood cells, particularly after x-ray doses of 550 and 675 rad, and the earlier hematological recovery is attributable to the known radioprotective effect of the enzyme on bone marrow stem cells.
TL;DR: In this article, the authors summarized techniques for solving the linear advective equation using, the method of lines on a digi tal or hybrid computer, and assesses how suitable they are for incorporation into large simulations.
Abstract: The linear advective equation is simple in form and yet it is one of the most difficult equations to solve accurately by numerical means. Because its be havior is similar to that of the conservation equa tions of compressible one- or two-phase flow, the advective equation is extremely useful for testing numerical schemes.This paper summarizes techniques for solving the ad vective equation using, the method of lines on a digi tal or hybrid computer, and assesses how suitable they are for incorporation into large simulations. Some of the dangers of using artificial dissipation terms are described, and a weighted-residual tech nique is shown to be very effective.
TL;DR: The growth of mackinawite, an iron-rich sulphide, on an iron electrode at constant potential in alkaline sulphide solutions is preceded by the fast growth of a thin imperfect film of magnetite as discussed by the authors.
TL;DR: In this paper, a detailed investigation of the Pt(111) surface has been carried out, using the MeV heliumscattering technique, and the anomalously large surface relaxation effect reported previously has been identified as an experimental artifact resulting from an unexpectedly large surface damage effect at low temperature.
TL;DR: In this paper, the authors measured the yield strength of well-annealed, polycrystalline Zr3 Al with respect to temperature, strain rate and grain size, and showed that at temperatures below ∼-875 K, yielding is controlled by dislocation generation and by the subsequent transmission of slip across grain boundaries.
TL;DR: In this paper, the dispersion curves for phonons propagating along the trigonal axis of the layer-structure emiconductor Bi2Te3 at 77 K have been determined by coherent inelastic neutron scattering techniques.
Abstract: The dispersion curves for phonons propagating along the trigonal axis of the layer-structure emiconductor Bi2Te3 at 77 K have been determined by coherent inelastic neutron scattering techniques. Analysis of these results in terms of a simple interplanar force model shows a) that the forces between adjacent planes of Te atoms are comparable to those between nearest neighbour planes of Bi and Te and b) that foreces between next-nearest-neighbour planes have to be considered. In addition, a limited number of phonons were measured at 300 K and some low-frequency modes propagating along the bisectrix within the planes were determind. The results are compared, where possible, with previous Raman scattering, infrared reflection, and elastic constant measurements.
TL;DR: The present state of knowledge of Ataxia telangiectasia is summarized, attention is drawn to gaps in understanding, and future research directions are suggested.
Abstract: Ataxia telangiectasia , a rare hereditary disorder featuring neurovascular and immune abnormalities and predisposition to lymphoreticular cancer, exhibits many traits expected of an ionizing radiation analogue of the ultraviolet light-sensitive disease, xeroderma pigmentosum. These traits include elevated radiosensitivity extending from the clinical to the cellular level and in vitro hallmarks of deficient repair of radiogenic damage to DNA. This paper summarizes the present state of knowledge, draws attention to gaps in our understanding, and suggests future research directions. Speculation on the pathogenesis of the disorder implies a key role for DNA repair in embryonic development.
TL;DR: In this paper, the dynamic response of the fluoride-selective electrode was shown to result from four distinct processes: ion diffusion, an undefined reaction, LaF3 dissolution and a calibration drift.
TL;DR: In this paper, high resolution (0.09 eV) UPS spectra have been obtained of condensed films of N2 and CO. All spectral features are broadened by ≳ 0.6 eV upon condensation.
TL;DR: The catalyzed exchange of deuterium between hydrogen and liquid water has been studied as the basis for a heavy water production process as mentioned in this paper, and it was found that mass transfer plays a very important role in the overall exchange and the conventional theory of vapour/liquid mass transfer does not adequately describe the absorption process.
Abstract: The catalyzed exchange of deuterium between hydrogen and liquid water has been studied as the basis for a heavy water production process. Platinum catalyst which had been waterproofed with Teflon was tested in a 0.2 m diameter trickle bed reactor at pressures and temperatures up to 6 MPa and 440 K. Extensive experimental data were used to test a model of the system which was developed from fundamental principles. It was found that mass transfer plays a very important role in the overall exchange and the conventional theory of vapour/liquid mass transfer does not adequately describe the absorption process. Modelling of the data has resulted in the postulation of a second method of mass transfer whereby HDO transfers directly from the catalyst to the bulk liquid phase.
On a etudie l'echange catalytique du deuterium entre l'hydrogene et l'eau a l'etat liquide comme base d'un procede de production de l'eau lourde. On a fait l'essai d'un catalyseur de platine, qui avait ete impermeabilise avec Teflon dans un reacteur a lit a ruissellement, a des pressions absolues allant jusqu'a 6 MPa et des temperatures s'elevant a 440 K. On a utilise des donnees experimentales etendues pour eprouver un modele du systeme qu'on a mis au point a partir de principes fondamentaux. On a constate que le transfert de masse jouait un role tres important dans l'echange global et que la theorie classique du transfert de masse entre vapeur et liquide ne decrit pas d'une maniere adequate le procede d'absorption. La representation par modele des resultats obtenus a donne naissance a la postulation d'une seconde methode de transfert de masse par laquelle HDO est transfere directement du catalyseur a la phase liquide globale.
TL;DR: Caesium and rubidium counter-ions increase peroxidation in irradiated micelles of linoleic and linolenic acids and their effect on fatty acid micelle structure may be significant for studies of per oxidation in highly structured cell membranes.
Abstract: SummaryCaesium and rubidium counter-ions increase peroxidation in irradiated micelles of linoleic (18 : 2) and linolenic (18 : 3) acids. The effect is specific to Cs+ and Rb+ in the alkali metal series. The effect is independent of the salts used (Cl−, NO3−, ClO4−) and, therefore, independent of the chaotropic nature, and reactivity with hydroxyl radicals of Cl−, NO3− and ClO4−. The promotion of peroxidation by Cs+ and Rb+ is interpreted in terms of their effect on fatty acid micelle structure. The dependence of radiation peroxidation on lipid structure in the micelles may be significant for studies of peroxidation in highly structured cell membranes.
TL;DR: In this article, the authors investigated the photochemical formation of metastable species from 1,3-diphenylisobenzofuran (DPBF) in solutions and showed that the resulting products do not all show fluorescence.
Abstract: — Photochemical formation of metastable species from 1,3-diphenylisobenzofuran (DPBF) in solutions has been investigated. On irradiation at 410 nm, in the presence of oxygen, DPBF is bleached. The bleached solutions show two fluorescence bands, one at ˜380nm and the other at ˜420nm. None of these fluorescence bands are due to o-dibenzoylbenzene, which is the main stable product formed on photo-bleaching of DPBF in the presence of O2. The species showing fluorescence at ˜380nm and ˜420nm are also formed on reaction of DPBF with 1O2 and undergo further reactions with light as well with 1O2; the resulting products do not all show fluorescence. After the photo-bleached solutions have stood for some time in the dark, or are warmed, regeneration of DPBF seems to occur. The triplet energy of DPBF has been estimated by energy transfer studies to be between 22 and 29 kcal/mol (between 92 and 121 kJ mol-1).
TL;DR: The conformation of adenosine 5′-monophosphate at the active site of5′-nucleotidase is inferred and this conformation is not in agreement with a previous proposal.
TL;DR: In this paper, the crystal structure and morphology of the hydride was examined to determine its effect on the delayed hydrogen cracking process in CANDU-PHW pressure tubes, which are made from cold-worked Zr−2.5 wt. % Nb.