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Showing papers by "Chalk River Laboratories published in 1995"


Journal ArticleDOI
TL;DR: In this article, a level scheme is proposed to calculate an expected spectrum for comparison with the observed spectrum, and a graphics-based editor is included to allow fast and easy modification of the proposed level scheme, and least-squares fits to the matrix or cube can be performed to extract optimum values for the energies and intensities of the level scheme transitions.
Abstract: Programs for analysis of γ-γ matrices and γ-γ-γ cubes from HPGe coincidence experiments are described. The programs are intended primarily for high-spin spectroscopy studies. Users are able to inspect background-subtracted gated spectra, or combinations of such spectra, quickly and easily. The programs also make use of a proposed level scheme, provided by the user, to calculate an expected spectrum for comparison with the observed spectrum. Electron conversion coefficients, detection efficiency and γ-ray energy calibrations are included in the calculation. A graphics-based editor is included to allow fast and easy modification of the proposed level scheme, and least-squares fits to the matrix or cube can be performed to extract optimum values for the energies and intensities of the level scheme transitions.

620 citations


Journal ArticleDOI
TL;DR: A mutant allele of AHAS3 responsible for sulfonylurea resistance in a Brassica napus cell line was isolated, revealing a single site essential for the binding of all the herbicide classes.
Abstract: Acetohydroxy acid synthase (AHAS) is an essential enzyme for many organisms as it catalyzes the first step in the biosynthesis of the branched-chain amino acids valine, isoleucine, and leucine. The enzyme is under allosteric control by these amino acids. It is also inhibited by several classes of herbicides, such as the sulfonylureas, imidazolinones and triazolopyrimidines, that are believed to bind to a relic quinone-binding site. In this study, a mutant allele of AHAS3 responsible for sulfonylurea resistance in a Brassica napus cell line was isolated. Sequence analyses predicted a single amino acid change (557 Trp→Leu) within a conserved region of AHAS. Expression in transgenic plants conferred strong resistance to the three classes of herbicides, revealing a single site essential for the binding of all the herbicide classes. The mutation did not appear to affect feedback inhibition by the branched-chain amino acids in plants.

121 citations


Journal ArticleDOI
TL;DR: In this paper, a method for correcting for a mixture of different reaction channels in the complete data set, by making use of one or more gates on background channels, in the energy region of the E2 bump, is presented.
Abstract: Algorithms for the subtraction of backgrounds from γ-γ matrices and higher-fold data sets, obtained from in-beam HPGe coincidence experiments with heavy-ion-induced nuclear reactions, are described. The backgrounds are parameterized as the cross-products of lower-dimensional projections of the data and a one-dimensional background spectrum. A novel method of correcting for a mixture of different reaction channels in the complete data set, by making use of one or more gates on background channels in the energy region of the “E2 bump”, is presented. In many cases, this new method provides a significantly better description of the background.

93 citations


Journal ArticleDOI
TL;DR: In this article, the authors used sediment chronology data from fourteen published studies of lake cores across much of North America and Scandinavia in order to make a large scale comparison of the different dating techniques.
Abstract: We used sediment chronology data from fourteen published studies of lake cores across much of North America and Scandinavia in order to make a large scale comparison of the different dating techniques. The uncertainty of210Pb derived dates was determined using common sediment event markers: the stable Pb rise, the137Cs rise, and theAmbrosia pollen rise. For all data combined, the 95% confidence intervals for the stable Pb rise and theAmbrosia rise, were approximately 30 years. These 95% confidence intervals are slightly higher than those derived by First-Order Error analysis performed by others on210Pb derived dates. When comparing the concordance of two210Pb models (CRS and CIC) against markers of known history, we found that the CRS model dates (constant rate of supply) had consistently better agreement than the CIC model dates (constant initial concentration). Major discrepancies between137Cs and210Pb were common, but were consistently more severe in sediments of soft water lakes pointing to an inability of sediments with low mineral content to ‘immobilize’ Cs.

91 citations


Journal ArticleDOI
TL;DR: In this article, the Holstein model in one dimension is examined using a variety of techniques, i.e., exact diagonalization, perturbation theory, and the adiabatic approximation.
Abstract: The Holstein model in one dimension is examined using a variety of techniques, i.e. exact diagonalization, perturbation theory, and the adiabatic approximation. In agreement with other authors we find that the model is polaronic for all coupling strengths. In the case of two electrons we examine the regimes under which binding occurs. We find that binding decreases as the phonon frequency increases, for a given coupling strength. We provide a numerical verification for the effect of retardation, which gives rise to the well-known pseudopotential effect.

80 citations


Journal ArticleDOI
TL;DR: The thermal conductivity of hyperstoichiometric SIMFUEL and UO 2+x was obtained from thermal diffusivity, specific heat and density measurements in this paper, where a reduction of 15%, 37% and 56% at 600 o C, and 11, 23% and 33% at 1500 o C was found for O/U ratios of 2.007, 2.035 and 2.084, respectively.

75 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the suitability of lithium-containing ceramics for tritium breeding materials for fusion reactor blankets, particularly because of their safety advantages and compatibility with structures and beryllium.

62 citations


Journal ArticleDOI
TL;DR: In this article, low-level radioactive waste leachates were analyzed for volatile fatty acids by gas chromatography as part of the continuing waste management program at the Chalk River Laboratories.

62 citations


Journal ArticleDOI
TL;DR: In this article, the authors measured the temperature dependence of the cell parameter of cubic β-cristobalite up to 1300°C by high-precision X-ray powder diffraction.
Abstract: We have measured the temperature dependence of the cell parameter of cubic β-cristobalite up to 1300° C by high-precision X-ray powder diffraction. The thermal expansion coefficient decreases on heating, until above 1000° C the cell parameter is virtually constant in value. We discuss this change in the thermal expansion with reference to the behaviour of low-frequency rigid unit modes and fluctuations associated with the α-β phase transition.

57 citations


Journal ArticleDOI
TL;DR: Cross sections for the scattering from mica of hypothetical weakly interacting dark-matter particles such as neutralinos will allow the interpretation of ongoing experiments that look for tracks due to the interaction of dark- Matter particles with nuclei in ancient mica.
Abstract: We calculate spin-dependent cross sections for the scattering from mica of hypothetical weakly interacting dark-matter particles such as neutralinos. The most abundant odd-A isotopes in mica, $^{27}\mathrm{Al}$ and $^{39}\mathrm{K}$, require different shell-model treatments. The calculated cross sections will allow the interpretation of ongoing experiments that look for tracks due to the interaction of dark-matter particles with nuclei in ancient mica.

52 citations


Journal ArticleDOI
TL;DR: In this article, a rotated triangular tube bundle of tube-to-diameter ratio of 1.5 was tested over a broad range of void fractions and mass fluxes, and well defined fluidelastic instability, random turbulence excitation, and damping were investigated.
Abstract: Two-phase cross-flow exists in many shell-and-tube heat exchangers. The U-bend region of nuclear steam generators is a prime example. Testing in two-phase flow simulated by air-water provides useful results inexpensively. However, two-phase flow parameters, in particular surface tension and density ratio, are considerably different in air-water than in steam-water. A reasonable compromise is testing in liquid-vapor Freon, which is much closer to steam-water while much simpler experimentally. This paper presents the first results of a series of tests on the vibration behavior of tube bundles subjected to two-phase Freon cross-flow. A rotated triangular tube bundle of tube-to-diameter ratio of 1.5 was tested over a broad range of void fractions and mass fluxes. Fluidelastic instability, random turbulence excitation, and damping were investigated. Well-defined fluidelastic instabilities were observed in continuous two-phase flow regimes. However, intermittent two-phase flow regimes had a dramatic effect on fluidelastic instability. Generally, random turbulence excitation forces are much lower in Freon than in air-water. Damping is very dependent on void fraction, as expected.

Journal ArticleDOI
TL;DR: The PCR-based assay shows promise as a diagnostic tool for the take-all pathogen in turfgrass pathology and did not amplify DNA from many other fungi including the important turfgrass root pathogens Magnaporthe poae and Leptosphaeria korrae.
Abstract: A region comprising the 5.8S RNA gene and internal transcribed spacers 1 and 2 of the take-all patch fungus, Gaeumannomyces graminis var. avenae, was cloned and sequenced using primers from the flanking 17S and 26S ribosomal RNA genes. The sequenced region had 99% similarity between the two G. graminis isolates, and from 70% to 80% similarity between these two isolates and several other species of fungi. From the sequence, oligonucleotide primers were selected which permitted specific amplification of DNA from G. graminis vars. avenae and graminis using the polymerase chain reaction (PCR). The assay could detect DNA of G. graminis strains obtained from a wide variety of hosts but did not amplify DNA from many other fungi including the important turfgrass root pathogens Magnaporthe poae and Leptosphaeria korrae. The primers also did not amplify DNA from G. graminis var. tritici, M. rhizophila or Phialophora graminicola. The PCR-based assay shows promise as a diagnostic tool for the take-all pathogen in turfgrass pathology.

Journal ArticleDOI
TL;DR: In this article, the effective non-steady state diffusivity of sulfate ingress from a mixed sulfate-chloride solution into Type 50 cement concrete was determined from concentration profiles at various times up to five years.

Journal ArticleDOI
TL;DR: In this paper, a section of commercial X70 pipeline is characterized using microstructural examination, X-ray diffraction (to determine crystallographic texture) and neutron diffraction for residual stress measurement.
Abstract: Gas pipelines are inspected for defects such as corrosion. The most commonly used nondestructive inspection tool uses the magnetic flux leakage (MFL) technique. The MFL signals depend on the magnetic behaviour of the pipe, which is sensitive to its microstructure and crystallographic texture as well as both residual and applied stresses. Here a section of commercial X70 pipeline is characterized using microstructural examination, X-ray diffraction (to determine crystallographic texture) and neutron diffraction (for residual stress measurement). The results correlate well with the manufacturing steps used for this type of pipe. Magnetic characterization is also performed using magnetic Barkhausen noise measurements, which reflect the magnetic anisotropy in the pipe and thus the MFL signal. These results do not correlate simply with crystallographic texture and residual strain results, but this is not unexpected given the complex nature of the material and its stress state.

Journal ArticleDOI
TL;DR: In this article, the utility of the mud deposition boundary depth (mud DBD) theory as a means of maximizing sampling efficiency in paleolimnological investigations, particularly those that apply to210Pb dating, was evaluated.
Abstract: In this paper we test the utility of the mud deposition boundary depth (mud DBD) theory (Rowanet al. 1992) as a means of maximizing sampling efficiency in paleolimnological investigations, particularly those that apply to210Pb dating. The mud DBD is defined by the relationship between near bottom wave velocity and particle threshold velocity, with wave and particle threshold theory simplified to terms of exposure and depth. Mud DBD theory can be used to define the depositional zone in lakes, and within the depositional zone defined by the mud DBD: 1) there is a high probability of obtaining a representative core, 2) variation in mass sediment accumulation rate (MSAR) is not correlated with water depth, and 3) variation in MSAR is considerably reduced from the whole lake average. This suggests that mud DBD theory can account for the effects of sediment focusing, and that the mud DBD defined depositional zone is the zone to which fine-grained sediments are focused. Finally, we have shown that to optimize sampling effort, 5 to 10 cores within the depositional zone are necessary for a reasonably precise estimate of the mean mass sediment accumulation rate. In addition, the use of mud DBD theory prior to sampling can dramatically reduce the cost associated with analyzing large numbers of cores for210Pb.

Journal ArticleDOI
TL;DR: To help resolve uncertainties as to the most appropriate weighting factor for tritium beta rays, a large experiment was carried out to measure the relative biological effectiveness of tritiated water compared to X rays for the induction of myeloid leukemia in male mice of the CBA/H strain.
Abstract: To help resolve uncertainties as to the most appropriate weighting factor for tritium beta rays, a large experiment was carried out to measure the relative biological effectiveness (RBE) of tritiated water compared to X rays for the induction of myeloid leukemia in male mice of the CBA/H strain. The study was designed to estimate the lifetime incidence of myeloid leukemia in seven groups of about 750 mice each; radiation exposures were approximately 0, 1, 2 and 3 Gy both for tritiated water and for X rays. The lifetime incidence of leukemia in these mice increased from 0.13% in the control group to 6-8% in groups exposed to higher radiation doses. The results were fitted to various equations relating leukemia incidence to radiation dose, using both the raw data and data corrected for cumulative mouse-days at risk. The calculated RBE values for tritium beta rays compared to X rays ranged from 1.0 +/- 0.5 to 1.3 +/- 0.3. A best estimate of the RBE for this experiment was about 1.2 +/- 0.3. A wR value of 1 would thus appear to be more appropriate than a wR of 2 for tritium beta rays.

Journal ArticleDOI
TL;DR: In this article, two different techniques were used to determine the hydride dissolution and precipitation/nucleation temperatures on heatup and cooldown of the Excel alloy, including differential scanning calorimetry (DSC) and dynamic elastic modulus (DEM) techniques.

Journal Article
TL;DR: In this article, a microbial biofilm formed on the wall of an excavated granite vault in a deep underground laboratory was examined by 57 Fe Mossbauer spectroscopy, and iron compounds were found in aerobically and anaerobically cultured samples of the biofilm.
Abstract: The specimens from a microbial biofilm formed on the wall of an excavated granite vault in a deep underground laboratory were examined by 57 Fe Mossbauer spectroscopy. In the aerobic face of the biofilm, iron was found in a form of protoferrihydrite, whereas in the anaerobic face at the rock-biofilm boundary, it was found as very fine particles of siderite, typically 2-3 nm in size. The same iron compounds were formed in aerobically and anaerobically cultured samples of the biofilm. To the best of our knowledge, this is the first clear experimental evidence of biogeochemically formed siderite and ferrihydrite in the natural environment. Finding microbial consortia capable of precipitation of Fe (super 2+) and Fe (super 3+) in close proximity may have a bearing on the development of early forms of life and, in particular, on the deposition of banded iron-formations.

Journal ArticleDOI
TL;DR: In this article, the X-ray anisotropic alignment was observed in both the separate ionization probabilities and the X ray anisotropy in the channel, where the various possible m states being non-degenerate in a channel are separable.
Abstract: Hydrogenic ions penetrating a crystal are perturbed by the frequency with which they pass atoms lying in rows or ordered planes. This frequency, when resonant, can cause excitation of the ion with subsequent collisional ionization or radiative relaxation following escape from the crystal. The various possible m states being non-degenerate in the channel are separable. The associated alignment is observed in both the separate ionization probabilities and X-ray anisotropy.

Book ChapterDOI
TL;DR: In this article, the axial-vector and pseudoscalar coupling constants in the nucleon are determined from neutron decay and muon capture on the proton respectively, and evidence for these coupling constants being reduced relative to their free-nucleon values is discussed.
Abstract: Beta-decay and muon-capture experiments in nuclei are reviewed. The conserved vector current hypothesis is confirmed through the observed constancy of the vector coupling constant determined from the superallowed Fermi transitions and from the measurement of the weak-magnetism term in mirror Gamow-Teller transitions. The axial-vector and pseudoscalar coupling constants in the nucleon are determined from neutron decay and muon capture on the proton respectively. In finite nuclei, evidence for these coupling constants being reduced relative to their free-nucleon values is discussed. Meson-exchange currents are shown to be an important correction to the time-like part of the axial current as evident in first-forbidden beta decays. Tests of the Standard Model are discussed, as well as extensions beyond it involving right-hand currents and scalar interactions.

Journal ArticleDOI
TL;DR: Water bath hyperthermia alone is effective in the treatment of psoriatic lesions in heatable locations and reduces edema and relieved pruritus in all patients, both during the treatment period and for up to several months after lesions had returned.
Abstract: An eight week trial, involving superficial hyperthemia delivered biweekly via simple water bath immersion, was tested for its ability to clear mild to moderate psoriatic lesions. Seven patients were treated and three cases rapidly improved. In the remaining patients, the treatment frequency was increased to alternate days; two cases improved significantly, one patient showed a partial response, and the fourth had no visible change (this was the only patient taking concurrent drug therapy–etretinate). In addition to resolving psoriatic lesions, water bath hyperthermia also reduced edema (swelling) and relieved pruritus (itching) in all patients, both during the treatment period and for up to several months after lesions had returned. Lesion reappearance occurred within one to three months after the last heat treatment. We retreated one patient and produced a second complete remission. These results indicate that simple repetitive water bath hyperthermia alone is effective in the treatment of psoriatic lesi...


Journal ArticleDOI
TL;DR: In this article, the diffraction elastic constants in a ferritic steel for the [1 1 0], [0 0 2] and [2 2 2 2] crystallographic axes, in directions parallel and perpendicular to the applied stress are compared with theoretical diffusion elastic constants.
Abstract: Experiments on bent steam-generator tubing have shown that different diffraction peaks, (1 1 1) or (0 0 2), give different results for the sign and magnitude of the stress and strain. From an engineering standpoint, the macroscopic stress field cannot be both positive and negative in the same volume, so this difference must be due to intergranular effects superposed on the macroscopic stress field. Uniaxial tensile test experiments with applied stresses beyond the 0.2% offset yield stress, help to understand this anomaly, by demonstrating the different strain response to applied stress along different crystallographic axes. When Zr-alloys are cooled from elevated temperatures, thermal stresses always develop, so that it is difficult to obtain a stress-free lattice spacing from which residual strains may be derived. From measurements of the temperature dependence of lattice spacing, the temperature at which the thermal stresses vanish may be found. From the lattice spacing at this temperature the stress-free lattice spacings at room temperature can be obtained readily. To interpret the measured strains in terms of macroscopic stress fields it is necessary to know the diffraction elastic constants. Neutron diffraction measurements of the diffraction elastic constants in a ferritic steel for the [1 1 0], [0 0 2] and [2 2 2] crystallographic axes, in directions parallel and perpendicular to the applied stress are compared with theoretical diffraction elastic constants.

Book ChapterDOI
TL;DR: In this paper, a regression model including organic content of sediments and the ratio of the catchment area/lake surface explained 60% of the variation in sediments Hg concentrations.
Abstract: Surficial sediments were sampled with a light-weight gravity corer at 175 sites in 73 Ontario and Quebec lakes and zooplankton was collected with a 225 μm mesh size net in 24 lakes. Hg concentrations in surficial sediments (0–2 cm) ranged from 3 to 267 ng g−1 dry weight with a mean of 80 ng g−1 dry weight for all sites. A regression model including organic content of sediments and the ratio of the catchment area/lake surface explained 60% of the variation in sediments Hg concentrations. Hg in zooplankton ranged from about 25 to 377 ng g−1 dw with a mean of 108 ng g−1 dw and was weakly correlated with catchment area, primary productivity and TOC. Our data indicate that an important fraction of Hg originates from the catchments, but do not show a clear west-east regional gradient for Hg concentrations in surficial sediments or in zooplankton.

Journal ArticleDOI
TL;DR: In this paper, an anion exchange technique has been developed and used to study the chemical speciation of radionuclides in a contaminant plume originating from an infiltration pit used for managing low-level wastes.

Journal ArticleDOI
TL;DR: Pebble bed ceramic breeders have been under development in Canada for over ten years as mentioned in this paper, with the main focus on 1.2 mm diameter Li2ZrO3 and Li2TiO3 pebbles.

Journal ArticleDOI
TL;DR: They are suited for reforestation programs in Zaire and other tropical countries sharing similar biogeoclimatic conditions and additional genetic gains in growth and wood density could be obtained through selection and breeding of superior individuals from these provenances.

Journal ArticleDOI
TL;DR: In this article, the effects of organic horizon removal, ashes, soil water, and shade on jack pine (Pinus banksiana Lamb) seedling emergence were investigated. But they did not consider the effect of weeds.
Abstract: The effects of organic horizon removal, ashes, soil water, and shade on jack pine (Pinus banksiana Lamb) seedling emergence were investigated. For this purpose soil monoliths were taken to the laboratory and received prescribed burning, leading to 100%, 75%, 50%, 25%, and 0% organic horizon removal. One half of each monolith contained ashes generated from burning whereas the other half was kept ash-free. Each half of every monolith was sown with jack pine seeds and the monoliths were then watered under four watering schedules (100%, 75%, 50%, and 25% of the regional average daily June rainfall) or shaded under four shading levels (100%, 75%, 50%, and 25% photosynthetically active radiation). Seedling emergence was most successful under high watering schedules, increased depth of burn, high shading, and without ashes. Ash had an inhibitory effect on seedling emergence.

Journal ArticleDOI
TL;DR: In this paper, a rotational band based on a two-quasineutron (h 11 2 ) 2 configuration was observed from its 10+ bandhead to spin 28 Ħ.

Journal ArticleDOI
TL;DR: It is shown that the [Delta][ital I]=2 staggering effect recently discovered in superdeformed rotational bands could be explained by a phenomenological theory of [ital C][sub 4[ital v]] bifurcation.
Abstract: It is shown that the \ensuremath{\Delta}I=2 staggering effect recently discovered in superdeformed rotational bands could be explained by a phenomenological theory of ${\mathit{C}}_{4\mathit{v}}$ bifurcation. In this scenario, the energy staggering is associated with the alignment of the total nuclear angular momentum along the axis perpendicular to the long deformation axis of the prolate nucleus.