Showing papers by "Chalk River Laboratories published in 1990"
TL;DR: In this article, a high-pressure neutron diffraction study of the deuterated H(D)-ordering material PbDPO4 was carried out and it was shown that much, and possibly all, of the increase in Tc on deuteration is attributable to the accompanying changes in the hydrogen-bond dimensions.
Abstract: IT has long been known that the substitution of deuterium for hydrogen in hydrogen-bonded materials can lead to a change in the geometry of the hydrogen bonds—the so-called Ubbelohde effect1. There can also be significant accompanying changes in the physical properties of the material. Among the most striking examples is the increase in the transition temperature, Tc, of hydrogen-ordering systems of the KH2PO4 type by >100K on full deuteration. In all of these systems, Tc decreases under pressure, making it possible in principle to compare protonated and deuterated forms at the same Tc by applying pressure to the latter. Here we report the results of a high-pressure neutron diffraction study of the deuterated H(D)-ordering material PbDPO4. We find that much, and possibly all, of the increase in Tc on deuteration is attributable to the accompanying changes in the hydrogen-bond dimensions. This suggests that purely mass-dependent effects on the quantum-mechanical tunnelling between the equivalent H(D) potential minima—an explanation that has been favoured previously—have little or no direct influence on Tc. Substantial revisions to the theory of this type of ordering transition are apparently required.
115 citations
TL;DR: In this article, the authors measured soil respiration in immature aspen (Populus tremuloides Michx. and P. grandidentata Michx.) ecosystems of eastern Ontario subjected to cutting and burning treatments in relation to vernal leaf flush.
114 citations
15 Mar 1990-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this paper, the first use of a polarized 3 He spin filter to polarize epithermal neutrons was reported and the 3 He was polarized to 70% by spin exchange with optically pumped Rb vapor and had a cross sectional area of 0.65 cm 2 and a thickness of 3 × 10 20 atoms cm −2 of 3 He.
Abstract: We report the first use of a polarized 3 He spin filter to polarize epithermal neutrons. The 3 He was polarized to 70% by spin exchange with optically pumped Rb vapor and had a cross sectional area of 0.65 cm 2 and a thickness of 3 × 10 20 atoms cm −2 of 3 He. Neutron polarization up to 20% at 0.734 eV was produced in an epithermal neutron beam at the Los Alamos Neutron Scattering Center and measured by observing the change in neutron transmission produced by the 3 He polarization and also the helicity dependent transmission for a parity-nonconserving resonance in 139 La.
66 citations
TL;DR: The growth of all five ectomycorrhizal fungi was significantly reduced when subjected to concentrations above 50 μl formulation litre−1 (glyphosate) or 50 μg formulation Litre−2 (hexazinone).
Abstract: The effects of two herbicides, glyphosate (as a 359 g litre−1 SL) and hexazinone (as a 50gkg−1 granule) on soil microbial population, carbon dioxide evolution, and in-vitro growth of five species of ectomycorrhizal fungi were investigated. Glyphosate at 0–54 and 3.23 kg a.i. ha−1 and hexazinone at 1. 2 and 8 kg a.i. ha−1 did not reduce soil microbial population or carbon dioxide evolution in the long term (6 months). However, there was a significant short-term (2 months) effect of glyphosate on both fungal and bacterial counts at the 0.54 kg ha−1 treatment. In in-vitro tests, Cenococcum graniforme. Hebeloma crustuliniforme and Laccaria laccata were more susceptible to both herbicides than was Suillus tomentosus. which was, in turn, more susceptible than Paxillus involutus. The growth of all five ectomycorrhizal fungi was significantly reduced when subjected to concentrations above 50 μl formulation litre−1 (glyphosate) or 50 μg formulation litre−1 (hexazinone).
54 citations
TL;DR: Despite the changes in environmental conditions during the plantation establishment period, the ability of trees to successfully adjust to environmental stress increased from the first growing-season to the second.
47 citations
TL;DR: Survival and early growth and yield of Salix alba L. over two successive 2‐year rotations were evaluated under nursery conditions that included irrigation during the first growing season.
Abstract: Survival and early growth and yield of Salix alba L. over two successive 2‐year rotations were evaluated under nursery conditions that included irrigation during the first growing season. A six‐yea...
45 citations
TL;DR: In this paper, field and laboratory incubations were used to assess nitrogenase (acetylene reduction) activity, nitrogen mineralization and respiration in three mature forests in the northern hardwoods.
Abstract: Field and laboratory incubations were used to assess nitrogenase (acetylene reduction) activity, nitrogen mineralization and respiration in three mature forests in the northern hardwoods—boreal transition zone of eastern North America. A 66-yr-old jack pine (Pinus banksiana Lamb.) forest had 45.41 ha−1 of forest floor, ca 33% more than older mixedwood and hardwood forests in the same vicinity. Jack pine forest floor was more acid, mineralized only one-third as much N and half as much C during laboratory incubations, had little or no nitrogenase activity on eight sampling dates during the growing season, and contained 40- to 70-fold lower numbers of N2-fixing bacteria. Low nutrient turnover in older jack pine stands may result in buildup of surface organic horizons and declining tree growth. At the moister hardwood site, temperature variations largely accounted for seasonal trends in C2H2 reduction: activity at the drier mixedwood site increased following rainfall events. Although asymbiotic N2 fixation in surface soils is a small N input (< 1 kg ha−1 yr−1) compared to precipitation in these more productive northern forests, it may stimulate litter decay and N dynamics.
34 citations
TL;DR: On the upland site, the mature trees were more inbred, possibly due to the conditions under which regeneration occurred and because of weak selective pressure, while on the lowland site, clustering of similar genotypes was detectable on a local scale but the mature Trees were not inbred.
Abstract: Several hundred dominant and co-dominant individuals in two populations of black spruce, located within 2 km of each other and representing upland and lowland site types, were sampled and mapped. Multilocus isozyme genotypes were determined and the genetic organization of the two populations examined by means of nearest-neighbour analysis and spatial autocorrelation of alleles. On the upland site type, population density was much higher and variation in age considerably less than on the lowland site type, which was interpreted as evidence for fire origin in the former. On the upland site, the mature trees were more inbred, possibly due to the conditions under which regeneration occurred and because of weak selective pressure. On the lowland site, clustering of similar genotypes was detectable on a local scale but the mature trees were not inbred. The two populations were very similar in terms of allozyme frequencies.
32 citations
TL;DR: Vegetative reproduction, above-ground biomass and nutrient pools, and litterfall and substrate nutrient conditions were evaluated in eastern Ontario immature aspen ecosystems which had been subjected to the following four treatments in relation to vernal leaf flushing: burning before; burning after; cutting before; and cutting after flushing.
25 citations
TL;DR: An algorithm is introduced for finding “economic” weights that will ensure maximum simultaneous progress in all index traits and the solutions are functions of the eigenvalues and eigenvectors of a quadratic form of the additive genetic and phenotypic covariance matrices.
Abstract: Selection indices that maximize the correlation between an individual organism's index score and its breeding value frequently require a priori known “economic” weights before the optimum phenotypic weights can be estimated. The long generation intervals and economic uncertainty that surround forest tree breeding can make the choice of weights arbitrary. In this paper an algorithm is introduced for finding “economic” weights that will ensure maximum simultaneous progress in all index traits. At the outset the traits are assumed to be of equal preference. The solutions are functions of the eigenvalues and eigenvectors of a quadratic form of the additive genetic and phenotypic covariance matrices. Examples of applications in tree breeding emphasize the practical aspects of the method.
24 citations
TL;DR: Glyphosate at 0–54 and 3–23 kg ha−1 did not reduce seedling growth or ectomycorrhizal development under greenhouse conditions and under field conditions, and there was no seedling mortality due to glyphosate treatment at either rate.
Abstract: The effects of the herbicide glyphosate [N-(phosphonomethyl)glycine]on seedling growth of Pinus resinosa and on the ectomycorrhizal development of the symbiotic fungus Paxillus involutus were investigated under greenhouse and field conditions. Glyphosate at 0–54 and 3–23 kg ha−1 did not reduce seedling growth or ectomycorrhizal development under greenhouse conditions. There was no seedling mortality due to glyphosate treatment at either rate. Under field conditions, seedling growth of P. resinosa and ectomycorrhizal development of P. involutus were not affected by the above rates. Seedlings (46–48%) failed to survive in non-glyphosate-treated plots, presumably because of weed competition, whereas all survived in glyphosate-treated plots. All the non-mycorrhizal seedlings were colonized bv indigenous mvcorrhizal fungi within 2 months after planting in both control and glyphosate-treated plots. The injection rates varied from 74–86 %.
TL;DR: In this article, a new approach for monitoring radionuclide migration in soil facilitates the determination of most of the fundamental coefficients required to model the transport process, including particle and solution transport coefficients.
TL;DR: In this paper, the ion exchange of Fe3+ with sodium in NaZSM-5 was performed with a maximum exchange level of 90% at 25°C and the subsequent exchange of the sodium for NH+4 ions was made with no loss of iron, but the thermal decomposition necessary for conversion of these ammonium ions to protons leads to reduction of Fe 3+ to Fe2+.
TL;DR: Ingestad's concept of relative addition rate was used to grow a range of seedling types, of both black and white spruce, and found that black spruce seedlings grew fastest, had significantly more root development or had a higher efficiency of nitrogen uptake when nutrients were applied at exponentially increasing amounts.
Abstract: Ingestad's concept of relative addition rate was used to grow a range of seedling types, of both black (Picea mariana) (Mill.) B.S.P.), and white spruce (Picea glauca (Moench) Voss). Seedlings were grown for about 18 weeks in styrofoam containers under greenhouse conditions, and fertilized at exponentially increasing rates of either one, two, four or six per cent per day, following a one month pretreatment period. Pretreatment consisted of applying a nutrient solution proportionally low in nitrogen, but that had a relatively high conductivity compared to the initial solutions used in the exponentially increasing fertilizer treatments. Black spruce seedlings grew fastest, had significantly more root development or had a higher efficiency of nitrogen uptake when nutrients were applied at exponentially increasing amounts. In contrast, white spruce grew more rapidly when fertilized with a constant level of fertilizer (control treatment). Biomass allocation and nitrogen concentrations in seedlings of both spec...
02 Mar 1990-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this article, precise energy and angular distributions of 8538 MeV/u Ar ions in solids are measured with the high-resolution spectrometer SPEG at GANIL.
Abstract: Precise energy and angular distributions of 8538 MeV/u Ar ions in solids are measured with the high-resolution spectrometer SPEG at GANIL The nonuniformities of the target thickness were investigated with a laser-interferometric method Stopping power, energy loss straggling, and angular scattering data are presented and compared with experimental data and theories
TL;DR: The level schemes of both nuclei have been extended to excitation energies above 18.5 MeV, with assigned spins up to 83 2 in 147 Gd and up to 46 in 148 Gd as discussed by the authors.
01 Feb 1990-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this article, the hyperfine interactions of 57 Fe ions implanted into diamond crystals that were heated to 830 K during implantation were investigated. And the authors compared the s-electron densities and electric field gradients at Fe nuclei implanted in diamond are compared with the corresponding values in other IV-group matrices and are found to correlate with the atomic volumes of the corresponding host elements.
Abstract: We investigated the hyperfine interactions of 57 Fe ions implanted into diamond crystals that were heated to 830 K during implantation. The implantation of radioactive parent 57 Co ions was performed to a fluence of 2 × 10 13 ions/cm 2 , using the 50 kV isotope separator. The Mossbauer emission spectra were measured in the temperature range between 4 and 300 K. using a helium flow cryostat. About 20% of the implanted ions end up in high-symmetry (HS, presumably substitutional) sites, with the remaining 80% of ions appearing in low-symmetry (LS, presumably hexagonal interstitial) sites. The HS sites are characterized by very high Debye temperature θ D ~ 1300 K and by high s-electron density characteristic for Fe 4+ (3d 4 sp 3 ) electron configuration. Impurities at LS sites exhibit a Debye temperature of 550 ± 50 K and a very large electric field gradient, V zz = 1.2 × 10 18 V cm 2 . An anomalous rise of the recoil-free factor for LS sites below 100 K was observed. This effect can be an evidence of localized jumps of interstitial impurity atoms between adjacent tetrahedral and hexagonal positions in the host lattice. The values of the s-electron densities and electric field gradients at Fe nuclei implanted in diamond are compared with the corresponding values in other IV-group matrices and are found to be correlated with the atomic volumes of the corresponding host elements.
TL;DR: In this article, the removal of radioactive and stable Fe in experimental limnocorrals was used to test different sediment-water exchange models, and the results showed that the removal rate of Fe from the water column of the lake depends on the coagulation rate of non-filterable particles into settling particles.
20 Dec 1990-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this paper, three groups of experiments were described, for objects with low, medium and high levels of radioactivity, including an examination of individual ceramic reactor-fuel (uranium dioxide) pellets, fuel samples from the Three Mile Island reactor, and a CANDU (CANada Deuterium Uraniun: registered trademark) nuclear-fuel bundle which underwent a simulated loss-of-coolant accident resulting in high-temperature damage.
Abstract: Computed tomography (CT) has been performed on a number of radioactive objects and materials. Several unique technical problems are associated with CT of radioactive specimens. These include general safety considerations, techniques to reduce background-radiation effects on CT images and selection criteria for the CT source to permit object penetration and to reveal accurate values of material density. In the present paper, three groups of experiments will be described, for objects with low, medium and high levels of radioactivity. CT studies on radioactive specimens will be presented. They include the following: (1) examination of individual ceramic reactor-fuel (uranium dioxide) pellets, (2) examination of fuel samples from the Three Mile Island reactor, (3) examination of a CANDU (CANada Deuterium Uraniun: registered trademark) nuclear-fuel bundle which underwent a simulated loss-of-coolant accident resulting in high-temperature damage and (4) examination of a PWR nuclear-reactor fuel assembly.
TL;DR: In this paper, a zirconia film was implanted at room temperature with 100 keV57Fe+ to a fluence of 8×1016 ions/cm2, and the analysis of the conversion electron Mossbauer spectra showed that iron is distributed among different charge states: Fe0 (in a form of small and large metallic iron aggregates) Fe2+ and Fe4+.
Abstract: A zirconia film was implanted at room temperature with 100 keV57Fe+ to a fluence of 8×1016 ions/cm2. The analysis of the Conversion Electron Mossbauer spectra shows that iron is distributed among different charge states: Fe0 (in a form of small and large metallic iron aggregates) Fe2+ and Fe4+. The evolution of the iron depth profile deduced from Rutherford backscattering measurements as well as the change in the charge states of iron as a function of annealing under argon atmosphere are presented.
TL;DR: In this paper, the state of iridium on Pt−Ir catalysts prepared by impregnation of amorphous silica with H2IrCl6 and H2PtCl6 was studied by193Ir Mossbauer spectroscopy after different steps of preparation.
Abstract: The state of iridium on Pt−Ir catalysts prepared by impregnation of amorphous silica with H2IrCl6 and H2PtCl6 was studied by193Ir Mossbauer spectroscopy after different steps of preparation. The Ir is adsorbed in its trivalent state, presumably as [IrCl6]3−. Calcination in air at 450°C converts this to IrO2. The metallic clusters formed by subsequent reduction in H2 at 200°C show a strong tendency towards segregation of Ir and Pt and re-oxidize partially when exposed to air at ambient temperature. In both respects the behaviour is similar to that of samples prepared by co-exchange from [Ir(NH3)5Cl]Cl2 and Pt(NH3)4Cl2. H2O.
TL;DR: In this article, the authors make a prediction for the change in lattice constants of electron-doped oxide superconductors under hydrostatic pressure expected within the theory of hole superconductivity given the observed pressure dependence of T c.
Abstract: To differentiate between different theories of high- T c superconductivity it is useful to spell out clearly their predictions before the experiments are performed. Here we make a prediction for the change in lattice constants of electron-doped oxide superconductors under hydrostatic pressure expected within the theory of hole superconductivity given the observed pressure dependence of T c .
20 Dec 1990-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this paper, analytical expressions were developed for quantitative analysis of radioactivity induced by radiation processing of products with electrons or photons, which provided reasonable estimates of induced activity much faster than Monte Carlo simulations.
Abstract: Analytic expressions are developed for quantitative analysis of radioactivity induced by radiation processing of products with electrons or photons. These expressions provide reasonable estimates of induced activity much faster than Monte Carlo simulations. Analysis of radioactivity from processing of meat with 10 MeV electrons shows an induced activity of less than 10 mBq/(kgkGy) just after irradiation. This is 4 orders of magnitude less than the natural background activity of about 100 Bq/kg found in meat. Five days after processing the induced activity will reduce by a factor of 300.
TL;DR: Cell suspensions of hybrid poplar NM1 (Populus nigra × P. maximowiczii) were used to select cells that had a higher tolerance to the active ingredient in the herbicide Roundup, and numerous cell lines were recovered that were able to grow in 10 m m glyphosate.
TL;DR: Three healthy men with psoriatic plaques unresponsive to tar, anthralin, and UVB were treated with 2450 MHz microwave heating for 30 minutes at 42 degrees C, and two patients had plaques over bony prominences.
Abstract: Three healthy men with psoriatic plaques unresponsive to tar, anthralin, and UVB were treated with 2450 MHz microwave heating for 30 minutes at 42°C. Two patients had plaques over bony prominences. Pain developed in both patients, and one had a hypotensive episode during the first treatment. The third patient, whose plaque was greater than 2 cm and was not located over a bony prominence, completed the 5 weeks of biweekly treatments with complete resolution of the plaque and no complications.
TL;DR: In this paper, the techniques employed for X-ray diffraction analysis of dislocation substructures in hexagonal close-packed metals are descibed and assessed by comparison with direct observations using transmission electron microscopy.
Abstract: The techniques employed for X-ray diffraction analysis of dislocation substructures in hexagonal close-packed metals are descibed and assessed by comparison with direct observations using transmission electron microscopy.
TL;DR: In this paper, an electrically heated, natural-convection loop was designed and constructed to investigate the thermal-hydraulics aspects of the Slowpoke-2 research reactor design, including its behaviour under extreme conditions, and measurements of the simulated core, via a variety of intrusive and nonintrusive techniques.
TL;DR: In this paper, a mathematical model based on the elasticity of isotropic materials was formulated and used to estimate the magnitude and range of stresses caused by the growth of an oxide intrusion into the substrate metal.
TL;DR: In this article, the authors combined pulse radiolysis with laser photolysis to elucidate the mechanism for energy dissipation in a high pressure Ar afterglow and showed that photolyzed states were highly excited vibrational levels of the metastable Ar 2 (O u − (I)) excimer.
TL;DR: Based on the sine-Gordon formulation of one-dimensional Coulomb gas with a relaxation length scale l 0, a simple model for the deconfinement phase transition is proposed in this article.
Abstract: Based on the sine-Gordon formulation of one-dimensional Coulomb gas with a relaxation length scale l0, a simple model for the deconfinement phase transition is proposed. The model gives a simulation of the deconfinement in the quark-antiquark system.