Showing papers by "Chalk River Laboratories published in 1988"

A Study of the Relation of Meteorological Variables to Monthly Provincial Area Burned by Wildfire in Canada (1953–80)

Abstract: The relation between meteorological variables and the monthly area burned by wildfire from May to August 1953–80 in nine Canadian “provinces” was investigated. A purely statistical approach to estimating the monthly provincial area burned, using meteorological variables as predictors, succeeded in explaining 30% of the variance west of Lake Nipigon and about 11% east of Lake Nipigon. Long sequences of days with less than 1.5 mm of rain or days with relative humidities less than 60% proved to have the highest correlation with area burned. These long sequences were assumed to be associated with blocking highs in the westerlies. Bad fire months were independent of rainfall amount but significantly dependent on rainfall frequency, temperature, and relative humidity.

Handbook of Record Linkage: Methods for Health and Statistical Studies, Administration, and Business

Abstract: Introduction. Part 1 The basics and their application: including probabilistic linkage, betting odds and frequency ratios, using "global" and "specific" discriminating powers. Part 2 Exploiting more of the discriminating power: including what to do with missing identifiers, comparing names, years of birth, places of birth, geographical identifiers and marital status, linked and unlinkable pairs, some pitfalls. Part 3 Saving central processor time: including blocking the files, the preliminary rejections, the comparison sequence and its early cut-off, the application of value-specific discriminating powers. Part 4 Organizing the product: including calculating absolute versus relative odds, setting an "optimum" threshold, grouping the matched pairs. Part 5 Recapitulation and further thoughts. Appendices: A - definitions. B - derivations. C - typical identifier frequencies. D - linking special disease registers. E - errors, their sources and magnitudes. F - calculating the outcome frequencies for a non-existent file of unlinkable pairs. G - constructing a file of randomly matched unlinkable pairs. H - details of phonetic coding systems for names. I - design of a computer linkage system. Bibliography. Index.

Allozyme variation within and among mature populations of speckled alder (alnus rugosa) and relationships with green alder (a. crispa)

Abstract: Vegetative tissues from 14 sexually mature populations of speckled alder (Alnus rugosa (Du Roi) Sprengel) in Quebec have been analyzed for electrophoretically demonstrable variation in 9 enzymes encoding a total of 15 loci. Speckled alder demonstrated a diploid-like expression for all polymorphic loci investigated. Populations were in Hardy-Weinberg equilibrium for the 9 polymorphic loci observed. The total expected heterozygosity was 0.173. Analysis of fixation indices indicated a slight deficiency of heterozygotes, relative to panmictic expectations. This was likely due to weak population differentiation, which did not follow any particular geographical trend. Qualitative estimates of interpopulation rates of gene flow were high, and in good agreement with the small pair-wise population genetic distances and among-population fixation index. Levels of genetic diversity and partition of this diversity were similar to previous observations obtained with the sympatric species A. crispa (Ait.) Pursh. However, no phenomena of interspecific hybridization were noted. The average genetic distance between these two alder species was large, with a value of 0.4, emphasizing the different ecological niches colonized by each of the two species. The estimate of divergence time between these two taxa was two million years. It is in agreement with the hypothesis of repetitive spatial isolation of each species in ice-free refugia during the Pleistocene, thus promoting their reproductive isolation. The interspecific divergence noted at the enzyme level allowed for the easy electrophoretic identification

Chiral Model of the Nucleon and $\Delta$ Isobar: The Coherent Pair Approximation

Abstract: The linear chiral \ensuremath{\sigma} model with quark fields and elementary pion and \ensuremath{\sigma} fields is used to describe static properties of the nucleon and the \ensuremath{\Delta} resonance. To this end baryon Fock states with good spin and isospin are constructed from summations of components in which three quarks in s states with the SU(2)\ifmmode\times\else\texttimes\fi{}SU(2) quantum numbers of the nucleon and \ensuremath{\Delta} are coupled to multipion states and a scalar-isoscalar coherent state of the \ensuremath{\sigma} fields. The multipion states are constructed to have coherent properties as well as definite spin-isospin quantum numbers. Ignoring the effects of vacuum polarization the baryon energy is made stationary, resulting in a set of four coupled nonlinear eigenvalue equations and a diagonalization procedure between frozen fields. The corresponding solitonic solutions are used to evaluate the relevant nucleon properties. A comparison is made with the results from the cloudy-bag model, the projected mean-field chiral-soliton model, and the Skyrme approach.

Impact on radiogenic cancer risk of persons exhibiting abnormal sensitivity to ionizing radiation.

Abstract: Human genotypes are known “that confer both increased susceptibility or resistance to DNA damage and increased cancer risk after exposure to carcinogenic agents, including ionizing radiation” (NAS 1980). The existence of sensitive subgroups at elevated risk, if they are of appreciable size, could have significant impact on the actual distribution of risk. The radiosensitive disorder ataxia-telangiectasia (A-T) serves as a good example: the significant “at risk” group, A-T heterozygotes, is estimated to comprise between 0.5% and 5% of the total population, and has a twofold elevated lifetime risk of fatal neoplasia. Other genetic syndromes that manifest abnormal radiosensitivity are also known, but no estimates are available for the population frequency of all such phenotypes, or for their overall degree of increased risk. As the first part of a program addressing these questions, we have developed a rapid and inexpensive assay for screening members of the general population for abnormal radiosensitivity; such persons would be regarded as at presumptive elevated risk of radiogenic cancer. Our method utilizes lymphoblastoid cell lines and chronic as opposed to acute gamma-ray exposure to amplify the difference between normal and somewhat sensitive strains. A simple “grow-back” assay assesses the survival response. Information on the extent of natural variation in inherited suscepribility to radiogenic cancers could be most useful for radiation protection in the future.

Does a point lie inside a polygon

Abstract: A superficially simple problem in computational geometry is that of determining whether a query point P lies in the interior of a polygon if it lies in the polygon's plane. Answering this question is often required when tracking particles in a Monte Carlo program; it is asked frequently and an efficient algorithm is crucial. Littlefield has recently rediscovered Shimrat's algorithm, while in separate works, Wooff, Preparata and Shamos and Mehlhorn, as well as Yamaguchi, give other algorithms. A practical algorithm answering this question when the polygon's plane is skewed in space is not immediately evident from most of these methods. Additionally, all but one fails when two sides extend to infinity (open polygons). In this paper the author review the above methods and present a new, efficient algorithm, valid for all convex polygons, open or closed, and topologically connected in n-dimensional space (n {ge} 2).

Effect of analytical method on thickness measurements of thin oxide films

Abstract: The thickness of thin natural oxide films formed on silicon, nickel, aluminium, iron, tantalum and zirconium has been measured using nuclear reaction analysis (NRA) and Auger electron spectroscopy (AES) in combination with ion beam sputtering. It is shown that ion beam effects severely limit the use of AES and ion beam sputtering in measuring thin oxide thicknesses. Relatively non-destructive techniques such as NRA or angle-resolved x-ray photoelectron spectroscopy (XPS) provide more reliable information.

193 Ir Mössbauer study of bimetallic platinum-iridium catalysts

Abstract: Using the 73.0 keV Mossbauer resonance in193Ir, the chemical form of iridium in bimetallic Pt−Ir catalysts supported on amorphous silica has been determined after ionic co-exchange, calcination and reduction in hydrogen. The compositions of the highly dispersed bimetallic Pt1−xIrx clusters as determined from the measured isomer shifts reveal a strong tendency for segregation of iridium and platinum.

Measuring contaminant transport rates between water and sediments using limnocorrals

Abstract: Radiotracers injected as soluble salts into ≈1.2 m3 limnocorrals in a shallow dystrophic lake were transported rapidly (2 to 12% d−1) from the water to the bottom sediments. Removal rates of most contaminants declined after ≈14 days. Tracers were removed from the water much more rapidly than stable element analogs present naturally. After 3 weeks Am, Co, Ra, Hg, Sn and Fe activities on the enclosure walls were greater than 15% of the activity in the water. However, activity on the walls was a small fraction (< 6%) of the total amount of tracer injected. Particle fluxes inside the corrals were lower and much less variable than those measured outside. This difference appears to result from greater resuspension of bottom sediments in the lake than in the enclosures. Both particle-bound and soluble tracers were measured in cores of bottom sediments. Tracer sorption onto particles, diffusion into the bottom sediments, and uptake on the plastic enclosure walls were rapid and reversible. Tracer kinetics were very reproducible in replicate enclosures, providing a simple, experimental system in which limnological conditions can be manipulated. Loss rates and distributions of stable isotopes and radioisotopes can be used to develop and test a general model of element transport applicable to both short and long term analyses.

Control of microstructure to increase the tolerance of zirconium alloys to hydride cracking

Abstract: The microstructure of Zr-2.5 Nb has been altered in three ways in attempts to increase the alloy's tolerance to delayed hydride cracking, namely: - breaking up the β-phase reduces diffusivity of hydrogen and decreases crack velocity, - a gettering element (yttrium) reduces susceptibility to cracking although the yttrium alloy has low toughness and poor corrosion resistance, and - reducing the number of basal plane normals in the main stressing direction improves resistance to crack growth.

Measurements of the differential cross sections for recoil tritons in 4He−3T scattering at energies between 0.5 and 2.5 MeV

Abstract: Differential cross-sections for recoil detection of tritons from elastic scattering of α-particles on tritium were measured at forward recoil angles from 10° and 40° and over incident 4 He energies ranging from 0.5 to 2.5 MeV. Thin solid state targets consisted of about 10 16 T at. cm 2 either absorbed in a thin film of titanium or implanted at low energy in the matrix of amorphous silicon. The recoil yields were normalized against the yields of the T(d, α)n reaction measured on the same targets. It is found that the cross sections obtained are considerably enhanced as compared to the Rutherford recoil cross section, what can be attributed to the combined effect of Coulomb and nuclear potentials and formation of compound 7 Li nuclei. The applications of the elastic recoil detection as a means for depth profiling of tritium in materials are briefly considered. The measured dependence of the triton recoil cross section on the incident energy of 4 He + ions allows profiling the concentration of tritium across a range ∼ l μ m below the surface of solids.

Corrosion response of nuclear reactor materials to mixtures of decontamination reagents

Abstract: An experimental study of the corrosiveness of mixtures of citric acid, oxalic acid, and EDTA to nuclear reactor materials was undertaken. Specimens of type 304 stainless steel (SS), type 410 SS, carbon steel (CS) 1018 and A508, and heat-treated alloy 600 were suspended in recirculating mixtures of two or more combinations of citric acid, oxalic acid, and EDTA at temperatures of 90 C or 117 C for 22 hours. The results suggest that removal of oxalic acid from decontamination solutions should lower the corrosiveness of the solutions to nuclear reactor materials, particularly types 304 SS and 410 SS.

Magnetic correlations in La2NiO4+δ and La2-xSrxCuO4

Abstract: Neutron scattering and muon spin relaxation studies of some materials related to high-T c superconductors are described. For La 2− x Sr x Cu O 4 with x as large as 0.05, our data indicate spin glass greezing with a frozen local moment of the same size as in the nominally pure(x=0) antiferromagnet. Magnetic fluctuations similar to those for La 2 Cu O 4 are found for La 2 Ni O 4 , which thus far has not been shown to be the parent compound of a superconductor.

Fracture control using elastic-plastic fracture mechanics

Abstract: Fracture control is the prevention of failure in engineering structures due to crack propagation. It requires a thorough knowledge of the susceptibility of the structural material to all pertinent crack growth mechanisms, an ability to determine critical crack sizes in the structure and the ability to detect, through inspection, flaws which develop in service. Established Engineering codes governing failure by unstable crack propagation in metallic structural components are biased mainly towards preventing brittle cleavage crack propagation in ferritic steels. The near future should see new procedures established for more ductile materials based on the emerging understanding of sub-critical crack growth mechanisms and the development of elastic-plastic instability assessment procedures. This paper describes the philosophy of fracture control by using quantitative data on crack growth behavior combined with state-of-the-art methodologies for instability assessment.