Showing papers by "Chalk River Laboratories published in 1993"
TL;DR: In this paper, in-situ neutron diffraction experiments on Fe-C alloys were performed to determine the lattice parameter of the austenitic and ferritic phases in a temperature region from just below to just above the bi-phasic austenite/ferrite region.
Abstract: Despite its relevance for various calculations involving phase transformations in Fe-C alloys, little information is available on the lattice parameter of austenite at elevated temperatures and its dependence on the carbon concentration. Furthermore, severe scatter exists in the literature for the lattice parameter at high temperature. Most literature data were acquired using X-ray diffraction, although neutron diffraction seems to be a more suitable technique penetrate and probe a large volume of material, the advantages of neutron diffraction over X-ray diffraction are its reduced sensitivity to surface decarbonization and improved crystal statistics (both decarbonization and grain growth can occur during diffraction experiments at high temperatures requiring long exposure times). In this work in-situ neutron diffraction experiments on Fe-C alloys were performed to determine the lattice parameter of the austenitic and ferritic phases in a temperature region from just below to just above the bi-phasic austenite/ferrite region.
213 citations
15 Nov 1993-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this paper, the high-current low-emittance microwave proton source introduced two years ago at the Chalk River Laboratories has been extensively redesigned and the 2.45 GHz microwave line was modified to incorporate a 50 kV dc break and a rectangular-to-ridged waveguide transition.
Abstract: The high-current low-emittance microwave proton source introduced two years ago act the Chalk River Laboratories has been extensively redesigned. The 2.45 GHz microwave line was modified to incorporate a 50 kV dc break and a rectangular-to-ridged waveguide transition. The layered microwave window has been replaced by a single plate of aluminum nitride. The solenoids were electrically isolated from the plasma chamber. Only the plasma chamber remains at the extraction potential. The total beam current and the proton beam current have been measured as a function of the microwave power, the hydrogen mass flow and the solenoid positions and currents. More than 95 mA dc of hydrogen ions with a proton fraction in excess of 85% were extracted from a single 2.5 mm radius aperture with only 500 W of microwave power and 2.0 sccm (3 μg/s) of hydrogen mass flow. The perveance at minimum divergence and the minimum emittance have been determined for various extraction geometries. The variation of the perveance with the aspect ratio of the extraction system was found to be virtually identical for microwave and arc discharge ion sources. The normalized rms emittance was less than 0.13 p mm mrad whatever the extraction geometry.
96 citations
TL;DR: In this paper, the authors used the vibrational energies of the Si-Si-O and Si-O bonds of tourmalines to determine the fractional fractionation factors of quartz, muscovite, illite, chlorite, and biotite.
77 citations
TL;DR: For pure hexagonal-close-packed (hcp) metals, the principal habit plane for dislocation loop nucleation is generally the most close-packed plane and this varies with c/a ratio as discussed by the authors.
77 citations
TL;DR: The Biolistic® microprojectile DNA-delivery method was used to test the usefulness in conifers of eight gene constructs based on the 35S promoter, the AMV translational enhancer, and gene fusion between the P-glucuronidase and the neomycin phosphotransferase II genes.
Abstract: The Biolistic® microprojectile DNA-delivery method was used to test the usefulness in conifers of eight gene constructs based on the 35S promoter, the AMV translational enhancer, and gene fusion between the P-glucuronidase and the neomycin phosphotransferase II genes. The evaluation was done with embryogenic cells of Picea glauca, where the relative strengths of the promoters were 35S-35S-AMVE>35S-AMVE>35S-35S>35S as evaluated by transient gene expression. The fusion gene of GUS and NPT II gave lower levels of transient gene expression than the unfused GUS gene as detected by X-GLU histochemical assays. Experiments comparing the EM promoter of wheat and the 35S-35S-AMVE promoter (with and without fusion between GUS and NPT II) were done in Picea rubens, P. mariana, P. glauca, and Larix x eurolepis. The unfused gene with the 35S-35S-AMVE promoter gave higher levels of transient gene expression than the fused GUS-NPT II gene. The fluorescent MUG assay was more sensitive than the histochemical X-GLU assay to detect the activity of the β-glucuronidase gene.
72 citations
TL;DR: The basic processes responsible for radiation-induced changes in critical cell components and their biological consequences will be discussed and current theories of aging will be examined including those involving wear-and-tear, genetic, metabolic, immunologic and biochemical factors.
54 citations
TL;DR: Results from 768,000 simulated family trials in complete randomized block designs demonstrated a serious upward bias in estimates of family variance components from multi-unit plot designs when the phenotypic observations were compatible with a first-order autoregressive (AR1) process.
Abstract: A central problem in the analysis of genetic field trials is the dichotomy of “genetic” and “environmental” effects because one cannot be defined without the other. Results from 768,000 simulated family trials in complete randomized block designs demonstrated a serious upward bias in estimates of family variance components from multi-unit plot designs when the phenotypic observations were compatible with a first-order autoregressive (AR1) process. The inflation of family variances and, thus, additive genetic variance and narrow sense individual heritabilities progressed exponentially with an increase in the nearest neighbor correlation (ϱ) in the AR1 process. Significant differences in inflation rates persisted among various plot configurations. At ϱ = 0.2 the inflation of family variances reached 48–73%. Inflation rates were independent of the level of heritability. Modified Papadakis nearest neighbor (NN) adjustment procedures were tested for their ability to remove the bias in family variances. A NN-adjustment based on Mead's coefficient of interplant interaction and one derived from Bartlett's simultaneous autoregressive scheme removed up to 97% of the bias introduced by the phenotypic correlations. NN-adjusted estimates had slightly (5–8%) higher relative errors than did unadjusted estimates.
53 citations
TL;DR: Airflow proportional counters currently under development look promising for measuring tritium-in-air in the presence of high gamma and/or noble gas backgrounds, however, these detectors are currently limited by their poor performance in humidities over 30%.
Abstract: Current methods for sampling and measuring tritium are described. Although the basic techniques have not changed significantly over the last 10 y, there have been several notable improvements in tritium measurement instrumentation. The design and quality of commercial ion-chamber-based and gas-flow-proportional-counter-based tritium monitors for tritium-in-air have improved, an indirect result of fusion-related research in the 1980s. For tritium-in-water analysis, commercial low-level liquid scintillation spectrometers capable of detecting tritium-in-water concentrations as low as 0.65 Bq L-1 for counting times of 500 min are available. The most sensitive method for tritium-in-water analysis is still 3He mass spectrometry. Concentrations as low as 0.35 mBq L-1 can be detected with current equipment. Passive tritium-oxide-in-air samplers are now being used for workplace monitoring and even in some environmental sampling applications. The reliability, convenience, and low cost of passive tritium-oxide-in-air samplers make them attractive options for many monitoring applications. Airflow proportional counters currently under development look promising for measuring tritium-in-air in the presence of high gamma and/or noble gas backgrounds. However, these detectors are currently limited by their poor performance in humidities over 30%.
52 citations
TL;DR: In this article, the spectral function for a Holstein polaron in one dimension is calculated using exact diagonalization techniques, as a function of the phonon frequency and electron-phonon coupling strength.
45 citations
TL;DR: In this paper, the nucleus 108Sn has been populated via the 54Fe(58Ni, 4p) reaction channel at a beam energy of 243 MeV, and the high-spin structure is dominated by three ΔI = 2 rotational sequences.
39 citations
TL;DR: It was concluded that RGR expressed the competitive status of stands better than AGR, and the effect of competition was to reduce the efficiency of small trees relative to large trees.
TL;DR: ESR spectrometry of sugars and biological samples is being evaluated for emergency personnel dosimetry, and sucrose and dextrose are the most sensitive and the ESR signals are proportional to X- or gamma-ray doses over the range of 0-10 Gy.
TL;DR: In this paper, a model for irradiation growth of zirconium is described, in which primary clusters formed during cascade damage are taken into account, based on the concept of "production bias".
TL;DR: In this paper, the effect of alloying additions and impurities on radiation damage in Zr-alloys has been studied using a high voltage electron microscope (HVEM) and the electron damage results have been compared with neutron damage results for the same materials.
TL;DR: In this article, the microstructure and distribution of Nb and Fe in a standard Zr-2.5Nb pressure tube alloy has been studied by analytical electron microscopy before and after irradiation.
TL;DR: In this article, a 3.6 MeV proton irradiation of annealed Zr-2.5Nb was performed to determine whether proton-irradiation will enhance the precipitation of Nb-rich β-phase precipitates within the α-grains.
TL;DR: In this article, the microstructural factors responsible for tube-to-tube variability in fracture toughness were identified and further evidence was presented which demonstrates that the variation in toughness for specimens fractured on the radial-axial plane is related to decohesion or fissuring on the transverse axial plane.
TL;DR: The vibrational densities of states in the lattice translation region below 130 cm −1 (3 THz) for structure I xenon hydrate and structure II krypton hydrates have been determined from incoherent inelastic neutron scattering experiments as mentioned in this paper.
TL;DR: Restriction fragment length polymorphisms between Larix leptolepis and Larix decidua were identified in heterologous hybridization experiments, using wheat mitochondrial DNA probes specific for atp9, coxI, nad3/rps12, and orf25.
Abstract: Restriction fragment length polymorphisms between Larix leptolepis and Larix decidua were identified in heterologous hybridization experiments, using wheat mitochondrial DNA probes specific for atp9, coxI, nad3/rps12, and orf25. Analysis of eight individuals of each reciprocal hybrid of these two species revealed that mitochondrial DNA was maternally inherited. Furthermore, sequences homologous to wheat orf25 were also identified in Larix gmelini, Larix siberica, Larix olgensis, and Larix laricina, as well as Ginkgo biloba, Picea mariana, Picea glauca and Pinus contorta.
TL;DR: In this article, the physical, chemical and biological aspects of HX corrosion were analyzed using electrochemical and surface characterization techniques, and the results indicated that microorganisms play an important role in the degradation process.
TL;DR: In this paper, the authors used the 8π γ-ray spectrometer at the Chalk River TASCC facility to study superdeformed rotational bands in the chain of isotopes 145 −149 Gd.
TL;DR: In this article, the authors measured the onset, spread and final size of the amorphous region, factoring in the Gaussian distribution of the beam, and obtained a kinetic description of amorphization in terms of dose, dose rate and temperature.
TL;DR: Elastic-neutron-scattering and magnetization measurements have been performed on a single crystal of UPd 2 Si 2 in the 12-160-K temperature range and two magnetically ordered phases are observed with the magnetic moment parallel to the c axis.
Abstract: Elastic-neutron-scattering and magnetization measurements have been performed on a single crystal of ${\mathrm{UPd}}_{2}$${\mathrm{Si}}_{2}$ in the 12--160-K temperature range. Two magnetically ordered phases are observed with the magnetic moment parallel to the c axis. At low temperatures (T108 K), there is a simple body-centered-tetragonal antiferromagnet with an ordered moment of 2.3\ifmmode\pm\else\textpm\fi{}0.3${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$. At higher temperatures (108 KT136 K), there is an incommensurate spin-density wave with wave vector q=(0,0,0.732) and magnetic moment 2.3\ifmmode\pm\else\textpm\fi{}0.3${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ at 120 K. The phase transition at 108 K is first order while there is a critical phase transition at 136 K to the paramagnetic phase with critical index \ensuremath{\beta}=0.30\ifmmode\pm\else\textpm\fi{}0.03. The low-temperature phase contains a small amount of a (0,0,2/3) phase; the maximum intensity from this phase is about 0.8% of that from the simple antiferromagnetic phases at 90 K. The magnetization in low field shows an analogous peak at 90 K.
TL;DR: In this paper, Probabilistic vault, geosphere, and biosphere models are implemented using Monte Carlo simulation techniques to trace nuclides transported in groundwater to the surface environment and humans far into the future.
TL;DR: High selectivity for separation of [sup 91]Zr from other Zr isotopes was observed during triple resonant ionization of Zr vapors, in excellent agreement with predictions derived using only geometric components of the transition dipole moment.
Abstract: High selectivity (g10) for separation of $^{91}\mathrm{Zr}$ from other Zr isotopes was observed during triple resonant ionization of Zr vapors. Linearly polarized lasers were used to prepare aligned states, from which further excitation to a presently discovered J=0 level could be suppressed for even-mass isotopes, by a suitable choice of relative laser polarization. Photoionization of the odd-mass isotope $^{91}\mathrm{Zr}$ could be retained by use of transitions with relatively strong hyperfine interactions, because of associated population redistributions in the magnetic sublevels. The dependence of the even-mass-isotope signals on relative laser polarization followed sinusoidal forms, which are in excellent agreement with predictions derived using only geometric components of the transition dipole moment. The isotopic selectivity for $^{91}\mathrm{Zr}$ can be increased by use of saturating fluences, because of the effects of saturation, population trapping in the even-mass isotopes and strong hyperfine interactions in the odd-mass isotopes. For the same reasons, biases in even:odd isotope ratio measurements cannot always be eliminated by polarization scrambling or magic angles.
TL;DR: The structures of the three phases of DBr and DI were determined using neutron powder profile techniques as mentioned in this paper, and the structure is triclinic, with space group P1.
Abstract: The structures of the three phases of DBr and DI were determined using neutron powder profile techniques. The highest temperature phases are cubic, Fm3m, with the deuteriums in twelvefold disordered positions about the halogens. The intermediate temperature phases are orthorhombic, Cmca, with the deuteriums in twofold disordered positions about the halogens in the mirror planes. In the lowest temperature phase of DBr, molecular ordering results in zigzag chains of molecules in the mirror planes of an orthorhombic structure with space group Cmc21. Molecular ordering appears in a different way in DI giving distorted diamonds (almost squares), rather than chains, and the rotational sense within the diamonds differs from one plane to the next. DI molecules are parallel or perpendicular to each other but the molecules point 6·27° away from the lines joining the iodines. the structure is triclinic, with space group P1.
TL;DR: In the inertial regime, the particle transport rate is dominated by the contribution from inertial forces for t + p ⩾ 0.02, in contrast to aerosol systems, where diffusion dominates up to T + p = 0.20.
TL;DR: In this paper, the authors measured the distribution coefficient (Kd) of 210Po and 210Pb in laboratory systems and in natural freshwater systems and observed an inverse relationship between the particle concentration of sand or lake sediment, and the distribution coefficients of210Po and210Pb.
Abstract: We have measured the distribution coefficient (Kd) of210Po and210Pb in laboratory systems and in natural freshwater systems. In the laboratory systems, an inverse relationship was observed between the particle concentration of sand or lake sediment, and the distribution coefficients of210Po and210Pb. The slope of the log-linearK
d
vs particle concentration relation is consistent with existingK
d-particle concentration theories. These laboratory observations are consistent with similar measurements in two lakes. TheK
d values of Po and Pb for the bottom sediment-pore water system with a high particle concentration were 10 to 100 times lower than those for dilute concentrations of particles suspended in the lake water. TheK
d of210Pb in the sediments was >104 so that the diffusive transport of210Pb has only a small influence on the interpretation of210Pb concentration-depth profiles and the210Pb dating of these sediments.
TL;DR: Small-angle neutron scattering was used to determine the intralamellar location of (-)-delta 8-tetrahydrocannabinol (delta 7-THC) in hydrated dipalmitoylphosphatidylcholine (DPPC) bilayers, and a Gaussian function analysis of the data indicates that the delta 8- THC molecule is significantly delocalized in the DPPC membrane in the liquid crystal phase.
TL;DR: In this paper, decay products emitted in Kr+Au collisions at 60 MeV/u have been detected with a large experimental array, and the data are compared to two fragmentation models in which fragments are emitted either sequentially or simultaneously.