Showing papers by "Atomic Energy of Canada Limited published in 1970"

A rapid reading technique for nuclear particle damage tracks in thin foils

Abstract: The low background of damage track detectors allows them to measure low integrated fluxes of charged particles or neutrons. When good statistical accuracy is desired, the long times required for visual track counting under the microscope may seriously limit the number of measurements, particularly when the track density is low. A technique has been developed for automatically counting etched tracks that pass through a thin film. Very simple and inexpensive equipment is required. The insulating film is placed between a plane, high-voltage electrode and a thin layer of Al. A spark, passing through the film along a damage track, evaporates a hole in the Al. A second spark is prevented from starting through the same hole, so that the discharge passes successively along each track and then stops. Sparks are counted with a scaler. The pattern of holes in the Al provides a visible replica of the pattern of tracks. Track densities from background level to 3000 tracks/cm2 can be measured. Areas up to 100 ...

The diffusion of iron in aluminium

Abstract: The diffusion of radioactive 59Fe has been measured in both single crystals and polycrystalline specimens of aluminium in the temperature range 520 to 660°c. The material for the diffusion samples was between 99·99 and 99·999% pure aluminium. The temperature dependence of the diffusion coefficient for single crystal specimens could be expressed by in the temperature range 580 to 660°c. The results are not in agreement with values previously published for this system by Hirano, Agarwala and Cohen (1962). The earlier results are thought to be in error as a result of tracer hold-up at the surface-oxide film on the aluminium specimens. This effect was overcome in the present work by implanting the 59Fe tracer atoms below the surface-oxide layers using a 40 kev 59Fe ion beam. Analysis of the data indicates the activation energy for diffusion is dominated by an iron-vacancy repulsive interaction term. Calculations of the difference between the activation energies for self and solute diffusion in alumin...

Presence of nucleoside triphosphate phosphohydrolase activity in purified virions of reovirus.

Abstract: A nucleoside triphosphate phosphohydrolase activity has been discovered in reovirus virions. This activity converts nucleoside triphosphates to nucleoside diphosphates in vitro. Properties of this enzyme are presented, with evidence that this activity is an integral part of the virion core.

Crystal Dynamics and the Ferroelectric Phase Transition of Sodium Nitrite

Abstract: The crystal dynamics of sodium nitrite has been studied by coherent neutron inelastic scattering techniques. The normal modes of vibration propagating along the three principal symmetry axes in the crystal at 296°K have been measured. The results have been used to find the parameters of rigid ion models for NaNO 2 in which the NO 2 ion was treated as a group. Although none of the models are entirely satisfactory they do give a fair description of the results. The temperature dependence of the frequencies of some of the normal modes was measured and none were found to be very temperature dependent near the ferroelectric transition. Ferroelectric critical scattering was observed which was quasi-elastic showing that the ferroelectric fluctuations change slowly compared with the frequencies of almost all the normal modes of vibration. A model is deduced for the ferroelectric fluctuations incorporating the motion of the atoms but it is found that the motion of the atoms in these fluctuations cannot be describe...

Ferroelectric Transition in K D 2 P O 4

Abstract: The ferroelectric transition in K${\mathrm{D}}_{2}$P${\mathrm{O}}_{4}$ has been investigated both experimentally and theoretically. Coherent neutron scattering by fluctuations associated with the transition was studied both above and below the transition temperature. None of the optic-phonon modes was found to change in frequency near the Curie temperature, in contrast with materials such as SrTi${\mathrm{O}}_{3}$. The ferroelectric fluctuations gave rise to quasi-elastic scattering, increasing in intensity as the transition was approached. The intensity distribution showed that the pattern of displacement of the atoms in these fluctuations was similar to that which relates the crystal structures of K${\mathrm{H}}_{2}$P${\mathrm{O}}_{4}$ above and below the transition temperature. It was found that the macroscopic electric field plays a large part in determining the probability distribution of the fluctuations. The results have been analysed in terms of an Ising model with one "spin" per unit cell. The intensity of the scattering is shown to be consistent with a relation connecting the dielectric and scattering properties. The implications of these results for the theory of ferroelectricity in K${\mathrm{H}}_{2}$P${\mathrm{O}}_{4}$ and K${\mathrm{D}}_{2}$P${\mathrm{O}}_{4}$ are discussed.

Intermolecular dynamics of hexamethylenetetramine

Abstract: The technique of coherent inelastic neutron scattering has been used to measure the dis-persion curves of intermolecular modes propagating along various high symmetry directions in the organic molecular crystal deuterated hexamethylenetetramine, at 100 and 298 K. The results are analysed in terms of phenomenological models involving interactions between supposedly rigid molecules. Interactions with both first and second nearest-neighbour molecules are found to be necessary for an adequate description. A simplified five-parameter model, which assumes centrosymmetric molecules, provides almost as good a fit to the results as that given by a generalized twelve-parameter model. Group theory shows that the effects of assuming centrosymmetry may be significant in the [££0] or E direction. Assuming that the replacement of deuterium by hydrogen does not change the intermolecular forces, the frequency distribution of function and the heat capacity of hydrogenous hexamethylenetetramine are calculated. The agreement between the computed and measured heat capacities is good. The frequency distribution function shows many obvious critical points and other singular features. The existence of logarithmically infinite singularities in this function is investigated. The elastic constants computed from the force models show discrepancies from those measured ultrasonically, and these discrepancies are thought to be significant. The long wavelength optical librational frequency measured in the present work differs considerably from that deduced from optical measurements, and an explanation of this apparent discrepancy is suggested. The 2 % hydrogen content in the specimen results in the presence of hydrogenous 9defect’ molecules, and the effects of these on the normal vibrations of the host lattice are shown to be very small.

Dislocation movement and slip systems in ?-SiC

Abstract: Plastic-carbon replicas taken off the fracture surfaces of self-bonded SiC were found to have transparent flakes ofβ-SiC attached. Certain of the flakes contained dislocations which were shown to have moved during the fracture process. The dislocations were shown to move on a {111} slip plane and to have a Burgers vectora/2 〈110〉.

Influence of crystalline defects on 2-beam crystal lattice images-Experimental

Abstract: Of particular interest in the study of crystal lattice imperfections are the magnitude and extent of their influence on atornic structure. In the present work two-beam crystal lattice images have been used to examine directly the perturbing influence of Guinier-Preston zones in Al-4% Cu, damaged regions in neutron irradiated Ge and dislocations in deformed and partially crystallized Ge. The 2–02 A; spacing of (200) planes was resolved in Al-4% Cu while the 3–26 A spacing of (111) planes was resolved in the Ge specimens. The crystal lattice images were obtained using a high vacuum, short focal length (2.1 mm) Siemen's Elmiskop 1 operated at 100 kv with pointed filaments and thin film objective apertures. The experimental observations reveal: (1) that the G.P. [1] zones are coherent with the matrix (200) planes and produce an observable tensile distortion out to ∼ 20 A on either side of its centre; (2) that when a damaged region in Ge has a size equal to the foil thickness, then the lattice image d...

Phonon Frequencies in NaBr

Abstract: The frequencies of phonons in NaBr at 295\ifmmode^\circ\else\textdegree\fi{}K propagating along the [001], [110], and [111] directions have been obtained from measurements of slow-neutron scattering made with a time-of-flight spectrometer and with a triple-axis spectrometer. The results have been fitted by least-squares techniques to both rigid-shell and deformable-shell models. The most satisfactory fit is obtained using a rigid-shell model with six disposable parameters and no second-neighbor force constants. Frequencies given by a variety of models with parameters determined by macroscopic constants are compared with the measured frequencies, and the effect of using zero-sound elastic constants is examined. The agreement is comparable to that found in other polarizable alkali halides. Finally, the frequency distribution at room temperature is obtained, and the temperature dependence of the specific heat and of the reduced moments are calculated with allowance for temperature-dependent quasiharmonic frequencies.

Studies on cocurrent gas‐liquid flow in helically coiled tubes. II. Theory and experiments on turbulent mass transfer with and without chemical reaction

Abstract: Pure carbon dioxide was absorbed into distilled water and sodium hydroxide solution, in cocurrent two phase annular flow in helically coiled tubes in order to measure physical and chemical mass transfer coefficients and interfacial areas. (k*La) was correlated by the pressure drop in the test sections and interfacial areas were found to vary with the liquid phase energy dissipation. According to a new theory, (k*L) has been shown to be a function of the root mean square vorticity near the interface. The root mean square vorticity has been related to the pressure drop, gas density, liquid flow rate and liquid velocity. The physical mass transfer coefficients theoretically predicted are in good agreement with experimental results. On a fait absorber de l'anhydride carbonique pur par de l'eau distillee et une solution de soude caustique, dans un ecoulement annulaire et parallele a deux phases dans des tubes enroules en forme d'helice, afin de mesurer les coefficients de transfert de masse (physique et chimique) et les surfaces interfacilales. On a etabli la valeur de par la chute de pressiou dans les sections etudiees et trouve que les surfaces interfaciales variaient avec la perte d'energie de la phase liquide. On a montre dans une nouvelle theorie que etait fonction de la racine carree moyenne du tourbillonnement pres de l'interface, laquelle a une relation avec la chute de pression et la densite du gaz ainsi qu'avec le debit et la velocite du liquide. Les coefficients de transfert physique de masse qu'on a predits theoriquement concordent bien avec les resultats experimentaux.

Long-Wavelength Phonons in Liquid Helium

Abstract: High-resolution neutron-scattering measurements have been made of long-wavelength-phonon energies $\ensuremath{\hbar}\ensuremath{\omega}$ in liquid helium at 1.1 \ifmmode^\circ\else\textdegree\fi{}K as a function of wave vector $Q$. The results are approximately described by $\ensuremath{\omega}=cQ(1\ensuremath{-}\ensuremath{\gamma}{\ensuremath{\hbar}}^{2}{Q}^{2}\ensuremath{-}\ensuremath{\delta}{\ensuremath{\hbar}}^{4}{Q}^{4})$, with $\ensuremath{\gamma}$ very small (2\ifmmode\times\else\texttimes\fi{}${10}^{36}$ ${\mathrm{g}}^{\ensuremath{-}2}$ ${\mathrm{cm}}^{\ensuremath{-}2}$ ${\mathrm{sec}}^{2}$) and $\ensuremath{\delta}=(2.4\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}{10}^{75}$ ${\mathrm{g}}^{\ensuremath{-}4}$ ${\mathrm{cm}}^{\ensuremath{-}4}$ ${\mathrm{sec}}^{4}$.

Calcium and Strontium Discrimination by Aquatic Plants

Abstract: Sr/Ca ratios are given for 22 species of aquatic plants from Perch Lake, Ontario. When compared with the lake water, 16 species are found to discriminate against calcium relative to strontium. Consequently, these species introduce a strontium enrichment step into any food chain in which they participate. One species (Nymphaea odorata) however, shows a remarkable discrimination against strontium. See full-text article at JSTOR