Atomic Energy of Canada Limited

About: Atomic Energy of Canada Limited is a company organization based out in Ottawa, Ontario, Canada. It is known for research contribution in the topics: Neutron & Zirconium alloy. The organization has 4845 authors who have published 4826 publications receiving 102951 citations.

Temperature dependence of S(Q, omega ) in liquid 4He under pressure.

Abstract: The temperature dependence of the dynamic form factor, S(Q,\ensuremath{\omega}), of liquid $^{4}\mathrm{He}$ at p=20 bars has been determined by inelastic neutron scattering measurements. Two wave vectors, Q=1.13 A${\r{}}^{\mathrm{\ensuremath{-}}1}$ and Q=2.03 A${\r{}}^{\mathrm{\ensuremath{-}}1}$, corresponding to the maxon and roton regions of the phonon-roton dispersion curve, were studied over a wide range of energy transfer, \ensuremath{\Elzxh}\ensuremath{\omega}. Based on previous data at SVP, Woods and Svensson proposed that S(Q,\ensuremath{\omega}) could be represented as a sum of two components, one proportional to the superfluid density, ${\ensuremath{\rho}}_{S}$(T), and one proportional to the normal density ${\ensuremath{\rho}}_{N}$(T). The component proportional to ${\ensuremath{\rho}}_{S}$(T) contained the sharp one-phonon peak which vanished at T=${T}_{\ensuremath{\lambda}}$. The aim here is, firstly, to present data on the temperature dependence of S(Q,\ensuremath{\omega}) at 20 bars and, secondly, to explore whether or not the Woods-Svensson decomposition of S(Q,\ensuremath{\omega}) holds at higher pressure. At 20 bars and for the Q values investigated here, we find that the sharp peak of S(Q,\ensuremath{\omega}) does indeed decrease rapidly in intensity as T increases and the corresponding excitation either vanishes or changes abruptly in character at ${T}_{\ensuremath{\lambda}}$.The sharp nature of the one-phonon peak ${T}_{\ensuremath{\lambda}}$ does therefore appear to be associated with superfluidity or a Bose condensate at these Q values. However, the weight of the one-phonon peak does not scale as ${\ensuremath{\rho}}_{S}$(T) and subtracting a contribution proportional to ${\ensuremath{\rho}}_{N}$(T) from S(Q,\ensuremath{\omega}) leads to negative values of the superfluid component of S(Q,\ensuremath{\omega}) at low \ensuremath{\omega}. Thus S(Q,\ensuremath{\omega}) at 20 bars does not naturally separate into a part proportional to ${\ensuremath{\rho}}_{S}$ and one proportional to ${\ensuremath{\rho}}_{N}$. We also explore the consequences of a simple subtraction of the multiphonon component, assumed temperature independent, as an alternative method of extracting one-phonon parameters from the total scattering intensity. The values of the one-phonon properties such as the frequency and the lifetime obtained by the simple multiphonon subtraction method also show a marked change at ${T}_{\ensuremath{\lambda}}$.

Contaminant Enrichment and Properties of Soil Adhering to Skin

Abstract: The adhesion of contaminated soil to skin has potentially important health implications, because the contaminants may ultimately be ingested or absorbed through the skin. Previous studies indicated that the adhering soil is enriched in contaminant concentration relative In the original soil because of the selective adhesion of finer particles. This study investigated this enrichment using 11 markedly different soils. Two sandy soils consistently gave very high contaminant enrichment ratios, with a mean enrichment of 10-fold. The other soils all had enrichment ratios above unity. Scanning electron microscopy illustrated the potential for strong adhesion of very fine clay particles. The contaminant enrichment ratios were positively correlated to enrichments in specific surface area, organic matter content, and extractable Fe content. Correlations to soil textural properties and detailed particle-size analysis of the adhering soil indicated that 50 to 100 {mu}m may be a critical particle size: larger grains and aggregates do not adhere readily to skin. Because of this, enrichment ratios will vary positively with the proportion of particles in the whole soil that am greater than 50 {mu}m. A simple model is provided to predict enrichments using information from routine soil particle-size analysis. 44 refs., 4 figs., 4 tabs.