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: Zirconium alloy & Neutron. The organization has 4845 authors who have published 4826 publications receiving 102951 citations.

Slow-neutron multiple scattering

Abstract: Slow-neutron scattering is perhaps the most powerful method presently available for investigating the structure and dynamics of materials on the atomic level. With relatively few exceptions it can be used to advantage for any material whether it be in the solid, liquid or gaseous state. In the past few years the importance of applying multiple-scattering corrections has come to be recognized, particularly in the case of liquids and gases for which one is interested in mapping the complete scattering function. The present article presents a review and extension of the theoretical basis for such corrections from the point of view of the Vineyard theory of multiple scattering. The theory is formulated for a sample of arbitrary size and shape and a general expression is obtained for the effective scattering function as an expansion in terms of orders of scattering (single, double, etc.). The general properties of this expansion are investigated with particular emphasis on the question of convergence ...

Normal Modes of Germanium by Neutron Spectrometry

Abstract: The frequency wave-number relations of the lattice vibrations in germanium which propagate in the symmeiric STA100! and STAlll! directions were obtained by studying energy distributions of neutrons scattered by a germanium single crystal. The characters of the phonons were ascertained from the intensities and positions of the neutron groups in the reciprocal lattice. The methods are discussed. The results cannot be fitted by simple models using the Born-von Karman theory, but explain satisfatorily the specific heat. The far- infrared spectrum of germanium can be interpreted as combination bands in terms of the results. (auth.)

Crystal Dynamics of Lead. I. Dispersion Curves at 100°K

Abstract: Frequency/wave vector $\ensuremath{ u}(\mathrm{q})$ dispersion curves for lead at 100\ifmmode^\circ\else\textdegree\fi{}K have been measured by neutron spectrometry along the lines [$\ensuremath{\zeta}00$], [$\ensuremath{\zeta}\ensuremath{\zeta}\ensuremath{\zeta}$], and [$\ensuremath{\zeta}10$] in the reduced zone. The experiments were performed with the triple-axis crystal spectrometer, making extensive use of the "constant Q" method. The results show many interesting features. The dispersion relations have local minima at the point (1,0,0), leading to extra critical points in the frequency distribution. The dispersion curves are analyzed into Fourier components (within the estimated errors), according to the equation $M{\ensuremath{\omega}}^{2}={{\ensuremath{\Sigma}}_{n=1}}^{N}{\ensuremath{\Phi}}_{n}[1\ensuremath{-}cos(\frac{\ensuremath{\pi}\mathrm{nq}}{{q}_{M}})]$ with $N\ensuremath{\le}12$. The existence of high Fourier components is definitely established. These high Fourier components imply the existence of very long range forces between the atoms in lead. In some cases the forces are of alternating sign. The dispersion curves show small anomalies which are believed to arise from the effect predicted by Kohn. The positions in reciprocal space at which these anomalies occur agree well with the quasi-free model for the electrons in lead, proposed by Gold. In the [111] direction (extended zone scheme) the Fermi radius is less than 1% greater than the free electron value of $1.24(\frac{2\ensuremath{\pi}}{a})$; in the [110] direction the Fermi radius is $(1.19\ifmmode\pm\else\textpm\fi{}0.01)(\frac{2\ensuremath{\pi}}{a})$. The Kohn effect is discussed in terms of theoretical work of Bardeen and Toya and the reasons for its observability in Pb are elucidated.