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.

Fluorometric method for rapid detection of DNA strand breaks in human white blood cells produced by low doses of radiation.

Abstract: DNA strand breaks can be detected with great sensitivity by exposing crude cell lysates to alkaline solutions and monitoring the rate of strand unwinding. As little as one strand break per chromosome can be detected. Previous methods for measuring strand unwinding have required physical separation of single- from double-stranded molecules. We now describe conditions under which unwinding can be monitored directly using a fluorescent dye, thus greatly simplifying the analysis. Breaks due to irradiation of blood samples by 60Co gamma-rays at doses as low as 0.05 to 0.1 gray (5 to 10 rads) were detectable. Rapid rejoining of strand breaks during in vitro incubation at 37 degrees could readily be observed following a dose of one gray. Since the procedure is very rapid and cells can be analyzed directly without the requirement for culturing or radiolabeling, the procedure could be useful in cancer chemotherapy if in vivo damage is to be monitored or for testing the in vitro sensitivity of cells to drugs.

Magnetic excitations and ordering in the heavy-electron superconductor URu2Si2.

Abstract: Neutron scattering demonstrates the coexistence of antiferromagnetic order and superconductivity below 1 K in the heavy-electron system ${\mathrm{URu}}_{2}$${\mathrm{Si}}_{2}$. It is found that the upper (17.5 K) transition is to an antiferromagnetic phase with a (100) modulation wave vector and spins along the tetragonal c-axis. The ordered moment is unusually small, (0.03\ifmmode\pm\else\textpm\fi{}0.01)${\mathrm{\ensuremath{\mu}}}_{\mathrm{B}}$. However, spin waves develop from damped, finite-gap excitations above ${\mathrm{T}}_{\mathrm{N}}$, and they are intense, propagating, and longitudinal with a zone centre gap of 1.8 meV.

Crystal Stability and the Theory of Ferroelectricity

Abstract: The phenomenon of ferroelectricity in pseudo-cubic crystals is discussed in terms of the normal modes of vibration. It is shown that the parameters which determine the lattice vibrations of a diatomic ionic crystal may be chosen in such a way that the crystal will exhibit ferroelectric properties, and that ferroelectric or anti-ferroelectric transitions may be regarded as the result of an instability of the crystal for a certain normal mode of vibration. The theory is extended to apply to other cubic crystals, including barium titanate, and the concepts of ‘ionic polarizability’ and ‘a polarizability catastrophe’ are discussed in terms of lattice dynamics. Certain of the parameters which appear in Devonshire's phenomenological theory of ferroelectricity are found to be expressible in terms of atomic parameters. Values for the latter which are physically reasonable are found to account quite well for the dielectric properties of barium titanate and for the relative movements of the atoms which occ...

Lattice Dynamics of Alkali Halide Crystals

Abstract: The paper comprises theoretical and experimental studies of the lattice dynamics of alkali halides. A theory of the lattice dynamics of ionic crystals is given based on replacement of a polarizable ion by a model in which a rigid shell of electrons (taken to have zero mass) can move with respect to the massive ionic core. The dipolar approximation then makes the model exactly equivalent to a Born-von K\'arm\'an crystal in which there are two "atoms" of differing charge at each lattice point, one of the "atoms" having zero mass. The model has been specialized to the case of an alkali halide in which only one atom is polarizable, and computations of dispersion curves have been carried out for sodium iodide. We have determined the dispersion $\ensuremath{ u}(\mathrm{q})$ relation of the lattice vibrations in the symmetric [001], [110], and [111] directions of sodium iodide at 110\ifmmode^\circ\else\textdegree\fi{}K by the methods of neutron spectrometry. The transverse acoustic, longitudinal acoustic, and transverse optic branches were determined completely with a probable error of about 3%. The dispersion relation for the longitudinal optic (LO) branch was determined for the [001] directions with less accuracy. Frequencies of some important phonons with their errors (units ${10}^{12}$ cps) are: TA[0,0,1]1.22\ifmmode\pm\else\textpm\fi{}0.04, LA[0,0,1] 1.82\ifmmode\pm\else\textpm\fi{}0.06, TA[\textonehalf{},\textonehalf{},\textonehalf{}]1.52\ifmmode\pm\else\textpm\fi{}0.05, LA[\textonehalf{},\textonehalf{},\textonehalf{}]2.32\ifmmode\pm\else\textpm\fi{}0.06, TO[0,0,0] ${3.6}_{0}$\ifmmode\pm\else\textpm\fi{}0.1, TO[0,0,1]${3.8}_{0}$\ifmmode\pm\else\textpm\fi{}0.1, TO[\textonehalf{},\textonehalf{},\textonehalf{}]${3.5}_{0}$\ifmmode\pm\else\textpm\fi{}0.1. The agreement between the experimental results and the calculations based on the shell model, while not complete, is quite satisfactory. The neutron groups corresponding to phonons of the LO branch were anomalously energy broadened, especially for phonons of long wavelength, suggesting a remarkably short lifetime for the phonons of this branch.