Showing papers by "Chalk River Laboratories published in 1973"

Structure and excitations of liquid helium

Abstract: During the past decade there has been considerable progress in the study of the structure and elementary excitations of liquid helium. This has largely arisen from the development and refinement of neutron, X-ray and light scattering techniques and also from more detailed ultrasonic measurements. A large part of this review is concerned with describing the results of these experiments and their implications for theories of liquid helium. During the last few years there has also been considerable progress made in the theory of the excitations in liquid helium. These developments are briefly reviewed and the most promising lines of development indicated.

Time Patterns of Peromyscus Activity and Their Correlations with Weather

Abstract: The activity of Peromyscus maniculatus in an Ontario forest and Peromyscus truei and Peromyscus californicus in California chaparral was observed directly and monitored electronically. The activity of all three species outside the burrow was pulsed through the night, with different individuals not in tight synchrony and a depression in overall activity in the middle of the night. Activity of P. californicus was similar to that of P. truei , but P. californicus had in addition a pronounced burst of activity before dawn. As summer progressed, the amount of activity of P. maniculatus diminished and was compressed into the early part of the night. Wind and moonlight had no strong effect upon activity within a night. From night to night, P. truei had conspicuous fluctuations in total nightly activity (at a period of about 4 days), the entire population usually being in synchrony. Night-to-night fluctuations in P. californicus activity were in phase with those of P. truei . Night-to-night fluctuations in vole tracks in Quebec (unpublished data from R. Bider) had low correlations with P. maniculatus tracks in the same area. Night-to-night fluctuations in P. truei activity had a positive correlation with barometric pressure and a negative correlation with low pressure weather variables (humidity, temperature). There was no correlation with wind or cloud cover. None of the weather variables had a strong periodicity at 4 days, but P. truei activity was in phase with the 4-day-component of barometric pressure, out of phase with temperature, and leading humidity. The evidence suggested that sundown temperature was the key variable. Fluctuations in tracks of P. maniculatus (Quebec) had similar properties, except they were in-phase with low pressure weather variables. Vole tracks ( Microtus pennsylvanicus and Clethrionomys gapperi ) showed the same periodicities as weather and were tightly correlated with weather.

Dynamic strain aging during creep of α-Zr

Abstract: In the temperature range 723 to 823 K (450° to 550°C) annealed, crystal bar α-Zr exhibits anomalous behavior with respect to both single stress and incrementally stressed creep tests. The nature and extent of the anomalous behavior depends on temperature, stress, and impurity content. Specimens with low oxygen content exhibit: 1) normal, three-stage creep behavior during single stress tests, and 2) normal transients during incremental stress and temperature tests. Specimens with higher oxygen contents exhibit: 1) multi-stage creep curves whose shapes depend on temperature and stress, 2) inverse transients following stress and temperature increments, and 3) peaks in activation energy-tempera-ture curves. The nature of the anomalous behavior is consistent with a model for strain aging in which the possibility of localized depletion of the strain aging species exists. In the material being studied oxygen is probably responsible for the observed effects.

States in86Sr,84Sr and87Y populated in the (p, t) reaction

Abstract: The (p,t) reactions on88Sr,84Sr and89Y have been carried out at a bombarding energy of 49.5 MeV. Some low-lying excitations in86Sr and84Sr associated with configurations of 1g9/2 and 2p1/2 neutrons have been identified. Levels populated to 4 MeV of excitation in the strontium nuclei and to 2.5 MeV in87Y have been studied in the present experiment. In the case of87Y most of the levels populated are of a complex nature.

Damage Profiles in Ion-Implanted Semiconductors at Low (25°K) Temperatures

Abstract: The damage profiles of 300-keV Ar+ implants in Si, GaP, GaAs and InP and of 500-keV Kr+ implants in Si, GaP and Ge have been studied theoretically and experimentally. The profiles were measured using the channeling-effeet technique. To minimize any influence of annealing the target was kept at 25°K throughout the implantation and the subsequent back-scattering analysis with 2.0 MeV He+. Reasonable agreement is obtained between the measured and theoretically calculated damage profiles.

Lattice Location of Low-Z Impurities in Medium-Z Targets Using Ion-Induced X-Rays

Abstract: The common method of Rutherford backscattering and channeling of light energetic ions is in general not suited to lattice location studies of impurity atoms having a mass similar to or lower than the host. While specific nuclear reactions are sometimes available they usually require high beam doses and yield high backgrounds of scattered particles. In two such situations we have used ion induced x-ray yields to determine lattice location viz. for 32S and 31P implants in Ge single crystals. In the course of this work we have had to identify and optimize a number of experimental parameters, in particular how the beam type affects (a) ψ1/2,xmin and crystal damage rates, (b) x-ray yields (P-K, S-K, Ge-L and Ge-K), target bremsstrahlung and recoil-induced molecular x-ray intensities. Choice of detector geometry, aperture and window also proved to be important. Detection limits for P and S are now certainly better than 1 x 1014 atoms.cm-2 in a thick Ge target for 0.5 MeV proton excitation. We have found that a room temperature implant of 40 keV 31P annealed at 450oC is highly (93%) substitutional in Ge for a dose of 0.7 x 1015 ions.cm-2, but shows a much lower fraction at 2.7 x 1015 ions.cm. Lattice location of S implanted into Ge parallels the pattern from Group VI impurities implanted and annealed in Si, showing ≤ 50% xmin. values for the S signals in and directions. A different distribution for S is implied by channeling data and and angular scans.