Chalk River Laboratories

About: Chalk River Laboratories is a based out in . It is known for research contribution in the topics: Neutron diffraction & Neutron scattering. The organization has 2297 authors who have published 2700 publications receiving 73287 citations.

Susceptibility of Zirconium Alloys to Delayed Hydrogen Cracking

Abstract: Smooth and notched cantilever beams and round-notched bars were machined from pressure tubes of cold-worked Zr-2.5 Nb and Zircaloy-2. They were loaded in the temperature range 290 to 520/sup 0/K. After two thermal cycles and at high stress, cracks were initiated in smooth beams of cold-worked Zr-2.5 Nb. Under the same test conditions, cold-worked Zircaloy-2 plastically deformed with no cracking. When notches were present, cracks propagated at the same rate in both materials by delayed hydrogen cracking. In cold-worked Zr-2.5 Nb, the crack velocity followed an Arrhenius plot with an apparent activation energy of 42 kJ/mol. Below 420/sup 0/K, the threshold stress intensity factor for delayed hydrogen cracking was about 5 MPa root m. Therefore, cracking can be prevented by keeping tensile stresses very low.

Radiation-induced genetic mosaicism and lethal sectoring in yeast

Abstract: The induction of masaics for recessive lethal mutations by X-rays was studied in a diploid strain of Saccharomyces cerevisiae . Mosaicism was detected by genetic analysis (frequencies of live and dead spores within asci) of individual third generation vegetative lines of descent from irradiated cells. Only about 30% of radiation-induced mutants were mosaic, and most if not all of this mosaicism was exposed at the first post-irradiation cell division. It was concluded that the genetic effects of X-rays ussually appear as lesions in both original strands of DNA as well as in both newly replicated strands. Lethal sectoring, the presence of sub-clones of dead cells, was common in the early generations of macro-colonies developing from X-irradiated cells. No evidence could be found that this mosaicism for dominant lethality was genetic in origin. However, the frequency of recessive lethals was higher among sectored colonies. It was demonstrated that lethal sectoring grossly distorts the estimate of genetic masiacism as inferred from the relative frequencies of mosaic and wholly colonies.

Neutron dose study with bubble detectors aboard the International Space Station as part of the Matroshka-R experiment

Abstract: As part of the Matroshka-R experiments, a spherical phantom and space bubble detectors (SBDs) were used on board the International Space Station to characterise the neutron radiation field. Seven experimental sessions with SBDs were carried out during expeditions ISS-13, ISS-14 and ISS-15. The detectors were positioned at various places throughout the Space Station, in order to determine dose variations with location and on/in the phantom in order to establish the relationship between the neutron dose measured externally to the body and the dose received internally. Experimental data on/in the phantom and at different locations are presented.

Novel structural features of the ripple phase of phospholipids

Abstract: We have calculated the electron density maps of the ripple phase of dimyristoylphosphatidylcholine (DMPC) and palmitoyl-oleoyl phosphatidylcholine (POPC) multibilayers at different temperatures and fixed relative humidity. Our analysis establishes, for the first time, the existence of an average tilt of the hydrocarbon chains of the lipid molecules along the direction of the ripple wave vector, which we believe is responsible for the occurrence of asymmetric ripples in these systems.