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.

Chain formation in a magnetic fluid under the influence of strong external magnetic fields studied by small angle neutron scattering

Abstract: We studied the aggregation of magnetic particles into chain-like structures in a cobalt-based magnetic fluid, exposed to external magnetic fields. The length of chain segments in very strong magnetic fields of up to 2 Tesla was measured in situ using small angle neutron scattering. Arrangement of the magnetic particles was studied with the scattering vector aligned parallel to the magnetic field lines, and at angles of 30° and 60° with respect to . Although chains several hundred particles in length were predicted, we observe a maximum correlation length of ∼65 nm equivalent to 3–4 particles up to highest fields. We speculate that the interaction between chains, i.e., the interplay between the entropy and energy of the system combined with the particular properties of the magnetic dipole–dipole interaction ultimately decide the length of the particle chains.

Highly stable cooperative distortion in a weak Jahn-Teller d2 cation: perovskite-type ScVO3 obtained by high-pressure and high-temperature transformation from bixbyite.

Abstract: A novel ScVO3 perovskite phase has been synthesized at 8 GPa and 1073 K from the cation-disordered bixbyite-type ScVO3. The new perovskite has orthorhombic symmetry at room temperature, space group Pnma, and lattice parameters a = 5.4006(2) A, b = 7.5011(2) A, and c = 5.0706(1) A with Sc3+ and V3+ ions fully ordered on the A and B sites of the perovskite cell. The vanadium oxygen octahedra [V–O6] display cooperative Jahn–Teller (JT) type distortions, with predominance of the tetragonal Q3 over the orthorhombic Q2 JT modes. The orthorhombic perovskite shows Arrhenius-type electrical conductivity and undergoes a transition to triclinic symmetry space group P-1 close to 90 K. Below 60 K, the magnetic moments of the 4 nonequivalent vanadium ions undergo magnetic long-range ordering, resulting in a magnetic superstructure of the perovskite cell with propagation vector (0.5, 0, 0.5). The magnetic moments are confined to the xz plane and establish a close to zigzag antiferromagnetic mode.

Molecular dynamics simulations of a mixed DOPC/DOPG bilayer.

Abstract: We have constructed a mixed dioleoylphosphatidylcholine (DOPC) and dioleoylphosphatidylglycerol bilayer (DOPG) bilayer utilizing MD simulations. The aim was to develop an explicit molecular model of biological membranes as a complementary technique to neutron diffraction studies that are well established within the group. A monolayer was constructed by taking a previously customized PDB file of each molecule and arranging them in a seven rows of ten molecules and duplicated and rotated to form a bilayer. The 140-molecule bilayer contained 98 DOPC molecules and 42 DOPG molecules, in a 7:3 ratio in favour of DOPC. Sodium counter ions were placed near the phosphate moiety of DOPG to counteract the negative charge of DOPG. This was representative of the lipid ratio in a sample used for neutron diffraction. The MD package GROMACS was used for confining the bilayer in a triclinic box, adding Simple Polar Charge water molecules, energy minimization (EM). The bilayer/solvent system was subjected to EM using the steepest descent method to nullify bad contacts and reduce the potential energy of the system. Subsequent MD simulation using an initial NVT (constant number of particles, volume and temperature) for a 20 ps MD run followed by a NPT (constant number of particles, pressure and temperature) was performed. Structural parameters including volume of lipid, area of lipid, order parameter of the fatty acyl carbons and electron density profiles generated by the MD simulation were verified with values obtained from experimental data of DOPC, as there are no comparable experimental data available for the mixed bilayer.

A militarily fielded thermal neutron activation sensor for landmine detection

Abstract: The Canadian Department of National Defence has developed a teleoperated, vehicle-mounted, multi-sensor system to detect anti-tank landmines on roads and tracks in peacekeeping operations. A key part of the system is a thermal neutron activation (TNA) sensor which is placed above a suspect location to within a 30 cm radius and confirms the presence of explosives via detection of the 10.835 MeV gamma ray associated with thermal neutron capture on 14N. The TNA uses a 100 μ g 252Cf neutron source surrounded by four 7.62 cm × 7.62 cm NaI(Tl) detectors. The system, consisting of the TNA sensor head, including source, detectors and shielding, the high-rate, fast pulse processing electronics and the data processing methodology are described. Results of experiments to characterize detection performance are also described. The experiments have shown that anti-tank mines buried 10 cm or less can be detected in roughly a minute or less, but deeper mines and mines significantly displaced horizontally take considerably longer time. Mines as deep as 30 cm can be detected for long count times (1000 s). Four TNA detectors are now in service with the Canadian Forces as part of the four multi-sensor systems, making it the first militarily fielded TNA sensor and the first militarily fielded confirmation sensor for landmines. The ability to function well in adverse climatic conditions has been demonstrated, both in trials and operations.

Chronic Exposure to External Low-Dose Gamma Radiation Induces an Increase in Anti-inflammatory and Anti-oxidative Parameters Resulting in Atherosclerotic Plaque Size Reduction in ApoE–/– Mice

Abstract: Populations living in radiation-contaminated territories, such as Chernobyl and Fukushima, are chronically exposed to external gamma radiation and internal radionuclide contamination due to the large amount of 137Cs released in the environment. The effect of chronic low-dose exposure on the development of cardiovascular diseases remains unclear. Previously reported studies have shown that low-dose radiation exposure could lead to discrepancies according to dose rate. In this study, we examined the effect of very low-dose and dose-rate chronic external exposure on atherosclerosis development. ApoE-/- mice were chronically irradiated with a gamma source for 8 months at two different dose rates, 12 and 28 μGy/h, equivalent to dose rates measured in contaminated territories, with a cumulative dose of 67 and 157 mGy, respectively. We evaluated plaque size and phenotype, inflammatory profile and oxidative stress status. The results of this study showed a decrease in plaque sizes and an increase in collagen content in ApoE-/- mice exposed to 28 μGy/h for 8 months compared to nonexposed animals. The plaque phenotype was associated with an increase in anti-inflammatory and anti-oxidative gene expression. These results suggest that chronic low-dose gamma irradiation induces an upregulation of organism defenses leading to a decrease in inflammation and plaque size. To our knowledge, this is the first study to describe the possible effect of chronic external very low-dose ionizing radiation exposure for 8 months. This work could help to identify the potential existence of a dose threshold, below that which harmful effects are not exhibited and beneficial effects are potentially observed. Furthermore, these findings permit consideration of the importance of dose rate in radiation protection.