Showing papers by "Atomic Energy of Canada Limited published in 2013"

A high capacity silicon–graphite composite as anode for lithium-ion batteries using low content amorphous silicon and compatible binders

Abstract: In this study, silicon–graphite composites were prepared and investigated as anode materials for Li-ion batteries with small amounts of silicon and different binders. The silicon powders were prepared by ball-milling crystalline silicon for 100 h and 200 h. After 200 h, an average silicon particle size of 0.73 μm was obtained and XRD measurements confirmed the formation of an amorphous powder embedded within nanocrystalline regions. XPS analysis of the silicon samples showed that silicon particles were covered with a native silicon oxide layer that grows during ball-milling. Battery cycling of the silicon powders in half cells showed that the powder ball milled for 200 h gave the lowest first-cycle irreversible capacity and the highest reversible capacity reaching over 500 mA h g−1 after 50 cycles at C/12. Composites were made using graphite and only 5 wt% silicon powders. The silicon was found to be uniformly dispersed into the composites as evidenced by X-ray mapping and SEM. When tested in half cells using different binders, it was found that the polyetherimide binder showed the highest capacity reaching 514 mA h g−1 after 350 cycles at C/12, which is 1.6 times greater than commercial graphite anode. High rate cycling showed good capacity retention reaching half the capacity at 5 C.

miR-200c enhances radiosensitivity of human breast cancer cells

Abstract: Due to the intrinsic resistance of many tumors to radiotherapy, current methods to improve the survival of cancer patients largely depend on increasing tumor radiosensitivity. It is well-known that miR-200c inhibits epithelial-mesenchymal transition (EMT), and enhances cancer cell chemosensitivity. We sought to clarify the effects of miR-200c on the radiosensitization of human breast cancer cells. In this study, we found that low levels of miR-200c expression correlated with radiotolerance in breast cancer cells. miR-200c overexpression could increase radiosensitivity in breast cancer cells by inhibiting cell proliferation, and by increasing apoptosis and DNA double-strand breaks. Additionally, we found that miR-200c directly targeted TANK-binding kinase 1 (TBK1). However, overexpression of TBK1 partially rescued miR-200c mediated apoptosis induced by ionizing radiation. In summary, miR-200c can be a potential target for enhancing the effect of radiation treatment on breast cancer cells.

Gamma-radiolysis-assisted cobalt oxide nanoparticle formation

Abstract: The formation of Co3O4 nano-scale colloid particles by gamma irradiation of CoSO4 solutions was investigated. Solutions of 0.2–0.3 mM CoSO4 at pH 6.0 and 10.6 (air-saturated and Ar-purged) were irradiated at an absorbed dose rate of 5.5 kGy h−1. The resulting concentrations of H2, H2O2, CoII and CoIII species in solution and the chemical composition and sizes of particles that were formed were measured as a function of irradiation time. Particle formation was observed only for initially air-saturated CoSO4 solutions at pH 10.6. Analysis of the particle formation as a function of irradiation time shows that the particles evolve from Co(OH)2 to CoOOH and then to Co3O4. The radiolytic oxidation of CoII to CoIII was completed in 100 min and the chemical composition of the final particles was identified as Co3O4 by XPS, Raman and UV-Vis spectroscopy. Transmission electron microscopy (TEM) images show the final particles are approximately uniform in size, ranging from 8 to 20 nm. A mechanism is proposed to explain the particle formation. A key factor is the low solubility of Co(OH)2 in air-saturated solutions at high pH. This mechanism for particle formation is compared with the mechanism previously reported for the radiolytic formation of γ-FeOOH nanoparticles.

The Probability and Timing of Power System Restoration

Abstract: Power restoration following a large outage or widespread blackout is time critical and complex. A new method is presented for determining the timing and chance of electric power recovery and restoration. The present advance over previous work is explicitly integrating human, component and system reliability, which unifies the topic of power system restoration with the general theory for errors, accidents and outcomes for other technological systems.

The Effect of Irradiation on Ni-Containing Components in CANDU® Reactor Cores: A Review

Abstract: For nickel-containing alloys irradiated in thermalized neutron fluxes, the formation and reaction of 59 Ni with thermal neutrons can lead to time-varying changes in displacement damage rate, expres...

In vivo γ-irradiation low dose threshold for suppression of DNA double strand breaks below the spontaneous level in mouse blood and spleen cells

Abstract: There is a considerable controversy as to whether DNA damage induced by low doses and low dose rates of ionizing radiation is treated by cellular defence mechanisms in ways similar to that induced at high doses and high dose rates, and what downstream delayed effects may be caused by low doses compared to moderate and high doses. This constitutes the major challenge for the linear no-threshold model currently used for radiological risk estimates. Among the various DNA lesions induced by ionizing radiation, DNA double strand breaks (DSBs) are considered the most important due to their potential to cause cell death, mutagenesis and carcinogenesis. This study examined the accumulation of DNA DSBs in mouse blood leucocytes and splenocytes after long-term, chronic low dose γ-irradiation in vivo, and how this exposure may alter cell sensitivity to acute high dose irradiation. Animals were irradiated for 40, 80 or 120 days at a dose rate of 0.15 mGy/h, with total accumulated doses of 144, 288 and 432 mGy. DNA DSBs were measured in blood leucocytes and splenocytes using the neutral comet assay. We found that after an initial slight increase in the level of DNA DSBs at 40 days of exposure compared to controls, there was a subsequent drop after either 80 (P

A critical role of toll-like receptor 4 (TLR4) and its' in vivo ligands in basal radio-resistance.

Abstract: Toll-like receptor-4 (TLR4) plays a critical role in innate and acquired immunity, but its role in radio-resistance is unknown. We used TLR4 knockout (KO,−/−) mice and gut commensal depletion methods, to test the influence of TLR4 and its' in vivo agonist on basal radio-resistance. We found that mice deficient in TLR4 were more susceptible to IR-induced mortality and morbidity. Mortality of TLR4-deficient mice after IR was associated with a severe and persistent bone marrow cell loss. Injection of lipopolysaccharide into normal mice, which is known to activate TLR4 in vivo, induced radio-resistance. Moreover, TLR4 in vivo ligands are required for basal radio-resistance. We found that exposure to radiation leads to significant endotoxemia that also confers endogenous protection from irradiation. The circulating endotoxins appear to originate from the gut, as sterilization of the gut with antibiotics lead to increased mortality from radiation. Further data indicated that Myd88, but not TRIF, may be the critical adaptor in TLR4-induced radio-resistance. Taken together, these data strongly suggest that TLR4 plays a critical role in basal radio-resistance. Our data suggest, it is important not to give antibiotics that may sterilize the gut before the whole body irradiation. Further, these data also suggest that management of gut flora through antibiotic or possibly probiotic therapy may alter the innate response to the total body irradiation.

Low-Dose Radiation Exposure and Protection Against Atherosclerosis in ApoE–/– Mice: The Influence of P53 Heterozygosity

Abstract: We recently described the effects of low-dose γ-radiation exposures on atherosclerosis in genetically susceptible (ApoE–/–) mice with normal p53 function. Doses as low as 25 mGy, given at either early or late stage disease, generally protected against atherosclerosis in a manner distinctly nonlinear with dose. We now report the influence of low doses (25–500 mGy) on atherosclerosis in ApoE–/– mice with reduced p53 function (Trp53+/–). Single exposures were given at either low or high dose rate (1 or 150 mGy/min) to female C57BL/6J ApoE–/– Trp53+/– mice. Mice were exposed at either early stage disease (2 months of age) and examined 3 or 6 months later, or at late stage disease (7 months of age) and examined 2 or 4 months later. In unirradiated mice, reduced p53 functionality elevated serum cholesterol and accelerated both aortic root lesion growth and severity in young mice. Radiation exposure to doses as low as 25 mGy at early stage disease, at either the high or the low dose rate, inhibited lesion growth...

Freeform Laser Consolidated H13 and CPM 9V Tool Steels

Abstract: As a novel computer-aided materials additive manufacturing process, the freeform laser consolidation (LC) can directly produce functional shapes (features or structures) through a “layer-upon-layer” deposition. In this research, LC processability of both H13 and CPM 9V tool steels and their mechanical performance thus obtained were investigated. Both laser-consolidated tool steels were metallurgically sound with no crack, exhibiting layer-wise refined solidified structures with dominated martensite and small amount of retained austenite, as well as composition-dependent carbides. Laser-consolidated H13 could outperform its wrought counterpart mechanically as measured by tensile strength/strain, and bonding strength as well as sliding wear resistance; laser-consolidated CPM 9V could provide excellent sliding wear resistance superior to the conventional widely used tool steel (such as wrought D2). These unique microstructures and mechanical properties could be tailored for niche applications in additive manufacturing of tools, molds, and dies.

Gamma-radiation induced formation of chromium oxide nanoparticles from dissolved dichromate

Abstract: The formation of chromium oxide nanoparticles by gamma radiolysis of CrVI (CrO42− or Cr2O72−) solutions was investigated as a function of pH and initial CrVI concentration by measuring [CrVI], the particle concentration ([CrIII(col)]) and [H2], and by characterizing the particles using TEM, Raman, FTIR and XPS The results show that CrVI is easily reduced to CrIII by a homogeneous aqueous reaction with ˙eaq−, but, due to the stability of CrIII colloids, the growth of the Cr(OH)3 particles is very slow As the particles grow the interior of the particle dehydrates to form Cr2O3 while the outer layer remains hydrated When most of the CrVI that is initially present in the solution is converted to Cr(OH)3 further redox reactions of chromium species occur on the particle surfaces The redox system reaches a pseudo-equilibrium state due to cyclic reactions of CrIII with ˙OH and H2O2, and reactions of CrVI with ˙eaq− and H2O2 The size distribution of the particles that are formed is controlled by these solution–solid interface reactions

Self-radiolysis of tritiated water. 1. A comparison of the effects of 60Co γ-rays and tritium β-particles on water and aqueous solutions at room temperature

Abstract: Monte Carlo simulations were used to investigate the chemistry of pure water and aqueous solutions after irradiation with different kinds of radiation: tritium β-rays and high-energy electrons or 60Co γ-rays The objective of this work was to elucidate the mechanisms involved in the self-radiolysis of tritiated water, and to examine the importance of the effects of higher “linear energy transfer” (LET) by comparing 3H β-electrons (mean initial energy of ∼57 keV) with 60Co γ-rays (∼1-MeV electrons) We considered several chemical systems for which experimental data were available These included pure water, aqueous solutions of sulfuric acid, and aqueous ferrous sulfate solutions in aerated 04 M H2SO4 (Fricke dosimeter) Simulations clearly showed quantitatively different yields of radical and molecular products produced by the radiolysis of water with tritium β− particles compared with corresponding yields from γ or energetic electron radiolysis As a rule, lower radical and higher molecular yields were observed for 3H β-rays These differences in yields are completely consistent with differences in the nonhomogeneous distribution of primary transient species (ie, the structure of electron tracks) in the two cases In the “short-track” (columnar) geometry of tritium β-electron radiolysis, radicals were formed in much closer initial proximity than in the “spur” (spherical) geometry of γ radiolysis The “short-track” geometry favors radical-radical reactions in the diffusing tracks, which increases the proportion of molecular products at the expense of the radical products The same trend in yields of radical and molecular products was also found under acidic conditions as well as in the aerated Fricke dosimeter Unfortunately, comparison with experimental data was rather limited due to the paucity of experimental information for the radiolysis of water by 3H β-particles Despite this deficiency, our simulations reproduced very well the significant increase observed in the yield of H2 at the microsecond time scale for 3H β-electrons (∼06 molecule/100 eV) compared to 60Co γ-rays (045 molecule/100 eV) Furthermore, our predicted yield of Fe3+ ions for tritium β-electron radiolysis of Fricke (acidic ferrous sulfate) solutions compared well with the literature values (∼119–129 molecules/100 eV) In particular, it was shown that the measured yield of the Fricke dosimeter was best reproduced if a single, “mean” or “equivalent” electron energy of ∼78 keV was used to mimic the energy deposition by the tritium β-particles (rather than the commonly used mean of ∼57 keV that mimics the tritium beta energy spectrum), in full accordance with a recommendation of ICRU Report 17 This decrease in G(Fe3+) compared to the value observed for 60Co γ-rays (155 ± 02 molecules/100 eV) was mostly due to the decrease in the yield of the escape radical products Such results, even if fragmentary, corroborate very well with previous experimental and theoretical work, and support a model of tritium β radiolysis mainly driven by the chemical action of short tracks of high local LET

A bioassay method for americium and curium in feces

Abstract: Fecal radiobioassay is an essential and sensitive tool to estimate the internal intake of actinides after a radiological incident. A new fecal analysis method, based on lithium metaborate fusion of fecal ash for complete sample dissolution followed by sequential column chromatography separation of actinides, has been developed for the determination of low-level Am and Cm in a large size sample. Spiked synthetic fecal samples were analyzed to evaluate method performance against the acceptance criteria for radiobioassay as defined by ANSI N13.30; both satisfactory accuracy and repeatability were achieved. This method is a promising candidate for reliable dose assessment of low level actinide exposure to meet the regulatory requirements of routine radiobioassay for nuclear workers and the public.

Determination of uranium, thorium and plutonium isotopes by ICP-MS

Abstract: Quantitative and isotopic measurement of actinide elements is required in many circumstances in the nuclear industry. For example, determination of very low levels of these alpha emitters in human urine samples is used to assess the internal committed dose for nuclear workers. Quantifying actinide isotopes in radioactive waste from nuclear processing and nuclear facility decommissioning provides important information for waste management. Accurate determination of the uranium isotopic ratios in reactor fuels provides fuel burnup information. Inductively coupled plasma mass spectrometry (ICP-MS) has been used for the determination of Th, U, and Pu in various samples including urine, nuclear waste, and nuclear fuel in our laboratory. In order to maximize the capability of the technique and ensure quality analyses, ICP-MS was used to analyze samples directly, or after pre-treatment to separate complicated matrices or to concentrate the analyte(s). High-efficiency sample introduction techniques were investigated. Spectral interferences to minor isotopes caused by peak tails and hydride ions of major actinide isotopes were studied in detail using solutions prepared with light and heavy waters. The quality of the isotopic ratio measurement was monitored using standard reference materials.

A rapid method for determining strontium-90 in urine samples

Abstract: Rapid bioassay methods for 90Sr in urine samples are needed to provide an early estimation of possible internal dose resulting from exposure to radiostrontium in the event of a radiological and nuclear emergency. In this work, a fast column separation method followed by liquid scintillation counting for detection of 90Sr in urine was developed. Replicate spike and blank samples were analyzed for performance evaluation of the method. Using this method, a detection limit of ~10 Bq L−1 for 90Sr can be achieved with a sample analysis turn-around time of 4 h for a set of 12 samples. The method is adequate to meet the radiobioassay acceptance criteria and is suitable for quick dose assessment of 90Sr exposure following a radiation emergency.

Evaluation of the Airborne Particles Fraction Responsible for Adverse Health Effects

Abstract: A new approach to evaluation of the fraction of airborne particles that is responsible for adverse health effects has been developed. In this approach a two-fraction concept for the adverse health effects is proposed. This concept considers aerosol particles in the air, the fraction of particles deposited in the respiratory system (captured by the system) and the fraction of particle accumulated in the body (captured by the body). The latter fraction of airborne particles actually causes the adverse health effects and associated with the health risk. The approach has been applied to workers in crystal glass industry exposed to lead. A size resolved sampling technique was employed to characterize nanoparticles at work places at several plants involved in lead processing. Lead aerosol size distributions were obtained across the entire aerosol particle size range from 1 nm to 30 μm (diameter). Size distributions were used to calculate the total lead intake due to particle deposition in the respiratory system of workers. A bio-kinetic model was employed to evaluate various size fraction contributions to the total blood lead level in workers. A comparison was made between calculated blood lead levels and actual measurements of blood lead levels of workers exposed to atmospheres containing lead. It was found that nanoparticles cause the major health risk due to high deposition efficiency and low clearance rate by the mucociliary escalator.