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.

Apoptosis and the adaptive response in human lymphocytes.

Abstract: Purpose: To determine whether the sensitivity of human lymphocytes for apoptosis induced by either a membrane oxidizing agent or a DNA damaging agent is modified by an adaptive response. Materials and methods: Peripheral blood lymphocytes from normal human donors were exposed to low doses of the DNA damaging agent gamma-radiation, or the membrane oxidizing agent t-butyl hydroperoxide (t-BuOOH), incubated for various times and then tested for their sensitivity to induction of apoptosis by a subsequent exposure to a high dose of either agent. Apoptosis was measured using a fluorescent assay of DNA unwinding or a terminal deoxynucleotide transferase assay. Results: The results show that Go lymphocytes pre-exposed to an adapting dose of radiation or DNA strand breaking agent are not protected but can become sensitized to subsequent apoptosis induced by radiation (a kinetically slow process). Inter- and intra-individual variations were observed. However, neither pre-exposure to radiation nor to a membrane oxid...

A Lower Dose Threshold for the In Vivo Protective Adaptive Response to Radiation. Tumorigenesis in Chronically Exposed Normal and Trp53 Heterozygous C57BL/6 Mice

Abstract: Mitchel, R. E. J., Burchart, P. and Wyatt, H. A Lower Dose Threshold for the in vivo Protective Adaptive Response to Radiation. Tumorigenesis in Chronically Exposed Normal and Trp53 Heterozygous C57BL/6 Mice. Radiat. Res. 170, 765–775 (2008). Low doses of ionizing radiation to cells and animals may induce adaptive responses that reduce the risk of cancer. However, there are upper dose thresholds above which these protective adaptive responses do not occur. We have now tested the hypothesis that there are similar lower dose thresholds that must be exceeded to induce protective effects in vivo. We examined the effects of low-dose/low-dose-rate fractionated exposures on cancer formation in Trp53 normal or cancer-prone Trp53 heterozygous female C57BL/6 mice. Beginning at 6 weeks of age, mice were exposed 5 days/week to single daily doses (0.33 mGy, 0.7 mGy/h) totaling 48, 97 or 146 mGy over 30, 60 or 90 weeks. The exposures for shorter times (up to 60 weeks) appeared to be below the level necessary t...

Anisotropy of yielding in a Zr-2.5Nb pressure tube material

Abstract: The anisotropy of yielding, as measured by the ratio of yield stress in the axial and transverse directions of Zr-2.5Nb pressure tubes used in Canada Deuterium Uranium (CANDU) nuclear reactors, was determined experimentally by testing samples in uniaxial tension. The yield anisotropy was measured in uniaxial tension in samples obtained from the three directions of a Zr-2.5Nb plate and in shear, by testing in torsion “mini” pressure tubes from the same material. From these experiments, the temperature and strain-rate dependence of the yield stress and the dependence of the anisotropy of yielding on temperature were also determined. It is shown that the yield anisotropy of pressure tube material is constant for temperatures up to about 800 K and that the strain-rate sensitivity is also constant up to about 700 K and is equal to ∼0.02. In addition, the activation energy (Q) of this material was estimated by using the temperature dependence and rate sensitivity of the yield stress. It was found to be of the same order of magnitude as that determined earlier by other investigators. A polycrystalline, nonlinear self-consistent model that takes into account the crystallographic texture of the material was used to derive the values of the critical resolved shear stress (CRSS) which are consistent with prismatic, basal, and pyramidal glide and the values of the Hill’s plastic anisotropy coefficients which are consistent with the observed anisotropy of yielding. The model provided an estimate of the complete stress tensor, describing yielding of a Zr-2.5Nb pressure tube material.

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