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.

Deflection of high energy channeled charged particles by elastically bent silicon single crystals

Abstract: An experiment has been carried out to observe the deflection of charged particles by planar channeling in bent single crystals of silicon for protons with energy up to 180 GeV. Anomolous loss of particles from the center point of a three point bending apparatus was observed at high incident particle energy. This effect has been exploited to fashion a “dechanneling spectrometer” to study dechanneling effects due to centripital displacement of channeled particle trajectories in a bent crystal. The bending losses generally conform to the predictions of calculations based on a classical model.

Biological and biophysical techniques to assess radiation exposure: a perspective.

Abstract: Biological dosimeters measure biologically relevant effects of radiation exposure that are in some sense an estimate of effective dose, whereas biophysical indicators serve as surrogates of absorbed dose in a manner analogous to conventional thermoluminescent dosimeters (TLD). The biological and biophysical dosimeters have the potential to play an important role in assessing unanticipated or occupational radiation exposures. For example, where the exposure is large and uncertain (i.e. radiation accidents), accurate dose information can help in deciding the most appropriate therapy and medical treatment. Another useful area is that of lifetime accumulated dose determination, and the ability to distinguish between and integrate the exposures from natural and anthropogenic (medical X-rays, indoor radon, natural background radiation, occupational and non-occupational exposures). Also, the possibility to monitor individual response and differences in inherent or induced radiation sensitivity may have important implications for radiation protection. More commonly, this type of dosimetry could be used for routine monitoring to detect and quantify unsuspected exposure, for regulatory purposes or for epidemiological studies of the long-term effects of radiation exposure (e.g. in Japanese A-bomb survivors or in the population surrounding Chernobyl). This review is a comparative study of the existing techniques and their future prospects. It summarizes the sensitivity, reproducibility, limiting dose, dose-rate, energy, LET response, sources of variability and uncertainty, and other practical aspects of each bio-indicator. The strengths and weaknesses of each approach are evaluated on the basis of common criteria for particular applications, and are summarized for each assay both in the text and in tabular form, for convenience. It is clear that no single indicator qualifies to reliably measure occupational exposures at the current levels of sensitivity conventional dosimetry services provide. Most of the bio-techniques are applicable to the detection of relatively high radiation exposures at relatively short times after exposure. Some of the bio-indicators have been identified that are, or offer future prospects for becoming, appropriate bio-indicators for dosimetry needs. However, all methods are subject to biological and other variables that are presently uncontrolled, and represent a major source of uncertainty. These include variations in background signals not directly associated with radiation exposure, inter- and intra-individual variability of radiation response, and genetic and environmental effects. Although these factors contribute to the lack of confidence in biological dosimetry, promising bio-indicators may be applied to large populations to establish the inherent variability and confounding factors that limit quantitative data collection and analysis, and reduce reliability and reproducibility.

Irradiation-induced phase transformations in zirconium alloys

Abstract: Ion and electron irradiations were used to follow the irradiation-induced crystalline-to-amorphous transformation in Zr3Fe, ZrFe2, Zr(Cr,Fe)2 and ZrCr2, as well as in Zr(Cr,Fe)2 and Zr2(Ni,Fe) precipitates in Zircaloy-4. 40Ar and 209Bi ion irradiations of Zr3Fe were performed at 35–725 K using ions of energy 15–1500 keV. The effect of the deposited-energy density θ v in the collision cascade on the nature of the damaged regions in individual cascades was investigated. The amorphization kinetics of Zr3Fe during in situ electron irradiation were also determined. The electron fluence required for amorphization increased exponentially with temperature, and the critical temperature for amorphization was about 220 K, compared with 575–625 K for ion irradiation. The difference between the heavy ion and electron irradiation results is attributed to the fact that ion irradiation produces displacement cascades, while electron irradiation produces isolated Frenkel pairs. The dependence of the damage production of the incident electron energy was determined for Zr3Fe and the results could be analysed in terms of a composite displacement cross-section dominated at high energies by displacements of Zr and Fe atoms; by displacements of Fe atoms at intermediate energies; and by secondary displacements of lattice atoms by recoil impurities at low energies. An investigation was initiated on ZrFe2, Zr(Cr,Fe)2 and ZrCr2 to study the effect of variation of the stoichiometry and the presence of lattice defects on irradiation-induced amorphization. The irradiation-induced amorphization of the intermetallic precipitates Zr(Cr,Fe)2 and Zr2(Ni,Fe) in Zircaloy-4 was also studied during in situ bombardment by 40Ar ions of energy 350 keV. The amorphization morphology was shown to be homogeneous. These results are discussed in the context of previous experimental results of neutron and electron irradiations, and likely amorphization mechanisms are proposed.