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Chalk River Laboratories

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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.


Papers
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Journal ArticleDOI
TL;DR: The optimization of instruments and preparation techniques, as well as the new possibilities offered by protein deuteration, have opened up new avenues for the study of lipid/protein interactions that were not previously possible.
Abstract: Membranes that surround cells and separate their contents from the external environment are ubiquitous in biological systems. These membranes are organized assemblies consisting mainly of lipids and proteins, and are highly selective permeability barriers which control the flow of information between cells and their environment. It is accepted that the lipid bilayer is the underlying structure of most, if not all, biomembranes. As such, over the years scientists have exerted much effort in studying lipid bilayers and their biological relevance in hopes of understanding the functional mechanisms taking place at membrane interfaces. Neutron and X-ray scattering techniques are powerful tools for the characterization of the structure and dynamics of biomimetic systems as they provide unique access to microscopic structure and dynamics at length scales ranging from microns to intermolecular and/or atomic distances. The optimization of instruments and preparation techniques, as well as the new possibilities offered by protein deuteration, have opened up new avenues for the study of lipid/protein interactions that were not previously possible. One can now look at the insertion of biomolecules into membranes and accurately determine the structure as well as the dynamics of the interaction. To illustrate the usefulness of diffraction and scattering techniques with regard to biologically relevant systems, we review some of the leading edge studies that have taken place over the last couple of years in which these scattering techniques have played a central role.

25 citations

Journal ArticleDOI
TL;DR: In this article, the authors investigated the performance and the potential background of Am and Cm analyses with low energy AMS and concluded that ultra-trace analyses of am and cm isotopes for bioassay are very well possible with low-energy AMS.
Abstract: Accelerator mass spectrometry (AMS) has evolved over the past years as one of the most sensitive, selective, and robust techniques for actinide analyses. While analyses of U and Pu isotopes have already become routine at the ETH Zurich 0.5 MV AMS system “Tandy”, there is an increasing demand for highly sensitive analyses of the higher actinides such as Am and Cm for bioassay applications and beyond. In order to extend the actinide capabilities of the compact ETH Zurich AMS system and to develop new, more sensitive bioassay routines, a pilot study was carried out. The aim was to investigate and document the performance and the potential background of Am and Cm analyses with low energy AMS. Our results show that 241Am and Cm isotopes can be determined relative to a 243Am tracer if samples and AMS standards are prepared identically with regard to the matrix elements, in which the sample is dispersed. In this first test, detection limits for Cm and Am isotopes are all in the sub-femtogram range and even below 100 ag for Cm isotopes. In a systematic background study in the mass range of the Cm isotopes, two formerly unknown metastable triply charged Th molecules were found on amu(244) and amu(248). The presence of such a background is not a principal problem for AMS if the stripper pressure is increased accordingly. Based on our first results, we conclude that ultra-trace analyses of Am and Cm isotopes for bioassay are very well possible with low energy AMS.

25 citations

Journal ArticleDOI
01 Sep 1949-Genetics
TL;DR: The underlying cause of the delayed appearance of mutants, could be either induced gene instability causing an increase in the spontaneous mutation rate over a number of cell generations, or induced gene mutation requiring one or more cell divisions in order to affect the phenotype of the organism.
Abstract: HAT mutations are produced in bacteria following treatment with X-rays T and ultra-violet light has been shown by a number of workers (GRAY and TATUM 1944; GOWEN 1941; ROEPKE, LIBBY, and SMALL 1944; and TATUM 1945, 1946). However, where irradiated bacteria have been tested for the presence of induced mutants immediately after treatment few have been found, and detailed studies show that appreciable growth must take place in the treated population before the bulk of the induced changes appear (DEMEREC 1946; DEMEREC and LATARJET 1946). The proportion of the total mutations which are delayed in this manner amounts to 99 percent or more in the one case studied (mutation of E. coli strain B / r to resistance to bacteriophage T I ) ; and the population increase required in order for all of them to appear is approximately 212 to 213 times. This “delayed effect” of irradiation is similar in both X-ray and ultra-violet treated material, and parallel phenomena have recently been demonstrated following exposure to nitrogen mustard (BRYSON 1947), sodium desoxycholate and acriflavine ( WITKIN, personal communication). The underlying cause of the delayed appearance of mutants, could be either (a) induced gene instability causing an increase in the spontaneous mutation rate over a number of cell generations, or (b) induced gene mutation requiring one or more cell divisions in order to affect the phenotype of the organism. The first of these two interpretations (gene instability) assumes an effect of radiation which has not been observed in higher organisms, and thus implies a fundamental peculiarity of bacterial genes. However, gene instability lasting over many cell generations has been produced in Drosophila by the action of mustard-gas (AUERBACH 1947) and it is conceivable that a similar effect is produced in bacteria by irradiation (see PONTECORVO 1946). The alternative interpretation assumes delayed phenotypic expression, an effect already demonstrated in a class of spontaneous mutations of E. coli (resistance to phage TI, NEWCOMBE 1948). However, spontaneous mutations require only two or three generations in order to become detectable, and this would seem inadequate to explain more than a part of the prolonged delay associated with induced mutation. The two interpretations raise a number of points of fundamental importance: (a) If there is a delay in the phenotypic expression of gene mutation, the evidence is relevant to the general problems of gene action and cell physiology.

25 citations

Journal ArticleDOI
TL;DR: The Advanced Radiation Monitoring Device (ARMD) as mentioned in this paper is a compact handheld instrument for radioisotope identification and localization using C 2 LiYCl 6 :Ce 3+ (CLYC) scintillators.
Abstract: Cs 2 LiYCl 6 :Ce 3+ (CLYC) scintillator has gained recent interest because of its ability to perform simultaneous gamma spectroscopy and thermal neutron detection. Discrimination between the two incident particle types owes to the fundamentally unique emission waveforms, a consequence of the interaction and subsequent scintillation mechanisms within the crystal. Due to this dual-mode detector capability, CLYC was selected for the development of an Advanced Radiation Monitoring Device (ARMD), a compact handheld instrument for radioisotope identification and localization. ARMD consists of four 1 in.-right cylindrical CLYC crystals, custom readout electronics including a suitable multi-window application specific integrated circuit (ASIC), battery pack, proprietary software, and Android-based tablet for high-level analysis and display. We herein describe the motivation of the work and engineering design of the unit, and we explain the software embedded in the core module and for radioisotope analysis. We report an operational range of tens of keV to 8.5 MeV with approximately 5.3% gamma energy resolution at 662 keV, thermal neutron detection efficiency of 10%, battery lifetime of up to 10 h, manageable rates of 20 kHz; further, we describe in greater detail time to identify specific gamma source setups.

25 citations

Journal ArticleDOI
TL;DR: Vegetative reproduction, above-ground biomass and nutrient pools, and litterfall and substrate nutrient conditions were evaluated in eastern Ontario immature aspen ecosystems which had been subjected to the following four treatments in relation to vernal leaf flushing: burning before; burning after; cutting before; and cutting after flushing.

25 citations


Authors

Showing all 2298 results

NameH-indexPapersCitations
Michael D. Guiver7828820540
Robert J. Birgeneau7858722686
Mike D. Flannigan7121121327
Martin T. Dove6139614767
Luis Rodrigo5834112963
André Longtin5626016372
David Mitlin5619615479
John Katsaras552209263
John E. Greedan5539112171
Gang Li484067713
Matthew G. Tucker452247288
Bruce D. Gaulin452846698
Erick J. Dufourc431445882
Norbert Kučerka431197319
Stephen J. Skinner421948522
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Performance
Metrics
No. of papers from the Institution in previous years
YearPapers
20231
202284
202176
202072
201974
2018104