Analyse des sédiments contaminés de la portion sud-ouest du Lac Saint-Pierre (Québec, Canada)

Des campagnes de terrain ont été menées en automne 2006 dans la portion sud-ouest du lac Saint-Pierre en vue de déterminer la concentration des contaminants dans les sédiments sommitaux (entre 0-50 cm) et de fond (>50 cm) des carottes prélevées. Ces campagnes de forages ont été menées sous la direction d’une équipe d’experts du ministère de la Défense nationale (MDN). La zone à l’étude fait partie de l’ancienne zone de tir (zone CYR 606) du Centre d’essais et d’expérimentation en munitions des Forces armées canadiennes. Elle présente des risques environnementaux en raison de la présence de munitions non explosées (UXO) dans les sédiments. Cette zone a aussi été identifiée comme une zone affectée par divers contaminants, dont des éléments métalliques (EM) et des polluants organiques. Les analyses effectuées dans la portion sud-ouest du lac Saint-Pierre indiquent que les concentrations des EM et autres contaminants (BPC, HAP) dans les sédiments sont relativement faibles sur l’ensemble des sites d’échantillonnage. Ce sont surtout l’arsenic et le chrome qui affichent les plus fortes concentrations, dépassant le seuil des concentrations d’effets occasionnels (CEO) et le seuil des concentrations produisant un effet (CSE), tels que définis par les critères pour l’évaluation de la qualité des sédiments élaborés conjointement par le fédéral et le provincial. Sur le plan granulométrique, ce sont surtout les sables loameux ou les loams sableux qui constituent les matrices dominantes. En comparant avec les travaux antérieurs réalisés dans cette portion du lac Saint-Pierre, la contamination des sédiments serait moins importante que par le passé, ce qui présume à une amélioration de la qualité de l’eau et des sédiments depuis les premières analyses effectuées au cours des années 1976-1986. À la lumière des résultats obtenus, cette partie du bassin n’apparaît pas comme un secteur problématique pour la contamination des sédiments par les éléments métalliques (EM), les biphényles polychlorés (BPC) et les hydrocarbures aromatiques polycycliques (HAP).Field campaigns were conducted during autumn 2006 in the southwest portion of Lake Saint-Pierre in order to determine the concentration of contaminants in subsurface (0-50 cm) and deep sediments (>50 cm) of the cores collected. These coring campaigns were conducted under the leadership of a team of experts from the Department of National Defence (DND). The study area is part of the former firing range (encompassed by the no fly CYR 606 zone) from the Munitions Experimental Test Centre of the Canadian Armed Forces. It presents environmental risks because Unexploded Explosive Ordnance (UXO) are found in sediments. This zone was also identified as an area affected by various contaminants, including metallic elements and organic pollutants. The analysis in the southwest portion of Lake Saint-Pierre indicates that the concentrations of metallic elements (ME) and other contaminants (PCBs, PAHs) are relatively low at all sampling sites. Arsenic and chromium show the highest concentrations, exceeding the occasional effect level (OEL) and the threshold effect level (TEL), as defined by Federal and Provincial sediment quality guidelines. For sediment classification, loamy sand or sandy loam are the dominant mineral matrices. In comparison with previous work in this portion of Lake Saint-Pierre, sediment contamination has been reduced, which indicates an improvement in the quality of water and sediment. In light of these results, this part of the basin is not seen as a problematic area in terms of sediment contamination by metallic elements (ME), polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs)

Experimental study of granular surface flows via a fast camera: a continuous description

Depth averaged conservation equations are written for granular surface flows. Their application to the study of steady surface flows in a rotating drum allows to find experimentally the constitutive relations needed to close these equations from measurements of the velocity profile in the flowing layer at the center of the drum and from the flowing layer thickness and the static/flowing boundary profiles. The velocity varies linearly with depth, with a gradient independent of both the flowing layer thickness and the static/flowing boundary local slope. The first two closure relations relating the flow rate and the momentum flux to the flowing layer thickness and the slope are then deduced. Measurements of the profile of the flowing layer thickness and the static/flowing boundary in the whole drum explicitly give the last relation concerning the force acting on the flowing layer. Finally, these closure relations are compared to existing continuous models of surface flows.Comment: 20 pages, 11 figures, submitted to Phys. FLuid

Energy and angular momentum sharing in dissipative collisions

Primary and secondary masses of heavy reaction products have been deduced from kinematics and E-ToF measurements, respectively, for the direct and reverse collisions of 93Nb and 116Sn at 25 AMeV. Light charged particles have also been measured in coincidence with the heavy fragments. Direct experimental evidence of the correlation of energy-sharing with net mass transfer has been found using the information from both the heavy fragments and the light charged particles. The ratio of Hydrogen and Helium multiplicities points to a further correlation of angular momentum sharing with net mass transfer.Comment: 21 pages, 20 figures. Submitted to European Physics Journal

A new cross section measurement of reactions induced by 3He-particles on a carbon target

International audienceThe production of intense beams of light radioactive nuclei can be achieved at the SPIRAL2 facility using intense stable beams accelerated by the driver accelerator and impinging on light targets. The isotope 14O is identied to be of high interest for future experiments. The excitation function of the production reaction 12C(3He, n)14O was measured between 7 and 35 MeV. Results are compared with literature data. As an additional result, we report the rst cross-section measurement for the 12C(3He, +n)10C reaction. Based on this new result, the potential in-target 14O yield at SPIRAL2 was estimated: 2.4x1011 pps, for 1 mA of 3He at 35 MeV. This is a factor 140 higher than the in-target yield at SPIRAL1

Method for Efficiency and Time Response Measurement on Diverse Target Ion Sources with Stable Alkali

International audienceDevelopments of new setups for radioactive ion beam production by the isotope-separator-on-line (ISOL) method are underway at GANIL in the frame of the SPIRAL (Système de Production d'Ions Radioactifs Accélérés en Ligne) and SPIRAL-II projects. The measurement of total efficiency and time behaviour of these new target/ion-source systems (TISSs) is a crucial step for these devices which aims to produce short-lived isotopes with high intensity. The overall atom-to-ion transformation efficiency depends on several processes: diffusion of the atoms out of the production target, effusion towards the ion source and ionization. The efficiency can be extracted using the ratio between the emerging yield and implanted flux in the TISS. Several methods have already been developed to achieve these measurements: the use of stable or radioactive beams, gas injection, or the introduction of solid material into the TISS. This paper focuses primarily on a method that uses stable alkali. A pulsed/CW alkali ion gun has been built and will be used to optimise diverse TISSs

Isotopic distribution of fission fragments in collisions between 238U beam and 9Be and 12C targets at 24 MeV/u

Inverse kinematics coupled to a high-resolution spectrometer is used to investigate the isotopic yields of fission fragments produced in reactions between a 238U beam at 24 MeV/u and 9Be and 12C targets. Mass, atomic number and isotopic distributions are reported for the two reactions. These informations give access to the neutron excess and the isotopic distribution widths, which together with the atomic-number and mass distributions are used to investigate the fusion-fission dynamics.Comment: Submitted to PR

Collapse of the N=28 shell closure in 42^{42}Si

The energies of the excited states in very neutron-rich $^{42}$Si and $^{41,43}$P have been measured using in-beam $\gamma$-ray spectroscopy from the fragmentation of secondary beams of $^{42,44}$S at 39 A.MeV. The low 2$^+$ energy of $^{42}$Si, 770(19) keV, together with the level schemes of $^{41,43}$P provide evidence for the disappearance of the Z=14 and N=28 spherical shell closures, which is ascribed mainly to the action of proton-neutron tensor forces. New shell model calculations indicate that $^{42}$Si is best described as a well deformed oblate rotor.Comment: 4 pages, 3 figures, accepted for publication in Phys. Rev. let

Thinking through time: From collective memories to collective futures

In this chapter I look at the links between collective memory and the imagination of collective futures. Drawing on works on imagination and autobiographical memory, I first discuss the role of past experiences in imagining the future. I then explore the consequences of such a perspective for collective memories and collective futures, which will lead me to argue that the former provides the basis for the latter. Three case studies are presented, each illustrating a different type of relation between collective memory and collective imagination: 1) collective memory as a frame of reference to imagine the future; 2) collective memory as a source of experiences and examples to imagine what is likely, possible or desirable; and 3) collective memory as generalisable experience from which representations of the world – Personal World Philosophies – are constructed and in turn used to imagine the collective future. This will lead me to the conclusion that representations of the world are characterised by “temporal heteroglossia”, the simultaneous presence of multiple periods of time, and that they mediate the relation between collective memory and collective imagination, allowing us to “think through time”

New pathway to bypass the 15O waiting point

We propose the sequential reaction process $^{15}$O($p$,$\gamma)(\beta^{+}$)$^{16}$O as a new pathway to bypass of the $^{15}$O waiting point. This exotic reaction is found to have a surprisingly high cross section, approximately 10$^{10}$ times higher than the $^{15}$O($p$,$\beta^{+}$)$^{16}$O. These cross sections were calculated after precise measurements of energies and widths of the proton-unbound $^{16}$F low lying states, obtained using the H($^{15}$O,p)$^{15}$O reaction. The large $(p,\gamma)(\beta^{+})$ cross section can be understood to arise from the more efficient feeding of the low energy wing of the ground state resonance by the gamma decay. The implications of the new reaction in novae explosions and X-ray bursts are discussed.Comment: submitte