The provenance of tills overlying the eastern part of the South Mountain Batholith, Nova Scotia

Happing of quarternary deposits on the South Mountain Batholitb (SMB) has resulted in a four-fold subdivision of tills, divided primarily on the basis of clast lithology, texture, stratigraphic position and morphology. Three tills have clast lithologies characterized by granites eroded from the South Mountain Batholih. The oldest granite till is a compact till of restricted distribution, mianly observed In drumlin cores. Two younger granite tills dominate the surficial deposits of portions of the SMB and have textural properties ascribed to melt-out tills. The fourth till represents a farther-travelled till with a variable clast provenance typified by pebbles derived from both the SMB and regions to the north. Clast dispersal evidence suggests that all tills were transported in a general southward direction. Detailed clast examinations allow reliable conclusions concerning direction of Ice flow and lithologic relationship between till and bedrock of the SMB. The SMB is an area of multiple glaciatlon where till prospecting cannot be successful unless the direction of till transport and source areas are established. RÉSUMÉ Dn levé cartographique des dépôts quaternaires recouvrant le Batholite de South Mountain à permis de mettre en évidence quatre varlétés de tills en fonctlon de la lithologie des clastes, la texture, la position stratlgraphlque et la morphologic Dana trola tills, les clastes nontrent des lithologles caractérisées par des granites arrachés au Batholite de South Mountain (BSM). Le plus vleux till de granite est un till tasse. de faible étendue, observe surtout dans les noyaux de drumlins. Dans certaines portions du BSM, les dépôts de surface sont dominés par deux tills de granite plus recents qui possedent des caractéristlques texturales rapportées aux tills d'ablation. Le quatriéme till a parcouru une plus grande distance; la source de ses clastes est variable et comprend typiquement des galets provenant tant du BSM que des régions plus au nord. La dispersion des blocaux suggère un direction générale de transport des tills vers le sud. Un exanen approfondi des clastes permet de tirer de solides conclusions à propos de la direction de l’écouleroent glacialre et de la relation lithologique entre le till et le socle du BSM. Le BSM a subi de multiples glaciatlons et la prospection du till n'y est done guère profitable à molns de déterminer la direction de transport et la source du till. [Traduit par le journal

Reactive transport modelling of the long-term interaction between carbon steel and MX-80 bentonite at 25 °C

The geological disposal in deep bedrock repositories is the preferred option for the management of high-level radioactive waste (HLW). In some of these concepts, carbon steel is considered as a potential canister material and bentonites are planned as backfill material to protect metallic waste containers. Therefore, a 1D radial reactive transport model has been developed in order to better understand the processes occurring during the long-term iron-bentonite interaction. The numerical model accounts for diffusion, aqueous complexation reactions, mineral dissolution/precipitation and cation exchange at a constant temperature of 25 °C under anoxic conditions. Our results suggest that Fe is sorbed at the montmorillonite surface via cation exchange in the short-term, and it is consumed by formation of the secondary phases in the long-term. The numerical model predicts precipitation of nontronite, magnetite and greenalite as corrosion products. Calcite precipitates due to cation exchange in the short-term and due to montmorillonite dissolution in the long-term. Results further reveal a significant increase in pH in the long-term, while dissolution/precipitation reactions result in limited variations of the porosity. A sensitivity analysis has also been performed to test the effect of selected parameters, such as corrosion rate, diffusion coefficient and composition of the bentonite porewater, on the corrosion processes. Overall, outcomes suggest that the predicted main corrosion products in the long-term are Fe-silicate minerals, such phases thus should deserve further attention as a chemical barrier in the diffusion of radionuclides to the repository far field

Performance of the reconstruction algorithms of the FIRST experiment pixel sensors vertex detector

Hadrontherapy treatments use charged particles (e.g. protons and carbon ions) to treat tumors. During a therapeutic treatment with carbon ions, the beam undergoes nuclear fragmentation processes giving rise to significant yields of secondary charged particles. An accurate prediction of these production rates is necessary to estimate precisely the dose deposited into the tumours and the surrounding healthy tissues. Nowadays, a limited set of double differential carbon fragmentation cross-section is available. Experimental data are necessary to benchmark Monte Carlo simulations for their use in hadrontherapy. The purpose of the FIRST experiment is to study nuclear fragmentation processes of ions with kinetic energy in the range from 100 to 1000 MeV/u. Tracks are reconstructed using information from a pixel silicon detector based on the CMOS technology. The performances achieved using this device for hadrontherapy purpose are discussed. For each reconstruction step (clustering, tracking and vertexing), different methods are implemented. The algorithm performances and the accuracy on reconstructed observables are evaluated on the basis of simulated and experimental data

Synthetic smectite colloids: Characterization of nanoparticles after co-precipitation in the presence of lanthanides and tetravalent elements (Zr, Th)

The magnesian smectite hectorite is a corrosion product frequently detected in nuclear waste glass alteration experiments. The structural incorporation of a single trivalent lanthanide was previously demonstrated. Hectorite was presently synthesized, for the first time, in the presence of several lanthanides (La, Eu, Yb) following a multi-step synthesis protocol. The smallest-sized particles (nanoparticles, NPs) were isolated by centrifugation and analyzed by asymmetrical flow field-flow fractionation (AsFlFFF) coupled to ICP-MS, in order to obtain information on the elemental composition and distribution as a function of the size. Nanoparticles can be separated from the bulk smectite phase. The particles are able to accommodate even the larger-sized lanthanides such as La, however, with lower efficiency. We, therefore, assume that the incorporation proceeds by substitution for octahedral Mg accompanied by a concomitant lattice strain that increases with the size of the lanthanides. The presence of a mixture does not seem to affect the incorporation extent of any specific element. Furthermore, syntheses were performed where in addition the tetravalent zirconium or thorium elements were admixed, as this oxidation state may prevail for many actinide ions in a nuclear waste repository. The results show that they can be incorporated as well

Population of neutron unbound states via two-proton knockout reactions

The two-proton knockout reaction 9Be(26Ne,O2p) was used to explore excited unbound states of 23O and 24O. In 23O a state at an excitation energy of 2.79(13) MeV was observed. There was no conclusive evidence for the population of excited states in 24O.Comment: 6 pages, 3 figures, Proc. 9th Int. Spring Seminar on Nucl. Phys. Changing Facets of Nuclear Structure, May 20-34, 200