Simulation of radiation damage via alpha decay in BFS:PC grouts using 4He2+ ion acceleration

The impact of alpha radiation on cements used to encapsulate intermediate-level waste (ILW) is not well understood. ILW wastes can contain high levels of alpha-emitting radionuclides, meaning that the grouts used to encapsulate them are exposed to significant ionising radiation. Thus, a damaged region could develop in the grout adjacent to the alpha-emitting species. This work attempted to recreate this behaviour through nonradioactive 4He2+ ion-accelerator experiments, which have not previously been applied to common encapsulation grouts. The influence of this irradiation on a slag-Portland cement was investigated at different ages via transmission electron microscopy energy-dispersive x-ray spectroscopy (TEM-EDX) and supporting techniques, to assess whether 4He2+ irradiation caused textural or chemical zonation. No significant changes in hydrate phases or textures were observed, other than minor variations associated with carbonation. This paper provides a proof of concept for using ion acceleration techniques on cements and furthers knowledge on their radiation response

Imaging the radical channel in acetaldehyde photodissociation: Competing mechanisms at energies close to the triplet exit barrier

The photodissociation of acetaldehyde in the radical channel has been studied at wavelengths between 315 and 325 nm using the velocity-map imaging technique. Upon one-photon absorption at 315 nm, the molecule is excited to the first singlet excited state S1, which, in turn, undergoes intersystem crossing to the first excited triplet state T1. On the triplet surface, the molecule dissociates into CH3 and HCO radicals with large kinetic energy release (KER), in accordance with the well characterized exit barrier on T1. However, at longer wavelengths (>320 nm), which correspond to excitation energies just below the triplet barrier, a sudden change in KER is observed. At these photolysis wavelengths, there is not enough energy to surpass the exit barrier on the triplet state, which leaves the possibility of unimolecular dissociation on S0 after internal conversion from S1. We have characterized the fragments’ KER at these wavelengths, as well as determined the energy partitioning for the radical fragments. A new accurate estimate of the barrier height on T1 is presented.Depto. de Química FísicaFac. de Ciencias QuímicasTRUEpu

Recent progress in the massively parallel solution of implicit problems

Explicit strategies for the solution of finite element problems, such as crash simulation, scale well on computing platforms with thousands of cores. In contrast, it is a widely held view that implicit analysis is not suited to parallel computing. The purpose of this paper is to challenge that belief. The open source parallel finite element software, ParaFEM, uses an “element by element” approach with iterative solvers to solve problems in an implicit way; such as static equilibrium, material nonlinearity, fluid flow, and free and forced vibrations. This iterative strategy leads to a program structure similar to explicit algorithms and the consequence is excellent scalability of implicit analysis on parallel platforms. The software is modularised in such a way that the parallel code is hidden away in a library of subroutines, enabling engineers and researchers who have no training in parallel programming to adapt the software for their own needs. In this paper, we report on recent progress in community-based extensions to ParaFEM including support for stochastic random fields, large strain plasticity, transient thermal analysis and the multiscale modelling of polycrystalline structures. We will report on how well each of those types of problem, analysed using massively parallel implicit solvers, scale on hardware platforms with tens of thousands of cores