[Academic] FW: Seminar and visit of Prof. Jorge Kohanoff

[Catherine Cheshire]

Dear All

Please see details below of a seminar taking place on 6th Nov that may be of interest to you.

Catherine



Seminar
6 November 2013, 2:00pm
Royal College, Room R669
Prof. Jorge Kohanoff, Queen's University Belfast


Title: Are ionic liquids any good to store nuclear waste?



Abstract:

Nuclear waste is here with us whether we want it or not. Even if all the fusion power plants are closed today, there is a large amount of

radioactive waste accumulated that has to be taken care of. What to do then? For a long time already, the preferred solution was to disperse and

store the radioactive substances into materials that can stand the decay without perceptible long-term degradation. Depending on the lifetime of the unstable species, various different materials such as perovskite ceramics and borosilicate glasses have been evaluated and are being used at present. The main limitation of such materials is the amount of waste they can store without becoming dangerous. Neutrons are produced in the decay process that can activate other radioactive atoms and produce a chain reaction. That is why boron is preferred, as it has a large neutron capture cross section.



An alternative medium that has been proposed to this end are room temperature ionic liquids (IL). These are very viscous, almost glassy substances made of bulky, generally organic, cations and a variety of anions (that can contain boron, like BF4-). Apart from neutrons, the radioactive decay process produces gamma-rays and alpha-particles, whose main effect is to ionize the medium generating secondary, low-energy electrons that eventually become solvated in the IL. The dynamics of such excess electrons has been studied experimentally by means of transient optical spectroscopy, revealing a non-trivial evolution of the absorption bands.



We have studied these systems using ab initio molecular dynamics simulations. Firstly, we have identified the origin of the absorption bands in the "dry" electron (at time zero) and interpreted them in terms of the localization of the excess electron in cations and anions. Secondly, we have followed the evolution of the absorption spectra well into the psec regime, and showed that its evolution is due to the process of solvation of the "dry" electron, i.e. the localization in a single ion, and the subsequent decomposition of the ion that leads to the degradation of the IL. These results are also relevant from the electrochemical point of view.


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