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Reference : UMR3685-SOPLEC-001
Workplace : GIF SUR YVETTE
Date of publication : Saturday, February 29, 2020
Type of Contract : FTC Scientist
Contract Period : 12 months
Expected date of employment : 1 June 2020
Proportion of work : Full time
Remuneration : gross monthly salary around 2800 €, depending on experience
Desired level of education : PhD
Experience required : Indifferent
An important issue of the nuclear industry is to find suitable and sustainable ways to dispose nuclear wastes. For instance, outflows composed of organic liquids and arising from nuclear facilities can contain significant concentrations of various radionuclides generating ionizing radiation. It is therefore important to develop new solutions for these wastes. In this context, radionuclide sorption and immobilization in mesoporous material could be one of them. In this project, we have chosen to work with mesoporous silica exhibiting high specific surfaces (up to 1000 m²/g) and mesopores that can be easily tuned from 2 nm to 10 nm. Organic ligands can be grafted inside the pores to obtain specific sorption properties towards radionuclides. Once being synthesized, it is important to understand how these grafted materials behave towards ionizing radiation in order to evaluate how their sorption properties can change upon irradiation.
The purpose of this 1-year post-doc position is then to decipher reaction mechanisms induced by radiolysis in mesoporous silica grafted with various organic ligands. This will guide the choice of the best material (i.e. the less prone to be affected by ionizing radiation). To reach this goal, radiolysis will be mainly induced by 10 MeV electrons (linear accelerator). The materials will be characterized in details before and after irradiation using different techniques (thermogravimetric analysis, solid state Nuclear Magnetic Resonance, infrared spectroscopy….). The gases released during irradiation will be analyzed by gas chromatography mass spectrometry, and quantified by mass spectrometry and also by micro gas chromatography. Thus, the nature and the amounts of gases released in the different systems will be compared. In irradiated samples, solid state Nuclear Magnetic Resonance will enable understanding which bonds are the most prone to be cleaved under ionizing radiation. Electron Spin Resonance (ESR) experiments will also enable detecting the radical species created upon irradiation. From all these experiments, reaction mechanisms will be proposed and will account for the different bond modifications occurring in the different studied materials. Lastly, our linear accelerator enables performing irradiation at a relatively high irradiation dose. After having irradiated the materials at this high dose, we will be able to determine if the materials have lost (or not) a part of their retention properties, and, if yes, to propose then a wiser choice for an ideal material.
The candidate will:
* characterize the materials before irradiation (thermogravimetric analysis, infrared spectroscopy, NMR ...)
* measure the gases produced under irradiation (gas chromatography, mass spectrometry ...)
* characterize the radicals produced under irradiation (electron paramagnetic resonance)
* characterize the materials after irradiation
* propose reaction mechanisms of phenomena occurring under radiation
The successful candidate is expected to hold a PhD in a relevant area of physical chemistry since no more than 2 years. He/she will have prior experience in analytical techniques and material sciences. Background in EPR (electron paramagnetic resonance) technique and radiolysis will be an asset.
The work is carried out on the CEA Saclay site in the UMR 3685 CEA CNRS NIMBE.
The themes of NIMBE are based on the mastery of the design, shaping and analysis of matter from the micron to the nanometric scale, as well as on the understanding of physico-chemical mechanisms and their synergies at these scales. All of these approaches are applied as a priority to the major societal challenges that are (nano) materials for sustainable energy management, the environment or information processing, biomedical diagnosis, etc.
The work will be more precisely carried out in the LIONS laboratory (Interdisciplinary Laboratory on Nanometric and Supramolecular Organization).
Constraints and risks
The irradiation experiments take place under very strict safety conditions after training at the workplace.
These experiences do not present any danger, once the safety rules are respected.
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