Design and accelerated testing of corrosion FOSs for reinforced concrete structures

Corrosion of steel reinforcement is the main pathology threatening the durability of civil engineering structures. Today, structures are mainly monitored by means of periodic visual inspections or even auscultation (corrosion potentials, ultrasonic measurements, core sampling, etc…), which are not very satisfactory. There is therefore a need for instrumentation capable of detecting the initiation and location of corrosion of reinforcement in concrete and ensuring long-term monitoring (several decades or more). In the context of Civil Engineering (CE) structures, Optical Frequency-Domain Reflectometry (OFDR) appears to be a suitable metrological solution because of its centimetre resolution and measurement range (70 metres in the standard version, i.e. several thousand measurement points along an optical fibre).
Content of work: The aim will be to adapt the design of this fibre optic sensor (FOS) to increase its durability and then to verify its applicability in the laboratory. Initially, the person recruited on a fixed-term research contract will be asked to work on the durability of the connexion between the optical fibre and the armature. Two different methods are envisaged: plasma torch spraying of ceramic powders and sol-gel. Both of these processes prevent the galvanic coupling because they involve insulating materials (ceramics) and are already deployed in industry in various civil and military fields. Secondly, test specimens equipped with the FOS will be tested in the laboratory according to classic civil engineering situations, i.e. localised corrosion (pitting induced by exposure to chloride ions) and uniform corrosion (generalised corrosion induced by carbonation of the embedding concrete). OFDR acquisitions will be carried out periodically over time in parallel with conventional metrology (potential, etc.).

Development of a new spectrometer for the characterization of the radionuclide-based neutron sources

Since few years, the LNHB is developing a new instrument dedicated to the neutron spectrometry, called AQUASPEC. The experimental device consists of a polyethylene container that is equipped with a central channel accommodating the source and 12-measurement channels (in a spiral formation) around the source, into which detectors can be placed. The container is filled with water in order to moderate neutrons emitted from the source. Measurements have performed with 6Li-doped plastic scintillators, optimized for the simultaneous detection of fast neutrons, thermal neutrons and gamma rays through the signal processing based on pulse shape discrimination (PSD). The spectrum reconstruction is performed with an iterative ML-EM or MAP-EM algorithm, by unfolding experimental data through the detector's responses matrix calculated with MCNP6 code. The candidate will work in the general way on issues related to the neutron spectrometry in the laboratory: Contribution to the development and validation of the new spectrometer AQUASPEC; Participation to the sources measurements and working on aspects of neutron detection and signal processing, in particular issue of the discrimination of neutron/gamma based on the pulse shape discrimination technique (PSD); Usage of Monte Carlo simulation codes and algorithms to reconstruct initial neutron energy distribution; Investigation and integration of information related to neutron/gamma coincidence specific to the XBe type sources.

Postdoc in Multi-instrumented operando monitoring of Li-ion battery for ageing

Nowadays, the development of new battery technology requires increasing the knowledge of degradation mechanisms occur inside the cell and monitor the key parameter in real time during cycling to increase the performances, lifetime and safety of the cells. To achieve these goals development of new sensing technology and integration inside and outside the cell is needed. The goal of the SENSIGA project is used advanced sensing technology to improve the monitoring of the cell by acquiring useful data correlate to the degradation process and develop more efficient battery management system with accurate state estimators. SENSIGA is a part of PEPR Batteries lead by CNRS and CEA and funding by the French Research Programme FRANCE 2030 to accelerate the development of new battery technology.
You will have the opportunity to work in a stimulating scientific environment focusing on the characterisation of both state of the art and latest generations of battery materials. Based on the sensing technology developed at CEA and from the state of the art, the SENSIGA project will reach the objective of the BATTERY2030+ roadmap goals for smart cells (https://battery2030.eu/research/roadmap/). One of the objectives of the project is to use external sensors to monitor the key parameters of the cell related to performances, ageing and safety behaviours.

Separation microsystem coupled to mass spectrometry for on-line purification and characterisation of nuclear samples

The miniaturisation of analytical steps commonly carried out in laboratories offers many advantages and particularly in the nuclear sector, where the reduction of material consumption and waste production is of major interest. In this context, one of our laboratory’s focus area is the miniaturisation of analytical tools, particularly chromatographic separation techniques. The aim of this project is to reduce the scale of the purification steps of nuclear samples by solid phase extraction chromatography, prior to the analytical processes. Obtaining these miniaturised extraction devices is based on the in situ synthesis and anchoring of monoliths, in the channels of cyclic olefin copolymer (COC) microsystems. Since this material is chemically inert, COC functionalisation strategies are currently under development to covalently graft reactive sites on its surface, before locally anchoring actinide-specific monoliths in the micro-channels. The aim is to design and fabricate chromatographic extraction microsystems in COC, and to implement them for chemical purification and mass spectrometry measurements, both off-line and on-line.

Simulation of the interaction of a high energy pulsed X-ray beam with a scintillator

In the context of hydrodynamic experiments, the CEA-DAM uses pulse radiography facilities which generate, in a few tens of nanoseconds, a very high dose of energetic X-ray photons, up to 20 MeV. After crossing the studied object, the X photons interact with a detector, composed of a scintillator crystal converting the X photons into visible photons, which are then detected by a CCD camera. The objective of this post-doctorate is to set up a complete simulation chain of the detector, including the emission of visible photons by the scintillator and their transport by the optical chain to the CCD camera. Initially, the candidate will have to model the different mechanisms involved in the detection chain and identify the most relevant simulation tools to reproduce them. In a second step, he (she) will be required to compare the simulation results with experimental characterization campaigns, carried out using a pulsed X source. Finally, the candidate will be able to propose, using the chosen simulation chain, possible developments for future detection chains. This work may lead to publications.

Design of a photonic Doppler velocimetry diagnostic in the mid-infrared for high velocities

This post-doctorate aims to design, using innovative technological éléments, a photonic Doppler velocimetry diagnostic operating in the mid-infrared (between 3 µm and 5 µm) to probe clouds of dense particles moving at high speeds (up to 5000 m/s), in shock physics. Schematically, two laser waves slightly offset in frequency are caused to interfere on a photodetector connected to a digitizer, one serves as a reference and the other carries the speed information of the targeted object, by Doppler effect. The development of new optical components and advanced technologies in this range of wavelengths is currently in full swing, for applications in Defense, gas detection, etc... In a first design phase, the candidate will therefore have to identify and choose the most relevant photonic components for our needs. To do this, he or she will have to optimize the overall performance of the measurement chain, using commercial simulation tools or tools developed at CEA-DAM. In a second step, he (she) will constitute the measurement chain with the selected optical elements. He (she) may also be required to participate in the design and manufacture of precision mechanical elements to ensure the interface between the elements. Depending on the state of progress, the system thus designed may be deployed on dedicated experiments. This work may lead to publications.

Study and modeling of fiber Bragg grating acoustic receivers

CEA List has been working for several years on the development of advanced monitoring solutions using fibre optic acoustic receivers called Fiber Bragg Gratings. These optical sensors have a great potential for structural health monitoring, both because of their ability to be integrated into materials (concrete, organic composites, metal) and because of their ability to be deployed in severe environments (embedded, radiative, high temperature).
A post-doctoral work is proposed to carry out modelling of these Fiber Bragg Grating transducers in order to refine the understanding of their sensitivity to ultrasonic guided elastic waves and to help in the design of an associated control system thanks to an intelligent placement of the sensors. Ultimately, the aim is to be able to simulate their response within the Civa non-destructive testing software developed by CEA List, and more particularly via its module dedicated to Structural Health Monitoring (SHM). Such work would strongly contribute to the adoption and exploitation of this technology for Structural Health Monitoring applications.

Implementation of a sensor allowing the online monitoring of the corrosion of stainless steels in a hot and concentrated nitric acid medium

The control of materials (mainly stainless steel) aging of the spent nuclear fuel reprocessing plant is the subject of permanent attention. Some installations at La Hague plant will have to be replaced very soon. In this context, it is important for the industry to develop sensors that are resistant to concentrated nitric acid (˜ 2.5 mol / L) and temperature (from ambient to 130 °C), allowing the online monitoring of the corrosion.
The aim of this work is to manufacture one sensor for the detection of corrosion of the steel intended for handling by the operators of the plant. In case of a positive response, the second sensor is used.
The challenges of this work are essentially technological since it will develop or use materials adapted to concentrated and hot nitric acid media.
The laboratory is specialized in the corrosion study in extreme conditions. It is composed of a very dynamic and motivated scientific team.

Fast-scintillator-based device for on-line FLASH-beam dosimetry

New cancer treatment modalities aim to improve the dose delivered to the tumor while sparing healthy tissue as much as possible. Various approaches are being developed, including the temporal optimization of the dose delivered with very high dose rate irradiation (FLASH).
In this particular case, recent studies have shown that FLASH irradiation with electrons was as effective as photon beam treatments for tumor destruction while being less harmful to healthy tissue. For these beams, the instantaneous doses are up to several orders of magnitude higher than those produced by conventional beams. Conventional active dosimeters saturate under irradiation conditions at very high dose rates per pulse, therefore on-line dosimetry of the beam is not possible.
We propose to develop a dosimeter dedicated to the measurement of beams in FLASH radiotherapy based on an ultra-fast plastic scintillator coupled with a silicon photomultiplier sensor (SiPM). The novelty of the project lies both in the chemical composition of the plastic scintillator which will be chosen for its response time and its wavelength emission to have a response adapted to the impulse characteristics of the beam, and in the final sensor with the possibility of coupling the plastic scintillator to a miniaturized SiPM matrix.
The final goal is to be able to access, with a reliable methodology, the dosimetry and in-line geometry of FLASH beams.

Measurement of active cell nematics by lensless microscopy

At CEA-Leti we have validated a video-lens-free microscopy platform by performing thousands of hours of real-time imaging observing varied cell types and culture conditions (e.g.: primary cells, human stem cells, fibroblasts, endothelial cells, epithelial cells, 2D/3D cell culture, etc.). And we have developed different algorithms to study major cell functions, i.e. cell adhesion and spreading, cell division, cell division orientation, and cell death.
The research project of the post-doc is to extend the analysis of the datasets produced by lens-free video microscopy. The post-doc will assist our partner in conducting the experimentations and will develop the necessary algorithms to reconstruct the images of the cell culture in different conditions. In particular, we will challenge the holographic reconstruction algorithms with the possibility to quantify the optical path difference (i.e. the refractive index multiplied by the thickness). Existing algorithms allow to quantify isolated cells. They will be further developed and assessed to quantify the formation of cell stacking in all three dimensions. These algorithms will have no Z-sectioning ability as e.g. confocal microscopy, only the optical path thickness will be measured.
We are looking people who have completed a PhD in image processing and/or deep learning with skills in the field of microscopy applied to biology.

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