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.
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.
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.
IMPROVING OPTICALLY PUMPED MAGNETOMETERS FOR BIOMEDICAL IMAGING
Our lab works on optically pumped magnetometers (OPM) based on helium-4 metastable atoms. Our main achievement in last years has been the design and space qualification of the most advanced OPMs available for spatial exploration, which were launched on ESA Swarm mission [1]. With this very same species we have developed OPMs for medical imaging of brain (MEG) and heart (MCG), which have the advantage of operating at room temperature. The development of these two imaging techniques is an opportunity to better understand and diagnose pathologies like epilepsy, Alzheimer or arrhythmia.
A few years ago we performed proof of concept measurements of both MCG and MEG with primitive versions of our sensors [2,3]. After getting a better understanding of our sensors physics [4] and implementing substantial improvements, we are now developing arrays of OPMs and collaborating with several clinical teams in order to test them for different applications and environments. The purpose of this post-doctoral position is to contribute to the development of magnetometer arrays. It involves experimental work to improve the current prototypes of medical OPM arrays: the post-doc will be notably in charge of improving the intrinsic noise of the sensor and identifying the best way to build robust, reproducible architectures that could be replicated in arrays of several hundreds of sensors.
This work is aimed at bringing this technology to the medical imaging market, in collaboration with a start-up currently prepared by CEA-Leti. It will be carried out in a multidisciplinary team, composed of researchers, experienced engineers, PhD students and post-docs, specialized in the fields of optics, lasers, magnetism and electronics. It will also rely on collaborations with medical research teams in neurology and cardiology.
[1] http://smsc.cnes.fr/SWARM
[2] S. Morales et al.,
[3] E. Labyt et al., IEEE Transactions on Medical Imaging (2019).
[4] F. Beato et al. Physical Review A (2018)
LAB AND FIELD WORK ON OPTICALLY PUMPED MAGNETOMETERS
Our lab works on optically pumped magnetometers (OPM) based on helium-4 metastable atoms. Our main achievement in last years has been the design and space qualification of the most advanced OPMs available for spatial exploration, launched on ESA Swarm mission [1].
With this same species we have developed OPMs for medical imaging of brain (MEG) and heart (MCG), which have the advantage of operating at room temperature, with no heating or cooling.
The development of these two imaging techniques is an opportunity to better understand and diagnose pathologies like epilepsy, Alzheimer or arrhythmia.
A few years ago we performed proof of concept measurements of both MCG and MEG with primitive versions of our sensors [2,3]. After getting a better understanding of our sensors physics [4] and implementing substantial improvements, we are now developing arrays of OPMs and collaborating with several clinical teams in order to test them for different applications and environments.
The purpose of this post-doctoral position is to contribute to the development of magnetometer arrays. It involves mainly the deployment of OPM arrays in the clinical environments where they are going to be tested by several of our partner medical research teams in both neurology and cardiology. The post-doc should be able to deploy and operate the sensors in these environments, solve the practical issues, and bring feedback on all kind of improvements that are needed. He or she will also participate in the implementation of some of these improvements, and their tests in lab environment.
This work is aimed at bringing this technology to the medical imaging market. It will be carried out in a multidisciplinary team, composed of researchers and experienced engineers.
[1] http://smsc.cnes.fr/SWARM
[2] S. Morales et al., Phys. Med. B
[3] E. Labyt et al., IEEE Transactions on Medical Imaging (2019).
[4] F. Beato et al. Physical Review A (2018)
Analysis of low abundance 144Ce and 106Ru isotopes by mass spectrometry
The aim of this project is to develop the high precision analysis of 144Ce and 106Ru by mass spectrometry in irradiated samples for the qualification of neutronic calculation codes. These two isotopes are present at low abundances in the samples of interest and display significant isobaric interferences with 144Nd and 106Pd respectively. To complete this project, the candidate will carry out the appropriate analytical developments in conventional laboratory on inactive samples. Then the procedure will be transposed in the active laboratory for validation with the analysis of real samples. In the case of 144Ce, the implementation of a coupling between high performance liquid chromatography (HPLC) and ICPMS-MC, combined with the isotope dilution technique for the precise determination of atomic contents is envisaged. For 106Ru, the 101Ru concentration will first be determined by ICPMS-Q and the 101Ru/106Ru ratio will be determined by HPLC/ICPMS-Q or HPLC/ICPMS-MC coupling to remove the 106Pd/106Ru interference.
Development of femtosecond Fiber Bragg Grating acoustic receivers for the Structural Health Monitoring using passive acoustic tomography
The proposed post-doctoral fellowship is part of a transverse project initiated by the CEA and which consists in developing a prototype of a continuous monitoring system of a metallic structure (pipe for example) using fiber Bragg gratings acoustic receivers and passive imaging (or passive tomography). It aims to demonstrate the relevance of the SHM (Structural Health Monitoring) concept for nuclear facilities using optical fiber sensors operating in continuous and in extreme environment. This project is based on two recent developments: new generation of fiber Bragg gratings developed for severe environments and defect imaging algorithms based on ambient noise analysis. A demonstration of elastic wave reconstruction from passive algorithm applied to fiber Bragg gratings was carried out at the CEA in 2015, which is a world first, patented. The project aims more particularly to produce a demonstrator and to equip a pipeline on a test loop. It will provide input data relating to the ability of a moving fluid to generate elastic waves that can be analyzed in passive tomography.