Towards a multimodal photon irradiation platform: foundations and conceptualization
Photonic irradiation techniques exploit the interactions between a beam of high-energy photons and matter to carry out non-destructive measurements. By inducing photonuclear reactions such as photonic activation, nuclear resonance fluorescence (NRF) and photofission, these irradiation techniques enable deep probing of matter. Combining these different nuclear measurement techniques within a single irradiation platform would enable precise, quantitative identification of a wide variety of elements, probing the volume of the materials or objects under study. The high-energy photon beam is generally produced by the Bremsstrahlung phenomenon within a conversion target of a linear electron accelerator. An innovative alternative is to exploit the high-energy electrons delivered by a laser-plasma source, converted by Bremsstrahlung radiation or inverse Compton scattering. A platform based on such a source would open up new possibilities, as laser-plasma sources can reach significantly higher energies, enabling access to new advanced imaging techniques and applications. The aim of this thesis is to establish the foundations and conceptualize a multimodal photonic irradiation platform. Such a device would aim to be based on a laser-plasma source and would enable the combination of photonic activation, nuclear resonance fluorescence (NRF) and photofission techniques. By pushing back the limits of non-destructive nuclear measurements, this platform would offer innovative solutions to major challenges in strategic sectors such as security and border control, radioactive waste package management, and the recycling industry.
3D ultrasound imaging using orthogonal row and column addressing of the matrix array for ultrasonic NDT
This thesis is part of the activities of the Digital Instrumentation Department (DIN) in Non-Destructive Testing (NDT), and aims to design a new, fast and advanced 3D ultrasound imaging method using matrix arrays. The aim will be to produce three-dimensional ultrasound images of the internal volume of a structure that may contain defects (e.g. cracks), as realistically as possible, with improved performance in terms of data acquisition and 3D image computation time. The proposed method will be based on an approach developed in medical imaging based on Row and Column Addressed (RCA) arrays. The first part will focus on the development of new data acquisition strategies for matrix arrays and associated ultrafast 3D imaging using RCA approach in order to deal with conventional NDT inspection configurations. In the second part, developed methods will be validated on simulated data and evaluated on experimental data acquired with a conventional matrix array of 16x16 elements operating in RCA mode. Finally, a real-time proof of concept will be demonstrated by implementing the new 3D imaging methods in a laboratory acquisition system.
Development of a multiphysics stochastic modelling for liquid scintillation measurements
The Bureau international des poids et mesures (BIPM) is developing a new transfer instrument named the "Extension of the International Reference System" (ESIR), based on the Triple-to-Double Coincidence Ratio (TDCR) method of liquid scintillation counting with a specific instrumentation comprising three photomultipliers. The aim is to enable international comparisons of pure beta radionuclides, certain radionuclides that decay by electron capture, and to facilitate international comparisons of alpha emitting radionuclides.
The TDCR method is a primary activity measurement technique used in national laboratories. For the activity determination, its application relies on the construction of a model of light emission requiring knowledge of the energy deposited in the liquid scintillator. Depending on the decay scheme, the combination of different deposited energies can be complex, particularly when it results from electronic rearrangement following electron capture decay. The stochastic approach of the RCTD model is applied by randomly sampling the different ionizing radiation emissions following a radioactive decay. The recent addition of modules for automatically reading nuclear data (such as those available in the Table des Radionucléides) in radiation/matter simulation codes (PENELOPE, GEANT4), means that all possible combinations can be rigorously taken into account. The stochastic approach makes it possible to consider the actual energy deposited in the liquid scintillation vial, taking into account interactions in the instrumentation as a whole.
The aim of this thesis is to develop a multiphysics stochastic approach using the GEANT4 radiation/matter simulation code, to be applied in particular to the BIPM's ESIR system. The choice of the Geant4 code offers the possibility of integrating the transport of ionizing particles and scintillation photons. This development is of great interest for radioactivity metrology, with the aim of ensuring metrological traceability to a larger number of radionuclides with the BIPM's ESIR system. The thesis will be carried out in collaboration with the Commissariat à l'Energie Atomique et aux Energies Alternatives (CEA), which already has experience in developing a stochastic model with the GEANT4 code for its instrumentation dedicated to the TDCR method at the Laboratoire National Henri Becquerel (LNE-LNHB).