Ph.D. candidate in Nuclear Physics for applications in nuclear energy (M/F)

Job Description

Thesis Subject

Experimental study of (n,2n) and (n,3n) reactions on uranium-238 at the NFS facility (GANIL/SPIRAL2), using prompt gamma spectroscopy data collected in 2024. The objective is to extract reaction cross sections with reduced uncertainties and to compare the results with activation measurements and with predictions from the TALYS code. This work is part of the activities of the DNR group (IPHC-CNRS) on the measurement of nuclear data for reactor applications.
Context :
The activities of the Nuclear Data for Reactors (DNR) group focus on nuclear data for applications in the nuclear energy sector. The development of new nuclear reactor systems and fuel cycles relies primarily on computer simulations, which require high-quality evaluated nuclear data. Improving these databases demands both experimental and theoretical work to reduce uncertainties in simulations for nuclear applications.
Within this framework, our group focuses on the (n, xn) process by measuring the reaction cross sections (n, xnγ). Combining our experimental results with model predictions allows us to deduce the total reaction cross section (n, xn).
Our measurement programs are primarily dedicated to reactions involving actinides. To date, experiments have been conducted using the "white" neutron beam at GELINA (EC-JRC in Geel, Belgium), where we developed the GRAPhEME device, consisting of an array of HPGe planar detectors and a fission chamber. Particular attention has been paid to minimizing all sources of uncertainty related to our measurement instruments and the environment. The GELINA facility provides a neutron beam with an energy range well-suited to studying inelastic neutron scattering reactions (n,n').
The arrival of the new SPIRAL2/NFS (Neutrons for Science) facility at GANIL has opened up a whole new field of investigation. The neutrons produced by this facility make it possible to study higher threshold processes, such as (n,2n) and (n,3n) reactions. The DNR team, in collaboration with EC-JRC Geel, IFIN-HH Bucharest, and ESRIG Groningen, therefore proposes to conduct measurement campaigns of the (n,2n) and (n,3n) cross sections of actinides using prompt γ-ray spectroscopy. The methodology, proven for the study of (n,n') reactions at GELINA, can be adapted to NFS. After a series of tests in 2021 and 2022, a first experiment dedicated to measuring the reactions 238U(n, 2nγ) and (n, 3nγ) was carried out in the fall of 2024. Part of this experiment focused on the study of the (n, 2n) reaction by measuring activation.
Experimental method :
The experiments conducted at NFS (Neutrons For Science) rely on prompt gamma spectroscopy combined with time-of-flight (ToF) measurements. This approach allows the (n, xnγ) reactions to be studied with high precision, by exploiting the pulsed neutron beam of SPIRAL2/NFS.
The MAELS (Multi-Array for Elastic and Inelastic Scattering) device is used to detect gamma rays emitted during nuclear reactions. It consists of an array of HPGe (High-Purity Germanium) detectors optimized for high energy resolution and high detection efficiency. These detectors are arranged around the actinide target, providing optimal angular coverage for prompt gamma ray measurement.
The NFS neutron beam has a wide energy range (from a few keV to several tens of MeV), ideal for studying high-threshold reactions such as (n,2n) and (n,3n). Neutrons are produced by the spallation reaction on a carbon or beryllium target and then transported to the experimental area. Time-of-flight measurements allow for the highly accurate determination of the incident neutron energy by correlating the gamma-ray detection signal with the neutron arrival time.
The collected data are then analyzed to extract the partial cross sections (n, xnγ), which are combined with theoretical models to reconstruct the total cross sections (n, xn). This methodology has already been validated in previous campaigns, notably for the study of (n,n'γ) reactions on nuclei such as uranium-238 or thorium-232, and will be adapted for measurements on plutonium-239 and other actinides.
Objectives :
The proposed thesis topic involves analyzing data recently recorded at NFS to study the ²³⁸U(n, 2nγ) and (n, 3nγ) reactions.
This involves analyzing experimental data collected during the 2024 campaign at the NFS facility. The objective of this thesis is to extract reaction cross sections with reduced uncertainties. The results from prompt γ-speech spectroscopy analysis will be compared to the ²³⁸U(n, 2n) cross section estimate obtained by activation measurement during the same campaign.
Furthermore, the work will consist of comparing these experimental results with the predictions of the TALYS nuclear reaction code.
References
M. Kerveno, et al., From γ emissions to (n, xn) cross sections of interest: The role of GAINS and GRAPhEME in nuclear reaction modeling, Eur. Phys. J. A 51, 167 (2015)
M. Kerveno, G. Henning, et al., How to produce accurate inelastic cross sections from an indirect measurement method?, European Physical Journal N 4, 23 (2018).
M. Kerveno, et al., Measurement of ²³⁸U(n, n′γ) cross section data and their impact on reaction models, Phys. Rev. C 104, 044605 (2021).
Maëlle Kerveno, Neutron inelastic scattering, EPJ Web Conf. 322, 08001 (2025).
Greg Henning, Maëlle Kerveno, Philippe Dessagne, Nuclear Structure and Reaction Data for Reactor Applications at IPHC, Third International Workshop on Nuclear Data for the Next Decade, Paris, France (2026). ⟨hal-05553687⟩
https://box.in2p3.fr/s/PEkXS8G8zD6XsN4

Your Work Environment

This Ph.D. program will be affiliated with the “Physics and Physical Chemistry Doctoral School” at the University of Strasbourg (ED182). The candidate (M/F) will be based at the Institut Pluridisciplinaire Hubert Curien (IPHC) in Strasbourg (DRS Department).
The IPHC, a joint research unit jointly supervised by the CNRS and the University of Strasbourg (UMR7178), is a multidisciplinary laboratory where research teams from different scientific backgrounds (ecology, physiology and ethology, chemistry, and subatomic physics) develop high-level research programs based on scientific instrumentation. The IPHC is organized into three departments and has a total staff of 393 employees (M/F), including 257 permanent staff (119 researchers and faculty members and 138 engineers and technicians, M/F), 46 employees on fixed-term contracts, and 102 doctoral students (M/F).
The candidate (M/F) will join the IPHC's Nuclear Data for Reactors team, which consists of three researchers and one emeritus researcher. The team works in close collaboration with the JRC-Geel (Belgium) and IFIN-HH (Bucharest, Romania) institutes, as well as with two teams from CEA DES/Cadarache and CEA/DAM/DIF. The collaboration contributes to the JEFF project (OECD/NEA), and its work is internationally recognized. The thesis work is part of Project 1, “Nuclear Data for the Fuel Cycle and Reactors,” of the PEPR “Upstream Nuclear Fission Science” (SCIAM) program, funded by the APED (Program Agency for Research on Decarbonized Energies), France 2030.
He or she will have access to a staff cafeteria, partial reimbursement of transportation costs, a works council, the option to work remotely for some tasks, and training to help them adapt to the job.
Strasbourg is one of the most attractive cities in Europe. It boasts a rich historical and architectural heritage, with Strasbourg's historic center listed as a UNESCO World Heritage Site. Its human scale, pedestrian-friendly downtown, and 500 km of bike paths make it a very pleasant city to explore. Vibrant and affordable, Strasbourg is a true student city offering an excellent environment for learning and living (watch the New York Times video: 36 Hours in Strasbourg).
Requirements:
• Master's degree in Nuclear Physics
• Skills in gamma spectroscopy, data analysis, C/C++ and Python programming
• Strong knowledge of nuclear physics (nuclear reactions, cross sections) and experimental methods
• Autonomy, tenacity, mobility, creativity, and strong motivation.
• Good level of English, both spoken and written, at level B2 according to the Common European Framework of Reference for Languages (CEFR), to interact with all project partners and disseminate results through scientific publications and conference presentations.
Candidates will need to send a CV and cover letter, their master's summary and associated notes, as well as contact information for references and, if applicable, one or two independent letters of recommendation.

Constraints and risks

· Travel to participate in experimental campaigns and collaborative meetings (primarily in France/Europe) and workshops/conferences in the field.
· Part of the work will involve access to controlled areas for protection against ionizing radiation.

Compensation and benefits

Compensation

2300 € gross monthly

Annual leave and RTT

44 jours

Remote Working practice and compensation

Pratique et indemnisation du TT

Transport

Prise en charge à 75% du coût et forfait mobilité durable jusqu’à 300€

About the offer

About the CNRS

The CNRS is a major player in fundamental research on a global scale. The CNRS is the only French organization active in all scientific fields. Its unique position as a multi-specialist allows it to bring together different disciplines to address the most important challenges of the contemporary world, in connection with the actors of change.

CNRS

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