Post-doctoral position in nuclear physics on the analysis of exotic decays modes with ACTAR TPC (M/F)

Job Description

Missions

The selected candidate's main mission will be to work on data analysis methods related to the radioactive decay of exotic nuclei, data collected during experiments conducted using the ACTAR TPC device. The goal is to explore the possibility of using innovative analysis methods (such as "deep learning" or others) to, on the one hand, identify the different types of observed decays (number and type of emitted particles) and, on the other hand, determine their energies and emission directions, as well as assess the efficiency and limitations of the analysis. Such methods could also be considered for identifying the ions produced during these experiments (see work context).
The successful candidate will also be involved in all activities related to the ACTAR TPC collaboration. This may include testing the detector as part of a new geometry currently under development or participating in measurement campaigns within the collaboration.
Additionally, the candidate will have the opportunity to participate to some of the team's other research activities, which cover a variety of topics.

Activity

The candidate will initially focus on implementing data analysis techniques and evaluating them within the context detailed below. The analyses developed must be precisely documented so that the work can potentially be continued within the team or the collaboration.
He/she will also participate in the preparation and execution of experiments conducted on-site as part of the ACTAR TPC collaboration, as well as any tests of the device.
He/she will have the opportunity to take part in other experimental activities of the team.
He/she will present their work at international conferences and will be responsible for drafting scientific articles related to their research.

Your Profil

Skills

- Knowledge of nuclear physics and experimental techniques used in the field;
- Strong experience with data analysis tools, excellent knowledge of the C++ programming language and the ROOT environment; ability to develop and implement complex data analyses;
- Ability to integrate into a research team and work within a collaboration;
- Ability to communicate clearly about studies and developments conducted, and to produce detailed documentation;
- Good knowledge of written and spoken English.

Your Work Environment

This postdoctoral position is part of the activities of the “Exotic Nuclei” team at the Laboratoire de Physique des 2 Infinis de Bordeaux (LP2iB). The group conducts fundamental experimental nuclear physics research, focusing on tests of the weak interaction through β decay, atomic mass measurements, studies of heavy nucleus de-excitations and fission, and investigations of exotic radioactive decay modes near the drip-line. In this context, the team is involved in the ACTAR TPC collaboration.
The ACTAR TPC device is a detector developed for fundamental nuclear physics studies. It is based on the principle of a time projection chamber and enables 3D reconstruction of the trajectories of charged particles involved in the reactions under study. It was designed as a versatile instrument that can be used either in “active target” mode to study various types of reactions (charge exchange, transfer, elastic or inelastic scattering, etc.) or in “implantation-decay” mode for characterizing exotic radioactive decays (primarily involving proton emission).
The “Exotic Nuclei” group at LP2iB is particularly involved in the ACTAR TPC collaboration through experiments of this type (implantation-decay). Specifically, an experiment was performed at GANIL using the LISE3 separator to produce proton drip-line nuclei near ⁴⁸Ni via fragmentation reactions. The exotic fragments are implanted in the active volume of the gaseous detector and subsequently undergo particle emission during their radioactive decay. While the experiment primarily aimed to study direct 2-proton radioactivity (from ⁴⁵Fe and ⁴⁸Ni), all the produced nuclei exhibit other decay modes, including β-p, β-2p, β-3p, or even β-α.
Since the device is almost transparent to emitted β particles, decay events are characterized by 1 to 3 tracks of emitted protons or α particles. Studying the decay properties of these nuclei requires: (1) analyzing the number and type of emitted particles, (2) their respective energies and their emission directions. Currently, the type of emission is determined based on a multiparametric analysis of various global event information (track size, total or average collected charge, signal distribution covariance, etc.). This approach works for the simplest cases but becomes very challenging in many events for several reasons: particle trajectories curved by diffusion in the gas, short trajectories, particles escaping the detection volume, implanted ion drift toward the detector cathode before radioactive decay, etc. For determining energy and emission direction, this is currently achieved through a full 3D fit of the measured ionization charge distribution along the trajectory, based on a Bragg peak model. This method works relatively well for most events but is extremely computationally expensive, especially when processing large datasets.
The primary objective of the postdoctoral contract is therefore to study more efficient methods for classification of decay events (type of decay) and to develop better-suited and faster methods for reconstructing particle trajectories and energies.
Additionally, another aspect of this analysis work could benefit from innovative methods. Indeed, decay events are correlated with implanted ions based on emission position and decay time conditions. Since multiple types of ions are produced and implanted during measurements, it is necessary to identify them by mass and charge (A, Z). This is typically achieved through a series of energy loss and time-of-flight measurements of the ions along the beamline. However, in our case – and in the context of searching for very rare events – this is not sufficient for a clean identification. An analytical modeling-based procedure has been developed, but it has limitations due to physical cuts resulting from the separator's acceptance, which introduce distortions in the parameter distributions. More adapted algorithms could significantly improve the identification of the produced fragments.

Compensation and benefits

Compensation

Between €3,041 and €4,216 gross per month, depending on experience

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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