4 sujets /DPhN/LENA

Dernière mise à jour : 29-06-2022


 

Shape coexistence in nuclei around 96Zr

SL-DRF-22-0277

Research field : Nuclear physics
Location :

Service de Physique Nucléaire (DPhN)

Laboratoire études du noyau atomique (LENA) (LENA)

Saclay

Contact :

Magdalena Zielinska

Starting date : 01-10-2022

Contact :

Magdalena Zielinska
CEA - DRF/IRFU/DPhN/LENA

01 69 08 74 86

Thesis supervisor :

Magdalena Zielinska
CEA - DRF/IRFU/DPhN/LENA

01 69 08 74 86

This PhD project is focused on nuclear structure, and, more precisely, nuclear shapes in the transitional (A~100) region of the nuclear chart.

The shape is one of the fundamental properties of a nucleus. It is governed by an interplay of macroscopic and microscopic effects like the shell structure. Some of these nuclei are known to exhibit the shape-coexistence phenomenon: the nucleus changes drastically its shape at low excitation energy. Recently, observation of a low-lying deformed state in the magic 96Zr nucleus has been explained by a reorganization of nuclear shells in function of their occupation by protons and neutrons. The present project deals with the neighbouring 100Ru nucleus, which is suggested to present similar features as 96Zr, but is more accessible experimentally. Two experimental techniques will be applied: gamma-ray spectroscopy following neutron capture, and Coulomb excitation, which is the most direct way to determine shapes of nuclear excited states.The PhD student will analyse the data from experiments performed at two facilities: FIPPS (ILL, Grenoble) and HIL (Warsaw University, Poland).

NEW PATHS FOR THE STUDY OF HEAVY NUCLEI

SL-DRF-22-0247

Research field : Nuclear physics
Location :

Service de Physique Nucléaire (DPhN)

Laboratoire études du noyau atomique (LENA) (LENA)

Saclay

Contact :

barbara sulignano

Starting date : 01-10-2022

Contact :

barbara sulignano
CEA - DRF/IRFU/DPhN/LENA

01 69 08 42 27

Thesis supervisor :

barbara sulignano
CEA - DRF/IRFU/DPhN/LENA

01 69 08 42 27

Hunting for super heavy elements is one of the most exciting and active topics during the last few years and has already produced new elements such as 113, 115, 117 and 118 in accelerator experiments. All these nuclei can be produced through fusion-evaporation reactions. However their studies are greatly hampered by the extremely low production rates, hence experimental information in this region is very scarce. The high-intensity stable beams of the superconducting linear accelerator of the SPIRAL2 facility at GANIL coupled with the Super Separator Spectrometer (S3) and a high-performance focal-plane spectrometer (SIRIUS) will open new horizons for the research in the domains of such rare nuclei and low cross-section phenomena at the limit of nuclear stability. The student will take an active part in the tests of the SIRIUS detector at GANIL.

Information on the heaviest elements have been obtained up to now via fusion evaporation reactions. It is however well known that the only nuclei one can reach using fusion-evaporation reactions are neutron deficient and moreover in a very limited number (because of the limited number of beam-target combinations). An alternative to fusion-evaporation could be a revolutionary method based on deep-inelastic collisions. The student will take, therefore, an active part in the new scientific activities of the group having as primary aim the investigation of nuclear structure in the heavy elements using the new alternative method using multi-nucleon transfer reactions.

First measurement of the pygmy resonance using neutron inelastic scattering at GANIL/NFS

SL-DRF-22-0240

Research field : Nuclear physics
Location :

Service de Physique Nucléaire (DPhN)

Laboratoire études du noyau atomique (LENA) (LENA)

Saclay

Contact :

Marine VANDEBROUCK

Diane DORÉ

Starting date : 01-10-2022

Contact :

Marine VANDEBROUCK
CEA - DRF/IRFU


Thesis supervisor :

Diane DORÉ
CEA - DRF/IRFU

01.69.08.41.24

The well-known giant dipole resonance, which corresponds to the oscillation of the neutron fluid against the proton fluid, is a broad resonance with a mean energy between 12 and 24 MeV. An additional dipole resonance has been observed at lower energy in neutron-rich nuclei, near the neutron separation threshold. This small-size structure, in comparison to the giant dipole resonance, is commonly known as the pygmy dipole resonance (PDR) and can be described as the oscillation of a neutron skin against a symmetric proton/neutron core. The PDR has been the subject of numerous studies, both experimental and theoretical. Indeed, the study of the PDR has raised a lot of interest since it can constrain the symmetry energy, an important ingredient of the equation of state which describes the matter in neutron stars. In addition, the enhancement of the dipole strength close to the neutron separation energy is expected to impact the astrophysical r-process (process that could explain the synthesis of heavy nuclei) by increasing the neutron capture rates. However, despite many experimental results, a consistent description of the PDR could not be extracted. In this context, we propose to study the PDR using a new experimental method: the neutron inelastic scattering. This new probe which is elementary from a nucleonic point of view and neutral, thus not influenced by the Coulomb interaction, is an original approach that will provide a new perspective on the nature of the PDR.



The LENA laboratory (Laboratoire d’Etude du Noyau Atomique), which belongs to the Nuclear Physics Department of IRFU, is strongly involved in the study of the structure of atomic nuclei. For many years, LENA researchers have been working in collaboration with teams from GANIL (France), GSI (Germany), the University of Jyväskylä (Finland)… where they conduct their experiments. The high intensity beams produced by GANIL-SPIRAL2, combined with the neutron beam production system available at NFS (Neutron For Science), allow since 2021 to produce neutron beams at the energy suited for inelastic scattering studies with unprecedented intensities.



The objective of the thesis is to study for the first time the pygmy resonance by inelastic neutron scattering. The thesis will consist of: i) participation in the experiment, ii) data analysis, and iii) interpretation of the results in collaboration with theorists.

Search for a new mode of radioactivity: double alpha decay

SL-DRF-22-0356

Research field : Nuclear physics
Location :

Service de Physique Nucléaire (DPhN)

Laboratoire études du noyau atomique (LENA) (LENA)

Saclay

Contact :

Christophe THEISEN

Elias KHAN

Starting date : 01-10-2022

Contact :

Christophe THEISEN
CEA - DRF/IRFU/DPhN/LENA

01 69 08 74 54

Thesis supervisor :

Elias KHAN
CNRS - Université Paris-Saclay - IJCLab Orsay

+33 1 69 15 71 73

Personal web page : https://irfu.cea.fr/Pisp/christophe.theisen/

Laboratory link : https://irfu.cea.fr/dphn/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=2647

We propose a theoretical and experimental study of a new type of nuclear radioactivity that remains to be discovered: the double alpha decay. The theoretical part will allow to determine the nucleus for which the experimental signature of the double alpha radioactivity is the most clear. As regards the experimental part of the thesis, it will consist in optimizing the detection device in view of new experiments which could be carried out at CERN and lead to the discovery of this new radioactivity.

• Nuclear physics

 

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