5 sujets /DPhN/LENA

Dernière mise à jour : 10-07-2020


 

Simulation and tests of a compact neutron source based on the IPHI accelerator

SL-DRF-20-0717

Research field : Neutronics
Location :

Service de Physique Nucléaire (DPhN)

Laboratoire études du noyau atomique (LENA) (LENA)

Saclay

Contact :

Loïc THULLIEZ

Antoine DROUART

Starting date : 01-10-2020

Contact :

Loïc THULLIEZ
CEA - DRF/IRFU/DPhN/LEARN

0169087453

Thesis supervisor :

Antoine DROUART
CEA - DSM/IRFU/SPhN/Structure Noyau

01 69 08 73 52

Neutron beams are used for many applications in materials science, engineering, archaeology or the study of works of art, where they complement other non-destructive analyses, such as X-ray imaging. These beams are traditionally supplied by nuclear research reactors or spallation sources.

The choice of the source depends on the characteristics of the desired neutron beam (energy spectrum, frequency of neutron pulses, etc.). Today a large proportion of reactors are reaching the end of their life cycle. For example, the Orphée research reactor will be closed in October 2019. To compensate for the reduction in the available neutron beam time (limiting the number of experiments that can be carried out), new alternative sources are being developed. These, called CANS (Compact Accelerator Neutron Sources) produce neutrons through nuclear reactions of charged particles (proton, deutons) on a target, the material of which depends on the type and energy of the incident particles. A CANS is being developed at CEA-Saclay (tests and measurements are under way) at the IPHI-neutrons facility with the longer-term objective of developing the SONATE source. IPHI-neutrons uses high intensity (>10mA) and low energy (3MeV) proton beams on a beryllium or lithium target. The neutrons generated with energies above > 100 keV are then moderated to energies below 50 meV. These new facilities have the advantage of being cheaper and more flexible than nuclear reactors or spallation sources. However, due to their lower power compared to reactors, neutron fluxes are less important. This is why it is necessary to optimise these installations as much as possible and therefore to be able to model their operation from the production of primary neutrons to their final use.

This thesis topic proposes to carry out a full simulation of a CANS, within the framework of the IPHI-neutrons project. This simulation will integrate the production of primary neutrons in the target, the propagation of these neutrons and their slowing down by a cold moderator as well as their transport to the measurement point by an optimized collimator, allowing the minimization of the background noise on the experimental device. Finally, the use of the neutron beam for a radiography application will also be modelled. These simulations will be based on tests and measurements performed on the IPHI-neutrons facility. These will aim at the characterization the neutron beam (energy, spatial distribution, flux) as well as the gamma background noise at the point of detection. The student will actively participate in the installation of equipment, tests and data analysis.

Pushing ab initio calculations of atomic nuclei throughout the nuclear chart

SL-DRF-20-0439

Research field : Nuclear Physics
Location :

Service de Physique Nucléaire (DPhN)

Laboratoire études du noyau atomique (LENA) (LENA)

Saclay

Contact :

Vittorio SOMA

Thomas DUGUET

Starting date : 01-10-2020

Contact :

Vittorio SOMA
CEA - DRF/IRFU/DPhN/LENA

0169083236

Thesis supervisor :

Thomas DUGUET
CEA - DRF/IRFU/DPhN/LENA

0169082338

Laboratory link : http://irfu.cea.fr/dphn/index.php

The theoretical description from first principles, i.e. in a so-called ab initio fashion, of atomic nuclei containing more than ~12 nucleons has become possible only recently thanks to crucial developments in many-body theory and the availability of increasingly powerful high-performance computers. Such ab initio techniques are being successfully applied to study the structure of nuclei starting from the lighter isotopes and reaching today mid-mass nuclei containing up to about 80 nucleons. The extension to even heavier systems requires decisive breakthroughs regarding the storage and running time induced by any of the available many-body methods. In this context, the goal of the thesis is to formulate and apply the recently proposed Importance Truncation (IT) techniques within the frame of Gorkov Self-consistent Green’s function calculations, a specific ab initio technique devised at CEA Saclay over the last 9 years, as a way to select a priori and systematically many-body basis states that do contribute significantly to many-body correlations. The project will exploit the latest advances in nuclear theory, including the use of nuclear interactions from chiral effective field theory and renormalisation group techniques, as well as high-performance computing codes and resources. The work will consist in formal developments, computational tasks and application of the new technology to cases of experimental interest. International collaborations constitute an integral part of the project.
SHAPE EVOLUTION IN NEUTRON-RICH EXOTIC NUCLEI

SL-DRF-20-0011

Research field : Nuclear physics
Location :

Service de Physique Nucléaire (DPhN)

Laboratoire études du noyau atomique (LENA) (LENA)

Saclay

Contact :

Magdalena Zielinska

Wolfram KORTEN

Starting date : 01-10-2020

Contact :

Magdalena Zielinska
CEA - DSM/IRFU/SPhN/Structure Noyau

01 69 08 74 86

Thesis supervisor :

Wolfram KORTEN
CEA - DRF/IRFU/DPhN/LENA

+33169084272

Personal web page : https://www.researchgate.net/profile/Wolfram_Korten

Laboratory link : http://irfu.cea.fr/Sphn/Phocea/Vie_des_labos/Ast/ast_sstheme.php?id_ast=293

More : https://www.phy.anl.gov/atlas/

One of the most fundamental properties of the atomic nucleus is its shape, which is governed by the interplay of macroscopic, liquid-drop like properties of the nuclear matter and microscopic shell effects, which reflect the underlying nuclear interaction. In some cases, configurations corresponding to different shapes may coexist at similar excitation energies, which results in the wave functions of these states mixing. Experimental observables such as quadrupole moments and the electromagnetic transition rates between states are closely related to the nuclear shape. The experimental determination of these observables, therefore, represents a stringent test for theoretical models. This thesis is integrated in our ongoing programme to study nuclear shapes by means of Coulomb excitation and more specifically such an experiment is planned on 100Zr. This method allows to extract the excitation probability for each excited state and to extract a set of electro magnetic matrix elements, and in particular the quadrupole moment which determines the shape of the nucleus. The radioactive 100Zr beam is provided by the ATLAS-CARIBU facility at Argonne National Laboratory (ANL), which is currently the only facility world-wide able to deliver beams of such refractory elements. The programme advisory committee has already accepted the experiment with high priority and we expect it to be scheduled in Q4/2020. The PhD student will participate in the preparation and setting-up of the experiment. It would be advantageous if he/she started already working on the subject already during the stage M2. He/she will be responsible for the data analysis, the presentation of the scientific results (at conferences or workshops) and their publication in a scientific journal. During the thesis work the PhD student may also participate in other experiments of the research group. All experiment(s) take place in international collaborations and may require prolonged stays at foreign laboratories (e.g. 4-6 weeks at ANL, USA).
Neutron-Proton interaction and spectroscopy of neutron-rich chlorine isotopes

SL-DRF-20-0472

Research field : Nuclear physics
Location :

Service de Physique Nucléaire (DPhN)

Laboratoire études du noyau atomique (LENA) (LENA)

Saclay

Contact :

Alain GILLIBERT

Starting date : 01-10-2020

Contact :

Alain GILLIBERT
CEA - DRF/IRFU/DPhN/LENA

0169082584

Thesis supervisor :

Alain GILLIBERT
CEA - DRF/IRFU/DPhN/LENA

0169082584

In nuclear physics, atomic nuclei are described in the framework of shell models, with formal analogies to atomic physics. Orbitals characterized with angular momentum are successively filled from the bottom of the nuclear well. « Magic nuclei » correspond to to the full filling of orbitals before a major energy gap is crossed, with a net gain of stability. Not only stable nuclei were successfully described this way, but it also provides a framework for the evolution of nuclear properties versus the neutron/proton asymmetry parameter. Evolution of orbitals and associated magic numbers is under study with increasing neutron number for exotic nuclei far from stability. For calcium isotopes with a magic proton number Z=20, the relative ordering of proton orbitals 0d3/2 and 1s1/2 evolves from 40Ca (N=20) to 48Ca (N=28) and filling the neutron 0f7/2 orbital as an effect of the neutron-proton interaction in nuclei [1]. It was evidenced by the measurement of energies and spins of ground states and first excited states of potassium isotopes Z=19, which can be described as a proton hole in a calcium core. We propose to extend this study of low-energy spectroscopy to the neighbor chlorine isotopes Z=17 and a valence proton in 0d3/2 and 1s1/2 orbitals.

This study will be the aim of an experiment to be done in 2020 at the RIBF facility (Tokyo). An intense secondary beam including 46,48Ar isotopes will be obtained from fragmentation of a primary 70Zn beam at 345 MeV/u. In beam spectroscopy will be studied from one proton removal reaction in inverse kinematics 46,48Ar (p,2p) 45,47Cl and a cryogenic thick liquid hydrogen target surrounded by a time-projection chamber used for proton tracking and reconstruction of the reaction vertex in the target [2]. In flight emitted photons from 45,47Cl at target will be detected with the high resolution HiCARI array of Ge detectors, dedicated to this 2020 experimental campaign. We will measure the momentum distribution of 45,47Cl fragments to determine the angular momentum (s or d wave) of the knocked proton, giving access to the spin of the final state.

The experiment will be examined in 2019 December for an expected realization in 2020. A close collaboration with nuclear structure theoreticians will be an opportunity to analyze the results and develop the theoretical skills of the student.

Search for pear-shaped nuclei in actinides: study of a new reaction mechanism for the production of neutron-deficient actinides and development of a detector dedicated to the laser spectroscopy of actinides

SL-DRF-20-0270

Research field : Nuclear physics
Location :

Service de Physique Nucléaire (DPhN)

Laboratoire études du noyau atomique (LENA) (LENA)

Saclay

Contact :

Marine VANDEBROUCK

Starting date : 01-10-2020

Contact :

Marine VANDEBROUCK
CEA - DRF/IRFU/DPhN/LENA


Thesis supervisor :

Marine VANDEBROUCK
CEA - DRF/IRFU/DPhN/LENA


Understanding the limits of the nucleus cohesion, and in particular its mass limit, is currently one of the major areas of research in nuclear physics. The study of heavy nuclei, located in the upper part of the nuclear chart, has recently benefited from a new experimental approach: the laser spectroscopy. This is a method from atomic physics, allowing the properties of the nucleus to be deduced through the study of atomic levels, independent of nuclear models.

In this region of heavy nuclei, neutron-deficient actinides are of particular interest. Indeed, several theoretical calculations predict strong octupole deformations (pear shape).

The objective of the thesis is to study octupole deformations in neutron-deficient actinides. It will be done in collaboration with the University of Jyväskylä. The thesis is divided into two parts: i) an experiment at Jyväskylä to study the production of neutron-deficient actinides by a new reaction mechanism, ii) the development of a detector that will couple laser spectroscopy and delayed spectroscopy at S3/LEB at GANIL-Spiral2.

• Neutronics

• Nuclear Physics

• Nuclear physics

 

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