Étude expérimentale et théorique de la structure nucléaire des isotopes de sélénium riches en neutrons.

par Ivan Grachev

Projet de thèse en 2MGE : Matériaux, Mécanique, Génie civil, Electrochimie

Sous la direction de Gabriela Thiamova et de Gary Simpson.

Thèses en préparation à Grenoble Alpes , dans le cadre de I-MEP2 - Ingénierie - Matériaux, Mécanique, Environnement, Energétique, Procédés, Production , en partenariat avec Laboratoire de Physique Subatomique et Cosmologie (laboratoire) depuis le 17-11-2014 .


  • Résumé

    Today there are several indications of a rapid onset of quadrupole deformation around the neutron number N=60. This shape change has made of the neutron-rich A=100 region a very active area of experimental and theoretical studies. The nuclei of this mass region are the best examples of the interplay between single-particle and collective modes of excitation in the nuclear matter. This is very well seen in the spectroscopic data measured at a particular proton or neutron number which shows spectacular variations. In particular, nuclear spectroscopy measurements have shown shape coexistence in most neutron-rich N=59 isotones. Certain theoretical predictions indicate that yet another shape change should occur when going to lower Z values. For very neutron-rich selenium (Se, Z=34) isotopes a stable octupole deformation (pear-shaped nuclei) is predicted to exist, similar to that recently discovered at ISOLDE-CERN in radium. Nuclear spectroscopy of very neutron-rich isotopes can be performed via γ-γ or γ-γ-γ coincidences with efficient Ge detector arrays such as EXOGAM. Mass and nuclear charge are usually identified via coincidences with known γ-rays of complementary fragments. In December 2012, the EXOGAM array was used at the ILL (EXILL campaign) to measure γ-rays emitted from various fission fragments that are produced in the thermal neutron induced fission of 235U. The primary aim of the proposed PhD project is to analyze the 235U EXILL data to investigate excited states in 88-89Se and 91-92-93Br. In the second half of the PhD thesis, the student will participate actively in the interpretation of the obtained experimental data using several theoretical models. In this region, far from the shell closures Z=28,50 and N=50, theoretical interpretations using shell model calculations become difficult. Different models can be used to describe shape coexistence and the interplay of single-particle and collective degrees of freedom in nuclear systems. One of the models to be used is the Quasi Particle-phonon Model (QPM) applicable to deformed nuclei. Another model is the Interacting Boson Model (IBM) and its extensions for even-odd and odd-odd nuclei (IBFM and IBFFM respectively). The student will be located in Grenoble (LPSC or ILL) and be integrated in the Ecole Doctorale de Physique of the Grenoble university (Universite Joseph Fourier). The student will be under the responsibility of Gabriela Thiamova (LPSC, Grenoble) and Aurelien Blanc (ILL, Grenoble) and collaborate also with Petr Alexa (Technical University of Ostrava, Czech Republic) on theoretical aspects.

  • Titre traduit

    Experimental and theoretical study of the nuclear structure of the neutron-rich selenium isotopes.


  • Résumé

    Today there are several indications of a rapid onset of quadrupole deformation around the neutron number N=60. This shape change has made of the neutron-rich A=100 region a very active area of experimental and theoretical studies. The nuclei of this mass region are the best examples of the interplay between single-particle and collective modes of excitation in the nuclear matter. This is very well seen in the spectroscopic data measured at a particular proton or neutron number which shows spectacular variations. In particular, nuclear spectroscopy measurements have shown shape coexistence in most neutron-rich N=59 isotones. Certain theoretical predictions indicate that yet another shape change should occur when going to lower Z values. For very neutron-rich selenium (Se, Z=34) isotopes a stable octupole deformation (pear-shaped nuclei) is predicted to exist, similar to that recently discovered at ISOLDE-CERN in radium. Nuclear spectroscopy of very neutron-rich isotopes can be performed via γ-γ or γ-γ-γ coincidences with efficient Ge detector arrays such as EXOGAM. Mass and nuclear charge are usually identified via coincidences with known γ-rays of complementary fragments. In December 2012, the EXOGAM array was used at the ILL (EXILL campaign) to measure γ-rays emitted from various fission fragments that are produced in the thermal neutron induced fission of 235U. The primary aim of the proposed PhD project is to analyze the 235U EXILL data to investigate excited states in 88-89Se and 91-92-93Br. In the second half of the PhD thesis, the student will participate actively in the interpretation of the obtained experimental data using several theoretical models. In this region, far from the shell closures Z=28,50 and N=50, theoretical interpretations using shell model calculations become difficult. Different models can be used to describe shape coexistence and the interplay of single-particle and collective degrees of freedom in nuclear systems. One of the models to be used is the Quasi Particle-phonon Model (QPM) applicable to deformed nuclei. Another model is the Interacting Boson Model (IBM) and its extensions for even-odd and odd-odd nuclei (IBFM and IBFFM respectively). The student will be located in Grenoble (LPSC or ILL) and be integrated in the Ecole Doctorale de Physique of the Grenoble university (Universite Joseph Fourier). The student will be under the responsibility of Gabriela Thiamova (LPSC, Grenoble) and Aurelien Blanc (ILL, Grenoble) and collaborate also with Petr Alexa (Technical University of Ostrava, Czech Republic) on theoretical aspects.