MATNEC · Microscopic and Algebraic Theory of Nuclei under Extreme Conditions

Microscopic and Algebraic Theory of Nuclei under Extreme Conditions

The atomic nucleus is a quantum many-body system of protons and neutrons, where the strong, the weak and the electromagnetic fundamental interactions play an important role at the most profound level. The atomic nucleus is a unique laboratory that helps to elucidate the origin of matter, test fundamental symmetries and also allow practical applications. The way to understand the structure of nuclei is interdisciplinary since it applies to other fields of quantum physics such as condensed matter, atomic and molecular physics. The advent of the state-of-the-art radioactive-ion-beam (RIB) facilities in, e.g. Europe (CERN, GANIL and GSI), the US (FRIB), and Japan (RIKEN) allows access to short-lived or exotic nuclei. The nucleus acquires stunning collective aspects characterized by a remarkable regularity of its energy levels. The collective motion is induced by the multi-nucleon dynamics of the deformation of the nuclear surface. The shape can change with addition/removal of a few nucleons, giving rise to spherical vibrational and deformed rotational states, and those in between. The understanding of the nuclear collective structure from a microscopic perspective is an intriguing subject in nuclear many-body physics. This project aimed at the theoretical description of low-energy structure of atomic nuclei and related quantum many-body systems. The primary emphasis has been on low-energy collective motion and shape phenomena including quantum phase transitions (QPTs), symmetries and phases in finite nuclei, and on the structure of N~Z (equal number of protons and neutrons) exotic nuclei far from the valley of stability. The project has further pursued the application to other quantum many-body systems like molecules. To describe the nuclear shapes and collective excitations based on a robust framework, the project proposed to develop a novel theory constructed by combining microscopic theories (i.e., nuclear shell model and nuclear energy density functional theory (DFT)) with the algebraic model, such as the interacting boson model (IBM). The method is general and has been applied to the phenomenon of interdisciplinary character. Most of the objectives originally defined in the proposal have been addressed during the fellowships’ duration of 2 years. The major achievements are the following: 1) Description of shape transition in neutron-rich A~100 nuclei 2) Microscopic calculation of octupole collective states 3) Theoretical formulation of proton-neutron mixed symmetry 4) Partial- and quasi-dynamical symmetries 5) Shell model study of the structure of N~Z nuclei 6) Role of proton-neutron pairs in neutrino-less double beta decay 7) Theoretical support for experimentalists around RIB facilities 8) Application of algebraic theory to nuclear clustering and molecules Collaborations with the state-of-the-art RIB experiments has been essential to this fellowship research. The RIB physics rather obviously has vast applications to the studies of the origin of matter, subatomic physics, condensed matter physics, molecules, material sciences, medical sciences and industrial applications. The theoretical method developed during the fellowship has provided scientific results that are directly compared with the experiments at the RIB facilities, to be more specific, the host institute GANIL. So, the major conclusion of this fellowship research is that it has made advances in the RIB physics, which has been becoming of primary interest in nuclear physics community, and thus has impacts on the society. To be more specific, the ruthenium and the paradium isotopes, which have been specifically pursued within the theory-experiment joint collaboration (achievement 5 in the above list), are actually used as materials in industry.

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