The nuclear structure group actively uses and/or develops various theoretical models to describe the structure of the atomic nucleus.
These include
- Quasi-Particle Phonon Model
- Quasi-Particle-Rotor Model
- Shell-Model Calculations
- Interacting Boson-Model (IBM)
In collaboration with the nuclear structure group from the Technical University of Ostrava, Czech Republic we are using the Quasi-Particle Phonon Model (QPM) (V. G. Soloviev, Theory of Complex nuclei (Pergamon Press, Oxford 1976)) and the Generalized Intermediate Coupling Model (GICM) (P.Alexa, J. Kvasil, N. Viet Minh and R. K. Sheline, Phys. Rev. C 55, 179 (1997)) to describe the properties of nuclei in the neutron-rich mass 150 region, where octupole modes are present. It is not clear how octupole modes evolve as a function of nucleon number and deformation in this region. By comparing recently obtained experimental data to the model predictions we can better understand the evolution of these modes and the key roles played by some orbits. Moreover, a theoretical description of the octupole correlations requires application of models that include quadrupole and octupole correlations on an equal footing as done, for example in the QPM.
The QPM is a semimicroscopic model which allows for the description of the structure of vibrational and two-quasiparticle states of spherical and deformed even-even nuclei and of admixtures of vibrational states in one-quasiparticle wave functions of spherical and deformed odd nuclei and in two-quasiparticle wave functions of odd-odd spherical and deformed nuclei. It is used to describe the intrinsic degrees of freedom of the nuclear motion and can be combined with the axially symmetric rotor model including Coriolis coupling between the odd particle and RPA phonon vibrations of the even-even core to describe deformed odd nuclei (P. Alexa, Z. Hons and J. Kvasil, J. Phys. G 36, 045103 (2009)).
The GICM is a generalization of the intermediate coupling model to spherical odd-odd nuclei. Nuclei are assumed to consist of a vibrating even-even core and two outer nucleons (odd proton and odd neutron). Compared to the other models (e.g. shell model) the GICM provides in some cases, especially for the low-energy region (but in some cases also for the intermediate-energy region where vibrational admixtures may be important) a better description of the experimental data.
Developments and applications of an algebraic version of Bohr's collective model (BM) called the algebraic collective model (ACM) (D. J. Rowe, T. A. Welsh and M. A. Caprio, Phys. Rev. C 79, 054305 (2009)) have shown that fully converged calculations can be performed for a large range of Hamiltonians. This way the rich algebraic structure of the BM can be used very effectively in analyzing a wide range of experimental data. Moreover, the BM possesses several solvable limits characterized by a dynamical symmetry and the respective submodels naturally remain solvable also in it's algebraic version ACM. Another model that is expressed in algebraic terms and thus can be used effectively and quickly to describe the nuclear structure is the interacting boson model (IBM). Similarly to the BM, exactly solvable dynamical symmetry limits can be defined that contract to those of the BM. The ACM combines the advantages of both the BM and the IBM and it is thus of interest to investigate the relationship between the ACM and the IBM models because one can learn from the complementary perspectives they afford ( D. J. Rowe and G. Thiamova, Nuclear Physics A 760, 59 (2005) . We are also investigating relationship between the IBM and the ACM in its beta-rigid triaxial limit (G. Thiamova, D. J. Rowe and M.A. Caprio, accepted in NPA), an approximation applicable to well-deformed nuclei. The full ACM Hamiltonian can be adapted to the description of even-even nuclei with any equilibrium value of the beta deformation and any degree of rigidity.
The quasi-particle-rotor model has been used by our group to interpret experimental data on deformed odd-A and odd-odd nuclei. The code, written by P. Semmes and I. Ragnarsson, even allows triaxal nuclei to be correctly described.
Thanks to the powerful computing facilities at the LPSC we are able to perform large-scale shell-model calculations using the codes Antoine, NuShellX, NuShellX-MSU and the Oslo codes. The machines at the LPSC have up to 64 Gb of RAM. We use state-of-the-art shell-model interactions developed either by the Napoli group, or included in the NuShellX-MSU package, and compare them to the experimental data obtained by our group. The shell-model calculations are used to interpret level schemes, transition rates and magnetic moments close to double shell closures. We are especially interested in the neutron-rich nuclei close to 132Sn and 78Ni as it is not clear how the nucleon-nucleon interaction evolves in very neutron-rich regions.
