Investigation of nuclear cluster phenomenology with the relativistic EDF approach

Relativistic energy density functionals (REDF) allowed to bring these last years a complementary understanding to the nuclear clustering phenomena. Three steps forwards are reported: i) localisation as a function of the nucleonic quantum numbers, indicating related cluster effects over the nuclear chart; ii) detailed comparisons with experimental data available on spectroscopy of light nuclei such as 20Ne and 12C and iii) investigation of pairing and quarteting effects within the REDF

Localization and clustering in the nuclear Fermi liquid

Using the framework of nuclear energy density functionals we examine the conditions for single-nucleon localization and formation of cluster structures in finite nuclei. We propose to characterize localization by the ratio of the dispersion of single-nucleon wave functions to the average inter-nucleon distance. This parameter generally increases with mass and describes the gradual transition from a hybrid phase in light nuclei, characterized by the spatial localization of individual nucleon states that leads to the formation of cluster structures, toward the Fermi liquid phase in heavier nuclei. Values of the localization parameter that correspond to a crystal phase cannot occur in finite nuclei. Typical length and energy scales in nuclei allow the formation of liquid drops, clusters, and halo structures.Comment: 6 pages, 3 figure

Halos and related structures

The halo structure originated in nuclear physics but is now encountered more widely. It appears in loosely bound, clustered systems where the spatial extension of the system is significantly larger than that of the binding potentials. A review is given on our current understanding of these structures, with an emphasis on how the structures evolve as more cluster components are added, and on the experimental situation concerning halo states in light nuclei.Comment: 27 pages, 3 figures, Contribution to Nobel Symposium 152 "Physics With Radioactive Beams

Quadrupole and octupole collectivity and cluster structures in neon isotopes

The lowest positive- and negative-parity bands of 20Ne and neutron-rich even-even Ne isotopes are investigated using a theoretical framework based on energy density functionals. Starting from a self-consistent relativistic Hartree-Bogoliubov calculation of axially symmetric and reflection- asymmetric deformation energy surfaces, the collective symmetry-conserving states are built using projection techniques and the generator coordinate method. Overall a good agreement with the experimental excitation energies and transition rates is obtained. In particular, the model provides an accurate description of the excitation spectra and transition probabilities in 20Ne. The contribution of cluster configurations to the low-energy states is discussed, as well as the transitional character of the ground state. The analysis is extended to 22Ne and the shape-coexisting isotope 24Ne, and to the drip-line nuclei 32Ne and 34Ne. The role of valence neutrons in the formation of molecular-type bonds between clusters is discussed

Cluster structures in C12 from global energy density functionals

Spectroscopic properties of low-lying states and cluster structures in 12C are analyzed in a beyond mean-field framework based on global energy density functionals (EDFs). To build symmetry-conserving collective states, axially symmetric and reflection-asymmetric solutions of the relativistic Hartree-Bogoliubov equations are first projected onto good values of angular momentum, particle number, and parity. Configuration mixing is implemented using the generator coordinate method formalism. It is shown that such a global microscopic approach, based on a relativistic EDF, can account for the main spectroscopic features of 12C, including the ground-state and linear-chain bands as well as, to a certain approximation, the excitation energy of the Hoyle state. The calculated form factors reproduce reasonably well the available experimental values, and display an accuracy comparable to that of dedicated microscopic cluster models

Microscopic Description of 2α2\alpha Decay in 212^{212}Po and 224^{224}Ra Isotopes

International audienceA microscopic calculation of half-lives for both the α and 2α decays of Po212 and Ra224 is performed, using a self-consistent framework based on energy density functionals. A relativistic density functional and a separable pairing interaction of finite range are used to compute axially symmetric deformation energy surfaces as functions of quadrupole, octupole, and hexadecapole collective coordinates. Dynamical least-action paths are determined, that trace the α and 2α emission from the equilibrium deformation to the point of scission. The calculated half-lives for the α decay of Po212 and Ra224 are in good agreement with data. A new decay mode, the symmetric 2α emission, is predicted with half-lives of the order of those observed for cluster emission

Low-energy cluster vibrations in N=ZN = Z nuclei

Significant transition strength in light $\alpha$-conjugate nuclei at low energy, typically below 10 MeV, has been observed in many experiments. In this work the isoscalar low-energy response of N=Z nuclei is explored using the Finite Amplitude Method (FAM) based on the microscopic framework of nuclear energy density functionals. Depending on the multipolarity of the excitation and the equilibrium deformation of a particular isotope, the low-energy strength functions display prominent peaks that can be attributed to vibration of cluster structures: $\alpha$+$^{12}$C+$\alpha$ and $\alpha$+$^{16}$O in $^{20}$Ne, $^{12}$C+$^{12}$C in $^{24}$Mg, 4$\alpha$+$^{12}$C in $^{28}$Si, etc. Such cluster excitations are favored in light nuclei with large deformation