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[en] Strongly correlated many-body systems often display the emergence of simple patterns and regular behaviour of their global properties. Phenomena such as clusterization, collective motion and appearance of shell structures are commonly observed across different size, time, and energy scales in our universe. Although at the microscopic level their individual parts are described by complex interactions, the collective behaviour of these systems can exhibit strikingly regular patterns. This contribution provides an overview of the experimental signatures that are commonly used to identify the emergence of shell structures and collective phenomena in distinct physical systems. Examples in macroscopic systems are presented alongside features observed in atomic nuclei. The discussion is focused on the experimental trends observed for exotic nuclei in the vicinity of nuclear closed-shells, and the new challenges that recent experiments have posed in our understanding of emergent phenomena in nuclei.
[en] Deformation-energy surfaces of 54 even-even isotopes of Pt, Hg and Pb nuclei with neutron numbers up to 126 are investigated within a macroscopic-microscopic model based on the Lublin-Strasbourg-Drop macroscopic energy and shell plus pairing-energy corrections obtained from a Yukawa-folded mean-field potential at the desired deformation. A new, rapidly converging Fourier shape parametrization is used to describe nuclear shapes. The stability of shape isomeric states with respect to non-axial and higher-order deformations is investigated.
[en] E1 transition properties such as the reduced transition probabilities, excitation energies and photon–absorption cross-sections have been theoretically investigated for Ta nucleus within the framework of Translational and Galileo Invariant-Quasiparticle Phonon Nuclear Model (TGI-QPNM). The model Hamiltonian includes the single-particle and the isovector dipole–dipole interaction terms along with the restoration forces. The strength of the isovector dipole–dipole interaction has been chosen to be χ=500/A MeV⋅fm. Theoretical calculations show that in addition to the M1 excitations, there is considerable amount of E1 transitions especially between 2.6–3 MeV, which gives remarkable contribution to the fragmentation in the low-energy region of the dipole spectrum. Thus, the agreement between theory and experiment in terms of the fragmentation increases. Furthermore, the photon–absorption cross-sections in the Pigmy Dipole Resonance (PDR) region below the neutron separation energy (S) is compatible with experimental data.
[en] The exact solution of spherical mean-field plus multi-pair interaction model with two non-degenerate j-orbits, which is an extension of the widely used standard (two-body) pairing model, is derived based on the Bethe–Richardson–Gaudin approach. The Bethe–Richardson–Gaudin equations in determining eigenstates and the corresponding eigen-energies of the model are provided and exemplified with up to three-pair interactions. With a suitable parameterization of the overall multi-pair interaction strengths, the model with one adjustable parameter and valence nucleons confined in the 1d and 0g orbits is applied to fit binding energies of Sn. It is shown that the ground-state occupation probabilities of nucleon pairs calculated from this model and those from the standard pairing model are almost the same with perfect ground-state overlap of the two models. A noticeable feature of the multi-pair interactions is that the even-odd staggering of pairing interaction strength appearing in the standard pairing model due to the Pauli-blocking is suppressed. As the result, the pairing interaction strength of the model only depends on the number of valence nucleon pairs in the system.
[en] The constrained Hartree-Fock-Bogoliubov approximation, based on the recent parametrization D1M* of the Gogny energy density functional, is used to describe fission in 435 superheavy nuclei. The Gogny-D1M* parametrization is benchmarked against available experimental data on inner and second barrier heights, excitation energies of the fission isomers and half-lives in a selected set of Pu, Cm, Cf, Fm, No, Rf, Sg, Hs and Fl nuclei. Results are also compared with those obtained with the Gogny-D1M energy density functional. A detailed study of the minimal energy fission paths is carried out for isotopic chains with atomic numbers 100 ≤Z≤ 126 including very neutron-rich sectors up to around 4 MeV from the two-neutron driplines. Single-particle energies, ground state deformations, pairing correlations, two-nucleon separation energies and barrier heights are also discussed. In addition to fission paths, the constrained Hartree-Fock-Bogoliubov framework provides collective masses and zero-point quantum rotational and vibrational energies. Those quantities are building blocks within the Wentzel-Kramer-Brillouin formalism employed to evaluate the systematic of the spontaneous fission half-lives tSF. The competition between spontaneous fission and -decay is studied, through the computation of the -decay half-lives t using a parametrization of the Viola-Seaborg formula. From the comparison with the available experimental data and the results obtained with other theoretical approaches, it is concluded that D1M* represents a reasonable starting point to describe fission in heavy and superheavy nuclei.
[en] The phase transitions and spectral statistical properties in Nd, Sm, Gd, and Dy isotopes are investigated by spherical mean-field plus standard pairing model. The results of the model calculations successfully reproduce the critical phenomena observed experimentally in the two-neutron separation energy, odd–even mass differences, α-decay, double β-decay energy and the first pairing excitation states of these isotopes with the critical point at the neutron number N∼90. As the only parameter in the model, the pairing interaction strength G is determined by fitting the binding energies, the odd–even mass differences and the energies of the first and second pairing excitation states for the Nd, Sm, Gd, and Dy isotopes. The spectral statistical properties of the excited levels of Sm isotopes show that the quantum chaos exists in Sm which corresponds to the critical point at N∼90. It is inferred that the transitional region is the most sensitive region to perturbation, leading generically to the typical signature of quantum chaos. Moreover, the results indicate that this critical behavior is related not only to the ground-state but also to the excited-state under the present model. It may provide us a microscopic picture that the ground-state phase transition and the quantum chaos behaviors may drive by the competition between the spherical mean-field and the pairing interaction based on the present model for Nd, Sm, Gd, and Dy isotopes.
[en] The fission pathway of even–even actinide nuclei have been systematically calculated using the deformation-constrained nuclear density functional theory beyond the second fission barriers within the UNEDF1 energy-density functionals (EDFs). Our calculated results show that, allowing for triaxial deformation, the second fission barriers are lowered by a few hundreds of keV to 2 MeV. For the heaviest actinides, it is found that inclusion of triaxial deformation reduces the outer barrier significantly.
[en] The FAMU experiment aims to measure for the first time the hyperfine splitting of the muonic hydrogen ground state. From this measurement the proton Zemach radius can be derived and this will shed light on the determination of the proton charge radius. In this paper, we describe the scientific goal, the method and the detailed preparatory work. This includes the outcome of preliminary measurements, subsequent refined simulations and the evaluation of the expected results. The experimental setup being built for the measurement of the hyperfine splitting to be performed at the RAL laboratory muon facility is also described.
[en] The production of light (anti-)nuclei and (anti-)hypernuclei in ultra-relativistic heavy-ion collisions, but also in more elementary collisions as proton–proton and proton–nucleus collisions, became recently a focus of interest. In particular, the fact that these objects are all loosely bound compared to the temperature and energies, e.g. the kinetic energies involved, is often stressed out to be special for their production. The binding energies of these (anti-)nuclei is between 130 keV (Λ separation energy in the hypertriton) and about 8 MeV per nucleon. Whereas the connected temperatures are of the order of 100 to 160 MeV. This lead to some difficulties in the interpretation of the usually discussed production models, i.e. coalescence and statistical-thermal models, as will be discussed here. In this brief review we discuss selected highlights of the production of light (anti-)nuclei, such as (anti-)deuteron, (anti-)helium and (anti-)alpha nuclei. In addition, we will discuss the current status of the highly debated lifetime of the (anti-)hypertriton and connected measurements and model results.
[en] Binary collisions of either stable or radioactive heavy ions at Fermi energies allow to study the nuclear reaction mechanisms under dynamical conditions of non-equilibrium and the formation of transient pieces of nuclear matter of very short mean life times at sub-normal density. An important role in the evolutionary phase of the collision is played by the gradient of the nuclear density affecting the isospin asymmetry of the reaction products by typical transport phenomena such as the isospin diffusion and drift. Experimental determination of the value of the nuclear matter density in the early phase of the collision is a crucial step towards understanding the underlying mechanism responsible for the production of clusters. In this paper a method for evaluating the nuclear density in semi-peripheral collisions in the reaction Sn+Ni at 35 MeV/nucleon as studied with the CHIMERA multi-particle detector is described.