Narrow Results

It is now known that in neutron-rich nuclei, old magic numbers disappear and new ones appear. Single nucleon and double nucleon separation energies are plotted here in all possible manner. Using this data it is shown here that nuclei with pair of proton number Z and neutron number N(Z,N): (6, 12), (8, 16), (10, 20), (11, 22) and (12, 24) exhibit exceptional stability or magicity. As such these magic numbers appear in pairs. This correlation is shown here to be indicative of predominance of tritons in the ground state of these neutron-rich nuclei. Thus has the structure of 10 in the ground state. It is shown here that this is due to fundamental symmetry arguments based on a new symmetry group nusospin.

t+t clustering in He isotopes is investigated by using two theoretical approaches. A role of the t+t cluster component in the ground state is examined with AMD triple-S, allowing the wider configuration space containing simultaneously the "t+t+valence neutrons" structure and "⁴He+valence neutrons" structure. We understand the importance of the t+t component even for the ground state. Further, t+t resonances are investigated with RGM type approach. We obtained many t+t states as resonances near to t+t threshold.

In a shell-model calculation with traditional effective charges, theoretical B(E2) values are larger than experimental values for neutron-rich carbon isotopes ¹⁶C and ¹⁸C. Using the shell-model with 2ħw excitations in the first order perturbation theory, we investigate the B(E2) values and the effective charges for stable and neutron-rich carbon isotopes.

The generalized two-center cluster model (GTCM), which can treat various single particle configurations in general two center systems, is applied to the light neutron-rich system, ¹²Be= α+α+4N. We discuss the change of the neutrons' configuration around two α-cores as a variation of an excitation energy. We show that the covalent, ionic and atomic configurations appear in the unbound region above the α+⁸He_g.s. particle-decay threshold, and they coexist within a quite small energy interval.

We developed an m-scheme approach of the cluster-orbital shell model formalism. The radial wave function is treated as the super position of the Gaussian functions with different width parameters. Energies and r.m.s. radii of oxygen isotopes are studied.

The generalized two-center cluster model (GTCM), which can treat various single particle configurations in general two center systems, is applied to light neutron-rich systems, Be isotopes (α+α+XN). We discuss the change of the neutrons' configuration around two α-cores as a variation of an excitation energy. We show that the asymmetric clusters, which correspond to the atomic or ionic configurations, appear in the unbound region above the α particle-decay threshold systematically.

We have developed an m-scheme cluster-orbital shell model approach to study neutron- and proton-rich nuclei toward the drip-lines. We discuss the property of the neutron-rich oxygen isotopes with analyzing the relation between the energy and r.m.s. radius.

We propose a local energy density functional for global description of pairing correlations by focusing on the neutron excess dependence. We show the clear correlation between pairing gaps and effective mass parameters as a function of neutron excess. This effect can be taken into account to the density functional by the isovector density dependence in the particle-particle channel.

We investigate isovector pygmy dipole resonance (IVPDR) for the case of neutron-rich nuclei ⁶⁸Ni, ¹³⁰Sn and ¹³⁴Sn using effective nucleon–nucleon Skyrme interaction. We use the Hartree–Fock–Bogoliubov (HFB) theory and employ the (quasiparticle) random phase approximation (Q)RPA. We calculate and compare the PDR strength in the PDR energy region for the case of density dependent central and full interaction modes for RPA and QRPA calculations. We observe that the results for the pygmy dipole resonance for neutron-rich soft nuclei ⁶⁸Ni that we consider are in reasonable agreement with their experimental results in both interactions and calculations. We also study the PDR for highly neutron-rich heavy nuclei, such as ¹³⁰Sn and ¹³⁴Sn. We see that only the QRPA calculation with full interaction is in good agreement with the experimental results for these nuclei and with a recent study in the literature. We find that the PDR strength distribution sensitively depends on the chosen interaction modes, especially for the neutron-rich heavy nuclei ¹³⁴Sn.

The generalized two-center cluster model (GTCM), which can treat various single particle configurations in general two center systems, is applied to the light neutron-rich system, ¹²Be= α+α+4N. We discuss the change of the neutrons' configuration around two α-cores as a variation of an excitation energy. We found that the covalent, ionic and atomic configurations appear with a prominent degenerating feature above the α+⁸He_g.s. particle-decay threshold.

The physical properties of the nuclear shape have been investigated through the charge square radius (<r²>) and the quadrupole (Q₂) and hexadecapole (Q₄) moments of the even–even neutron-rich rare-earth nuclei. The single-particle energies used are those of a deformed Woods–Saxon mean-field. The pairing effects have been included by means of an exact projection method. The model has been tested for the "ordinary" nuclei near the shell closure N = 82 and has correctly reproduced the experimental data and particularly the "Kink" effect. The study has then been extended to the neutron-rich nuclei and has shown a stability of the <r²> and Q₂ results for N≃100 which may be attributed to the existence of a new magic number. On the other hand, a saturation of the prolate shape appears around N = 108 for the elements Nd, Sm and Gd and near N = 102 for the Dy, Er and Yb. These observations could not be confirmed by the investigation of the hexadecapole moment.

The variation of the two-neutron separation energy (S_2N), as a function of the neutron number N, is studied using a microscopic model that includes the pairing effects rigorously within the Fixed-Sharp-BCS method. The model was first tested on "ordinary" nuclei and allowed one to suitably reproduce the experimental data and to confirm the results of previous studies. The model was then applied to the even–even neutron-rich isotopes in the rare-earth region and showed, on the one hand, a relatively important variation of S_2N, when N = 100, that could lead to the assumption of the existence of a new magic number in this region, and on the other hand, a weak variation of S_2N when N > 100. These findings corroborate the previously obtained results for the charge mean square radius and the quadrupole and hexadecapole moments within the same model.

Level schemes of even–even neutron-rich ^88-92Kr and ⁸⁶Se have been investigated by measuring triple-γ coincidence data from the spontaneous fission of ²⁵²Cf with the Gammasphere detector array. The level scheme of ⁸⁸Kr has been extended up to 7169 keV state. Several new excited states with new transitions have been identified in ^90,92Kr and ⁸⁶Se. Spins and parities have been assigned to levels in these nuclei by following regional systematics and angular correlation measurements. The level structures of the N = 52, 54, Se, Kr, and Sr isotones are discussed.

We investigate tensor effects in pygmy dipole excitations for the case of neutron-rich nuclei ⁶⁸Ni and ¹²⁴Sn using effective nucleon–nucleon Skyrme interaction. We use the Hartree–Fock–Bogoliubov (HFB) theory and employ the quasiparticle random phase approximation (QRPA). We calculate and compare the PDR and also GDR strength in the PDR–GDR energy region for QRPA calculations with and without tensor correlations. The most obvious results for the dipole excitations calculations are strongly dependent on the tensor terms. We see that the tensor correlations are more active at around 14–20 MeV, especially for the neutron-rich nuclei ⁶⁸Ni. We also compare the PDR calculations with their experimental results for the different proton–neutron tensor coupling constants.

We study Uranium isotopes and surrounding elements at very large neutron number excess. Relativistic mean field and Skyrme-type approaches with different parameterizations are adopted in the study. Most models show clear indications for isotopes that are stable with respect to neutron emission far beyond N = 184 up to the range of around N = 258.

We studied the charge radius ($r_c$), neutron radius ($r_n$), and neutron skin-thickness ($\mathrm{\Delta }r=r_n-r_p$) over a chain of isotopes from C to Zr with the stable region to the neutron drip line. Theoretical calculations are done with axially deformed self-consistent relativistic mean-field theory (RMF) and effective nonlinear NL3 and NL3* interactions. The theoretically estimated values are compared with available experimental data and a reasonable agreement is noted. We additionally assessed the two-neutron separation energy ($S_{2n}$) to mark the drip line nuclei of the considered isotopic series. In the reference of $S_{2n}$, neutron magicity is also discussed. The calculated neutron radii are compared with empirical estimation made by $r=r_0{N}^{1/3}$ to examine the abnormal trend of the radius for neutron drip line nuclei. In view to guide the long tails, the density distribution for some skin candidates is analyzed. Finally, neutron skin thickness is observed for the whole considered isotopic series.

Nuclear structure studies beyond ¹³²Sn on the shell evolution, the competition or coexistence of single-particle and collective structures and the GT strength are performed using prompt and decay spectroscopy. Here, we present an overview of our recent data from such experiments on neutron-induced fission products in the mass chain A=136 using the EXILL and Lohengrin spectrometers at the ILL in the framework of other studies we have recently performed in the region around ¹³²Sn.

In this paper the experimental results on the total cross sections for the ⁸He + ²⁸Si reaction in the beam energy range 6–25 A MeV are reported. The experimental cross sections were obtained by registration of the prompt gamma and neutron radiation accompanying the interaction of ⁸He neutron-rich nuclei with ²⁸Si nuclei. The analysis of reaction channels was made using fusion-evaporation model and numerical solution of the time-dependent Schrödinger equation for the external weakly bound neutrons of the projectile nucleus ⁸He.

Gamma-rays de-exciting isomeric states in a number of heavy neutron-rich nuclei have been observed following relativistic projectile fragmentation of a 1 GeV per nucleon ²⁰⁸Pb beam. New information on the excited states of the spherical N = 126 ²⁰⁴Pt and ²⁰⁵Au, N = 125 ²⁰³Pt, and on the oblate ¹⁹⁸Os have been obtained.

A new shell model Hamiltonian for p-shell nuclei which properly takes into account important roles of spin-isospin interactions, especially the tensor force, is shown to significantly improve the description of magnetic moments and Gamow-Teller transitions of p-shell nuclei as well as neutrino induced reactions on ¹²C. The Hamiltonian is further modified to take full account of the roles of tensor and two-body spin-orbit interactions, and applied to study shell evolutions toward drip-lines and magnetic and spin properties of light neutron-rich nuclei, where the effects of the spin-isospin interactions become essential and more pronounced. Anomalous behavior of magnetic dipole transitions in ¹⁷C and electric quadrupole transitions in ¹⁶C and ¹²Be recently observed are found to be rather well explained.