Gound State Properties of Nuclei in (295)118 alpha-Decay Chain

The properties of nuclei belonging to the alpha-decay chain of superheavy element (295)118 have been studied in the framework of axially deformed relativistic mean field (RMF) theory with the parameter set of NL-Z2 in the blocked BCS approximation. Some ground state properties such as binding energies, deformations, and alpha-decay energies Q(alpha) have been obtained and agree well with those from finite-range droplet model (FRDM). The single-particle spectra of nuclei in (295)118 alpha-decay chain show that the shell gaps present obviously nucleon number dependence. The root-mean-square (rms) radii of proton, neutron and matter distributions change slowly from (283)112 to (295)118 but dramatically from (279)110 to (283)112, which may be due to the subshell closure at Z = 110 in (279)110. The alpha-decay half-lives in (295)118 decay chain are evaluated by employing the cluster model and the generalized liquid drop model (GLDM), and the overall agreement is found when they are compared with the known experimental data. The alpha-decay lifetimes obtained from the cluster model are slightly larger than those of GLDM ones. Finally, we predict the alpha-decay half-lives of Z = 118, 116, 114, 112 isotopes using the cluster model and GLDM, which also indicate these two models can corroborate each other in studies on superheavy nuclei. The results from GLDM are always lower than those obtained from the cluster model.

Observation of Three-Quasiparticle Doublet Bands in I-123: Possible Evidence of Chirality

A new band in the odd proton nucleus I-123 is identified via in- beam gamma- ray spectroscopy using the N-14+Cd-116 reaction. This band shows up as doublets with the previously assigned pi g(7/2) circle times (nu h(11/2))(2) band. Possible configurations of the new band are discussed in the framework of the cranked shell model and the geometrical model. It is argued that the new band might be a chiral partner of the previously known pi g(7/2) circle times (nu h(11/2))(2) band.

Competition in rotation-alignment between high-j neutrons and protons in transfermium nuclei

The study of rotation-alignment of quasiparticles probes sensitively the properties of high-j intruder orbits. The distribution of very-high-j orbits, which are consequences of the fundamental spin-orbit interaction, links with the important question of single-particle levels in superheavy nuclei. With the deformed single-particle states generated by the standard Nilsson potential, we perform Projected Shell Model calculations for transfermium nuclei where detailed spectroscopy experiments are currently possible. Specifically, we study the systematical behavior of rotation-alignment and associated band-crossing phenomenon in Cf, Fm, and No isotopes. Neutrons and protons from the high-j orbits are found to compete strongly in rotation-alignment, which gives rise to testable effects. Observation of these effects will provide direct information on the single-particle states in the heaviest nuclear mass region.

Shell effect and capture cross sections in the synthesis of superheavy nuclei

The shell effect is included in the improved isospin dependent quantum molecular dynamics model in which the shell correction energy of the system is calculated by using the deformed two-center shell model. A switch function is introduced to connect the shell correction energy of the projectile and the target with that of the compound nucleus during the dynamical fusion process. It is found that the calculated capture cross sections reproduce the experimental data quantitatively at the energy near the Coulomb barrier. The capture cross sections for reaction (35) (80) Br + (82) (208) Pb -> (117) (288) X are also calculated and discussed.

Half-Lives of Superheavy Nuclei in Z=113 Alpha Decay Chain

The generalized liquid drop model (GLDM), including the proximity effects and centrifugal potential, and the cluster model with Cosh potential are used to study the half-lives of some Z=113 isotopes and their alpha-decay products.The experimental half-lives of (284)113, (283)113, (282)113and their alpha-decay products are well reproduced by the two models when zero angular momenta transfer is assumed. For (278)113 and its alpha-decay products, both the GLDM andthe cluster model could provide satisfactory results if we assume the alpha particle carry five units of angular momenta, which indicates that possible non zero angular momenta transfer and need further experimental measurements with high precision. Finally, we show that half-lives of alpha-decay are quite sensitive to the angular momentum transfers, and a formula could be used to describe the correlation between alpha-decay half-life and angular momentum transfer successfully.

Shell model study of single-particle and collective structure in neutron-rich Cr isotopes

The structure of neutron-rich Cr isotopes is systematically investigated by using the spherical shell model. The calculations reproduce well the known energy levels for the even-even Cr52-62 and odd-mass Cr53-59 nuclei, and predict a lowering of excitation energies around neutron number N = 40. The calculated B(E2; 2(1)(+) -> 0(1)(+)) systematics shows a pronounced collectivity around N = 40; a similar characteristic behavior has been suggested for Zn and Ge isotopes. Causes for the sudden drop of the 9/2(1)(+) energy in Cr-59 and the appearance of very low 0(2)(+) states around N = 40 are discussed. We also predict a new band with strong collectivity built on the 0(2)(+) state in the N = 40 isotope Cr-64.

Nuclear shape-phase diagrams

Ground-state energy functions of even-even and odd-A nuclei are derived from simple parameter-dependent Interacting Boson Model (IBM) and Interacting Boson-Fermion Model (IBFM) Hamiltonians. Exact nuclear shape-phase diagrams in the two-parameter (eta, chi) plane are explicitly described using the energy functions on the basis of the condition of phase equilibrium.

Identification of a new band and its signature inversion in Re-174

High spin states in Re-174 are investigated via the Sm-152(Al-27, 5n gamma)Re-174 reaction and gamma-gamma coincidence relationships are analysed carefully. A new band is identified due to its spectroscopic connection with the known pi 1/2(-)[541] circle times nu 1/2(-)[521] band. This band is proposed to be the ground-state band built on the pi 1/2(-)[541] circle times nu 5/2(-)[512] configuration in view of the low-lying intrinsic states in the neighbouring odd-mass nuclei. It is of particular interesting that the new band exhibits a phenomenon of low-spin signature inversion, providing a new situation for theoretical investigations.

beta-Delayed proton decays in the rare-earth region near drip line

The history of experimental study on beta-delayed proton decays in the rare-earth region was simply reviewed. The physical results of the beta-delayed proton decays obtained at IMP, Lanzhou over the last 10 years were summarized, mainly including the first observation of 9 new beta-delayed proton precursors along the odd-Z proton drip line and the new data for 2 waiting-point nuclei in the rp-process. The results were compared and discussed with different nuclear model calculations. Finally, the perspective in near future was briefly introduced.

Low-spin signature inversion in the pi h(9/2)circle times nu i(13/2) oblate band

Excited states in Tl-188,Tl-190 have been studied experimentally by means of in-beam gamma spectroscopy techniques, and resulted in the identification of a strongly coupled band based on the pi h(9/2) circle times nu i(13/2) configuration with oblate deformation. The oblate band in doubly odd Tl nuclei shows low-spin signature inversion. It is the first experimental observation of low-spin signature inversion for a band associated with the oblate pi h(9/2) circle times nu i(13/2) configuration.

Observation of a pi h(9/2) circle times nu i(13/2) oblate band in Tl-188

Excited states in Tl-188 have been studied experimentally using the Gd-157(Cl-35;4n) reaction at a beam energy of 170 MeV. A rotational band built on the pi h(9/2) x nu i(13/2) configuration with oblate deformation has been established for Tl-188. Based on the structure systematics of the oblate pi h(9/2) x nu i(13/2) bands in the heavier odd-odd Tl nuclei, we have tentatively proposed spin values for the new band in Tl-188. The pi h(9/2) x nu i(13/2) oblate band in Tl-188 shows low-spin signature inversion, and it can be interpreted qualitatively by the two-quasiparticle plus rotor model including a J-dependent p-n residual interaction.

Anomaly in the charge radii and nuclear structure

The axially deformed relativistic mean field theory is applied to study the isotope shift of charge distributions of odd-Z Pr isotope chain. The nuclear structure associated with the shell and the isotope effect is investigated. The mechanism of link in the isotope shift at the neutron magic number N = 82 is revealed to be dependent on the neutron energy level structure at the Fermi energy, demonstrating that the spin-orbit coupling interaction and p-n attraction are well described by the relativistic mean field theory.

Properties of the pi h(9/2)circle times nu i(13/2) oblate band in Tl-188

High spin states in Tl-188 have been investigated via the Gd-157(Cl-35,4n) reaction at beam energy of 170 MeV. A rotational band built on the pi h(9/2) circle times nu(13/2) configuration with oblate deformation has been established. Considering the similarity between the band structure observed in odd-odd Tl nuclei, spin values have been tentatively proposed for the new band in Tl-188. The pi h(9/2) circle times nu(13/2) oblate band in Tl-188 shows low-spin signature inversion, and it can be interpreted qualitatively by the two quasiparticle plus rotor model including a J-dependent p-n residual interaction.

Production cross sections of superheavy nuclei based on dinuclear system model

The barrier distribution function method is introduced in the dinuclear system model in the calculation of the transmission probability, which is the first stage in the synthesis of superheavy nuclei. Dynamical deformation and averaging collision orientations are considered in the calculation of the fusion probability by solving master equation numerically. Survival probability with respect to xn evaporation channel (x = 1-5) in the de-excitation process of the thermal compound nucleus is calculated, in which the level density of the Fermi-gas model is used. Production cross sections of a series of superheavy nuclei formed in the reactions taken magic and deformed nuclei as target in Ca-48 induced reactions are studied systematically. The calculated results are in good agreement with available experimental data. Isotopic dependence of the production cross sections in the reactions Ca-48 + Pu is analyzed.

Properties and structure of N = Z nuclei within relativistic mean field theory

The axially deformed relativistic mean field theory with the force NLSH has been performed in the blocked BCS approximation to investigate the proper-ties and structure of N=Z nuclei from Z=20 to Z=48. Some ground state quantities such as binding energies, quadrupole deformations, one/two-nucleon separation energies, root-mean-squaxe (rms) radii of charge and neutron, and shell gaps have been calculated. The results suggest that large deformations can be found in medium-heavy nuclei with N=Z=38-42. The charge and neutron rms radii increase rapidly beyond the magic number N=Z=28 until Z=42 with increasing nucleon number, which is similar to isotope shift, yet beyond Z=42, they decrease dramatically as the structure changes greatly from Z=42 to Z=43. The evolution of shell gaps with proton number Z can be clearly observed. Besides the appearance of possible new shell closures, some conventional shell closures have been found to disappear in some region. In addition, we found that the Coulomb interaction is not strong enough to breakdown the shell structure of protons in the current region.