All Results

A new barrier penetration formula and its application to α-decay half-lives

Lu-Lu Li; Shan-Gui Zhou; En-Guang Zhao; Werner ScheidSubjects: Physics >> Nuclear Physics

Starting from the WKB approximation, a new barrier penetration formula is proposed for poten- tial barriers containing a long-range Coulomb interaction. This formula is especially proper for the barrier penetration with penetration energy much lower than the Coulomb barrier. The penetra- bilities calculated from the new formula agree well with the results from the WKB method. As a first attempt, this new formula is used to evaluate α decay half-lives of atomic nuclei and a good agreement with the experiment is obtained. |

Spherical-box approach for resonances in presence of Coulomb interaction

Shan-Gui Zhou; Jie Meng; En-Guang ZhaoSubjects: Physics >> Nuclear Physics

The spherical-box approach is extended to calculate the resonance parameters and the real part of the wave function for single particle resonances in a potential containing the long-range Coulomb interaction. A model potential is taken to demonstrate the ability and accuracy of this approach. The calculated resonance parameters are compared with available results from other methods. It is shown that in the presence of the Coulomb interaction, the spherical-box approach works well for not so broad resonances. In particular, for very narrow resonances, the present method gives resonance parameters in a very high precision. |

Neutron halo in deformed nuclei

Shan-GuiZhou; JieMeng; P.Ring; En-GuangZhaoSubjects: Physics >> Nuclear Physics

Halo phenomena in deformed nuclei are investigated within a deformed relativistic Hartree Bo- goliubov (DRHB) theory. These weakly bound quantum systems present interesting examples for the study of the interdependence between the deformation of the core and the particles in the halo. Contributions of the halo, deformation effects, and large spatial extensions of these systems are described in a fully self-consistent way by the DRHB equations in a spherical Woods-Saxon basis with the proper asymptotic behavior at large distance from the nuclear center. Magnesium and neon isotopes are studied and detailed results are presented for the deformed neutron-rich and weakly bound nucleus 44Mg. The core of this nucleus is prolate, but the halo has a slightly oblate shape. This indicates a decoupling of the halo orbitals from the deformation of the core. The generic conditions for the occurence of this decoupling effects are discussed. |

Particle-number conserving analysis of rotational bands in 247,249Cm and 249Cf

Zhen-Hua Zhang; Jin-Yan Zeng; En-Guang Zhao; Shan-Gui ZhouSubjects: Physics >> Nuclear Physics

The recently observed high-spin rotational bands in odd-A nuclei 247,249Cm and 249Cf [Tandel et al., Phys. Rev. C 82 (2010) 041301R] are investigated by using the cranked shell model (CSM) with the pairing correlations treated by a particle-number conserving (PNC) method in which the blocking effects are taken into account exactly. The experimental moments of inertia and alignments and their variations with the rotational frequency ω are reproduced very well by the PNC-CSM calculations. By examining the ω-dependence of the occupation probability of each cranked Nilsson orbital near the Fermi surface and the contributions of valence orbitals to the angular momentum alignment in each major shell, the level crossing and upbending mechanism in each nucleus is understood clearly. |

Subjects: Physics >> Nuclear Physics

The shapes of light normal nuclei and Λ hypernuclei are investigated in the (β,γ) deformation plane by using a newly developed constrained relativistic mean field (RMF) model. As examples, the results of some C, Mg, and Si nuclei are presented and discussed in details. We found that for normal nuclei the present RMF calculations and previous Skyrme-Hartree-Fock models predict similar trends of the shape evolution with the neutron number increasing. But some quantitative aspects from these two approaches, such as the depth of the minimum and the softness in the γ direction, differ a lot for several nuclei. For Λ hypernuclei, in most cases, the addition of a Λ hyperon alters slightly the location of the ground state minimum towards the direction of smaller β and softer γ in the potential energy surface E ? (β,γ). There are three exceptions, namely, 13C, 23C, and ΛΛ 31Si in which the polarization effect of the additional Λ is so strong that the shapes of these three Λ hypernuclei are drastically different from their corresponding core nuclei. |

Subjects: Physics >> Nuclear Physics

For the first time the potential energy surfaces of actinide nuclei in the (β20, β22, β30) deformation space are obtained from a multi-dimensional constrained covariant density functional theory. With this newly developed theory we are able to explore the importance of the triaxial and octupole shapes simultaneously along the whole fission path. It is found that besides the octupole deformation, the triaxiality also plays an important role upon the second fission barriers. The outer barrier as well as the inner barrier are lowered by the triaxial deformation compared with axially symmetric results. This lowering effect for the reflection asymmetric outer barrier is 0.5 ? 1 MeV, accounting for 10 ? 20% of the barrier height. With the inclusion of the triaxial deformation, a good agreement with the data for the outer barriers of actinide nuclei is achieved. |

Subjects: Physics >> Nuclear Physics

The rotational bands in nuclei with Z ≈ 100 are investigated systematically by using a cranked shell model (CSM) with the pairing correlations treated by a particle-number conserving (PNC) method, in which the blocking effects are taken into account exactly. By fitting the experimental single-particle spectra in these nuclei, a new set of Nilsson parameters (κ and μ) and deformation parameters (ε2 and ε4) are proposed. The experimental kinematic moments of inertia for the rotational bands in even-even, odd-A and odd-odd nuclei, and the bandhead energies of the 1- quasiparticle bands in odd-A nuclei, are reproduced quite well by the PNC-CSM calculations. By analyzing the ω-dependence of the occupation probability of each cranked Nilsson orbital near the Fermi surface and the contributions of valence orbitals in each major shell to the angular momentum alignment, the upbending mechanism in this region is understood clearly. |

Systematics of capture and fusion dynamics in heavy-ion collisions

Bing Wang; Kai Wen; Wei-Juan Zhao; En-Guang Zhao; Shan-Gui ZhouSubjects: Physics >> Nuclear Physics

We perform a systematic study of capture excitation functions by using an empirical coupled-channel model. In this model, a barrier distribution is used to take effectively into account the effects of couplings between the relative motion and intrinsic degrees of freedom. The shape of the barrier distribution is of an asymmetric Gaussian form. The effect of neutron transfer channels is also included in the barrier distribution. Based on the interaction potential between the projectile and the target, empirical formulas are proposed to determine the parameters of the barrier distribution. Theoretical estimates for barrier distributions and calculated capture cross sections together with experimental cross sections of 220 reaction systems with 182 ZPZT 1640 are tabulated. The results show that our empirical formulas work quite well in the energy region around the Coulomb barrier. This model can provide prediction of capture cross sections for the synthesis of superheavy nuclei as well as valuable information on capture and fusion dynamics. |

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