张量力在~(16)O+~(16)O熔合动力学中的效应

利用时间相关Hartree-Fock理论和完整Skyrme有效相互作用研究了~(16)O+~(16)O碰撞在库仑位垒附近的熔合动力学。数值计算是在没有任何对称性约束的三维笛卡尔基下完成。将时间相关Hartree-Fock理论和冻结密度近似下的能量密度泛函方法给出的库仑位垒与实验结果进行了比较,发现同位旋标量的张量项能降低自旋饱和体系~(16)O+~(16)O的库仑位垒,而库仑位垒高度随着同位旋矢量的张量项的耦合常数减小而降低。并计算了包含和不包含张量力的~(16)O+~(16)O熔合截面,发现张量力对~(16)O+~(16)O碰撞在库仑位垒附近的熔合动力学影响较小。     

近垒重离子熔合反应中的中子转移效应(英文)

近势垒及其以下能区重离子熔合反应中的中子转移耦合道效应是一个复杂且有争议的问题。简要介绍了近年来在中国原子能科学研究院的HI-13串列加速器上,基于静电偏转板装置完成的32S+90,94,96Zr,18O+74Ge和18O+58Ni等几个典型体系的熔合反应研究情况,并结合耦合道理论对实验数据进行了分析。选取反应体系时同时关注了正Q值的中子拾取和削裂道。另外,基于完全耦合道理论计算,提出了一种能够定量提取熔合反应中中子转移效应的自洽方法。这些研究进一步证实了垒下重离子熔合反应中的中子转移效应,同时指出了其复杂性。需要进一步的实验和理论研究来澄清相关核反应机制。The effect of neutron transfers on near-and sub-Coulomb-barrier fusion of heavy-ions is still a complicated and controversial problem. This paper reviews the recent experimental results of the fusion excitation functions of several typical systems, which have been measured by using an electrostatic deflector setup at the HI-13 tandem accelerator of CIAE. Both the neutron pickup and stripping effects were studied. Moreover, a self-consistent method to reliably isolate the transfer effect quantitatively based on the coupledchannels calculation is proposed. These studies give a further support for the neutron transfer effect on sub-barrier fusion of heavy-ions and its complexity. Further experimental and theoretical studies are needed for clarifying the relevant reaction mechanisms.     

协变密度泛函理论中的张量力效应

张量力是核子-核子相互作用的重要成分,被认为是理解奇特原子核中壳结构演化规律的关键要素。然而,目前对于核介质中的张量力及其效应的定量认识,仍存在很多亟待解决的关键问题。着重梳理了在原子核密度泛函理论框架下,研究有效相互作用中的张量力成分以及相应的张量力效应的相关工作,重点包括:基于相对论Hartree-Fock理论,以同位素链中的质子幻数壳演化为例,定量提取与分析其中的张量力效应;以及基于第一性原理的相对论Brueckner-Hartree-Fock理论,以中子滴单粒子能谱中的自旋-轨道劈裂演化为例,提出与张量力效应相关联的"准实验数据"。最后,展望原子核密度泛函理论今后可能的发展策略。Tensor force is one of the most important components of the nucleon-nucleon interaction. It plays a critical role in understanding the shell evolution in exotic nuclei. However, there are still several puzzles concerning the tensor force and its effects in the nuclear medium. In this paper, we mainly focus on the studies of tensor force in the effective interactions and its effects in finite nuclear systems within the scheme of nuclear density functional theory. In particular, we highlight the recent developments, including the quantitative analysis of tensor effects in the relativistic Hartree-Fock theory by taking the evolution of proton magic shells in the isotopic chains as an example, and the "meta-data" of tensor effects provided by the ab initio relativistic Brueckner-Hartree-Fock theory by taking the evolution of spin-orbit splitting in the single-particle spectra of neutron drops as an example. Perspectives are focused on the possible strategies for the future developments of nuclear density functional theory.     

40, 48Ca+90, 96Zr近垒熔合反应的动力学研究

发展了一种改进的量子分子动力学模型,并用这一模型研究了40,48Ca+90,96Zr的近垒熔合反应.改进的量子分子动力学模型能很好地描述一系列核,从6Li到208Pb,的基态性质及它们的时间演化.在相同参数下计算得到的40Ca+90Zr以及40Ca+96Zr这两个熔合反应的激发函数与实验结果都符合得相当好.在分析丰中子核熔合截面增强机制中,发现丰中子核熔合反应初始阶段颈部的N/Z值明显偏大,促使反应中动态位垒降低,从而引起了丰中子核反应熔合截面的增强. An improved Quantum Molecular Dynamics (QMD) model is proposed and the fusion reactions 40, 48Ca+90, 96Zr are studied by using this model. With our improved QMD model, the ground state properties and their time evolution of nuclei from 6Li to 208Pb can be reproduced reasonably well and the excitation functions of fusion cross section for reactions40Ca+96Zr and 40Ca+96Zr at near barrier can be reproduced remarkably well with the same set of parameters...     

Fusion cross section of the 16O + 16O collision

It is shown that the gross structure of the fusion cross section of the ¹⁶O + ¹⁶O collision is well reproduced by a simple coupled channel method including only elastic and inelastic ¹⁶O + ¹⁶O(3^?) channels, as well as the excitation functions of the elastic and total inelastic ¹⁶O + ¹⁶O(3^?) cross sections.     

Phase-shift analysis of 16O + 16O elastic scattering

A phase-shift analysis has been carried out for ¹⁶O + ¹⁶O elastic scattering, resulting in unambiguous values for the reflection coefficients in the energy range of the first gross structure of the 90° excitation function, and answering some of the questions still open regarding the calculations existing so far.     

Phase-shift analysis of 16O + 16O elastic scattering data

A phase-shift analysis of precisely measured elastic ¹⁶O + ¹⁶O data has been carried out in order to establish the existence of molecular resonances between E_c.m = 15.5 and 18 MeV and to investigate the possible structure of these resonances.     

The heavy-ion reaction channels of the system 16O + 16O

The reaction channels of the system ¹⁶O + ¹⁶O with outgoing heavy particles from lithium to magnesium have been measured using a ΔE-E telescope. Excitation functions from 49 to 65 MeV at θ_Lab = 30° and angular distributions from θ_Lab = 10° (20°) to 50° at E_Lab = 51.5 MeV are presented for the strong transitions. The excitation function of the ¹²C-²⁰Ne (4.25 MeV) channel shows a pronounced regular cross structure with peaks at 52 and 60 MeV. A selective excitation of certain states in the inelastic scattering and the ¹²C-²⁰Ne channel is observed; the yields of the other heavy-ion channels being weaker by at least one order of magnitude. An explanation of this phenomenon is given by considering the angular momentum matching between entrance and exit channels. Furthermore it is shown that no strong dependence of the cross sections on the transferred angular momentum or on the nuclear structure of the final states is observed. Possible implications of these results on the reaction mechanism are discussed.     

Low energy fusion of 12C + 12C and 16O + 16O systems

The adiabatic time-dependent Hartree-Fock method (ATDHF) is applied to the calculation of low energy fusion of ¹²C + ¹²C and ¹⁶O + ¹⁶O systems. The energy dependence of the results is in good agreement with experiment, while the order of magnitude is not correct. It is shown that the dynamical effects included in ATDHF are very important and cannot be neglected at the energies of astrophysical interest.     

Interaction potential between two 16O nuclei derived from the Skyrme interaction

The energy functional for the Skyrme density-dependent force is used to calculate the interaction potential between two ¹⁶O nuclei. A two-centre harmonic oscillator potential is employed to construct the density and kinetic energy density of the ground state of the combined system and of the separated nuclei. The antisymmetrization effects are investigated. The relative motion of the nuclei is taken approximately into account and the energy dependence of the potential derived from the Skyrme force is presented.     

Formation and deexcitation of the 32S compound nucleus via the 20Ne+12C and 16O+16O entrance channels

Reaction-product cross sections following ²⁰Ne+¹²C and ¹⁶O + ¹⁶O collisions at several incident energies have been measured with a E-ΔE counter telescope. They are compared to statistical model predictions. Fair agreement is obtained for the high-Z evaporation residue cross sections, but a strong discrepancy is observed for the lower-Z reaction products. Possible explanations are discussed. It is shown that the compound nucleus formation does not depend on the structure of the colliding ions in the entrance channel and also that it is not limited by the ³²S yrast line.     

Generator-coordinate study of elastic 16O + 40Ca scattering

Elastic ¹⁶O + ⁴⁰Ca phase shifts are calculated using a generator-coordinate method. A rotational band of molecular resonances is found with a rotational constant of about 30 keV. The width of these resonances should make them observable in the energy range 30 to 50 MeV. These features can be approximately reproduced by a shallow local potential. Properties of the imaginary part of the optical potential are discussed qualitatively. The optical potential should be transparent in a window of J-values comprised between about 16 and 25. Odd-even effects are shown to be negligible in the real part of the potential but might be important in its imaginary part. A possible confirmation of these predictions is found in an experimental excitation function.     

Microscopic study of the 12C + 16O system

An angular momentum projected microscopic calculation is performed for the ¹²C + ¹⁶O system with an effective nuclear force and the exact Coulomb interaction. The ¹²C wave function is projected on a 0⁺ state. Parametrizations of the Coulomb interaction between the nuclei are fitted. The L-projected energy curves present a quite complicated structure especially for the negative parity states. The role played by critical angular momenta is put into evidence. A generator coordinate calculation gives several bands of bound, quasibound and virtual states. Excellent agreement in energy and angular momentum is obtained with the 13.7 MeV (J = 9), 19.7 MeV (J = 14), 22.7 MeV (J = 15) and other resonances.     

Microscopic study of elastic 12C+16O scattering

The L=0 to 17 phase shifts are calculated microscopically for elastic ¹²C+¹⁶O scattering with a generator coordinate method. The experimental resonances are shown to belong to four different bands. Interpretations and spin assignments are suggested for several recently observed anomalies. A spin J=15 seems likely for the 22.8 MeV resonance. A missing J=13 resonance should be searched for between 17 and 18 MeV.