Impact Parameter Dependence of the Double Neutron/Proton Ratio of Nucleon Emissions in Isotopic Reaction Systems

Within the transport model IBUU04, we investigate the double neutron/proton ratio of free nucleons taken from two reaction systems using two Sn isotopes at a beam energy of 50 MeV/nucleon and with impact parameters 2fm, 4fm and 8fm, respectively. It is found that the double neutron/proton ratio from peripheral collisions is more sensitive to the density dependence of the symmetry energy than those from mid-central and central collisions.     

The influence of Isospin Dependence of In-Medium NN Cross Sections on the Ratio of Emitted Neutrons to Protons in HICs

The influence of isospin dependence of in-medium nucleon-nucleon cross sections on the nip ratios for emitted nucleons in reactions 96Zr-j-96Zr and 96Ru-j-96RH at Eb z 400 AMeV is investigated by means of an improved quantum molecular dynamics model. Our results show that the high energy part of the spectra of the n//p ratios for emitted nucleons is sensitive to the isospin dependence of in-medium nucleon-nucleon cross sections for neutron-rich reaction systems. Therefore, we propose that the nip ratio of emitted high energy nucleons in a very neutron-rich reaction system at several hundreds of AMeV can be taken as sensitive observables to constrain the isospindependence of in-medium nucleon-nucleon cross sections.     

Low-energy monopole and dipole response in nuclei at finite temperature

The multipole response of nuclei at temperatures T=0–2 MeV$T=0\text{–}2\text{MeV}$ is studied using a self-consistent finite-temperature RPA (random phase approximation) based on relativistic energy density functionals. Illustrative calculations are performed for the isoscalar monopole and isovector dipole modes and, in particular, the evolution of low-energy excitations with temperature is analyzed, including the modification of pygmy structures. Both for the monopole and dipole modes, in the temperature range T=1–2 MeV$T=1\text{–}2\text{MeV}$ additional transition strength appears at low energies due to thermal unblocking of single-particle orbitals close to the Fermi level. A concentration of dipole strength around 10 MeV excitation energy is predicted in ^60,62Ni. The principal effect of finite temperature on low-energy strength that is already present at zero temperature, e.g. in ⁶⁸Ni and ¹³²Sn, is the spreading of this structure to even lower energy and the appearance of states that correspond to thermally unblocked transitions.     

Core Polarization and Tensor Coupling Effects on Magnetic Moments of Hypernuclei

Effects of core polarization and tensor coupling on the magnetic moments in ¹³_ΛC, ¹⁷_Λ, and ⁴¹_ΛCa Λ-hypernuclei are studied by employing the Dirac equation with scalar, vector and tensor potentials. It is found that the effect of core polarization on the magnetic moments is suppressed by Λ tensor coupling. The Λ tensor potential reduces the spin--orbit splitting of p_Λ states considerably. However, almost the same magnetic moments are obtained using the hyperon wavefunction obtained via the Dirac equation either with or without the Λ tensor potential in the electromagnetic current vertex. The deviations of magnetic moments for p_Λ states from the Schmidt values are found to increase with nuclear mass number.     

Exploration of Pseudospin Symmetry in the Resonant States

Taking ^120Sn as an example, we discuss the pseudospin symmetry in the single proton resonant states by examining the energies, widths and the wavefunctions. The information of the single proton resonant states in spherical nuclei are extracted from an analytic continuation in the coupling constant method within the framework of the self-consistent relativistic mean field theory under the relativistic boundary condition. We find small energy splitting in a pair of pseudospin partners in the resonant states. The lower components of the Dirac wavefunctions of a pseudospin doublet agree well in the region where nuclear potential dominates. It is concluded that the pseudospin symmetry is also well conserved for the resonant states in realistic nuclei.     

Mechanism of Proton-Induced Reactions on Targets ^16O, ^27Al, ^56Fe, ^112Cd, ^184W and ^208Pb At Ep = 800 MeV

We investigate the 800 MeV proton-induced spallation reactions on various targets by the improved quantum molecular dynamics （ImQMD05） model incorporated with a statistical decay model （SDM）. The influence of the nucleon-nucleon effective interaction on proton induced spallation reactions is studied by using different Skyrme interactions. It is found that the low energy part of the neutron double differential cross sections （DDCS）, which is mainly contributed from the decay of the excited residue, is influenced by the effective nucleon-nucleon interaction strongly., while the high energy part of neutron DDCS is influenced weakly. Among the Skyrme interactions used in the calculations, the calculation results with SkP give the best agreement with the experimental data.     

Calculations of 6He + p elastic-scattering cross-sections using folding approach and high-energy approximation for the optical potential

Calculations of microscopic optical potentials (OPs) (their real and imaginary parts) are performed to analyze the ⁶ He + p elastic-scattering data at a few tens of MeV/nucleon (MeV/N). The OPs and the cross-sections are calculated using three model densities of ⁶He . Effects of the regularization of the NN forces and their dependence on nuclear density are investigated. Also, the role of the spin-orbit terms and of the non-linearity in the calculations of the OPs, as well as effects of their renormalization are studied. The sensitivity of the cross-sections to the nuclear densities was tested and one of them that gives a better agreement with the data was chosen.     

从Sn质子滴线核到Sn中子滴线核的自旋对称性和赝自旋对称性

在球形相对论平均场模型下, 采用NLSH相互作用全面研究了从Sn质子滴线核到Sn中子滴线核的自旋对称性和赝自旋对称性. 发现: 1) 随着核子数的增大, 中子和质子的赝自旋波函数劈裂基本上都是减小的, 并且质子的变化趋势更加明显. 中子高能级的自旋波函数劈裂随着核子数的增大也是减小的. 2) 对于特定的同位素, 当n=1时, 赝自旋波函数劈裂随着l的增大而增大. 当n=2时, 中子的自旋波函数劈裂随着l的增大而增大. 当l=2或l=3时, 中子的自旋波函数劈裂随着n的增大而增大. 3) 中子和质子的赝自旋劈裂之间的差别总是比自旋劈裂的差别更大一些.     

Systematic Study on System Size Dependence of Global Stopping: Role of Momentum-Dependent Interactions and Symmetry Energy

Using the isospin-dependent quantum molecular dynamical model, we systematically study the role of symme- try energy with and without momentum-dependent interactions on the global nuclear stopping. We simulate the reactions by varying the total mass of the system from 80 to 394 at different beam energies from 30 to 1000 Me V/nucleon over central and semi-central geometries. The nuclear stopping is found to be sensitive towards the momentum-dependent interactions and symmetry energy at low incident energies. The momentum-dependent interactions are found to weaken the finite size effects in nuclear stopping.     

Neutron and Proton Diffusion in Fusion Reactions for the Synthesis of Superheavy Nuclei

The restriction of the one dimensional （1D） master equation （ME） with the mass number of the projectile-like fragment as a variable is studied, and a two-dimensional （2D） master equation with the neutron and proton numbers as independent variables is set up, and solved numerically. Our study showed that the 2D ME can describe the fusion process well in all projectile target combinations. Therefore the possible channels to synthesize super-heavy nuclei can be studied correctly in wider possibilities. The available condition for employing 1D ME is pointed out.     

Entrance-Channel Dependence of Isospin Effects on Double n/p Ratio in HIC

Within the hadronic transport model IBUU04, we investigate the effect of density-dependent symmetry energy on double neutron/proton (n/p) ratio of free nucleons in heavy ion collisions by taking four isotopic Sn+Sn reaction systems. Especially the entrance-channel asymmetry and impact-parameter dependence of the effect of symmetry energy are discussed. It is found that in both central and semi-central collisions the sensitivity of the double n/p ratio to the density-dependent symmetry energy is more pronounced in neutron-richer systems. Our results also indicate clearly that the effect of symmetry energy is stronger in central collisions than that in semi-central collisions.     

Comparison of Properties of the Simplest Neutron Stars in Three RMF Models

We study some properties of the simplest neutron stars （NSs） in the Glendenning Moszkowski （GM） model, the hybrid derivative coupling （HD） model and the Zimanyi Moszkowski （ZM） model in the framework of relativistic mean field （RMF） theory with and without the interaction by exchanging the ~-meson. We show that the maximal mass of the NSs becomes smaller, but the redshift becomes larger from the GM model to the HD model, then to the ZM model. The interaction with the 6-meson exchange enlarges the maximal mass of neutron stars, increases the relative population of charged particles （proton, electron and muon） and descends the relative population of neutron.     

The low-energy limit of validity of the intranuclear cascade model

The intranuclear cascade model is generally considered to be valid when the incident particle has a sufficiently small de Broglie wavelength to interact with individual nucleons. On this basis, a lower limit of 200 MeV is usually quoted for the incident energy in nucleon-induced reactions. Here this statement is questioned. A pragmatic approach is used, which compares the predictions of the Liège intranuclear cascade model with available data at incident energy between 40 and 250 MeV. It is found that this model gives surprisingly good results at energies well below the limit mentioned above. Results are also compared with the predictions of other models commonly used in this energy range. Received: 2 September 2002 / Accepted: 22 October 2002 / Published online: 6 March 2003 RID="a" ID="a"e-mail: cugnon@plasma.theo.phys.ulg.ac.be RID="b" ID="b"e-mail: P.Henrotte@ulg.ac.be Communicated by G. Orlandini     

Influence of D-state in 4He on S Factor for the 2H（d, γ）^4He Reaction

We employ a direct capture method to study the influence of D-state in ^4He on S factor for the ^2H（d,γ）^4He reaction, in which the D-state component of the colliding deuterons and D-state component in ^4He ground state are considered. The parameters of Woods-Saxon （WS） potentials are obtained by reproducing the binding energy of d-d （i.e. ^2H-^2H） system, and d-d elastic scattering phase shifts calculated by the resonating group method. The theoretical results are in good agreement with the experimental data at Ec.m〈 3 MeV. The impact of the D state probability in ^4He on the extrapolated value of the astrophysical S factor for ^2H（d, γ）^4He reaction is discussed.     

Structure of nuclei far from the stability in relativistic approach

The recent progress of the relativistic many-body approach by the group at Peking University will be reviewed. In particular, axially deformed relativistic Hartree-Bogoliubov approach in Woods-Saxon basis aiming at halo nucleus, time-odd triaxial RMF approach, the adiabatic and configuration-fixed constrained triaxial RMF approaches, a Reflection ASymmetric RMF (RAS-RMF) approach, and a new relativistic Hartree-Fock (RHF) approach with density-dependent σ,ω,ρ and π meson-nucleon couplings for finite nuclei and nuclear matter, will be highlighted.     

The transparency of nuclei to nucleons and pions in a relativistic Glauber approximation

We present a selection of results obtained within the context of a relativistic eikonal model. First, results of relativistic Glauber calculations for the nuclear transparency extracted from photon-induced pion production are presented. Second, computed differential cross-sections for the ¹² C(p, 2p) are compared to data.     

Light-ion-induced reactions in mass measurements of neutron-deficient nuclides close to A = 100

A survey of neutron-deficient nuclides which can be produced via proton- and ³He -induced fusion-evaporation reactions in the A = 100 region was made using a Penning trap as a high-resolution mass filter. A comparison of the measured isotopic rates with a statistical model calculation for the proton-induced reactions shows the importance of using the precise binding energy values for the final reaction products. In particular, proton separation energies were found to play an important role in the evaporation process. In addition, accurate masses of 12 nuclides, ^{97-99, 101}Pd , ¹⁰⁰Ag , ^101-105Cd and ^{102, 104}In , were determined with uncertainties of less than 10keV.     

13.5-14.6MeV能区中子引起的铂同位素核反应截面测量

用活化法以93Nb(n，2n)92mNb和27Al(n，a)24Na反应截面为中子注量标准，对198Pt(n，2n)197m+gPt，198Pt(n， 2n)197mPt， 192Pt(n，2n)191Pt，194Pt(n，p)194Ir，195Pt(n，p)195mIr和 196Pt(n，p)196mIr反应截面进行了测量，由(13.5±0.2)，(14.1±0.1)和(14.6±0.2)MeV中子引起的198Pt(n，2n)197m+gPt反应截面分别为(2038±159)，(1919±73)和(1836±68)mb，198Pt(n，2n)197mPt反应截面为(974±37)，(1055±39)和(1042±39)mb；由(14.1±0.1)，(14.4±0.2)和(14.6±0.2)MeV中子引起的192Pt(n，2n)191Pt反应截面为(1680±103)，(1810±67)和(2047±97)mb；由(14.1±0.1) 和(14.4±0.2)MeV中子引起的194Pt(n，p)194Ir反应截面为(3.8±0.4)和(5.4±0.5)mb；由(14.1±0.1)，(14.4±0.2)MeV和(14.6±0.2)MeV中子引起的195Pt(n，p)195mIr反应截面为(1.0±0.2)，(1.6±0.2)和(1.8±0.2)mb；由(13.5±0.2)和(14.4±0.2)MeV中子引起的196Pt(n，p)196mIr反应截面分别为(1.13±0.07)和(1.18±0.06)mb. 本工作的数据和其他一些作者的数据进行了比较.