A Sensitivity Test of Extracting the Optical Potential Parameters for 6He＋209Bi from the Transfer Reaction 208pb（7Li,6He）209Bi

Recently, an indirect method has been proposed to study the optical model potential of exotic nuclear systems by fitting the transfer reaction angular distribution. The sensitivity test of this transfer method is performed with 2~8 pb（T Li,6 He）2~9 Bi as an example, by varying the potential parameters individually. The results indicate that, except for the ambiguity in the real potential depth V, other optical potential parameters of 6He＋209Bi as well as the structural information of the reactions can be extracted reliably, Moreover, the radius parameter of the bound state, rbound, is an extraordinarily sensitive parameter, which should be taken care of in the calculation procedure. The present work provides a theoretical reference for the application of the transfer method.     

Angular Distribution of the 12C（6He, 7Li）nB Reaction

Angular distribution of the 12C（6He, 7Li）llB transfer reaction is measured with a secondary 6He beam of 36.4 MeV for the first time. The experimental angular distribution is well reproduced by the distorted-wave Born approxima- tion （DWBA） calculation. The success of the present experiment shows that it is feasible to measure one-nucleon transfer reaction on a light nucleus target with the secondary beam facility of the 1-11-13 tandem accelerator at China Institute of Atomic Energy （CIAE）, Beijing.     

Neutron Spectroscopic Factors of ^7Li and Astrophysical ^6Li（n,γ）^7Li Reaction Rates

Angular distributions of the ^7Li（^6Li, ^6Li）^7Li elastic scattering and the ^7Li（^6Li, ^7Lig.s.）^6Li, ^7Li（^6Li, ^7Li0.48）^6Li transfer reactions at Ec.m. = 23.7 MeV are measured with the Q3D magnetic spectrograph. The optical potential of ^6Li ＋ ^7Li is obtained by fitting the elastic scattering differential cross sections. Based on the distorted wave Born approximation （DWBA） analysis, spectroscopic factors of ^7Li =^6Li n are determined to be 0.73 ± 0.05 and 0.90 ± 0.09 for the ground and first exited states in ^7Li, respectively. Using the spectroscopic factors, the cross sections of the ^6 Li（n, γ0,1）^7 Li direct neutron capture reactions and the astrophysical ^6Li（n, γ）^7 Li reaction rates are derived.     

Search for the Halo Effect in the ^1H（^6He,^6Li）n Reaction

The angular distributions of the charge exchange reaction ^1H(^6He,^6Li)n were measured in reverse kinematics with a secondary ^6He beam at the energy of 4.17 A MeV.The data were analysed in the context of a microscopic calculation.It is shown that both the ground state of ^6He and the second excited state of ^6Li(3.563MeV,0^ ) have a halo structure.     

Isotopic effects in the 7Li + 10, 11B elastic and inelastic scattering

Angular distributions of the ⁷Li + ¹⁰B elastic and inelastic scattering were measured at the energy E _lab (¹⁰B) = 51 MeV (21 MeV c.m.). These and previously measured ⁷Li + ¹⁰B elastic-scattering data known at the ⁷Li-beam energies 24 MeV (14.1 MeV c.m.) and 39 MeV (22.94 MeV c.m.) were analyzed within the optical model and coupled-reaction channels method to determine the energy dependence of the parameters of the scattering potential and find the difference of these parameters from that of ⁷Li + ¹¹B scattering. It was found that the ⁷Li + ¹¹B potential parameters fail to describe the ⁷Li + ¹⁰B scattering data. The biggest difference is observed between the depths of the imaginary potentials that describe these scatterings.     

How does fusion hindrance show up in medium-light systems? The case of Ca + Ca

The fusion excitation function of ⁴⁸Ca + ⁴⁸Ca has been measured above and well below the Coulomb barrier, thereby largely extending the energy range of a previous experiment down to very low cross sections. This system has a negative Q  -value for compound nucleus formation. The fusion cross section decreases steadily below the barrier with no conspicuous change of slope below ?300 μb$?300\text{μb}$. Coupled-channels calculations using a Woods–Saxon potential indicate that a large diffuseness parameter is needed to reproduce the sub-barrier cross sections. A close analogy with the case of ³⁶S + ⁴⁸Ca, with Q>0$Q>0$, is pointed out. The sign of the Q-value does not influence fusion cross sections down to the 300–600 nb level.     

Enhanced neutron pair transfer and collective excitations in the system 206Pb + 118Sn at barrier energies

At energies below the Coulomb barrier, neutron transfer and Coulomb excitation have been measured in a very heavy asymmetric nuclear system, in ²⁰⁶Pb + ¹¹⁸Sn. These are semi-magic nuclei showing super-fluid properties. Particle-γ coincidence techniques using 5 Euroball Cluster detectors (EB), combined in a set-up with the Heidelberg-Darmstadt NaI Crystal Ball (CB), have been used. Position-sensitive detectors allowed the observation of scattering processes covering angles from 110 up to 150 degrees. The fragments are identified via the known γ-decays of the lowest excited states using the high resolution of EB. Using the unique feature of the set-up with the CB, transfer to well-defined final channels with known quantum numbers is selected using the high-efficiency multiplicity filter of the CB with no second γ-ray, i.e. without feeding. The data are analysed using the semi-classical approach and transfer probabilities are obtained. Coulomb excitation has been analysed using known transition probabilities. The enhancement is deduced for the two-neutron transfer populating the low-lying super-fluid 2⁺ states in ¹²⁰Sn and ¹¹⁶Sn, while the 2n transition remains in the ground state for the ^20NPb nuclei. Large enhancements up to EF ≃ 10³ are observed. This is the first observation of neutron pair transfer enhancement for a heavy nuclear binary system with super-fluid properties with experimentally separated levels. The calculations with microscopic 2-neutron wave functions, with configuration mixing over six shell model configurations and using the coupled reaction channels approach, reproduce well the observed probabilities and the enhancement. Received: 27 August 2002 / Accepted: 9 December 2002 / Published online: 25 March 2003 RID="a" ID="a"e-mail: oertzen@hmi.de Communicated by D. Schwalm     

Microscopic approach to calculating cross sections and optical potentials for nucleus-nucleus interaction at intermediate energies

Nucleus-nucleus scattering is considered in the high-energy approximation and on the basis of Glauber-Sitenko microscopic theory in the optical limit. Analytic expressions for eikonal phase shifts are given for the case of Fermi-type realistic potentials and nuclear-density distributions. The effect of taking into account the distortions of the trajectories of the nuclei involved and the nuclear-density dependence of nucleon-nucleon forces on the total reactions cross sections is illustrated. The sensitivity of the reaction cross sections to the choice of model for the ⁶He projectile nucleus, which involves a neutron halo, is explored. Semimicroscopic optical potentials are introduced in order to describe differential cross sections for elastic scattering. The results of the present calculations are compared with available experimental data.