Optical model analyses of 6,7Li + 208Pb elastic scattering near the Coulomb barrier

doi:10.1016/0375-9474(94)90064-7

Nuclear Physics A

Volume 571, Issue 2, 25 April 1994, Pages 326-336

https://doi.org/10.1016/0375-9474(94)90064-7 Get rights and content

Abstract

The elastic scattering of ⁶Li and ⁷Li by ²⁰⁸Pb has been measured at several energies near the Coulomb barrier and analysed in terms of the optical model. Previous reports have suggested that the normalization factor, N_R, for the double-folded real potential is approximately 0.6 for both isotopes at bombarding energies well above the Coulomb barrier. In this paper we show that, whereas this low value for N_R persists for ⁶Li at energies close to the barrier, for ⁷Li it is somewhat greater than unity, and indicates the existence of a threshold anomaly for this projectile.

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A phenomenological study of peripheral reactions induced by strongly bound, weakly bound and exotic projectiles on different targets is presented. A large number of experimental elastic scattering differential cross sections at energies close to the Coulomb barrier is studied on the basis of a simple nuclear optical model potential that depends on a small number of parameters. The derived wave functions, together with the imaginary component of the optical potential, allow the analysis of the radial peripheral absorption density distributions for the different kind of projectiles. These distributions, when appropriately normalized, show a clear correlation with the type of projectile regardless of the involved target and indicate that projectiles more prone to break up show a more peripheral absorption density distribution. This manifests in their magnitude, location and width. The relationship of these variables in the strongly bound group and the weakly bound group are described with a simple exponential function, while the exotic projectiles show two distinct groups, namely the neutron-halo and the proton-halo. For the neutron-halo projectiles such as ${}^{6}{He}$ , ${}^{11}{Li}$ and ${}^{11}{Be}$ there is a notable increment of the radial peripheral absorption density peak and the total reaction cross section as the breakup separation energy decreases. The same relationship is established for the proton-halo projectiles ${}^{8}B$ and ${}^{17}F$ but their reduced effective dipole charge leads to a lower probability of dipole Coulomb breakup that results in a substantial reduction in the extent of their peripheral absorption.
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Citation Excerpt :
The effect of resonance coupling in breakup cross-section was investigated and contribution of the resonance states is found to be ∼5-10% as given in Table 2. In order to investigate the mass dependence of potential in consistent way using HFB densities near Coulomb barrier, elastic scattering data of 6Li with targets in different mass regions viz. 27Al [19,51], 28Si [12,52,53], 58Ni [54,22], 64Zn [55], 90Zr [14], 116Sn [56], 138Ba [57], 144Sm [58], 208Pb [59,60], 209Bi [48], were systematically analyzed in the double folding framework. The static version of the Time Dependent Hartree Fock (TDHF) code Sky3D [35] was used to calculate the target density distributions in order to eliminate any parametric dependence of density distribution extracted from different electron scattering experiments.
Elastic scattering for ⁶Li+⁵¹V system is measured around Coulomb barrier energies. The behavior of the nuclear potential is extracted from elastic scattering angular distributions measured in wide angular range. The data have been analyzed using phenomenological Woods-Saxon shaped optical potential and microscopic double folding potential frameworks. Sensitivity radius was determined using optical model and potential behavior thus analyzed shows breakup threshold anomaly (BTA). Continuum discretized coupled channel (CDCC) calculations give a good description of the measured elastic scattering data with breakup coupling effects. The contribution of breakup coupling through resonance states is significant. The potential behavior has been analyzed in the double folding framework using density distribution calculated from Hartree-Fock-Bogoliubov (HFB) method to understand the dependence of BTA in a wide mass range. It is observed that BTA exist from lower to higher mass targets for ⁶Li projectile. The systematic target dependence of the reaction cross-sections for ⁶Li projectile follows an universal scaling behavior. An enhancement in reaction cross section is observed for exotic compared to weakly and strongly bound projectiles with ⁵¹V target.
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¹: Present address: Department of Physics and Astronomy, Wayne State University, 666, West Hancock, Detroit, MI 48201, USA.

²: Present address: Department of Physics, University of Sevilla, Sevilla, Spain.

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Nuclear Physics A

Abstract

References (27)

Phys. Reports

Heavy ion collisions at energies near the Coulomb barrier 1990

Phys. Rev.

Phys. Reports

Phys. Rev.

Nucl. Phys.

Phys. Rev.

J. of Phys.

Phys. Rev.

Prog. Theor. Phys.

Phys. Rev.

Arabian Journal for Science and Engineering

Z. Phys.

Phys. Rev. Lett.

Cited by (235)

Peripheral reactions and elastic scattering induced by strongly bound, weakly bound and exotic nuclei

Elastic scattering for <sup>6</sup>Li+<sup>51</sup>V and systematic study of breakup threshold anomaly

Simultaneous calculation of elastic scattering, fusion, and direct cross sections for reactions of weakly bound projectiles

Elastic scattering of <sup>13</sup>C and <sup>14</sup>C isotopes on a <sup>208</sup>Pb target at energies of approximately five times the Coulomb barriers

Dynamics of <sup>7</sup>Li breakup and its influence on elastic scattering: a study of <sup>7</sup>Li + <sup>144</sup>Sm system

Folding potential with modern nuclear density functionals and application to <sup>16</sup>O+<sup>208</sup>Pb reaction