Coupled channels description of single and mutual excitation in the scattering of 7Li from 12C and 24, 26Mg

doi:10.1016/0375-9474(82)90117-8

Nuclear Physics A

Volume 386, Issue 2, 27 September 1982, Pages 346-366

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Abstract

Coupled channels calculations have been made for the scattering of ⁷Li from ¹²C at 63 and 79 MeV and from ^24,26Mg at 88 MeV. The calculations describe, simultaneously, the elastic scattering, excitation of ⁷Li to the 478 keV $12$ ⁻ state, excitation of the target to its first 2⁺ state, and the mutual excitation of both projectile and target to their $12$ ⁻ and 2⁺ states respectively. The potentials have been calculated by a double folding model using the M3Y effective interaction for the real part, and a gaussian effective interaction for the imaginary part. Realistic densities have been used for the ground states of ⁷Li, ¹²C and ^{24, 26}Mg and also the transition densities to the excited states using a microscopic plus macroscopic prescription. For the mutual excitation, both one-step processes with l = 0, 2 and 4 and two-step processes were included. The calculations show that the two-step processes are the dominant contribution to the mutual excitation, but at forward angles, the oscillations in the data are only reproduced with the coherent addition of the one-step processes, which are dominated by the l = 4 contribution. Even when coupling to all single and mutual excitations are included the real potential still requires a normalization of about 0.6. The addition of the quadrupole re-orientation matrix element for the ground state does not significantly change this value. These calculations confirm that the coupling to the first excited inelastic levels of target and ejectile is not the source of the anomalous M3Y normalization, and that the dominant mode for mutual excitation is a two-step process. However, direct one-step mutual excitation is important for small angles (θ ≲ 20°).

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^6,7Li-nucleus double-folding optical potentials have been constructed using the JLM and a gaussian shape of the effective nucleon–nucleon interaction. Angular distributions of the differential cross sections of ^6,7Li elastic scattering from ¹²C, ²⁸Si, ⁴⁰Ca, ⁵⁸Ni, ⁹⁰Zr and ²⁰⁸Pb targets at 12.5–53 MeV/u were analyzed using the derived potentials. An energy-dependent reducing renormalization coefficient was required for the real component of the JLM optical potential in order to obtain successful predictions of the observed cross sections even when the projectile density-dependence was considered. A similar behavior was found for calculations based on the density-independent gaussian version of the effective nucleon–nucleon interaction. However, no renormalization was needed when a density-dependence approximation was involved. The energy- and target mass number-dependence in the renormalization factor, real volume integrals and total reaction cross sections are investigated.
Double-folding model analysis of the threshold anomaly in the scattering of polarized 7Li from 208Pb
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The scattering of polarized ⁷Li by ²⁰⁸Pb in a wide range of energies around the Coulomb barrier is described using double-folding potentials and the dispersion relations. The effect of the dipole polarizability of ⁷Li is also discussed using energy-dependent polarization potentials and the adiabatic approximation. These calculations reproduce adequately the experimental data, and provide useful information about the specific reaction channels responsible for the peculiar threshold anomaly exhibited by this system.
Strong mutual excitation of 148Nd+20Ne
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The angular distribution for mutual excitation has been measured for ¹⁴⁸Nd+²⁰Ne scattering. The colliding system studied was chosen for its very strong Coulomb coupling. Mutual excitation as strong as the single excitation of ²⁰Ne 2⁺ has been observed, which is much stronger than in previously measured cases. The angular distribution of the mutual excitation is not bell shaped and is similar to that of the Ne 2⁺ state. Coupled-channels calculations fail to reproduce the data.
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Angular distributions of the cross sections and analyzing powers up to third rank have been measured for the one-neutron transfer reactions ²⁶Mg(⁷Li,⁶Li)²⁷Mg, ¹²⁰Sn(⁷Li,⁶Li)¹²¹Sn and ¹²⁰Sn(⁷Li, ⁸Li)¹²⁹Sn initiated by polarized ⁷Li ions of 44 MeV. Third-rank analyzing power has been measured for the first time in transfer reactions. Coupled-channels calculations in which the ground and first excited states of ⁷Li are coupled together by collective interactions and one-neutron transfers are calculated in exact finite range explain the experimental data for low-lying states in final nuclei. Extracted spectroscopic factors are in good agreement with those obtained from other one-neutron transfer reactions on the same targets.

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^†: Present address: Department of Physics, Florida State University, Tallahassee, Florida 32306.

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Nuclear Physics A

Abstract

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Strong mutual excitation of <sup>148</sup>Nd+<sup>20</sup>Ne

Projectile breakup effect in elastic scattering of <sup>9</sup>Be

Elastic and inelastic scattering of polarized <sup>7</sup>Li ions from a <sup>26</sup>Mg target

Study of the one-neutron transfer reactions induced by polarized <sup>7</sup>Li ON <sup>26</sup>Mg and <sup>120</sup>Sn