Dynamic polarization potentials and dipole polarizabilities of ${}^{11}$Li, ${}^6$He and ${}^6$Li compared

Elastic scattering data for ${}^{11}$Li, ${}^6$Li, and ${}^6$He $+$ ${}^{208}$Pb at incident energies of 29.8 MeV, 29 MeV, and 18 MeV, respectively, were analyzed by means of coupled discretized continuum channels (CDCC) calculations. Dynamic polarization potentials (DPPs) of the trivially equivalent local potential (TELP) type were derived from these calculations and compared. The dipole polarizability factor $\alpha$ for ${}^{11}$Li obtained by fitting a Coulomb polarization potential to the long-range part of the real DPP is consistent with the theoretical value of $5.7$ fm${}^3$. These results point to the dineutron model providing a very good description of ${}^{11}$Li breakup coupling effects. The much larger Coulomb dipole polarizability of ${}^{11}$Li suggests the persistence of large deviations from Rutherford scattering at sub-barrier energies for medium mass targets, a prediction confirmed by CDCC calculations.

Figure 1

CDCC calculations compared to the elastic scattering data for: (a) 29.8 MeV ${}^{11}$Li $+$ ${}^{208}$Pb, (b) 29 MeV ${}^6$Li $+$ ${}^{208}$Pb, and (c) 18 MeV ${}^6$He $+$ ${}^{208}$Pb. The solid and dashed curves represent the results of the full CDCC and no-coupling calculations, respectively. The dotted curves denote the results of CDCC calculations with no Coulomb couplings (but retaining the diagonal Coulomb potentials). The dot-dashed curves denote the results of optical model calculations with the bare potentials $+$ DPPs, see text. Note the linear cross section scale.

Figure 2

TELP-type DPPs derived from the CDCC calculations for ${}^{11}$Li, ${}^6$He, and ${}^6$Li $+$ ${}^{208}$Pb. The dotted curves in (a) denote the Coulomb polarization potential of Eq. (1) with values of $\alpha =5.7$ fm${}^3$ and $1.3$ fm${}^3$ for ${}^{11}$Li and ${}^6$He, respectively.

Figure 3

CDCC calculations for 11.6 MeV ${}^{11}$Li $+$ ${}^{58}$Ni elastic scattering. The solid and dashed curves represent the results of the full CDCC and no-coupling calculations, respectively. The dotted curve denotes the result of a CDCC calculation with no Coulomb couplings (but retaining the diagonal Coulomb potentials). The dot-dashed curve denotes the result of an optical model calculation with the bare potential $+$ DPP. Note the linear cross section scale.