Experimental study of ${}^6\mathrm{He}+{}^9\mathrm{Be}$ elastic scattering at low energies

New data for the ${}^6\mathrm{He}+{}^9\mathrm{Be}$ reaction at $E_{\mathrm{lab}}=16.2$ and 21.3 MeV have been taken and analyzed. The effect of the collective couplings to the excited states of the target has been studied by means of coupled-channels calculations, using a double-folding potential for the bare interaction between the colliding nuclei, supplemented with a phenomenological imaginary part of Woods-Saxon type. In addition, three- and four-body continuum-discretized coupled-channels calculations have been performed to investigate the effect of the projectile breakup on the elastic scattering. Both effects, the coupling to target and projectile excited states, are found to affect significantly the elastic scattering. The trivial local polarization potential extracted from the continuum-discretized coupled-channels calculations indicates that continuum couplings produce a repulsive real part and a long-range imaginary part in the projectile-target interaction.

Figure 1

RIBRAS facility installed in the 45B Pelletron beam line.

Figure 2

Scheme of the procedure used to mitigate the effect of the beam divergence.

Figure 3

Biparametric spectrum obained with ${}^6\mathrm{He}$ beam and (a) ${}^9\mathrm{Be}$ and (b) ${}^{197}\mathrm{Au}$ targets at ${\theta }_{\mathrm{lab}}={15}^{°}$.

Figure 4

Absolute differential cross sections for the ${}^6\mathrm{He}+{}^9\mathrm{Be}$ elastic scattering. The solid circles are the data from the present experiment at (a) $E_{\mathrm{lab}}$ = 16.2 MeV and (b) $E_{\mathrm{lab}}$ = 21.3 MeV, and the open circles are the experimental data from Majer et al. at $E_{\mathrm{lab}}$ = 16.8 MeV [23].

Figure 5

Elastic scattering angular distribution for ${}^6\mathrm{He}+{}^9\mathrm{Be}$ at (a) $E_{\mathrm{lab}}=16.2$ MeV and (b) $E_{\mathrm{lab}}=21.3$ MeV. The solid circles are the data from the present experiment and the open circles (top panel) are the experimental data from Majer et al. [23]. The dotted line is the optical model calculation performed with the bare interaction. The dashed line is the CC calculation, including the coupling to the $2_1^{+}$ resonance in ${}^6\mathrm{He}$ and some states of the target, as described in the text. The solid line corresponds to the same calculation, convoluted with the experimental angular resolution.

Figure 6

Elastic scattering angular distributions for ${}^6\mathrm{He}+{}^9\mathrm{Be}$ at (a) $E_{\mathrm{lab}}=16.2$ MeV and (b) $E_{\mathrm{lab}}=21.3$ MeV. In both panels, the dashed line corresponds to the 3b-CDCC calculation and the solid line to the 4b-CDCC calculation. The dotted line is the 3b-CDCC calculation omitting the coupling to the continuum.

Figure 7

Elastic scattering angular distribution for ${}^6\mathrm{He}+{}^9\mathrm{Be}$ at (a) $E_{\mathrm{lab}}=16.2$ MeV and (b) $E_{\mathrm{lab}}=21.3$ MeV. The solid circles are the data from the present experiment and the open circles (top panel) are the experimental data from Majer et al. [23] for $E_{\mathrm{lab}}=16.8$ MeV. The dashed and solid lines correspond to the 3b- and 4b-CDCC calculations, respectively, convoluted with the experimental angular resolution. The dotted lines are the 3b-CDCC calculations omitting the coupling to the continuum, also convoluted with the experimental angular resolution.

Figure 8

TLP potential extracted from the 3b- and 4b-CDCC calculations for ${}^6\mathrm{He}+{}^9\mathrm{Be}$ at $E_{\mathrm{lab}}=21.3$ MeV with dashed and solid lines, respectively. The top (a) and bottom (b) panels correspond to the real and imaginary parts. The dotted line in each panel is the Watanabe-like potential obtained by folding the sum of the $2n$-${}^9\mathrm{Be}$ and $\alpha$-${}^9\mathrm{Be}$ interactions with the ground-state density of ${}^6\mathrm{He}$, calculated in a dineutron cluster model.