Elastic scattering and breakup reactions of the proton drip-line nucleus ${}^8\mathrm{B}$ on ${}^{208}\mathrm{Pb}$ at 238 MeV

Elastic scattering and breakup angular distributions of the weakly bound radioactive nucleus ${}^8\mathrm{B}$ on a ${}^{208}\mathrm{Pb}$ target at an incident energy of 238 MeV, which corresponds to four times the Coulomb barrier, have been measured at the HIRFL-RIBLL facility (Institute of Modern Physics, Lanzhou). The data have been analyzed using the optical model and the continuum discretized coupled channels (CDCC) formalism. The measured and calculated elastic scattering angular distributions do not show any significant Coulomb rainbow suppression. The angular distribution for the breakup reaction was measured for the first time at this energy. The angular distribution of the ${}^7\mathrm{Be}$ fragments could be reproduced considering elastic plus nonelastic breakup contributions, with the former evaluated with the CDCC calculations and the latter with the model of Ichimura, Austern, and Vincent [Phys. Rev. C 32, 431 (1985)]. The comparison of the breakup cross section of ${}^8\mathrm{B}$ with that of ${}^{11}\mathrm{Be}$ suggests that the Coulomb and centrifugal barriers encountered by the valence proton may suppress the breakup cross section.

Figure 1

Sketch of the detector setup. Two DSSDs (${\mathrm{Si}}_{\mathrm{A}}$ and ${\mathrm{Si}}_{\mathrm{B}}$) were placed upstream from the target for measuring the beam position. The reaction products were detected with two telescopes, symmetrically mounted around the beam axis, which were composed of two DSSDs, a silicon detector, and an array of CsI(Tl) crystals.

Figure 2

The calibrated two-dimensional $\mathrm{\Delta }E\text{−}E$ particle identification spectra for the (a) ${}^7\mathrm{Be}$ and (b) ${}^8\mathrm{B}$ projectile nuclei obtained by the TelR telescope, gated by their corresponding ToF. The solid-red-line ellipsoids represent the loci of the elastic scattering events for ${}^7\mathrm{Be}$ and ${}^8\mathrm{B}$. The dashed line represents the band for ${}^7\mathrm{Be}$ (breakup events), which have the same ToF as ${}^8\mathrm{B}$ but different energy.

Figure 3

Elastic scattering angular distributions for ${}^3\mathrm{He}+{}^{208}\mathrm{Pb}$ at $E_{\mathrm{lab}}=55\mathrm{MeV}$ (black empty diamond), ${}^7\mathrm{Be}+{}^{208}\mathrm{Pb}$ at $E_{\mathrm{lab}}=175\mathrm{MeV}$ (blue solid circle), and ${}^8\mathrm{B}+{}^{208}\mathrm{Pb}$ at $E_{\mathrm{lab}}=238\mathrm{MeV}$ (red solid square) and comparisons with OM calculations. Error bars are due to the statistical uncertainty only.

Figure 4

Elastic scattering angular distributions for the ${}^8\mathrm{B}+{}^{208}\mathrm{Pb}$ reaction at $E_{\mathrm{lab}}=$ 238 MeV. Experimental data from the present experiment (black squares) are compared with OM and CDCC calculations. Error bars are statistical only.

Figure 5

Experimental ${}^7\mathrm{Be}$ angular distributions from the ${}^8\mathrm{B}+{}^{208}\mathrm{Pb}$ reaction at $E_{\mathrm{lab}}=$ 238 MeV (yellow circle) and comparisons with calculations. Error bars are statistical only.