Evidence for a proton halo inB8: Enhanced total reaction cross sections at 20 to 60 MeV/nucleon

Total reaction cross sections ${\mathrm{\sigma }}_{\mathit{R}}$ for ${}_{}{}^8{}_{}{}^{}\mathrm{B}$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, and ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ on ${}_{}{}^{\mathrm{nat}}{}_{}{}^{}\mathrm{Si}$ were measured from about 20 to 60 MeV/nucleon. The ${\mathrm{\sigma }}_{\mathit{R}}$ for ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ compared reasonably well with conventional strong absorption and microscopic calculations. Measured ${\mathrm{\sigma }}_{\mathit{R}}$ for ${}_{}{}^8{}_{}{}^{}\mathrm{B}$ were slightly larger than those for the two heavier nuclei, and notably larger than the conventional calculations. The ${}_{}{}^8{}_{}{}^{}\mathrm{B}$ data were well reproduced by microscopic calculations using the same matter distribution used to explain the ${}_{}{}^8{}_{}{}^{}\mathrm{B}$ quadrupole moment data, and therefore provide new evidence for the existence of a proton halo in ${}_{}{}^8{}_{}{}^{}\mathrm{B}$.