Dominance of nucleon-nucleon interactions inα+C12total reaction cross sections

We have measured $\alpha$ + ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ total reaction cross sections (${\sigma }_R$) at $E_{\mathrm{lab}}=94\mathrm{} \mathrm{and} 173$ MeV/N using the attenuation method. Our data indicate a decreasing ${\sigma }_R\mathrm{}\left(E\right)\mathrm{}$ at intermediate incident energies. These results, along with existing measurements, are in quantitative agreement with theoretical predictions for ${\sigma }_R\mathrm{}\left(E\right)\mathrm{}$ which are based on nucleon-nucleon total cross sections.