Surface Transparency and Resonant Behavior in Some Lighter-Heavy-Ion Reactions

Resonance phenomena observed experimentally in some lighter-heavy-ion collisions at energies well above the Coulomb barrier are discussed in terms of the number of open channels available to direct reactions for the even-even C + C, C + O, and O + O systems. The calculated number of open channels shows a characteristic energy dependence which reflects the surface transparent absorption needed to observe resonant structure. The weak absorption is particularly pronounced in reactions involving ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$, and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ nuclei.