Fluctuations in Excitation Functions forC12(O16, α)Mg24

Cross sections were measured at five angles for alpha-particle groups from the reaction ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}({}_{}{}^{16}{}_{}{}^{}\mathrm{O}, \alpha ){}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$. The measurements were made with 40-50-keV resolution over energy intervals as long as 9.9 MeV (c.m.). The data provided large samples for fluctuation analyses over compound-nucleus excitation energies from about 25 to 35 MeV. The average coherence width, which is dominated by compound states with $J\sim 10$, was found to be about 118 keV. It does not vary significantly with exit channel, angle, or excitation energy in the compound nucleus. Most of the data are well represented by the simple Ericson-Brink-Stephen statistical model and show no significant direct-interaction component. A pronounced peak appearing in several of the excitation functions near 31.8-MeV bombarding energy is not consistent with this model.