Fluctuations in Angular Distributions ofC12(O16, α)Mg24

Abstract

Angular distributions for a number of $\alpha$-particle groups from ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}({}_{}{}^{16}{}_{}{}^{}\mathrm{O}, \alpha ){}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ were measured with 45-keV resolution at closely spaced energies centered on bombarding energies of 19, 31, 42, and 49 MeV. Fluctuations of the type described by Ericson were observed. The data near 31 MeV were extensive enough to permit a statistical analysis. Compound levels with spins of about 10 are predominant at this energy. The average coherence width is about 125 keV and is independent of angle. No finer structure was found when the energy resolution was reduced to 15 keV. The strength of the fluctuations is generally in agreement with the expectation for a pure compound-nucleus process, though some anomalies were discovered. The coherence angle is about 6°, in agreement with expectation based on the size of the nucleus and the wave number. The angle-integrated average cross sections near 31 MeV are proportional to the statistical weights of the final levels.