The ${\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}}=180\mathrm{}°$ elastic and inelastic excitation functions have been measured for the systems ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ ($27.8\le E_{\mathrm{c}.\mathrm{m}.\mathrm{}}\le 31.5$ MeV) and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ ($30.0\le E_{\mathrm{c}.\mathrm{m}.\mathrm{}}\le 32.7$ MeV) in small steps ($\delta E_{\mathrm{c}.\mathrm{m}.\mathrm{}}<100\mathrm{}$ keV). In both systems it is observed that the gross structures previously found ($\Gamma \approx 1-2$ MeV) are strongly split into finer structure. A statistical analysis of the data has been made to determine the average width, strength, and cross correlation of these narrow structures. The results are compared to the predictions of Hauser-Feshbach calculations. It is concluded that it is impossible within the standard statistical model to simultaneously reproduce both the observed widths and the average fluctuating cross sections.

NUCLEAR REACTIONS Measured elastic and inelastic excitation functions at ${\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}}=180\mathrm{}°$ for ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$+${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$, $27.8<~E_{\mathrm{c}.\mathrm{m}.\mathrm{}}<~31.5$ MeV, and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$+${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$, $30.0<~E_{\mathrm{c}.\mathrm{m}.\mathrm{}}<~32.7$ MeV. Deduced average width, strength, and cross correlation of observed structures. Compared with Hauser-Feshbach predictions.

• Received 12 June 1979

DOI:https://doi.org/10.1103/PhysRevC.20.1759