Intermediate structure inO12system through alpha-induced reactions onMg24in the energy rangeEα=26–37 MeV

The excitation functions have been measured in the energy range E/sub ..cap alpha../ = 26--37 MeV for the reaction /sup 24/Mg(/sup 4/He,/sup 12/C)/sup 16/O at theta/sub lab/ = 30/sup 0/, 40/sup 0/, and 50/sup 0/ and for /sup 24/Mg(/sup 4/He,/sup 4/He')/sup 24/Mg at theta/sub lab/ = 152/sup 0/--160/sup 0/. Prominent structures are observed in the excitation functions. The cross sections are compared with the Hauser-Feshbach statistical-model calculations. Probability distributions of the deviations from the average are calculated for all the excitation functions and compared with the statistical-model expectations for the fluctuations. The coherence width is estimated to be 176--214 keV from the observed number of maxima in the excitation functions and it is in agreement with the expected value for the excitation region of 32--42 MeV in the compound nucleus. Cross-channel correlations have been calculated between the /sup 12/C channel and alpha elastic and inelastic scattering channels. At E/sub ..cap alpha../ = 27.8 and 28.6 MeV where large cross-channel correlations have been observed, angular distributions of /sup 12/C have been measured and found to follow the pattern (P/sub 11/(costheta))/sup 2/. These results show that the excitation functions are all generally in agreement with the fluctuations expected from the statistical model.more » However, at E/sub ..cap alpha../ = 27.8 and 28.6 MeV where large cross-channel correlations are observed, though there is a small chance of less than 6 x 10/sup -4/ for these to be due to statistical fluctuations, the possibility that these structures at these two energies are nonstatistical in origin cannot also be ruled out.« less