Study of Cross-Section Fluctuations forLi6+C12Reactions

Differential cross-section measurements for ${\mathrm{Li}}^6$+${\mathrm{C}}^{12}$ reactions are presented in 100-keV steps between 2.4 and 8.5 MeV at 0° and in 200-keV steps between 3.4 and 7.4 MeV at 40° (lab). Fluctuations in the cross sections are observed at all energies, but they are superimposed upon a rapid rise in cross section for beam energies below 4 MeV due to the Coulomb barrier effects. Coulomb barrier effects are accounted for by calculating the average differential cross section from the Hauser-Feshbach formula in which the transmission coefficients are determined from an optical-model potential. The ratios of the observed-to-calculated cross sections fluctuate about an almost constant value. These ratios are analyzed in terms of the Ericson fluctuation theory from which the coherence width is estimated to be ${\Gamma }_0=250\mathrm{}$ keV (c.m.). The average cross-section ratio for the ${\mathrm{C}}^{12}({\mathrm{Li}}^6,{\alpha }_1){\mathrm{N}}^{14}$ reaction indicates a 30% violation of isobaric-spin conservation in the 3.4- to 6.0-MeV interval.