Elastic Scattering of Alpha Particles byC12in the Bombarding Energy Range 10 to 19 MeV

Abstract

The scattering of alpha particles by ${\mathrm{C}}^{12}$ has been studied in the bombarding energy range 10 to 19 MeV. Many anomalies were observed in the excitation curves which correspond to ${\mathrm{O}}^{16}$ compound system energy levels in the excitation energy range 14 to 21 MeV. Fifteen detailed angular distributions were measured and the data have been analyzed with a smooth cutoff model which was modified to include appropriate resonant phase shifts. The spins and parities of the more prominent resonances have been assigned. Real well depths of 100 MeV or more were required in an optical-model analysis to yield theoretical cross sections comparable with experimental values. In general, optical-model fits were not satisfactory. Two series of levels in ${\mathrm{O}}^{16}$ were observed which obey rotational band systematics. The substantial widths of the band members suggest an alpha-particle cluster configuration for these excited states.