Origin of the structures in the /sup 12/C(/sup 16/O,. cap alpha. ) reaction: Dominance of /sup 20/Ne/sup / and /sup 16/O/sup / sequential. cap alpha. -decay processes

A series of experiments was carried out on the /sup 12/C(/sup 16/O,..cap alpha..) reaction to search for the population of molecular resonances as final state interactions. Contrary to our expectation, no positive evidence was found in ..cap alpha..-/sup 12/C coincidence measurements for molecular states. The experimental configuration was arranged to selectively observe events corresponding to decays into the /sup 12/C+ /sup 12/C resonance channel. A study of the incident energy dependence of the /sup 12/C(/sup 16/O,..cap alpha..) reaction clearly indicates the importance of sequential processes in the ..cap alpha..-particle yield. In particular, the process where the incident /sup 16/O picks up an ..cap alpha.. forming /sup 20/Ne( resonances and then decays back to ..cap alpha..+ /sup 16/O can reasonably explain most of observed structures in the inclusive ..cap alpha.. spectra. The sequential process caused by the inelastic excitation of /sup 16/O to /sup 16/O(..--> cap alpha..+ /sup 12/C can also contribute to the broad peaks observed in the inclusive spectra, but only in the high excitation region.