A study of highly-deformed α-cluster structures in light nuclei
The inelastic scattering reaction 160+12C has been studied in the centre-of-mass energy region from 37.7 MeV to 51.4 MeV, in a search for evidence for a seven-alpha chain state in 28Si. The decay products were detected in coincidence at angular separations around 90° in the centre of mass using two position-sensitive strip detectors. Kinematic reconstruction of the quasi-three body final states yielded the differential cross-sections for the decay channels leading to excited states in 12C, 160 and 20Ne. The excitation functions measured for the 12 C(0+2)-12C(0+2)-U+03B1 and 12C(02)-8Be-8Be final states agree broadly between the three experiments that were performed, but contain no structure. Reaction channels have also been identified leading to the 8Be-20Ne* and 12C*-160* final states. The cross-sections for the 8Be-20Ne* decay channels, with the 20 Ne in its lowest excited states, have been compared with previous measurements and provide good agreement. However, none of the excitation functions for these channels contain any structure. The absence of structure in any of the final states, that were identified in this study, indicates that a 28Si chain state is probably not being observed. The same model, that predicts that the seven-alpha chain state should lie in this excitation region in 28Si, has also been used to assign a six alpha chain structure to a resonance at Ex=46.6 MeV in 24 Mg. These two results are compared, and possible reasons for the absence of evidence for a 28Si chain structure are discussed.