Entrance channel effects by populating resonances in theAl26,Si29, andSi30systems

Abstract

Excitation functions have been measured for the elastic, recoil, and alpha-particle exit channels for four reactions: /sup 17/O+/sup 12/C (E/sub lab/ = 30.0--57.0 MeV), /sup 16/O+/sup 13/C (E/sub lab/ = 29.5--52.6 MeV), /sup 17/O+/sup 13/C (E/sub lab/ = 30.0--57.0 MeV), and /sup 16/O+/sup 10/B (E/sub lab/ = 42.4--60.1 MeV). The alpha particles were detected at theta/sub lab/ = 10/sup 0/ while the elastic and recoil particles were detected at theta/sub lab/ = 34/sup 0/. Statistical analyses of the data are used to search for correlated, nonstatistical structures in the excitation functions. The resonant properties of three compound nuclei (/sup 26/Al, /sup 29,30/Si) are studied by comparing the excitation energies at which nonstatistical structures are seen when the nuclei are formed via different well matched (in terms of J/sub max/) entrance channels. These resonancelike structures seen in the various entrance channels (for a given compound nucleus) are found to be uncorrelated in excitation energy, thereby implying a dependence upon the properties of the entrance channel. The lack of entrance channel correlations and the short lifetimes of the structures seen are viewed as evidence that the reaction may proceed through a quasimolecule, or that the compound nucleus itself is so highly excitedmore » and deformed that its formation is entrance channel dependent.« less