Structure phenomena in the orbiting 12C+24Mg system

The backward-angle yield from 12C+24Mg has been studied with the technique of inverse kinematics, using 24Mg beams with energies from 90 to 126 MeV. In the different exit channels with 5≤Zejectile≤9 the Q-integrated differential cross sections dσ/dθ are consistent with isotropy at 130deg≤θc.m.≤165deg, which is taken as signature of orbiting. The most probable exit energies in the strongly predominant even-Z channels as a function of bombarding energy give evidence for complete damping at angular momenta close to the critical ones for fusion. The results for the weakly populated odd-Z channels suggest that the conditions of damping are affected by the large negative ground-state Q-values. Structures are observed in the Q-value spectra and in the excitation functions at given Q. The former are identified with high-spin states close to the yrast lines, which are shown to be selectively populated due to the matching conditions for deep-inelastic reactions in light heavy-ion systems. An additional selectivity for natural-parity transitions gives evidence for the conservation of the dinuclear parentage. Narrow fluctuations observed in the excitation functions for fixed narrow Q-windows are attributed to the overlapping of unbound states of the intermediate complex. In the Q-integrated excitation functions these fluctuations cancel, but weak gross structure of a few MeV width remains visible. A statistical analysis of the narrow fluctuations yields coherence widths around 400 keV, corresponding to lifetimes of the intermediate dinucleus around 2x10-21s. (orig.)