Observation of a critical angular momentum for deep inelastic processes with light heavy ions

Studies of collisions between nuclei have shown that the large incoming orbital angular momenta play an important role in systems where Coulomb and centrifugal repulsion for the dominant (near grazing) partial waves are of comparable magnitude (A/sub p/,A/sub t/ < 40). The kinetic energy of the fully damped fragments contains significant centrifugal energy contributions. Recent measurements have shown that the yield of fragments from strongly damped processes dominates the spectra at backward angles, and the angular distributions associated with this yield indicate that the fragments emerge from a long-lived rotating dinuclear complex (orbiting). These measurements at backward angles provide a means for studying the products from deep inelastic processes in the absence of contributions from quasielastic processes. In our study of deep inelastic processes in 28Si + 12C at backward angles we show here results which demonstrate that the orbital angular momentum of the rotating dinuclear system formed in this collision reaches a critical value beyond which it ceases to increase with increasing bombarding energy