Importance of nuclear effects in the dissociation of 6He and 6Li at 65 MeV/u

Alpha particles with the beam velocity have been observed at a laboratory angle of 5 degrees from the dissociation of 6He and 6Li beams incident on Al and Au targets at bombarding energies near 65 MeV/u. Coincident γ-rays were observed by an array of eight BaF2 scintillation detectors surrounding the target subtending a solid angle near 90% of 4π. For all of the beam-target combinations studied, a substantial fraction of the events (often more than half) are accompanied by one or more γ rays, implying significant excitation of the target via the nuclear force. The differential cross section data for a particles with no accompanying γ rays will be compared with theoretical predictions for Coulomb excitation (derived from experimental El strengths for 6Li and a 3-body calculation for 6He) using a Monte Carlo simulation of the decay of the excited mass-6 nucleus. Coulomb perturbations of the orbits are treated exactly. The results suggest that Coulomb excitation alone can not account for all of the events observed with the Au target