(alpha,2 alpha) cluster knockout reaction on Be-9 and C-12 at 580 MeV

Cross-section measurements of the Be-9,C-12(alpha,2 alpha) reaction at 580 MeV bombarding energy are presented. The data are compared with distorted-w ave impulse approximation calculations. The agreement between theory and ex periment suggests a dominance of the quasifree knockout mechanism. The extr acted ct-particle spectroscopic factors are in reasonable agreement with th eory and proton-induced knockout reactions, unlike measurements for the (a, 2a) reaction at energies less than or equal to 140 MeV, but still show sign ificant angular dependence. [S0556-2813(99)0402-2].