Angular distributions of the alpha -particle production differential cross
section from the breakup of Li-6 and Li-7 projectiles incident on a Pb-208
target have been measured at seven projectile energies between 29 and 52 Me
V. The alpha -breakup cross section of Li-6 was found to be systematically
greater than that of Li-7 across the entire energy range. These data have b
een compared with previously reported results and with the predictions of c
ontinuum-discretized coupled channels (CDCC) calculations including resonan
t and nonresonant projectile breakup. The present data compare well with pr
evious measurements, while the CDCC calculations provide a reasonable predi
ction of the relative alpha -breakup cross sections but underpredict their
absolute values. The calculations confirm that a major factor in the enhanc
ement of the Li-6 to Li-7 alpha -breakup cross section is the difference be
tween the alpha -breakup thresholds of the two isotopes. These results have
implications for structural studies of light exotic nuclei based on elasti
c scattering.