Isotopic dependence of fusion barrier energies in reactions forming heavy elements

The systematic dependence of fusion barrier energies on neutron excess can be determined over a broader range using radioactive nuclei. It is shown that precise measurements with a wide range of stable isotopes are necessary for optimum interpretation of radioactive beam measurements. New precision cross-section data for fusion of S32,34,36 projectiles with Pb isotopes are presented, aiding in a revised interpretation of recent S38 fusion data, which now appears more likely to follow the same trend as the stable isotopes than to show the unexpected behavior previously inferred.