Charge-pickup by Heavy Relativistic Nuclei

In the interactions of relativistic heavy projectile nuclei with target nuclei there is a measurable probability for the projectile nuclei to pick up a charge during the interaction. We report here new measurements, made in a wide range of targets, of the cross sections for charge-pickup of gold nuclei with energies of 10.6 GeV/nucleon, and of silver and krypton nuclei with energies between 1.4 and 0.5 GeV/nucleon. The excitation functions of these cross sections are discussed using all the measurements available to us and indicate that there are significant decreases in the cross sections as the energies increase. A weak target dependence is seen. Previously these cross sections have been reported to have a strong, approximately quadratic, dependence on the projectile mass. This conclusion has to be modified in the light of these new measurements. Instead, we suggest that the cross sections show a strong exponential dependence on either the fractional neutron excesses or, equivalently, on the neutron to nucleon ratios of the projectile nuclei.