Capture, ionization, and pair-production processes in relativistic heavy-ion collisions in the 1-GeV/nucleon energy range

The cross sections for capture, ionization, capture from pair production, and free pair production were measured for 0.96-GeV/nucleon U⁹²⁺ and 0.405-, 0.96-, and 1.3-GeV/nucleon La⁵⁷⁺ ions incident on Au, Ag, and Cu targets. The cross sections for capture from pair production, free pair production, ionization, and total capture (the sum of capture from pair production, radiative electron capture, and nonradiative capture) are analyzed as a function of collision energy, projectile, and target atomic numbers. We find that, when the collision energy is increased from 0.405 GeV/nucleon to 1.3 GeV/nucleon, the capture from pair production and the free pair production cross sections increase by almost a factor of 6, while the capture cross section decreases by two orders of magnitude. The ionization cross section is found to vary very weakly with the collision energy in the 1-GeV/nucleon energy range. We found a dependence of free pair production cross sections on the target and projectile atomic number to be close to Z², characteristic of an ionizationlike process. We also found a dependence of the capture from pair production cross sections on the target atomic number to be usually steeper than Zₜ², and on the projectile atomic number, somewhat steeper than the Zₚ⁵, characteristic of a capturelike process. Theory and experiment are in some disagreement for capture from pair production, and free pair production, cross sections, but are in general agreement for the other capture processes and for ionization.