Measurements of positrons from pair production in Coulomb collisions of 33-TeV lead ions with fixed targets

Free positrons from electron-positron pairs produced by 33-TeV ${\mathrm{Pb}}^{82+}$ ions in Coulomb collisions with targets of carbon $\left[\right(\mathrm{CH}{)}_x],$ aluminum, palladium, and gold have been measured to determine cross sections and momentum distributions. Upper limits have been established for contributions from multiple pair formation. Comparison with similar data taken for 6.4-TeV ${\mathrm{S}}^{16+}$ ions shows that cross sections scale as the product of the squares of the projectile and target nuclear charges. Positron momentum distributions for ${\mathrm{S}}^{16+}$ and ${\mathrm{Pb}}^{82+}$ ions on all targets are observed to be similar, but indicate a tendency for higher-energy positron emission for the ${\mathrm{Pb}}^{82+}$ projectiles.