High-Energy-Proton Fission Cross Sections of U, Bi, Au, and Ag Measured with Mica Track Detectors

The interaction of 0.6-29-GeV protons with U, Bi, Au, and Ag was studied with mica track detectors. Binary fission events were identified as correlated pairs of tracks. A fragment registered an acceptable track if its mass was ≥30 and its kinetic energy >6-8 MeV. The results show: The U fission cross section ${\sigma }_f\left(\mathrm{U}\right)$ is 1400 mb up to 1.0 GeV and decreases monotonically to 670 mb at 29 GeV; ${\sigma }_f\left(\mathrm{Bi}\right)$ increases from 125 mb at 150 MeV to a broad maximum of 215 mb at ∼600 MeV, and then decreases to 105 mb at 29 GeV; ${\sigma }_f\left(\mathrm{Au}\right)$ varies little, 59-76 mb, in the energy region 0.6-29 GeV (the highest values appear at 2 and 3 GeV); no binary events were observed from Ag targets: upper limits are 0.3 mb at 0.6 GeV, 2 mb at 1.0 GeV, 5 mb at 2-13 GeV, and 6 mb at 29 GeV. Effects of secondary particles were shown to be negligible; the experimental uncertainty varies from ±10 to ±20%. Ternary fission events (140) were seen for U starting at 1.0 GeV, and for Bi and Au starting at 2.0 GeV. The yields are about 1-2 per 1000 binaries. Many single unpaired tracks were also observed, and their yield increases with beam energy. From U, most of these seem to be from a small fraction of asymmetric fissions where one of the partners is below recording threshold. From Bi and Au, most of the single tracks are high-energy spallation residues.