Antiproton- and Pion-Induced Fission at 2.5 GeV/c

Mica track detectors were used to measure the fission cross sections of U, Bi, and Au irradiated with 2.5-GeV/c antiprotons and negative pions. The binary-fission results in mb are: U, 2170 ± 330 for $\overline{p}$ and 1090 ± 160 for ${\pi }^{-}$; Bi, 293 ± 60 for $\overline{p}$ and 191 ± 40 for ${\pi }^{-}$; Au, 210 ± 40 for $\overline{p}$ and 107 ± 20 for ${\pi }^{-}$. The ${\pi }^{-}$ cross sections are about the same as for protons but the $\overline{p}$ cross sections are higher by about a factor of 2. Approximate ternary-fission results in mb are: U, 8 for $\overline{p}$ and 4 for ${\pi }^{-}$; Bi, 6 for $\overline{p}$ and 1.5 for ${\pi }^{-}$; Au, 6 for $\overline{p}$ and 2 for ${\pi }^{-}$. Ternary fission induced by antiprotons appears to be about an order of magnitude more probable than that induced by protons of the same momentum. The results are discussed relative to the large annihilation cross section of antiprotons.