Meson-Induced Fission

Several batches of plates loaded with uranyl acetate have been exposed to ${\pi }^{-}$ mesons in the Berkeley cyclotron. The mesons were generated by the 350-Mev proton beam striking a carbon target and the plates were shielded from the direct beam, or positive particles generated at the target, by several inches of copper. They received negative mesons over a wide range of energies. About one in a hundred of the mesons observed to end in these plates, ended in a characteristic fission event. Twenty-two such fissions were observed. This was in rough qualitative agreement with what might be expected if it is assumed that the capture of a negative $\pi$-meson by the uranium nucleus always produces fission. Three of these events showed 3-way fission, a light particle coming off at about 90° to the tracks of the heavy fission fragments.