Electron-Induced Fission in ${\mathrm{U}}^{238}$, ${\mathrm{Bi}}^{209}$, and ${\mathrm{Ta}}^{181}$

The fission cross sections of ${\mathrm{U}}^{238}$ and ${\mathrm{Bi}}^{209}$ induced by 250- and 500-MeV electrons have been measured using mica detectors. Pulse-height distributions of the fission fragments from ${\mathrm{U}}^{238}$ were also measured using semiconductor detectors, and the distributions showed two peaks characteristic of excitation energies less than about 40 MeV. Several methods were used to prove that the observed fission events were induced by electrons and not by bremsstrahlung or background radiations. Preliminary measurements of fission-fragment angular distributions show less than 10% deviations from isotropy.