Photofission Cross Sections of ${\mathrm{U}}^{235}$, ${\mathrm{U}}^{238}$, ${\mathrm{Th}}^{232}$, ${\mathrm{Bi}}^{209}$, and ${\mathrm{Au}}^{197}$ at Energies of 150 to 500 Mev

Photofission cross sections for ${\mathrm{U}}^{238}$, ${\mathrm{U}}^{235}$, ${\mathrm{Th}}^{232}$, ${\mathrm{Bi}}^{209}$, and ${\mathrm{Au}}^{197}$ have been measured by use of bremsstrahlung spectra whose maximum energies ranged from 150 to 500 Mev. The fissions were detected in $2\pi$ geometry with a double ionization chamber. A suggested correlation of the resulting cross sections with those for proton fission and for photomeson production is made.