Helium-Ion-Induced Fission Cross Sections ofU233andU238and the Nuclear Radii of Heavy Elements

New radiochemical data of the total fission cross sections have been obtained for ${\mathrm{U}}^{233}$ and ${\mathrm{U}}^{238}$, which can be used to derive nuclear radii for these isotopes. This and certain accurate previous results on ${\mathrm{U}}^{235}$ and natural bismuth can be interpreted in terms of an $r_0$ value of 1.41×${10}^{-13\mathrm{}}$ cm, when $R_{\alpha }=2.19\mathrm{}\times {10}^{-13\mathrm{}}$ cm, using the Weisskopf square-well nuclear model. Further, the nuclear radii obtained by this analysis are also in good agreement with the radii obtained by others from alpha-particle scattering data with a similar model. A diffuse-potential nuclear model proposed by Igo shows agreement with experiment in the lower energy range. The agreement, however, is not observed with data for higher energies. Certain features of the ${\mathrm{U}}^{233}$ fission curves are also discussed.