Total Cross Sections for Fission of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi mathvariant="normal">U</mml:mi></mml:mrow><mml:mrow><mml:mn>238</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>Induced by<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi mathvariant="normal">He</mml:mi></mml:mrow><mml:mrow><mml:mn>4</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>and Heavy Ions

The total fission cross sections have been measured for bombardment of ${\mathrm{U}}^{238}$ with ${\mathrm{He}}^{4}$, ${\mathrm{B}}^{11}$, ${\mathrm{C}}^{12}$, ${\mathrm{N}}^{14}$, ${\mathrm{O}}^{16}$, and ${\mathrm{Ne}}^{20}$ ions at energies up to 10.4 MeV/nucleon. Because of the high fissionability of these systems, it is assumed that the fission cross section is equal to the total reaction cross section for heavy-ion reactions. The data have been compared with the theoretical cross-section calculations of Thomas, assuming (1) a square-well nuclear potential, and (2) a parabolic approximation to the real part of the optical potential. At energies well above the Coulomb barrier, the data are well represented using a square-well potential and ${r}_{0}=1.50$F. Near the barrier, however, the agreement is poor. With the parabolic approximation, the entire excitation function can be generally reproduced except in the case of ${\mathrm{Ne}}^{20}$. For the ${\mathrm{He}}^{4}$ data, these calculations used a well depth ${V}_{0}=\ensuremath{-}67$ MeV, a nuclear radius ${r}_{0}=1.17$F, and a diffuseness parameter $d=0.574$F. These values for heavy ions were ${V}_{0}=\ensuremath{-}70$ MeV, ${r}_{0}=1.23 \mathrm{to} 1.26$F, and $d=0.50 \mathrm{to} 0.44$F, ${r}_{0}$ increasing and $d$ decreasing as a function of increasing heavy-ion mass.

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