Binary and Ternary Fission ofU238Induced by Intermediate-EnergyHe3Ions

Cross-section data for 33 nuclides have been obtained radiochemically and used to construct a mass-yield curve for the fission of ${\mathrm{U}}^{238}$ induced by 31-MeV ${\mathrm{He}}^3$ ions. The mass range studied was $24\le A\le 212$ and the yields varied over seven orders of magnitude. The data for ${\mathrm{Na}}^{24}$, ${\mathrm{Mg}}^{28}$, ${\mathrm{Si}}^{31}$, ${\mathrm{S}}^{38}$, ${\mathrm{Ca}}^{47}$, ${\mathrm{Au}}^{199}$, ${\mathrm{Pb}}^{209}$, and ${\mathrm{Pb}}^{212}$ confirm the existence of ternary fission in compound-nuclear processes at intermediate energies, as previously reported from these laboratories. These data also establish the transition region between ternary and highly asymmetric binary processes at $A\sim 45$. Recoil-range data indicate some small but significant differences between ${\mathrm{He}}^3$- and ${\mathrm{He}}^4$-induced ternary fission. On the assumption that there is a peak in the ternary mass-yield curve at $A\sim 24$, the total ternary-fission cross section for 31-MeV ${\mathrm{He}}^3$ ions on ${\mathrm{U}}^{238}$ is ∼3.3×${10}^{-30\mathrm{}}$ ${\mathrm{cm}}^2$, and $\frac{{\sigma }_{\mathrm{ternary}}}{{\sigma }_{\mathrm{binary}}}\sim 4.4\times {10}^{-6\mathrm{}}$.