Spallation-Fission Competition in Heaviest Elements: Triton Production

Abstract

Stacked foils of ${\mathrm{Au}}^{197}$, ${\mathrm{Th}}^{232}$, and ${\mathrm{U}}^{238}$ were bombarded, in a series of experiments, with 48-Mev helium ions, 24-Mev deuterons, and 32-Mev protons. Tritium from each foil was collected and then measured by a gas-counting technique. The qualitative results indicate that high-energy tritons are emitted in relatively large abundance from all targets and with each of the bombarding particles. Cross sections for triton production from fissionable ${\mathrm{U}}^{238}$ and ${\mathrm{Th}}^{232}$ and from nonfissionable ${\mathrm{Au}}^{197}$ are comparable. The integrated ($\alpha , t$) cross sections thus determined for ${\mathrm{U}}^{238}$ and ${\mathrm{Th}}^{232}$ are nearly the same as the integrated cross sections for the "($\alpha , p2n$)" reactions as determined by measuring the yield of the product heavy isotopes in radiochemical experiments. All of the facts are consistent with a picture of emission of high-energy tritons (whether due to a stripping, pickup, or other mechanism) in which fissionable intermediate nuclei are formed mainly at levels of excitation below their fission thresholds.