Mass-Spectrometric Measurements ofH3,He3, andHe4Produced in Thermal-Neutron Ternary Fission ofU235: Evidence for Short-RangeHe4

The mass-spectrometric technique has been used to obtain relative and absolute yields for ${}_{}{}^3{}_{}{}^{}\mathrm{H}$, ${}_{}{}^3{}_{}{}^{}\mathrm{He}$, and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ and energy distributions for ${}_{}{}^3{}_{}{}^{}\mathrm{H}$ and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ emitted in ternary fission of ${}_{}{}^{236}{}_{}{}^{}\mathrm{U}_{}^{*}{}_{}{}^{}$. Evidence has been obtained for a short-range (<7.7-MeV) component of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$. The ${}_{}{}^3{}_{}{}^{}\mathrm{He}$/${}_{}{}^4{}_{}{}^{}\mathrm{He}$ ratio is lower by 2 to 4 orders of magnitude than the values previously found in studies of other fissile nuclides. ${}_{}{}^3{}_{}{}^{}\mathrm{H}$/${}_{}{}^4{}_{}{}^{}\mathrm{He}$ is lower by about a factor of 2 than values obtained for ${}_{}{}^{236}{}_{}{}^{}\mathrm{U}_{}^{*}{}_{}{}^{}$ using other experimental techniques. Energy distributions obtained for long-range ${}_{}{}^3{}_{}{}^{}\mathrm{H}$ and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ particles are in agreement with results from other experiments.