Relative Ionization Yields for Fission Fragments in Various Gases

The ionizations resulting from U²³⁸ fission have been measured in He, Ne, A, Kr, N₂, A+3 percent CO₂, and A+5 percent N₂. Comparison of these values with those obtained for alpha particles in the same chamber fillings permit the calculation of ionization defect differences. It was found that about half of the 7-Mev defect previously ascribed to argon-CO₂ mixtures was due to CO₂. Nitrogen and krypton exhibited relatively large defects. No significant difference was observed between argon and helium. Several possible explanations for this are suggested and discussed.