Relative Ionization Yields for Fission Fragments in Various Gases

The ionizations resulting from ${\mathrm{U}}^{238}$ fission have been measured in He, Ne, A, Kr, ${\mathrm{N}}_2$, A+3 percent C${\mathrm{O}}_2$, and A+5 percent ${\mathrm{N}}_2$. 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-C${\mathrm{O}}_2$ mixtures was due to C${\mathrm{O}}_2$. 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.