IonizationvsEnergy Relation for Fission Fragments

The ionization $\mathrm{vs}$ energy relation has been measured for fission fragments stopped in nitrogen, neon, argon, and argon plus C${\mathrm{O}}_2$ (3%). The fission fragments were obtained from thermal-neutron-induced fission of ${\mathrm{U}}^{235}$. Results of these measurements are consistent with the nuclear recoil effect and show that the ionization produced is not simply proportional to the fragment energy.