[en] The interaction of fast neutrons in tissue results in the production of recoil ions that deposit energy along densely ionizing charged particle tracks. Although a great deal of information exists regarding ionization by the recoiling of protons and by nuclear reaction induced alpha particles, little is known about the detailed ionization cross sections for the heavier recoil ions (such as carbon, oxygen, and nitrogen) that also may be produced by interactions of neutrons in tissue. Measurements were conducted for oxygen ion energies from 1.3 to 3.3 MeV. The cross sections for emission of low-energy electrons increase as the ion charge state increases. The interaction strength is proportional to its net charge. For high-energy ejected electrons similar cross sections are expected for all charge states. However, a clear decrease was shown in the cross sections for electrons ejected with energies higher than about 500 eV by the higher-charged ions compared to electrons of similar energy that are ejected by lower-charged ions. For intermediate- to low-energy ion collisions it may be speculated that the emission cross sections should depend more on the kinetic parameters of the collision and the total number of electrons involved than on the detailed atomic or molecular structure of the colliding partners. Because outer-shell ionization involves numerous potential curve crossings, rearrangement on a statistical basis would be expected with individual states losing their identity relative to the observed electron spectra. If this concept has any validity, similar electron spectra and yields would be expected to be produced by collision systems of similar relative velocities and total electron number