Samples of nominally pure single crystal KCI were irradiated by H, H2, He, C and N positive ions in the energy range 0–2 MeV. The growth of F-type centers was recorded as a function of ion fluence. Depth profiles of damage by H and He ions were constructed, and it was found that the damage profile does not follow the stopping power as a function of penetration depth in the target. Determinations of damage track radii, based on the data, were done, and found to be on the order of 10 Å. Comparisons of defect production by H2with H at the same fluences of nuclei and the same energy per mass showed at low energies more defects by H than by H2, the difference attributable to track overlap.