The validity of the track formation model proposed by Fleischer, Price and Walker was tested for a sensitive cellulose nitrate track detector using protons, deuterons and alpha particles. Quantitative data are given on the threshold energies and etchable track lengths of these particles. The same data were also calculated for3H,3He,6He and8He by means of the model of primary radiation damage density presented in the paper. A simple empirical relation was found for the evolution of the etch rate ratio along the particle trajectory.