In the production of biological radiation effects a temporal sequence of different physical, physico-chemical and biological actions can be distinguished. At each step radiation action can be produced from single particle tracks with intratrack interaction leading to linear increase with absorbed dose of the mean number of actions. If, however, inter-track interaction takes place, a quadratic dependence of the mean number of actions on absorbed dose has to be expected. It is shown here that no inter-track interactions can be observed in experiments with mammalian cells during the production of reparable and irreparable primary DNA lesions. Such interaction may take place during repair, misrepair and lesion fixation.