[en] Aberrations largely form from the interaction of pairs of entities (breaks/lesions/DSBs), and hence interaction distance can control aberration formation. This is at present puzzling in that (for low-LET radiations) interaction distances for lesion interaction appear to be of the order of a few to a few tens of nanometers in the initial (linear) part of the dose-response curve and micrometers in the latter (quadratic) part of the dose-response curve. Overall, for ionizing radiations the principal determinant of aberration likelihood is the linear energy transfer (LET) of the radiation. When studying radiations of well-characterized LET, knowledge of morphometry of the irradiated cell leads to a direct estimate of aberrations per particle. For radiation protection considerations, one energy deposition event per nucleus is the ultimate low dose, and such an approach bypasses traditional concepts of absorbed dose and relative biological effectiveness. While there are variations in sensitivity to aberration induction through the cell cycle, as LET per particle increases linearly, aberration frequency increases quadratically