Figure 2.

Schematic showing a typical track produced by the ubiquitous low-energy electron track-ends produced in a cell by ionizing radiation (dark circle = ionization event; light circle = excitation event). Individual DNA lesions are produced either by direct interaction with DNA or indirectly as a result of reactive radicals (most notably hydroxyl radicals) produced in the surrounding water (diffusion distance ∼6 nm). Clustered DNA damage, comprising combinations of two or more strand breaks and/or base damage, produced within one to two helical turns.