Specific Ionization & Linear Energy Transfer

    LET (linear energy transfer) is the amount of energy released by a radioactive particle or wave over the length of its decay track. Specific Ionization is the number of ion pairs produced per unit track length.

    High LET radiation (like alpha & beta particles) ionizes water into H and OH radicals over a very short track. In the example, two events occur in a single cell so as to form a pair of adjacent OH radicals that recombine to form peroxide, H2O2, which can produce oxidative damage in the cell.

    Low LET radiation (like X- or gamma rays) also ionizes water molecules, but over a much longer track. In the example, two events occur in separate cells, such that adjacent radicals are of the opposite type: the H and OH radicals reunite and reform H2O.

All figure & text material © 2007 by Steven M. Carr