Present status of radiation interaction with DNA–strand-break cross-section and fragment-size distributions

Abstract

A cross-section formula for single strand brakes via radiation in the DNA molecule is reviewed and discussed, showing that it describes well-existing data for a wide range of linear energy transfer (LET). Recently published DNA fragment-size distributions (FSDs) data, obtained by irradiation of plasmids with electrons and neutrons, are presented. These results are analyzed and interpreted on the basis of a model developed by the Sao Paulo group, in which by introducing a long-range correlation among the jumps in a random walk, a power-law function is obtained for the probability distribution. The power-law exponent is a function of both the correlation potential and the degree of freedom of the system. It is shown that plasmidial DNA behaves as a nonextensive system, with FSDs described by power laws but not by exponential functions (as in extensive statistics). A pronounced crossover for electron-irradiation data and a change from 1 to 3 in the degree of freedom for neutron irradiation at a high dose were observed. A likely interpretation for these two features is presented and discussed. Perspectives for further developments in this area are presented and addressed.