A laser-plasma source emitting photons with energies in the water window spectral range has been used to reveal the radiation chemical yields of single-strand breaks in plasmid DNA as a function of ·OH radical scavenger concentration. Direct and indirect effects were investigated separately using DNA samples with various levels of hydration. We experimentally determined the value of the efficiency factor for strand cleavage in DNA caused by the reaction with ·OH radicals at 0.11, which was previously found in the theoretical studies. Additionally, the radiation chemical yield of ·OH radicals specific to the water window radiation emission of the source was determined by comparison with the gamma radiation-induced strand break yields. The ·OH radical yield determined using the plasmid DNA samples as a model was similar to the yield found using sensitive fluorescent dosimeters in previous experiments.

Institute of Optoelectronics Military University of Technology Kaliskiego 2 Str 00 908 Warsaw Poland

Institute of Physics of the Czech Academy of Sciences Na Slovance 1999 2 182 00 Prague 8 Czech Republic

Nuclear Physics Institute of the Czech Academy of Sciences Řež 130 250 68 Řež Czech Republic

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