X-ray-induced luminescence and optical absorption in DNA films.

For DNA films, X-irradiated at 77 K, a comparative study was performed on (a) light emission (fluorescence and phosphorescence) during irradiation, (b) afterglow and thermoluminescence, (c) optical absorption after irradiation, and (d) free-radical reactions in similar gamma-irradiatied DNA samples. Spectra are reported for the various kinds of light emission and for the optical absorption. From temperature-dependence studies, it was concluded that the light-emission phenomena are unrelated to the reactions of the free radicals as studied by electron paramagnetic resonance. The optical absorption on the other hand, is strongly correlated to the presence of free radicals in the DNA. Some mechanisms possibly involved in the observed luminescence reactions are discussed.