Auger effects on bromo-deoxyuridine-monophosphate irradiated with monochromatic X-rays around bromine K-absorption edge.

In order to study the enhanced effect by Auger cascade, samples of bromo-deoxyuridine-monophosphate (Br-dUMP) in aqueous solutions were irradiated with monochromatic X-rays at 13.49 keV and 13.43 keV, just above and below the K-absorption edge of bromine, using synchrotron radiation as a source. Radiolytic products such as deoxyuridine-monophosphate (dUMP), uracil and bromo-uracil (Br-uracil) were isolated using high performance liquid chromatography. Their amounts were quantitatively analysed as a function of the absorbed dose in the solutions containing Br-dUMP for the energy of the X-rays. G values for these products were calculated on the basis of the absorbed energy. As the results, the ratios of G values of radiolytic products from Br-dUMP between X-rays of 13.49 keV and 13.43 keV were 2.2 for dUMP, 1.02 for Br-uracil and 1.23 for uracil, suggesting clearly the energy dependent enhancement. On the other hand, little significant difference between X-rays of 13.49 keV and 13.43 keV was observed for the G values of uracil released from dUMP irradiated in aqueous solutions. It seemed to confirm that the Auger electrons from K-shell of bromine atoms might play the main role for energy-dependent enhancement at induction of these radiolytic products.