Energy Deposition Events Produced by Fission Neutrons in Aqueous Solutions of Plasmid DNA

Abstract

Using an agarose gel electrophoresis assay, single-strand breaks (ssb) induced by fission neutrons and ⁶⁰Co γ-rays in aerobic aqueous solutions of pBR322 plasmid DNA were studied. The energy-deposition events of the two radiations were characterized using a Rossi-type proportional counter to measure lineal-energy spectra. For neutrons, the dose-weighted lineal-energy mean, y_D, is 63 keV µm⁻¹–about 30 times that for γ-rays. With increasing y_D, hydroxyl radicals produced within spurs or tracks are less likely to survive due to recombination effects, resulting in decreased ssb yields. In TE buffer solution, the ssb yield induced by γ-rays is 3·2 ± 0·66 times that induced by neutrons at the same dose. Since the direct radiation effect is small under these conditions, we can estimate that the previously unknown G for hydroxyl radical production by fission neutrons is 0·088 µmol J⁻¹. For glycerol concentrations that give the solution a hydroxyl radical scavenging capacity similar to that of cellular environments, the ssb yield induced by γ-rays is about 2·0 ± 0·24 times that induced by neutrons. Analysis shows that this trend with added scavenger is caused primarily by hydroxyl radical yields.