ENERGY DEPOSITION EVENTS PRODUCED BY FISSION NEUTRONS IN AQUEOUS-SOLUTIONS OF PLASMID DNA

Using an agarose gel electrophoresis assay, single-strand breaks (ssb) induced by fission neutrons and Co-60 gamma-rays in aerobic aqueous s olutions of pBR322 plasmid DNA were studied. The energy-deposition eve nts of the two radiations were characterized using a Rossi-type propor tional counter to measure lineal-energy spectra. For neutrons, the dos e-weighted lineal-energy mean, (y) over bar(D), is 63 keV mu m(-1)-abo ut 30 times that for gamma-rays. With increasing (y) over bar(D), hydr oxyl radicals produced within spurs or tracks are less likely to survi ve due to recombination effects, resulting in decreased ssb yields. In TE buffer solution, the ssb yield induced by gamma-rays is 3 . 2 +/- 0 . 66 times that induced by neutrons at the same dose. Since the dire ct radiation effect is small under these conditions, we can estimate t hat the previously unknown G for hydroxyl radical production by fissio n neutrons is 0 . 088 mu mol J(-1). For glycerol concentrations that g ive the solution a hydroxyl radical scavenging capacity similar to tha t of cellular environments, the ssb yield induced by gamma-rays is abo ut 2 . 0 +/- 0 . 24 times that induced by neutrons. Analysis shows tha t this trend with added scavenger is caused primarily by hydroxyl radi cal yields.