Abstract
Many studies of Monte Carlo track simulation have suggested that the susceptibility of DNA damage to repair strongly depends on the track structure of the radiation. These studies have predicted an increase of the yield of DSB with increasing level of LET. DSB is thought to be produced mainly by the interaction of particle track with DNA (direct effect). We have measured the yield of DSB induced in pUC18 plasmid as a model DNA. In order to focus on the effect of direct energy deposition from radiation track, we prepared hydrated DNA (35 water molecules per nucleotide). In this condition DNA structure is the B-form which is the same conformation with cellular DNA. There is very little balk water in the sample. Thus OH radicals, if produced, hardly diffuse in the sample. TIARA in JAEA-Takasaki and HIMAC in NIRS are used as He, C and Ne ion beam sources. The track structures are different among the ions if they have the same LET values. Hence we have investigated the yield of DSB by systematically changing LET of identical ion. The obtained results show that 1) there is a minimum around 20 keV/µm for He ion irradiation, and the DSB yield increases precipitously toward 120 keV/µm, and then decreases again above the LET value, 2) similarly the yield of DSB increases with increasing level of LET of C ion in 80-500 keV/µm though the trend is not noticeable rather than He ion irradiation, 3) the DSB yield does not significantly depend on LET 300-900 keV/µm for Ne ion irradiation. These results suggest that the DSB yield increases with increasing level of LET, though the trend of increase strongly depends on ion species.
