ブラックピーク近傍の炭素イオン線によるイイン固有DNA損傷の研究

用不同位置的低能量He、C、Ar、Fe、Xe离子束照射T1噬菌体，测定了诱导质粒DNA单链和双链断裂(DSB)的作用截面和T1噬菌体的致死效应。我们开发了新的系统，用于在千叶NIRS的中能束课程中照射布拉格峰周围的离子。用金属薄片将6 MeV/n的离子引出到空气中，在离出射窗口不同距离的空气中用电离室测量它们的能量损失，在136 mm处观察到离子的Bragg峰。用CR39固体径迹探测器测定注量。结果如下：(1)干DNA：用He、C、Ar、Fe、Xe离子辐照后，测得单链断裂和双链断裂的诱导截面：从He到Fe，再到Xe，单链断裂和双链断裂的诱导截面逐渐增大。与DSB相比，SSB的截面从Bragg峰下降到磁道末端的速度更快。DSB/SSB比值向轨端逐渐增大，最大值为1.7，说明DSB的诱导作用大于SSB。(2)溶液中的脱氧核糖核酸：用一种新的方法制作含有质粒DNA的10-μm琼脂糖凝胶薄膜，用离子照射溶液中的脱氧核糖核酸，它在水中的范围很短，只有100μm量级。DSB/SSB比值的最大值为2.0。(3)干T_1噬菌体：测定C、Ar、Xe离子辐照后T_1噬菌体灭活截面。截面向离子径迹末端单调减小。Rbe为0.036，最大LET为8783 keV/μm(Xe)。

We determined the action cross-sections for the induction of single- (ssb) and double-strand breaks (dsb) in plasmid DNA and lethal effect in T1 phage after irradiation with low energy He, C,Ar, Fe and Xe ion beams at different positions along with the Bragg curve. We developed the new system for the irradiation of ions around the Bragg peak at the Medium-Energy Beam Course at the NIRS (Chiba). Ions with 6 MeV/n were extracted into air through a thin metal foil, and their energy loss was measured by an ionization chamber in air at different distances form the exit window ; the Bragg peak was observed at 136 mm for Cions. The fluence was determined with the CR39 solid state track detector. Results are as follows : (1) Dry DNA : the cross-sections for ssb and dsb induction were determined after irradiation with He, C,Ar, Fe and Xe ions : those increased from He to Fe and then decreased to Xe. The cross-sections decreased from the Bragg peak to the track end more rapidly for ssb than dsb. The dsb/ssb ratio increased toward the track end and the maximum value was 1.7, demonstrating that dsb was induced more than ssb. (2) DNA in solution : using a new method making a 10-μm thin films of agarose gel containing plasmid DNA, DNA in solution was irradiated with Cions, which have a very short range of the order of 100μm in water. Results were similar to those for dry DNA.The maximum value of the dsb/ssb ratio was 2.0. (3) Dry T1 phage : the cross-sections for T1 phage inactivation were determined after C,Ar and Xe ion irradiation. The cross-sections monotonously decreased toward the ion track end. The RBE decreased with the increase in LET : RBE was 0.036 at the highest LET, 8783keV/μm (Xe).