Abstract
It is well known that neutron has more damaging effects with high RBE or a weighing factor depending on neutron energy, compared with low-LET ionizing radiations. In the present study, we aimed to evaluate the contribution of indirect action induced by radicals for the purpose of studying mechanisms of fast neutron effects or mechanisms of boron neutron capture therapy (BNCT) using relatively lower energy neutrons. Plasmid pBR322 DNA was irradiated with fast neutrons (1-10MeV) in the "Yayoi" fast neutron source reactor core installed at the University of Tokyo, and thermalized neutrons passing through a phantom made of acrylic resin to simulate human body. The single strand breaks (ssb) and double strand breaks (dsb) of the plasmid were detected by agarose gel electrophoresis. The amount of native DNA with a closed circular form decreased exponentially with the absorbed dose of fast neutron. The decrease was inhibited by DMSO in a concentration dependent manner. Contributions of the indirect action to strand breaks by fast neutrons and thermalized neutrons were calculated as 50 to 65 %, which was slightly lower than the value for X-rays. In the case of thermalized neutrons, ssbs and dsbs were increased by the addition of boric acid. Moreover, the increase of the concentration of 10B was found to increase the ratio of dsb/ssb.
