DNA Strand Breaks Induced by Fast and Thermal Neutrons from YAYOI Research Reactor in the Presence and Absence of Boric Acid.It is well known that neutrons have more damaging effects, with high relative biological effectiveness or a radiation weighting factor depending on neutron energy, compared to low-LET ionizing radiations.  Plasmid pBR322 DNA with a supercoiled structure was irradiated with fast neutrons (1-10 MeV) in the reactor core of the YAYOI research reactor at the University of Tokyo, and with thermalized neutrons passing through a phantom made of acrylic resin to simulate a human body.  The contributions of the indirect effect to DNA strand breaks by fast neutrons and thermalized neutrons were calculated to be 50-65% which, while lower than the value for X rays, still accounts for the majority of the DNA strand breaks.  In the case of thermalized neutrons, SSB and DSB yields were increased by the addition of boric acid. 
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