The contribution of boron to radiobiological effects of thermal neutrons in rice

Abstract

Seeds of rice ( Oryza sativa L.) which had been previously soaked in aqueous solution of boric acid at different concentrations (0 to 4000 ppm) were exposed to thermal neutrons in a swimming pool type reactor. Chemical analysis was made for boron, nitrogen and hydrogen in each organ of seeds to estimate the distribution of thermal neutron capture dose by the elements in boron-enriched and unenriched control seeds. It was found from the results that the captured radiation dose absorbed in embryo was more than twice as much as those in other organs or overall seeds both in boron-enriched seeds and control ones. This suggests that when seeds are irradiated, the RBE values of thermal neutrons which have been calculated hitherto in a number of plant species should be corrected to a lower value. The degree of M 1 damage per unit of thermal neutron fluence was increased by boron-enrichment, but the RBE for boron enriched seeds was estimated to be lower than that for control seeds, even if that was calculated from the absorbed dose in embryo, suggesting that incorporated boron atoms were not distributed uniformly inside the cells. Effects of alpha-particles emitted from the 10B( n, α) 7Li capture reaction during thermal neutron irradiation on damage in M 1 plants and chlorophyll mutation in M 2 plants were also discussed.