| Co-Investigator(Kenkyū-buntansha) |
MATSUBARA Sho Yokohama City Univ. Faculty of Med., Prof., 医学部, 教授 (40014120)
SAWADA Shozo Hiroshima Univ. Inst. Nuclear Med., Prof., 原爆放射能医学研究所, 教授 (60034625)
SUZUKI Fumio Kanazawa Univ. Faculty of Pharmacy, Ass. Prof., 薬学部, 助教授 (10019672)
KOBAYASHI Katsumi Inst. for High Energy Physics Photon Factory, Ass. Prof., 放射光実験施設, 助教授 (20114077)
HIEDA Kotaro Rikkyo Univ. Faculty of Sci., Prof., 理学部, 教授 (20062656)
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| Research Abstract |
The present research has been carried out to explore the primary process of radiation action on living material by the use of currently developing radiation sources for energy regulated low-energy X-rays and neutrons. Dissociation of DNA, when it was dry, could be explained by the specific energy absorption of constituent atoms, but was due to the ionization by secondary electrons for the wet DNA.This has been confirmed in the experiments on the mutation induction by ultrasoft X-rays in yeast cells and chromosome aberration formation in cultured mouse cells, where biological effects could not be explained by a simple photoabsorption of phosphorus atoms in DNA.Moreover, the effectiveness of low-energy, but not high-energy, photons increased with the increase in the concentration of macromolecules, indicating a significant contribution of Auger elecrtons. The lymphocyte chromosome aberrations were proved to be enhanced by resonance absorption of X-ray energy by iodine atoms in X-ray contrast medium, suggesting the possible use of photoreactivation therapy for cancer treatment. Neutrons with energy around 1 MeV were highly effective in the induction of mutation, cell killing and morphological transformation. Surprisingly, low-eneregy neutrons obtained be neutron filters were found to have similar biological effectiveness. This finding may pose a re-evalution of radiation weighting factor for low-energy neutrons. Indeed, somatic mutation frequencies in Atomic-bomb survivo13EA\rs were found to be higher in Hiroshima than in Nagasaki, suggesting that the contribution of neutrons could not be ignored in Hiroshima.
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