A study was carried out on 205 4? year old children who had been exposed to the atomic bomb blast during the first half of intra-uterine life. Eleven were exposed within 1200 meters of the bomb hypocenter, and the remaining 194 were beyond this distance.Seven of these 11 children exposed within 1200 meters had microcephaly with mental retardation. This diagnosis was not made on any of the 194 children exposed at greater distances.Correlation between head size and mental development of the child with distance from the hypocenter, symptoms of radiation effect and type of shielding of the mother is discussed.The conclusion drawn from the present study is that central nervous system defects can be produced in the fetus by atomic bomb radiation, provided that exposure occurs within approximately 1200 meters of the hypocenter and that no effective shielding, such as concrete, protects the fetus from direct irradiation.
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