Dose Estimation of Human Fetus Exposed in Utero to Radiations from Atomic Bombs in Hiroshima and Nagasaki

Abstract

The absorbed dose in the head of human fetus exposed in utero to gamma-rays and neutrons from the 1945 atomic bombs in Hiroshima and Nagasaki has been estimated as a function of distance from the hypocenter. The ratios of the absorbed dose in the fetal head to the inair tissue absorbed dose was determined using a depth-dose curve and a dose build-up factor experimentally determined with simulated radiation sources of the atomic bombs. The ratio was corrected for the angular distribution of the atomic bomb radiations. The results showed that the ratios varied depending on a distance from the hypocenter, a posture of mother and her stage of pregnancy at the time of exposure, and ranged from the minimum value of 0.56 to the maximum value of 0.70 for initial gamma-rays; 0.072 to 0.16 for recoil protons ; 0.075 to 0.11 for gamma-rays from ¹H (n, γ) ²D reaction ; 0.0030 to 0.0082 for protons from ¹⁴N (n, p) ¹⁴C reaction. The absorbed dose in the fetal head at the end of first month of gestation and at 1, 000m from the Hiroshima hypocenter was 194 rads for initial gamma-rays; 22.2 rads for recoil protons ; 15.8 rads for gamma-rays from the ¹H (n, γ) ²D reaction, and 1.22 rads for proton from the ¹⁴N (n, p) ¹⁴C reaction.