Radiation Effects for Entrants after the Bombing

Radiation Effects for Entrants after the Bombing

The incidence rates of acute radiation disease were examined by G. O-ho (ibid) among
the people who entered from the day after the bomb exploded to after 34 days in the
region within 1km from the hypocenter of Hiroshima. From analysis of the incident
rates exposure effects for entrant people are estimated. For the entrant on the day of the
explosion (6 August) the accumulated exposed effective dose for onset of acute
radiation disease is equivalent to external acute exposure to gamma rays of 1.05􀂜0.53
Gy. The accumulated exposed effective dose exponentially decreases to almost half for
those who entered the central region 9 to 10 days after the day of the bombing.
Accumulated exposure dose received from external radiation induced by neutrons can
be calculated for staying at the hypocenter, and at 0.5 km and 1 km from the hypocenter.
Even at the hypocenter the accumulated exposed dose from external radiation is 0.8 Gy,
those at 0.5 km is 0.09 Gy and 0.0017 Gy at 1 km. The large discrepancies between
exposure effects estimated from acute radiation disease among the entrants after
bombing and measured external accumulated dose suggest that effects of residual
radiation from chronic internal exposure due to inhalation of radioactive matter were
very large compared to those of external exposure.
As is shown by analysis of the incident rate of the acute radiation diseases,
however, for the survivors bombed in the region beyond 1.5 km the effects of internal
exposure of radioactive fallout are more severe than the effects of external exposure by
the initial radiation. Therefore application of DS86 or DS02 for the estimation of
exposure of distant survivors and the entrant survivors is a complete mistake.