By use of the relationship given by Kyoizumi et al, total exposure at 2 km from the
hypocenter of Hiroshima can be obtained as follows. The incidence rate of epilation at 2
km is about 5% as seen in Fig. 3. From the relationship of Kyoizumi et al shown in Fig.
4 this 5% rate corresponds to exposure of 1.44 Gy. The initial radiation exposure is
estimated as 0.04 Gy by assuming the shielding effect is 0.5. Then the exposure from
fallout is estimated as about 1.4 Gy. By use of a similar statistical method the exposed
effects from the radiation of the Hiroshima atomic bomb are obtained as shown in Fig. 5
from the incidence rates of epilation among the LSS Hiroshima group. The doses of
total, initial nuclear radiation and fallout exposure are shown by a bold dashed curve, a
thin dashed curve and a bold solid curve, respectively and the initial nuclear radiation
doses estimated by DS02 are also shown by a thin solid line in Fig. 5. As seen in Fig. 5,
the effects of fallout exposure increase with distance from the hypocenter up to 1 km,
12
but this has large ambiguity because the incidence rates in the region below 1 km were
not employed in the present analysis. Exposure from the initial radiation rapidly
decreased with distance from the hypocenter and at about 1.2 km the fallout effects
cross over that of initial nuclear radiation and beyond this distance the fallout effects
become dominant. The estimated exposure from fallout radiation reaches about 1.5 Gy
at around 1.45 km then decreases slowly. Beyond 4 km the exposure effect of fallout
takes an almost constant value of 0.79 Gy. This result from the incidence rates of
epilation, one of the actual accepted and universally agreed conditions of the bombed
survivors, indicates overwhelming effects of fallout beyond about 1.5 km from the
hypocenter of Hiroshima. For example at 2.25 km and 2.75 km from the hypocenter the
dose estimation of the initial radiation by DS02 are 0.0302 Gy and 0.0053 Gy while the
incidence rates of epilation among the LSS-Hiroshima group at these distances are
3.5 % and 2.1 %. The estimated fallout exposure effects from these incidence rates are
1.34 Gy and 1.16 Gy, about 44 and 219 times the DS02 initial radiation.
The maximum cumulative exposure from fallout of the Hiroshima bomb has been
considered hitherto between 0.006 and 0.02 Gy in the Koi-Takasu region mentioned in
the DS86 report and adopted by the Japanese government as the criteria of atomic bomb
diseases which are shown by cross marks in Fig. 5. These absorbed doses were obtained
from measurement of radiation from fallout matter retained in the soil of these regions
which are located between 2 and 4 km to the west of the hypocenter where light
radioactive fallout rain fell but heavy rain caused by the big whole city fire did not. As
seen in Fig. 5 exposure from fallout estimated from epilation incidence rates in the 2 to
4 km region are 1.4 Gy to 0.85 Gy which are 40 to 230 times the physically obtained
values. This large discrepancy suggests that the physically measured values are only
measurements of a part of fallout and that large effects of internal exposure should be
taken into account which can be deduced only by biological methods. It is noteworthy
that the values obtained here are average exposures in the same distant regions from the
hypocenter irrespective of direction. This result supports the understanding that fallout
particles were distributed in the air very widely under the mushroom cloud.
There are many examinations of incidence of epilation, for example by the Joint
Commission for the Investigation of the Atomic Bomb and Tokyo Imperial University
in 1945 and investigated by a medical doctor O-ho in 1957. These examinations give
results that almost coincide with each other indicating the reliability of all these
investigations. Then from analysis of incidence rates of epilation of these examinations
almost the same results are obtained.
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