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Frequently Asked Questions

How many cancers in atomic-bomb survivors are attributable to radiation?
Table 1 summarizes the number of cancers (from 1950 to 2000 for leukemia deaths and from 1958 to 1998 for solid cancer occurrence) in the Life Span Study (LSS) A-bomb survivors in relation to radiation dose. The proportion of cancer deaths attributable to radiation exposure is considerably higher in those exposed closer to the hypocenters (as is the case with acute deaths from injuries and burns) (see also tables in "Solid cancer risks" and "Leukemia risks" in "Radiation Health Effects"). Overall, nearly half of leukemia deaths and about 10% of solid cancers are attributable to radiation exposure. If one assumes that LSS survivors represent about half of all survivors in the two cities, the total number of cancers attributable to radiation exposure through 2000 may be about 1,900 cases.
Table 1. Excess numbers of leukemia deaths and solid cancer occurrences in relation to dose

* Weighted bone marrow dose (10 × neutron dose plus gamma-ray dose) for leukemia and weighted colon dose for solid cancers. For indication of the corresponding distance, please see Table 2.
** These include not-in-city (NIC) group, which is not included in the leukemia data.
  Table 2 presents the rough idea regarding the distance from the hypocenters and radiation dose.
Table 2. Mean weighted colon dose of LSS subjects and the corresponding distance from the hypocenter. (Since shielding conditions differ among the survivors, this radiation dose-distance relation does not apply to everyone.)
Weighted colon dose Approximate distance from hypocenters
Hiroshima Nagasaki
0.005 Gy
2,500 m
2,700 m
0.05 Gy
1,900 m
2,050 m
0.1 Gy
1,700 m
1,850 m
0.5 Gy
1,250 m
1,450 m
1 Gy
1,100 m
1,250 m