From several years after the atomic bombings to the present day

Early radiation effects, such as acute radiation syndrome, result from doses high enough to kill cells and thus cause direct tissue damage (1 Gy or greater). In contrast, late effects, such as cancer (and possibly other diseases), reflect DNA mutations induced in living cells by radiation exposure. While the exact mechanisms by which such mutations lead to cancer are not clear, it is believed that the process requires a series of mutations, accumulated over periods of years. Mutations can occur either spontaneously or as a result of exposure to any of a wide range of environmental mutagens, including radiation. Since many years must pass before a given cell and its progeny acquire sufficient mutations to result in clinical disease, excess cancers attributable to radiation do not become evident until years after exposure (or somewhat fewer years in the case of leukemia). Excess cancer risks in RERF data correspond broadly with the age-time patterns predicted by such hypothetical considerations.

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