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Frequently Asked Questions

How many atomic-bomb survivors are included in the group being studied by RERF and how were they chosen for this study?
To establish a population framework in which to conduct long-term follow-up of mortality and cancer incidence, about 94,000 people were selected from 280,000 A-bomb survivors who were resident in Hiroshima or Nagasaki at the time of the October 1950 Japanese national census. Of these, about 54,000 were exposed to significant radiation doses (Question 11) within about 2,500 meters from the hypocenters. Another 40,000 members of the study population were exposed beyond 2,500 meters and received very low doses.

In the 1950 Japanese national census, approximately 280,000 people indicated that they had been exposed to the atomic bombs. RERF’s study population probably includes about 50% of those proximally exposed (within about 2,500 meters of the hypocenters) and 25% of those distally exposed (greater than 2,500 meters from the hypocenters). These percentages are not precise because the census did not record the location of exposure in reference to the hypocenters.

An additional 27,000 who were not in Hiroshima or Nagasaki at the time of the bombs, but whose family registries were in Hiroshima or Nagasaki and who lived in either city at the time of the 1950 census also were included as an unexposed comparison group. These groups constitute the 120,000-member Life Span Study (LSS) cohort.

In addition to studying the LSS cohort, RERF scientists are involved in studies of several other populations: the Adult Health Study (AHS), in utero-exposed, and F1 cohorts. The AHS population comprises 23,000 members of the LSS, who, since 1958, have been asked to participate in biennial medical examinations carried out at RERF. The in utero-exposed cohort is a group of about 3,600 people who were exposed to the bomb while in the womb. The F1 population consists of about 77,000 people born in Hiroshima or Nagasaki between 1 May 1946 and the end of 1984 to parents with and without exposure to the bombs.