AP Photo

In 1945, a profoundly sad experiment in public health began when U.S. forces dropped a 13-kiloton nuclear fission bomb on Hiroshima, Japan. Three years later, President Harry Truman ordered the National Academy of Sciences to study the long-term health effects of radiation on roughly 100,000 survivors. (A hundred thousand more perished in the blast and its immediate aftermath.) As the most rigorous research of its kind (no longitudinal study of the Chernobyl disaster's survivors was ever done), the Life Span Study of the Hiroshima...