Denise Kiernan, author of “The Girls of Atomic City,” interviews Ruth Heddleston, Peggy Stuart, and Hazel Franklin, three of the “Calutron Girls” who operated the machines that produced uranium for the first atomic bomb. The three were teenagers when the U.S. entered World War II and were among scores of women hired to monitor calutrons at the Y-12 plant. They carefully monitored gauges on the electromagnetic separators to ensure the machines remained within the range needed to separate uranium 235 from uranium 238. The rare isotope was used in Little Boy, the bomb dropped on Hiroshima, Japan. The women shared memories with Kiernan for an audience at the American Museum of Science and Energy in Oak Ridge, Tenn., on Sept. 23, 2015.