life: Radioactive cloud from nuclear test, Bikini Atoll, July 1946. See more photos on LIFE.com here. (Fritz Goro—Time &amp; Life Pictures/Getty Images)

life: Radioactive cloud from nuclear test, Bikini Atoll, July 1946. See more photos on LIFE.com here. (Fritz Goro—Time & Life Pictures/Getty Images)

life: Radioactive cloud from nuclear test, Bikini Atoll, July 1946. See more photos