On this date, the U.S. dropped a 9,000 lb bomb, "Little Boy" on Hiroshima, Japan. Effects: 66 thousand people died instantly. Everything within 1/2 miles in diameter was vaporized. There was total destruction for 1 mile in diameter and serious fires for 3 mi. Nagasaki: 3 days later, the U.S. dropped "Fat Man" on Nagasaki. That bomb weighed 10,000 lbs. Effects: In 1 second, the population went from 422,000 to 383,000. Long term: radioactive rain. scientists learned to harness nuclear energy.