About 4.7 square miles.
The first atomic bomb, dropped on Hiroshima in 1945, leveled an area of about 4.7 square miles.
The yield of the Trinity Atomic Bomb Test was approximately 20 kilotons of TNT. It was the first detonation of a nuclear weapon and took place on July 16, 1945, in New Mexico, USA.
Edward H. Wright was the first African American appointed to the US Atomic Energy Commission. He was appointed by President Dwight D. Eisenhower in 1955.
J. Robert Oppenheimer was the first American physicist in charge of the development of the first atomic bomb during the Manhattan Project in World War II.
The first atomic clock was a cesium atomic clock. It was developed in 1955 by Harold Lyons at the National Physical Laboratory in the United Kingdom.