(In August 1945, the United States dropped atomic bombs in Japanese cities in Hiroshima and Nagasaki, Japan.
BBC climate and science journalist Esme Stallard explains why the radiation from the explosion has been undetectable for 80 years.
World War II in Europe ended in May 1945, but allies including Britain, the United States and the Soviet Union were fighting against Japan in East Asia.
About 71,000 soldiers from Britain and the Commonwealth died in the war against Japan, including more than 12,000 prisoners of war died in Japanese captivity.
The Allies told Japan to surrender in July 1945, but the deadline was over.
The United States dropped its first atomic bomb on Hiroshima on August 6, 1945, and the second three days later was in Nagasaki. About 214,000 people were killed in the explosion and Japan surrendered.
