You must have heard of an ‘Atom Bomb’. But do you know how it works? An atom bomb is a nuclear weapon, which triggers a huge explosion powerful enough to destroy a city. The reactions in an atom bomb are based on uncontrolled fission chain reaction. When a neutron bombards the nucleus of a heavy element like uranium, it breaks into two large fragments and two or three fresh neutrons are produced. These neutrons further collide with other uranium nuclei causing more fission to take place. In this process, large amounts of energy are released. If the chain reaction continues, a tremendous, devastating explosion takes place. This is what is known as an atomic explosion. When critical mass of uranium-235 or plutonium-239 undergoes fission chain reaction with the help of stray neutrons, a tremendous amount of energy is released. This is how an atom bomb is made. Based on the fission chain reaction, the first atomic bomb was developed during the Second World War by a team of American scientists. J. Robert Oppenheimer was the head of this team. The first atom bomb, made of uranium-235, was tested on July 16, 1945 under his supervision at Alamogordo, New Mexico. Another bomb was dropped on August 6, 1945 on Hiroshima and three days later on August 9, the second bomb based on plutonium was dropped on Nagasaki — both cities in Japan. These were the most tragic events to take place in the history of mankind. Destruction caused by these bombs led to Japan’s surrender, and ended the Second World War. After this incident, Russia, Britain, China and France also tested their atom bombs. The French atomic bomb tested on Mururoa Atoll in the South Pacific is suspected to have caused cancer of the larynx in the people of Polynesia.