Littleboy, the first Atom bomb has 9000 lb (pound) in weight and uses Uranium as the fuel. It has an yield of 20 kt of TNT. The bomb was dropped by Capt Paul Tibbets, the US pilot of Enola Gay. Plane has 9 crews & 4 scientists. The bomb was dropped at 0815 am and it exploded after 51 second at 2000 ft above sea level at Hiroshima, Japan. During explosion, light, heat and radiations with shock waves (high pressure waves) were released. Fireball followed the mushroom cloud.

Nuclear explosives are highly destructive - Atomb bomb (Nuclear fission), Hydrogen Bomb (Nuclear fusion by E. Teller) and Neutron Bomb (destructive only to living things).

Nuclear fission by Otto Hann and Strassman in 1939. In nuclear fission, a heavy nucleus is split into two or more lighter nuclei with tremendous release of energy.