Little Boy:The Gun-Type Bomb

The Gun Method

Little Boy used the gun method of explosion.  Two subcritical masses of plutonium were used (subcritical means not fissionable). The one half was placed at the end of the "barrel". The other half was placed in front of chemical explosives. When the explosives detonated, the one half of the plutonium assembled with the other, creating a supercritical mass (supercritical means fissionable). When one nuecleus smashed into the other, a chain reaction was started. This reaction released immense heat and light, which was the explosion.  This bomb held an explosive yield of about 13,000 tons of TNT. 

Little Boy:The Bomb

Compared to Fat Man, Little Boy looked like something a toddler would play with, but Little Boy didnt play nice with others.  At 8,800 pounds, 10 feet long, and 28 inches in diameter, it packed a bit of a punch.  With an explosive yield of about 13 thousand tons of TNT, Little Boy lived up to expectations, and killed an estimated 140,00 people including after effects of the blast, like radioactive fallout.