A nuclear weapon is an explosive device that derives its strength from nuclear reactions involving fission and fusion. These reactions release a large amount of energy from relatively small amounts of matter. Nuclear weapons are considered weapons of mass destruction, and their use has been a topic of discussion since their debut in 1945. There are two basic types of nuclear weapons (Wikipedia 2013). The first type derives most of its energy from nuclear fission reactions alone. Weapons whose explosive production is achieved only by fission reactions are commonly called atomic bombs or atom bombs (abbreviated as atomic bombs). The first atomic bomb was used by the United States during the Cold War and was called “Little Boy” (Wikipedia 2014). Figure 1.1 shows the structure of a pistol-type fission weapon similar to the "little boy" bomb. The second type uses fission reactions to initiate nuclear fusion reactions which in turn produce a large amount of the total energy produced. Such fusion weapons are known as thermonuclear weapons or hydrogen bombs (abbreviated as H-bombs). Figure 1.2 shows the structure of such a weapon. There are other types of nuclear weapons such as a boosted fission weapon and a neutron bomb. Most variations in nuclear weapon design are intended to achieve different outcomes for different situations and to manipulate design elements to minimize the size of the weapon (Wikipedia 2013). Nuclear weapons were used twice during the war, both times by the United States, near the end of World War II, bombing Hiroshima and Nagasaki. Since then, they have been detonated for testing and demonstration purposes more than 2000 times. Countries that have recognized the possession of… half paper… heirs to nuclear arsenals (Deen 2013). Yet nuclear weapons are not the currency of international status and power they once were (Street 2013). what might be called the persistence of deterrent thinking. This will effectively require redrawing our mental maps of how to best defend ourselves against 21st century threats.” Kile says. However, he pointed out that this may actually be the greatest challenge in the transition to a world free of nuclear weapons (Deen 2013). “The best way to eliminate the nuclear threat everywhere is to eliminate nuclear weapons everywhere,” says General Ban Ki-moon. , who is counted among the strongest opponents of nuclear weapons (Deen 2013). Indeed, the road to a world free of nuclear weapons appears to be a long way off.