A nuclear bomb is an explosive weapon that uses nuclear reactions, through either nuclear fission or fusion. These weapons can release huge quantities of energy, causing widespread destruction and death from a small amount of matter.
Nuclear weapons were first developed and used during World War II. J. Robert Oppenheimer led a scientific team that developed the first nuclear weapons. These weapons are extremely destructive and one bomb has the ability to kill millions of people and destroy entire cities.
The weapons work by releasing the energy that is stored in the nuclei of atoms; vast amounts of energy can be released from a relatively small amount of matter. There are two types of nuclear weapons: fission and thermonuclear. Fission bombs release energy using fission reactions where heavy nuclei are split into lighter nuclei, releasing energy. Thermonuclear bombs (also known as hydrogen bombs or H-Bombs) use both fission and fusion reactions. Fission reactions are used to trigger the fusion reactions. A fusion reaction is where two light nuclei are combined together to form a heavier nucleus. Most modern thermonuclear weapons use a reaction between two isotopes of hydrogen: deuterium and tritium. Most modern-day weapons are thermonuclear as they are more efficient.
So far, two nuclear weapons have been used during wartime, both by the United States. Towards the end of World War II, two bombs were dropped in the Japanese cities of Hiroshima and Nagasaki. These bombings resulted in the deaths of 120,000 people, mostly civilians. The bomb dropped on Hiroshima had the explosive impact of 15,000 tons of TNT which resulted in 70% of the buildings being destroyed in the city. Ninety percent of people within 500 meters of the blast died from severe burns or high doses of radiation within three weeks. Those who survived the attack had a higher chance of cancer than those who were not in the cities. The use of these bombs brought about the end of World War II, but their use is still widely debated.
Counties who hold nuclear weapons mainly have them as a deterrent. Just having nuclear weapons and the threat of using them was thought to be enough to stop a country from attacking. There are currently nine countries thought to have nuclear weapons, with Russia and the USA having the majority of weapons. Many countries and international organizations, such as the United Nations, are calling for the number of nuclear weapons to be reduced, or even for complete international disarmament.