Nuclear weapon


August 15, 2022

A nuclear weapon is an unconventional weapon which uses the energy released by the fission of heavy atomic nuclei (uranium, plutonium in the case of A-bombs), or by a combination of this phenomenon with that of the fusion of light nuclei (hydrogen in the case of H-bombs). The energy released by the explosion is expressed by its equivalent in TNT. The nuclear weapon was used operationally only by the United States during the bombings of the Japanese cities of Hiroshima and Nagasaki during the Second World War, resulting in between one hundred thousand and two hundred and twenty thousand deaths. Its destructive effects are mainly due to the blast, as with conventional explosives, but also to burns and fires caused by its high temperature, and to the effect of radiation. Because of these destructive capacities unmatched by those of conventional weapons, nuclear weapons became, from the end of the years following their use against Japan, a weapon of deterrence aimed at discouraging any attack against the vital interests of a nation out of fear for the aggressor to suffer in return massive destruction which would far exceed the expected benefits. Different nuclear deterrence strategies are developed during the Cold War, during which up to 70,000 nuclear warheads will be accumulated by the United States, the Soviet Union, China, the United Kingdom and France, the five states also permanent members of the UN Security Council. Since the end of the Cold War, stockpiles of nuclear weapons have been greatly reduced to about 14,000 nuclear warheads at the end of 2017. In contrast, despite the 1968 Nuclear Non-Proliferation Treaty, India, Pakistan, Israel and North Korea have developed nuclear weapons, bringing the number of states possessing them to nine.

Nuclear weapons and testing

Types of Nuclear Weapons

The two main types of nuclear weapons are nuclear fission bombs or “A-bombs” and nuclear fusion bombs, also called thermonuclear bombs or “H-bombs”. Their power is measured by equivalence with that of the trinitrotoluene (TNT) explosion: two units are used, the kilotonne (kt) equaling 1,000 tons of TNT and the megaton (Mt) equaling 1 million tons of TNT. In these two large families, more specialized weapons have been designed according to sought-after special effects, such as the neutron bomb.

The first bombs

The first nuclear test was carried out on July 16, 1945 by the United States; it is an A-bomb with a yield of 19 kt. The A-bombs used for the bombings of Hiroshima and Nagasaki are of comparable power. A-bombs have a power of less than 500 kt and most of the tests carried out do not exceed a power of 100 kt. The Soviet Union carried out its first nuclear explosion in 1949, the United Kingdom in 1952, France in 1960 and China in 1964. H-bombs are much more powerful. The first test of a thermonuclear bomb was carried out by the United States on November 1, 1952, its power of 10 Mt being more than 500 times greater than that of the A-bombs of Hiroshima and Nagasaki. Codenamed Ivy Mike, this 82-ton machine is purely experimental. In 1954, the United States exploded an H-bomb codenamed Castle Bravo on Bikini Atoll, which released a power of 15 Mt, two and a half times more than expected, designed in the goal of developing a weapon for military use. The most powerful bomb tested by the Americans, it caused the worst radioactive contamination in the history of their nuclear tests. In 1955, the United States began to mass-produce the Mk-21 bomb with a power of 4 Mt, the dimensions of which (3