Nuclear weapon in the context of "Salted bomb"

World War II or the Second World War (1 September 1939 – 2 September 1945) was a global conflict between two coalitions: the Allies and the Axis powers. Nearly all of the world's countries participated, with many nations mobilising all resources in pursuit of total war. Tanks and aircraft played major roles, enabling the strategic bombing of cities and delivery of the first and only nuclear weapons ever used in war. World War II is the deadliest conflict in history, causing the death of 70 to 85 million people, more than half of whom were civilians. Millions died in genocides, including the Holocaust, and by massacres, starvation, and disease. After the Allied victory, Germany, Austria, Japan, and Korea were occupied, and German and Japanese leaders were put on trial for war crimes.

The causes of World War II included unresolved tensions in the aftermath of World War I, the rise of fascism in Europe and militarism in Japan. Key events preceding the war included Japan's invasion of Manchuria in 1931, the Spanish Civil War, the outbreak of the Second Sino-Japanese War in 1937, and Germany's annexations of Austria and the Sudetenland. World War II is generally considered to have begun on 1 September 1939, when Nazi Germany, under Adolf Hitler, invaded Poland, after which the United Kingdom and France declared war on Germany. Poland was divided between Germany and the Soviet Union under the Molotov–Ribbentrop Pact. In 1940, the Soviet Union annexed the Baltic states and parts of Finland and Romania. After the fall of France in June 1940, the war continued mainly between Germany, now assisted by Fascist Italy, and the British Empire, with fighting in the Balkans, Mediterranean, and Middle East, the aerial Battle of Britain and the Blitz, and the naval Battle of the Atlantic. Through campaigns and treaties, Germany gained control of much of continental Europe and formed the Axis alliance with Italy, Japan, and other countries. In June 1941, Germany invaded the Soviet Union, opening the Eastern Front and initially making large territorial gains.

Air warfare was a major component in all theaters of World War II and, together with anti-aircraft warfare, consumed a large fraction of the industrial output of the major powers. Germany and Japan depended on air forces that were closely integrated with land and naval forces; the Axis powers downplayed the advantage of fleets of strategic bombers and were late in appreciating the need to defend against Allied strategic bombing. By contrast, Britain and the United States took an approach that greatly emphasized strategic bombing and (to a lesser degree) tactical control of the battlefield by air as well as adequate air defenses. Both Britain and the U.S. built substantially larger strategic forces of large, long-range bombers. Simultaneously, they built tactical air forces that could win air superiority over the battlefields, thereby giving vital assistance to ground troops. The U.S. Navy and Royal Navy also built a powerful naval-air component based on aircraft carriers, as did the Imperial Japanese Navy; these played the central role in the war at sea.

The neutron is a subatomic particle, symbol n or n
, that has no electric charge, and a mass slightly greater than that of a proton. The neutron was discovered by James Chadwick in 1932, leading to the discovery of nuclear fission in 1938, the first self-sustaining nuclear reactor (Chicago Pile-1, 1942), and the first nuclear weapon (Trinity, 1945).

Neutrons are found, together with a similar number of protons in the nuclei of atoms. Atoms of a chemical element that differ only in neutron number are called isotopes. Free neutrons are produced copiously in nuclear fission and fusion. They are a primary contributor to the nucleosynthesis of chemical elements within stars through fission, fusion, and neutron capture processes. Neutron stars, formed from massive collapsing stars, consist of neutrons at the density of atomic nuclei but a total mass more than the Sun.

An explosive lens—as used, for example, in nuclear weapons—is a highly specialized shaped charge. In general, it is a device composed of several explosive charges. These charges are arranged and formed with the intent to control the shape of the detonation wave passing through them. The explosive lens is conceptually similar to an optical lens, which focuses light waves. The charges that make up the explosive lens are chosen to have different rates of detonation. In order to convert a spherically expanding wavefront into a spherically converging one using only a single boundary between the constituent explosives, the boundary shape must be a paraboloid; similarly, to convert a spherically diverging front into a flat one, the boundary shape must be a hyperboloid, and so on. Several boundaries can be used to reduce aberrations (deviations from intended shape) of the final wavefront.

Nuclear weapons tests are experiments carried out to determine the performance of nuclear weapons and the effects of their explosion. Over 2,000 nuclear weapons tests have been carried out since 1945. Nuclear testing is a sensitive political issue. Governments have often performed tests to signal strength. Because of their destruction and fallout, testing has seen opposition by civilians as well as governments, with international bans having been agreed on. Thousands of tests have been performed, with most in the second half of the 20th century.

The first nuclear device was detonated as a test by the United States at the Trinity site in New Mexico on July 16, 1945, with a yield approximately equivalent to 20 kilotons of TNT. The first thermonuclear weapon technology test of an engineered device, codenamed Ivy Mike, was tested at the Enewetak Atoll in the Marshall Islands on November 1, 1952 (local date), also by the United States. The largest nuclear weapon ever tested was the Tsar Bomba of the Soviet Union at Novaya Zemlya on October 30, 1961, with the largest yield ever seen, an estimated 50–58 megatons.

The nuclear arms race was an arms race competition for supremacy in nuclear warfare between the United States, the Soviet Union, and their respective allies during the Cold War. During this same period, in addition to the American and Soviet nuclear stockpiles, other countries developed nuclear weapons, though no other country engaged in warhead production on nearly the same scale as the two superpowers.

The race began during World War II, dominated by the Western Allies' Manhattan Project and Soviet atomic spies. Following the atomic bombings of Hiroshima and Nagasaki, the Soviet Union accelerated its atomic bomb project, resulting in the RDS-1 test in 1949. Both sides then pursued an all-out effort, realizing deployable thermonuclear weapons by the mid-1950s. The arms race in nuclear testing culminated with the 1961 Tsar Bomba. Atmospheric testing was ended in the 1963 Partial Nuclear Test Ban Treaty. Subsequent work focused on the miniaturization of warheads at LLNL and VNIITF, and the neutron bomb.

Radioactive waste is a type of hazardous waste that contains radioactive material. It is a result of many activities, including nuclear medicine, nuclear research, nuclear power generation, nuclear decommissioning, rare-earth mining, and nuclear weapons reprocessing. The storage and disposal of radioactive waste is regulated by government agencies in order to protect human health and the environment.

Radioactive waste is broadly classified into 3 categories: low-level waste (LLW), such as paper, rags, tools, clothing, which contain small amounts of mostly short-lived radioactivity; intermediate-level waste (ILW), which contains higher amounts of radioactivity and requires some shielding; and high-level waste (HLW), which is highly radioactive and hot due to decay heat, thus requiring cooling and shielding.