Nuclear weapon in the context of "Russia and nuclear weapons"

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.

This article shows various estimates of the nuclear weapon stockpiles of various countries at various points in time. This article also shows the number of nuclear weapons tests conducted by each country at various points in time.

A strategic bomber is a medium-to-long-range bomber aircraft designed to drop large amounts of air-to-ground weaponry onto a distant target for the purposes of debilitating the enemy's capacity to wage war. Unlike tactical bombers, penetrators, fighter-bombers, and attack aircraft, which are used in air interdiction operations to attack enemy combatants and military equipment, strategic bombers are designed to fly into enemy territory to destroy strategic targets (e.g., infrastructure, logistics, military installations, factories, etc.). In addition to strategic bombing, strategic bombers can be used for tactical missions. There are currently only three countries that operate strategic heavy bombers: the United States, Russia and China.

The modern strategic bomber role appeared after strategic bombing was widely employed, and atomic bombs were first used during World War II. Nuclear strike missions (i.e., delivering nuclear-armed missiles or bombs) can potentially be carried out by most modern fighter-bombers and strike fighters, even at intercontinental range, with the use of aerial refueling, so any nation possessing this combination of equipment and techniques theoretically has such capability. Primary delivery aircraft for a modern strategic bombing mission need not always necessarily be a heavy bomber type, and any modern aircraft capable of nuclear strikes at long range is equally able to carry out tactical missions with conventional weapons. An example is France's Mirage IV, a small strategic bomber replaced in service by the ASMP-equipped Mirage 2000N fighter-bomber and Rafale multirole fighter.

A thermonuclear weapon, fusion weapon or hydrogen bomb (H-bomb) is a second-generation nuclear weapon, utilizing nuclear fusion. The most destructive weapons ever created, their yields typically exceed first-generation nuclear weapons by twenty times, with far lower mass and volume requirements. Characteristics of fusion reactions can make possible the use of non-fissile depleted uranium as the weapon's main fuel, thus allowing more efficient use of scarce fissile material. Its multi-stage design is distinct from the usage of fusion in simpler boosted fission weapons. The first full-scale thermonuclear test (Ivy Mike) was carried out by the United States in 1952, and the concept has since been employed by at least the five NPT-recognized nuclear-weapon states: the United States, Russia, the United Kingdom, China, and France.

The design of all thermonuclear weapons is believed to be the Teller–Ulam configuration. This relies on radiation implosion, in which X-rays from detonation of the primary stage, a fission bomb, are channelled to compress a separate fusion secondary stage containing thermonuclear fuel, primarily lithium-6 deuteride. During detonation, neutrons convert lithium-6 to helium-4 plus tritium. The heavy isotopes of hydrogen, deuterium and tritium, then undergo a reaction that releases energy and neutrons. For this reason, thermonuclear weapons are often colloquially called hydrogen bombs or H-bombs.

The explosive yield of a nuclear weapon is the amount of energy released such as blast, thermal, and nuclear radiation, when that particular nuclear weapon is detonated. It is usually expressed as a TNT equivalent, the standardized equivalent mass of trinitrotoluene (TNT) which would produce the same energy discharge if detonated, either in kilotonnes (symbol kt, thousands of tonnes of TNT), in megatonnes (Mt, millions of tonnes of TNT). It is also sometimes expressed in terajoules (TJ); an explosive yield of one terajoule is equal to 0.239 kilotonnes of TNT. Because the accuracy of any measurement of the energy released by TNT has always been problematic, the conventional definition is that one kilotonne of TNT is held simply to be equivalent to 10 calories.

The yield-to-weight ratio is the amount of weapon yield compared to the mass of the weapon. The practical maximum yield-to-weight ratio for fusion weapons (thermonuclear weapons) has been estimated to six megatonnes of TNT per tonne of bomb mass (25 TJ/kg). Yields of 5.2 megatonnes/tonne and higher have been reported for large weapons constructed for single-warhead use in the early 1960s. Since then, the smaller warheads needed to achieve the increased net damage efficiency (bomb damage/bomb mass) of multiple warhead systems have resulted in increases in the yield/mass ratio for single modern warheads.

The Tsar Bomba (code name: Ivan or Vanya, internal designation "AN602") was the most powerful nuclear weapon or weapon of any kind ever constructed and tested. A project of the Soviet Union, it was a thermonuclear aerial bomb, tested on 30 October 1961 at the Novaya Zemlya site in the country's far north. The bomb yielded 50 megatons of TNT.

The Soviet physicist Andrei Sakharov oversaw the project at Arzamas-16, while the main work of design was by Sakharov, Viktor Adamsky, Yuri Babayev, Yuri Smirnov [ru], and Yuri Trutnev. The project was ordered by First Secretary of the Communist Party Nikita Khrushchev in July 1961 as part of the Soviet resumption of nuclear testing after the Test Ban Moratorium, with the detonation timed to coincide with the 22nd Congress of the Communist Party of the Soviet Union (CPSU).

The effects of a nuclear explosion on its immediate vicinity are typically much more destructive and multifaceted than those caused by conventional explosives. In most cases, the energy released from a nuclear weapon detonated within the lower atmosphere can be approximately divided into four basic categories:

• the blast and shock wave: 50% of total energy
• thermal radiation: 35% of total energy
• ionizing radiation: 5% of total energy (more in a neutron bomb)
• residual radiation: 5–10% of total energy with the mass of the explosion.

Depending on the design of the weapon and the location in which it is detonated, the energy distributed to any one of these categories may be significantly higher or lower. The physical blast effect is created by the coupling of immense amounts of energy, spanning the electromagnetic spectrum, with the surroundings. The environment of the explosion (e.g. submarine, ground burst, air burst, or exo-atmospheric) determines how much energy is distributed to the blast and how much to radiation. In general, surrounding a bomb with denser media, such as water, absorbs more energy and creates more powerful shock waves while at the same time limiting the area of its effect. When a nuclear weapon is surrounded only by air, lethal blast and thermal effects proportionally scale much more rapidly than lethal radiation effects as explosive yield increases. This bubble is faster than the speed of sound. The physical damage mechanisms of a nuclear weapon (blast and thermal radiation) are identical to those of conventional explosives, but the energy produced by a nuclear explosion is usually millions of times more powerful per unit mass, and temperatures may briefly reach the tens of millions of degrees.

Nuclear blackout, also known as fireball blackout or radar blackout, is an effect caused by explosions of nuclear weapons that disturbs radio communications and causes radar systems to be blacked out or heavily refracted so they can no longer be used for accurate tracking and guidance. Within the atmosphere, the effect is caused by the large volume of ionized air created by the energy of the explosion, while above the atmosphere it is due to the action of high-energy beta particles released from the decaying bomb debris. At high altitudes, the effect can spread over large areas, hundreds of kilometers. The effect slowly fades as the fireball dissipates.

The effect was known from the earliest days of nuclear testing when radar systems were used to track the nuclear mushroom clouds at very long distances. Its extended effects when exploded outside the atmosphere were first noticed in 1958 as part of the Hardtack and Argus nuclear tests, which caused widespread radio interference extending over thousands of kilometers. The effect was so disconcerting that both the Soviets and US broke the informal testing moratorium that had been in place since late 1958 to run series of tests to gather further information on the various high-altitude effects like blackout and electromagnetic pulse (EMP).

Nuclear disarmament is the act of reducing or eliminating nuclear weapons. Its end state can also be a nuclear-weapons-free world, in which nuclear weapons are completely eliminated. The term denuclearization is also used to describe the process leading to complete nuclear disarmament.

Disarmament and non-proliferation treaties have been agreed upon because of the extreme danger intrinsic to nuclear war and the possession of nuclear weapons.

The Defense Threat Reduction Agency (DTRA) is both a defense agency and a combat support agency within the United States Department of Defense (DoD) for countering weapons of mass destruction (WMD; chemical, biological, radiological, nuclear, and high explosives) and supporting the nuclear enterprise. Its stated mission is to provide "cross-cutting solutions to enable the Department of Defense, the United States Government, and international partners to Deter strategic attack against the United States and its allies; Prevent, reduce, and counter WMD and emerging threats; and Prevail against WMD-armed adversaries in crisis and conflict." DTRA is headquartered in Fort Belvoir, Virginia. The DTRA mission, organization and management, responsibilities and functions, relationships, authorities, and administration are defined in DoD Directive 5105.62, Defense Threat Reduction Agency (DTRA).