Nuclear explosion in the context of Ionizing radiation

A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either nuclear fission (fission or atomic bomb) or a combination of fission and nuclear fusion reactions (thermonuclear weapon), producing a nuclear explosion. Both bomb types release large quantities of energy from relatively small amounts of matter.

Nuclear weapons have had yields between 10 tons (the W54) and 50 megatons for the Tsar Bomba (see TNT equivalent). Yields in the low kilotons can devastate cities. A thermonuclear weapon weighing as little as 600 pounds (270 kg) can release energy equal to more than 1.2 megatons of TNT (5.0 PJ). Apart from the blast, effects of nuclear weapons include extreme heat and ionizing radiation, firestorms, radioactive nuclear fallout, an electromagnetic pulse, and a radar blackout.

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.

Nuclear fallout is residual radioisotope material that is created by the reactions producing a nuclear explosion or nuclear accident. In explosions, it is initially present in the radioactive cloud created by the explosion, and "falls out" of the cloud as it is moved by the atmosphere in the minutes, hours, and days after the explosion. The amount of fallout and its distribution is dependent on several factors, including the overall yield of the weapon, the fission yield of the weapon, the height of burst of the weapon, and meteorological conditions.

Fission weapons and many thermonuclear weapons use a large mass of fissionable fuel (such as uranium or plutonium), so their fallout is primarily fission products, and some unfissioned fuel. Cleaner thermonuclear weapons primarily produce fallout via neutron activation. Salted bombs, not widely developed, are tailored to produce and disperse specific radioisotopes selected for their half-life and radiation type.

A nuclear electromagnetic pulse (nuclear EMP or NEMP) is a burst of electromagnetic radiation created by a nuclear explosion. The resulting rapidly varying electric and magnetic fields may couple with electrical and electronic systems to produce damaging current and voltage surges. The specific characteristics of a particular nuclear EMP event vary according to a number of factors, the most important of which is the altitude of the detonation.

The term "electromagnetic pulse" generally excludes optical (infrared, visible, ultraviolet) and ionizing (such as X-ray and gamma radiation) ranges. In military terminology, a nuclear warhead detonated tens to hundreds of miles above the Earth's surface is known as a high-altitude electromagnetic pulse (HEMP) device. Effects of a HEMP device depend on factors including the altitude of the detonation, energy yield, gamma ray output, interactions with the Earth's magnetic field and electromagnetic shielding of targets.

A nuclear close call is an incident that might have led to at least one nuclear explosion, but did not. They can be split into intentional use and unintentional use close calls.

Intentional use close calls may occur during increased military tensions involving one or more nuclear states. They may be a threat made by the state, or an attack upon the state. They may also come from nuclear terrorism.

A hypocenter or hypocentre (from Ancient Greek ὑπόκεντρον (hupókentron) 'below the center'), also called ground zero or surface zero, is the point on the Earth's surface directly below a nuclear explosion, meteor air burst, or other mid-air explosion. In seismology, the hypocenter of an earthquake is its point of origin below ground; a synonym is the focus of an earthquake.

Generally, the terms ground zero and surface zero are also used in relation to epidemics, and other disasters to mark the point of the most severe damage or destruction. The term is distinguished from the term zero point in that the latter can also be located in the air, underground, or underwater.

A mushroom cloud is a distinctive mushroom-shaped flammagenitus cloud of debris, smoke, and usually condensed water vapour resulting from a large explosion. The effect is most commonly associated with a nuclear explosion, but any sufficiently energetic detonation or deflagration will produce a similar effect. They can be caused by powerful conventional weapons, including large thermobaric weapons. Some volcanic eruptions and impact events can produce natural mushroom clouds.

Mushroom clouds result from the sudden formation of a large volume of lower-density gases at any altitude, causing a Rayleigh–Taylor instability. The buoyant mass of gas rises rapidly, resulting in turbulent vortices curling downward around its edges, forming a temporary vortex ring that draws up a central column, possibly with smoke, debris, condensed water vapor, or a combination of these, to form the "mushroom stem". The mass of gas plus entrained moist air eventually reaches an altitude where it is no longer of lower density than the surrounding air; at this point, it disperses, drifting back down, which results in fallout following a nuclear blast. The stabilization altitude depends strongly on the profiles of the temperature, dew point, and wind shear in the air at and above the starting altitude.

"Daisy", sometimes referred to as "Daisy Girl" or "Peace, Little Girl", is a controversial American political advertisement that aired on television as part of Lyndon B. Johnson's 1964 presidential campaign. Though aired only once, it is considered one of the most important factors in Johnson's landslide victory over the Republican Party's candidate, Barry Goldwater, and a turning point in political and advertising history. A partnership between the Doyle Dane Bernbach agency and Tony Schwartz, the "Daisy" advertisement was designed to broadcast Johnson's anti-war and anti-nuclear positions. Goldwater was against the Nuclear Test Ban Treaty and suggested the use of nuclear weapons in the Vietnam War, if necessary. The Johnson campaign used Goldwater's speeches to imply he would wage a nuclear war.

The commercial begins with three-year-old Monique Corzilius standing in a meadow, picking the petals of a daisy as she counts from one to ten incorrectly. After she reaches "nine", she pauses, and a booming male voice is heard counting the numbers backward from "ten", in a manner similar to the start of a missile launch countdown. A zoom of the video still concentrates on the girl's right eye until her pupil fills the screen, which is then replaced by the flash and sound of a nuclear explosion. A voice-over by Johnson states emphatically:

Substantial debate exists over the ethical, legal, and military aspects of the atomic bombings of Hiroshima and Nagasaki on 6 August and 9 August 1945 respectively at the close of the Pacific War theater of World War II (1939–45), as well as their lasting impact on both the United States and the international community.

On 26 July 1945 at the Potsdam Conference, United States president Harry S. Truman, British prime minister Winston Churchill and President of China Chiang Kai-shek issued the Potsdam Declaration, which outlined the terms of surrender for the Empire of Japan. This ultimatum stated if Japan did not surrender, it would face "prompt and utter destruction". Some debaters focus on the presidential decision-making process, and others on whether or not the bombings were the proximate cause of Japanese surrender.