Mushroom cloud

In 1798, Gerhard Vieth published a detailed and illustrated account of a cloud in the neighborhood of Gotha that was "not unlike a mushroom in shape".

[2] The atomic bomb cloud over Nagasaki, Japan, was described in The Times of London of 13 August 1945 as a "huge mushroom of smoke and dust".

[3] In 1946, the Operation Crossroads nuclear bomb tests were described as having a "cauliflower" cloud, but a reporter present also spoke of "the mushroom, now the common symbol of the atomic age".

One way to analyze the motion, once the hot gas has cleared the ground sufficiently, is as a "spherical cap bubble",[5] as this gives agreement between the rate of rise and observed diameter.

When the detonation altitude is low enough, these afterwinds will draw in dirt and debris from the ground below to form the stem of the mushroom cloud.

Once the mass of hot gases reaches its equilibrium level, the ascent stops, and the cloud begins to flatten into the characteristic mushroom shape, often assisted by surface growth from decaying turbulence.

The ascending, roughly spherical mass of hot, incandescent gases changes shape due to atmospheric friction, and the surface of the fireball is cooled by energy radiation, turning from a sphere to a violently rotating spheroidal vortex.

A Rayleigh–Taylor instability is formed as the cool air underneath initially pushes the bottom fireball gases into an inverted cup shape.

[6] A mass of air ascending from the troposphere to the stratosphere leads to the formation of acoustic gravity waves, virtually identical to those created by intense stratosphere-penetrating thunderstorms.

The heads of the clouds consist of highly radioactive particles, primarily the fission products and other weapon debris aerosols, and are usually dispersed by the wind, though weather patterns (especially rain) can produce nuclear fallout.

[10] A higher-yield detonation can carry the nitrogen oxides from the burst high enough in atmosphere to cause significant depletion of the ozone layer.

Large amounts of newer, more radioactive particles deposited on skin can cause beta burns, often presenting as discolored spots and lesions on the backs of exposed animals.

[14] A detonation significantly below ground level or deep below the water (for instance, a nuclear depth charge) does not produce a mushroom cloud, as the explosion causes the vaporization of a huge amount of earth or water, creating a bubble which then collapses in on itself; in the case of a less deep underground explosion, this produces a subsidence crater.

An underwater detonation near the surface may produce a pillar of water which collapses to form a cauliflower-like shape, which is easily mistaken for a mushroom cloud (such as in the well-known pictures of the Crossroads Baker test).

Initially, the fireball contains a highly ionized plasma consisting only of atoms of the weapon, its fission products, and atmospheric gases of adjacent air.

Particles formed only from the weapon are fine enough to stay airborne for a long time and become widely dispersed and diluted to non-hazardous levels.

[9] The particle sizes range from submicrometer- and micrometer-sized (created by condensation of plasma in the fireball), through 10–500 micrometers (surface material agitated by the blast wave and raised by the afterwinds), to millimeter and above (crater ejecta).

Refractory elements (Sr, Y, Zr, Nb, Ba, La, Ce, Pr, Nd, Pm) form oxides with high boiling points; these precipitate the fastest and at the time of particle solidification, at temperature of 1400 °C, are considered to be fully condensed.

Intermediate elements have their (or their oxides) boiling points close to the solidification temperature of the particles (Rb, Cs, Mo, Ru, Rh, Tc, Sb, Te).

Smaller particles are carried to higher altitudes and descend more slowly, reaching ground in a less radioactive state as the isotopes with the shortest half-lives decay the fastest.

The smallest particles can reach the stratosphere and stay there for weeks, months, or even years, and cover an entire hemisphere of the planet via atmospheric currents.

The higher danger, short-term, localized fallout is deposited primarily downwind from the blast site, in a cigar-shaped area, assuming a wind of constant strength and direction.

Chemical reactivity of the elements and their oxides, ion adsorption properties, and compound solubility influence particle distribution in the environment after deposition from the atmosphere.

Ingested or inhaled particles cause an internal dose of alpha and beta radiation, which may lead to long-term effects, including cancer.

This was deduced, and the origin traced, when Eastman Kodak found x-ray films were being fogged by cardboard packaging produced in the Midwest.

Unanticipated winds carried lethal doses of Castle Bravo fallout over the Rongelap Atoll, forcing its evacuation.

The crew of Daigo Fukuryu Maru, a Japanese fishing boat located outside of the predicted danger zone, was also affected.

[16] The intense radiation in the first seconds after the blast may cause an observable aura of fluorescence, the blue-violet-purple glow of ionized oxygen and nitrogen out to a significant distance from the fireball, surrounding the head of the forming mushroom cloud.

[citation needed] The shape of the shock wave is influenced by variation of the speed of sound with altitude, and the temperature and humidity of different atmospheric layers determines the appearance of the Wilson clouds.

The entrainment of higher-humidity air, combined with the associated drop in pressure and temperature, leads to the formation of skirts and bells around the stem.