Anatomy of a Fireball

Given an estimated mass of 10 pounds of 239Pu at an estimated temperature of 20million degrees, the yield is equivalent to 1million pounds or 500 tons at 200 degrees (boils 500 cubic meters of water: an 8-meter cube). But since an airblast has little mass, the fireball proceeds outward until it finds sufficient air mass to dissipate its energy content: the mass-to-gas expansion is about 22,000 liters or 22million cc's per gram (or 22million times for water) (near RSTP Room-Standard Temperature-and-Pressure), requiring about 10billion cubic meters of atmosphere, or roughly 1 kilometer radius ... a coarse, first approximation for a small fission device, typically 10Kton 'dynamite'.

A larger device of 10M ton [thermonuclear fusion device] will thus have a radius about 10 kilometers ... this is a little shy of common estimates, but it explains the anatomy of the fireball seeking its dissipation in any available mass.

An effective energy transfer may be estimated based on the cross-section exposed to the fireball ... noting however that the fireball is a 'gas' plasma, and tends to surround objects further from the detonation, rather than blast-passed the objects closer-in (little advantage, as the temperature in-closer is hotter).

Grand-Admiral Petry
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Nuclear Emergency Management