Nuclear Fireball

The write-up

The first seconds of a nuclear explosion. Temperatures reach tens of millions of degrees.

1. Exhibit A

   Hotter than the Reel says

   Glasstone and Dolan put the maximum temperature of fission weapon residues at several tens of millions of degrees, similar to the center of the Sun. A conventional high explosive peaks at about 5,000 °C. The heat turns all the weapon's materials into gas, at pressures probably over a million times atmospheric.

2. Exhibit B

   How the fireball forms

   Within less than a millionth of a second, the hot residues radiate energy mainly as invisible X-rays. The surrounding sea-level air absorbs them within a few feet, forming an extremely hot, luminous sphere of air and weapon gases. That sphere is the fireball.

3. Exhibit C

   Growth, then the blast wave

   According to FM 8-9, a 1-megaton air burst's fireball is about 150 m across within a millisecond and reaches a maximum of about 2,200 m within 10 seconds while rising like a hot-air balloon. Its initial rapid expansion compresses the surrounding air, producing the blast wave.

4. Exhibit D

   Where the energy goes

   As a rule of thumb, for a fission weapon burst below about 40,000 feet, about 50% of the energy goes into blast, 35% into thermal radiation and 15% into nuclear radiation. Of that 15%, about 5% is initial radiation within the first minute and 10% is residual radiation, mostly fallout. The split varies with yield, altitude and weapon design.

5. Exhibit E

   The flash

   After about a millisecond, the fireball of a 1-megaton weapon would look many times brighter than the noon Sun to an observer 50 miles away. Its infrared component causes widespread burns and fires, at ranges that depend on yield.