From: Tony Williams 

Don Hills wrote:
> In article , Tony Williams
 wrote:
>
>>The pictures suggest that you're right. The one at the top of the page I
>>linked to seems to show several fronts moving out in different
>>directions from a common centre.
>
>
> From nuclearweaponsarchive.org:
>
> Cause of the surface mottling.
> At this point in the explosion, a true hydrodynamic shock front has just
> formed. Prior to this moment the growth of the fireball was due to radiative
> transport, i.e. thermal x-rays outran the expanding bomb debris. Now however
> the fireball expansion is caused by the shock front driven by hydrodynamic
> pressure (as in a conventional explosion, only far more intense). The
> glowing surface of the fireball is due to shock compression heating of the
> air. This means that the fireball is now growing far more slowly than
> before. The bomb (and shot cab) vapors were initially accelerated to very
> high velocities (several tens of kilometers/sec) and clumps of this material
> are now splashing against the back of the shock front in an irregular
> pattern (due to initial variations in mass distribution around the bomb
> core), creating the curious mottled appearance.

So it's the shape of the container, not the actual bomb material that
controls the mottling. That's even more interesting because it seems to
allow for the possibility of directional effects - shaped nucear charge
anyone? Good find.

--
Tony

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