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Comment by Lumich | Hacker News Reader

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Heat alone is not insufficient, the heat generated is so intense that is turns the surrounding air into a plasma which then absorbs the x-rays emitted creating a stupendous over-pressure in the air which drives the shockwave.

Reactors don't explode because the amount of heat then generate is carefully monitored and matched the the rate at which that heat can be pulled from the reactor and converted into work.

Thanks. This is a novel explanation to me. So to rephrase, some volume of air (~1,2 kg/m³ at sea level) is “plasmarized” and then eats the X-rays, upon which it expands in a shockwave.

It is usually stated, however, that the X-rays go first, and at the speed of light. Plasmarization, OTOH, would be subject to some inertia, however little, wouldn't it. So there'd be a delay before plasma formation, and the X-rays would already be “over the horizon” (joke – they wouldn't follow Earth's curvature, would they).

The x-rays aren't just emitted in a single moment, they are the result of the initial core heating up to millions of degrees, so the light they emit just as a result of being hot is in the x-ray and lasts for some amount of time. This is long enough to generate the ionised air which continues to expand and absorb more x-rays until the initial core cools down somewhat. At that point you have a large amount of incredibly hot, incredibly high pressure plasma which then expands and causes the shockwave.

The extreme radiation of the bomb almost instantly vaporizes everything near it (water in the air, earth, parts of the bomb, etc), expanding it in volume.

That’s what causes the shockwave.

As a corollary, having more material around the bomb that can capture some of its radiation means a bigger shockwave, but less radiation further away from the detonation.

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