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I wondered how much energy could pass through some area 1000 miles away from the explosion, so I made some rough calculations.

Assumption: all energy of the nuclear explosion is radiation uniform in every direction.

The energy E would be spreading in a sphere with area 4*pi*R^2. Area A being a part of that sphere would capture E*A/(4*pi*R^2) of energy. So with:

  energy E = 209 PJ (Tsar bomba for an extreme example)
 
  area A = 1 m^2

  radius of the sphere R = 1000 miles (1609 km)
That would give:

  2.09 * 10^17 J * 1 m^2 / (4 * pi * (1.609 * 10^6 m) ^ 2) = 6.4 kJ
So at the distance of 1000 miles an 1 m^2 object would be exposed to 6.4 kJ of radiation. I don't know how destructive would that be. That energy would be equivalent to 6 seconds of sun irradiating a 1 m^2 area above the Earth's atmosphere, but of course sun's radiation is less dangerous (very little gamma/x-ray), and all of that radiation would be almost instant.

From what I'm reading about high-altitude nuclear testing, it can cause artificial radiation belts around the Earth (composed of high-energy electrons). I think that may be more dangerous to satellites at distances like 1000 miles (or at any distance) than the immediate gamma/x-ray radiation.



Radiation is measured in gray, which is 1 J absorbed by 1 kg. I can't find the conversion between flux to absorbed dose. 5 gray is fatal. If even a fraction of that energy is absorbed, it would be fatal.

I found that satellites get 100-1000 rad per year. Getting that much in a moment would cause problems.


> Radiation is measured in gray, which is 1 J absorbed by 1 kg. I can't find the conversion between flux to absorbed dose. 5 gray is fatal. If even a fraction of that energy is absorbed, it would be fatal.

It's measured in a lot of different ways depending on the need, and the unit "sievert" is Gy times a conversion factor that depends on the kind of radiation (for equivalent dose) and which body parts (for effective dose): https://en.wikipedia.org/wiki/Sievert#Radiation_type_weighti...

But also, beta radiation (electrons) will be stopped by a thin sheet of tinfoil, while alpha radiation (helium-4 nuclei) by paper or the outer layer of dead skin on your body and therefore only matters if you eat a source of it, and a significant fraction of any gamma radiation you're exposed to will pass right through you without getting absorbed.


So, given that human body area viewed from the front is around 0.5 m^2, then a 70 kg human in space 1000 miles from the explosion would get 6.4 kJ * 0.5 / 70 kg = 45 gray. That would mean that even being a couple thousand miles away could be fatal. But that's assuming 100% of Tsar Bomba energy would be ionizing radiation, I don't know what % would that be in reality.




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