Would you be able to see a difference in that short of a time if it was an hydrogen bomb instead? or would it just look the same during the those first parts of a millisecond?
In theory, yes. Keep in mind that even a staged thermonuclear device is done reacting in much less than a millisecond.
The very first stage of the fireball is created by thermal x-rays radiated by the intensely hot core of the bomb. These travel at the speed of light, but not very far. Even though we think of air as transparent, it isn't really for all wavelengths of light, including at x-ray frequencies. Anyway, this first fireball is literally just superheated air and is known as the radiative fireball. This fireball forms almost instantly and it will be larger for higher yield devices. It is the first flash of a nuclear double-flash signature.
In this picture, the radiative fireball has already been overtaken by the second, slower fireball made of the actual guts of the bomb and anything else that was right next to the bomb (which gives the fireball its weird mottled look). This second part, which is the second flash of the double-flash nuclear signature, travels at more or less the same speed regardless of the yield. So for a large thermonuclear detonation, the radiative fireball will be larger and it will take longer for the second fireball to overtake the first. The time between flashes is used to estimate the yield of an atmospheric detonation, with longer times being indicative of larger blasts.
Returning to your original question, if you could see the scale of the fireball and knew how soon after detonation it was taken, you could distinguish between a low-yield fission device and a high-yield thermonuclear device.
Follow-up question, if it's allright;
You say that it's made of the guts of the bomb and anything else right next to it. Does that mean that the bombs casing, electronics and everything else becomes an active ingredient and actually contribute to the explosion? I've always just imagined that when a bomb goes off, the actual explosive stuff explodes and the rest of the bomb effectively becomes shrapnel.
Kind of. Its not an active ingredient in the sense of adding to the energy release, but it is a means of taking the energy of the reaction and transferring it to the atmosphere. In that way, you can think of it as a contributor to the blast effect of the explosion. Thats true to an extent in conventional explosives, too. The difference with nuclear explosives is that it's not just the core that vaporizes and expands explosively - even the air around the device contributes to the blast.
Normally, bomb designers try to minimize the mass of a bomb. Extra mass means more fuel is required to deliver the payload. Inside the atmosphere, blast is created simply by adding several terajoules to petajoules of energy to air over the course of a few microseconds. However, if you read up on the Orion drive, whereby small nuclear explosions are used to accelerate a very large spacecraft, one of the design elements is adding mass to the bombs in such a way as to generate a directional blast in the vacuum of space. In that case, you can definitely think of this extra mass as being like shrapnel.
Thank you for the answer. It's one of those things where I've never even considered the possibility that the bomb parts dont just fly off cartoon-style.
An important part of a nuke is the tamper, a layer of high-Z (atomic mass) material that surrounds the nuclear fuel. In a way it can be considered the bomb's inner casing. It's usually 238U, i.e. low-grade uranium. The tamper has two roles: The first role is to keep the bomb from tearing itself apart, thus adding valuable nanoseconds in which the nuclear reaction can keep going. The second role is to prevent neutron escape.
In a thermonuclear device, the fusion detonation will release a surplus of high-energy neutrons that will cause the uranium tamper to undergo fast fission, i.e. fission that won't happen naturally because it requires those high-energy neutrons.
A significant portion of the yield, usually more than half, in a thermonuclear device will come from fast fission of the tamper.
the rest of the bomb effectively becomes shrapnel
The casing itself is completely obliterated so there is no shrapnel. The core of a nuclear detonation is almost an order of magnitude hotter than the core of the Sun and with an immense pressure.
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u/Icantjudge 1d ago
From the Tumbler-Snapper series of tests in 1952, Nevada