H vs. A; bombs

I am an afficionado of all weaponry, and there is this question I have which has bugged me for a while. What, exactly, makes a Hydrogen bomb different from an atomic bomb? I realize that the explosive is Hydrogen as opposed to Uranium or Plutonium, but why is it more powerful?

malawi_glenn
Homework Helper
I think it is the amount of fuel: E = mc^2, in a hydrogen bomb you use fusion and hydrogen has no critical mass, hence you can have more mass in a safe state before you ignite the bomb. Also fusion relases more energy per unit mass than fission:

http://web.mit.edu/jinseok/www/notes/notes_20031217/notes_20031217.files/image002.jpg

the slope is greater when going from left to right (fusion) than going from right to left (fission)

I hope this gave you the basic explanation.

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Astronuc
Staff Emeritus
The binding energy per nucleon is higher for fusion than for fission. In fission, the U-235 or Pu-239 nuclei absorb a neutron becoming excited U-236 and Pu-240 respectively, which then fission releasing about 180 MeV promply (with about 20-25 MeV coming from delayed neutron, gamma and beta-decay in fission products), so fission releases less the 1 MeV/nucleon. The prompt part is key, because a fission device has on the order of 10 microseconds to fission as much as possible before the supercritical mass dissipates.

Fusion (thermonuclear) weapons are actually initiated (triggered) by fission devices. The extreme heat of the fission detonation is used to heat the fusile material (e.g. d+t, or li+d) very rapidly. The d+t fusion reaction releases 14.6 MeV or about 3.5 MeV/nucleon.

Another resource for understanding binding energy is -
http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/nucbin.html#c2

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Well, thanks for clearing that up for me! Always great to learn something new, even at 14 :)

mgb_phys