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Comment by UnpossibleJim | Hacker News Reader

Thermonuclear bombs work on nuclear fission not fusion, just to clear up any confusion. Nuclear power plants also achieve power from fission, which is the breaking of nuclear bonds.

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No, the defining characteristic of thermonuclear bomb is a second stage fusion device. The first stage fission device sets off the second stage.

https://en.m.wikipedia.org/wiki/Thermonuclear_weapon

Edit: just acknowledging the funny set of identical replies!

Oh! My bad =) I should have looked it up first. I always thought it was take the unstable uranium isotope and surround it with a horrible amount of explosive material which was set at a controlled time to pressure the uranium into a cascading reaction. Turns out, I'm running on the 1940's Popeye cartoon explanation =[

You're right but for the name. That's how the fission nuclear bomb works. Then you combine it with a heavy hydrogen fusion stage to get a thermonuclear ('hydrogen') bomb.

No, the person you're replying to is right, the bulk of the energy is from fission. What the fusion does is serve essentially as a "tamper" - it's in a ring around the fissile core and as it explodes it compresses the fissile core. Since the fission rate increases exponentially this tamping dramatically increases the overall energy yield.

I think we all agree that fission AND fusion are involved in a thermonuclear weapon.

No, that is NOT what the 'tamper' is or does. See my (or various other) nearby comments where I describe the actual process, or just read the Wiki article linked in another comment...

No, thermonuclear bombs [1] are fusionbombs. Nuclear bombs can be of both types but the term thermonuclear specifically means (partly) fusion-powered bombs. These bombs always use a fission reaction as a starter for the fusion reaction, depending on the type of bomb the power output can be anywhere from mostly fusion to largely fission.

[1] https://en.wikipedia.org/wiki/Thermonuclear_weapon

No, thermonuclear bombs actually work on nuclear fusion (started by a smaller fission bomb).

Well, GP didn't mean this, but most thermonuclear bombs derive a large amount of their yield from fission of a U238 "tamper" and "sparkplug", driving by neutrons from D-T fusion.

Technically, there is no pure fusion bomb so I guess in a way you could say everything is fission powered, but that's like saying your gasoline car is battery powered because that's what started the engine.

Nope! Essentially all modern large thermonuclear devices are fission-fusion-fission devices, where the last fission stage (again, driven by fusion neutrons) produces the majority of the yield. You can omit that stage, by using a non-fissile material, for easier testing (...do you really want to test a 100MT device?...) with less fallout, but in actual use, they would all have fissile tampers.

Except that in a thermonuclear bomb, fission also occurs at the end as well as the start... The initial fission explosion starts off a fusion reaction, and then neutrons from the fusion process carry on to start another fission reaction, usually of the LEU 'tamper' encasing the bomb. In fact, a large proportion of the energy output is from this third stage fission reaction.

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