A few days ago I asked about a fusion reactor design I was thinking about and got a well-founded answer by #BowlOfRed#.

There is the question I posted: Another cold-fusion reactor scheme :) Is it feasible?

He explained why it wouldn't work and he proceeded to point out that even the Sun's core isn't very efficient "reactor" since only one collision per $10^{26}$ attempts is a successful fusion. This got me thinking...

If that is the successful fusion rate in a hydrogen bomb the presence of hydrogen wouldn't make much difference, would it?! As far as I know an H bomb consists of several small fission bombs surrounding a load of hydrogen which is not much, only like 100 grams or so. Is that right? When they explode they compress and heat up the hydrogen greatly so hydrogen atom start to fuse...

So in order for the hydrogen in the bomb to make it significantly more powerful then the fusion rate per nuclei should be quite large. That to me says, that the core of an H bomb has better conditions for fusion than the core of the sun?! It's mind boggling to think that the fusion failure rate is that big in the Sun's core, considering the pressure and heat that exist there. Knowing that I'd say why do we even consider fusion as energy source?...

I'm probably missing a lot here, so can you guys clear that up for me. :)

  • $\begingroup$ possible duplicate of How much faster is the fusion we make on earth compared to the fusion that happens in the sun? $\endgroup$
    – ProfRob
    Commented Apr 24, 2015 at 11:06
  • $\begingroup$ Despite the name, an H bomb is not really a fusion bomb, is it? $\endgroup$ Commented Apr 24, 2015 at 15:45
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    $\begingroup$ The fusion reactions are a nice way to 'boost' the yield by generating lots of neutrons to get more fission going sooner. A D-T reaction generates about 18MeV, while a U fission releases more like 180MeV, so, no, it isn't a fusion bomb. $\endgroup$
    – Jon Custer
    Commented Apr 24, 2015 at 15:51
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    $\begingroup$ It depends on the design. It's perfectly possible to make an H-bomb which gets most of its energy from fusion, and this has been done. But for maximum energy from minimum size you use the fusion radiation to induce fission in an unenriched uranium jacket, so a majority (sometimes a large majority) of the released energy comes from fission. It depends on exactly which design parameters are considered most important. "Clean" H-bombs are mostly fusion, but they are bulkier and heavier than equivalent-energy "dirty" bombs which are predominately fusion-boosted fission. $\endgroup$ Commented Apr 24, 2015 at 21:47
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    $\begingroup$ I'm rather happy that the sun is so inefficient. $\endgroup$ Commented Apr 25, 2015 at 9:28

1 Answer 1


The Sun fuses protons, and this is a very slow process because there is no bound state of two protons. Hydrogen bombs fuse deuterium and tritium, and this is much, much faster because there is a bound state of these nucleides.

You might like to have a look at:

as these cover related issues.


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