From: g_d_pusch_remove_underscores@xnet.com   
      
   iain-3@truecircuits.com (Iain McClatchie) writes:   
      
   > It sounds like fusion in the Sun is rate limited by the production of   
   > deuterium.   
      
   That is correct.   
      
      
   > So it sounds like exploding a nuclear bomb in the sun is very similar   
   > to simply releasing the equivalent mass of deuterium at sufficient   
   > depth. The local fusion rate goes up, consumes all the deuterium, and   
   > then drops right back down again.   
      
   Crudely but approximately correct.   
      
      
   > But I wonder about deuterium production being sped up by the local   
   > pressure and temperature around the bomb's fireball.   
      
   As already stated, the energy released by the bomb is negligible compared   
   to the energy density that already exists at the core of the sun ---   
   it's be light tossing a match into a blast furnace !!!   
      
      
   > Gordon says the hydrogen density in the star core is around 100 g/cc.   
   > A quick google says the core temp might be 1.5e7 K.  Henry says the   
   > mean time for a H+H->D is 7 billion years in those conditions.   
   >   
   > To speed up deuterium reactions to the point that the explosion would   
   > be self-sustaining, the mean time for H+H->D would have to be   
   > measured in ns, or 1e26 times faster.  This does seem like a pretty   
   > good safety factor.   
   >   
   > Suppose you detonated a 100 MT bomb closer to the surface of the Sun,   
   > where the hydrogen was at about 1 g/cc.  It doesn't seem out of the   
   > realm of possibility that for a few ns, the surrounding plasma would   
   > be compressed to > 100 g/cc.   
      
   A few nanoseconds is insufficient. One needs to maintain those temperatures   
   for _BILLIONS_ of years, as henry has already noted.   
      
      
   > According to Carey Sublette's FAQ, the temperature of the early nuclear   
   > fireball is 6e7 to 10e7 K.  That's quite a bit hotter than the Sun's core.   
      
   ...But still not hot enough to make the p+p --> d + e^+ + \bar\nu reaction   
   go significantly faster: 10e7 kelvin is only a mere 10 keV, whereas typical   
   nuclear reactions require energies two orders of magnitude higher, on the   
   order of several MeV, and weak interactions are characterized by energies   
   on the order of many tens of GeV, almost seven orders of magnitude higher.   
   (The only reason fusion can occur in the core of the Sun at all is that   
   two protons can quantum mechanically "tunnel" through the coulomb energy   
   barrier that separates them to (briefly!) get close enough to fuse, if one   
   of them _also_ happens to coincidentally inverse-beta decay to a neutron   
   withing the time limitations imposed by the Heisenberg Uncertainty Principle   
   for energy.)   
      
   Furthermore, "hotter" is not "better:" Deuterium is a very fragile nucleus;   
   it is just _barely_ bound by the nuclear force (1.1 MeV/nucleon), so heat it   
   up past 12 billion kelvin or so, and you start breaking it apart into protons   
   and neutrons instead of fusing protons together...   
      
      
   > I suppose we don't know much about the rate vs (temperature, density)   
   > curve for the H+H->D reaction if it's so slow.   
      
   "Abysmally slow" would be a good term for it. (Essentially all of   
   the _minuscule_ amount of deuterium in the universe was created by   
   the Big Bang, and stellar and brown-dwarf fusion have been steadily   
   consuming it ever since...)   
      
      
   > Assuming that it's exponential in temperature, the rate would have to   
   > double for every million degrees K in order to keep up with the rate at   
   > which the fireball would otherwise cool down.   
      
   ...Which in fact it does not. The characteristic energies are MUCH higher,   
   corresponding to temperatures of _BILLIONS_ of degrees, not millions!   
      
      
   > Is there any information on the temperature or pressure sensitivity   
   > of the H+H->D reaction?   
      
   Sure --- check any textbook on stellar physics. You'll find that the   
   reaction-rate sucks under even "Big Bang" conditions, and that if you   
   get it _too_ hot, the breakup reaction d --> p + n overwhelms the   
   p + p --> d + e^+ + \bar\nu reaction.   
      
      
   >> Nothing short of a supernova reaches conditions severe enough to burn   
   >> ordinary hydrogen quickly.  Hydrogen bombs aren't even in the same league.   
   >   
   > I suppose this gets back to your original quip, Henry.  If H+H->D was   
   > fast enough at 100M K, then three-stage bombs probably wouldn't bother   
   > with deuterium since plain hydrogen would work fine.   
      
   A-yup...   
      
      
   -- Gordon D. Pusch   
      
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