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Nuclear detonation inside the sun
What would happen if you detonated a nuclear bomb inside the sun?
I realize that getting any bomb to the sun would take an amazing delta-V, and that surviving the thermal and pressure environment long enough to get to any significant depth is... maybe not in the realm of possibility. But I'm curious about the effects of detonating a bomb in a dense hydrogen medium. I would imagine the neutron and radiation burst would stimulate fusion reactions in the surrounding hydrogen. Is there a critical hydrogen density at which the reaction becomes self-sustaining? And, does anyone have an idea what the pressure/density gradient in the sun might be? The average density is about 1.4 g/cc, but I imagine you have to get in a long way before it gets that soupy. |
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Nuclear detonation inside the sun
In article ,
Iain McClatchie wrote: But I'm curious about the effects of detonating a bomb in a dense hydrogen medium. I would imagine the neutron and radiation burst would stimulate fusion reactions in the surrounding hydrogen. Not significant ones, or people wouldn't bother doing isotope separation for building hydrogen bombs. The easiest fusion reaction burning ordinary hydrogen is the proton-proton chain, which starts with two hydrogens fusing into deuterium plus some odds and ends. Even in star-core conditions -- much hotter and denser than anything you will get at a reachable depth -- that reaction is so slow that burning a mass of hydrogen that way takes billions of years. (The time taken for the average pair of protons to undergo that reaction, in star-core conditions, is estimated at seven billion years. Theoretical estimates are all we have -- the reaction is far too slow to be measured in the laboratory.) The only reason the Sun can stay lit at all, with such a slow reaction powering it, is that it has such a tremendous volume for that reaction to take place in, and -- comparatively speaking -- such a very small surface area for heat to be lost through. (Imagine a hypothetical big fusion reactor, a sphere 150 meters across -- the supporting cradle for the sphere is roughly the size and shape of a football stadium. Assume that its outer shell is a magical perfect reflector, except for one tiny hole, a barely-visible pinhole 0.1mm across, so that all the energy generated within that reactor has to come out through that hole. That's about the same ratio of surface area to volume as the Sun.) Is there a critical hydrogen density at which the reaction becomes self-sustaining? Nothing short of a supernova reaches conditions severe enough to burn ordinary hydrogen quickly. Hydrogen bombs aren't even in the same league. -- MOST launched 30 June; science observations running | Henry Spencer since Oct; first surprises seen; papers pending. | |
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Nuclear detonation inside the sun
you don't think that the sun is currently a self-sustaining fusion reaction?
fascinating. "Iain McClatchie" wrote in message om... What would happen if you detonated a nuclear bomb inside the sun? I realize that getting any bomb to the sun would take an amazing delta-V, and that surviving the thermal and pressure environment long enough to get to any significant depth is... maybe not in the realm of possibility. But I'm curious about the effects of detonating a bomb in a dense hydrogen medium. I would imagine the neutron and radiation burst would stimulate fusion reactions in the surrounding hydrogen. Is there a critical hydrogen density at which the reaction becomes self-sustaining? And, does anyone have an idea what the pressure/density gradient in the sun might be? The average density is about 1.4 g/cc, but I imagine you have to get in a long way before it gets that soupy. |
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Nuclear detonation inside the sun
"Iain McClatchie" wrote ...
What would happen if you detonated a nuclear bomb inside the sun? Sod all. The Sun is Big. If I was to use the term 'drop in the ocean' I would be vastly over-stating the significance of the 'drop'. |
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Nuclear detonation inside the sun
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Nuclear detonation inside the sun
Henry, Gordon,
once again you provide fascinating info. Thanks. It sounds like fusion in the Sun is rate limited by the production of deuterium. 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. But I wonder about deuterium production being sped up by the local pressure and temperature around the bomb's fireball. 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. 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. 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. 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. Is there any information on the temperature or pressure sensitivity of the H+H-D 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. |
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Nuclear detonation inside the sun
Iain McClatchie wrote:
Henry, Gordon, once again you provide fascinating info. Thanks. It sounds like fusion in the Sun is rate limited by the production of deuterium. 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. But I wonder about deuterium production being sped up by the local pressure and temperature around the bomb's fireball. The p+p reaction is very slow, so it's doubtful much would happen. Now, if the Sun were a really old red dwarf ( current age of the universe), it would have accumulated a lot of 3He in its core. It might be possible to get *that* to explode. Paul |
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Nuclear detonation inside the sun
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Nuclear detonation inside the sun
In article ,
Iain McClatchie wrote: It sounds like fusion in the Sun is rate limited by the production of deuterium... Quite so. The other reactions in the proton-proton chain are not exactly speed demons either -- if memory serves, the average time to add a proton to deuterium to make He3 is seconds, and then the time for two He3's to fuse to make He4 and two protons is thousands of years -- but production of deuterium is definitely the rate-limiting step. 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. My understanding is that we have no experimental data at all, but the theoreticians could probably venture a guess. I don't know what it would be, though. -- MOST launched 30 June; science observations running | Henry Spencer since Oct; first surprises seen; papers pending. | |
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Nuclear detonation inside the sun
"Henry Spencer" wrote in message ... In article , Iain McClatchie wrote: It sounds like fusion in the Sun is rate limited by the production of deuterium... Quite so. The other reactions in the proton-proton chain are not exactly speed demons either -- if memory serves, the average time to add a proton to deuterium to make He3 is seconds, and then the time for two He3's to fuse to make He4 and two protons is thousands of years -- but production of deuterium is definitely the rate-limiting step. 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. My understanding is that we have no experimental data at all, but the theoreticians could probably venture a guess. I don't know what it would be, though. For the best overview of this subject, to the man himself - Bethe's Nobel lectu http://www.nobel.se/physics/laureate...e-lecture.html You will see (pg. 11 of the PDF) that the H+H-D reaction is very insenstive to temperature, and the rate of increase flattens out as the temperature rises, and is nearly flat above 30 million K. Thus no amount of heating will increase the rate markedly, the limiting increase is about a factor of 10 over the sun's energy production rate in the core - this is 70 erg/g-sec (Sun's core rate is 7 erg/g-sec, its average rate is 2 erg/g-sec). If you do the math, you find that 70 erg/g-sec is 0.5% of the average metabolic rate of a human. That is to say - average human tissue produces heat 7000 times faster than the Sun's average. The theoreticians estimates on this are very, very good. Models based on theory accurately describe the observable behavior of stars. Carey Sublette |
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