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Are there any fundamental obstacles to using a nuclear explosion as a trigger for antimatter generation and thus considerably increasing the yield?

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    $\begingroup$ Hi Anna, welcome to Worldbuilding! Interesting first question. One bit of advice - it's often a good idea to wait 24 hours before accepting an answer, in case there's an expert or particularly ingenious user asleep somewhere else on the planet who hasn't yet seen it. Many users will skip questions that are already answered, so giving out that green check too early can reduce the quantity and quality of other answers that are on their way. $\endgroup$ – Dubukay Aug 5 at 17:27
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    $\begingroup$ Uh, the title and the question are asking two different things. Do you want boosting or generation? $\endgroup$ – Starfish Prime Aug 5 at 18:03
  • $\begingroup$ (I understood it as generating antimatter to boost the weapon's yield?) $\endgroup$ – Qami Aug 5 at 18:08
  • $\begingroup$ @CarlWitthoft PET uses radioisotopes that decay by positron emission.. that's what the P and E stand for, after all. No pair production involved. $\endgroup$ – Starfish Prime Aug 5 at 20:19
  • $\begingroup$ @StarfishPrime correct -- I was writing too fast. the emitted positron meets up with an electron to produce a pair of $ \gamma $ ; that's the pair-production I meant to identify $\endgroup$ – Carl Witthoft Aug 6 at 11:14
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Unfortunately, it wouldn't increase the yield.

When matter and antimatter annihilate each other, yes, they do liberate a huge amount of energy. But, you don't get energy for free - no matter how it's produced, creating antimatter will take up exactly as much energy as annihilating it will release.

So, even if it were plausible that a fission or fusion bomb could be rigged to produce antimatter, the antimatter annihilation would only give you back energy that it borrowed from the fission/fusion reaction in the first place.

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  • $\begingroup$ Yup this was my first, and second, thought as well. $\endgroup$ – Ash Aug 5 at 16:05
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    $\begingroup$ Thermodynamics says creating antimatter will actually take more energy than annihilating it will release... 2nd Law rules all. $\endgroup$ – stix Aug 5 at 16:29
  • $\begingroup$ Now I am curious if using fission/fusion to make antimatter would make the bomb 'cleaner' and produce less radioactives. $\endgroup$ – Andon Aug 5 at 17:19
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    $\begingroup$ @Andon no, it won't, but primarily because you can't just magically choose the output products of a nuclear reaction. $\endgroup$ – Carl Witthoft Aug 5 at 18:45
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Are there any fundamental obstacles to using a nuclear explosion as a trigger for antimatter generation and thus considerably increasing the yield

No...

What you refer to is the yield limit (I believe it was first pointed out by Ulam) to a fusion device, caused by the explosion disrupting the conditions that allow fusion to take place. By carefully constructing the device so it explodes in "stages", the yield figure of around 7-8 megatons per ton can be maintained in the tens of tons range.

Beyond that, the explosion is no longer controllable and any additional fusion material (typically lithium deuteride) will only add a negligible amount to the bang, in the form of a "fizzle".

So, converting matter to anti-matter, which will explode no matter what - pardon the pun - however widely dispersed, would appear as a practical shortcut around the yield limit, even if the laws of conservation of energy mandate that the total maximum theoretical yield will be the same. Antimatter conversion would simply allow coming closer to that yield.

This is somewhat akin to the technique of injecting nebulized water into gas engines. While the total chemical energy available can't change (it actually decreases slightly), the deflagration becomes smoother, more thorough and better suited to supplying expansion work; the result is therefore an increase in power yield, through a reduction of wasted energy (and fuel).

...or rather, yes.

The fundamental obstacle lies in the conversion itself - there is no known process that can lead to the creation of matter/antimatter particle pairs from a fusion event with any efficiency.

Currently, antiprotons are produced by shooting very high energy protons (to the tune of 26+ GeV) against suitable targets, and the antimatter yield is about four antiprotons every million collisions. So we currently need to expend around 25,000 Teraelectronvolts to create four particles with a rest mass of around four GeV.

If the whole energy of the Tsar Bomba at full design spec (100 Mt) were to be converted into antimatter with such yields, we could squeeze a yield increase of maybe 1-2 Mt. It is entirely probable that to achieve this, though, the explosive power of the Bomba would be greatly diminished, so that the operation would turn out as a net loss.

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Yes, there's a huge fundamental stumbling block.

Conservation of energy. The energy to create the antimatter has to come from the nuclear fission and/or fusion of the "trigger", so the net, final yield can't exceed that of the nuclear material in the original bomb.

Now, John W. Campbell once wrote a series of books in which, among other completely implausible things (even for the 1950s), he had a ray that converted 50% of matter to antimatter. And then, somehow, rather than erasing Chicago the first time it was tested, his character managed to turn it into an energy generator and propulsion system. This amounted to annihilating matter by converting it to its equivalent energy, but that's a whole different thing from using the (minuscule) quantity of matter/antimatter pairs produced in a nuclear explosion to boost the yield (they're already part of it).

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