Be advised: this thread is not for serious in-depth discussion of weighty topics (we have a link for that), this thread is not for anything Culture War related. This thread is for Fun. You got jokes? Share 'em. You got silly questions? Ask 'em.
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Notes -
Goldbugs in shambles (if and when anyone actually makes fusion power): https://x.com/MasterTimBlais/status/1946291116954763388
Also some nominative determinist fun.
This was a really fun paper to read, especially since I just noted that I'm going through an MIT OCW nuclear course right now. My actual knowledge on the topic still rounds to approximately zero, but it was actually enjoyable to just go through the proposed reactions/decays, just pull up the same tables they're using, do the incredibly simple energetics calculations, and see that they are, indeed, correct. I would have had no clue how to do even that just a few months ago.
So, can confirm that the stone simple energetics work; they're not so far out to lunch that they've made such a stupidly basic error (we're not dealing with total cranks). I can't say much of anything on any of the many many other questions involved concerning reactor/process design, materials handling, economics of it, etc. They do point out some prior works that had looked into this in the past, so it's also not unprecedented, but the current authors get an order of magnitude more production in their calculations. The current authors, correctly in my view, point out that the prior works (in the 80s) didn't really show their work for how they got their estimate for gold production, as they were focused on cobalt (and the current authors write reasonably significantly on mercury enrichment, which prior works didn't, and I don't have the knowledge to evaluate). There may be (and probably is?) some other technical barrier to the rest of the scheme that an experienced nuclear engineer would spot in an instant, but if not...
What a time to be alive!
Then you seem like the best person to ask this rather obvious question: why is nobody doing that in conventional fission reactors right now? At least the fast breeders should have suitable neutron flux, right?
@Lizzardspawn for visibility
I think there is a 'basic' answer here, just in terms of energetics.
Looking at a single atom version of the reaction they're talking about to create gold, the idea is that you have an atom of mercury-1981, and you hit it with a neutron. If all goes well, the end result is one atom of mercury-1972 and two neutrons coming out. You can just compute the energetics of this reaction just from mass/energy conservation. This is, indeed, one of the first things I computed when going through the paper. The answer is that the reaction is endothermic, which is similar to what you might have seen in chemistry - the reaction requires you to put energy in in order for it to happen. The way you typically put energy in is to have a fast-moving neutron that is flying in to hit the mercury-198 atom. When you do the calculation, the required energy in for the neutron is just under 8.5MeV. You must have a neutron flying at least this fast into a mercury-198 atom to accomplish the desired reaction.
Common uranium-235 fission reactors do produce neutrons flying around; that's necessary for them to keep the chain reaction going. But the energy of those neutrons is low in comparison. It does produce a spectrum of neutron energies, but the peak of that spectrum (the most number of neutrons produced) is around 0.7MeV, the average being about 1.9MeV (it's a bit skewed)3. You can find that the spectrum does continue to tail off toward the higher energies, but eyeballing the chart, you have about a two-and-a-half order of magnitude reduction in the production of neutrons that are at the sufficient >8.5MeV range than you have at the lower energies. If I actually integrated the curve, the number of sufficiently energetic neutrons produced would surely be <<1% of the total neutrons produced, and the question really is about the number of zeros I should put after the decimal point before we get something non-zero.
Now, fast breeder reactors. They do also split plutonium, which does produce a slightly faster neutron spectrum... but it's not much. The curves are quite close to U235. The 'fast' part of the name is just that they use the (primarily ~1-2MeV) neutrons they have directly (when they're "fast", where "fast" means >1MeV) rather than slowing them wayyyy down with a moderator like they do in traditional reactors.
That is, the short answer is that existing fission reactors just don't produce enough neutrons that have enough energy to convert mercury isotopes (see footnote 2 again). Whereas with deuterium-tritium fusion reactors, the primary reaction is just H2+H3=>He4+neutron. If you do the energetics here, assuming worst case scenario with no kinetic energy coming from the input hydrogen atoms, you still get neutrons coming out with just over 14MeV. That's plenty of energy to hit some mercury and get what you want. If, of course, you can design your reactor right (and there are a bunch of other considerations that I won't get into here; just this basic consideration of energetics should be sufficient for the instant question).
1 - Mercury-198 is a 'relatively' abundant natural isotope, about ten percent of all the naturally-existing mercury in the world. In gathering it up, you'll likely be digging it out of the ground. Then, you take that ore and process it until it's the kind of stuff you want. Generally, people use chemical/physical means to get rid of other stuff and 'isolate' the 'good stuff'. This is the 'enrichment' bit.
2 - Thereafter, Mercury-197 naturally decays to gold with a half-life of like 20-70 hours (I didn't go back and look up the exact numbers for this comment).
3 - A weirdness that requires getting into looking at cross-sections is that they actually prefer even slower neutrons for further U235 fission. This is why they have 'moderators' in reactors - to slow neutrons down to a speed that is best for further fission events. There's fun back story here in the history of the development of ideas for the possibility of sustained fission; it took some work to figure out which isotopes of uranium would split with different energies of incoming neutrons; it turned out to be important that U235 would do fine with slower neutrons (which it could, itself, readily produce), whereas U238 required faster neutrons and couldn't sustain itself with its own production of neutrons.
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just asked myself the same. My wild guess is - it requires some major redesign.
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