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Making gold by nuclear reactions -- what efficiency?

  1. Nov 2, 2014 #1
    This was one of the alchemists' big quests, and it is evident that it is impossible with the methods that they had available. But how feasible is it to do that with nuclear reactions? Especially nuclear reactions that start with relatively common materials, like hydrogen or carbon or silicon or iron or lead.

    This question can be broken down into parts.

    How energy-efficient are particle accelerators? Efficiency being how much energy goes into a particle divided by the wall-plug electrical energy involved in accelerating that particle. In effect,
    (particle flux) * (energy per particle) / (total energy consumed by the accelerator)

    I'd only need this for accelerators that do a few MeV per unit charge, because those are what one would need for nuclear reactions.

    What are the most suitable sorts of reactions? Direct acceleration of nuclei into targets? Or releasing neutrons by spallation and then using those neutrons. What branching fractions to such reactions typically have?

    I'm asking this here because it's hard to find the appropriate numbers, like for particle-accelerator energy efficiency. If this forum is an unsuitable place for this question, then feel free to move it elsewhere.
     
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  3. Nov 2, 2014 #2

    SteamKing

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    There's a whole wiki article about this:

    http://en.wikipedia.org/wiki/Synthesis_of_precious_metals

    The short answer is this transmutation process is incredibly expensive, such that the value of the metal produced could pay back only a tiny fraction of the cost involved in its production. More often than not, the isotopes of the precious metals produced are radioactive and thus could not be sold without exposing people to radiation.
     
  4. Nov 2, 2014 #3

    e.bar.goum

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    If we could do this, nuclear physics would be a much better funded field.

    "Hey Bob, we need a new detector!"

    "Sure, let me fire up the accelerator!"

    That'd be great.
     
  5. Nov 2, 2014 #4

    mfb

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    You'll have to start with something close to gold, otherwise the energy requirements are really bad, the fraction of gold very low and you produce all sorts of nasty radioisotopes.
    Platinum is sometimes a bit cheaper, sometimes more expensive, but it's not really an interesting material to transform to gold. Mercury (cheap) has a proton more than gold.

    In the range up to a few MeV, you can use electrostatic acceleration, the efficiency of the acceleration itself is close to 100% and the wall plug -> acceleration efficiency is still good enough to not worry about it. It is still not reasonable, however. At ~$40/g and about 12 cents per kWh (US-value), you can spend at most 2.5 MeV per gold atom. There is no way to get one atom of gold with that energy. Just electricity costs ruin the plan.
     
  6. Nov 2, 2014 #5

    arivero

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    You need to use isotope 201 of Mercury AND you need to have a way to induce alpha-decay. This is the real problem, no energy. Most elements beyond Iron-Nickel are really metastable for alpha-decay, it is just that the decay time should be higher that the lifespan of the universe.

    I can not tell why most people think that there is an energy requeriment "really bad".

    Assuming that you have a method (say, collisions, thermal, gamma excite, whatever) to enhance alpha decay of 201Hg and to do not enhance the subsequent decay of other elements, you are done. You decay 201Hg to 197Pt and then it will beta decay by itself to your beloved 197Au.

    (PS the wikipedia article http://en.wikipedia.org/wiki/Isotopes_of_mercury#cite_note-10 notes that this decay is "believed" to exist).
     
  7. Nov 2, 2014 #6

    arivero

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    With 201Hg--->197Pt--->197Au

    201 Hg -> 197Au ---> 200.970277- 196.9665516 = 4.0037254 amu
    4 He is 4.0026032 amu
    The diference is 4.0037254-4.0026032=0.0011222 amu = 1.04532 MeV produced by gold atom.

    I can use my transmutator to power yours :D

    EDIT: ok, I see now that your argument is that you can allow, from market prices, to waste up to 2 MeV per atom... but the point is that you do not waste them! The reaction is exoenergetic, you need the energy to jump the barrier, but you recover the energy (and one extra MeV) after you have got the gold.
     
    Last edited: Nov 2, 2014
  8. Nov 3, 2014 #7

    arivero

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    Let me add, if you look in this forum the keywords 201 Hg, you will find that the question has been already reviewed from time to time.

    So there is a meta-question: Why do we keep "lying" by giving the simple answer of "energetically unfeasible"? In this case it is valid because the OP ask to start from Iron, which is in the peak of the nuclear stability curve. But we answer the same even when asked to start from elements lower in the curve! I think that we do it because we know that practically any attempt to do this conversion is a scam (red mercury comes to mind) and we try to protect the OPs either of being scammed, or of the temptation of becoming scammers themselves.
     
    Last edited: Nov 3, 2014
  9. Nov 3, 2014 #8
    So starting with mercury will make it relatively easy, even though it takes around 2.5 MeV per atom. It's easy to estimate how much it costs to make gold with that energy input.

    Gold is often measured in troy ounces: 1 troy ounce = 31.1034768 grams
    Gold has exactly one stable isotope: Au-197 with atomic weight: 196.9666 amu
    Avogadro's number: 6.02214*1023
    1 troy ounce of gold = 9.51*1022 Au-197 atoms

    1 electron volt = 1.602177*10-19 joules
    Energy per atom = 4.01*10-13 joules

    Energy per troy ounce of gold-197: 3.81*1010 joules

    I'll use US electricity prices from U.S. Energy Information Administration (EIA) - Data > Sales (consumption), revenue, prices & customers > Average retail price of electricity to ultimate customers > By end-use sector, by provider, latest year
    Residential: 11.88, Commercial: 10.09, Industrial: 6.67 cents/kWh

    These prices gives $1300, $1100, and $700 per troy ounce.

    Checking Gold Price: Latest Price & Chart for Gold - NASDAQ.com recent gold prices have been around $1170 / troy ounce

    So at 100% efficiency, one would need relatively cheap electricity to compete.

    I still haven't been able to find typical numbers for the energy efficiency of small particle accelerators.
     
  10. Nov 3, 2014 #9

    arivero

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    No, no... Sorry I induced you to misinterpret the statement of mfb. He was just telling that with current electricity prices, you could at most to push 2.5 MeV into each atom. You are doing some similar calculation. I am in doubt that the calculations are realistic, for sure Hg is not cheap either, and you must put some preprocessing.

    To be clear: no method is known to produce such transmutation in an industrial, regular way.

    Consider also that the relative abundance of atoms with similar weight is similar. The supply of Hg is also scarce.

    The existence of a cataliser for this transmutation has been a well-known scam for hundred of years. As part of the tradition, the cataliser is always named "red mercury", and it is still used with this name in the camerunese scam of "wash-wash", where some black papers are transmuted into dollar or euro bills.
     
  11. Nov 3, 2014 #10

    mfb

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    Assuming I have some magic device that allows easy hydrogen fusion at room temperature, I can make as many fusion power plants as I like. There is just some tiny detail missing....

    Particle accelerators can be used to induce nuclear reactions, but then you will need energy. A lot of energy. More than 2.5 MeV per gold atom of the right isotope.

    I found mercury prices in the range of 50 to 100 USD/kg, less than 10% of the gold price. If you do isotope separation, you can sell most of the mercury back again. Well, it adds the cost of the isotope separation of course, probably more than the gold costs afterwards.


    Yes the 2.5 MeV per atom were calculated as the point where electricity costs equal the costs of the produced gold.

    Good enough to not worry about it. Electrostatic acceleration is close to 100%.
     
  12. Nov 3, 2014 #11

    e.bar.goum

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    I would place real money on the odds that isotopically pure 201Hg being more expensive than gold. It's only 13% of natural, and enrichment is expensive.

    How expensive? Gold is just about the cheapest target material you use in Nuclear physics.
     
  13. Nov 3, 2014 #12

    arivero

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    Actually the figure is not so bad if we had the magical device to put all the energy to excite the alpha... To be in the range of hours to minutes in decay time, we should need a excitation about 6 MeV, and we already have 1MeV from the difference, so just 5MeV by atom could do the break-even. We loss money at the current price, but we could reconsider if energy price halves or gold price doubles. And we could use the recovered energy, at least as thermal source for something, it does not need to be a full loss.

    Of course without magic the system would do a nice spectrum of gamma instead of the desired alpha.
     
  14. Nov 3, 2014 #13

    arivero

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    Besides, as the only argument to do the try is for sentimental reasons, I think that if we are at it, enrichment should be done in the traditional alchemical way: by repeating distillation of Hg in a multiple horned distillation column or alambic until the operator becomes mad as a hat-maker due to the vapours.
     
  15. Nov 3, 2014 #14

    e.bar.goum

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    Also! Recall that there is only a certain probability of any one given reaction occurring. Most of the time, you'll just get elastic scattering. So that'll severely limit your efficiency.
     
  16. Nov 3, 2014 #15
    Why is that? Lead has similar numbers of protons and neutrons and is MUCH less expensive.
     
  17. Nov 3, 2014 #16

    e.bar.goum

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    There is only one stable isotope of gold, unlike lead, which has four, and quite a few long-lived isotopes. 208Pb is only 52% abundant, 206 and 207Pb have abundances ~20%

    So if you want to study lead, you first have to enrich it to get isotopically pure samples.
     
  18. Nov 12, 2014 #17
    It might be worthwhile to extract gold from spent nuclear fuel.

    Sure, reprocessing is expensive, but if you _already_ do it for other reasons such as extraction of uranium and plutonium, reduction of the volume of waste, you can add more steps to the process and extract gold or other expensive elements.

    Gold is easy-ish since it has no long-lived radioactive isotopes, so you'd need only chemical separation. Compare to platinum, where Pt-193 with half-life of 50 years makes recovered metal very dangerous.

    Other suitable expensive metals are Rhenium, Osmium, Ruthenium.

    I suspect that after more detailed accounting, it would still be uneconomical, though.
     
    Last edited: Nov 12, 2014
  19. Nov 12, 2014 #18
  20. Nov 15, 2014 #19
    Hello, this will be my first reply on the forum.

    So, I think the efficiency energy wise and time wise of transmuting elements into something like gold, as far as we know, is beyond inefficient. If one had access to free energy even, I think it would be a lot more efficient to pursue asteroid mining once accessible supplies of minerals on earth are exhausted. The asteroids in near earth orbit could contain more precious metal and industrial metal then has been mined in human history, (All the gold in human possession put together would make a cube with sides about 18.2 meters in length, (60 feet) or fill 3 Olympic swimming pools I do believe.) in fact asteroids are the source of such minerals in the earths crust, however this leads to the same outcome as the discovery of efficient alchemy: The purchasing power of precious metal plummets to nill, making the reestablishment of an economy backed by precious metal (Today 95% of money is actually debt in the form of magical numbers we view with value called bank credit.) implausible as everyone can have heated golden toilet seats.
     
  21. Nov 15, 2014 #20

    mfb

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    Sure, but the same is true for the earth's crust. The average cubic kilometer has several tons of gold, platinum, more than 100 tons of silver, millions of tons of iron and various other valueable materials. There are billions of tons of gold in the upper part of the crust. The challenge is the separation from all the irrelevant stuff.
     
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