Transmutation of Mercury into Gold.

[NNadir]

Recently I stumbled upon some work on an early nuclear reactor, the Clementine reactor, which operated in the late 1940's and was the first fast spectrum reactor every built, in essence, the first plutonium based breeder reactor. It was cooled by the toxic liquid element mercury.

The reactor is described here: Hannah K. Patenaude & Franz J. Freibert (2023) Oh, My Darling Clementine: A Detailed History and Data Repository of the Los Alamos Plutonium Fast Reactor, Nuclear Technology, 209, 7, 963-1007

Surprisingly it is the only reactor ever built with a mercury coolant.

The article just linked is open to the public to read, and comes with lots of pictures of the reactor, built in a period of less than a year. Norris Bradbury, who succeeded Robert Oppenheimer as director of the Los Alamos laboratory in 1945, is quoted in the article with an amusing observation, some 25 years after the fact:

The critical assembly of Clementine was reconstructed on November 21 (note: 1946) (CitationRef. 14), and some preliminary results were sent from the Halls to Morrison by December. An entire reactor was built and assembled within a single year. An unimaginable amount of work was accomplished in an unbelievably small timeframe. More than 20 years after her disassembly, Norris Bradbury reflected on his tenure as director of the Laboratory throughout Clementine’s lifetime and summed up the project nicely:

We made the first plutonium reactor, called Clementine, and it was the first reactor that operated upon a fast neutron spectrum. I only pause to note that today it would take you ten billion dollars and fifty thousand volumes of environmental reports and nobody’d let you do it anyway, but we just did it. And it worked beautifully; we finally shut it down when it became clear that some of the components were a little tired.Citation19

The size of the reactor core is obviated in this picture:



The core, as small as it is, was housed in a much larger structure to afford shielding and control devices, but not huge:



One of the interesting points to which no attention seems to have been drawn, is that the mercury coolant, in a neutron flux, and exposed to his energy fission gamma rays, should have, and quit possibly did, transmute mercury into gold, including gold's only stable isotope, ¹⁹⁷Au.

This first case of why this should be is pretty obvious with some basic understanding of nuclear physics with respect to neutrons:

A stable isotope of gold, ¹⁹⁶Hg, can capture a neutron which makes it into the radioactive isotope ¹⁹⁷Hg, a radioactive isotope with a half life of 64.94 hours, whereupon it decays into stable gold. The problem is that although ¹⁹⁶Hg is thought to be radioactive and to decay via alpha emission into platinum 192, this with a half life is so long, that it has never been observed, it is an extremely rare natural isotope of mercury, less than 0.2% of the total stable isotopes found in natural mercury. In Clementine, it was probably not worth looking for it, since the reactor was quite small.

The second case is far more subtle, and involves a mercury isotope heavier than gold ¹⁹⁸Hg. Exposed to high energy gamma rays, ¹⁹⁸Hg can emit a neutron, yielding an isotope that is one amu (atomic mass unit) lighter, ¹⁹⁷Hg. (This isotope is radioactive, with a half life of 64.94 hours. It decays to stable non-radioactive gold.) This is a photonuclear reaction and, although the property has been known for a long time (I discovered it on Wikipedia a few years ago) photonuclear reactions are covered in a very recent paper out of Russia:

O.V. Poriadina, S.S. Belyshev, N.Yu. Fursova, V.V. Khankin, A.A. Kuznetsov, Photonuclear reactions on mercury isotopes, Nuclear Physics A, Volume 1063, 2025, 123206.

To avoid the limitations of the DU editor, an excerpt of the full paper above is posted as a graphic object about the purpose of transmuting mercury isotopes into radioactive isotopes of gold for use, largely in medical settings:



The paper contains a list of mercury isotopes, along with radioactive gold species along with the half-lives of each:



Note that the gold isotopes have short half-lives, on the order of hours to a few days, meaning that any gold removed from the system will relatively rapidly decay to ground state stable nuclei. Note that there are two nuclear isomers of ¹⁹⁷Hg, the nuclear isotopes ^197gHg and ^197mHg. If these nuclear isomers decay via isomeric transition (IT), they will end up as the ground state radioactive mercury isotope ¹⁹⁷Hg that will be in a few weeks time, non-radioactive natural gold, ¹⁹⁷Au. It is possible, not specified in the paper, that they will also decay directly to ¹⁹⁷Au; it really doesn't matter much except in an academic sense. If this gold remains in the reactor some of it, certainly not all of it, will capture neutrons to become the radioactive isotopes of gold mentioned for medical use, but within a few weeks of cooling, will essentially be pure natural non-radioactive gold.

The lowest threshold for neutron emission in ¹⁹⁸Hg is reported in the paper as being 8.48 MeV, very energetic gamma rays, not accessible from fission products, but certainly accessible from the gamma rays associated with fission itself. It does seem to me therefore that a mercury cooled reactor might well, transmute toxic mercury into biologically inert gold, left to cool for a few weeks to deal with any radioactive gold isotopes.

We are entering an age of renewed nuclear engineering creativity not seen since the early 1960's. To my knowledge, no one is interested in developing a mercury cooled reactor like the Clementine reactor of the 1940's. Nevertheless, it would be cool I think, should one ever be built, to check out if transmutation of mercury into gold does take place. It turns out, even if mercury is not lead, that the alchemist's dream is actually possible.

It's a weird little thought, but one that strikes me as interesting.

Have a nice day tomorrow.

[marble falls]

1. Great. Now EVERYBODY knows, thank-you very much. Note to self: sell off gold holdings.

[NNadir]

2. Don't worry; be happy. No one is building a modern Clementine reactor. If they did, it wouldn't smash the market.

[ret5hd]

3. he ALWAYS ruins stuff...ask him about perpetual motion!

[Norrrm]

4. Ironic considering that mercury is often used to mine/separate gold, polluting the environment.

[3Hotdogs]

5. I got an old thermometer somewhere in the house.

Ya don't suppose .......

[Ponietz]

6. I saw on Reddit that Marathon Fusion is a start up with this very idea

Fusion Startup Says It's Figured Out How to Turn Mercury Into Gold

https://www.reddit.com/r/STEW_ScTecEngWorld/s/1h9k15laLp

Also, there’s the account of James Price.

James Price was an 18th-century English alchemist who claimed he could turn mercury into gold. When challenged, he agreed to prove it before credible witnesses. But instead of performing the experiment, he drank prussic acid and killed himself in front of them.

https://www.reddit.com/r/interesting/s/6bQPfrQ5KD