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It’s only after we gave up searching for this element that we found it out in the universe.
Featured above: Doctors use this white fluid to wash technetium-99 off radioactive molybdenum in a process called “milking.”
Show Notes
Show notes, I’m afraid, are light again this week. But I did want to mention Przybylski’s Star, which I can almost spell without looking it up now!
It’s one of the stranger stars in our galaxy. It does have high levels of technetium in it — and also gives off a lot of emission spectra that look like nothing we’ve seen before. It’s possible that this star contains elements that we haven’t yet discovered anywhere else. I’ll let SciShow take it from here:
Episode Script
Every element we’ve investigated so far is a substance that was discovered as part of the natural world, but many of the entries on the periodic table are synthetic, and have only ever existed in a laboratory.
Almost all of those elements are late entries on the periodic table, too large and too unstable to exist for very long. By sheer bad luck, technetium is also highly unstable, and all of its isotopes are radioactive. Element 43 really sticks out in this regard. We won’t see much more of this kind of behavior until we get close to period seven, the last row of the periodic table.
Since today’s element is so radioactive, any that might have been around at the birth of our solar system would have long since dried up, decaying into other, more stable elements a long time ago.
For this reason, element 43 is the first in chemical history that was not discovered as part of the natural world, but was synthesized in a lab by human hands. Its name reflects this, coming from the Greek word for “artificial.”
So it’s kind of funny that in the decades following its discovery, we found that some of the strangest places in the universe are hard at work producing a steady stream of raw, locally sourced, all-natural technetium.
You’re listening to The Episodic Table Of Elements, and I’m T. R. Appleton. Each episode, we take a look at the fascinating true stories behind one element on the periodic table.
Today, we’re making an episode about technetium.
When Dmitri Mendeleev published his version of the periodic table a century and a half ago, one of his greatest ideas was to leave blank spaces for elements that had not yet been discovered. It wasn’t very long before those gaps started closing. Gallium was the first, as we mentioned in its episode, and germanium and scandium soon followed.1
By the 1920s, most of those blanks were filled in — which made those few that remained a source of great frustration for element chasers.2 Ironically, without the periodic table, scientists wouldn’t have known what they didn’t know. But that empty slot at the forty-third position tempted some scientists toward a very unscientific way of thinking.
Several chemists had claimed the discovery of the missing element, but each was swiftly and summarily debunked. Usually, these were misidentified samples of known elements like iridium and yttrium. In 1925, the German team of Otto Berg, Walter Noddack, and Ida Tacke claimed a discovery that couldn’t be so easily dismissed.
The trio announced the discovery of two elements: seventy-five, and forty-three. They dubbed these rhenium and masurium, respectively — names that the scientific community didn’t take especially well. Rhenium takes its name from the Rhine, Germany’s most famous river, and Masuria, a region of what was Prussia at the time. Perhaps the team didn’t mean to send a political message, but both of those locations were the sites of major German victories in the first World War. It was largely seen as a nationalistic and petty move in extremely poor taste.3
Their work on rhenium was solid, and an element’s discoverers still had naming rights at this point, so their peers begrudgingly had to let that slide. But their paper on masurium was a little more suspect — and scientists outside of Germany were eager to poke holes in their research.
Ultimately, Berg, Noddack, and Tacke might have made that discovery, maybe, but the work they showed did not inspire confidence in their already-skeptical peers. It was genuinely poor and sloppy research. The score was one to one, but the space below manganese remained annoyingly empty.
Twelve more years passed before anyone else laid claim to that territory. Emilio Segré and Carlo Perrier were on the case while working at the University of Palermo in Italy. While everyone else searched for samples of element 43 in mineral samples, these two had a different idea.
American scientist Ernest Lawrence had recently invented a room-sized particle accelerator called the “cyclotron,” which was used to produce significant quantities of radioactive material for study. Segré visited Lawrence’s lab in Berkeley in 1937, and Lawrence casually mentioned that as part of the cyclotron’s operation, it would spend months irradiating strips of molybdenum. His heart might have quickened, and his eyes may have dilated, but for the moment, Segré remained silent.
A few months later, back in Palermo, Segré could wait no more. He asked Lawrence if it might be possible to send some of those molybdenum strips to Italy, just so he could take a gander. It was practically garbage anyway, right?
Lawrence thought this was a rather silly request, but one that was easy enough to fulfill. With the sample in hand, it didn’t take long for Segré and Perrier to confirm the presence of element 43, created by the radioactive assault of molybdenum, element 42. Lawrence and his team were the ones to actually synthesize the element — but they had no idea. By combing through Lawrence’s scraps, Segré and Perrier became the undisputed discoverers of element 43.
Well — mostly undisputed. Who came literally marching into their lab a month later but Walter Noddack himself, wearing a fake military uniform emblazoned with swastikas, like some kind of fascist cosplay.4 Whatever he was trying to accomplish, it’s safe to say he didn’t. Segre’s results were well-founded, and he gets the credit for the discovery, along with Perrier.
This is the only element on the periodic table to be discovered in Italy, but notably, it’s not called “italium” or “panormium” — although the University would have loved that. Segré and Perrier wanted to avoid the sort of controversy that the German trio had attracted with their aggressively patriotic element names. Even if the two Italians hadn’t actually created the sample, element 43 was the first in history to have been synthesized by humans, rather than found in nature. “Technetium” was far less controversial, and honestly, a lot more appropriate.
So it might be surprising to hear that only a few years later, the first artificial element was discovered in a completely natural setting.
In 1972, some French physicists had a big problem. They were assessing uranium ore they had gathered from the Oklo mine in the African nation of Gabon. Based on the age of the Earth and the half-life of uranium, they knew that the ore should consist of 0.72% uranium-235. It didn’t matter where on Earth the uranium came from — it should always be 0.72% uranium-235.
The concentration of uranium-235 in this ore was 0.717%.
That might not sound like a big deal. Those numbers are very close together! The thing is, they had extracted enough ore that this tiny discrepancy meant they were missing 200 kilograms of uranium-235. With that much material, a sufficiently motivated person could build six nuclear bombs.
No one had stolen the fissile material, though. They could see evidence of fission byproducts — including evidence, at one point, of plenty of technetium.
The French had dug up this uranium for fuel in their nuclear power plants. But the reason the ore was poorer in uranium-235 was because it had already been used as fuel in a nuclear reactor — a nuclear reactor that was two billion years old, and entirely natural.
In theory, a nuclear reactor is a pretty simple thing. It only requires a few ingredients: A bunch of atoms to be split, a bunch of neutrons to split them, and some kind of moderator to make sure the whole thing doesn’t happen too quickly.
Oklo just so happened to have all of those ingredients in one place. Obviously, there was a lot of uranium there — that’s what had attracted the French miners in the first place. Two billion years ago, about 3% of it was uranium-235, which is the isotope used as nuclear fuel. Every so often, one of those atoms of uranium-235 would decay and eject a neutron.5 6
Ordinarily, that wouldn’t do much — the neutron is ejected so quickly that it doesn’t ram into another atom, it just keeps going. But at Oklo, there was a moderator: A steady influx of groundwater. The water slowed down those neutrons to the point that they could collide with another atom of uranium-235… which would eject two more neutrons, which would in turn collide with another atom of uranium-235, and so on. This is the critical chain reaction at the heart of fissile power generation.
The chain reaction releases tremendous amounts of energy — so much that the moderating groundwater would heat up and eventually boil off. Thus dried up, the ejected neutrons would no longer be able to sustain the chain reaction, and the whole mess would cool down… until groundwater flooded the chamber once again.7
The caves at Oklo underwent this cycle for hundreds of thousands of years. It wasn’t the most efficient nuclear reactor, but it generated around 100 kilowatts of energy — enough to power about one hundred washing machines.
Of course, there were no washing machines at the time, and the energy didn’t power anything. Eventually, the natural nuclear reactor ran through its fuel until it no longer contained a critical mass of uranium-235. At that point, it was pretty much the same as any other uranium deposit on Earth, decaying at a constant rate, just waiting for some French folks to come along and get very confused.
Part of the reason they figured out the situation so quickly was because this naturally occurring arrangement had been predicted by physicist Paul Kuroda in 1956, and eight years later, Kuroda found a sample of pitchblende that did include a small amount of technetium-99.8
So just because element 43 was the first to be artificially synthesized in a scientists’ laboratory, it didn’t have to be.
Nowadays, we produce tons of technetium, but it might be difficult to claim it for your element collection. It’s a significant waste product of our nuclear power plants — just like it was produced at Oklo — but most government agencies aren’t too keen to send a lump of radioactive nuclear waste to your home just because you’re an avid collector of elements.
There is another kind of natural nuclear reactor that generates technetium, not through fission, but fusion: Stars.
We’ve discussed stellar nucleosynthesis before, specifically in the episodes on helium and iron, so I’ll recap very briefly: Stars smash little atoms together to make bigger atoms. That’s their whole thing. It’s what they do. Generally, stars can keep churning out elements until they get to iron, at which point, it requires too much energy to go any further.
But clearly, elements heavier than iron are somehow naturally generated. Those, too, are created inside of stars. But these heavier elements aren’t a byproduct of a star’s life. They are a consequence of the varied and violent ways a star can die. When a star becomes a red giant, or when it explodes as a supernova, or when two stars crash into each other with cataclysmic force, they can create the rest of the elements beyond iron.9 10 11 12 13
And then there are the literal oddballs. It’s very rare, but every once in a while, we come across a very peculiar kind of star. That’s actually what they’re called — “peculiar stars” — because they contain high amounts of heavy metals like technetium. They might be producing these elements through a process we don’t yet understand, or they might come from somewhere else. But the very fact that there are stars that contain technetium, an element that simply doesn’t last very long before falling apart, tells us that it’s being freshly made somehow.14
A fat lot of good that does you, though, since you can’t just pop by Przybylski’s Star for a cup of technetium on your way home. Lucky for you, and for a lot of sick people, we produce an awful lot of technetium here on Earth that has nothing to do with power plants. We make it so doctors can inject it into people’s bloodstreams.
Technetium, as we’ve learned, is quite radioactive. By mixing it with another chemical that binds to cancerous cells, then sending it coursing through a patient’s body, doctors can create an image that shows the exact size, shape, and locations of tumors. The technetium breaks down within a few hours, so the radiation doesn’t pose a significant risk for the patient.
It’s a different story for the medical staff that need to handle the stuff every day. It’s usually created on-site at the hospital from a much longer-lived isotope of molybdenum, then carted through the building in a thick-walled container that’s carefully kept a few feet away from staff at all times. It surely must be an intimidating sight when the doctor says he wants to put that inside you.
For as frightening as it can be, technetium imaging is a life-saving procedure that’s performed millions of times each year. But for those people who do interact with element 43 on a regular basis, perhaps they would rather not.
Thanks for listening to The Episodic Table of Elements. Music is by Kai Engel. To learn where else you might not want to encounter technetium, visit episodic table dot com slash T c.
Next time, we’ll regain our stability with ruthenium.
Until then, this is T. R. Appleton, reminding you that one person’s trash is another person’s historical discovery.
Sources
- Foundations Of Chemistry, Mendeleev’s Predictions: Success And Failure. Philip J. Stewart, April 5, 2018.
- The Chemogenesis Web Book, 1923: Lewis’ Periodic Table. Dr. Mark R. Leach.
- Lise Meitner: A Life In Physics, p. 465. Ruth Lewin Sime, 1996.
- The Hexagon, Rediscovery Of The Elements: Rhenium And Technetium. James L. Marshall and Virginia R. Marshall, Winter 2013.
- Scientific American, Nature’s Nuclear Reactors: The 2-Billion Year Old Natural Fission Reactors In Gabon, West Africa. Evelyn Mervine, July 13, 2011.
- International Atomic Energy Agency, Meet Oklo, The Earth’s Two-Billion-Year-Old Only Known Natural Nuclear Reactor. Laura Gil, August 10, 2018.
- SciShow, Oklo, The Two Billion Year Old Nuclear Reactor. January 12, 2015.
- Journal Of Inorganic And Nuclear Chemistry, Technetium In Nature. B. T. Kenna, P. K. Kuroda, April 1964.
- Science Blog From The SDSS, Origin Of The Elements In The Solar System. Jennifer Johnson, January 9, 2017.
- APS Physics, Viewpoint: Neutron-Star Implosions As Heavy-Element Sources. Hans-Thomas Janka, August 7, 2017.
- Science, Populating The Periodic Table: Nucleosynthesis Of The Elements. Jennifer A. Johnson, February 1, 2019.
- Space.com, What Is A Supernova? Andrea Thompson, February 9, 2018.
- CrashCourse Astronomy, High Mass Stars. Phil Plaitt, September 10, 2015.
- The Conversation, Elements From The Stars: The Unexpected Discovery That Upended Physics 66 Years Ago. Artemis Spyrou and Hendrik Schatz, May 2, 2018.
This was a great help. Thank you very much.