27. Cobalt: Mischief Managed

Cobalt is a tricksy little element, which means the scientists who’ve dealt with it the most are some of the cleverest people to have ever walked the Earth.

Featured above: Chien-Shiung Wu doing what she loved most.

Show Notes

Dog People Or Dragon People? Gamers among the audience will recognize “kobolds” as the trap-crafting cave-dwellers from many fantasy role-playing games. This is their origin, as well! However, Dungeons & Dragons is responsible for creating a distinction where previously there was none, as kobolds, goblins, bugbears, boogeymen, and many other creatures from European folklore used to all be different words for the same thing, with the same etymological origin.

Master of DMCA Takedown Notices: You might have noticed that the music played in the background is definitely not Ride the Lightning by Metallica. If you were around for the downfall of Napster, you understand why.

“The Wu Experiment” Would Be A Decent Band Name: Suffice it to say, I simplified things a great deal for the sake of explaining Chien-Shiung Wu’s parity experiment. My aim was to make it as easy to grasp as possible without actually misleading any listeners, so anyone curious could continue studying what Wu did.

First of all, parity symmetry *does* hold true in the vast majority of circumstances, in the same way that you don’t need to employ the theory of relativity when calculating the trajectory of a cannonball. For the strong nuclear force and for electromagnetism, parity symmetry holds up. Wu directly tested the veracity of parity on the weak nuclear force.

And, just for the record, Wu’s experiment suggests that our universe is “a semiambidextrous southpaw.”

Veritasium made a pretty great video recently that explains the experiment in a little more detail:

Nonetheless, this is still kind of a watered-down explanation. That’s kind of necessary. To wit: On the Ask Science subreddit, /u/Greebo24 explained what made cobalt the ideal material for Wu’s experiment:

  1. It is a Gamow-Teller decay with a spin difference of 1 (ground state of 60 Co is 5+, decaying into the first 4+ state in 60 Ni) Quote: “One might point out here that since the allowed beta decay of Co involves a change of spin of one unit and no change of parity, it can be given only by the Gamow-Teller interaction. This is almost imperative for this experiment.” It is required so that the electron helicity and the neutrino helicity are well defined. Both the electron spin and the neutrino spin have to add in a maximally stretched configuration to the Ni 4+ state to get the Co 5+ state. This makes it possible to deduce the neutrino helicity from all other observables.
  2. Co can be polarised “by the Rose-Gorter method in cerium magnesium (cobalt) nitrate, and the degree of polarization detected by measuring the anisotropy of the succeeding gamma rays.” This cools the salt containing the Co down into the mK range.

If that makes sense to you, congratulations, because you’re in the 1% of people who might not be alienated by that kind of heady material.

Ain’t No Blues: Blue is not a common color in nature. Even blueberries aren’t exactly blue. Joe Hanson spends an episode of It’s Okay To Be Smart explaining why that is — and explains how butterflies created the color blue not with pigments or dyes, but with tiny microscopic structures:

And Vsauce2 discusses the “invention” of blue here — more of a slow acknowledgement that blue is its own color, but nonetheless interesting:

Fun Fact: If you search youtube for “cobalt blue” you’re gonna see a lot of spiders. You’ve been warned.

Episode Script

Mining is a hazardous job. Not only do miners brave the dangers of cave-ins, suffocation, and floods, but often, whatever material they’re fetching is lethal in its own subtle ways. Coal miners take precautions against black lung, and we’ve learned about berylliosis and “manganese madness” in episodes 4 and 25, respectively.

For centuries, German copper and silver miners dealt with a danger that was not only subtle, but deceptive: Sometimes, when they brought their ores back for smelting, the process would completely fail to yield any metal. Even worse, the fumes would cause people to fall terribly ill, or even die.

The miners would shake their fists in the mine’s direction and curse the mischievous subterranean spirits that had played such a mean trick on them. They called these creatures kobolds.

In 1735, Georg Brandt analyzed such ore and found that it contained an as-yet-unknown element. His decision to name the material after those devilish rapscallions was a nod to those hardworking miners, but coincidentally, it’s pretty appropriate for the character of this transition metal, too. Cobalt is colorful, and crafty. And under a particular set of circumstances, it could — hypothetically — be quite calamitous.

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 turn to cobalt.

Imagine you’re looking down on a crowd milling about, waiting for a Metallica concert to start. They’re facing all different directions, talking to each other or standing in line for a beverage, maybe shouting at other people across the floor. Everyone is doing their own thing.

This is kind of similar to what’s usually going on with matter. If you have a lump of cobalt, the atoms within are all doing their own thing with little regard for each other.

But now, let’s imagine James Hetfield walks onstage and starts playing the opening chords to Ride the Lightning. Amidst the cheers and screams, everyone in the crowd is going to immediately turn to face the stage.

When we expose our lump of cobalt to a magnetic field, a similar sort of thing happens. Its constituent atoms will now immediately turn to align themselves with that field.

That’s what’s called ferromagnetism, and it’s a pretty rare property among the elements. Only iron, cobalt, and nickel reliably exhibit ferromagnetism. A few others can be cajoled into acting this way under certain conditions, but the whole group numbers fewer than a dozen.

Being part of this elite squad was one of the factors that led to its use in an experiment that completely shattered our understanding of the universe.

By the time she turned 40, Chien-Shiung Wu was already an admirably accomplished scientist. She had performed research and taught classes in the new field of x-ray crystallography, she had done important work on the Manhattan Project during World War II, and she had broken barriers of racism and sexism both in her native China and in her new home, the United States. In 1942, she became the first woman to teach at Princeton University, and ten years later she was the first woman to achieve tenure at Columbia University.1 2 3

By 1956, she was quite understandably ready for a break. War and political turmoil had rendered it impossible for her or her husband to visit their family in China since they had left twenty years earlier, so they were planning to finally make that trip that December.4 5

But for as excited as she was to see her family, her mind was elsewhere. Her colleagues in the lab had recently proposed an idea that she just couldn’t stop thinking about. To understand it, we’ll need to start with a little background first.

There’s an idea in physics called “symmetry,” which contends that nature doesn’t prefer whether you do things forwards or backwards.

There are different kinds of symmetries. For instance, charge symmetry suggests that if you were to swap all the particles in a chemical equation for their antiparticles — positrons for electrons and antiprotons for protons — the calculations will work out the same. It’s kind of like comparing the equation “two plus three” against the equation “negative two minus three.” Either way, you wind up with an absolute value of five.

Another kind of symmetry is called parity symmetry. The idea here is that if left were swapped for right, the rules of chemistry and physics should work exactly the same as they do now. Nature shouldn’t care if the universe is left-handed or right-handed. It should, in theory, be impossible for a scientist to conduct an experiment that will tell them whether they’re in the regular universe or the mirror universe.6

In the 1950s, this idea was taken for granted — it made so much sense that physicists just assumed it was true, in the same way you assume that if you jump in the air, gravity will pull you back to the surface of the Earth. You don’t for a second imagine that you might keep flying upwards.

But two of Chien-Shiung Wu’s colleagues had recently pointed out that no one had ever actually tested this theory, and, well, shucks, isn’t that what scientists are supposed to do?

That was the annoying fact that Wu couldn’t shake. She was one of the world’s leading experts in this stuff, and she knew just how she would conduct such an experiment. But if she went on vacation, surely some other scientist would beat her to it and publish their results first.

She insisted that her husband go on the trip as planned, but Wu stayed behind. She resolved to visit her family as soon as she could. For now, she had work to do.

The linchpin of Wu’s experiment was cobalt-60, an isotope of element 27 that’s not only ferromagnetic, but also mildly radioactive. Every so often, a sample of cobalt-60 will emit a beta particle.

So Wu took her sample of cobalt-60 and magnetized it. Remembering our prior illustration, this means that all the atoms of cobalt-60 were pointing in the same direction. Now, if parity symmetry were true, the cobalt sample shouldn’t show a preference for what direction it throws its beta particle while undergoing radioactive decay.

Let’s return to our concert example from earlier. The crowd has been magnetized, so everyone is looking at the stage. To represent radioactivity, let’s say that this crowd is particularly rowdy, so every once in a while, someone in the audience violently throws their beverage. That beverage is like a beta particle.

Even though everyone is looking at the stage, you shouldn’t be able to predict which direction the crowd is going to throw its beverage. It might get thrown stage left, or stage right, or smashed down on the ground, or toward the exit.

But what Wu observed was that the magnetized cobalt-60 did show a preference. It emitted almost all of its beta particles in only one direction. It’s like if everyone at the Metallica concert decided to hurl their bottles only at drummer Lars Ulrich, pelting him incessantly the whole time.

The implication was that if the experiment were conducted in a mirror universe, the beta particle would be emitted the other way — that is, everyone in the crowd would whip their bottles and cans over their shoulders, in the opposite direction of Lars.

This was a shocking and unexpected result. According to parity symmetry, it should be impossible to deduce whether we live in a “regular” universe or a mirror universe, but that’s exactly what this experiment suggested.

These results took the scientific community by storm. Wolfgang Pauli, a prominent contemporary of Wu, declared that it was “total nonsense!” But the results were easily reproduced by other scientists, and the fact was undeniable: parity symmetry had fallen. This was one of the key experiments that would eventually lead to the Standard Model of physics, the most complete understanding of the universe that science has yet achieved.

The 1957 Nobel Prize in Physics was in the bag. …But not for Chien-Shiung Wu. The committee awarded the prize to her two colleagues who had suggested the experiment — colleagues who just so happened to be male. For actually conducting the experiment that proved that subatomic particles display a preference for left versus right, the Nobel Prize Committee didn’t recognize Wu at all.7

A few years later, during a symposium at MIT, she commented,

I wonder whether the tiny atoms and nuclei, or the mathematical symbols, or the DNA molecules have any preference for either masculine or feminine treatment.”8

Chien-Shiung Wu might have broken the rules of nature with a piece of cobalt, but most people probably didn’t notice. Around the same time, nuclear physicist Leo Szilard proposed a use for cobalt that would have been impossible to miss.

Szilard was one of the numerous brilliant scientists who fled to America in the 1930s due to the threat of war in Europe. He was the man who first theorized the nuclear chain reaction, which was the mechanism at the heart of the first atomic bombs. But before those could be built, someone would have to convince the government that it would be worth all the time, money, and research necessary to build them.

He decided to write a letter to Franklin D. Roosevelt, then president of the United States, outlining the unimaginable danger of such a weapon and warning that Nazi Germany was surely trying to develop one. The only option, Szilard implied in his letter, was for the United States to beat them to the punch.

But getting the attention of the American President was at least as difficult in 1938 as it is today, and Szilard knew that he didn’t have that kind of pull. He did, however, have one very influential friend: Albert Einstein.

Einstein was just as much of a household name in the 1930s as he is today, largely thanks to his theory of relativity. So he signed his name to Szilard’s letter. Even so, it almost never made its way to FDR’s desk — there was a World War going on, after all, which tends to be a rather distracting thing.9

Of course, FDR did read the letter, and the years-long Manhattan Project was successful in creating the atomic bomb… and Szilard was horrified.

The problem wasn’t that the U.S. had built the bomb. Szilard had directly worked pretty extensively on the Manhattan Project, after all. But he had also written the Szilard Petition, a proposal signed by 70 scientists urging that the bomb be used only as a deterrent, not ever as a weapon. Further, it suggested that after the war, the bomb should be placed under international control in an effort to discourage an arms race.

This letter would never make its way to the president’s desk. Secretary of State James F. Byrnes thought the idea was preposterous, and refused to deliver the letter. Most of the signees never worked on a weapons project again, and of course, the United States dropped atomic bombs on the Japanese cities of Hiroshima and Nagasaki, killing hundreds of thousands.

Szilard was disappointed in the country and in himself. He spent much of his life trying to convince the public that nuclear weapons were something that should be destroyed, not stockpiled. To illustrate that point, on a radio program in 1950, he explained how these bombs were capable of destroying not just entire cities, but all life on earth.

The way to accomplish this would be with what Szilard called a “salted” nuke. That is, the bomb would have a little extra something added, in the same way you might “salt” your food. The extra something he proposed was cobalt.

The cobalt wouldn’t have any effect at all on the nuclear explosion. It was the other way around: The explosion would transform the cobalt into its radioactive form of cobalt-60, then spread it all across the globe as extremely potent fallout. This would be especially lethal because cobalt-60 occupies a sort of radioactive middle ground: Other elements emit more radioactive energy, but they run out of juice in a matter of hours. On the other hand, some elements stay radioactive for centuries, but emit radiation so slowly that they’re not really a threat. Cobalt-60 would strike just the right balance: Potent enough to kill a human, with a long enough half-life to keep the landscape uninhabitable for a decade or more.10

Again, Szilard wasn’t suggesting that this was a good idea. He was trying to convince people that nuclear weapons are far too horrible to consider using.

Clearly, we did not collectively destroy our nuclear stockpiles. But, in one of the few historical examples of human restraint, neither did anyone start building cobalt bombs. (At least, as far as the public knows.) And the morbid picture painted by Szilard tended to stick with people. In 1958, Frederick Winsor wrote The Space Child’s Mother Goose, which contained the following rhyme:

The hydrogen dog and the cobalt cat
side by side in the armory sat.
Nobody thought about fusion or fission,
Everyone spoke of their peacetime mission.
Till somebody came and opened the door.
There they were, in a neutron fog,
The Codrogen cat and the hybalt dog;
They mushroomed up with a terrible roar–
And Nobody Never was there — Nomore.

In an odd twist of fate, in 1960, radioactive cobalt would actually save Leo Szilard’s life. That year, he was diagnosed with bladder cancer, and cutting-edge radiotherapy that employed cobalt-60 completely eradicated the disease from his body.11

Considering we’ve spent most of this episode discussing one rather dangerous isotope of element 27, you’ll be relieved to know that you’re far more likely to encounter cobalt as a completely stable and ordinary metal that nonetheless has plenty of uses.

For centuries, cobalt has been used as a naturally occurring source of the color blue, particularly in paints and for decorating porcelain. Similarly, it’s almost certainly present in any beautiful blue glass you can get your hands on.

Alongside vanadium and lithium, cobalt is an element that’s important in the production of batteries, so if you prefer to collect your elements by adding them to your portfolio of financial assets, you’ll find plenty of experts trying to convince you that there’s a fortune to be made with cobalt.

Personally, I have no idea if that’s correct or crap. But speaking of crap, you could try to harvest element 27 from cat litter. It’s sometimes added to the mixture in the form of blue crystals that change color when it’s time to throw it out. That’s a practice that’s losing popularity, however, as veterinarians warn that it might not be the healthiest thing for your cat.

Similarly, there was at least one case, in the 1960s, where cobalt was added to a particular brand of Canadian beer as a foam stabilizer. But when customers started suffering a higher-than-average rate of heart disease, cobalt was removed from that, too.12

The discerning collector will need to pack their bags this time, because the most reliable place to find pure cobalt is right at the source, and the Democratic Republic of the Congo is responsible for producing over half the world’s supply. To put it lightly, raiding the mines of the Congo would be a perilous journey.

But please, don’t let all this scare you away. Like many of the others we’ve looked at, today’s element is a crucial part of a balanced diet. In the same way magnesium sits at the center of chlorophyll, so does cobalt sit at the center of the vitamin B12 molecule, a nutrient that’s used by every cell in the human body.

British chemist Dorothy Hodgkin discovered that little tidbit using a technique called protein crystallography, and for that, she won the 1964 Nobel Prize in Chemistry — one of only five women who have earned that honor, as of 2018.

There is probably no more concentrated food source of vitamin B12 than the yeast byproduct known either as Vegemite or Marmite, depending on where you’re from. It’s a beloved victual, especially in Australia and the United Kingdom, but it would be an understatement to say it’s something of an acquired taste. Personally, I believe you should always have a jar on hand, whether you’re an element collector or not, just in case you unexpectedly need to provide a snack for your most hated enemy.

Thanks for listening to The Episodic Table of Elements. Music is by Kai Engel. To learn how I grossly oversimplified the Wu experiment, and see how butterflies solved a chemistry problem with engineering, visit episodic table dot com slash c o.

Next time, we’ll buy ourselves something nice with nickel.

Until then, this is T. R. Appleton, reminding you to take my culinary recommendations with a grain of salt as I am but a boorish and uncouth American.


  1. Scientific American, Channeling Ada Lovelace: Chien-Shiung Wu, Courageous Hero Of Physics. Maia Weinstock, October 15, 2013.
  2. Time, The Manhattan Project Physicist Who Fought For Equal Rights For Women. Joanna Scutts, June 14, 2016.
  3. ThoughtCo, Chien-Shiung Wu: A Pioneering Female Physicist. Jone Johnson Lewis, February 10, 2018.
  4. The New Inquiry, Where State Politics Meets Gender Politics: Chien-Shiung Wu And The Manhatthan Project. Kanta Dihal, January 18, 2018.
  5. Gizmodo, Madame Wu And The Holiday Experiment That Changed Physics Forever. Jennifer Ouellette, December 31, 2015.
  6. Hackaday, There Is No Parity: Chien-Shiung Wu. Will Sweatman, September 28, 2017.
  7. Berkeley Lab, Chien-Shiung Wu, Physicist Who Helped Change The World. May 19, 2015.
  8. Biography.com, Chien-Shiung Wu.
  9. The Atomic Heritage Foundation, Einstein-Szilard Letter. Primary source.
  10. Nuclear, Biological, And Chemical Warfare, p. 76. K. Bhushan, G. Katyal, 2002.
  11. MotleyTech.net, The Man Who Changed War, Peace, And The World. March 29, 2015.
  12. Cambridge Polymer Group, Cobalt Brew: Frothy Foam, Sick Heart. May 18, 2017.

5 Replies to “27. Cobalt: Mischief Managed”

  1. I’ve just discovered your podcast, and am enjoying it on several levels. Despite you mentioning the website in each episode, it has taken me until chromium to take a look. I had to say that your sting-in-the-tale “recommendation” for marmite made me chuckle, as a marmite-loving Brit. Having initially missed your final few seconds, I have now read in the transcript your final caveat on your culinary recommendations and thus I forgive your boorish American-ness 😉

Leave a Reply