What Really Happened the First Time We Split a Heavy Atom in Half




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This episode of SciShow is brought to you by Emerson. Visit Emerson.com/WeLoveSTEM to learn more. [♩INTRO] Some of the most important scientific discoveries were famously made by accident like penicillin, plastic, and vulcanized rubber. But there’s one that you don’t hear about quite as often: that time in 1938 when scientists accidentally split an atom and changed the course of history. At first, they did not realize what they had done. That is, until an Austrian physicist named Lise Meitner figured out that they had discovered what we now call nuclear fission. But when a Nobel Prize was awarded for the discovery, it was her research partner who got it. Meitner was born in 1878 in Vienna, Austria. Although Austrian women weren’t taught much math or science at the time, she was curious about the world from an early age as a child, she kept a math book under her pillow. She went on to earn a doctorate in physics from the University of Vienna in 1906, which made her the second woman to receive a doctorate in any science from the school. There weren’t many opportunities for female scientists in Vienna, though, so in 1907 Meitner moved to Berlin, where she became the first woman Max Planck allowed to attend his lectures. Yeah, that Max Planck the guy who basically invented quantum mechanics. It was a good time to be a talented physicist in western Europe. Within a year, she was working as Planck’s assistant, and by 1909 she partnered with Otto Hahn, a chemist, to do research at the Berlin Institute for Chemistry. They both wanted to study how different substances produced different types of radiation. There was a problem, though: the head of the institute didn’t allow women because he was afraid their hair would catch fire. Not kidding. That’s the real reason. Eventually, Meitner and Hahn got him to agree to let them work together in an old carpenter’s shop in the basement, because it had a separate entrance… presumably so that when her hair caught fire, it was really easy to go outside. Research into radiation was still in its early days, so there was a lot to discover. Among other things, they studied what happened to different atoms when they released radiation, and discovered some new isotopes, or versions of the same element with different weights. Then, in the 1930s, physicists discovered that if you bombard atoms with neutrons, you can make them undergo radioactive decay, where they release particles and become slightly lighter elements. Meitner, Hahn, and another scientist named Fritz Strassmann started their own bombardment experiments to try and figure out how those reactions worked. And then … they were interrupted by the Nazis. When Hitler annexed Austria in March 1938, Meitner, who was of Jewish ancestry, realized that she had to get out of Germany. She escaped to Stockholm, Sweden, where she continued to correspond with Hahn about their ideas and experiments. And in November 1938, Hahn secretly left Germany to share some strange results with her: When they bombarded uranium with neutrons, one of the products of the reaction was what looked like a form of radium, which is a little lighter than uranium. They thought it was radium because of the way it reacted with other atoms and molecules, but they couldn’t figure out how bombarding uranium with neutrons would produce radium. The calculations just didn’t work out. So Meitner suggested Hahn and Strassmann study this so-called radium more. When Hahn returned to Germany, they did, and found that it wasn’t radium at all. It was barium, a much smaller element that’s about half uranium’s weight. Hahn and Strassmann were then super confused. They had no idea how neutrons could make uranium turn into an element half its size. In December, Hahn sent a letter to Meitner about their findings asking for her help explaining them. And in the meantime, he and Strassmann submitted a paper to a German scientific journal describing these surprising results. Meitner’s nephew, Otto Frisch, was visiting her at the time, and he also happened to be a nuclear physicist. So the two of them worked on the problem together. Meitner proposed that they imagine atomic nuclei as liquid droplets, which was an idea some physicists were exploring at the time. By thinking that way, Meitner realized that when a neutron hits a uranium nucleus, it could make the nucleus sort of stretch out, and then pinch together in the middle and then split in two like one drop of water splitting into two smaller droplets. She and Frisch calculated that the larger uranium atom would split into two lighter elements — barium and krypton plus a bunch of neutrons and a whole lot of energy. In other words: she figured out nuclear fission. Since she was essentially in exile, Meitner couldn’t publish a paper with Hahn and Strassmann. Instead, she and Frisch published their conclusions in the journal Nature in February of 1939. Fission was an idea with a ton of potential. It was a relatively simple way to produce huge amounts of energy which is the main thing we use it for today, in nuclear power plants. But Meitner realized that it had destructive potential, too, and she included a warning about that in the paper. Other scientists were … alarmed. Especially because they knew the Germans had this knowledge through Hahn and Strassmann. Three physicists in the U.S. then got Albert Einstein, who was already very famous, to write to President Roosevelt to explain the danger. And that is how the Manhattan Project that developed the atomic bomb was born. Meitner was asked to help with the project, but she refused she didn’t want anything to do with using this new science for destructive purposes. After the war, the Nobel committee awarded the Nobel Prize in Chemistry for discovering nuclear fission to Otto Hahn. Just Otto Hahn. Even though Meitner figured out how nuclear fission actually worked, Hahn got all of the credit just because he ran the experiments that led to the discovery. And it’s not like he acknowledged her contributions, either. Meitner continued to do nuclear research in Stockholm including on R1, Sweden’s first nuclear reactor until 1960, when she retired and moved to the U.K. In 1966, she, Hahn, and Strassmann shared the U.S. Department of Energy’s prestigious Enrico Fermi Award for the discovery of nuclear fission. But it still wasn’t a Nobel. Two years later, on October 27, 1968, Lise Meitner died at the age of 89. Since her death, she’s been memorialized in other significant ways this is actually way more rare than getting a nobel: Element 109, meitnerium, is named in her honor. And so are an asteroid and craters on Venus and the Moon. Which is fitting, given that her discoveries shaped a lot of the world as we know it, and her education and research helped pave the way for other women in STEM fields. But above all, she dedicated her life to the pursuit of truth and the peaceful advancement of our knowledge as a species whether she was recognized for it or not. So maybe the inscription on her tombstone is what best summarizes her legacy: “Lise Meitner: a physicist who never lost her humanity.” Thanks for watching this episode of SciShow, and thanks to Emerson for sponsoring it. If you want to keep getting smarter with us, just go to youtube.com/scishow and subscribe. And if you want to support us, check out Emerson.com/WeLoveSTEM to learn a little bit more about what Emerson’s about. [♩OUTRO]