Lise Meitner

Melvyn Bragg and guests discuss the decisive role of one of the great 20th Century physicists in solving the question of nuclear fission. It is said that Meitner (1878-1968) made this breakthrough over Christmas 1938 while she was sitting on a log in Sweden during a snowy walk with her nephew Otto Frisch (1904-79). Both were Jewish-Austrian refugees who had only recently escaped from Nazi Germany. Others had already broken uranium into the smaller atom barium, but could not explain what they found; was the larger atom bursting, or the smaller atom being chipped off or was something else happening? They turned to Meitner. She, with Frisch, deduced the nucleus really was splitting like a drop of water into a dumbbell shape, with the electrical charges at each end forcing the divide, something previously thought impossible, and they named this ‘fission’. This was a crucial breakthrough for which Meitner was eventually widely recognised if not at first. With Jess Wade A Royal Society University Research Fellow and Lecturer in Functional Materials at Imperial College, London Frank Close Professor Emeritus of Theoretical Physics and Fellow Emeritus at Exeter College, University of Oxford And Steven Bramwell Director of the London Centre for Nanotechnology and Professor of Physics at University College London Producer: Simon Tillotson Reading list: Frank Close, Destroyer of Worlds: The Deep History of the Nuclear Age, 1895-1965 (Allen Lane, 2025) Ruth Lewin Sime, Lise Meitner: A Life in Physics (University of California Press, 1996) Marissa Moss, The Woman Who Split the Atom: The Life of Lise Meitner (Abrams Books, 2022) Patricia Rife, Lise Meitner and the Dawn of the Nuclear Age (Birkhauser Verlag, 1999) In Our Time is a BBC Studios Audio Production

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  This is In Our Time from BBC Radio 4. And this is one of more than a thousand episodes you can find on BBC Sounds and on our website. If you scroll down the page for this edition, you'll find a reading list to go with it. I hope you enjoy the programme. Hello. Over Christmas 1938, the physicist Lisa Meitner, a Jewish Austrian refugee from Nazi Germany, solved the question of nuclear fission. It said she was sitting on a log in Sweden at the time on a snowy walk with her nephew Otto Frisch. Others had already broken uranium into the smaller atom barium, but couldn't explain their findings. Was the larger atom bursting, or the smaller atom being chipped off, or something else? They turned to Meitner.

• 2:32Speaker 06

  She deduced the nucleus was splitting like a drop of water, something previously thought impossible, and named this fissure. In all, a crucial breakthrough for which she was eventually widely recognised, but not as we'll hear at first. With me to discuss, Lisa Meitner, I just Wade, a Royal Society University Research Fellow and lecturer in functional materials at Imperial College London; Frank Close, Professor Emeritus of Theoretical Physics and fellow emeritus at Exeter College, University of Oxford; and Stephen Bramwell, Director of the London Centre for Nanotechnology and Professor of Physics at University College London. Jess, Lisa Meitner was born in 1878 in Vienna. Can you tell us something about her early life?

• 3:16Speaker 07

  Yeah, fantastic. She was born to a Jewish father, actually, who was one of the first Jewish lawyers to be registered in Austria. She was one of eight children, and she grew up in this incredibly liberal, free-thinking household where she was encouraged, amongst her brothers and sisters, to go and pursue higher education. All of the children went to pursue higher education, including five daughters, four of whom went on to get PhDs. So they were incredibly committed to raising children who were really strong in academia. She was always passionate about science, grew up doing her own experiments, had a little science logbook that she kept underneath her pillow to document observations that she made about the world around her.

• 3:53Speaker 06

  At the age of 10?

• 3:54Speaker 07

  At the age of 10. So you could see her commitment, but actually recognised that she may not be able to achieve the things that she wanted to in science, in academia, because of the restrictions placed on women at the time. So completed via some private tuition exams or training to be able to complete exams, to be able to get into university, but also undertook training to become a teacher if she couldn't pursue those ambitions she had in the sciences. So very forward-thinking, very, very ambitious scientifically, very, very creative, but not sure about what future it could hold for her because she was a woman.

• 4:27Speaker 06

  To go back a few sentences on what you said, which is, what opportunities were there in Austria and Germany for someone who wanted to, for a woman, who wanted to be a scientist?

• 4:36Speaker 07

  I suppose Lisa Meitner came at this really interesting time because everything was changing, you know, in the late 1800s, I think 1897, Austria allowed women to go to university. It took a few years after that for them to be able to go and study medicine and the sciences. Lisa Meitner entered university in 1901, actually after undergoing some private tuition and completing an exam at the boys' school. So she had to go and do an exam at the boys' school to be able to get in. Of the people who passed that exam, of the girls who passed that exam, there were four out of 13 of them who took the exam. She ended up going to university in the University of Vienna to study physics. And doing a PhD, she was only the second woman physicist to earn a PhD at the University of Vienna. So there were a lot of barriers to women being able to progress their scientific careers.

• 5:20Speaker 07

  But she was at the right time for that transition starting to happen. So she eventually managed to get her degree and get her PhD at the University of Vienna. But almost every room she went into, she was one of a handful, if not the only woman, and treated differently as a result of it. And you saw it throughout her scientific career. Whilst her contemporaries were allowed to practise science, be paid salaries to practise science, she was eventually let into these spaces, allowed to be a scientist, but not paid properly. Eventually paid a little bit, but not recognised, not respected properly. So she had immense prowess. She was obviously phenomenally bright, very gifted in mathematics. Built this reputation on how brilliant she was. But there are a lot of institutional barriers that at the time weren't ready to accept women. When she went on to work with Planck, when she eventually got to Germany,

• 6:05Speaker 07

  he was very, very surprised that a woman would want to come and study these types of things, would only let her in originally to audit the lectures that he was giving to the community. Max Planck, who'd recently won a Nobel Prize, but had done huge amount of work in the early 1900s on discovering quantum theory. So that was all happening at the beginning of the 1900s, when Lisa Meitner was learning physics with Boltzmann. She then got to Germany, met Planck, and had this huge revelation about how much physics was working and evolving and developing during that time. And eventually Planck employed her as an assistant in 1912, and then she was the first woman professor of physics in 1926.

• 6:43Speaker 06

  Do we know how she stood up to this constantly being rebuffed one way or another?

• 6:47Speaker 07

  I think she stood up to it by just being incredibly resolute and headstrong and brilliant. You know, she found ways, she befriended a lot of these people. I think she had huge interpersonal skills when she got to Germany and worked under Planck, and Planck eventually paid her a salary. But there were all these times when she was either not paid at all or was only paid half of what she should have been. The thing I find most amazing about it is until her father died in 1910, he was responsible for paying her salary entirely. So her father had to maintain her abilities to be able to study and work in the sciences.

• 7:23Speaker 06

  Thank you. Frank Close, what was the understanding of the atom in the early 20th century when Meitner was still studying?

• 7:32Speaker 08

  Well, as you sort of intimated, Lisa Meitner arrived in science at a time of great change. At the end of the 19th century, chemistry was an established science. The idea that everything was made of elements was well established. And the idea that elements, the smallest piece of an element is an atom, and that the atom is indivisible, it's permanent, it's unchanging, that all the atoms of a particular element are identical, and that you could rate the atoms in relative order of masses. Mendeleev had got a periodic table, the idea that the hydrogen atom at number one is the lightest, right the way up to uranium at number 92, the heaviest naturally occurring

• 8:17Speaker 08

  one. And into this world, the discovery of radioactivity in 1896, really through the spanner in the works metaphorically, in that atoms of uranium were discovered to spontaneously emit radiant energy, radioactivity, without apparently changing. And it became clear that this had been going on without stimulus for as long as uranium had existed, you know, millions, billions of years, which itself was astonishing. The Curies then discovered that other elements are radioactive. They discovered radium and polonium. Radium was so active that it would glow in the dark.

• 8:58Speaker 08

  And the calculations that they did showed that if you had a piece of radium about the size of a pea, the amount of energy locked in the atoms somehow, if you could access it, would be enough to drive a ship across the Atlantic, which was astonishing.

• 9:14Speaker 06

  That's amazing.

• 9:15Speaker 08

  Absolutely amazing.

• 9:16Speaker 06

  Just a second while we recover from this.

• 9:18Speaker 08

  Well, yes, also you might have to wait a hundred years to get across because the problem was that this radioactivity was just dribbling out. It had been doing it for billions of years, but could you speed it up? Well, the first question was, what is it? Where is it coming from and so forth? So that was the world into which Lisa Meitner arrived. The fascination with radioactivity and indeed the work of Marie Curie was one of the inspirations for her. And it was that that brought her eventually to Berlin, where she met Otto Hahn, with which her research career began.

• 9:52Speaker 06

  What did he do?

• 9:54Speaker 08

  Otto Hahn was a chemist. He was, within a few months, the same age as Lisa Meitner. He had been studying, among others, with Ernest Rutherford, trying to understand radioactivity. He had discovered some other radioactive elements he thought they were. And then he met Meitner. He was in Berlin as a chemist and the physicists were more enthusiastic about this radioactivity phenomenon than the chemists were.

• 10:26Speaker 06

  Why?

• 10:27Speaker 08

  Well, it was very subtle. I mean, Hahn was able to detect the presence of things by the radiation they were emitting. But many of the chemists at that time, they would only believe that you got something if you could weigh it or at the very least smell it. The idea that this person could detect it by radiations, it was like a charlatan as far as they were concerned, whereas the physicists were, let's say, more adventurous. And so he started going to the physics lectures. And that is where he met Meitner as one of the students. And she struck him as very enthusiastic and also skillful. And he realised that the two of them together, he the chemist and she trained in physics and interested in radioactivity,

• 11:08Speaker 08

  could perhaps combine and start investigating what is this radioactive phenomenon? What is giving rise to it? What can we learn about it? And that's how they began in nineteen oh seven, I think it was.

• 11:19Speaker 06

  What did they learn, led on?

• 11:22Speaker 08

  Well, over a series of, well, the immediate next few years, but over the next decades, I think they're the people who probably established what I would call the radioactive ladder. I mean, uranium was the heaviest naturally occurring element, which was at number ninety-two, if you like. Lead, the heaviest stable element, is at number eighty-two. The discoveries by the curies of radium and polonium were somewhere in there. And it was Hahn and Meitner, who by studying radioactive decays, were able to establish the chain of order, uranium decaying into maybe thorium,

• 12:06Speaker 08

  down through polonium and radium, ending up as lead. This ladder they established. There were two types of radioactivity, alpha and beta. The alpha shifted you two places at a time, so ninety-two to ninety to eighty-eight, through the even numbers. Beta shifted you one, it took you from an even to an odd and tumbled down to bismuth. But one of the things that's coming clear from this is that radioactivity changes one element into another. The atoms are not permanent existing things, they themselves somehow change. So they established the ladder of radioactivity. And now the question was, what is causing this?

• 12:50Speaker 08

  What is going on inside the atom that can enable this energy to be emitted? And where in the atom is this energy stored?

• 12:59Speaker 06

  Before we go on, Stephen, Stephen Bramall, can you explain to the listeners and to me the difference between the chemist's approach to the atom and then the physicist's approach?

• 13:11Speaker 09

  Yeah, so the chemists, as Frank has already mentioned, had the concept of chemical elements, and that had become associated with particular atoms. But this revolution in physics that was going on was showing that it was more complicated than that. So, an atom of uranium, say, can also have what we now call different isotopes, which are different masses but the same chemical properties. And so, the basis of chemistry was evolving at this point, and the understanding of the physics of the atom was also evolving. And to do this sort of research, you needed both physics and chemistry. So you needed to detect the radiation to understand the processes that were going on.

• 13:53Speaker 09

  But you also needed chemistry to isolate different parts of your material sample, to sort of isolate the radiation in a certain place, and then you could study it. And this is very complicated work. I mean, Frank's described this ladder of radioactive decays, and it's complicated because as uranium goes down this ladder, for example, some isotopes are long-lived, some are short-lived, sometimes the radiation builds up, sometimes it goes away. You have to intervene and do a bit of chemistry, some quite complex chemistry, to separate out your different types of atom. And I think one thing to recognise here is that you need both physics and chemistry

• 14:37Speaker 09

  to do this, you have to have them working together. And at the same time, because both the basis of physics and chemistry are changing, it's not very clear to anyone, is this physics or is it chemistry? Is it both? Is it neither? And so, one thing I think that, to me, illustrates that dilemma quite a lot is that Rutherford, of course, who was fame, you know, was an extremely famous physicist, he was awarded the Nobel Prize in Chemistry, not in Physics, which amused him because he knew he wasn't a chemist, and he felt what he'd done was physics. But but I think it just goes to show that it was hard to classify this kind of research and very hard to put in a box.

• 15:15Speaker 08

  Can I just add something to what you're saying there? Because I made it sound very simple, though uranium's at number ninety two, lead's eighty two, there's just ten in there. There's ten chemical elements in there, but what Hahn and Meitner found, as Steve sort of alluded to, was there were lots of different radioactive sources in there. And that's what gave rise to the idea of isotopes, which this is maybe more Steve's area, but a given chemical element can have different radioactive behaviours.

• 15:42Speaker 06

  How did Meitner discover a new atomic element?

• 15:46Speaker 09

  Yeah, so this is a particularly interesting story because when chemists developed the periodic table in the eighteen sixties and eighteen seventies, the work of Mendeleev, they arranged the elements according to what was clearly became the mass of the atom, but also their chemical properties. But they left gaps in the periodic table. And it gradually became clear that there were elements to be discovered in these gaps. And it became a bit of a sport to discover a new element and fill in the gap in the periodic table. Now, now, one of these gaps was element ninety one, which is just to the left of uranium. And two spaces to the left of that, you have actinium.

• 16:31Speaker 09

  Actinium is a radioactive element that is found in uranium deposits. But no one knew how you got from uranium to actinium. But it became clear from, as Frank was saying earlier, alpha particle emission moves you two spaces to the left. So it became clear that actinium was coming from the unknown element ninety one that nobody had ever seen. So Meitner and Hahn decided to plunge into this game and try and find the mother substance of actinium. It is a very bold thing to do because This was really being competitive with the best groups in the world at that time.

• 17:12Speaker 09

  And it also involved experiments that would take years to complete because there was weak radioactivity, they had to wait for other sources of radioactivity to die down and then they could do their chemistry. So they set up these long-term experiments. And then the first war all started. Hahn signed up as a soldier. Meitner initially signed up as an X-ray operative, but didn't have much to do, so she came back to the lab. The lab was very empty at this point, the young men were either at war or they were working on military projects. So she, pretty much on her own, just, she did all the physics, she did all the chemistry, some very hard chemistry that most physicists would not want to do.

• 17:55Speaker 09

  Hydrofluoric acid and this sort of boiling concentrated sulfuric acid and this sort of stuff. And she did things like procuring the earth from which you, you got the, the starting products. He occasionally came back from the front and, and joined in. But it was mainly her and gradually she isolated the mother substance of actinium, this new element, element 91. She published it with Hahn. She properly recognised that he was involved, even though she'd done most of the work.

• 18:28Speaker 06

  More than he did about her on many occasions.

• 18:31Speaker 09

  Yeah, well, later on, when the tables returned, it wasn't so straightforward. But they called it protactinium, the mother substance of actinium, and they're now a day's recognised as the discoverers of that element.

• 18:43Speaker 06

  Thank you. Jess, Jess Wade, why was this thought to be such an enthralling, exciting time for Meitner and for science in general?

• 18:51Speaker 07

  Well, I suppose for Meitner, it's easy, she absolutely loved this, she was born to do this, she was a brilliant physicist, a brilliant mathematician, and as we've just heard, a brilliant chemist. So it was the exact perfect time in history for her to be. But because so many exciting things were happening in, in physics and in chemistry, populating the periodic table, there was the development of atomic theory, so many Nobel prizes being given to understanding atomic structure, there was the beginning of quantum physics, the development of electromagnetic theory, there was so much going on in science to be excited about.

• 19:20Speaker 06

  And so many fine scientists, could you give us a few names?

• 19:22Speaker 07

  So many fine scientists in the same place. I mean, Berlin seemed to be this hotspot of Einstein, of Planck, of Niels Bohr, of Lisa Meitner, of Nernst, of Laoi discovering these X-ray. Interference fringes and they had these colloquia on a Wednesday which attracted the biggest names in physics from all around the world to come and give talks. And I think that probably continuously inspired her to think in these different directions and be always curious, always creative in the approach that she took to trying to decipher these really tricky problems. Rutherford came on the way back from giving his Nobel Prize lecture in Stockholm and came back through Berlin, gave one of these Wednesday colloquia when he was very surprised to find Lisa Meitner was a woman because he'd read all of her work thinking Lisa was probably a man's name.

• 20:04Speaker 07

  But it was through these that she managed to build these social connections with physicists as well. She became great friends with Niels Bohr, great friends with Max Planck. When Niels Bohr first came to give his series of lectures and he'd go on to win a Nobel Prize later for atomic structure. All of the young, early career scientists, of which Lisa Meitner was one, in the audience felt very silly, felt they didn't understand anything, felt he was speaking a different language because his science jargon was different to their science jargon. Five of these early career scientists went on to win Nobel Prizes, so they were truly brilliant. But they got together and said, actually, can we invite Niels Bohr to do a special day for early career people to come out and explain this science to us? So they had a special meeting, this workshop, they called it the meeting without the big wigs.

• 20:49Speaker 07

  So that was the the formal title of this occasion, where they just got to ask questions to Niels Bohr about science and make sure they understood it. So I think it was a fantastic time for science because so many discoveries were happening where even though you had to be technically brilliant, you didn't need massively complicated scientific equipment to get it going. But also there was this kind of movement of great ideas through a system that allowed them to continuously be inspired.

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• 23:34Speaker 06

  Frank, let's come back to you. How is she earning the respect of her peers so early on?

• 23:40Speaker 08

  She was very careful and precise, and if she came out with an experimental result, people regarded that as most likely being correct. She was also very good at using apparatus and recognizing opportunities in novel ways. And the two examples of this are with what's called the beta radioactivity and gamma radioactivity. Beta particles are emitted by nucleus. Einstein's famous equation E equals M Z squared says if you've got a nucleus with a mass M, it's got an amount of energy E trapped in there somehow. And what radioactivity was understood as was you start off with a nucleus with a certain

• 24:20Speaker 08

  amount of energy, and it stabilizes by giving up some of that energy into the beta particle and ending up as another nucleus with a different energy. Now, if that was the whole story, the beta particle each and every time would carry off the precise amount of energy difference between the starting and the finishing. Experiments had begun to show that it looked as if this wasn't quite the case, but people didn't really believe it, until Meitner showed very clearly by careful measurements that indeed, from one experiment to the next, the beta particle energy would vary a little bit, sometimes a little bit more, sometimes a little bit less, but it was quite clear that there's a distribution. And this led the great Austrian theorist Wolfgang Pauli to come up with the explanation

• 25:05Speaker 08

  that in beta radioactivity, there's not one particle emitted, there are two. There's the beta particle that you're able to detect, but it's accompanied by a ghostly neutral thing which he called the neutrino. And we had a program on this many years ago that you can all now go and listen to, and that was because of Meitner's careful results that convinced him that this must be the case, and we now know indeed that was correct. The gamma experiments are interesting. Gamma rays are very high-energy forms of light. Well, she was studying the beta decay spectra in great care, and an assistant said that he was having great difficulty because he was using a Geiger counter. Good old Geiger counter which clicks when the radiation comes past.

• 25:50Speaker 08

  And the problem was that somewhere in the laboratory, there was a source of gamma rays which were causing the Geiger counter to click, making so much clicking that he actually couldn't do the experiment he wanted to. Now, whereas you or I might say, oh, that's a problem, you know, get rid of the source, might have thought, well, that's interesting. If the gamma radiation is causing the Geiger counter to click, we could use a Geiger counter to measure gamma radiation. And that's what she did. And she did the starting studies on gamma radioactivity of nuclei. And so this is the twenties, thirties, really established the whole details of the alpha, beta, and gamma radiation emitted by various nuclei, mapping the whole landscape out,

• 26:34Speaker 08

  eventually leading to the understanding of what the atomic nucleus is and how it all works.

• 26:39Speaker 06

  Stephen, who were the people who were recognizing her? Who brought her on, as it were?

• 26:45Speaker 09

  Well, after the discovery of protactinium, which is sort of around 1918, she got her own laboratory in Berlin where she worked and was head of the Physics Laboratory for Radiation Studies. And this is where she was, she was now independent of Hahn. This is where she launched the very careful studies of beta radiation that Frank's already described. And it was really in that period where the precision of her measurements and the care which she took to interpret them theoretically, according to the latest theories of the day, really started to put Berlin on the map, which hadn't really been on the map before in this sort of research.

• 27:29Speaker 09

  The theorists of the day, Frank's given the example of Wolfgang Pauli, really started to pay attention to what she was doing and the very careful results. This was not a... An environment in which you could just sit and theorise, you had to benchmark your theories against experiment.

• 27:47Speaker 08

  And also, you know, it comes across now with hindsight as if it's all straightforward, but there's a lot of confusion. You know, not everybody's experimental results are right. How do you know which ones to believe, which ones to give more emphasis to? And I think that is really what she was contributing.

• 28:02Speaker 09

  Yes, absolutely. And you see it, you see it time and again, that they, they really look closely at what she's doing and what she's contributing. And so maybe just to emphasise back on the neutrino, that was a sort of mini crisis, wasn't it, in physics, in that people like Bohr even started to suggest maybe the physicist's cherished concept of energy conservation may not be true inside the atom. But it was true, but that wasn't the right explanation. But the fact that they were building theories around her experiments rather than other people's experiments really showed in what esteem she was held.

• 28:44Speaker 09

  And the other thing that perhaps I could just slip in is that in that period of her careful studies of beta radiation, she discovered a few other things as well. So she discovered an effect which was actually later named after a French physicist, Auger. It's called the Auger effect, although nowadays it's increasingly called the Auger-Meitner effect, because Michener actually got there first. And this is an effect where you get electrons coming off the atom, the so-called secondary electrons. It produces low-energy electrons that are used in cancer therapy today. It's an important effect. And she actually discovered quite a few other things.

• 29:24Speaker 09

  If you drill down, you discover a lot of common things in physics textbooks were actually discovered by Michener in this period through her careful experimentation.

• 29:34Speaker 06

  Jess Wade, to talk about her life while this is going on, while her work is going on. It was in danger in the 1930s. Hitler had come to power and although she could call herself a Protestant, nevertheless, they went after her. She was under a lot of pressure. How did she cope?

• 29:51Speaker 07

  I think after 1933, her life changed quite dramatically. Her teaching rights were revoked and there were some of her students in the classes and researchers who joined the Nazi party and made it very obvious they did so. It changed completely in 1938 when Austria were annexed because she was no longer protected by her Austrian nationality, but actually she was just now a Jew in Germany. Other countries wouldn't take her in because her Austrian passport wasn't recognised anywhere. But actually, it was this network of incredibly powerful and well-connected physicists who conceived this international operation to be able to smuggle her out of Germany at all. Hahn became increasingly worried about her working with him, to the extent that eventually in 1938, it changed. Niels Bohr actually was quite influential and massively important in getting her out.

• 30:35Speaker 06

  How did he?

• 30:36Speaker 07

  Eventually, speaking to another chemist called Costa, who was in the Netherlands and managed to coordinate her passage out on a series of trains from Berlin. You know, now you read it through and it's this kind of international heist. She had to be prepared to leave at 8pm at night. She was in her, you know, she was approaching 60 at the time and she had to have her stuff packed in a suitcase. She was given an engagement ring in case she needed to bribe someone on border security. She had all of these papers. Costa had negotiated with local politicians and officials that she'd have a passage out of Berlin, eventually into the Netherlands, and eventually she ended up in Stockholm. But there are loads of descriptions of this time of her being absolutely terrified of

• 31:16Speaker 07

  that journey, of completely obvious reasons, of getting out, eventually landing in Stockholm and being completely afraid that she was going to start to be written out of this incredibly important time in physics and in history. Hahn became concerned that if he was seen to be publishing with a Jew, that would impact his life as well as his scientific career. And so actually, over this transition, once she had made that safe passage out, she started being left off papers. So once whilst originally they'd been collaborating and she'd been very generous putting him on these papers, she started being left off all of these incredibly important papers because she was a Jew and they were absolutely terrified about including her on there.

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  Do you want to come and understand?

• 31:55Speaker 09

  Yeah, yeah, perhaps I could just also add something there that after the war, with the benefit of hindsight, she was somewhat angry with herself for not having left Germany earlier. So Einstein left, I think it was in 1933 when Hitler came to power. But Meitner, she was so absorbed in her science, she kind of thought she could hang on in there. And she was upset with herself after the war for sort of dignifying the Nazi regime by staying. And also the sort of persecution of scientists happened almost immediately Hitler came to power. And when Germany later took over Austria, there was particularly awful persecution in Vienna, where Meitner was from. So, you know, scientists really were in danger of their lives. And as

• 32:40Speaker 09

  Jess has described, Meitner was terrified and with good reason.

• 32:44Speaker 07

  But absolutely loved her physics. You know, there are letters from her at the time saying, I just can't imagine what I'd do if I wasn't doing physics. I love it so much. So it's so incredibly difficult balancing the one thing that was keeping her going in life with this absolute fear for her own life.

• 32:57Speaker 09

  Yeah.

• 32:58Speaker 06

  Frank, Frank Close, it's a lot to fit in a small space, but in one sense, we're talking about the smallest spaces, aren't we? So let's, you have a go here and I can, listen, can you tell us how scientists knew they could get barium out of uranium, even if they couldn't explain their findings?

• 33:18Speaker 08

  Probably not, but that's the chemist answer. But what was happening was that the story really began a few years earlier with Enrico Fermi in Italy, who was bombarding atoms of elements in the periodic table with neutrons to see what happens. And what Fermi was wanting to do was to fire these neutrons gently enough that they would attach to the nucleus and then modify it and form perhaps radioactive forms, which he succeeded in doing. He worked his way up the periodic table and he was firing neutrons at uranium, the heaviest naturally occurring element, in the hope perhaps that he might be able to create an element beyond uranium.

• 34:04Speaker 08

  Uranus, Neptune, Pluto, uranium, neptunium, plutonium, the transuranic elements. And in his results, he found some very strange things that the chemists were not able to explain, given the knowledge that they had. And he then assumed that this was evidence that he had indeed, for the first time, produced these transuranic elements. And that is indeed what he won the Nobel Prize for in December 1938. Very ironically, because it was that very same month that actually the real explanation of what he had done became clear. And that was that the neutron, when it hits uranium, has broken into two, which might

• 34:46Speaker 08

  sound trivially obvious, but actually, given everything that people knew about the nucleus at that time, was effectively supposed to be impossible, because the nucleus was very strongly glued together. And the only thing that we knew for sure, thanks to Hahn and Meitner in particular, was that when you modified a nucleus, it moved maybe one place, or maybe two places down the periodic table, but that was it. But the chemical analysis that Hahn did showed that he was getting barium when he repeated the experiments. Now, barium is down number forty-something, halfway down the periodic table, made no sense whatsoever. And he couldn't understand this at all.

• 35:28Speaker 08

  And he wrote to Meitner, who, as we've heard, by then had left Germany, and she was in Stockholm. And she was visited over the Christmas by her nephew, Otto Frisch, who had also escaped from Nazi Germany. And they would all get together at Christmas time. So this time, he met her in Sweden. And she showed him this letter that she'd received from Hahn, in which he said that he had found barium in the results. What could this mean? And the first reaction was, well, this makes no sense at all. But she said, look, Hahn is a great chemist. If he says he's seeing barium, he's seeing barium. What can it possibly mean?

• 36:09Speaker 08

  And the two of them then walked through the woods, snow shoeing and so forth, and sat down and had a coffee break or something like that. And in this, they had this sudden insight that the picture of the atomic nucleus is like a liquid drop where surface tension would stop it breaking. There was one extra feature a nucleus has which a liquid drop doesn't, and that is electric charge. And they suddenly, and whether it was Meitner or Frisch, it's never been established, but they had the insight that if, when the neutron hits this liquid drop, it elongates slightly. So it's like a dumbbell. The two ends of the dumbbell are each positively charged and like charges repel. That could then push

• 36:50Speaker 08

  those two ends apart, making the nucleus fission, is the word that became known, into two, which would explain why things like barium halfway down the periodic table appear, because that's roughly half of a uranium nucleus. And so that, in my mind, is the moment when nuclear fission was discovered. That Frisch and Meitner had the insight, they did the calculation, and they found that the energy produced out of this, it fitted everything that you would expect. It turns out that Hahn, his discovery of barium in the production, which has always subsequently given him the credit for discovering fission, had actually, three months earlier,

• 37:32Speaker 08

  Marie Curie's daughter Irene in Paris had found pretty much the same phenomenon. She had found lanthanum, which is also down, down there, and couldn't make sense of it. But that was it. So then, three months later, Hahn does the same thing, doesn't understand it, but he writes a letter to Meitner, and Meitner explains it. So to my mind, fission was discovered on a tree stump in a wood in Stockholm.

• 37:59Speaker 09

  Yeah, yes, I agree completely with what Frank said. I just wanted to to make it even a bit stronger. So Hahn's first paper was very, very tentative. And they just say, this is mysterious, right? We know this this may not be right. We may have been misled somehow. And then Meitner sent her paper to Hahn. Now, the next paper Hahn publishes, which is after the Meitner-Frisch one. He's incredibly confident that what he discovered implied that the nucleus had split in half. But but it, science doesn't work that way. You know, you know, it's it's not true that he discovered.

• 38:39Speaker 08

  Steve mentioned the timing. It's quite remarkable that Fermi was getting the Nobel Prize in like the second week of December for supposedly discovering transuranic elements. But we now realise he had probably actually fissioned the uranium but not realised the fact. And then it's three weeks later that Hahn is writing this letter to Meitner and it all being sorted out.

• 39:00Speaker 09

  Absolutely. And the Meitner-Frisch paper, it's a short paper. And it's really lucid and a really enjoyable read as a scientist, great paper. Right? And it makes sense of everything, whereas the first Hahn paper is just confusing.

• 39:19Speaker 06

  Can we switch a bit here, Jess? Within months, Otto Frisch, who'd been sitting on a stump of wood in Sweden, was in Birmingham sketching out plans for an atom bomb. What did Meitner realise would flow from that?

• 39:35Speaker 07

  Well, I suppose the unfortunate part of their discovery, it came right before the Second World War. So it was a time when science was being weaponised in this way. Meitner, I think, realised the potential. I think scientists all around the world realised the potential. If you could release this immense amount of nuclear energy, the damage that would do. Meitner and Hahn's experiments, I suppose, showed that it was possible to do that. Meitner was incredibly devout in physics being used for good. I mean, lots of the earlier isotopes that her and Hahn had discovered were used for medical applications. She realised the huge implications of this as an energy generation source, you know. And she was very passionate that would happen. She was invited to be part of the Manhattan Project at Los Alamos, so to contribute to this discovery, this building with an atomic

• 40:17Speaker 07

  bomb, and absolutely refused to be part of it. So as soon as

• 40:21Speaker 06

  She wouldn't have anything whatsoever to do with making a bomb.

• 40:23Speaker 07

  She wouldn't have anything whatsoever to do with making a bomb. Even afterwards, when I think movie producers came to talk to her about making a film about making an atomic bomb, she said, absolutely not, I'm not even contributing or consulting on your film script. And she said, I'd sooner walk naked down Broadway than I would contribute to this. So she was headstrong in her capacity to think physics should be used as a force for good, not a force for evil. And maybe it came from her earlier experiences of being in the First World War and seeing the impact of death and loss around her and really not wanting to be part of that. She always had faith throughout her entire life. And she devoutly believed that science should contribute good to the world, not harm.

• 41:01Speaker 06

  Stephen, Otto Hahn was to get the Nobel Prize for Chemistry for Phishing in 1944. Why not Meitner?

• 41:08Speaker 09

  Well, that's a very good question. And I think there were several reasons. First of all, the obvious reason, the fact that she was a woman in the world as it was at that time. As one of the biographers put it, the grim realities of society came in. But I think there were other reasons as well. One of them was back to this old chemistry versus physics thing. So a prize was given by the Chemistry Committee to Hahn. He won the Nobel Prize for Chemistry for, quote, "the discovery of nuclear fission." There was clearly some sort of disciplinary bias going on there. It was really just a very bad call by the Nobel Committee. They hadn't researched it terribly carefully. They downplayed

• 41:50Speaker 09

  the physics aspect of it. It was just before Hiroshima, I think, yeah.

• 41:54Speaker 08

  Well, I think first of all, the thing about Meitner being a woman, there had been Nobel Prizes given to Marie Curie, Irene Curie, and others. The fact that she was Jewish, well, there are also prizes given to people who were Jewish. But I think had she not been Jewish, she would not have had to have left Berlin, and she would have been there with Hahn, and there would have been no debate about it whatsoever.

• 42:14Speaker 07

  And been there in the papers.

• 42:15Speaker 08

  Absolutely. But the date is a thing. Correct me. It's rather strange that it was indeed the Chemistry Prize that Hahn got, but it was backdated.

• 42:25Speaker 09

  Yes.

• 42:26Speaker 08

  And in 1945, no Chemistry Prize was awarded. In 1946, it's awarded to Hahn for fission and backdated, and I presume it's because in 1945, the experimental proof in quotation marks of fission was demonstrated in the atomic bombs, which is a horrendous thing.

• 42:44Speaker 09

  Yeah.

• 42:45Speaker 08

  But why did Meitner not get it is a very fair question. And I sort of feel that there are three possible ways you could imagine that prize for fission having been awarded. One is that it was awarded to Frisch and Meitner, who, in my opinion, are the real discoverers in explaining what had happened. The other possibility is that it would be given to Hahn and Meitner because they had worked together right through, and that the experiments that Hahn eventually did was, if you like, the tip of the iceberg on the whole work that he and Meitner had been doing for now decades, and it was indeed Meitner who led to the explanation of it. Or all three of them, Hahn, Meitner and Frisch.

• 43:29Speaker 08

  But however you slice that particular cake, because the Nobel can only be given to a maximum of three, Meitner is there on each occasion.

• 43:35Speaker 09

  Yeah, and maybe I could just add, I mean, there's a fourth name in all of this, which is Strassmann, who was the person who worked with Hahn, who actually did the chemistry. So Strassmann was the guy who did the chemistry. Strassmann always confirmed that Meitner was the intellectual leader of the group. Now, personally, I would say that Hahn actually made the smallest contribution of those four. That's a bit of a, bang goes my Nobel Prize there, but that's a bit controversial. But, I mean, just back to the misogyny question, after the war, Meitner was treated terribly in certain areas. She was described as Hahn's assistant and this sort of thing, which was just utterly false.

• 44:16Speaker 08

  And some newspaper article referred to her as the mother of the atomic bomb, which was awful on many scores. She said she had nothing to do with it and she would never have wanted to have anything to do with it.

• 44:25Speaker 06

  Yes, Meitner, which is working, she worked in Sweden and in England. She's buried in England with the epitaph, "A physicist who never lost her humanity." Why does she want that epitaph?

• 44:35Speaker 07

  Well, maybe you can catch it from the sentiment everyone else is sharing about Meitner, but she had this immense morality. She was a victim of this huge injustice. She wasn't recognised for her scientific contributions. She was ostracised for being Jewish, ostracised for being a woman, and yet seemed to bear no resentment. You know, she got frustrated by the ways that she was treated in Berlin, but continued to do this brilliant physics. You know, Frank described the work of Fermi in that inspiring lots of this. Meitner was the one who read the work of Fermi and said to Hahn, "We really need to start doing these experiments." So not only was she the one who devised this theory that could explain them, but she came up with the idea to do them in the first place. You could imagine that getting a lot of people quite angry, but she was just wondered by the discovery. So first and foremost, she's a physicist, right? She's

• 45:17Speaker 07

  a hardcore physicist. But she never lost her humanity within that. She campaigned for physics, as I mentioned before, to be used as this force for good. She was involved in these missions alongside Irin Kiri for nuclear disarmament. She absolutely did not want physics getting into the wrong hands and being weaponised against it. So I suppose that's the humanity part, that despite everything that the world threw at her, she was committed to her science. She was a scientist throughout, you know, her entire life. She went over to give a series of lectures in America in the late 1940s and met President Truman and sat next to him at dinner. And together, they both agreed that never again should these nuclear weapons be used in the way they had been. So she spread that humanity around the world wherever she went.

• 45:58Speaker 06

  Well, thank you very much. Thanks to Jess Wade, Frank Close, and Stephen Branwell. Next week, the invention of copyright, the legal system that protects your work and stops others using it without permission. Thank you for listening.

• 46:11Speaker 14

  And the In Our Time podcast gets some extra time now with a few minutes of bonus material from Melvyn and his guests.

• 46:19Speaker 06

  Well, that was terrific. I understood some of it. It was great. Now, you can't go yet because we now... That was really good. I loved it. You're so clear. We're going to do an extra bit for the podcast, as some of you will know. So Frank, it was a great leap from Meitner's work to the atom bomb, six years later. I'm sorry about this, but could you tell... Could you fill in those six years in about six minutes?

• 46:44Speaker 08

  Well, six minutes, that's great. I'm going to say six seconds. Well, the first surprise, the most significant thing perhaps, was the calculation of fission that Frisch and Meitner did, was the discovery that the amount of energy released out of the atom was vast compared to anything that radioactivity had released before, which in turn was millions of times bigger than chemical. So the fact that there was a huge amount of energy buried inside the atom, which fission could now release, was the first shock. But it's quite a long way from that to making a weapon.

• 47:19Speaker 08

  I mean, if you see the movie Oppenheimer, you get the impression that within minutes Oppenheimer had got a diagram of a bomb on the board, and it wasn't at all like that. Because as Niels Bohr pointed out, that if uranium spontaneously can explode, then why isn't it all that uranium in the rocks that Steve was talking about earlier on, isn't exploding around us all the time? And the insight that came initially with Bohr is that there are two particular isotopes of uranium, one, the common one called uranium-238, and the uncommon one, uranium-235. Those numbers are the relative weights of the things. The 235 is the one that is potentially fissioning and leading to explosion, but that is only

• 48:04Speaker 08

  seven atoms in every thousand. So when fission happens, it's the 235 that has been hit. The idea of a chain reaction is that when you split that thing in two, maybe a couple of neutrons also spill off, and those two neutrons could now hit further uranium atoms and split them, liberating energy and further neutrons. But seeing as it's only the 235 that does the job, and it's so few of those around, the chances that you find another one is pretty small. Ironically, it seemed that nobody really asked the question, if somehow you could make uranium 235, how much would you need to make an explosion?

• 48:49Speaker 08

  And the people who asked that question were her nephew Otto Frisch, now in Birmingham, and Rudolph Piles, two Jewish emigres working in Birmingham in 1940. And the shock that they had was that if you could have about a kilogram, about, yes, a few kilograms of uranium 235, you could make an explosion equivalent to a thousand tonnes of dynamite, it would emit lethal radiation, there would be no known defence against such a thing, other than to have such a device yourself.

• 49:23Speaker 06

  All this is happening in Birmingham.

• 49:24Speaker 08

  This is all happening in Birmingham, and it's an example of science. You could put yourself in the position of these two Jewish emigres, they fled Hitler, and they've done this calculation, and the moment you get the answer, everything is sort of obvious, and you think, has the Nazi scientists already had this insight? And the only defence against Hitler already building one of these things, and that will be the end of the war, and bear in mind, the Battle of Britain is taking place at this very time, the chances that we're about to be defeated anyway is right there, the possibility that here is a device that could change the nature of warfare, and I'm not overstating it because indeed it did, and that we have to have this. If you like, mutually assured destruction was invented at that moment of time, and

• 50:08Speaker 08

  that is what started the whole, initially called Tube Alloys Project, to develop a way of enriching uranium, to make pure uranium 235, eventually leading to the development of the weapon in Los Alamos.

• 50:22Speaker 06

  Stephen, she was very good at complexity, I read, yes, and she would crack things that others couldn't.

• 50:28Speaker 09

  Yeah, I mean, she was she was very versatile, as Jess mentioned right at the start, she was a good mathematician. So one of the things in the paper is they calculated, they managed to produce a, well, they didn't actually show the calculation, but they reported that they'd done a calculation to show that the conditions under which the nucleus would split apart like a liquid drop. Now, this is quite a complicated calculation, actually. I mean, the history books tend to say straightforward calculation is, actually, you have to know what you're talking about. The student will demonstrate. Pretty hard, you know, because it involves like 19th century science with Lord Aurelian and complicated maths, you know, but they did that. They were classy scientists.

• 51:11Speaker 09

  But but one of the interesting things there is that they actually answered a question that they didn't really make much of, but, you know, you might have asked in the early 20th centuries, why there are only a hundred or so elements? Why not a thousand? Why not a million? Why not a billion? And and they provided the answer because they show if you go much beyond a hundred, then they naturally fall apart by fission. There's so much electric charge there pushing out, they're no longer all together.

• 51:40Speaker 06

  What has the scientific community done to restore and enhance her reputation since her death?

• 51:45Speaker 09

  Yeah, yes, since her death, not not long after her death, a number of fantastic biographies came out, one by Ruth Lewin-Sime, one by Patricia Rife, and some others as well. And this started to change the dial a little bit, and it became recognised as an injustice and not getting the Nobel Prize. So, for example, in in the 1980s, some German scientists, led by a scientist called Peter Armbruster, discovered four new elements at the top of the periodic table, and they named one of them after Lisa Meitner, partly to try and put things straight, to put the record straight. They were clear about that. She became therefore one of the few people who've had an element named after them. And

• 52:27Speaker 09

  the, actually, the only woman who's had an element named just after her, the other, because Marie Curie has had Curium named after her, but that's also named after Pierre Curie, her husband. So she's in a group of about a dozen people who've had an element named after them. The other thing that's happened since then, there's been a gradual Rediscovery of Meitner's contribution. So as I mentioned earlier, the this Ogier effect, which is quite an important effect, is often now called the Ogier-Meitner effect. There's also some other effects that I counted, I think, four things that are now named after Meitner, and that number has increased in the last few years. So she's definitely, people

• 53:11Speaker 09

  have tried to put the record straight, especially scientists, because they recognise there's been an injustice.

• 53:17Speaker 07

  And there are buildings named after and prizes named after and big scientific fellowship schemes and awards. But I would say we still don't learn enough about her. If you think about undergraduate physics or maths lectures, or certainly high school physics, you don't come across Lisa Meitner's name.

• 53:30Speaker 06

  Yeah. Frank, why does she stand in the pantheon of nuclear scientists, a very distinguished group? Why does she stand in that group?

• 53:38Speaker 08

  Well, certainly, she was responsible, I think, for establishing, it all looks obvious now, looking back, but at the time, back in 1900, radioactivity had been discovered. It was a mess. And she forged the way through that, identified, as we said, the ladder of radioactivity, established which element created the radioactivity to lead to the next element and so forth. So created the whole landscape of radioactivity, from which, after Rutherford had discovered the atomic nucleus, that the dynamics of the atomic nucleus,

• 54:18Speaker 08

  the rules that control how radioactivity happens, how the energy in a nucleus is contained and can be liberated, are all directly or indirectly the result of the work that Meitner was doing over 20 or years or so. And the fact that she never got the Nobel Prize for fishing, we've discussed, I understand that she was nominated for the Nobel Prize about a score of the order of 20 times for physics and for chemistry, and never got it for either of them. In that sense, I think that, you know, for Nobel Prize runners-up, she must really be there at the top.

• 54:58Speaker 06

  Jess, what didn't you get a chance to say you'd like to have said?

• 55:03Speaker 07

  Probably during this time in her early career when she'd got to Berlin and she was not being paid properly, in the beginning not being paid at all actually, and then being paid very little to keep her on. She was getting a lot of offers from all around the world to go and be a professor in all of these different universities. Everyone wanted to hire her. And then Planck and Fisher, who was the director of the Chemistry Institute that she was in, said, okay, we'll pay you, we'll keep you, we'll work really hard to keep you. Eventually, she got made a professor and became this magnet for talent coming from all around the world to work in this institution because of her reputation. But also, her financial situation was changed by this discovery that her and Hahn made of a certain isotope, a thorium isotope, that had incredible medical applications, from which they got about 400,000 euros of royalties in one year.

• 55:48Speaker 07

  So that was quite a lot of money, 400,000 euros. And in his immense generosity, despite being her age and similar career stage, Hahn took 90% of the money that they got. She was given 10%. That was still a lot of money at the time. But despite this being a shared discovery, despite him being her contemporary and her friend, it was seen at the time as okay that he took 90% of it.

• 56:11Speaker 09

  Yeah, we didn't revisit the point actually that when she worked alone, she credited Hahn early on for the discovery of protactinium. When she was absent, Hahn didn't credit her, although even though it was her project.

• 56:28Speaker 08

  Yes.

• 56:28Speaker 09

  You know, so.

• 56:29Speaker 08

  I really would love to know more about the history of all of this because I had initially read somewhere, indeed, that, you know, the discovery of protactinium was Hahn and Meitner's name was their second. But actually, the first paper I was able to find on this was in her name alone with the assistance of Otto Hahn, which was sort of interesting in its way. But the fishing paper.

• 56:56Speaker 08

  There is a story, and I don't know what the provenance of it is, that Hahn wanted to have both Meitner's seal of approval on the paper, and that because she was in Sweden with Otto Frisch, that she didn't get this in time, and so he went ahead and published it under his own name anyway. But whether these things are people giving talks afterwards who then try to make themselves look better or not, I have no idea.

• 57:24Speaker 09

  I don't think Hahn did anything terribly bad before the, I mean, he was in a difficult situation in Nazi Germany. But after the war.

• 57:32Speaker 08

  What was that?

• 57:33Speaker 09

  Well, I mean, if he'd given a lot of credit to Meitner as an ethnically Jewish woman, he'd have been in trouble with the Nazis.

• 57:41Speaker 07

  And put her life at risk as well.

• 57:42Speaker 09

  And put her life at risk, right, but after she'd left, I mean, when she was in Sweden. But I think where Hahn goes wrong is after the war. He does lots of great things after the war, especially for German science, but he never admits Meitner's role, and it's pretty obvious that that was bad behaviour.

• 58:05Speaker 08

  Hahn was certainly a complex character, because you mentioned about the First World War. In fact, Hahn was one of the people involved in developing chemical warfare in the First World War. But to be fair to him, when he saw the effects, I think on the Russian front, what was done, that he then volunteered to be a guinea pig for gas masks to check indeed if gas masks would protect you. So that was something that he did positive there. She, of course, worked on with X-rays and so forth, like Marie Curie and her daughter in the First World War as well. You realise, you know, X-rays had been discovered only 20 years before, and were now being used to X-ray injured troops and so forth.

• 58:49Speaker 09

  Yes. The other thing I think is worth thinking about in all of this is the role of the Nobel Prizes in the... It's almost like they're making history official and that you can never quite get away from, you know, after that. So even biographers of Meitner who point to the injustice, they're still very reverential to the decision, this terribly bad decision of the Nobel Chemistry Committee in 1944 or whenever it was. And by the way, one thing I... So the year after Hahn got it, for inexplicable reasons, they gave it to somebody for improving cattle fodder.

• 59:26Speaker 08

  Which makes one wonder why it wasn't awarded the previous year.

• 59:30Speaker 09

  Exactly. So it's a bit comical almost, but they... I think you get this impression the committee was not at its best in this period. And, you know, they were maybe trying to dabble in politics a bit as well. They were maybe trying to rehabilitate German scientists, et cetera, after the war as well.

• 59:49Speaker 08

  I suppose one thing I probably should have said on air, which I would say on behalf of everybody who's actually had gamma radiation treatment for cancers and so forth, thank you to Lisa Meitner for having really done those studies on gamma rays in nuclear physics. One of the benefits that have come out of it. But nuclear physics has done good things.

• 1:00:08Speaker 09

  Yeah, absolutely.

• 1:00:09Speaker 08

  Well, thank you all very much. Thank you. Ironically, on VE Day. It's my daughter's birthday.

• 1:00:17Speaker 09

  Does anyone want tea or coffee?

• 1:00:19Speaker 06

  No, I'm all right. Thank you.

• 1:00:21Speaker 08

  I'd love some tea, please.

• 1:00:22Speaker 09

  Tea, what time?

• 1:00:23Speaker 06

  Tea'd be nice. I have to run.

• 1:00:25Speaker 08

  Yes, I'm going to have to get to Waterloo.

• 1:00:27Speaker 06

  I've got to judge a kid's science competition at a period.

• 1:00:28Speaker 08

  Well, thank you very much. I hope you enjoyed it. As always, and I hope it's not the last time. Thank you very much. No, it isn't the last time. Au revoir. Bye now.

• 1:00:36Speaker 00

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