In Our Time - Lise Meitner

Episode Date: June 5, 2025

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.WithJess Wade A Royal Society University Research Fellow and Lecturer in Functional Materials at Imperial College, LondonFrank Close Professor Emeritus of Theoretical Physics and Fellow Emeritus at Exeter College, University of OxfordAnd Steven Bramwell Director of the London Centre for Nanotechnology and Professor of Physics at University College LondonProducer: Simon TillotsonReading 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

BBC Sounds, music, radio, podcasts. 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 can find a reading list to go with it. I hope you enjoyed the programme. Hello, over Christmas 1938,

the physicist, Lisa Meitler, a Jewish Austrian refugee from Nazi Germany, solved the question of nuclear fission. It said she was sitting in, 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 Maitner. She deduced the nucleus was splitting like a drop of water, something previously thought

impossible, and named this fission. 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 Mitner, I 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 Stephen Bramwell, director of the London Centre for Nanotechnology and Professor of Physics at University College London. Jess, as I might know, was born in 1878 in Vienna. Can you tell us something about her early life? 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 PhD, 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. At the age of 10. At the age of 10. So you could see her commitments, 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. 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?

I suppose Lisa Maitner 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 Mitner 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, 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, 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 practice science, be paid salaries to practice science. She was eventually let into these spaces, allowed to be a scientist, but not paid properly, eventually paid a little bit, but not

recognized, 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, 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 Mitner was learning physics with

Boltzmann. She then got to Germany, met Plank, and had this huge revelation about how much physics was working and evolving and developing during that time. And eventually, and Planck employed her as an assistant in 1912, and then she was the first woman professor of physics in 1926. Do we know how she stood up to this, constantly being rebuffed one way and another? I think she stood up for it, by, 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 Plank 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 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. Thank you. Frank Close. What was the understanding of the atom in the early 20th century when Mike Newe still studying? Well, as you just sort of intimated, Lisa Mitner 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 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 spontaneous, 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, 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, and the calculations that they did showed that, If you had a piece of radium about the size of a P, 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. That's amazing. Absolutely amazing. It's a second one. Were you recover from that? Yes, also, you might have to wait 100 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 Mitner 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. What did he do? Otto Hahn was a chemist.

He was within a few months the same age as Lisa Mitner. 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 Mitner. He was in Berlin as a chemist, and the physicists were more enthusiastic about this radioactivity phenomenon than the chemists were.

Why? Well, it was very subtle. I mean, Han 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've 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 Mitner 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 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 1907, I think it was. What did they lead on? Well, over the 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 in the element, which was at number 92, if you like. Lead, the heaviest stable element, is at number 82. The discoveries by the curies of radium and polonium were somewhere in there. And it was Han and Naitner, who by studying radioactive decays were able to establish the chain of order, uranium decaying into maybe thorium 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 92 to 98 through the even numbers. Beta shifted you one. It took you from an even into an odd and tumble down to Bismuth. But one of the things that's becoming 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, what is going on inside the atom that can enable this energy to be emitted and where in the atom is this energy stored? Before we go on, Stephen Brammer, 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? 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-sake and 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. 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, Franks 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 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 extremely famous physicist. He was awarded the Nobel Prize in chemistry, not in physics, which amused him because he knew he wasn't chemist. And he felt what had done was physics. 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. Can I just add something to what you were saying there? Because I made it sound very simple, though. Uranium's at number 92, leds at 82, there's just 10 in there. There's 10 chemical elements in there. But what Hahn and Mitner 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. How did Mike and I discover a new atomic element? Yeah, so this is a particularly interesting, story because when the chemist developed the periodic table in the 1860s and 1870s, the work of Mendelef,

they arranged the elements according to what 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 in the periodic table. Now, one of these gaps was element 91, which is just to the left of uranium, and two spaces to the left of that, you have actinium. 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 your two spaces to the left. So, it became clear that Actinium was coming from the unknown element 91 that nobody had ever seen.

So Maitner 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. 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 world war started. Hahn signed up as a soldier. Maitner 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,

She did all the physics, she did all the chemistry, some very hard chemistry that most physicists would not want to do, hydrofluic acid and this sort of boiling concentrative sulphuric acid and this sort of stuff. And she did things like procuring the earth from which you got the starting products. He occasionally came back from the front 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. More than he did about her on many occasions. 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 recognized as the discoverers of that element. Thank you. Jess, Jess Wade,

why was this thought to be such an enthralling, exciting, for Maitner and for science in general. Well, I suppose for Maitner, 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 physics and in chemistry, we were 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. science to be excited about. So many fine scientists. Could you give us a few years? So many fine scientists

in the same place. I mean, Berlin seemed to be this hotspot of Einstein, of Plank, of Niels Bohr, of Lisa Mitna, of Nernst, of Lowy 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 and the approach that she took to trying to decide. for 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 might know as a woman, because he'd read all of her work thinking Lisa was probably a man's name. But it was through these that she managed to build these social connections with physicists as well. You know, 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 Mitner 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 Neal's board 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 bigwigs. So that was 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. Frank, let's come back to you. How is she earning the respect of her peers so early on? 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 recognising 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 was MZ squared. So 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 amount of energy and it stabilises 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 looks as if this wasn't quite the case, but people didn't really believe it, until Mitner 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 was a distribution. And this led the great Austrian theorist Wolfgang Power, to come up with the explanation 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 programme on this many years ago that you can all now go and listen to, and that was because of Maitner'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, And gamma rays are very high-energy forms of light. Well, she was studying the beta-dak 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 radiation comes past.

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 caught in 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 radio activity of nuclei. And so this is the 20s, 30s, really established the whole details of the alpha, beta and gamma radiation emitted by various nuclei, mapping the whole landscape out, eventually leading to the understanding of what the atomic nucleus is and how it all works. Stephen, who were the people who were recognising?

Who brought her on, as it were? 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 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.

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

to give more emphasis to. And I think that is really what she was contributing. Yes, absolutely. And you see it time and again that 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.

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 late in, named after a French physicist, Oge, it's called the Ogeé effect. Although nowadays it's increasingly called the Ogee-Mainer effect, because Maitner 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. If you drill down, you discover a lot of common things in physics, textbooks were actually discovered by Mychner in this period through a careful experimentation.

Just 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? I think after 1933 her life

changed quite dramatically. Her teaching rights were evoked, 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. How did he?

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. She had to have her stuff packed in a suitcase. She was given a 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 should 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 that journey, for 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 had been collaborating and she had 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. Do you want to come and know the studio?

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 Mainer, 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 Maitner was from. So, you know,

scientists really were in danger of their lives. And as just as described, Maitner was terrified and with good reason. But absolutely loved her physics. You know, there were letters from her at the time saying, I just can't imagine what I 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. Frank, Clios, it's a lot to fit in a small space, but in one sense we're talking about the smaller 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? 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. 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 he 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 it into two, which might 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 might 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, Berium is down number four. something, halfway down the periodic table, made no sense whatsoever. And he couldn't understand this at all. And he wrote to Mitner, 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 always 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? 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 Mitner or Frisch has 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 light charges repel, that could then push 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 Maitner 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 harm, his discovery of barium in the production, which has always subsequently given him the credit for discovering fission, had actually, three months earlier, Marie Curie's daughter, Irene, in Paris,

had found pretty much the same phenomenon. She had found Lampanum, which is also down there, and couldn't make sense of it. But that was it. So then three months later, harmed as the same thing. doesn't understand it, but he writes a letter to Mitner. And Mitner explains it. So, to my mind, fishing was discovered on a tree stump in a wood in Stockholm. Stephen?

Yes, I agree completely with what Frank said. I just wanted to make it even a bit stronger. So Hahn's first paper was very, very tentative. And they just say, this is mysterious. We know this may not be right. we may have been misled somehow. And then, Maitner has sent her paper to Harn. Now, the next paper Harn publishes,

which is after the Maitner Frisch one, he's incredibly confident. What he discovered implied that the nucleus had split in half. But science doesn't work that way. It's not true that he discovered. Steve mentioned the timing. It's quite remarkable.

But Fermi was getting the Nobel Prize in like the... second week of December for supposedly discovering transuranic elements, but we now realise here probably actually fissioned the uranium but not realise the fact. And then it's three weeks later that Hahn is writing this letter to Maitner and it all being sorted out. Absolutely. And the Maitner 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 town paper is just confusing 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 would it might now realise would flow from that? Well I suppose that unfortunate part of their discovery it came right before the Second World War so it was a time when science was being wetter,

in this way. Mitner, I think, realized the potential. I think scientists all around the world realized the potential if you could release this immense amount of nuclear energy, the damage that would do. Maitner and Hahn's experiments, I suppose, showed that it was possible to do that. Mitner 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 realized the huge implications of this as an energy generation source, you know, and she was very passionate that would happen. invited to be part of the Manhattan Project at Los Alamos, so to contribute to this discovery, this building with an atomic bomb,

and absolutely refused to be part of it. So as soon as... She wouldn't have anything whatsoever to do with making a bomb. 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. 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. Stephen, Otto Hahn was to get the Nobel Prize for chemistry, for fishing in 1944.

Why not mine? 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 Harney. He won the Nobel Prize of Chemistry for, quote, the discovery of nuclear fission. There was clearly some sort of discipline 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 the physics aspect of it. It was just before Hiroshima, I think. Yeah. I think first of all, the thing about mightner being a woman, there had been Nobel prizes given to Mary Curie, Irene

Curie and others. The fact that she was Jewish, well, also prizes given to people who were Jewish, but I think had she not been Jewish, she would have had to have left Berlin and she would have been there with Hahn and there'd have been no debate about it whatsoever. And been there on the papers. 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. Yes. 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, Marl. of Fission was demonstrated in the atomic bombs,

which is a horrendous thing. But why did Maitland not get it? It's 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 Maitner, who in my opinion are the real discoverers explaining what had happened.

The other possibility is that it would be given to Harn and Maitner 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 Maitner had been doing for now decades, and it was indeed Maitner who led to the explanation of it, or all three of them, Harn, Maitner and Frisch.

But however you slice that particular cake because the noble can only be given to a maximum of three, mightner is there on each occasion. Yeah, and maybe I could just add, I mean, there's a fourth name in all of this. which is Strassman, who was the person who worked with Hahn, who actually did the chemistry. So Strassman was a guy who did the chemistry.

Strassman always confirmed that Maitner 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 bangos my Nobel Prize there, but that's a bit controversial. But just back to the misogyny question, after the war, Maitner was treated ten. terribly in certain areas. She was described as Hans' assistant and this sort of thing, which was just utterly false. 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. Jess Reitner, when she was working 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? Well, maybe you can catch it from the sentiment everyone else,

sharing about mightner but she had this immense morality she she was a victim of this huge injustice she wasn't recognized for her scientific contributions she was ostracized for being jewish ostracized 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 and that inspiring lots of this mightner was the one who read the work of fermi and said to han we really need to start doing these experiments so not only was she were 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 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 Iren Kuree for nuclear disarmament. She absolutely did not want physics getting into the wrong hands and being weaponized 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

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. Well, thank you very much. Thanks to Jess Wade, Frank Close and Stephen Banwell. Next week, the invention of copyright, the legal system that protects your work and stops others using it without permission. Thank you for listening. And the In Our Time podcast gets some extra time now

with a few minutes of bonus material from Melvin and his guests. 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 greatly from mightness,

work to the atom bomb six years later. I'm sorry about this, but could you fill in those six years in about six minutes? Or six minutes, that's great. I'll have three. Six seconds. Well, the first surprise, the most significant thing, perhaps, was the calculation of Fisian

that Frisch and Maitner 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. 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 Neil's Ball pointed out, that if uranium spontaneously can explode, then why isn't it all that uranium in the rocks that Steve was talking about? early on isn't exploding around us all the time. And the insight that came initially with bore 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 seven atoms in every thousand. So when fission happens, it's the 2.35 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, this 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? And the people who asked that question were her nephew, Otto Frisch, now in Birmingham, and Rudolf 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 the, yes, a few kilograms of uranium 235, you could make an explosion equivalent to 1,000 tons 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. Oh, this is happening in Birmingham. This is all happening in Birmingham. And it's an example of science. You put yourself in the position of these two Jewish emigrates.

They fled Hitler. And they've done this calculation. 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 that is what started the whole initially called tube alloy's project to develop a way of enriching uranium to make pure uranium 2,3,5, eventually leading to the development of the weapon in Los Alamos. Stephen, she was very good at complexity, I read, yes, and she would crack things that others couldn't. Yeah, I mean, she was very versatile, as Jess mentioned right at the start, which was a good mathematician. So one of the things in the paper is they calculated,

they managed to produce, 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. Actually, you have to know what you're talking about.

The student will demonstrate that. It's pretty hard. You know, because it involves like 19th century science with Lord or Alien and complicated maths. You know, but they did that. They were classy scientists. 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 they are only 100 or so elements. Why not 1,000?

Why not a million? Why not a billion? And they provided the answer because they show if you go much beyond. 100, then they naturally fall apart by fission. There's so much electric charge they're pushing out, you can no longer hold together. What has a scientific community done to restore and enhance her reputation since her death? Yeah, so since her death, not long after her death,

a number of fantastic biographies came out, one by Ruth Lund's side, 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. not getting the Nobel Prize. So, for example, in the 1980s, some German scientists, led by scientists called Peter Ambruster, 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 actually the only woman who's had an element named just after her. Because Mary Curie has had Curiam named after her, but that's also named after Pierre Curie, her husband. So she's in her 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 mightness contribution. So as I mentioned earlier, this Oger effect, which is quite an important effect, is often now called the OJe-Michner effect. There's also some other effects that I counted I think four things that are now named after Maitner, and that number has increased in the last few years.

So she's definitely, people have tried to put the record straight, especially scientists, because they recognise there's been an injustice. 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 Maitner's name. Frank, why does she stand in a pantheon of nuclear scientists?

A very distinguished group. Why does she stand in that group? 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, the dynamics of the atomic nucleus, 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 results of the work that Mitner 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, never got it for either of them. In that sense, I think that for Nobel Prize runners-up, she must really be there at the top. Jess, what didn't you get a chance to say you'd like to have said? Probably that 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 Plank and Fisher, who was the director of the Chemistry Institute that she was in, said, okay, we'll pay 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. 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 OK that he took 90% of it. 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 even though it was her project. I really would love to know more about the history of all of this because I had initially read somewhere indeed that the discovery of Protactinium

was Han and mightness name was their second but actually the first paper I was able to find on this was in her name. name alone with the assistance of Ardaham which was sort of interesting in its way but the the fishing paper there is

a story and I don't know what the provenance of it is that Han wanted to have both might as 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've the idea. I don't think Hahn did anything terribly bad before. I mean, he was in a difficult situation in Nazi Germany. But after the war... What was he? Well, I mean, if he'd given a lot of credit to Maitner as an ethnically Jewish woman,

he'd have been in trouble with the Nazis. And put her life at risk as well. And put her life at risk. 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 Martin's role. And it's pretty obvious that that was bad behavior. Han 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 it 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 with x-rays and so forth, like Mary Curie and her daughter in the First of the War as well. You realise, you know, x-rays had been discovered only 20 years before, and we're now being used to x-ray injured troops and so forth. Yes. The other thing I think is worth thinking about in all of this is the role of the Nobel Prizes. It's almost like they're making history official

that you can never quite get away from after that. So even biographers of mightnard 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 said, the year after Hahn got it, for inexplicable reasons,

they gave it to somebody for improving cattle fodder. Which makes one wonder why it wasn't awarded the previous year. Exactly. So it's a bit comical almost, but I think you get this impression the committee was not at its best

in this period. They were maybe trying to dabble in politics a bit as well. They were maybe trying to rehabilitate German scientists, etc. after the war as well. I suppose one thing I probably should have said on there, which I would say on behalf of everybody who's actually had gamma radiation treatment for cancers and so forth, thank you to Lisa Mitner 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. Yeah, absolutely. Well, thank you all very much. Thank you. Thank you. Ironically, on VE Day. It's my daughter's birthday. It's my daughter's birthday.

Does anyone want tea or coffee, Melvin? No, I'm all right. Thank you. I love some tea, please. Tea, please. I have to run. I would have to get to Waterloo. I've got to judge a kid's science, good as well.

Well, thank you very much. I hope you enjoyed it. As always, and I hope it's the last time. Thank you very much. It's the last time. Or au revoir. Bye now. In our time with Melvin Bragg is produced by Simon Tillotson,

and it's a BBC Studios' audio. production. I'm David Dimbleby, and from the history podcast and BBC Radio 4, this is Invisible Hands. The story of the free market revolution. The free market isn't solving the problem of homelessness. Classic liberal values of free speech, free enterprise, free markets. A hidden force that changed Britain forever. Popular capitalism is a crusade.

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