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- [00:00]
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- [00:34]
Matt Elton
Welcome to the History Extra Podcast. Fascinating historical conversations from the makers of BBC History magazine in the closing years of the 19th century, scientists began recording strange phenomena, mysterious glowing gas and smudges on photographic plates. These findings triggered a process of scientific discovery in the field of nuclear physics that would ultimately lead to unprecedented devastation at the end of the Second World War. Frank Close, Professor Emeritus of Theoretical Physics at Exeter College, Oxford, spoke to Matt Elton about how a combination of people and politics shaped the nuclear age.
- [01:21]
Frank Close
Before we get into the more familiar aspects of this story, I wanted to start by exploring something you say towards the start of your book, which is that it's little appreciated that there were three industrial revolutions. Could you tell us what are these three industrial revolutions?
- [01:38]
Well, the first industrial revolution involved steam power. The second industrial revolution was what I called the electromagnetic one. By that stage, the mid to late 19th century, the idea that matter was made of atoms was now well established. The idea was that atoms are permanent and unchanging, like the hydrogen and oxygen atoms in water as they turn into steam. They were the basic bricks of everything that is matter, but the cement that held those bricks together were the electric and magnetic forces. And it was the understanding of electricity and magnetism by Michael Faraday in the mid 19th century that began what I called the electrical revolution of the dynamo and everything that flowed from that. The third revolution, which is the one that my book is about, is what I called the atomic or nuclear revolution. The discovery at the end of the 19th century and in the early years of the 20th century that the atoms have a deep inner structure which we call the atomic nucleus, that there's a vast amount of energy locked in there. And the question was, how could we get it and turn it into use? And that was the third nuclear revolution, if you like.
- [03:05]
It's really interesting to consider the development of nuclear science in this longer context. Is there anything else about those two first revolutions that we need to understand to make sense of the third?
- [03:17]
I think that the great advance in physics from the first revolution was the development of the ideas of thermodynamics, that energy is conserved, you can't create it or destroy it, it can be changed from one form into another, and that the idea of perpetual motion doesn't exist. In other words, nothing goes by itself. There's a price to pay that the production of energy involves change, involves waste of some sort. So those ideas certainly came out, and with the discovery of radioactivity in 1896, which was the very first hint that there is energy contained within atoms, this was a paradox at first, because it appeared that atoms could be liberating energy for millions, even billions of years without changing at all. And that violated all of the understanding that had developed from the first two revolutions.
- [04:21]
And you open the book by talking about the breakthroughs of the 1890s. And for a story that ends with power of a terrifying scale, it's interesting to me that the discoveries of this decade are glows and smudges and quite small scale things. Can we talk about some of the important people involved in these initial steps?
- [04:41]
The second revolution, the electricity and magnetism, left open the question of what actually is electricity? And attempts to answer that question occupied scientists in the latter half of the 19th century. And one of these was a man called Crooks, who had a tube of glass which was a vacuum inside, similar in the old days to television tubes, and passing electric current into the rear of it, he could observe the current passing through the gas in the tube. And the idea, or the hope, was that by watching electricity pass through a gas, as you removed more and more of the gas, you might be able to see the source of electric current itself. But in the course of doing this, he noticed some very strange phenomena, that within the gas in the tube, little sort of faint illuminations started happening, glowing in the dark, and it was quite eerie. And if you recall that the Victorian era, they loved the idea of seances, and Crookes thought that he had made ectoplasm in his tube. It received quite a bit of ridicule, but that gives an idea of perhaps the rather strange things that he was seeing. This led by accident to people repeating his experiments and trying to understand what was going on in there. And in Germany, a man, Wilhelm Runtgen, in 1895, by accident, discovered a new form of radiation. He didn't know what it was. It became known as X rays, X for the unknown. And it was that, I think, which really began the modern aspect of science, because the mystery of X rays was first of all remarkable. They could pass through matter. That was itself astonishing it was as he was holding a sheet of lead to try and see if he could interrupt these rays that he noticed and probably dropped the lead in shock, the skeleton of his hand, because we all know X rays can cast shadows of bones. And indeed, X rays were very rapidly being used to cast shadows of broken bones. So they became widely known almost overnight. But to the scientists, the question was, well, what's going on here? And that is what leads us then to Henry Becquerel. In 1896, Becquerel had spent quite a lot of time interested in fluorescence. That is the property of some minerals. In particular, it happens uranium containing minerals. If you illuminate them, they will then glow in the dark. And Becquerel wondered whether X rays were somehow linked to this fluorescence phenomenon. So what he did was he got some uranium salts, he illuminated them for a while and then put them in a drawer on a photographic plate with a piece of metal in there as well, to see if indeed he had energized the uranium and could detect the results. And then indeed he opened up his drawer and he found the shadow of the metal on the photographic plate, which confirmed that he had indeed irradiated the plate by this uranium stuff. And he announced it. At that stage, he thought that he was just generating fluorescence. It was the fact that he'd illuminated to energize the uranium in the first place that had done it. But we now know, no, it doesn't need all that stuff. Uranium does it spontaneously. And this was one of the great serendipitous moments, I think, which is that Becquerel then continued his experiments, and we're now talking late January, early February. And imagine him there in dank Paris in a really grotty winter, up in a little attic room with no light at all, and indeed the skies were gray for so many days that he wasn't able to irradiate his uranium sample at all. But, and this is where chance intervenes, he decided he would expose the plates anyway. And to his shock, when he removed this from the closed drawer, he discovered indeed yet again, that the uranium had had emitted radiation even without having been stimulated to do so. So this was the shock that uranium is spontaneously emitting radiation even in the dark. And that was the discovery which set the whole thing going. So rays were the thing of the day. X rays were sort of just another of them, and radioactivity, yet another. It was really Marie Curie and her husband Pierre, in the next three or four years that started the whole thing. Going. And it was they that coined the word radioactivity, by which we all know it.
- [09:52]
You write in the book that that was an inspired leap that they made in the 1890s, and that there's another leap made by perhaps a less familiar scientist, J.J. thompson. Can you introduce listeners to his work?
- [10:03]
J.J. thomson discovered the carrier of electricity, a particle which we call the electron today, and established that electrons are constituents of atoms. They are common constituents of all the atomic elements. And this was the moment when clear evidence comes out that atoms are not the final layer of matter, that there is something smaller than atoms and that electrons exist inside them. That was a remarkable discovery because it had itself huge industrial applications, and much that we take for granted today could be traced back to that. But for the story we're talking today about radioactivity and nuclear energy, the key thing that Thomson had demonstrated was not just that atoms have an internal structure, but that these electrons carry negative electric charge. So there is Thomson having discovered negatively charged particles inside atoms. Now, each breath you take, you inhale about a billion billion billion atoms of oxygen and nitrogen. And the amount of electric charge on the electrons in those is vast. It's enough to trigger a dozen thunderstorms. But the fact that it doesn't, and the fact we're having a conversation without electrocuting ourselves, is the clear evidence that matter overall has no electric charge, that there must be something positive inside the atoms to balance off the negative electrons. And it was the quest to find the positive charge that occupied a New Zealander called Ernest Rutherford. And later, he was the man who discovered where the positive charge in the atom resides. He discovered what we call the atomic nucleus. The shock was that. That if I draw an analogy of scaling an atom of hydrogen, which is the simplest of all, a single positive charge in the middle, which Rutherford called proton, and a single electron, remote on the outside, which is the electron. If you scaled that up to the size of the longest fairway that you'd ever find on a golf course, about 500 meters, if the proton was the same size as the hole that you're trying to get the ball into, then the electron is probably somewhere further away than the tee that you drove the ball off from. So that shows you, remarkably, how empty the atom is overall and how compact and small the nucleus is. So hydrogen atoms are the simplest. Just a single electric charge in the middle. Helium, the next in the periodic table, has got two, all the way up to uranium, which was the heaviest naturally occurring element, which has got 92 positive charges in the middle. Somehow These things compact in this very, very small volume, even though the adage like charges repel say, well, they should have blown themselves apart. So here you had the first hints. There must also be some very strong, powerful forces at work in the nucleus to hold the whole thing together. And from this is beginning to come the idea that the energy in these force fields inside the nucleus must be the source of the radioactivity that has been discovered.
- [13:41]
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- [14:09]
Frank Close
Something your book does really compellingly is set these discoveries, this science against the human stories. For instance, you write about how in August 1903, Rutherford, his wife Mary and the Curies dined together in Paris. What happened in that meeting? And is it important to tell the story of this as being about relationships between people?
- [14:29]
Ernest Rutherford, in 1903 visited Paris, which is where the Curies were living. Now, at this time, the Curies had discovered polonium and radium, two further radioactive elements. Indeed, it was they that showed that radioactivity is not unique to uranium. Becquerel had discovered it in uranium salts. They showed it was a more general phenomenon. Meanwhile, Ernest Rutherford in Canada had been measuring the amount of energy that is released in radioactive processes and calculating it all and putting it together, calculated that there must be vast amounts of energy in these atoms if they had been radiating this energy for millions or billions of years. And when he met the Curies, he got a huge shock because they went up onto the roof and it was a clear night and it was dark. And then Pierre Curie dramatically pulls from the pocket inside his coat a small glass phial containing radium. Now, radium is so radioactive, it glows in the dark. And Rutherford's wife, I think, recorded in the diaries afterwards this remarkable illumination that he was holding there against the night sky. It was brighter than the Milky Way, she said. But he also commented, being wise later, that they could already see that his fingers were getting gnarled. We now know from the act of being in contact with this radioactive stuff all the time. But at that stage, the hazards of this were still for the future. So that was the moment when it became clear that that vast amounts of energy are really being radiated. And this gave rise to something that was often said, and is still often said, that if you could somehow access the energy in just 1 kg of radium, that's something about the size of a tennis ball, there's enough energy there to send a ship across the Atlantic, which is indeed true, if you're prepared to spend 100 years on the trip. Because now we come to the catch 22 of all of this. We have discovered this amazing source of energy which goes on day and night without change. But that's a catch without change, you can't do anything to change it. It is just there dribbling out gradually, although there's vast amounts of Comes out so slowly, there's nothing very obvious that you can do with it, unless you can find a way of speeding it up. And so that was the situation in the early 1900s. One's beginning to get an idea of the structure of the atom. That energy is contained inside what we now call the atomic nucleus and is leaking out, but at such a slow rate that it doesn't offer any opportunities for making use of it.
- [17:47]
So what was the thing that happened to change that situation?
- [17:50]
The means of getting energy out of the atomic nucleus. Another 20 or more years elapsed before that one was cracked around 1911. The idea of the atomic nucleus has been established as a lump of positive charge. By 1920, the First World War, of course, intervenes, which is interesting also, sociologically. I mean, Marie Curie applies X rays in hospitals at the Somme, for example. So she's putting these discoveries already to use in a very helpful way. Ernest Rutherford is working on what we now call sonar, developing sonar in the First World War. But in the course of this, he occasionally managed to do some experiments. In the course of that, he identified what we now call the proton, that the positive charge in the nuclei of all atoms is carried by particles called protons. The simplest atom of all, hydrogen having 1 proton, helium having 2, up to uranium having 92. When you measured the relative masses of these different atomic elements, the numbers didn't match. So this gave Rutherford the idea that there must be something else in the nucleus which added to its mass, but didn't add to the charge. And so he invented the idea of the neutral proton or neutron, and that neutrons were also in the nucleus, and perhaps they somehow helped grip the nucleus together. And he gave a talk in 1920 and he proposed the idea that the atomic nucleus is made of neutrons and protons. And eventually, it turns out this is indeed correct. But this was, I think, the one occasion when Rutherford's intuition failed him. He was a brilliant physicist. He was probably one of the most brilliant experimental physicists of all time. And, well, let's try to imagine self in the situation they are in. All of matter can be explained in terms of electrons and protons. In other words, two basic particles. A negatively charged electron, a positively charged proton. The electron is very, very light, about 1 2,000th of the mass of the proton. So the mass of the atom is carried by these positive protons, negative electron, positive proton. Rutherford doesn't want to increase the number of particles by 50%. He doesn't want to invent the neutron as a new particle. His vision is that the neutron is somehow the conglomerate of a negative electron and a positive proton. Now, the problem with this is that in the hydrogen atom, I drew the analogy a little while ago, that the hydrogen atom is like the electron being out at the T, where the golfer is driving off and the proton being at the hole 500 meters away. And Rutherford, and that is how sort of nature is nicely balanced. That's what a hydrogen atom looks like. Rutherford is wanting somehow to make a veritable hole in one on a 500 meters golf course. How do you do this? He had no idea how to do it. And I think that is the reason why he never formally published this. But his idea that the neutron is there was certainly correct. But his vision that it was a composite of an electron and proton sent people in the wrong direction for 10, 12 years. And his colleague James Chadwick spent a decade trying, if you like, to blast this electron, proton composite apart and detect the neutron or find evidence of the neutron by seeing the sort of energy that would be released when that happened. And of course, he didn't succeed because that is not what a neutron looks like. It wasn't until 1932 that Chadwick finally discovered the neutron and established that it is a neutral particle, no more or less fundamental than the proton. So by 1932, the picture of the atom and the nucleus is at last at hand. Which doesn't get us very far into how to get that energy out of the nucleus faster, but at least we are getting some idea of what a nucleus looks like.
- [22:19]
So what was the first breakthrough that enabled things to be changed?
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This breakthrough took place in 1934 and has been described as second only to the discovery of the nuclear atom in all of the great discoveries in physics of the 20th century. And it was made by, in my opinion, the greatest female physicist of the early 20th century one of the Curies, not Marie Curie, who everybody has heard of, but her daughter Irene. Irene Curie and her husband, Frederick Joliot, were using alpha particles. Now, we haven't said what alpha particles are, but they were one of the forms of radioactivity that had been identified back at the start of the century. All we need to care about is they were positively charged, they are emitted naturally in radioactivity. And if you have your radioactive source inside a lead box with a little hole in one side, the alpha particles will pass through that hole in a collimated beam and you can then irradiate other things with them. And this is what the Jolio curies were doing, and they succeeded. In particular, they fired at aluminium, aluminum, which has been sitting there inert, if you like, for four and a half billion years since the Earth began, and induced radioactivity in it. And suddenly this meant that they were able to liberate some of the energy that had been trapped inside aluminium forever. They could liberate it by just irradiating it with alpha particles. So this is the first time that a way of getting energy out of the nucleus under our command had been achieved. Now, they won the Nobel Prize for that. Right. Lead has huge implications, not least if any of you have had a PET scan for cancer diagnosis, for example, you have benefited from this discovery. So nuclear physics can be a good thing is one of the messages to come out of all of this, which is somewhat ironic, seeing as my book is heading towards the terrible things that came from these discoveries. Now, in Italy, there was another great scientist, Enrico Fermi. Fermi was unusual in that he was both brilliant as a theoretical physicist and an experimental physicist. And the particular experiments that he did following on from the Jolio curies, was instead of using alpha particles to bombard the atoms with, he used neutrons. The idea being that neutrons, as their name suggests, are neutral. That if you fire positive alpha particles at nuclei, they're repelled by the electrical forces, but neutrons are not. They just get a free passage in. And so Fermi realized that by using neutrons, he wouldn't be restricted like the Jolio curies. Fermi thought he could go all the way up the periodic table. And indeed he. He did. He then irradiated uranium, which, at number 92, is the heaviest naturally occurring. And when he did that, he got some very unusual signals coming out that he couldn't interpret. And he thought that what he must have done was to have made what we call transuranic elements, you know, uranus Neptune, Pluto, uranium, neptunium, plutonium. Uranium was the heaviest naturally occurring nucleus with 92 protons. Fermi is firing neutrons at uranium. And if a neutron gets added to uranium, it makes the uranium unstable and by a series of radioactive processes moves it one place up the periodic table to number 93, neptunium, or number 94, plutonium. And so Fermi thought that the strange signals that he was getting that he couldn't otherwise interpret was because he was creating the transuranic elements. And indeed he won the Nobel Prize in December 1938 for that discovery. Now, he probably did produce some of those transurenics, but that is perhaps not the primary thing that he had done. And a German chemist called Ida Noddack raised the question back in the mid-30s, we're talking here of had Fermi really checked all of the chemical elements way, way down the periodic table to be totally sure that he might not have split uranium in two. Now, Ida Noddack was a chemist, and as a chemist, she knew that whatever it was that Fermi was seeing, it couldn't possibly be neptunium or plutonium. She didn't know what it was, but she knew it couldn't be that. And that's why she sort of naively asked this question, you know, could you split it in two? Now, the problem is that the physicists knew you couldn't possibly do that. You couldn't split uranium in two. End of the story. Now, Noddack was quite a controversial character in several ways, which may explain some of the negative reaction that she got. But whatever it was, she wasn't taken seriously and nobody gave it a second's thought. And we're talking here, incidentally, 1934-35, if indeed the idea of what became known as nuclear fission, which was the key moment of being able to release nuclear energy on a really large scale, which eventually would lead us to the atomic bomb. If that had been understood in 1935, four years before the Second World War starts, and you move history forward by four years, you get a totally different picture of what may well have happened. But that is an alternative story which is not for us to tell here. So that is how Noddock had asked the right question and got ignored. And we find ourselves only in 1938 finally getting to what's going on, namely the discovery of nuclear fission, which, if.
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I'm right in saying, was given its name in 1939 by Lise Meitner. Can you introduce listeners to her and her work?
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Lise Meitner was Austrian and Jewish. She had moved as a student to Berlin in 1907 because she had been inspired by the work of Marie Curie, a female scientist. She was very interested in radioactivity, and she was working in Berlin at a time when there weren't female students around. Now, a German physicist named Otto Hahn, who's a chemist, he was also interested in radioactivity. And they got talking and he realized that her expertise would complement his own. And he applied for her to do experimentation on this new field with him, which he was given that permission, but on condition that they did the experiments in the basement, away from where all the male students were, because if a woman was seen in the laboratories, you know, that was a bad thing at that time. So Hahn and Meitner became a very formidable team, and many of the things that we've been talking about are due to them for about 20 years. It was they that established what I call the ladder of radioactivity, that starting from uranium by a series of radioactive decays, uranium turns into other elements, going through radium and polonium and ending up as lead and so forth. A lot of that is due to the work that Hahn and Meitner had done together in Berlin. And by 1938, they had been nominated jointly for the Nobel prize on over 20 occasions. Sadly, of course, we've got the problem of the Nazis taking over in Germany in 1933, which caused a lot of Jewish scientists to escape. Lise Meitner, being Austrian, initially wasn't constrained by the racial laws, but when Austria itself was invaded, she overnight became subject to them and she had to escape. So we're now talking 1938, and she has escaped from Berlin and she is now working in Stockholm, in Sweden. She has a nephew, Otto Frisch, who was also Jewish, who also escaped from Germany. And he, at that stage was working in Copenhagen. And when she and Otto met, she said, I've had a very interesting letter from Otto Hahn. He's discovered something that makes no sense. Otto Hahn had been bombarding uranium with neutrons, just like Fermi had been doing four or five years before. And he too had seen strange things that you couldn't understand, just like Fermi had three or four years before when he did the chemical analysis of them. He thought that he was finding barium in there. He wrote a letter to Lise Meitner, who had been working with him on these experiments before she had fled. And Lise Meitner discusses this with Otto Frisch. They are walking through the woods in the snow, on snowshoes. They have a Break for a sandwich, and they start thinking about this. The picture of the nucleus that you have is that there's this very strong force holding it all together. It's like a liquid drop that's held together by its surface tension. If you've got two small drops of water, they will coalesce. But because a large lump is more stable than two smaller ones, and the uranium nucleus is like that, so that when you sort of gently hit it with a neutron, which is what was being done here, the drop would deform, but it wouldn't break. It was just impossible to do that. And then one of them, and we don't know whether it was fresh or minor, suddenly had the insight. But there's a difference between a uranium nucleus and a liquid drop of water, and that is that uranium is positively charged all over. So suppose you've got this drop of water and you tap it slightly so it wobbles, and suppose it's just deformed enough to form a small dumbbell. Now, the two ends of the dumbbell are each positively charged and like charges, repel, and the electrical repulsion maybe provides enough force to split the thing in two. They did the calculation and found it all worked. And the amount of energy that would be released was vast. So that was, in my mind, the moment when nuclear fission was discovered, knowingly. The reason I say this is because what Hahn and his assistant Strassermann had done in identifying barium was no more than Irene Joliot Curie she again had done the year before in Paris in 1937. She had bombarded uranium with neutrons and identified lanthanum, which is element number 57. She found lanthanum, didn't understand it. Hahn, Strassermann, the next year, discover bismuth, don't understand it. The only difference is that they write a letter to Lise Meitner, and Meitner and Frisch work it out. They're the ones that understand it. And in my mind it's Frisch and Meitner who are the true discoverers of nuclear fission. Though it was, ironically, Hahn in 1945 or 6, who gets the Nobel Prize for it?
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One figure that people listening to this conversation will almost certainly have heard of is Oppenheimer. I wondered if there was any ways in which you wanted people to think differently about him or his role in this story.
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Well, if the only thing you knew about this whole saga of what's coming now to the development of the atomic bomb was the movie Oppenheimer, you would probably think that the only thing the Brits contributed. Was Klaus Fuchs the spy? The reality is very far from that. I mean, Oppenheimer is described often as the father of the atomic bomb. I think he was the midwife of the atomic bomb, but not the father. So let's back up to where we are. Fission has been discovered in 1938. It's finally understood and people, by the start of 1939, it is out there. Every scientist is aware of it now. The next thing that was realized very quickly was that when a uranium nucleus is split in two by the arrival of one neutron, it doesn't always split cleanly into two. In fact, one or two neutrons might get chipped off. So the possibility of having one neutron coming in, splitting the uranium and liberating two neutrons, those two neutrons could hit two more uraniums, do the same thing, making four, and get what you call a chain reaction, an exponentially increasing release of energy. And that too was very quickly realized. The movie has Oppenheimer drawing a diagram of a bomb on his board and giving the impression that that is the moment the whole idea started. Well, I think lots of people probably instantly ask themselves whether you could make a bomb out of the explosive energy release that would take place. Niels Bohr, the great Danish theorist, seems to be the one person who asked the key question which once said is so obvious. Look, uranium isn't uncommon. It's in rocks all around the world. If uranium was that easy to explode, why is it that the rocks around us aren't exploding all the time? They're being hit by cosmic rays, natural radioactivity and so forth. And it was Bohr that pointed out that there are two isotopes, as they're called, of uranium. Uranium 238, which means it's got 238 protons and neutrons in total. And uranium 235, which has only got 235, Bohr had the insights that it is the uranium 235 that fissions and liberates this energy. The problem is that uranium 235 is only about seven in every 1,000 atoms. So that if a neutron hits an atom of uranium 235 and splits it and creates two neutrons, the chance that these neutrons find another of these very rare uranium isotopes is very small, that the Uranium 238 is like a blanket which stops the whole thing. So you can't make a bomb that way. Surprisingly, the only people who seem to have asked the question, but suppose we could make somehow a sample of pure uranium 235. How much would you need to actually make an explosive device? And this question was asked in 1940 by Otto Frisch, the same Frisch that is the nephew of, of Lise Meitner and Rudolf Peierls, another Jewish emigre from the Nazis. Frisch and Peierls did the calculation and discovered to their shock and horror, that you only needed to make about the size of a grapefruit of uranium 235. And that would have an explosive power equivalent to a thousand tons of dynamite. And it would also liberate radiation in the form of gamma rays, which would be lethal in its own right. I mean, this is so small, you could deliver it in a bomb, in a single plane. And that a single bomb could create the same amount of devastation that the whole three nights of bombing of Dresden by hundreds of planes had done. So suddenly you got a new level of warfare. And this was at a moment when the Battle of Britain was taking place and the possibility that the Nazis might be winning the war next week. And it's not overhyping it to say that they realized they have discovered a completely new weapon of warfare that could literally change, and we now know did literally change the nature of warfare. Now, when you do scientific research, and probably this is true in solving many problems in life, the moment you solve it, it seems so obvious, you wonder why it took so long. And so there's Frisch and Pyles who have done this calculation, and they realize that there is no defense against such a weapon other than to have one yourself. And they think, what if the Nazi scientists have already realized this themselves? Could Germany be building a bomb right now? And that is why this urgent message was sent up to Whitehall that we have got to develop this and do this. And of course, it was declared top secret. We do know now that in the Soviet Union around that time, two scientists also came to a similar conclusion that was declared secret and it was only publicly known after the Berlin Wall came down. Scientists in Germany, Italy and Japan never had this breakthrough, nor in the United States, incidentally, never had this breakthrough. So this was a secret that was known and taken action on solely in the United Kingdom. And it began a project which was called tube alloys, just to give it a code name that nobody would be alerted by. And for the next 18 months, they were pursuing ways of what's called enriching uranium. You start with ordinary uranium, which has only got seven atoms in every thousand. That's uranium 235. What is the best physical process to be able to get rid of the 238 and increase the relative amount of the 235. And that is what Frisch and Pyles started thinking about. And a huge effort began to take place in the United Kingdom to that end, and that for about 18 months, they decided that what was called diffusing a gaseous form of uranium through a series of membranes over and over again, would be a way of increasing the U235 content to a point where you could make a weapon. Now, United States is not yet in the war. Scientists there are exploring the idea of liberating energy from the uranium nucleus in order to make nuclear reactors, for example, or maybe power submarines and so on. But the possibility of making a weapon just is not there. It's not until Churchill is desperate to get the United States into the war in 1941, that a team of scientists goes across to the United States, basically, with a scientific dowry, telling the secrets of radar and so forth, and in particular, this thing about the uranium 235. And that's the first that the Americans have heard of it. Now, of course, Pearl harbor happens in December 41. They are into the war themselves. The whole project is now being developed both in North America and in Britain, and it moves across to North America for several obvious reasons, one being that Britain is still under threat of invasion. The engineering involved in enriching uranium is a vast industrial enterprise. You wouldn't be able to keep it secret. It could easily get bombed over here. That was the reason why a team of a dozen or so British scientists moved across the United States in the end of 1943, initially to New York to complete the design phase of making the facility to enrich uranium 235. And that became the huge laboratory at Oak Ridge in Tennessee, where the Uranium235 was created, which eventually became the fuel of the bomb that was dropped over Hiroshima. During the time out there, a new way of making a weapon was developed, and that was to use the transuranic element plutonium, which, by then it was clear that Fermi had done experiments in Chicago which showed how you could breed plutonium by irradiating large amounts of uranium in a nuclear reactor. And as well as liberating energy, it would also create, if you like, as the byproduct, plutonium. And so making plutonium one atom at a time until you got kilograms of the stuff to make a plutonium bomb. There were a lot of technical problems that made that almost impossible. So much so that they had to make a test of the whole concept, and that Is what on, I think it was the 16th of July 1945. The Trinity Test in the deserts of New Mexico was the moment when they tested the plutonium weapon and it indeed exploded. And that was the moment when the atomic age probably really began. And then another plutonium bomb was the one that was dropped over Nagasaki.
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And it's difficult to escape. How horrifying this moment is. How did the scientific community react?
- [44:53]
I think to understand this, which I, of course, I wasn't there. I could only read what people wrote after the event. So I try to imagine what it would have been like for me had I been there. The first thing that is perhaps not generally appreciated is the fact that the average age of the scientists involved was about 25. That the work on the atomic bomb was done very much by graduate students and young postdocs, many of whom later become exceedingly famous Nobel laureates, like Richard Feynman of the Challenger Inquiry. You know, we all know these people in their older age and we imagine that is what they were like in 1943. And of course they weren't. They were very young people. There were, of course, Jewish scientists at large working there on this very clearly. Their goal was to get an atomic bomb before the Nazis did. I mean, one of the great ironies of this is that Hitler's persecution of the Jews created the very conditions that led to the development of the atomic bomb.
- [46:03]
I wanted to start drawing things to a close by reading a quote that I thought was particularly striking from your book, which is that you say, had it not been for the unfortunate coincidence of fish discovery and fear of an imminent collapse of society to fascism, nuclear power rather than nuclear weapons would have led the way. Do you think that's the key way in which we should understand this history? That there were various moments at which the wider historical context shaped how this science developed?
- [46:31]
I think there's certainly key moments with hindsight. I mean, the first was the fact that Fermi in 1934 had unknowingly generated the fission of uranium. And had it been understood in 1934, the full import of what he was doing, then the whole of history could well have been changed because the ability to start inventing, creating, designing atomic explosives would have happened much earlier. That said, maybe to contradict myself slightly, I think that in practice the construction of the atomic explosion was so technically difficult and so much engineering was required. I think Niels Bohr made some remark that in order to make an atomic bomb you would have to industrialize a whole country. And indeed, that is how it turned out that you had got the full industrial might of the United States. I mean, Union Carbide, all of these big companies involved the number of things that had to be done. The basic physics of it was, relatively speaking, quite straightforward. That was discovered and understood quickly. But turning that into a realistic weapon was an engineering effort on its own. So the circumstances that would have led you to do all of these individual things, I can't say what would have driven that, but for the overriding need to have to make this weapon. Of course, once you have done it and it's been demonstrated how to do it, then it is much easier. So that was what I really had in mind. That the impetus of the war, the need, the fear that if we didn't do it before the Nazis did, we were sunk. That impetus was what caused the leading scientists of the whole free world to come together. It was the biggest campus of brain power at Los Alamos. And the whole project that has ever been assembled to do all of this. Why would one have been done that if this need had not been there? So in that context, I feel that the nuclear reactor route and maybe people's perceptions of nuclear physics might have been quite different as well.
- [49:10]
Matt Elton
That was Frank Close, professor emeritus of Theoretical physics at Exeter College, Oxford. His book Destroyer of the Deep History of The Nuclear Age, 1895-1965 is out now, published by Alan Lane. Frank was speaking to Matt Elton.
- [49:39]
Frank Close
Big news.
- [49:40]
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- [50:00]
Alex Von Tunzelman
So don't wait.
- [50:01]
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- [50:07]
Frank Close
Every style, every home.
- [50:09]
Alex Von Tunzelman
This is history's heroes. People with purpose, brave ideas and the courage to stand alone. Including a pioneering surgeon who rebuilt the shattered faces of soldiers in the First World War.
- [50:22]
Frank Close
You know, he would look at these.
- [50:24]
Matt Elton
Men and he would say, don't worry.
- [50:25]
Frank Close
Sonny, you'll have as good a face as any of us when I'm done with you.
- [50:29]
Alex Von Tunzelman
Join me, Alex Von Tunzelman for History's Heroes. Subscribe to History's Heroes wherever you get your podcasts.