In Our Time - Rutherford

Episode Date: February 19, 2004

Melvyn Bragg and guests discuss Ernest Rutherford. He was the father of nuclear science, a great charismatic figure who mapped the landscape of the sub-atomic world. He identified the atom’s constituent parts, discovered that elemental decay was the cause of radiation and became the first true alchemist in the history of science when he forced platinum to change into gold. He was born at the edge of the Empire in 1871, the son of Scottish immigrant farmers and was working the fields when a telegram came from the great British physicist J J Thomson asking him to come to Cambridge. Rutherford immediately laid down his spade saying "that’s the last potato I ever dig". It was. He went on to found a science, win a Nobel Prize and pioneer the ‘big science’ of the twentieth century. With Simon Schaffer, Professor in the History and Philosophy of Science at the University of Cambridge; Jim Al–Khalili, Senior Lecturer in Physics at the University of Surrey; Patricia Fara, Fellow of Clare College, Cambridge.

This BBC podcast is supported by ads outside the UK. Thanks for downloading the In Our Time podcast. For more details about In Our Time and for our terms of use, please go to BBC.co.com.uk forward slash radio 4. I hope you enjoy the programme. Hello, Ernest Rutherford was the father of nuclear science, the great charismatic figure who mapped the landscape of the subatomic world. He identified the atom's constituent parts,

discovered that elemental decay was the cause of radiation, and became the first true alchemist in the history of science when he forced platinum to change into gold. He was born at the edge of the empire he loved in 1871, the son of Scottish immigrant farmers, and he was working in the fields when a telegram came from the great British physicist J.J. Thompson, announcing that he'd won a scholarship to Cambridge.

He went on to founder science, win a bell prize, and pioneer the big science of the 20th century. Win me to discuss the life and legacy of the greatest scientists of nuclear age, Simon Schaffer, Professor in the History and Philosophy of Science at the University of Cambridge. Jim Al Kalili, Senior Lecture in Physics at the University of Surrey, and Patricia Farah, fellow of Clare College, Cambridge. Simon Schaffer, at the end of the 19th century,

what sort of intellectual world did this obviously brilliant young boy from New Zealand come into when he came across to Cambridge? What's happening when he arrives in Cambridge at the Cavendish Lab is concern really with two kinds of physical phenomena, and these concerns were organised by the lab's then director, J.J. Thompson, Rutherford's patron. One was to think hard about the relation between electricity, magnetism, and space. Indeed, Rutherford had got his fellowship to Cambridge, partly because he'd already, before he was 22, done very important cutting-edge work. on the relationship between radio waves and iron coil detectors.

This was a phenomenon that Heinrich Heertz had discovered really only eight or nine years earlier. On the other hand, there was a host of new radiations which began to be identified in the middle of the 1890s. Some of them legitimate, the substance uranium it was discovered in Paris, emitted rather strange and seemingly inexhaustible forms of energy. There were other forms of radiation that we now know were a bit more illusory. And the Cambridge physics program was to see if there was some kind of connection then between electromagnetism on the one hand and these new kinds of rays on the other. And that's the program that Rutherford joined in 1895, when he became the first research student.

at the Cambridge Physics Lab. But at that time, Max Planck had said that more or less all the big areas had been sold with Faraday, Clark Maxwell and Isaac Newton. It had been sorted out. All we needed to do is fill in the little bits between. And so he must have inherited that intellectual atmosphere as well. Yes, there was a sense amongst what one might call

the slightly older generation of physicists, both in Britain and in Germany, notably, that the fundamental problems of... physics had surely been solved. This is a feature of what physicists think that happens exactly once every hundred years in the final decade of each century, the 17th, 18th, and indeed 20th centuries all saw physicists saying something like that, spookily enough. But a lot of research physicists found this completely implausible. It was precisely these new kinds of radiations, for example, the production of x-rays in Germany and then throughout

Europe, in most of the European physics labs, in late 1895 and then very quickly at Cambridge in early 1896, that is the kind of phenomenon that begins to call into question whether really one has understood the fundamental constituents of matter and energy. And that gives a figure like Rutherford, and I think especially him, because he had an absolute genius for spotting the right question to ask, the sense that actually one knows almost nothing, that the field of exploration lies all before one. And he always had that ambition right to the end of his life. Jim Alcala, before he come to the Atom, which most people listening will know something about

and think of Rutherford Atom, let's start with radioactivity. It had been discovered in 1896. It must have seemed then rather on the fringes, rather a must have... not very significant part of the life of research. Why did he seize on it? Well, I think as Simon says, the mid-1890s saw these revolutions in science. I mean, remember at the time,

people weren't even sure whether atoms existed, whether matter could be infinitely divisible or whether it had fundamental building blocks. And then in the mid-1890s, there was a discovery of the electron by JJ Thompson, there was discovery of x-rays, and then Baccarole's radioactivity. And so there were all these mystery phenomena

that Rutherford came over to England at the same to coincide with. It was a very, very exciting time. You know, while people say that they believed that science was coming to an end, it was really in a glorious mess. And so Rutherford was fantastically lucky to have hit it at the right time.

So how did he approach this? You've got the uranium-keeping, it gives off energy, the Baccarell, the Maricure, and he shouldn't give off energy all the time, but it does. And where does he come in on that, and how does he develop his own line on that? It was a very slow process. I mean, during his time in Canada, McGill, he was working with Frederick Soddy, and they very, very slowly started to understand that whatever was being emitted by these materials,

it was changing the elements from one element to the other. They didn't know what was being given off, and by the early, 1903, 1904, I believe, they understood that these particles that are coming off were helium atoms without their electrons. No one understood what an atom really looked like at the time, but they knew that these were fundamental constituents of the element helium that was coming out of these materials like uranium.

So Patricia Farrow, where did that take, I mean, in 1980 he was awarded an Nobel Prize for his work on chemistry, for his work on radiation. What did they award it for? What had he found that was important enough for that? Well, he got the Nobel Prize for showing that one atom can naturally decay radioactively into another. Can change into another?

Can change into another. And some nuclei lose part of their constituent, whatever they were, whatever particles they were. People didn't know at the time. So one nucleus can change into another nucleus naturally as well as artificially. That was what he got the Nobel Prize for. I think it's quite interesting that in all these early experiments with radioactivity, Chance played quite a huge event. The Beccarell when he discovered completely accidentally

that uranium salts would fog a photographic plate, even when the salts hadn't been exposed to the sun. And then Soddy and Rutherford were also very lucky because they carried out some experiments on some radium salts and they wrapped them all up and put them in the drawer, and then the lab closed down for two weeks over the Christmas holidays. And when they came back after Christmas and unwrapped everything, they found that the radioactive characteristics of these salts that they left behind had changed.

The radioactivity in one of them had grown and then the other had fallen. And so completely by luck, they were presented with this phenomenon that they had to explain. And I think it's very important to recognise this, although Rutherford was very, very directed, and he always sort of had a goal in front of him, And in a way he knew what he was looking for because I think that's also important in research. There were also a lot of lucky events, which he, being forewarned, knew how to take advantage of.

Just to keep a little top line of the biography, Thompson had got him a place at McGill University in Montreal where he teamed up with a professor. A professor at the age of 27. He teamed up with this man Soddy, and they worked together. As Simon was saying earlier, he was very lucky in his collaborator. Soddy himself got a Nobel Prize sometime in the future. and then he came back to Manchester and eventually went to Cambridge.

But he's over there now. This changing is fascinating because when he became, when he was knighted, he chose Hermes Trismagistus, the legendary alchemist, as one of the elements of it, when he became a baron, actually, one of the elements of his coat of arms, yes. And his last essay he was writing was on the new alchemy. So this was what people, including Newton, had been trying to do for centuries,

change one element into another. Can you just explain how that was, how significant that was, that this was now being done? Even before they got their Nobel Prize, in the very, very early 1900s at McGill, Sadi was giving lectures saying that they were like the alchemists of the past, except that they were approaching the project of transmuting elements in a very logical, scientific manner.

And the first sort of transmutation of one element into another came when they bombarded nitrogen with helium nuclei, as we now know, they are what then they called alpha particles. And they discovered that some of the nitrogen atoms had changed into oxygen atoms and released a proton as well. They were forcing it to happen. Yes, there's a natural. And making and doing alchemical work. Exactly.

And that was the first time that radioactive disintegration had been stimulated artificially rather than occurring as a natural process. Let's turn to atoms now. His teacher and mentor had been J.J. Thompson, who had been delighted to welcome him to Cambridge. The atomic scientist who discovered the electron and developed a plum pie model of the atom. Now, what was the plum pie model of the atom? Or plum pudding model of the atom.

Plum pudding. Depends which part of the country you're coming. Absolutely, all right. Cumbrian plum ply. One of the great problems in the 1890s and right through to the outbreak of the First World War was that many simply didn't think there were atoms at all, that, as it were, matter is a continuum and infinitely divisible all the way down.

Cambridge House doctrine was very atomist, and Rutherford inherited it. But then there was the following problem that one had to work out how electric charge could be distributed inside an atom. If an atom is not a point, but as it were, think of it as a all-all sphere, how is the electrical sphere, how is the electrical? electric charge distributed through it. This becomes an urgent problem when after 1896-7 J.J. Thompson identifies the fundamental particle of negative charge, the electron. So if there are electrons, where's the positive charge, since atoms overall aren't charged, so there must be exactly as much positive as negative in them? And Lord Kelvin, the doyen of British physics at the time, rather a bugbear of young Rutherford, and JJ together develop this plum pudding model

in which you're to imagine a sphere of positive charge with the electrons like raisins, plums, dotted randomly through the sphere of positive. So overall, no charge, but a rather uniform distribution. Right. Now then, Jim, Uncle Lilley, Can you tell us what Rutherford did to destroy that model and to put an entirely different model in place, step by step, because we've got quite a way to go on this particular part. So that was the model he took. And given that it was Thompson's model,

and given that Thompson found the electron, and he was a mighty man, Thompson, this young pupil edged his way to what was a completely different notion. So how did he start doing that? Well, he, having understood that the strange rays or particles were being emitted from radioactive materials like uranium or radium. He was using these particles to try and probe the structure of matter. So he knew there was these tiny, minute things coming out,

being emitted by radioactive sources. And he could direct them in a stream and aim it at various materials. So the famous experiment that he did 19010, in 1910 was to have these alpha particles, which is what he'd called them, bombard thin sheets of metal. And he used, and the famous experiment was with a gold foil. Very, very thin gold foil, only a few thousand atoms thick. And the results that he saw were very unexpected. He assumed that these highly energetic alpha particles would shoot straight through this gold foil

because they had too much energy to be deflected. As Simon says, the electrons are much tinier, much lower in mass than the alpha particles, say they don't have enough oomph to knock the alpha particles to deflect them very much. And he used scintillation counter, something that Crooks had developed, zinc sulfide material that would give off a flash of light every time an alpha particle would hit it. And although Rutherford himself didn't have the patience to sit down and study these flashes of light, his assistant's Geiger and Marsden really would sit in these darkened laboratories for hours.

I don't know, they needed to have, you know, coffee breaks on a regular basis because it really hurts the eyes. But you can actually discern individual flashes of light which tell you that a single alpha particle has hit this zinc sulfide screen. And so they had these screens around to see which direction the alpha particles would get deflected when they hit the gold foil. It is a darkened room in, we're in Manchester.

We're in Manchester. at this time, yes. And they're shooting by what would now be called primitive means, they're shooting these particles at this oil. They're not having to fire them in it. They're being emitted naturally from the radioactive source, which is in a box, but with only one exit, hole for them to come out.

And they expected these alpha particles to be deflected from their original path, ever so slightly, by the atoms in the gold foil. And the amazing discovery, however they found, was that some significant fraction of these alpha particles would almost bounce back, certainly deflect by 90 degrees or more from their direction. And this was something incredible, because as Rutherford said, it was like firing a missile at a sheet of tissue paper and have it bounce back at you.

So how long did it take him to come to his conclusion about that? Can you take us on to know, Patricia? I think he realised sort of almost immediately that something, very, very, very strange was going on. And it's totally contradicted the idea of the, well, let's have pudding, as I'm saying, the plum pudding idea of the atom, this sponge of an atom with the raisins inside it. I think the fact that the alpha particles were being thrown back showed him immediately that something very, very odd was happening, although he must have had some idea,

otherwise he wouldn't have put the counters on that side of the tissue paper, as it were. On the same side that you're firing your missile at the tissue paper, you don't normally expect to have it coming back. So he would only have noticed them coming back if in some sense he'd thought that that might be going to happen. But the explanation that he came up with is that rather than having little particles scattered fairly uniformly throughout the gold foil,

that there were very, very heavy concentrations of matter and charge in particular points, and that was what became known as the atomic nucleus, and that in between the nuclei of the atoms, there was more or less empty space, with lots of electrons somehow moving around in that empty space. So, Simon, yeah. So we've got this new model of the atom.

Can we just summarise which is the model of the atom that we have now, that we've lived with ever since, right? So what is this amazing new model of the atom? What does it look like? Well, so this is a nuclear model in which instead of the pudding, one has almost all, all the positive charge gathered in a tiny, tiny centre. And we now know that that's made up of a competition.

of protons and neutral particles, neutrons. And then in orbits, rather like planets in the solar system, electrons orbit in shells very far away, but around this center. Now, unlike, so this is, I think, very important to understand, unlike the Rutherford and Sodi's story about transmutation, which was almost immediately accepted by everybody except Kelvin, the nuclear atom model was almost completely ignored by everybody for quite some time, partly because it just didn't seem to be useful for theory. It didn't seem to fit in with the basic physics theory stories of the time. This is where Nils Bohr comes in. The great Danish physicist when a young man visited Manchester often just before the First World War.

and hit it off with Rutherford. And what Boar showed to Rutherford and then to the international physics community was that the nuclear model that Rutherford and Marsden and Giger had constructed fitted perfectly with a whole range of puzzles and problems that international physics was worried about, spectral problems and energy problems. and it became called, rather interestingly, the Boer Rutherford atom. And by the beginning of the First World War, that model of the atom, this planetary model with a highly positively charged nucleus,

had become pretty widely accepted. Boar came to solve a problem that there was, as I understand it, Jim, because Rutherford's model, as I understand it, had a problem. Electrons are negatively charged in nucleus, is positive, So what's to stop the orbiting electrons being attracted to the nucleus of inflow? So that was a real problem. And that was where Bohr came in, literally came into Manchester. That's right.

Yes, the analogy with the planets in the solar system is a good one because, after all, gravity should attract the Earth to the Sun. But because the Earth is travelling around in orbit, it has enough speed in its orbit to keep its momentum going at a fixed distance from the Sun. The difference in Rutherford's model of the atom is that electrons having this negative charge should, by virtue of the fact they're accelerating, it was known at the time that accelerating electric charge

has to emit energy in the form of electromagnetic radiation. Now, by acceleration, it doesn't mean they're changing their speeding up or slowing down, but because they're going around in a circle, that's another form of acceleration. So by orbiting the nucleus, they should be continually emitting emitting electromagnetic radiation and losing energy. And so they should, by all accounts, be slowing down and spiraling into the nucleus, where they will collide with the positive nucleus.

So it wasn't understood how Rutherford's model could be correct. After all, atoms should then be unstable and how come atoms exist in this stable form. Is it too naive on my part to say that Bohr brought it, Einstein in 1905 published it, that bore that brought that to bear, and what we were talking about was something to do with quantum space here? Yes. What we have mentioned, Max Planck started the quantum

revolution in 1900, and Einstein had contributed to that. But this is before what we know today as modern quantum mechanics. That had to wait until the mid-1920s. But at this time, during and just before the First World War, Bohr was trying to apply

Plank and Einstein's ideas which had been applied to radiation, to light, to say that light or electromagnetic energy comes in tiny lumps or quanta, which we now know as photons, he tried to apply that same idea of discretization, not a continuum, to the structure of matter. In effect, what Bohr had said about,

to explain why electrons don't radiate energy and fall into the nucleus, was simply that they don't. There's a rule, there's a quantum rule that says they're not allowed to, and all they do is follow these fixed, quantized orbits around the nucleus. if you give an electron energy, it'll jump from an inner, lower energy orbit to a higher or outer orbit. Likewise, if an electron loses energy, it'll fall back into an inner orbit. And so there are these fixed quantized orbits around the nucleus that build up the structure of the atoms.

No one knew why they were. It was all very, you know, there were formerly that would explain it. And as Simon says, it explained a lot of problems to do with the spectra and properties of the light elements. but to understand really how these electrons arranged themselves had to wait until the 1920s. In 1990, after the death of JJ Thompson, Rutherford took over his head of the Cavendish Laboratory at Cambridge. How did his life and work change as a result of that? I think then he became one of the key figures in persuading the government to invest in scientific research, and that's one of the enormous contributions that he made.

He also was very, very keen on having a lot of research students, and some of the people in the laboratory wanted him to focus on specific problems and just use the limited amounts of money that they had. But he was very keen on getting more money in, getting more students, attacking a huge range of problems. And he was very active in the political integration of science into the British economy. And what would you say, Simon Chappell, what would you say his principal work was in the early 20s at Cabinet?

Well, I think what's interesting is that during the First World War, that's really where one has to start. He'd been commuting between Manchester, where he'd been running the most successful physics group in the world, and the Firth of Fourth, where he was working for the Navy in the hydrophone detection of submarines. Indeed, during the First World War, Rutherford had written most of the memoranda, which will later be used to invent sonar. So he'd already experienced both the delights of the cutting-edge world of research

and the perhaps less seductive delights of dealing with civil social socials. and naval officers. And I think those are the two themes that then will drive him forward at the Cavendish. In terms of pure research, in 1920 he gave a lecture at the Royal Society in which he pointed out that if you had a proton and an electron tightly bound to each other by electric forces, it would look like a neutral particle. And if it was a neutral particle, it would be extraordinarily penetrating, since it wouldn't be affected by other particle's charges. And this prophecy then drives forward a great deal of rather frustrating and difficult work at the Cavendish during the 20s. There were two reasons why it was frustrating and difficult. One was it was

extremely difficult to get your hands on a reliable source of radiation, especially during the economic collapse of the 1920s in Europe. Most radium, for example, was being produced in Austria, which was undergoing inflation and political disorder. The other problem was that it was extremely hard for the Cavendish group under Rutherford fully to understand, I think, how to integrate quantum mechanics into their experimental results, almost as hard as it was for quantum theoreticians fully to understand how to integrate all these rather nasty facts that the Cavendish physicists were producing. As a nucleus scientist yourself, Jim Alcalilli, are you,

You find yourself replicating the methodology of Rolfofert's sex where I'm seeing today? It is incredible that even now we are doing experiments with isotopes of helium, helium nuclei, scattering them off materials. We're not using alpha particles now. We're using rather exotic forms of helium nuclei, helium-6 and helium-8, which contain many more neutrons than an alpha particle. But we're still doing essentially the same experiments

of having alpha particles hitting nuclei. and watching what directions they scatter in. We now pick up this statement that he said with Simon brought up. The energy produced by the atom is a very poor kind of thing. Anyone who expects a source of power from the transforming of these atoms is talking moonshine. I think that ties in with part of the whole general aura that he was trying to convey, that he was a pure research scientist. He could have made a lot of money out of radio,

but he abandoned that when he started doing research into the nucleus. and he's a bit like Faraday in that sense. I mean, Faraday, who created the electromagnetic industry, always claimed that he was disinterested in the economic benefits of his research. So in a way, Rutherford, I think, was trying, and the people who've written about him were trying to create this aura of a pure scientist who was disinterested in such sort of things as money. And that was what he was doing in his address, the newer alchemy.

He was saying, yes, I am a new, subtle, intellectual alchemist, but no, I'm not a charlatan who's trying to do something as sordid as making money out of what I do. I love this scientific succession, really, sort of Newton, Faraday, Maxwell and then Rutherford, but putting that to one side, it's still quite a statement to say that when a few years after his death, they're working flat out on nuclear bombs, Sam. I think Patricia's absolutely right. There is a very well-cultivated image of the rather socially isolated and rather unconcerned research community, but that's a very carefully cultivated image in Rutherford's case.

I think one of the things that he didn't anticipate was the sheer scale of state industrial investment in the kind of physics and chemistry that he'd been pursuing. No one knew better than Rutherford, how extraordinarily difficult it was to get one guinea out of the Department of Scientific and Industrial Research. And I think that statement towards the end of his life, is partly a reflection of simply being incapable of imagining the Manhattan Project Los Alamos

and the vast scale of military and industrial investment which was about to begin. He certainly presided over very large scientific and industrial installations. He compared one of the particle accelerators that his boys, as he put it, built in Cambridge, to a tower in the film Things to Come, which he was rather a fan of. So he saw that part of the future. But what he didn't see was the energy with which the military industrial complex would be constructed after 39. Well, thank you all very much.

Thanks to Simon Schaffer, Patricia Farah, and Jim Al-Khaleli. Next week we're talking about the Mughal Empire. We hope you've enjoyed the... Radio 4 podcast. You can find hundreds of other programs about history, science and philosophy at BBC.com.com.uk forward slash radio 4.