The bomb (part 1): were nuclear weapons inevitable?

Summary

Summary of "The Bomb (Part 1): Were Nuclear Weapons Inevitable?"

Babbage from The Economist
Host: Alok Jha
Guest: Frank Close (Physicist and Author of Destroyer of Worlds)
Release Date: July 16, 2025

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Introduction to the Nuclear Age

The podcast episode begins with Alok Jha setting the stage for an in-depth exploration of nuclear weapons' origins, their development, and their enduring impact on global geopolitics. Frank Close, a renowned physicist and author, joins as the primary guest to unravel the complexities surrounding nuclear physics and the eventual creation of nuclear weapons.

The Birth of Nuclear Physics

Alok Jha delves into the early 20th-century scientific landscape, emphasizing the pivotal discoveries that reshaped the understanding of atomic structure. Frank Close explains, “[...] the picture of the atom was that all atoms of a given element were identical. They had no structure. They were permanent, unchanging, like miniature billiard balls” (05:16).

Key Discoveries:

• Henri Becquerel’s Discovery (1896): Accidental revelation of radioactivity through uranium minerals, leading to the realization that atoms could emit energy autonomously.
• Marie and Pierre Curie’s Contributions: Further exploration of radioactivity, discovering that elements could change into other elements through radioactive decay.
• Ernest Rutherford’s Insights: Differentiation between alpha and beta radiation, establishing that atoms are not immutable and contain a dense, positively charged nucleus.

Discovery of the Neutron

The conversation shifts to Ernest Rutherford’s groundbreaking experiments, which led to the identification of the nucleus and eventually the neutron. Frank Close narrates Rutherford’s gold foil experiment: “[...] when these alphas hit just a very thin piece of gold leaf [...] about 1 in 10,000 alpha particles bounced off at about 90 degrees” (13:07).

Implications of Rutherford’s Findings:

• Nucleus Composition: Concentration of positive charge within a small atomic nucleus.
• Niels Bohr’s Solar System Model (1913): Visualization of the atom with electrons orbiting a dense nucleus, akin to planets around a sun.

The Path to Nuclear Fission

Frank Close discusses the collaborative efforts and accidental discoveries that led to understanding nuclear fission:

• James Chadwick’s Neutron Discovery (1932): Confirmation of the neutron as a neutral particle with mass similar to that of a proton, a cornerstone for future nuclear research.
• Enrico Fermi’s Innovations (1934): Introduction of neutron irradiation to penetrate atomic nuclei without electrical repulsion, enabling experiments up the periodic table to heavier elements like uranium.

The Development of the Bomb

The narrative progresses to the realization of nuclear weapons' destructive potential:

• Lise Meitner and Otto Frisch’s Theory of Nuclear Fission (1938): Explanation of how a deformed nucleus could split, releasing vast amounts of energy.
• Chain Reaction Concept: The idea that one neutron-induced fission event could trigger subsequent fissions, leading to an exponential release of energy.

Frank Close emphasizes the pivotal calculation by Otto Frisch and Rudolf Peierls: “[...] a few kilograms of uranium-235 [...] would liberate the same amount of energy as 1,000 tons of dynamite” (29:41).

Ethical and Strategic Considerations:

• Mutually Assured Destruction: Early recognition of the bomb’s potential to end wars abruptly, shaping post-war military strategies.
• The Manhattan Project Initiation: Accelerated efforts in Britain and the United States to develop and enrich fissile materials for bomb creation.

The Trinity Test

The episode transitions to the culmination of these scientific endeavors with the Trinity Test:

• Location: New Mexico’s desert, a remote and strategically chosen site for secrecy.
• Preparation: Detailed account of assembling the bomb in a controlled environment, highlighting the meticulous precautions taken to ensure test success and security.

Frank Close recounts J. Robert Oppenheimer’s observations: “[...] the colors were pretty psychedelic. They were remarkable going through shades of green and purple and orange [...]” (43:44).

Test Outcome:

• Visual and Physical Impact: A blinding flash followed by a thunderous shockwave, confirming the bomb’s unprecedented destructive power.
• Aftermath: Validation of theoretical calculations and the onset of the nuclear age, fundamentally altering international relations and warfare.

Aftermath and Legacy

The discussion concludes with reflections on the lasting implications of nuclear weapons:

• Los Alamos National Laboratory: Continued growth and modernization, adapting to contemporary geopolitical climates.
• Nuclear Deterrence: The role of nuclear arsenals in maintaining global order through the threat of massive retaliation, a concept rooted in the very origins of the bomb.

Frank Close remarks on the unintended pathway from basic scientific inquiry to weaponization: “[...] this question was asked and answered at the critical moment, just less than 50 years after the discovery of a smudge on a photographic plate” (32:55).

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Notable Quotes

• Frank Close on Atomic Structure:
  “Atoms were like miniature billiard balls, unchanging and permanent” (05:16).

• Frank Close on Rutherford’s Gold Foil Experiment:
  “It was as if you had fired a 15 inch shell at a piece of tissue paper and it had come back and hit you” (13:35).

• Otto Frisch on Uranium-235’s Potential:
  “A few kilograms of uranium-235 would liberate the same amount of energy as 1,000 tons of dynamite” (29:41).

• Frank Close on the Accidental Nature of the Bomb’s Development:
  “[...] this question was asked and answered at the critical moment, just less than 50 years after the discovery of a smudge on a photographic plate” (32:55).

Conclusion

"The Bomb (Part 1): Were Nuclear Weapons Inevitable?" offers a comprehensive overview of the scientific breakthroughs and historical circumstances that led to the creation of nuclear weapons. Through insightful discussions with Frank Close, the episode elucidates how fundamental research in nuclear physics unexpectedly paved the way for one of humanity's most formidable inventions, highlighting the intricate interplay between scientific discovery and its profound ethical and geopolitical ramifications.

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Transcript

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[Frank Close]

The Economist.

[Alok Jha]

On July 16, 1945, at 5:29 in the morning, an audacious experiment took place in the deserts of New Mexico. It was the culmination of five decades of theories, arguments and experiments amongst physicists who'd been trying to crack a scientific mystery. What lay inside atoms? On that summer morning 80 years ago, it had all led to this.

[Frank Close]

First, the flash of light, that enormous fireball, the mushroom cloud rising thousands of feet in the sky. And then, a long time afterwards, the sound, the rumble, thunder in the mountains.

[Alok Jha]

An explosion bigger than anything anyone had ever seen before. It was the dawn of the nuclear age. Ever since that day, the world has been grappling with the devastating power of nuclear weapons warfare. International security and geopolitics have never been the same. Whatever you think of them, these doomsday weapons are here to stay. For 80 years, they've maintained order around the world, albeit in an uneasy, controversial way. And today, as political tensions rise, so does their importance. Over the next four weeks, in a special series for Babbage, we'll investigate the past, present and future of nuclear weapons. We'll speak to the people responsible for building America's stockpile of warheads. Find out how those weapons are being modernized, how they're being tested without being exploded, and how, for the first time in decades, new weapons are being developed. What started in the desert with the Manhattan Project in 1945 has now turned into a vast technological enterprise with thousands of scientists and engineers spread across dozens of sites around America. Those facilities include the world's most powerful lasers and its fastest and most capable supercomputer. And as they push the frontiers of high energy physics and high tech materials. America's nuclear scientists are also building tools that have uses beyond weaponry, from fusion to advanced manufacturing. I'm Alok Chah, and this is the bomb. A special series of babbage from The Economist today. Episode 1. After the birth of nuclear physics, were doomsday weapons inevitable? To understand where nuclear weapons came from, you first need to understand the nucleus. You see, this story doesn't start with scientists wanting to make a weapon. It begins instead with a curious and accidental discovery 130 years ago in an academic research lab in Paris. Back then, scientists still didn't really know that much about the most basic building blocks of matter.

[Frank Close]

Well, at that stage, chemistry was pretty well established. And the idea that matter was made of atoms was the perceived wisdom, if you like.

[Alok Jha]

Frank Close is a physicist and the author of a new book about the birth of nuclear physics called Destroyer of Worlds.

[Frank Close]

The picture of the atom was that all atoms of a given element were identical. They had no structure. They were permanent, unchanging, like miniature billiard balls, if you like. And the only difference between an atom of one element and another was its mass. That hydrogen atoms were the lightest. They were number one in what became known as Mendeleev's periodic table, helium 2, all the way up to uranium at 92, the heaviest then known. And if you combine atoms of one or more elements together, you made molecules and compounds. And that was the picture of the world of matter as it was in 1900 or so.

[Alok Jha]

And how complete did scientists think it was? Did they think that that's it? Now we know that's what atoms are? We're not going to investigate that any further now. We're just going to look at what compounds they can make and all of that. Or was there hints that that wasn't the base level of matter?

[Frank Close]

Well, in 1896, Henri Becquerel in Paris discovered by accident that minerals that contained uranium spontaneously radiated energy. And he discovered that by having left a mineral on a photographic plate in a darkened drawer. And he had been hoping to illuminate it with sunlight and generate fluorescence. But it was very dark in Paris that February, and after a couple of weeks, he decided to expose the plates anyway. And to his astonishment, he found this very faint smudge which showed that uranium was emitting energy even in the dark, which was a sensation. By that I mean Becquerel had discovered a phenomenon that atoms were somehow liberating energy. And Marie Curie and her husband immediately picked up on this, and they discovered that the ore that they had was emitting radiation more than just the uranium content alone could explain. And so radioactivity was a phenomenon that seemed to say that atoms could emit energy continuously. Ernest Rutherford in Canada discovered that in the process of this radioactivity, elements did indeed change from one to another. So this, for the first time, showed that atoms were not permanent and unchanging, and indeed that the dream of the alchemists, if you like, had been finally achieved by the ability to change one atom of one element into another. What was going on, nobody knew. But clearly something was going on.

[Alok Jha]

So how did the researchers go on to investigate why this seemingly magical process of atoms sort of transforming and changing, why that was happening?

[Frank Close]

The first clue, perhaps, was the fact that in 1897 in Cambridge, J.J. thomson discovered that inside the atoms of all elements are electrically charged particles. Electrons, the carriers of electricity, negative electricity. And the fact that atoms overall tend to be electrically neutral showed that there must be some positive charge in there to balance it out. So that was a state of knowledge. In the early 1900s, it was clear that atoms could somehow radiate energy. And it quickly became clear that the source of radioactivity was in the nucleus. And in the case of radium, if you could have a gram of radium that had been emitting energy, as far as they could tell, continuously ever since the start of time. And so the amount of energy that we contained in that little lump of radium would be enough to drive a ship all the way across the Atlantic Ocean, which, indeed is true if you Prepare to spend 100 years making the journey. Because the catch of all this was that although atoms are indeed spontaneously liberating this, what we now call nuclear energy, it was doing it so slowly that there was no obvious way that one could put it to use. So this was the enigma at the start of the 20th century. Energy is coming out. What's causing it? Is it possible to speed it up and make use of it?

[Alok Jha]

The picture that was emerging was that atoms weren't really like miniature billiard balls as had once been thought. They contained even smaller particles inside. And these subatomic particles had electrical charges. Since the electron was negatively charged and atoms were neutral overall, it meant that the radiation emitting nucleus had to be positively charged. But how were all these different bits of an atom actually arranged?

[Frank Close]

Ernest Rutherford is the person who really started and he focused on the radiation itself. What he did was he deduced that there were, in fact, two distinct forms of radioactivity, and he named them after the first Letters of the Greek Alphabet, alpha and beta. Alpha radiation, he established, was carried by positively charged particles. And the other form of radiation, beta radiation, was nothing other than very flighty, lightweight electrons, negatively charged particles. When Rutherford established that alpha particles are nothing other than the positive seeds of helium atoms, and helium is number two in the periodic table, it meant that every time an atom of, let's say, uranium, number 92, if that emitted an alpha particle as radioactivity, it had given up two units, moving uranium down to number 90, which is thorium. So each time an alpha particle would be emitted, you would move downwards in a chain from uranium to thorium and down, eventually ending up at lead at number 82. So over the period of 1900 through 1910, the radioactive ladder, if you like, began to be established that alpha particles would shift you from one element to another, moving you two places up or down the periodic table. Beta radioactivity turned out to shift you one place up or down the periodic table.

[Alok Jha]

Talk me through how Rutherford discovers the nucleus and what is surprising to him about the nature of the nucleus.

[Frank Close]

Rutherford knew there must be positive charge somewhere inside the atomic nucleus. He also knew that alpha radioactivity emits positively charged, relatively massive particles, the alpha particles. And he realized that he could use these, if you like, as atomic bullets to fire at atoms of gold, for example, and see what happened when they arrived. A bit like having a fire hose pointing at some object hidden behind a screen. And from the way that the water then sprays about after hitting the object, you try to work out the shape of the object.

[Alok Jha]

What was he expecting to find? And what did he find?

[Frank Close]

Well, I think he was probably expecting that most of the alpha particles would pass through with just a slight deflection. What he found was that when these alphas hit just a very thin piece of gold leaf, which is so thin you can almost see through it, about 1 in 10,000 alpha particles bounced off at about 90 degrees, which is remarkable.

[Alok Jha]

So what was the implication of that?

[Frank Close]

Well, it showed that the positive charge must be very tightly concentrated. Think of the alpha particles as being like a lightweight rubber ball, and the atomic nucleus of gold, we now realize, being like a heavy football. And so when the light ball hit the football, the light bulb bounced off at a violent angle. He said it was as if you had fired a 15 inch shell at a piece of tissue paper and it had come back and hit you.

[Alok Jha]

He was a clever man, but he wasn't expecting that. So he discovers that there's something positive, which is why the alpha particles are being scattered in this way, reflected, actually, in some cases. So that builds the picture of the atom as an electron sort of floating about the outside, and a very dense, positive thing in the middle. Is this where the beginning of the children's idea of an atom comes from, which is a sort of mini solar system.

[Frank Close]

This was indeed where Niels Bohr, the great Danish theorist who was visiting and working with Rutherford in Manchester, had the idea that the atom could be visualized as this miniature solar system of the negative electrons whirling around the positive lump in the middle. And nobody knew what the positive lump consisted of, but that was the picture that was established by 1913.

[Alok Jha]

Okay, so you've got this positive lump, the nucleus was there. What did he do next to try and sort of understand what was inside it?

[Frank Close]

Well, of course, what happened next was that he discovered that when he fired alpha particles at light elements, previously, he'd been firing them at heavy elements like gold, where the nucleus is very big, like the football, and the little alpha particle bounced off violently. But when he fired them at the lighter elements, he discovered that the nucleus of these lighter elements could be ejected forward. And in the course of this, he came to the insight that there is a unit of positive charge in the nucleus, which is. Which he called proton. And the idea was that hydrogen, the simplest atom, consists of one proton in the nucleus entrapping one electron on the outside, and that helium then would have two protons entrapping two electrons. So that was where he was around 19 19. But they had also been able to measure the relative masses of these atoms. And helium, for example, instead of being twice as heavy as hydrogen was about four times. And as they worked at the periodic table, they discovered that although you went from one element to the next and the charge on the nucleus increased by 1, the mass of the nucleus increased much faster. And this gave Rutherford the idea in 1920, which he mentioned in lecture at the Royal Society, that there could also be a neutral member in the nucleus.

[Alok Jha]

A third particle in the atom.

[Frank Close]

Yes, the electron on the outside. Now a proton and a neutron, as he called them, in the middle. This might not sound very surprising to us today, but realise that back then, Rutherford has just increased the number of known particles by 50%. You know, this is quite radical, but that was the idea in 1920.

[Alok Jha]

He had this idea of the neutron, but didn't know what it was exactly. And it took about a decade before the. The neutron's nature was finally discovered. And it was one of Rutherford's students, essentially one of the people in his laboratory. Who did it? James Chadwick. But before we get to him, I wonder if you can talk to me about some of the other people involved who also had some thoughts about what the neutron might be and who didn't quite get to the end before Chadwick got there.

[Frank Close]

Well, the story here, I think, really comes alive. In the 1930s, Irene Curie, the daughter of Pierre and Marie Curie, and her husband, Frederic Joliot, in Paris, fire alpha particles at the nuclei of elements like beryllium and other elements at the lighter end of the periodic table, and were saying that photons were coming out of the beryllium nucleus, far more energy than you could explain at all.

[Alok Jha]

They were saying photons were coming out.

[Frank Close]

They were saying that photons were coming out. All they really knew was that they fired an alpha particle in which hit beryllium. And then downstream, something had come off from the beryllium. And all they knew about this something was that it was electrically neutral. And so they assumed that it was photons because that was the only electrically neutral thing that they knew of. They hadn't read Rutherford's 1920 lecture proposing the neutron, ironically. But then in Italy, a brilliant student working with Enrico Fermi in Rome, a theorist called Et Mayorana, said, well, that's the neutron. They're absolutely stupid. There's no way that you can produce photons out of this, violating the conservation of energy by orders of magnitude. They have produced a massive neutral particle, the neutron, with the same mass as the proton. And Fermi said to him, you've got to publish that. Mayor Arnold said, no, no, that's so obvious. He's so stupid. I don't want to publish that. So he didn't. But actually, he was right. And it was then when Chadwick, the assistant of Rutherford at Cambridge, read the paper that the Joliot Curies had written, in which they reported what they thought to be photons, that Chadwick, too, realized, just a second. This has to be a massive particle. And he went to see Rutherford, and Rutherford said, they're absolutely wrong. And so Chadwick worked day and night for about three weeks and finally established the existence of the neutron as a massive neutral particle with a mass very similar to that of the proton, and announced it in February 1932. And we now know that the neutron indeed is the spark that would light the nuclear fire. Both literally and metaphorically.

[Alok Jha]

The neutron would turn out to be critical to the eventual development of nuclear weapons. But when it was discovered in the mid-1930s, scientists were still scratching their heads about how they might actually be able to liberate the enormous energy locked up inside the nucleus. It had only been a couple of decades since scientists had realized that the energy leaking out of the nucleus through radioactivity was potentially vast. But it came out very slowly. Remember, there was enough energy there to propel a ship across the Atlantic Ocean. But it would take over a century to think about turning it into a useful source of power. Then the nucleus would have to release its energy much more quickly.

[Frank Close]

The path to that really began with Enrico Fermi and his group in Rome in 1934. What had happened was that in Paris, the Joliot curies had been irradiating atoms with alpha particles and managed to change the nature of those atoms, nuclei. They discovered they could induce radioactivity in atoms that had previously been completely inert, like atoms of aluminium, which had existed for 5 billion years just by firing.

[Alok Jha]

Alpha particles at them?

[Frank Close]

Just by firing alpha particles at them. And I would actually argue that second only to the discovery of the atomic nucleus itself, this was the real breakthrough that enabled us to get in the atomic nucleus and start liberating the energy. Now they were using alpha particles, which are positively charged, and positive charges on the nucleus would repel those alpha particles. Like charges repel. So there's this electrical shield stopping the alphas getting in. So the Jolio curies were only able to irradiate a few atoms at the lower end of the periodic table. The further you got the periodic table, the bigger the nucleus is, the bigger the electrical shield is, and the other particles just couldn't get in.

[Alok Jha]

So alpha particles could induce radioactivity in lighter elements, but it didn't seem that they could do it in heavier ones. That's because heavier atoms have more protons in their nuclei and therefore more electrical shielding against the positively charged alpha particles. It was Enrico Fermi who came up with a solution to the problem.

[Frank Close]

Fermi had the idea of using neutrons. The neutron has no charge. There's no electrical barrier at all.

[Alok Jha]

Instead of firing alpha particles, which are positively charged at the atoms, why not try using neutrons instead, which have no electrical charge?

[Frank Close]

So Fermi starts irradiating with neutrons. He reproduces the same phenomena that the Joliot curies have done, which is great, but he can now carry on all the way up the periodic table because. Because there's no electrical barrier at all. And he gets to the heaviest element of all, uranium, at number 92. And when he irradiates uranium, he finds some sort of signals which he cannot interpret. Actually he probably split the uranium in two, but that was 1934, and thankfully, he didn't realize what he had done, because that would be the key to atomic weapons. And had it been known five years before the Second World War started, we would not be having this conversation today.

[Alok Jha]

In the late 1930s, many physicists were trying to explain the strange results they'd been seeing when they'd fired neutrons at uranium.

[Frank Close]

We now know that, indeed, Irene Curie and Pavel Savage, her assistant, had been doing similar experiments in 1937 and also found strange signals. Curie found, she thought, lanthanum number 57 in the periodic table far, far, far away from uranium number 92. Everything that was known about radioactivity was that it shifted you one or two at most. You know, 92 could get you to 90, but not 57. So Irene Curie didn't understand this and just reported it and did no more.

[Alok Jha]

The explanation finally came from two of Otto Hahn's longtime collaborators, Lise Meitner and her nephew Otto Frisch, both Jewish physicists who'd escaped Germany.

[Frank Close]

The thing that had been overlooked in all of this was that the atomic nucleus has a lot of electric charge, positive charge. So if it was deformed very slightly into a sort of dumbbell, the two opposite ends of the dumbbell would each be positively charged and would be repelling one another. And so the possibility suddenly was that the dumbbell would split in two, which could explain why you started with uranium at 92 and you end up with things in the 40s or 50s of the periodic table. Chance would determine how big the two ends of the dumbbell happened to be. But that could be what was going on. And they did the calculation and discovered indeed, that the amount of energy released was vast, that everything about this hypothesis fitted with what was being seen.

[Alok Jha]

Meitner and Frisch's theory of how atoms split became known as nuclear fission.

[Frank Close]

So in a lump of neutrons and protons making a nucleus, there's a certain amount of energy trapped. And what nature is trying to do is to lower the amount of energy trapped in there into the most stable form, which means radiating off the excess. And that is what the origins of radioactivity are. But that, we now know, was only the start of it, because the idea of what was called the chain reaction was out there. That one neutron coming in would split uranium in two, but also liberate two more neutrons. And you could then imagine those two neutrons hitting two more uranium nuclei, liberating energy, and 4 and 8 and 16 quickly within about a thousandth of a second. You could have 80 replications of these suddenly, explosively coming out. So the idea that fission plus the chain reaction could lead to an explosive release of energy on an unimaginable scale was the thought that came to people as of about the beginning of 1939.

[Alok Jha]

We've got all the pieces now to make a devastating weapon. We've got an understanding of the nucleus. We know that the nucleus leaks energy. We know that there's enormous amounts of energy in the nucleus. According to E MC squared, you can split the nucleus and release some of that energy, and then you've got the chain reaction. Of course, this is all nuclear physics. It's basic science at this point. But it doesn't take a very creative mind to think this could be a devastating weapon. Given all of this, is it inevitable that people are going to make weapons out of it?

[Frank Close]

Well, if you see the film Oppenheimer, you have the impression that Oppenheimer immediately had a diagram for a bomb on his blackboard the moment this idea was out, and that everybody was saying, you can make a weapon. Niels Bohr put his finger on the problem, which is this. If it's so simple, then why aren't the rocks all around us, which contain a lot of uranium, exploding all the time? So it was that insight, that question of Bohr, which he then brilliantly answered, was that there are isotopes. Atoms of a given chemical element exhibit different forms of radioactivity. It all depended upon the number of neutrons that were in there. All uranium atoms have 92 protons, but they are accompanied by the order of 140 or more neutrons, giving you 238 in total for most uranium atoms, which are called Uranium 238. But sometimes there's three less, giving you 235, known as Uranium 235. And Niels Bohr's understanding of the dynamics of the nucleus told him that nuclei with an odd number of constituents, like Uranium235, are inherently less stable than those with an even number. And it was the uranium 235 splitting or fissioning that was liberating the energy. And an explosive chain reaction would require you to have a sequence of collisions with uranium 235 each time. Now, in ordinary uranium, uranium 235 is only about seven in every thousand atoms. So the chance that that you split two or three in a row is very small. You split one, you liberate energy. But the neutrons that come out are more likely to find themselves hitting uranium 238 and basically doing nothing.

[Alok Jha]

And the chain reaction stops.

[Frank Close]

So the reaction stops. Nobody seems to have asked themselves the question R. But suppose I could make a pure lump of uranium 235. How much would I need in order to make an explosion?

[Alok Jha]

Well, Otto Frisch did ask that question, didn't he?

[Frank Close]

Well, indeed, in 1940, Otto Frisch, by now in Birmingham, working with Rudolf Peils, another Jewish emigre from the Nazis, they asked themselves that question, did the calculation, and to their astonishment discovered that if you had Jewish just a few kilograms of uranium, about the size of a grapefruit of uranium 235, that would liberate the same amount of energy as 1,000 tons of dynamite. And it would also liberate gamma rays and nasty radiation. I mean, something the size of a grapefruit you can deliver on a single plane. This would have the possibility of doing the same amount of damage that the three nights of bombing of Dresden involving hundreds of planes, had achieved, all in a single bomb. And there would be no known material that could resist the devastation of such a device.

[Alok Jha]

The pieces for a bomb were now in place. Inside an atom was the nucleus, a source of unimaginable energy. Neutrons could split those nuclei and release some of that energy, split the right type of atoms and you'd set up a chain reaction. And if those atoms happened to be uranium 235, then a small lump was all you needed to create an explosion.

[Frank Close]

You can now see the panic that they had because they're doing this at the same time the Battle of Britain is happening and the possibility that the war could be over for Britain within weeks. And their immediate thought is, this is so obvious. Have the Germans already realized this themselves? And the only defense against such a weapon would be to have one yourself. So actually, the idea of what we now call Mutually Assured destruction was there in the very original insight of Frisch and Pyles in 1940. But that is what started the project in Britain of being able to what we call enrich uranium, to make pure samples of uranium235 in an amount that you could then make an explosive device. It was declared top secret. And we now know that in America they hadn't had this insight at all. They were very much aware of fission. Fission was not a secret. The idea of the chain reaction was not a secret either. The idea that you could liberate energy from uranium if you had got tons of it in what we'd now call a nuclear reactor to liberate energy for the use of society that was limit of their vision at that time. But the possibility of making a real explosion with a lump of uranium that could be delivered in an aircraft that was unique to fishing piles in Britain.

[Alok Jha]

Do you think it was just a matter of time because it was such a simple calculation?

[Frank Close]

I guess many calculations are simple once you know what you want to do.

[Alok Jha]

Yes.

[Frank Close]

No. It is fascinating. It is one of those accidents of history that this question was asked and answered at the critical moment, just less than 50 years after the discovery of a smudge on a photographic plate.

[Cheryl Rofer]

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[Alok Jha]

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[Alok Jha]

In the early 1940s, as the Second World War was in full force, Britain began sharing its scientific knowledge of nuclear physics with America. A top secret military endeavor based in New Mexico began to turn theory into practice. Hi, nice to meet you.

[Frank Close]

Nice to meet you.

[Alok Jha]

It's such a lovely place. You were just looking at the scenery.

[Nick Lewis]

Let me show you. We have cactuses blooming.

[Alok Jha]

Now the view from Cheryl Rofa's veranda in Santa Fe is what you might imagine America's southwest desert to look like. Red and brown plains dotted with trees and cactuses. Mountain ranges rising up in the distance.

[Nick Lewis]

That's Mount Taylor. It's considered by the Native Americans traditionally to be one of the four corners of the earth. And it's by Gallup, which is, I don't know, probably 100 miles away.

[Alok Jha]

That's 100 miles away. It looks like. Like it's next door.

[Nick Lewis]

I know.

[Alok Jha]

For 35 years, Cheryl worked as a chemist at the Los Alamos National Laboratory, the top secret facility built to create the first atom bomb. Los Alamos sits on a 2200 meter high plateau between vast canyons and calderas. Almost an hour's drive from where Cheryl lives. Now.

[Nick Lewis]

Los Alamos is back that way. You can't really see Los Alamos from here.

[Alok Jha]

Los Alamos was the center of the Manhattan Project. But it wasn't the only site involved in building the first bomb. At Oak Ridge in Tennessee, engineers enriched the uranium that would be needed for fuel for one of the bombs. A research site in Hanford in Washington State was given the task of making plutonium for a second bomb.

[Nick Lewis]

Los Alamos was put together deliberately to bring it all together and build the actual bomb. So that was totally created, and that.

[Alok Jha]

Was created completely in the desert. There were no scientific laboratories there?

[Nick Lewis]

No, there were no scientific laboratories.

[Alok Jha]

Yeah, yeah. Can I ask you, you know, given what you know about the timeline of how the technology of the bomb was invented and created, what were the hardest things to do in terms of actually the engineering and creation of it?

[Nick Lewis]

Probably the most difficult part was engineering the implosion bomb. There were two ways to make a bomb with uranium and with plutonium. And they knew enough about uranium that they could do the calculations. And the calculations came out such that they said, oh, we could even make a mistake in this and it would still work. You have two pieces of your fissionable material and you slam one into the other. So you put explosives or propellant on one and slam it into the other. It turned out that the plutonium was going to be much more complicated to make a bomb than they had expected. So the plutonium was not suitable for a gun type weapon like the uranium.

[Alok Jha]

Bomb and the gun type explanation explosive that he talks about, where you have two bits of fissionable material, say uranium 235, that are amounts that won't sort of explode, and then you put them together and then it becomes the critical volume that will turn into a bomb. That's, that's, that is one version of the bomb. But, but with the plutonium bomb, what kind of bomb was that?

[Nick Lewis]

That's an implosion bomb. And for implosion you have to make a shot explosives with detonators spaced around it so that it will very uniformly shrink down and crush what is in the center of it. Getting that symmetry is tricky. And explosions, as everybody knows, are hard to control. And what they did was they had a solid sphere of plutonium in the center, but the explosives compressed it even more, which made it go critical and explode.

[Alok Jha]

So in terms of the Trinity Test of 1945, the very first test that was done with a Nuclear weapon. Just describe for us what that particular device was.

[Nick Lewis]

By the way, looking directly south from the. From where we're sitting now is about where the Trinity site is, maybe 100, 120 miles away. You can't see it from here because we've got a little ridge in Santa Fe, but it's basically a flat plain with mountains around it. A little bit rougher looking mountains than here.

[Alok Jha]

It's apt that we're talking about it as we look at the direction of where it actually happens.

[Nick Lewis]

Right. It was an implosion type weapon. And because the implosion design was difficult and because it hadn't been done, they decided they had to have a test. And the mushroom cloud went up much higher than the mountain. There were people in Los Alamos who went up on one of the hills and they could see the flash of light and they're still further north than we are here. So it must have been very impressive.

[Alok Jha]

The very first full scale nuclear detonation took place at a test site in New Mexico known as Trinity. Nick Lewis, a historian at the Los Alamos National Laboratory, told me how it.

[J. Robert Oppenheimer]

Played out on the day of the test. The gadget itself had arrived from Los Alamos in the back of an army truck. It was a very long, careful drive all the way from Los Alamos. I think they started at midnight the day before and they arrived the. The afternoon. The day before the test. July 15, the Nuclear Components were assembled in the ranch house. There was a special clean room, as clean as you could make a 1920s ranch house. They covered the walls and the floor with burlap and they wouldn't allow any smoking in the room because that was a very bad.

[Alok Jha]

It's about as clean as it gets. Yes.

[J. Robert Oppenheimer]

No smoking in this room. That was good precautions for the 40s. So the plutonium pit, after it was all assembled at the McDonald ranch house, was put into a case, put in the back of an army staff car and driven out to ground zero at the Trinity test tower where the gadget was already waiting. And they sealed it up and they hooked it up to a $30,000 electric winch and hauled it up into the top of the test tower. They threw mattresses from the back of the truck underneath it in case the winch failed and it fell back down. I guess that would help it somehow. And J. Robert Oppenheimer, who is the director of Los Amos, he was watching like an expectant parent as the gadget was prepared and hoist up into the tower. It's a hundred foot Tall shot tower. They had it lifted off the ground so that it could simulate better the effects of being dropped out of an aircraft. And Oppenheimer was afraid of saboteurs because of how many people on the site knew so much about how the gadget worked. And he assigned Donald Hornig, who is the youngest scientist present at Trinity site, to write out the night on the 100 foot tall shot tower next to the armed atomic bomb. And that became very harrowing as thunderstorms gathered and lightning was crashing all around him.

[Alok Jha]

The weather was about to scupper Oppenheimer's plan to conduct the test in secrecy at dawn. But by 5:29am the rain had cleared. The scientists were given the green light. The nuclear age had begun.

[J. Robert Oppenheimer]

They described a blinding flash of light that was brighter than noon. Even though this was still before dawn. It apparently lit up the mountains that were surrounding the entire test area. They said that the colors were pretty psychedelic. They were remarkable going through shades of green and purple and orange as the different temperatures and materials were undergoing reaction. It was very quiet at first because of how far away people were from the test. And it took, depending on how far away you were, time for sound to arrive. And then suddenly it was thunder. It was this roaring train that ran into you and it produced a shock wave that could be felt for strongly. And if you weren't careful, you could be knocked over.

[Alok Jha]

The Trinity test solved the puzzle of whether or not it would be possible to release the enormous energy locked within an atom. The physics questions had come to an end. The engineering challenge was about to start. To understand how the device tested at Trinity would turn into the vast network of labs and stockpile of weapons that we see today. We need to go back to Los Alamos, the town at the center of the atomic universe.

[Frank Close]

Growing up here, when you walk through the grocery store, you're hearing physics, you're hearing chemistry, you're hearing hearing health research. And it wasn't until I went to Omaha, Nebraska for college that I walked through the grocery store and I was hearing football and baseball being talked about. And it took me a little while to get used to that.

[Alok Jha]

Next week, we'll hear how the lab and Los Alamos itself are still growing today, 80 years after that first nuclear detonation.

[J. Robert Oppenheimer]

A major contributor to the growth of the town is the fact that the lab has been growing over the last several years. This is a reflection of the current geopolitical realities. And recognize the role that deterrence plays in the 21st century.

[Alok Jha]

And coming up on the rest of the series. The value for us is not in blowing up the target, it's in getting.

[Frank Close]

High quality precision data out in the very short amount of time before the.

[Alok Jha]

Target does blow up.

[Nick Lewis]

We've been able to produce fusion ignition in a controlled environment in the laboratory for the first time, so experiments that produce more fusion energy than the laser energy required to drive them. I absolutely believe that the nuclear deterrent does preserve our way of life and our ability to protect that. We don't want it ever to be used. We come to work and work is hard, hard as we can on it, but we never want it to be used.

[Alok Jha]

To continue listening to the bom, you'll need to be a subscriber. If you subscribe to the Economist already, thank you. If not, you can sign up right now and it'll cost you as little as $4 a month for your best offer. Just search economists podcast plus thanks to Frank Close, Cheryl Rofer and Nick Lewis. And thank you for listening. The Bomb is produced by Jason Hoskin with mixing and sound design by Nico Rofast. Special thanks to Alicia Burrell for help in producing this episode. The Executive producer is Hannah Mourinho. I'm Alok Jha and this is the Economist.

[Darina]

Foreign.

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