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National Museum of Nuclear Science & History

Alex Wellerstein’s Interview

In this interview, Alex Wellerstein, a historian of science and founder of “Restricted Data: The Nuclear Secrecy Blog,” discusses the basic science behind the atomic bomb and explains the difference between the uranium “Little Boy” bomb that was dropped on Hiroshima and the plutonium “Fat Man” bomb that was dropped on Nagasaki in August 1945. He also discusses Britain’s contribution to the Manhattan Project and provides a brief history of the German and Soviet atomic programs. Wellerstein also discusses the effects of nuclear fallout, including the short and long-term threats posed by radiation.

Date of Interview:
February 13, 2013
Location of the Interview:


Cindy Kelly: This is Wednesday, February 13, 2013. I’m Cindy Kelly, and we have with us Alex Wellerstein. Alex, could you say your name and spell it, please?

Alex Wellerstein: Alex Wellerstein, W-E-L-L-E-R-S-T-E-I-N, and it’s just Alex, nothing fancy.

Kelly: Great. Thank you, Alex. Alex, give us a little background as to your education and how you come to know about the Manhattan Project and related subjects.

Wellerstein: I’m a historian of science. I have a PhD from Harvard University. My work is on the history of nuclear weapon secrecy from the Manhattan Project to the present, and so I’ve been looking at nuclear weapons and everything about them for some time now.

Kelly: And tell us about your blog. 

Wellerstein: I run Restrictive Data, the nuclear secrecy blog at, which is a forum for all sorts of unusual nuclear things that I’ve run across in the course of my research, and a place to talk about some of the bigger issues that come up when looking into the history of nuclear weapons. 

Kelly: So how would you rate your sense of humor on a scale of 1 to 10?

Wellerstein: It really depends whether or not you have a dark sense of humor or not. I’ve found that some people would rate my sense of humor very highly, and some people would see it as an immense liability.

Kelly: I love your sense of humor [laughter]. As I explained, we are trying to sort of fill in the blanks on some of the issues related to Manhattan Project history, as a starter. We have some exhibits that we’re doing – one on the role that Columbia River played at Hanford. So with that introduction, can you tell us about the role of the Columbia River at Hanford?

Wellerstein: Well, the choice of the Hanford site was very much contingent on having good water source. They knew from very early on that they wanted a place that was both isolated, and also had a large amount of cool water. 

The selection of the Hanford site was contingent on finding a place that was both isolated and had excellent water supply. The Columbia River area completely supplied both of these requirements. It was sufficiently isolated that they could locate a very large plant with very large and potentially unsafe industrial facilities all along it and not be too close to human settlements, but also provide the water necessary for all the processing reactor. 

One of the interesting things about the Hanford site is that they explicitly tried to calculate how far apart they would need to put each of the facilities in case any one of them had a meltdown. So the idea was that even if they had a meltdown, they could keep the other ones running, so they were about a mile apart from one another using very conservative calculations about what would happen if one of these reactors exploded or something like that. They didn’t expect such a thing to occur and they were hoping such a thing did not occur, but it’s rather interesting that they were ready for such a thing to occur, to keep the front of their building even if it did.

Plutonium is a really tricky element. It’s extremely complicated on a chemical level and on a physical level. From a chemical level, it has six different allotropes, so these are different crystalline structures. It has a seventh under pressure. What that means is that little temperature changes in plutonium radically change its density, so that makes it a difficult product to work with, no matter what. Add to it that it’s radioactive and has a half-life of several tens of thousands of years but is so radioactive to matter, it’s also extremely toxic, as well.

So you have something which is difficult to use both from a chemical standpoint, from a toxicity standpoint, and a radioactivity standpoint. Add to it the fact that it is also fissile so it can explode or heat up if put into the wrong concentrations. It’s also pyrophoric, which means it catches on fire when you expose it to oxygen. It’s really trick metal, probably appropriately named plutonium for Pluto, originally the plantet, but also the Roman God of Death. Glenn Seaborg, when he discovered it, gave it the atomic abbreviation of Pu, not Pl, and it was partially as a joke because plutonium was so difficult and so nasty to work with so it’s Pu

Plutonium is a manmade substance. It’s an element that, generally speaking, does not exist in nature. The only place that plutonium exists in any great quantities on this planet is inside nuclear reactors or has been removed from nuclear reactors. It’s completely artificial. It’s just stable enough to be something that we can keep around and so it doesn’t radioactively decay into something different. But it’s also just unstable enough that you can use it inside a nuclear bomb.

During World War II, one of the main difficulties was concentrating enough plutonium in any one place that you could use it for a nuclear weapon, and that’s why they had to build these gigantic industrial sized huge nuclear reactors along the river.

The heaviest element that you find in nature is uranium. They named it at the time because Uranus was the farthest planet out. When they discovered one heavier than uranium, they named it neptunium for Neptune, and then the one out from that is plutonium.

Uranium-235, when it absorbs a neutron, will wobble. Wobbling causes it to split into two pieces. This is nuclear fission. When it splits into two pieces, it sends out a number of neutrons – between about two and three. If one of those neutrons hits another atom of uranium, Uranium-238, the heavier form of uranium, it doesn’t wobble and split again. What it does is it absorbs the neutron. It becomes neptunium and then, after a couple days, it becomes plutonium.

This is where all plutonium in the world more or less comes from, is this process of taking neutrons that are released by fission, absorbing them into other forms of uranium, and then getting a new substance out of it. 

What you then have to do is to put a lot of chemical processes—lots of acids and very complicated things going on—you can strip out all the plutonium and concentrate it. And this is what they were doing during World War II to concentrate only thirteen pounds or so of plutonium were necessary for the bomb but that took years of running these reactors because you’re creating little tiny, tiny amounts of it every time you run the reactor.

Plutonium is also fissile, so that means that if plutonium gets hit with a neutron, it too will wobble and split and release energy and neutrons. The amount of energy released every time the plutonium does that is about enough to move a speck of dust visibly. Which doesn’t sound very impressive, but remember, we’re talking about atoms here, which are absurdly small. So the best metaphor I can come up for understanding that order of magnitude, it’s as if an ant was kicking the space shuttle and the space shuttle shuddered a little bit, and that would be very impressive. Especially when you start ramping up how many fissions you have inside of a nuclear weapon.

Every one of those plutonium fissions is a generation. So if those neutrons go out and make two more atoms fission, that’s another generation. You do two or there more and each of those atoms do two or three more atoms, that’s another generation. When you get up to about eighty generations – so that’s two to the eighty—it’s a very large number, it has a lot of zeros after it—that’s about twenty kilotons, twenty thousand tons of TNT explosive equivalent. So all those little specks of dust, you add them up within the space of maybe a nanosecond—so a very small amount of time— and that’s enough to destroy an entire city. 

One thing that most people didn’t realize at the time of the first atomic bombs, and most people don’t realize now, is that the amount of plutonium you need for a nuclear weapon is very small. It’s actually much smaller than the amount of Uranium-235 they used during the war. So during the war, the highly enriched uranium they developed for the Little Boy bomb on Hiroshima, that’s about sixty-four kilograms of uranium, so that’s a hundred and something pounds of uranium that they were using. That’s a very large amount. 

The amount of plutonium they used was about nine kilograms, so that’s about thirteen pounds. That’s about the size of a softball. So it’s a softball’s amount of plutonium with all sorts of other things stacked around it, because the whole goal of that bomb is to compress the plutonium. That takes all these explosives and all these complicated detonators and electrical switches and things like that. But it’s really only about thirteen pounds of material that actually is responsible for that energy output. That’s something that even President Truman found completely flabbergasting. He wrote in the diary at the time, “Only thirteen pounds of this metal destroyed an entire city.” It’s a rather profound idea.

The uranium in the Little Boy bomb was not essentially large. I mean, sixty-four kilograms is a lot of uranium, but it’s very dense, it’s very heavy, and it’s much denser that the kinds of metals we deal with on a regular basis. So if you have a little cube of uranium, it will weight a substantial amount just by itself. The amount that they used in the bomb, they separated it into two pieces. One was sort of a stick and it was probably about this wide, so maybe five or six inches maybe, and then had a diameter of two or three inches, and so that’s at one end of the bomb, this sort of stick. 

And the other end is a tube, and the tube is somewhat larger. The tube is a little bit wider, but it’s still pretty small. And all of this is fitting within a standard artillery barrel so if you ever see any pictures of like a bazooka or something like that, it’s a little bit bigger than that. The way the Little Boy bomb worked is to take that uranium, the tube, and shoot it into that spike of uranium. That’s how you bring the critical mass together. It was a very crude bomb, and again, it used sixty-four kilograms of highly enriched uranium, which is a lot. That’s a lot of uranium. It took them years to accumulate that much uranium. 

After they used the implosion bomb for the first time in the Trinity test, Oppenheimer even said, he wrote, “Why don’t we not use the gun type of bomb? Why don’t we take that uranium and split it up into more implosion bombs?” But it would’ve taken too long. We don’t have the time to figure out that. It’s complete reengineering of the bomb.

One of the things in the postwar period that’s very important was finding ways to use highly enriched uranium and plutonium together, because that way they could have as many bombs as they wanted to. Because they had Oak Ridge producing all this uranium, they had Hanford producing all this plutonium. Being able to use both of them in the same bombs meant that they could very easily expand and scale up their stockpile.

Kelly: That’s interesting. Because I thought it was—talking about the fusion bomb—so you have a fission bomb detonating the fusion bomb.

Wellerstein: Well, they do that later. That’s in ’51, ’52, they figured it out.

Kelly: But they did mix the metals?

Wellerstein: Yes, that was one of the first things they tried to do in 1948 when they had their big Operation Sandstone. This was the first big, “Let’s try out new weapons designs.” The first test after the war, Operation Crossroads, was just the same weapons they had made during World War II— exact same weapons, exact same cores they have been experimenting with. That was just an effects test. Nothing new was done there. But by ’48, they were trying out brand new designs. Among them are using mixed fuels, so that’s high-density uranium and plutonium together. Also, new ways of designing a bomb so that you could use even less material and get the same amount of explosion, which allows you to, again, increase your stockpile. This was a major concern after the war. 

Hanford somewhat went to seed in the years immediately after World War II; the output declined. Part of this was technical because it turned out that their carbon in their reactor was expanding under all the irradiation. They didn’t completely understand how these materials would be influenced by having all these neutrons bouncing around; it’s still a tough thing to figure out ahead of time. And they had to shut down B Reactor for a while because of this and figure out how to make it work better. 

But also organizationally, after World War II, the Army was still in charge until 1947, but wasn’t sure what it was supposed to be doing. It was taking longer than they had expected for civilian legislation to pass for an atomic energy commission to take over. Even then, there was a whole difficulty of them figuring out what they were supposed to do. 

So it’s not until about 1948, 1949 that they start getting the atomic production back up to speed again. The American nuclear stockpile was almost nothing until about 1950. I mean, it sank to maybe double digits at the end of the end of the 1940s, but it was very small. This was actually one of the biggest secrets out there: that by 1947, they have basically no bombs ready to use in case they needed to. They could’ve put them together over the course of a couple months, they had fissile material, but it was so immensely small. By the 1950s, they’d ramped up the entire production line and suddenly we are now talking about hundreds and hundreds of bombs and things like that that we associated with the Cold War. But it was actually much later than most people realize.

In 1945, one of the big questions on everybody’s mind was: when will the Soviet Union get a nuclear weapon? Everybody assumed they wanted to get one, and the question was: how long will it take them? Most of the scientists at that time said it would be about three to five years, give or take. They have good scientists; they have a lot of resources. It’s really just a matter of them deciding to do it. 

Some people thought it would be longer. Some people thought ten to twenty years. General Groves thought it was about ten to twenty years. The reason he thought that was not because he was dismissive of the Soviet science, he actually believed the Soviets did have good science. He was a bit dismissive of their industrial capability. He thought they just didn’t know how to run the plants of this size. It wasn’t really what their economy looked like. He wasn’t completely wrong about that, they had a lot to learn. But it was mostly because he had tried to buy up all the uranium in the world during World War II.

General Groves had gone around and made all sorts of side deals with countries that have uranium works in them, when there were a bunch at the time—the Congo in Africa, Portugal, Brazil, India, Argentina—lots of countries where there were known uranium or thorium, which can be used like uranium, ores out there. Groves tried to basically buy them all up in secret. So he thought the Soviet Union would have a real hard time getting uranium, and without uranium you can’t do anything. You can’t make reactors, you can’t enrich it, so you don’t have highly enriched uranium, and you don’t have plutonium.

Indeed, this was actually a huge problem. The Soviet Union spent a lot of their time—most of their time—trying to find uranium reserves within their own borders. They had a little bit of uranium that they got from the Germans and from Czechoslovakia, which is one of the only other known uranium sources at the time, but they immediately instituted at the end of World War II a huge survey of their vast lands to see, “Do we have uranium on it?”

It turned out that uranium was much more common than was known in 1945, and they did have uranium mines. They had very low-grade uranium mines. Just to give you an idea of how poor these mines were: in the American Southwest, an economical uranium mine has about 5% uranium in it. Now, this is just natural uranium. We’re not talking about enrichment levels or anything like that. This is just how much uranium is in the ore. The rest of it has other stuff—vanadium and just rocks of different sorts. Five percent is considered economical to mine. 

The Belgian Congo uranium that we used during World War II, that had levels of up to 60% or 70% uranium, so that’s incredible. That’s the richest we’ve ever heard of, is in the Belgian Congo uranium. This is what we used to build Little Boy bomb and the reactors. We were very fortunate that we were able to get our hands on that. 

The mines in the Soviet Union were less than 1% uranium in them. By American standards, that would be not worth mining. But when you have gulags, you don’t have the same economic constraints. You have forced labor, and they were able to use that to great effect. They just threw a lot of people at the problem and they mined very poor ores and were able to, over time, accumulate a lot of uranium.

When the Soviet Union detonated their bomb in 1949, a lot of people were surprised. Part of this is because people are somewhat shortsighted. So in 1945, they said that it would be three to five years before the Soviet Union gets a bomb. In 1946, they said it will be three to five years before the Soviet Union will get a bomb. In 1947, they said three to five years. 1948, three to five years. And so in 1949, everybody said, “My God, we didn’t think they’d get a bomb for another three to five years.” But they really just hadn’t tallied up the numbers. 

They also didn’t know whether the Soviet Union had actually started its own bomb program, and they didn’t know when they would start its own bomb program. And we now know that the Soviet Union had been working on nuclear weapons since about 1943. Not to say that it was a full production project.

They didn’t really start trying to build a bomb until 1945, but they were thinking about it and they were getting American information through espionage. They had at least three major spies at Los Alamos. They had a number of other spies around. They may have had other information that we don’t even know about today. From this, they were able to get a very good picture of what the American work was, and a very good picture of what they needed to do to make a bomb. The spies can’t give you a bomb. They can tell you maybe how it is made, and maybe that will save you some time. 

I’m not 100% sure that it did save them very much time because the Soviet Union’s bomb program was run by [Lavrentiy] Beria, who was the head of Stalin’s Secret Service—what later became the KGB—abnd he was immensely paranoid. He didn’t believe the spies, and he didn’t believe his own scientists. So he played everybody against each other to try to figure out what the truth was, which is a very slow way of using information. They ended up recreating all the American data and all the American experiments. They didn’t take any real shortcuts that way. But it still takes time to do that, and they still needed to get all the uranium together. 

One of the amazing things about the Soviet nuclear project is that almost none of the people working on it knew that they had espionage information. There was literally one or two scientists who were working on the Soviet bomb who had any clue. This was part of what I sometimes like to call, somewhat jokingly, the Beria School of Management.

Beria’s an awful guy, Beria’s secretive. He was a KGB guy, he was in charge of Stalin’s purges, he was a rapist. He was just an awful, awful guy. He didn’t get to be where he was by being a trusting guy. He didn’t get to even survive in Stalin’s Soviet Union by trusting anybody. His entire job and way of life was predicated on not trusting. So he didn’t trust the scientists, he didn’t trust the spies. He thought the spies might be double agents trying to give the Soviet Union bad information so that they would’ve wasted their time on the bomb. He thought his own scientists might just be lying to him because he doesn’t trust scientists.

One of the ways he got around this was he had two sets of scientists, two teams working on any given problem, so that if they came up with different results, he would call them together. They wouldn’t know that the other team even existed. He would call them together and say, “So Scientist Team A, you got different answers than Scientist Team B. Which of you is correct?”

All these scientists know in the back of their head is, “If I’m wrong, then I’ll be accused of being a traitor and I’ll be sent to a gulag.” And so this is a very disturbing motivator, but it’ll do.

What he also did was he often took the intelligence information that they got from, say, Klaus Fuchs or Ted Hall at Los Alamos, and they would rewrite it as if it had been created by a Soviet lab, one that nobody had heard of—you know, Lab Number 456, you know—all these labs with just various code names. So they would present this to the scientists and say, “Lab 456 said that the bomb is made like this. What do you think about what they said?”

The scientists would then look at it and go, “Oh, I don’t know. Maybe they’re right, maybe they’re wrong.” They had no clue that it was espionage information.

So many of the Soviet scientists, for years afterwards, and even after the Cold War, said “We didn’t copy any bomb from the United States. We had to build it ourselves.” This is partially correct. They did have to rebuild every little part of that. The bombs are not exactly the same. They’re obviously related to one another.

Beria wanted the first Soviet bomb to basically be a copy of the Fat Man device, because he knew it would work. He also knew if he failed, he’d be in big trouble with Stalin himself. But only years later were they able to look at all of these different blueprints of things and say, “Oh, my God. These weren’t even made by Soviet scientists. We were really looking at American information.”

The initial impetus for the American bomb project was a fear that the Nazis were themselves trying to get an atomic bomb. It was not an entirely unjustified fear. Nuclear fission had been discovered by a team located in Berlin. [Werner] Heisenberg, the great scientist of his age, was living in Germany, and Hitler had a penchant for fantastical weapons. He pursued a number of out-of-the-box ideas for winning the war. He used these rockets, he had all sorts of weird plane designs for jet engines. I mean, a lot of things that were actually weapons that would become important to the next war, Hitler was trying to do during World War II. So imagining that he would be looking at atomic weapons is not a farfetched idea.

It turned out, in fact, though, that they never really got that far. The reasons for that are very complicated. People have been trying to figure that out since 1945. The Alsos Mission, one of Groves’ programs, its whole purpose was to try and figure out what did the Nazis do, why did it fail, can we get as many Nazi scientists as possible, things along those lines. 

What they found was a fairly complicated story. One is that the Germans were extremely disorganized. So they didn’t have any sort of centralizing committee that was in charge of everything. They had lots of little teams looking at different aspects of the problem, and some of these teams were very good and some of them came up with the same answers that we came up with in the United States. So they figured out very early on, just as we did, that theoretically, you could make a reactor. They figured out, just as early on as we did, that theoretically, that you could make plutonium at this reactor.

But they never did these things on a big scale. One of the reasons they found making a reactor very difficult was in their choice of a moderator. So in a nuclear reactor, what you want to do is slow down the neutrons. You have these fissioning neutrons of Uranium-235 and when they fission, the neutrons that are coming out of them are very fast. The faster they are, the less likely they are to be absorbed by other atoms to create more fissioning. The reason of this has to do with the speed of the neutron – is related to how large everything looks to the neutron. So a very slow neutron looks like a big fat target to run into other things. A very fast neutron is like a little tiny bee and it’s going to ricochet off of every other atom in a reactor.

The way you slow down a neutron is by bouncing it off other things. So in the United States, we looked at—and they looked at this is Germany, too—the use of carbon. Carbon on an atomic level, it’s sort of plump and squishy. It’s like a bumper in a pinball machine, and if a neutron hits it, it loses a little bit of energy and ricochets off again.

The other one that we looked at in the United States—and they looked at this in Germany, too—was heavy water. Heavy water is a type of water, deuterium, and it also is a nice, squishy target for these neutrons to hit. Now, in Germany, they decided that carbon wasn’t going to work. They had very bad results, and we had the same results in the United States. What we were able to figure out in the United States, though, was that the reason wasn’t something inherent in carbon. It had to do with the fact that carbon has impurities within it because of the mode of its normal production.

Most carbon, especially at that time, was not being used in nuclear reactors, so they weren’t worried about certain types of impurities. The biggest impurity that they were worried about was boron. Boron is an atom that will absorb neutrons. It’s very greedy. So it’s like if you had your pinball machine with your neutrons zipping around, suddenly there’s this big sticky bit, and that’s the end of your reaction going.

In the United States, our chemists and our physicists all worked together, along with the industrial people who were producing the carbon, to remove the boron from this carbon and getting extremely pure carbon, and that was what was used in the first nuclear reactor at the University of Chicago in 1942. Also, we ended up using it at Hanford for B Reactor.

In Germany, they didn’t do that. They didn’t figure out why carbon was so much of an issue, and they didn’t look at making better carbon. So they decided to put all of their effort into getting heavy water. The problem was that they didn’t have very much heavy water in Germany—it was all in Norway. The British figured this out in quite a very daring commando raid and destroyed the heavy water production facilities in Norway. That made it extremely hard for Germany to go forward. 

The broader issue, though, why Germany didn’t make the bomb, was that they never really tried to. In the United States, we had a very long period—you’re talking about 1939 to 1941—when we were still exploring should we make a bomb, can we make a bomb, is this a good idea. Finally, about 1942, people said we could do this, we should do this, let’s go for it. So they started building it up bigger and bigger, and they started centralizing all the work even more. By 1943, they got the Army involved, and the Army is building these massive – the biggest factories in the world at the time to build the atomic bomb and these reactors, and they were putting a lot of money and effort into it. 

In Germany, they never got beyond the figuring out whether they should do it or not do it stage. If the war had gone on for another five years or something, and if Germany hadn’t been so heavily bombed and was having so many troubles just getting basic things running, I imagine that they might’ve done such a thing. They were just at the end of the war in 1945, when Germany has basically lost and was being invaded from both sides by the Soviet Union and the United States and British. They were setting up a reactor experiment not too different from the one we did in 1942, so that was a three-year timeline they were behind. They didn’t even get it to work. They didn’t get the reactor to go critical.

So there’s nothing inherently why the Germans couldn’t have done it except that it would’ve taken a lot of effort to do so. And the time in which they would’ve had to make a decision in, say, 1941, 1942, they would’ve had to feel that they needed to do it. By 1941, 1942, Germany was still doing very well in the war, they didn’t think they would need such a thing. They had no idea, because of the secrecy that the United States had invested all of its efforts into doing.

One of the top nuclear physicists in the world at the beginning of World War II is Werner Heisenberg. Werner Heisenberg was, in the 1920s, one of the creators of quantum mechanics. He came up with the Heisenberg Uncertainty Principle, he worked with Niels Bohr in Copenhagen, he was one of the great physicists of the twentieth century, and we still use his name all the time.

He was not exceptionally enthusiastic about Hitler or the Nazi regime. In fact, he had been labeled sort of an enemy of the state for a while on account of the fact that he taught general relatively and quantum mechanics. These had been deemed by the Nazis to be Jewish physics.

Now, Heisenberg wasn’t a Jew, but they dubbed him a “White Jew” for a while, and some people tried to get him fired or worse, you know, very high consequences. It was partially because he was so eminent, but also because of the fact that physics was looking like it might be very important in the war, the Nazi state was willing to look the other way and say, “You know, Heisenberg, you can be one of us. We don’t have to get rid of you if you’ll just work for us.”

It’s not clear whether Heisenberg really wanted to give Hitler a bomb. Heisenberg has sometimes been interpreted as explicitly sabotaging the German project, but there’s almost no evidence of this. Even Heisenberg himself was very careful never to actually say that that was what he was trying to do. I don’t think that there’s any reason to think that he did it on purpose. He was not an incompetent scientist, but I think that he was just never actually trying to build a bomb, and that’s one of the main reasons he never built a bomb.

So one of the things that the Allies did as they invaded Germany was to take all the people who they thought might’ve involved with a Germany nuclear project and put them into one of these great manor houses in the British countryside, and this one was Farm Hall. They had bugged the place. The Germans may have known that they had bugged the place. They had worked with the Gestapo; they knew what bugging was about.

The reason they wanted to do this was one: they didn’t really know what to do with these people. They didn’t know how far they had gone, but they also didn’t want to sort of release that to the Russians, so they thought putting them in this house was a good place to put them for now. But also, they wanted to see what they would do when they heard about the bombing in Hiroshima. 

So they kept the transcripts of these bugs and so before Hiroshima, the scientists were very despondent, and they didn’t really know how they would fare. They were very unhappy, and they wondered if they’d ever be let go. Then, they played for them the BBC radio announcement of the bombing of Hiroshima and Truman’s announcement. They listened, what did the scientists say afterwards. It’s really a fascinating study.

So some of the scientists – Otto Hahn, who discovered fission, so he’s sort of the great, great grandfather of the bomb, in a way, was despondent, even talked of suicide. He felt that he had all this blood on his hands and that it was just an awful situation. Some of the people who had been more involved with looking to the bomb were much more conservative about it and started even coming up with the official story that these scientists would tell afterwards that “Well, we didn’t make a bomb because we didn’t want to make a bomb because we didn’t like Hitler.” Which was not true but they were starting to even think about this then.

One of the most interesting reactions from Werner Heisenberg, who was by far the best physicist in the room and by far the most eminent in the room. He said, at first, he said, “I don’t believe it.” 

He said, “They’ve got a very good PR person. They dropped a very big regular bomb, but they can’t do that, it’s just not possible.” Then he starts to loosen his ways.

After, the other scientists say, “Heisenberg, are you just saying this because you didn’t make one and you think you’re wrong?”

He said, “No, that’s not why I’m saying this.” 

Eventually though, they start giving more information, and by the next day, he’s ready to give a lecture to the other group about how they made a bomb and ready to tell them exactly what he thought happened. It’s just based on the information that he was able to get from the story, which was things like how large the explosion was and other little details that we dropped out of one plane and things like that, which limited how big it has to be and stuff like that.

So it’s actually kind of an amazing thing. The German scientists expressed genuine shock that the United States did this. None of them say, “Oh, yeah, we knew that was going to happen.” Part of that is a nice reflection of the secrecy, to some degree, did work. None of them realized that the United States was that far ahead of them in making a bomb.

On the other hand, once they knew that a bomb could be made, it did not take them very long to figure out, more or less, how the United States did it without any access to any other information. They just did it based on what they had already known about with their physics and about how to make a bomb.

So it tells you a lot, I think, about one, what the German state of mind was in the sense that they were not really as far along as the Americans had thought they were, but also that they were extremely capable people. They were not fools in any respect.

When we usually talk about how the Manhattan Project started, we talk about this letter that Albert Einstein wrote to President Roosevelt. He wrote this letter in October, 1949 [misspoke: 1939] that says, “Dear President Roosevelt, I’m worried about the Germans. Maybe we should spend some money looking into whether a nuclear bomb is possible.”

Roosevelt said, “Okay.” This is sort of the beginning of the American effort, but it was very disorganized. It was very small. It was not a bomb production program, it was an exploratory program—basic science. Is a bomb something to be worried about? It was very slow, even along those lines. It was run out of the National Bureau of Standards, not what anybody thinks of when they think of cutting edge science and research or anything like that. No offense to the National Bureau of Standards, but that’s not what they do, for the most part.

It was kept very secret. Roosevelt wanted it to be very secret. But it’s also the case that a lot of people just didn’t think it was very important. For even very top-level people, so like President James Conant, the head of Harvard University, as late as 1941, was saying, “I don’t think we should worry about this problem very much. We should be taking the physicists, having them work on things that look like will be really useful, like radar, for example, or all the other wartime issues where scientific problems are going to come up. An atomic bomb might be workable in the far future, but it’s not a problem for this war. It’s somewhat science fiction-like.”

And they were not entirely wrong. What they had found was that making an atomic bomb would be incredibly hard. It’s in this period, late 1941—two years now after the Einstein letter, and that’s kind of the conclusion they were at, which is that it could be done but it’s extremely hard—a group from the United Kingdom shows up and sends them a report, and this is what’s known as the MAUD Report. And the MAUD Report explains, more or less, that the British think that you can make an atomic bomb pretty easily. You wouldn’t need that much-enriched uranium and that it would be completely worth spending a lot of money on. 

And this actually completely changes the atmosphere in the United States. There were a few people who still thought a bomb was important in the United States before they got this report. But after this report, there becomes a sort of cabal of very top-level physicists and administrators who are really interested in trying to make an actual bomb. These include Vannevar Bush, who ran the Office of Scientific Research and Development; James Conant, the President of Harvard; Ernest Lawrence at UC Berkeley, at the Radiation Laboratory; Arthur Compton at the University of Chicago; and Harold Urey, who was working at the time, I think, at Columbia.

These people got very excited about the idea that the bomb was actually feasible, that it wasn’t just science fiction, that it wasn’t something that could only be built in ten years. So by early 1942, they had completely gotten control of this bomb research program from the National Bureau of Standards. What was initially called the Uranium Committee, which is a very explicit description of what they were looking into—they actually called themselves the Uranium Committee, which is a nice sign that it isn’t that secret—they changed that to the S1 Committee. S1 completely means nothing, it’s just a very secretive term and they didn’t want anybody to know that it’s concerned with uranium. 

So it’s really this British report that gets things started in the United States. Before then, if the British had not come in, the odds are that the United States would’ve continued to be disorganized and continued to just be a very exploratory program of the sort that was actually going on in Germany for this whole time. So the British report was sort of the spur. 

One of the ironic things is that the initial American assumptions were actually correct – it was really hard to make the bomb. It was not an easy thing at all. The initial estimate by Vannevar Bush for how much it would cost the United States to build a bomb was 400 million dollars. The reality was that it cost two billion dollars, so he was off by five times. That’s quite a difference in estimation. 

So there’s some irony. The British were required to get the Americans invested enough in the bomb project that they would actually pull it together, even though it was completely wrong about how easy it was to make a bomb.

One of the things that’s really distinguishing about the American nuclear weapons program is the level of secrecy. And it was, even during World War II, it was understood to be a level of secrecy higher than any other military program. This was actually language that President Roosevelt used. 

It all stems from Roosevelt. We often wonder why was it kept so secret. Well, Roosevelt, from the very beginning, said, “We’re going to keep this very, very secret.” He mandated to Vannevar Bush that he maintain absolute secrecy as he could. The fact that there even was a secret was, itself, a secret. The fact that they were even worried about the atomic bomb was, itself, a total secret.  

That’s a very unique situation. In most cases with military programs, you kind of know they’re a military program. So today, if someone was at Los Alamos, if you went over there and say, “What’s going on there?”

The fellow could say to you, “Oh, I can’t tell you, it’s a secret.”

You’d say, “Oh, yes, it’s a secret because I know that there’s a secret program there.” During World War II, even the fact that Los Alamos was a secret, was itself, a secret, which is very complicated. So if you went to Los Alamos and said, “What’s there?”

They couldn’t say, “A secret military program.” They would just say, “I don’t know what you’re talking about,” and hope that you went somewhere else.

The secrecy was sort of many forms. Even before the Army got involved, they had a lot of secrecy. So before General Groves and the Army and these people who have a reputation for having a lot of secrecy who were involved—they were already thinking about moving all their sensitive facilities to remote locations just to reduce the amount of people who were around.

So they were talking about creating a weapons lab like Los Alamos that would be in the middle of nowhere. They were talking already about trying to censor scientific publications. They had already been doing self-censorship since 1939, but had started to institute that on a less self level, so they were having committees that would review new publications in physics if they had anything to do with fission. They were already talking about compartmentalization. They weren’t using that term exactly, but that’s the “need to know,” so that one scientist, another scientist on the same bomb project working different parts of it wouldn’t necessarily be allowed to talk to each other. The idea that any one scientist doesn’t know the whole picture and any one worker doesn’t even really know what they were working on. They were already doing that by 1942.

When the Army came in in 1943, all of the secrecy ramped up. It becomes much, much bigger. And part of that was just because the project itself became much, much larger. So already by 1942, you’ve got several thousand people working on this project. By 1943, you’re talking about tens and hundreds of thousands of people who are involved producing this, and a lot of them are on the very low level—construction or technicians, people who are working at Hanford and Oak Ridge to put together these massive factories. 

So the amount of security just goes up incredibly. They start looking at people’s mail at Los Alamos, they start doing lots of background investigations on anyone who’s going to be involved in the project. They even start doing voluntary censorship of newspapers, which works, more or less. They had some problems, but there are more leaks that people realize, I think, but they did pretty well on that. 

After the war, General Groves listed eight targets for what the point of the secrecy was. What were the eight major objectives to secrecy? Number one, keeping it from the Germans and the Japanese – so that’s kind of one and two, actually. Number three was keeping it from Russia, which even in World War II, Groves was thinking about it. He knows that there are some big spies at Berkeley, for example, and he’s a little bit uncomfortable, even though the Soviet Union’s an ally. But Groves, not incorrectly, assesses them to be a somewhat temporary ally, not necessarily a long-term ally. So that’s three of them.

Number four, he’s concerned about compartmentalization, not just because it would keep a spy from knowing what another guy’s work was on, but also because he wanted the scientists to stay focused. So Groves doesn’t necessarily trust scientists. He’s an engineer himself, he trusts engineers. He believes that the scientists, if given sort of unlimited flows of money and asked to investigate interesting cutting edge scientific work, will not necessarily stay focused on the immediate role, which is producing a bomb for the purpose of war. He’s not entirely wrong on that. I mean, later, he feels he’s completely justified in that; it’s a very General Groves thing to say. But he’s not entirely wrong that they would tend to diverge if not watched over.

He wanted to keep Congress out of the loop, and this is sometimes a bit surprising. They ended up telling seven congressmen over the course of the war what they were doing just to make sure they were willing to sign off on their secret budget requests and things like that. He was very much afraid that if that information got to Congress that it would slow everything up. There would be hearings where every physics professor would get up and say, “We should be looking at nuclear weapons,” you know, things that he wouldn’t actually necessarily be in favor of. If people were going to go out and say we shouldn’t be going, he’s worried that people would say we should be, and then Groves would be in the awkward position of sort of denying that they were but kind of they are and things like that. So he actually wanted Congress out of the loop.

He also didn’t think – and this is probably also correct – that Congress would approve of spending this much money on what sounded like a science-fiction project. Until the bomb was actually made, it’s not at all clear that it was a good idea to make it. 

He was worried about people trying to talk to the President. He was worried about people trying to initiate policy decisions about whether the bomb could or should be used, and he just felt that that would gum up the entire works, and they would never build a bomb if everybody was constantly talking about it. Maybe he was right, for better or worse, on that.

So what’s interesting is that Groves had many reasons for secrecy. We can ask ourselves: did these work? Did each of these work? And in terms of Germany and Japan, they seemed to have been genuinely caught off guard by them. They were genuinely surprised, and this was one of the goals of the secrecy towards the end of the war. Groves wanted to surprise and shock the Japanese because if it was very shocking; he thought it might convince them to surrender. If it was something they expected to happen, it would be easier for them just to regard it as yet another horrible thing that happens in war.

As for the Russians, we now know that Groves was not successful in this. There were at least three spies at Los Alamos: David Greenglass, who was Julius Rosenberg’s brother-in-law, was not a very high level person, but he knew some things, and he did give away things that were classified, like information about the implosion bomb; Ted Hall, the youngest member of the Los Alamos scientific team, a Harvard undergraduate, he gave quite a lot of information to the Soviet Union; and most importantly was Klaus Fuchs, a member of the British delegation, originally a German. The mild-mannered Klaus Fuchs, who everybody trusted, and he was actually the babysitter when they would have these Los Alamos parties because he was so quiet and trustworthy, they’d give him their children to watch. He turned out to be the biggest spy of the Manhattan Project and he gave information on pretty much everything they were working on to the Soviet Union band continued to do so for many years after the war. 

So in that respect, the secrecy completely failed. Whether or not we want to evaluate whether the overall program was a success or a failure, it’s just a very complicated question because you have to take into account all the different ways to operate it and what the goals of it were.

So after it was found that Klaus Fuchs was a spy, General Groves was hauled before Congress to talk about how this could’ve happened. He was defensive in a way that you might expect him to be. But he said to Congress, “Look, our secrecy apparatus was mostly meant to protect from accidental leaks or disclosures.” So it was mostly about making sure that the Wall Street Journal or the New York Times did not have a big cover story about the Manhattan Project, because that would’ve ruined everything, especially with regard to the wartime goals in Germany and Japan. It was not designed to catch people who were sort of hardened spies, people who were dedicatedly deceptive at keeping people away.

He also said – this was when it was only known that Klaus Fuchs was a spy – he said we also weren’t in charge of Fuchs’ security. Fuchs was a British scientist. In fact, he was a member of the British delegation. Groves said to the British, “Do you want us to do security background checks on your scientists?”

The British said, “No, no, that wouldn’t be proper. We will take care of all the security on our end. We’ll worry about our scientists, you’ll worry about yours.” After the war, Groves was very unhappy with this outcome, because it turned out that they had done almost no background checks on Fuchs. If they’d done any background checks on Fuchs at all, they would’ve known that when he was in Germany, he was a dedicated communist, he was a member of the Communist Party.

The reason he had to flee Germany was because he was a communist, and he was fighting the brownshirts in the streets and things of that nature. He was not a mild-mannered guy in Germany. He was very politically on the edge of the spectrum. It was only when he went to the United Kingdom, and then the United States, that he became this quiet, not talkative, politically uninvolved person. Which in retrospect, it’s very easy to see a shift there and see that this person is potentially untrustworthy. But nobody really thought about it at the time. And Fuchs’ colleagues and friends were completely shocked by the fact that he was a spy, as well.

So Groves, in the end, tried to say, “The secrecy basically worked for what it was capable of doing, but you can’t expect it to get everything.” But even then, it’s not completely true because there were American spies, as well, so I don’t know. It doesn’t really work out.

But it did put Groves into a very tough situation after the war, because on the one hand, he wanted to argue that the Army secrecy was the sort of secrecy that he needed in the atomic energy project. But on the other hand, he had to acknowledge it completely failed when it came to the Soviet Union.

Klaus Fuchs was discovered to be a spy at the end of January, 1950. He was discovered partially through this project known as Venona, which was decrypted Soviet intelligence cables. They were able to triangulate who Fuchs was through there. This was one of the great decryption coups of the Second World War, was finding all these communications between Soviet spies and being able to figure out what they said. And they said things like our agent is at a secret place working on a secret program, and they were able to figure out that the secret place was Los Alamos and the secret program is the bomb, and the agent, they eventually figured out was Fuchs. 

And they confronted Fuchs in England, and Scotland Yard confronted him – he had gone back there. He confessed to the whole thing, which is very convenient because they didn’t want to actually tell how they knew it was Fuchs because they didn’t want to give away that they had encrypted all these Soviet cables. So Fuchs confessed to the whole thing and said, “I’ll collaborate.” 

They convicted him. Under British law, spying for an ally, he was spying for the Soviet Union when they were on their side, was not a serious crime. I mean, it was not serious enough to get you killed or it wasn’t a capital punishment. So they sentenced Fuchs to many years in prison. He only served a few of them, he served about seven years in prison, and then they let him immigrate to East Germany. 

When he went to East Germany, he was put in charge of a physics institute there, one of the biggest ones in East Germany and was regarded somewhat as a hero. But by that point, he was no longer doing anything military, as far as we know. He sort of became a very hardened communist. He lived out his life there and died in the 1980s, I believe.

One of the interesting things about Fuchs is that he was central to three nuclear weapons programs. He was part of the American Manhattan Project – he went to Los Alamos, he was involved in designing the initiator for the plutonium bomb. He was also involved in the electrical system at Oak Ridge and, of course, other issues – the implosion program. He then went back to the United Kingdom and he helped them build their first bomb in the 1950s. Of course, during this whole time, he was spying for the Soviet Union and was very crucial to them building their own bomb. So he’s actually one of the more central figures in the nuclear age, so he’s not as especially as well known as some of the other characters.

If we imagine an atom—and we have this idea we usually learn in grade school of a bunch of electrons zooming around—at the center is this very dense, positive nucleus. Now, we mean that it’s positive in the sense that it’s full of protons. Protons are positively charged. So it’s the same sort of positive that we mean with like a magnet being a positive or negative pole. As we know from if we take two magnets, if you try to put the positive and a positive pole together in a magnet, they’ll repel each other very violently. If you put a negative and a positive pole together, they stick.

So one question that immediately comes to mind is so why does a nucleus stay together at all? It’s all these little positively charged particles, protons, and positive and positive repel. So if you put two protons next to each other normally, they’ll zip apart very fast. They don’t want to be next to each other. 

The reason is that there’s another force at work in a nucleus, and this is known as the nuclear force – not a very interesting name, but that’s what it’s called. This means that all subatomic particles inside a nucleus are somewhat attracted to one another. So you have two forces at work. One is that positive things repel from each other, but also the nuclear forces cause these particles to want to stick together. 

This is where neutrons come in. So the neutrons are also subatomic particles in a nucleus, but they have no magnetic charge. So they’re not going to repelling whatever, they’re neutral. But they do have this nuclear force. So if you start trying to balance a bunch of protons in an atom and you put in all these neutrons as well, you’ll overcome that repulsive force and it will instead be a force that holds it together.

The nuclear force is extremely powerful, but it only works over very small distances, whereas the electrostatic forces work over very long distances. But at those very small distances, they are not very powerful. 

So we have our atom, and we’re building it up with positive things. We’re also putting all these neutrons in there to keep it together. You can do that up to a point. Around the point of uranium, these things start to get very unstable, and this was one of the reasons uranium was somewhat special.

So uranium-235, the fissile isotope of uranium, has 92 protons and 142 neutrons in it. That’s a very big unbalanced, uncomfortable, somewhat unstable arrangement. So if a neutron comes in and hits that atom and is absorbed into, it starts to wobble. As it’s wobbling, one half of it eventually gets kind of separated from the other. So it’s wobbling and it’s going kind of elongated. It gets just outside of the range of that nuclear force that’s holding it together. So it suddenly becomes two very positive atoms that their nuclei, they’re right next to each other, and that electromagnetic force that repels things – again, it’s like putting the positive ends of the magnet together – causes it to blast apart with great violence. And almost all the energy that’s released from nuclear fission is from that blasting. Then there’s a few other little neutron things like that.

But it’s actually very straightforward. It’s all about this balance of these forces. It’s the fact that it’s just on the edge of being stable. It takes just the slightest nudge. This was a huge surprise when it was discovered in 1939, because people thought of the atom as being a sort of fortress, this sort of impenetrable blocky thing. They weren’t thinking of it as something that was just on the verge of falling apart. That something as small and insignificant as a neutron could cause such a giant fortress to pull apart was completely unexpected and caused just a huge amount of excitement among the physicists today.

So Leo Szilard, one of the famous early instigators of the project, he had, by 1932, come up with the idea that you could use neutrons in some sort of yet unknown way to create a chain reaction. The reason you could do this is because neutrons eventually charge. So if you shoot them into atoms, they won’t just sort of bounce off the electrons or bounce off the protons. If you try to use charged particles, it will not work. 

The problem is he had no idea how he would do this. He wasn’t thinking about splitting the atom. He was thinking: what if there was a process by which you could put a neutron into an atom and three neutrons would pop out the other side? He didn’t know what atoms would work on this. He started going through all of the atoms that he could get his hands on – iridium, in particular, and barium and all sorts of other things – but he had no clue. It wasn’t until the discovery of fission that he suddenly was one of the first people to say, “This is the way to do it. Because if this process releases neutrons, which is highly possible, now we have this chain reaction.” 

In fact, it’s even worse than Szilard thought, because Szilard’s initial idea was you put in a couple neutrons, you get more neutrons out the other end. That’s a weapon you can use. The neutrons are hazardous and deadly. 

But nuclear fission releases a lot of energy, and that is not something that Szilard would’ve anticipated. This is, again, as much energy needed to kick a speck of dust, that’s a phenomenal amount of energy for an atomic process, something as small as a nuclear – the only things that rank higher than that are like antimatter collisions and things of that nature. But it’s a phenomenal amount there.

So in 1938, Enrico Fermi has a research program where he is using neutrons to irradiate different substances and see what happens. This is a good physics project in 1938. He’s doing things like slowing the neutrons down with paraffin, and Fermi is the first person who figured out if you slow neutrons down, you increase the chance of them running into other nuclei and new atoms and things like that. 

And he got very interesting results with that so far. He’d been able to make things very radioactive; he didn’t really know why. He got these results back from uranium, in particular, and Fermi thought he’d discovered a new element. He thought he had gone beyond uranium, and he dubbed this new transuranic element hesperium. He was very happy with this. He wrote a paper on it, and it was a lot of the reason they gave him the Nobel Prize.

It was later discovered by Otto Hahn and Lise Meitner that actually, Fermi was wrong. He wasn’t creating new, bigger elements at that stage. What he was doing was splitting uranium into tinier elements. He was confused. What he was calling hesperium was really a form of radioactive barium, which is just a regular small atom that had been split from nuclear fission.

So it’s one of the ironies that Fermi is the sort of first person who ever produced nuclear fission artificially, as far as we know. Now, he didn’t understand what was happening and he got a Nobel Prize for it anyway.

Well, fission was discovered by a team that was originally based in Berlin, and it was Otto Hahn and Fritz Strassmann, but also Lise Meitner and her nephew, Otto Frisch. And during World War II, Lise Meitner, who was a Jew, had to flee. She had to flee into Sweden, and that’s where she waited out World War II. While she was there, Otto Hahn and Fritz Strassmann were continuing their experiment. It was a very small experiment. It could fit onto a large dinner table. The idea was to bombard uranium with neutrons, like Fermi had done, and then to do a very complicated chemistry to figure out exactly what the result was. That was the real trick of what they were doing.

Hahn was a very skilled chemist, and he was one of the only nuclear chemists. So he was a chemist who also deals with radioactivity and things like that. He was able, through a very complicated process, to figure out that all that was left was barium. It was not a big, heavy new element. It was a light element that they already knew about, but a very radioactive form of it. He wrote Lise Meitner in Sweden and said, “I don’t really understand our results. What’s going on?”

Lise Meitner, who was the physicist of the team said “Well, the only answer here is that you’ve split the uranium in half. Barium’s about half the size of uranium. So what you’ve probably been doing is not just creating a new element through adding neutrons in, but these neutrons are causing this big, bulky uranium atom to shear across the center, and that’s what the result is.”

One of the great controversies is that Otto Hahn was given a Nobel Prize for this. Fritz Strassmann was also given a Nobel Prize for this. But Lise Meitner was not; she was overlooked by the Nobel Prize committee. Part of this has been ascribed sexism. Part of this has been ascribed to the fact that she also did not work to take a lot of credit for what she did for various reasons that were probably personal to her, but also, she wanted to distance herself a little bit from the atomic bomb and all that sort of thing. So she’s actually one of the great examples of people who were overlooked for Nobel Prizes, even though their colleagues were given prizes for the same work.

By the late nineteenth century, scientists realized that the atom is not the most fundamental unit of matter, that there are things inside that are even smaller than an atom – subatomic particles. They don’t really know what all these are yet, but they know that there’s a whole world out there that they don’t quite understand.

In 1898, Henri Becquerel took a piece of uranium and he put it on a piece of photographic film, put it into a dark desk drawer. He later took it out and he found that it had, in fact, developed on the film, that there had been sort of invisible light emanating from this piece of uranium that left a mark on the film. This was a big exciting discovery, and it was Marie Curie who gave it its name – radioactivity – for what is going on.

The basic answer is that atoms are not only made up of small subatomic particles, but they’re not always totally stable, that they can be just a little bit unstable, and that, for reasons that are still not completely understood, will occasionally shoot out an extra particle. Exactly when they will shoot out an extra particle is impossible to predict. Quantum mechanics says you can never know ahead of time why any individual atom is going to decay, as they call that, at any given period. 

But you can say for a group of materials, on average, how long it will be before they shoot out a particle, and that’s what we call half life. So that’s how long it will take for that amount of material to decay – for half of it to decay. So plutonium has a half life of, I believe, twenty thousand years or something like that. So if you have a lump of plutonium, after twenty thousand years, half of it will no longer be plutonium. It will be something else – shoot off neutrons or alpha particles or transmuted some of its protons into other things and things along that nature.

Radiation by itself is all around. There are lots of sources of radiation in the world. You get a lot of radiation from eating a banana – I mean, not a lot by health standards but just a detectable amount because there’s potassium in bananas. Potassium’s a little bit radioactive. You actually get some radiation if you sleep next to somebody at night because they are slightly radioactive and you were slightly radioactive, but actually, there is a measurable amount of radiation difference. 

What we worry about for radiation hazards are one of two things. One is a very large amount of radiation all at once. So an atomic bomb produces a huge burst of neutrons and gamma radiation. Inside of a nuclear reactor, there’s a lot of radiation. These are very, very powerful amounts of radiation, and that’s the kind of radiation that if you go too near to it, you can die within either seconds, or if you’re exposed to a burst of it, you can die within weeks. It’s a very unpleasant way to die. 

The other thing that we worry about with radiation are long-lived weakly radioactive substances that can be taken by the body. So there’s an inverse relationship to how powerful radiation is and how long it sticks around. So some atoms, like the ones that you get from a nuclear fission, these unstable pieces, are extremely radioactive. They’re the kind of thing that will kill you dead within seconds. But they only stick around for a couple of hours at the most, because they’re so radioactive that they spend all their energy at once and they don’t have anything left. 

Things that are right in the middle, in terms of – there’s stuff that has almost no radioactivity and is around forever. And then, there’s stuff that’s around for anywhere from thousands of years or hundreds of years or even tens of years. If those substances get inside of you, then they can sit inside of you and radiate and radiate and radiate. 

So this is one of the big fears with things like nuclear fallout. It’s not that initial radiation that kills you. It’s that later radiation that lingers, and maybe it’s radioactive carbon, for example, or radioactive strontium. Strontium looks very chemically like calcium. So if you drink milk with strontium in it, your body will say, “Oh, what a nice piece of calcium I have here,” and will put it into your bones and it will just sit there and radiate and radiate. If you get enough of that within you, you’re exposing yourself over the long term to a lot of radiation.

So in certain people who, say, work in uranium mines or are exposed to a lot of radon gas, then that can get into your body and radiate and radiate. And then, ten to twenty or thirty years later, you get lung cancer. 

So that’s the two types of hazards. There’s one that will kill you dead immediately, and then there’s one that takes a very long time for it to manifest with cancers and things like that because it’s very weakly radioactive, but it’s imbedded itself in key areas in your body.

So one of the big questions that people have asked for a while is: how much did they know about the radiation that comes from an atomic bomb before they used the atomic bomb. So did they regard the radiation as a special effect of the bomb, or were they were regarding it mostly as a source of fire and blast? It turns out that they weren’t thinking too much about the radiation. They knew the radiation would come out from the bomb, but they figured that the heat in the blast would be so much more powerful than the radiation that anybody exposed to those would be dead anyway.

Also, that the bomb was going to be detonated very high up. They chose the reason why it was high up not because of the radiation – they chose the height of the bomb to maximize the amount of area being destroyed. But it also is a side effect that there wasn’t going to be a lot of radiation sort of raining down on people afterwards.

It turned out that there was more radiation than they expected. Some of the radiation did rain on people afterwards, though not as much as a lot of people realized. Hiroshima did not become unoccupied, or it did not become a radioactive wasteland or anything like that. But you did have several thousands of people who did get enough of a radiation exposure that they acquired radiation sickness, which is a very painful, unpleasant way to die. Whether that’s a worse way to die than being set on fire or having your house fall down around you, you can debate that. Personally, I don’t really see a big difference between setting people on fire and killing with radiation. They’re both pretty unpleasant ways to die.

One of the reasons that they didn’t study the radiation problem as much, it’s not because they didn’t care about it but it’s because they didn’t completely understand.

They didn’t know a lot about the radiation during World War II from the bomb itself. They knew about radiation from reactors, they were taking that into account. They knew that at the Trinity test, they might have to worry about evacuations if the cloud blew the wrong way. The Trinity test was detonated much lower than the bombs in Hiroshima and Nagasaki. They knew the radiation was, in itself, a hazard. They had lots of experience with radiation, health, physics, and things like that. 

But they hadn’t really been considering the Japanese in this respect, and it wasn’t because they were cruel or unhappy or anything like that. It was just because they were not especially worried about what happened to the people who they were dropping an atomic bomb on, and they certainly weren’t worried about radiation effects, which would be a much more minor effect than everything else they were doing.

Almost none of the people who died in Hiroshima and Nagasaki died because of radiation. They died because of fire. Fire’s the number one – it’s very prosaic, so we don’t think about it as much as the more exotic effects of nuclear weapons. It’s what most of the people who died from nuclear weapons are going to die from – fire, if they’re exposed to one.

It was a really interesting period. There were some people at the time that they were building, they thought of it as being qualitatively completely different than anything else that had come before. Then there were other people who thought of it as being a better way to firebomb. So we were already running firebomb raids on Japan and Germany during World War II, and these were massive, massive raids. We’re talking about hundreds and hundreds of planes, B29s, dropping tons and tons and tons of napalm and magnesium and explosives and things to make these gigantic conflagrations, these very big fires to kill and destroy lots of houses and to kill lots and lots of people. They killed huge amounts of people. One major raid on Tokyo leaves a million people homeless. I mean, these are disasters on an almost unimaginable scale.

So there were some people who think, “Well, the atomic bomb is just another way to do that. You can do one plane, and it’s just very efficient and maybe scarier for that reason, but not very different.”

There were other people who said, “Look, maybe these bombs are only one bomb, but still, 20,000 tons of TNT from one bomb, that’s kind of incredible, even in itself.” It also means you can’t defend against it. There’s no way you’re going to shoot down all the planes that might have an atomic bomb. It’s going to completely change things.

This is only the beginning. They’re going to get much bigger. Many of the people on Manhattan Project knew that it could get much, much bigger, and they were looking forward to even things like hydrogen bombs, things that were in the millions of tons of TNT equivalent. They were already thinking about these things by 1945, and they thought it was going to be a real revolution.

So one of, actually, the goals of General Groves immediately after using the bomb on Hiroshima and especially – and also in Nagasaki – was sort of to convince the world and convince the public and convince the Japanese that this was a completely different weapon unlike any other weapon. Truman’s famous speech – which was not written by Truman, of course, it was produced by General Groves’ organization – says, “This is an atomic bomb. This is a force of nature. The idea was that maybe the Japanese, with their various religious beliefs and their sort of very hierarchical approach to things, maybe they won’t want to surrender to an American soldier. Maybe they will capitulate, though, to the power of the sun. Maybe they’ll capitulate to the formidability of the powers of the universe, as they called them.”

In a way, it’s public relations. I mean, on some level, they’re very similar. In some way, though, there’s a lot of evidence that this works. Not so much in a sense that the Japanese emperor said, “Well, there’s no way we can possibly— this is totally different.” But there is evidence that he looked at it and said, “Well, here’s a good way for me to save face. I can say to my people, “Well what am I going to do? They have the power of the universe on their side.’” Even if you may or may not have believed it. 

So there’s a lot of debate as to did the atomic bomb stop it. Was it a question of the atomic bomb and the invasion of the Soviet Union? Was it a question of they were going to lose anyway? It’s pretty clear they were going to lose anyway, but at what cost? It’s pretty clear the Soviet invasion, Manchuria, was very important to them, as would be anybody who didn’t want to be occupied by the Soviet Union, which most people at the time would’ve thought was a pretty bad way to go. It was also clear that they took the atomic bombs into consideration. 

I’m not a hardliner on it. I don’t think that you can say it was or wasn’t the bomb in any obvious way, but I think there’s a lot of evidence that says that they definitely did take the bombs into account in thinking about how to surrender and when they should surrender. Even though, in many ways, the atomic bombs were very small compared to some of the firebombing raids they’re already sustained.

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