The Manhattan Project and building the bomb

It would be remiss to talk about the science of the war, without talking about the science that ended it. World War Two ended on 15th August, 1945, after two atomic bombs had been dropped on the Japanese cities of Hiroshima and Nagasaki. Nuclear historian Alex Wellerstein from the Stevens Institute of Technology in New Jersey told Adam Murphy why they decided to pursue something like that...

Alex - After the discovery of nuclear fission, which is to say that you could split uranium atoms with neutrons, a lot of scientists and many different countries started to wonder whether you could apply that to weapons purposes. And it wasn't really until 1942 they got a copy of report from the United Kingdom where British scientists concluded that it was in fact very doable for a country like the United States to produce nuclear weapons relatively quickly and relatively cheaply and that led to the beginnings of the Manhattan project. The other side of it is they were very afraid at the beginning that the Germans might be building an atomic bomb and any indication that an atomic bomb was buildable they not only saw as an indication that they could do it, but that the Germans could be doing it. And they were assuming, both because nuclear fission was discovered in Germany and because they figured it was safest to assume the worst, that they were behind the Germans. It later became known to them that that wasn't the case but not until much later.

Adam - All atoms have a core called a nucleus that is full of protons and neutrons, but sometimes this gets too full and it makes the atom unstable. That kind of atom is radioactive. And over time it will break down into more stable elements, and every time it does, it will release a tiny bit of energy. But how do you go about taking that tiny amount of energy and turning it into a bomb that can level cities?

Alex - So to build a nuclear bomb the most difficult part is having the fuel for the bomb. So this is what they call fissile material. It's a high enough concentration of atoms that can, at will, be made to split and split other atoms. So this is enriched uranium and this is plutonium. So both of these made up the bulk of the work on the project, both the spending and the effort and the labor and the time, was in making the facilities that would be able to produce this fuel for the bombs. And you also needed a lot of scientists. Pretty early on in this effort the head of the military General Groves was looking for a scientist who could run the whole enterprise and be his sort of right hand man. And he ended up choosing J Robert Oppenheimer. This was a theoretical physicist at University of California Berkeley, also taught at Caltech, and he was an unusual pick because he had never done any kind of large scale management project before. That's not the kind of scientist he was. He was a chain smoking cigarettes while drawing equations on a Blackboard in a small room with 10 students kind of scientist. But he ended up being quite able to the task and quite accomplished at it. They had quite an array of scientific luminaries, both American and foreign involved in the project. And this was part of its success was having sort of the cream of the crop, not only of the United States, but the cream of the crop of many European countries, including many people who had fled the Germans and had very strong vested interests in making sure that the Germans did not win the war or get an atomic bomb before the Americans.

亚当——就只有放射性的概念been discovered a few decades prior by Marie and Pierre Curie on their lab bench. So did the scientists working on the Manhattan project really understand just the scope of what they had to do?

Alex - They were entering into this entire field with very little information about how to do any of this work on an industrial scale. And so their task was to go from these basically proofs of concepts to full-scale application in basically one step. And that's highly unusual, both for scientists and for industry. And so it turns out, for example, that if you scale up the reactors the way they did, they'll work for a while and then they'll sort of stop working. So this is the sort of difficulty and most of these questions, these scaling questions, they're exactly what would happen if you tried to scale anything up in that amount of time. They did not know the health effects completely of all of these materials. So they're simultaneously trying to develop say, safety guidelines while developing new artificial substances that have never been created before for which they do not know the health effects of them. So they're doing a lot of things that in a more ideal situation, you'd sort of slow things down a bit. Figure out, say, how toxic plutonium was, and then come up with the safety guidelines. And so they're doing these experiments that are incredibly dangerous - they call them the tickling the dragon's tail experiment in which you basically get as close as you can to a chain reaction that you're not in control of, and then back away from it. And they did have several accidents even during the war. After the war, they had two accidents that actually killed people. But even during the war there's, in their files, they have amazing writeup of how they're trying to figure out the critical mass of enriched uranium in water, and it got much more radioactive than they expected. They concluded that everything was fine, it didn't blow up or burn anything down, but one of the hair of the scientist who was working on it did fall out. And you read that in retrospect you think, wow, that's, that's really not very safe. That's not much margin for error at all. If your hair is falling out, it's a pretty bad sign. So these are just some of the examples, but take those couple examples and multiply them by a thousand and you get a sense for how much unknown there was across the entire edifice of this project.

Adam - And how much did they know about what this was going to do? The lives it would take, the cities it would level, and the people who would die from radioactive fall out.

亚历克斯-他们知道这会造成很大的火. They knew that it would cause a lot of damage from blast pressure. They had sort of a rough sense of what area would be affected by it, but there were a lot of things they didn't know. Oppenheimer estimated the casualties far too low. He estimated maybe 20,000 people would die at Hiroshima, was more like a hundred thousand and later he said that that bothered him quite a bit to be so wrong. They dramatically underestimated the effects of radiation. They really thought that basically if you were close enough to be hurt by the radiation, you'd be killed by the blast and the fire anyway, and the radiation wouldn't have a large effect. They were wrong on that. And the reason is that, you know, that real life is more complicated than a sort of physical, simple physical simulation. Sometimes you can be in a situation where you somehow survive all of the other effects, but the radiation is the main one you're going to have. And so their later estimates is that maybe as many as 20% of the deaths were directly attributable to the radiation.