Ep. 379: Fermi’s Atom Splitting

Enrico Fermi

Enrico Fermi

When he wasn’t puzzling the mystery of alien civilizations, Enrico Fermi was splitting atoms. He realized that when atoms were split, the neutrons released could go on and split other atoms, creating a chain reaction – and the most powerful weapons ever devised.

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Show Notes

Enrico Fermi
Who was Enrico Fermi?
Enrico Fermi


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Female Speaker: This episode of Astronomy Cast is brought to you by Swinburne Astronomy Online, the world’s longest running online astronomy degree program. Visit for more information.

Fraser Cain: Astronomy Cast episode 379, Fermi Splits the Atom. Welcome to Astronomy Cast, your weekly facts-based journey through the cosmos. We help you understand not only what we know, but how we know what we know. My name is Fraser Cain. I’m the publisher of Universe Today. And with me is Dr. Pamela Gay, a professor at Southern Illinois University Edwardsville and the director of CosmoQuest. Hey Pamela, how you doing?

Pamela Gay: I’m doing well. How are you doing, Fraser?

Fraser Cain: I am doing very well. So you know what? I’m just gonna – normally, we have something to kind of promote the beginning of the show. I’m just gonna promote two things. One, you should follow Pamela on Twitter. Her Twitter address is starstryder with a “Y.” And then you should also follow me. I’m just FCain. And both incredibly interesting feeds, perhaps the most important Twitter feeds you could possibly follow on all of Twitter. So if you’re a fan of Astronomy Cast, just connect with us. Give us some feedback, send us questions. We love it. That’s it. Let’s record – let’s do the episode.

Pamela Gay: Sounds good.

Female Speaker: This episode of Astronomy Cast is brought to you by 8th Light, Inc. 8th Light is an agile software development company. They craft beautiful applications that are durable and reliable. 8th Light provides discipline software leadership on demand and shares its expertise to make your project better. For more information, visit them online at Just remember, that’s www dot, the digit eight, T-H, L-I-G-H-T, dot com. Drop them a note. 8th Light: software is their craft.

Fraser Cain: So when he wasn’t puzzling the mystery of alien civilizations, Enrico Fermi was splitting atoms. He realized that when atoms were split, the neutrons released could go on and split other atoms, creating a chain reaction and the most powerful weapons ever devised.

So this is gonna be the final episode of our Famous Physics Experiments. And I think this is a pretty important one to wrap up on. So I think good call, Pamela, on suggesting this one as the final episode.

So I guess to set the stage as always, what was the landscape? When we sort of last left our heroes, they were really identifying the interior of what the atom was and performing a bunch of experiments to figure out what the protons were, what the neutrons were; they had figured out what the electrons were. Where do they get to to think that maybe you could actually split these up and that you could get a lot of power out of this?

Pamela Gay: Well, the amazing thing is when Fermi started his work, we didn’t actually know that fission was a thing. The idea that you could split an atom, people hadn’t gotten there yet. In fact, it was one of those things that he kind of mentioned during his Nobel Prize acceptance – that was one of those things that he admitted during his Nobel Prize acceptance speech as a, maybe we should’ve realized this already. Because he actually started splitting atoms before he knew he was splitting atoms.

Fraser Cain: So how was he splitting atoms?

Pamela Gay: So Enrico Fermi realized that you could actually harness the power of the neutron to grow atoms. He was one of the first people to start working with beta decay as a way of getting to new parts of the periodic table that had, up ‘til then, not been revealed. So working with a variety of different ways to bombard things with neutrons, he started finding, okay, if you bombard this, what do you get? If you bombard this, what do you get?

Fraser Cain: So let’s sort of explain that a little deeper here. So let’s say I’ve got something, a heavy atom like a uranium for example, or radium, or something at the high end of the heavier atoms. We’ll use uranium. And so the process of beta decay, what is that?

Pamela Gay: So the idea is that it’s possible for a neutron to decay into a proton and an electron. And then you have to also, because of conservation of momentum, give off a neutrino as well. And he was actually the person who first figured out, wait, we need this particle to compensate for momentum. So he figured out the idea of a neutrino.

Fraser Cain: He predicted the neutrino, like, 60 years before they were finally seen, right?

Pamela Gay: As one does.

Fraser Cain: Yeah.

Pamela Gay: And he also was one of the first people to systematically work his way through the periodic table bombarding things with neutrons and looking to see when do you get alpha particles coming off? When do you get beta decay? What are the resulting child atoms? And it was through this process that he started to discover what are referred to as transuranium atoms. These are the atoms that are beyond uranium on the periodic table.

Fraser Cain: So if you take an atom of uranium and you smash it, or I guess you fire a neutron beam at it – and I don’t know where he got all these neutrons from, these individual neutrons. Probably …

Pamela Gay: Well, you can get them through a variety of different things that are giving on neutrons through –


Fraser Cain: Okay.


Pamela Gay: – different radioactive processes.

Fraser Cain: Okay. And so you’re firing these neutrons at your uranium atom, and some of them are sticking, right? And they are –


Pamela Gay: Yeah.


Fraser Cain: They are sticking and they’re colliding with sometimes an electron, right? And you’re getting another proton. And you’re then walking those atoms up the periodic table. How far can you go?

Pamela Gay: Well, you don’t always walk up in a straightforward manner. That’s one of the crazy things about this. And there’s an amazing table of nucleotides that’s in the background of The Big Bang Theory and is in almost every physics department somewhere that actually shows you all the crazy chains that you can walk through. And usually, these are processes that you go down and go up in different steps.

So for instance, I’m gonna start with uranium since that was your example. So you have uranium, and it undergoes a alpha decay. It gives off an alpha particle. It ends up then becoming thorium. You bombard that –

Fraser Cain: But they don’t just do that on its own, right? Like, it’s just gonna –

Pamela Gay: Yeah.

Fraser Cain: – give uranium enough time, and it’s gonna give off an alpha particle. And another name for an alpha particle, right? Is …?

Pamela Gay: Helium.

Fraser Cain: Helium, yeah. So it’s gonna give off that alpha particle, and then it’s gonna turn into thorium.

Pamela Gay: So then that thorium undergoes a beta decay. So one of its neutrons has now become a proton. This bumps it up the periodic table. Now, the one that I’m looking at is calling it … protactinium is the intermediate step that it has it at. And then this can undergo another beta decay to end up back at uranium. That can then undergo another alpha decay to become a different version of thorium, which can undergo alpha decay to radium. All of these different processes, you basically go up and down via beta decay, inverse beta decay, and giving off alpha particles.

Everything that we deal with that isn’t stable is either going to decay through some sort of a beta process or through some sort of an alpha process, for the most part.

Fraser Cain: Okay. So I can just imagine Fermi – and we’ve talked about Fermi, and we talked about the Fermi Paradox. But this is sort of the other side of it, right? Of just about the – specifically about this. I can imagine he’s in some lab; he’s bombarding elements with all of these neutrons. But where did he get this idea that there was more to this, right? That there was a power source, that there was a weapon here?

Pamela Gay: Well, he didn’t initially go straight to power source. He didn’t initially go straight to weapon. What he went to was the realization that if you bombarded uranium with neutrons, the process that would proceed to go on where uranium actually broke down would end up producing more neutrons than went into this. So the idea was that if you bombarded uranium with n neutrons, you ended up getting n plus some number of neutrons coming out. So if that uranium you bombarded was surrounded by more uranium, then perhaps those excess neutrons could go on to trigger more uranium to break down, which would then release more neutrons.

And so his initial thought was that you could get a self-perpetuating process going on where the uranium was giving off neutrons that would keep this process going on its own.

Fraser Cain: Right. And if you just packed the uranium close enough so that enough of the neutrons would reach another atom of uranium and split it off and keep going, as long as you could keep uranium localized around where that chain reaction was happening, you would get a powerful energy release.

Pamela Gay: And the one –


Fraser Cain: But I mean, did they really understand, like, the –


Pamela Gay: No.


Fraser Cain: – the scale, right? I mean –


Pamela Gay: No. I mean, the crazy thing is as I was reading through this, it starts out he’s in Rome. He’s doing his work in Rome. Nothing truly terrible is happening. He’s getting neutron sources in glass jars shipped to him from other countries. He’s releasing the neutrons and watching the processes going on. And he was discovering new atoms. It was cool.

No one quite realized how bad radiation was at this point. But the fact that he started discovering – well, in all, he induced radioactivity in 22 new elements while he was working in Italy. And this led to the Nobel Prize, which was actually quite literally a lifesaver for him and his family, quite potentially. His wife was Jewish. This was the beginning of World War II. And so when he got the Nobel Prize, he took his entire family with him to Stockholm to receive the prize, and then conveniently flew – well, he didn’t fly – but then conveniently traveled not from Stockholm back to Italy, but from Stockholm to New York City and sort of went, “Okay, can anyone offer me a job?”

And so this having just received the Nobel Prize physicist saying, “Can someone please give me a job?” promptly had five different universities offer him professorships. And he accepted a job at Columbia in New York City, where he had previously been a summer lecturer.

So he went from Rome, where he was working with neutron sources and radioactive elements, to Columbia, where he’s now in New York City. And he starts collecting uranium on the seventh floor of the building he was working in. And he actually ended up with several tons of uranium.

And I’m not sure what disturbs me most about this, the fact that he was looking to potentially start building a nuclear reactor in New York City, or the fact that he had several tons of stuff piled up on the seventh floor of a fairly old building in New York City. There was all kinds of not exactly safe stuff going on when it came to watching Fermi’s research. So this was the next step of him –


Fraser Cain: Right.


Pamela Gay: – working on …

Fraser Cain: So then when did that transition to getting involved on The Manhattan Project? Because he had left Italy – received his Nobel Prize, left Italy in ’38, and was able to –


Pamela Gay: Got to America in ’39.


Fraser Cain: ’39 was able to get into – and just as war really broke out. And he was – and then how did that transition into getting involved in The Manhattan Project?

Pamela Gay: It was one of these things where he was one of the early scientists who began to realize that all of this is a process that can give off tremendous amounts of energy and that fission is actually part of what’s going on. It wasn’t until 1939 that they actually realized fission of atoms was an actual process. What Enrico Fermi had seen that he was doing up until then was he was building bigger and bigger atoms by bombarding things with neutrons? The fact that some of the atoms he was building were actually fragments, new isotopes that were smaller atoms, didn’t immediately become clear to him.

But in 1939 as other people began doing similar work, as other people began working to try and understand what they were doing a little bit better, it became clearer and clearer that this was actually a fission process, that by breaking apart larger atoms, you could actually get energy released and get smaller atoms.

So this was a new idea. If you think about it, as we discussed in earlier hangouts, when you fuse together atoms up to iron but not beyond iron, you get energy released. So now we’re talking about energy being released with the fission of bigger atoms.

When they realized what they were doing, they wrote to what would eventually become the Department of Energy saying, “Look, here’s this thing we figured out.” It was sort of a warning and sort of a, “Can we have money for research?” all tied together. And in fact, Fermi was able to turn this into getting $1,500.00 to continue working on trying to build a fission pile. But they still didn’t fully understand what they had on their hands at this point.

Fraser Cain: Right. And as you said, he had been stockpiling uranium on the seventh floor of the building. But I know that the folks who – the government, they were leading the war effort. They reached out to Fermi and his team and looked about how they could potentially weaponize it.

And I highly recommend, if you look for a thing called Chicago Pile 1, if you wanna look for a picture, this is the pile. Pile? It’s such a funny term, right? Because it’s a pile of uranium and surrounded by graphite, but it’s also –


Pamela Gay: And it had graphite inside of it as well to moderate the reaction.

Fraser Cain: Right. But this is sort of the first self-sustaining nuclear reaction that they actually started to create, right? They took it to that next step: demonstrated that you could make these things chain. And I guess that’s when they figured out this could be a bomb.

Pamela Gay: So it started in 1939 with Enrico Fermi basically giving a lecture to the Navy Department and saying, “Look, here’s what the concept of nuclear energy is.” They gave him $1,500.00 to continue his research, which I find kind of amusing.

Fraser Cain: I’m sure that it was worth $20 million back in 1939.

Pamela Gay: Not quite. It still wasn’t a huge amount for research, but it bought a fair amount of graphite. And then from there, it was he and many, many other famous scientists that ended up writing a letter to the president saying, “You need to be aware this kind of discovery will lead to the Nazis trying to produce nuclear bombs.” That was the start of The Manhattan Project.

Enrico Fermi was part of The Manhattan Project. He was able to spend most of his time staying up at Chicago working up there, where he proceeded to start nuclear reactions under football stadiums. But his primary role in a lot of this was the person doing the calculations to figure out, if you have this much of this and this much of this, you end up with this kind of an output. He was the calculation man.

While he was at Columbia, he managed to amass six tons of uranium oxide, 30 tons of graphite. And then he took all of this with him to the University of Chicago, where he eventually started producing self-perpetuating reactions. But he did actually start doing nuclear reactions in New York City. So it may be good that he wasn’t spending most of his time at Manhattan because he did just kind of put things together to see if they would radiate.

Fraser Cain: Now, do you, I mean, do you think that he had something that was dangerous when he was building it in Chicago?

Pamela Gay: I think he had something that was dangerous when he was building it in New York City.

Fraser Cain: Right.

Pamela Gay: So initially, he was building nuclear reactions that were mediated by water. Water is a strong absorber of neutrons. If you flush water through a uranium pile, the neutrons that are released through the fission process are mostly going to get absorbed by the water, so you’re not going to end up with a self-perpetuating reaction.

But if that water somehow leaks out, if you don’t have enough water, if the water evaporates, you can end up with a critical reaction, one that can’t be stopped once it’s started. That luckily didn’t happen. But nonetheless, this is someone who had several tons of uranium salts in New York City, not something I would generally recommend.

Fraser Cain: Right.

Pamela Gay: When he went to Chicago, they initially said, “Maybe we shouldn’t do this reaction in Chicago.” And they were originally going to do it out in the Argonne woods where Argonne National Labs is currently located. They ran into some problems with the construction: crew, plans. It just didn’t end up happening. And somehow, he managed to convince someone that while it wasn’t safe to do this in the metallurgy building – he wasn’t in the Department of Physics at this point; he was in the Department of Metallurgy – that it was somehow safe to do it underground in what some reports say is a squash court and others say is a volleyball court underneath the football field.

Fraser Cain: Which again, if that had gotten out of control, would have made for I guess, well, a super-powered mutant football team, which would have been interesting to watch.

So then, I mean, then at this point, I think the Army started to realize what they had on their hands, and they started to develop The Manhattan Project. And how did that sort of lead up to the final development of the –

Pamela Gay: Well, this –


Fraser Cain: – of the bombs?


Pamela Gay: – all happening at the same time as The Manhattan Project. So there were lots of things going on simultaneously all across the United States were feeding into The Manhattan Project. So it was in 1942 that his Chicago Pile No. 1 went critical. All of this was leading up to building the nuclear bomb. I have to admit, I didn’t prep on the nuclear bomb, so I’m kind of looking things up live while we record this.

Fraser Cain: That’s okay.


Pamela Gay: So pardon me if I screw up any of the dates.

Fraser Cain: We can actually talk more about splitting atoms if you want.

Pamela Gay: Yeah, I wasn’t prepared to –

Fraser Cain: Sure, no, that’s okay. It’s just sort of the natural … And you know me. I wanna talk about things blowing up and such, so it’s just a – you should have anticipated this, Pamela.

So then where are we at with modern physics then about this process? I mean, splitting atoms, putting them together. I mean, we’ve got these great tools now, right? The Large Hadron Collider, things like that. What is the process these days?

Pamela Gay: Well, with the Large Hadron Collider, that’s actually looking at a different area of physics. That’s trying to generate new particles by creating a large pocket of energy in a very small volume that will hopefully, in the process of going from energy to mass, create something new and exciting to study.

But what we’re able to do, following on with Enrico Fermi’s work, is a lot of the nucleotides that we use in medical research are actually produced through these neutron bombardment processes. So if, for instance, you need one of the nuclear capsules that they imbed inside of different cancerous tumors; if you need the radioactive splinters that they may use to treat brain tumors. All of these are produced by taking one kind of isotope and knowing that if you bombard it with neutrons, you’re going to take that one known type of isotope and change its identity into something that has a energy output that will kill off cancer cells.

So we’re essentially using the science started by Enrico Fermi to treat cancer. So you never know what basic research is gonna end up actually leading to. In this case, you had someone that was afraid for awhile that his research was leading to the hydrogen bomb. But it also led to one way to treat cancer.

Fraser Cain: But also the hydrogen bomb.

Pamela Gay: Also the hydrogen bomb.

Fraser Cain: Yeah, I mean, that happened, too.

Pamela Gay: Radiothermal generators, RTGs that we use in spacecraft. These are, again, something that are built up by changing the type of isotope that you’re dealing with inside of a breeder reactor. So lots and lots of processes. We’re essentially bombarding things with neutrons, changing their identity in the process, and getting something really useful out the other side.

Fraser Cain: And what is the state of the art? Because I know that scientists are still looking for – they’re using Fermi’s original methods to go further and further up the list of elements. And the amount of time that these things last is shorter and shorter and shorter. But hopefully, the goal is maybe to find a whole new class of elements that are stable again, right?

Pamela Gay: There’s some theory that leads to the notion that perhaps somehow you can find a second island of stability. Now, there’s absolutely no observational evidence to say this should be true. When we look out across the universe, we don’t see any atoms that can’t be explained. And at the end of the day, there’s no more effective neutron bombardment system than a supernova. So while there are theories that say that there may be another island of stability if you build atoms that are large enough, a lot of us are very skeptical of this actually being the situation.

Another reason to be skeptical about this is gluons, the boson that holds together the nuclei. It only has a very short distance over which it’s able to exert its pull together of protons that would otherwise much rather repel one another apart. And we’re sort of hitting the limit at which gluons can even temporarily, well, essentially glue protons together.

Fraser Cain: Right, I see. So it’s almost like the radius of the nucleus itself is so big that the gluons really just can’t hold.

Pamela Gay: Exactly. It’s sort of like there’s a limit to the size of a sphere I can hold with my arms. If a sphere gets bigger than that, there’s nothing for my arms to curve around because my arms just aren’t large enough. Well, it’s not the exact same problem, but it’s a similar problem in trying to hold together …

Fraser Cain: Right. But in this case, the individual protons, the spheres that you’re trying to hold, they’re all trying to push away from each other. Right?


Pamela Gay: Exactly.

Fraser Cain: And so that’s the trick is that you can imagine if you’ve got, like, three or four spheres, you could kind of just hold them into your arms and hold them all together. But you get to a certain point and you just can’t hold them, and they just keep falling away. So. They’re all pushing away.

But I guess the trick is is that they bombard these things with the neutrons, build up a bigger element, and then watch how that element splits apart to determine new pathways, the new kinds of math. I mean, being a particle physicist is a whole career that you can go into.

Pamela Gay: Exactly. And one of the really cool things about this is we are trying to basically prove our theoretical understanding of how things will decay by looking for actual evidence that this is the decay pathway that things take. If you get that amazing nucleotides poster that I mentioned, there are theoretical pathways through it, and there are observed pathways through it. And a lot of the theoretical ones are based on looking to see what is the ratio of child isotopes, looking at the energies involved, and doing calculations of this is most likely going to happen. But it’s even more cool when you can bombard something with neutrons and then actually look to see how it decays.

Fraser Cain: Right. And so if you were a potential particle physicist, you could make a whole career out of just proving one of the lengths or a couple of those pathways in the chains that are just theoretical, or disproving them.

Pamela Gay: Exactly.

Fraser Cain: Either way. Cool! Well, thanks, Fermi. Thanks for everything. Thanks for the power and not thanks for the weapons. I think we’ll hand those back.

Pamela Gay: But the accidental discovery of a cure for cancer is something I’ll take any day of the week.

Fraser Cain: Yeah, exactly. And a way to power spacecraft like Voyager so they can last for 50 years. That’s pretty awesome.

Pamela Gay: Yes.

Fraser Cain: Cool, well that wraps up our I don’t even know how many part series on physic experiments. And so next week we’re going to talk about something completely different. So thanks, Pamela.

Pamela Gay: Thank you, Fraser.

Fraser Cain: Thanks for listening to Astronomy Cast, a non-profit resource provided by Astrosphere New Media Association, Fraser Cain, and Dr. Pamela Gay.

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