บทถอดความฉบับเต็มของ Do fission reactors occur naturally?

expansion. 00:05:10 Speaker 1: That's true. The universe does seem relentless. 00:05:13 Speaker 4: And so there's a lot going on in the universe, and sometimes we wonder how does all this energy go out into the universe. 00:05:20 Speaker 1: That's right, because all the stuff around us contains an incredible amount of energy. All the matter around you are these tiny little systems bound together with incredibly strong forces, which, if manipulated in just the right way, can release them in incredible bursts of energy. 00:05:36 Speaker 4: Yeah, and somehow throughout the years, humans have figured out how to sort of take advantage of this idea of releasing the energy that's stored inside of the bonds of the things that make up to the universe, and sometimes for good reasons and sometimes for not so great reasons. 00:05:50 Speaker 6: That's right. 00:05:50 Speaker 1: And you can see around you in the night sky, for example, fusion reactions happening that last millions and billions of years. At the heart of stars, of course, is a kind of a nuclear reactor down here on Earth. We don't see that as often, thankfully, but we've been able to sort of engineer similar stuff happening so we can take advantage of it and power our air conditioners. 00:06:13 Speaker 4: Yeah, anytime that you hear a pop out in your day life, it's probably some sort of chemical bond breaking up and releasing energy out into the world. 00:06:23 Speaker 1: Does that happen to you a lot? You just like turn around and hear something pop? 00:06:27 Speaker 4: Isn't that what happens every time you hear a car running. 00:06:29 Speaker 1: I have an electric car now, so it's totally silent. 00:06:33 Speaker 4: Oh interesting, now, you can sneak up on people. 00:06:36 Speaker 1: That's exactly why I got it. I can sneak up on them and like steal a lick of their ice cream cone or don't there. 00:06:41 Speaker 4: Oh my goodness, that is a little disturbing. You're like the ice cream bandit, the electric ice cream Bandit. 00:06:48 Speaker 1: I've never actually done that, but now every time I'm going to get in my car, I'm going to think about maybe doing that. 00:06:53 Speaker 4: But yeah, it's sort of an interesting idea to think about the humans sort of harnessing this power of this ability to kind of release the energy inside of every day matter, right. I guess we started it with fire. Fire maybe was the first sort of maybe you know, chemical energy causing reaction that we came up with. 00:07:08 Speaker 1: Yeah. I think about it as if matter is like a bunch of tiny little springs bound together, and if you find just the right way to release those springs, you can capture all that energy and use it for something else. And exactly, fire is just that there are chemical bonds stored within the carbon and the other elements within wood, for example, and heat will release them in this chain reaction. That's the magic where some energy is released and then it causes the neighbors to release their energy, which causes the neighbors to release their energy. And that's the magic, because you don't want to release the energy of just like one atom. 00:07:39 Speaker 4: Yeah, and so we figured out fire, and then eventually humans invented I guess it exploses and gasoline and engines, and so we're pretty good, it seems at kind of releasing that energy, at least the chemical kind. 00:07:52 Speaker 1: Yeah, we are. And all these things so far also happen in nature, right, Like fire is started by lightning, and most of the chemical chain reactions that humans have taken advantage of you can also see happening in nature. 00:08:06 Speaker 4: Yeah, and eventually we were able to harness the energy inside of atoms, right, I mean, we've figured out fusion and fission for both reactors and bombs. 00:08:15 Speaker 1: That's right. And I actually grew up in the town where the bombs were invented, in Los Almos. So this, like capturing the power at the heart of an atom, is sort of essential theme to my childhood. 00:08:26 Speaker 4: There's a certain glow about you, Daniel. 00:08:29 Speaker 1: No, that's all the plutonium. I a it as a child. 00:08:31 Speaker 4: Oh I see that's different. All right. Well, yeah, we made fusion and fission bombs. And as you were saying, Daniel, fusion happens a lot in nature. It happens naturally every time there's a sun, and every time you look out into the night sky, each one of those stars is a fusion reactor. There's basically an ongoing fusion bomb at each one of those pinpoints in the sky. 00:08:51 Speaker 1: That's right. It's awesome because it's a fusion bomb into continuous explosion that's also held in place by gravity. So it's like a stable reaction, which you know we've discovered is not that easy to engineer, but the universe has done it. It's amazing to me that stars exist and that they last for so long. 00:09:08 Speaker 4: Yeah, definitely, this night sky would be a lot less prettier without fusion and stars in it. I mean, what would BEng Go have painted in Starry Night. 00:09:16 Speaker 1: The Blacky Blackie Knight. 00:09:19 Speaker 4: Yeah, so the stars are fusion, and so we know that happens out in nature a lot. But fission is different than fusion, right, it's sort of the opposite of fusion. 00:09:26 Speaker 1: That's right. Fusion is when you squeeze together light nuclei to make heavier ones, like squeeze hydrogen together to make helium. But fission is when you start with something which is already big and heavy, like uranium or plutonium, and you crack it into smaller nuclei, which also releases energy. 00:09:44 Speaker 4: Right, And so fission is the one that I think maybe most people associate with nuclear power right here on Earth that humans have been able to engineer. Right. I think most nuclear power plants and the nuclear bombs that we've made, and that people worry about our fission. 00:09:59 Speaker 1: Right, that's right. All of the nuclear power plants

are fission. We're working on fusion plants, but nobody's really made that work yet. Our nuclear weapons initially were fission because it's simpler and easier to get to work, but then more recently they are fusion powered because they's much more destructive. Actually, some of our nuclear weapons are fission bombs that are used just to trigger a fusion reaction. So they're like fission and fusion. 00:10:22 Speaker 4: It's a fusion of fission and fusion. 00:10:25 Speaker 1: It's insane. It's like, how do you light a fusion bomb. You need a fission bomb just to get it going. 00:10:30 Speaker 4: Just give it up a little extra fizz. But yeah, I guess there's sort of this weird thing that you know, we can't quite make fusion power happen here on Earth, but it had's happening all over the universe. And but then we can make fission bombs and fission reactors here on Earth. We've gone pretty good at engineering those, but you maybe don't quite see them out there in the universe as much. 00:10:49 Speaker 1: Yeah, fission reactors take really special conditions which you don't find out there in the universe. And it makes me wonder, like, are humans the only ones who are doing this? Are these reactions only happen in our laboratories? 00:11:02 Speaker 4: And so to the on the podcast, we'll be asking the question can a fission reactor happen naturally? And Daniel, this isn't one of those episodes where we actually like tell people how to make a fission bomb or or something dangerous out there. It's not another one of those episodes, is. 00:11:21 Speaker 1: No, this is not in the Supervillain how to series. Check out our YouTube series on how to become a Supervillain using physics. 00:11:32 Speaker 4: So I check out our lessons on our website. 00:11:34 Speaker 1: First, adopt a white cat, second by a volcano. Shave your head what you gotta shave your head. I'm out, nothing's worth that. 00:11:42 Speaker 4: Let's be honest. We're almost at at the barbling stage anyway. 00:11:45 Speaker 1: Not me. I'm forty six and I still have a vibrant head of hair, not a single. 00:11:49 Speaker 4: Gray Oh it's all that plutonium. 00:11:51 Speaker 1: It's all that plutonium exactly. 00:11:53 Speaker 4: Yeah. But anyways, so I guess the question is, like, can we know that a fusion reactor happens naturally in nature? It's in every at the center of every star. But the question is does a fission reactor happen naturally in the universe? Like can you have a fission star even out there in space? 00:12:08 Speaker 1: Yeah, we actually did a whole episode about can you have stars that are run by fission? That was a listener question, which is super awesome, and we decided it might be possible, but it was very unlikely to arrange the circumstances necessary. And what we'll discover in today's episode is that fission is delicate and you have to have just the right conditions arranged in just the right way, just the right time to make it happen, or you need clever human

engineers. 00:12:33 Speaker 4: Well, it seems kind of weird to me, right, because it seems generally that it's easier to break things than they is to put them back together. So it's kind of weird to think that fission is sort of like rarer or harder to achieve. 00:12:44 Speaker 1: Yeah, that's true, although the products that you need for fission, the heavy stuff, are generally more rare than the products you need for fusion, which is the light stuff. Like, remember, the universe still mostly hydrogen. We've been working at it for fourteen billion years and still most of the stuff in the un is just what it started as, which is hydrogen. 00:13:02 Speaker 4: All right, Well, as usual, we were wondering how many people out there had thought about this question and knew whether nuclear fission reactors can happen in nature, So Daniel went out there into the Internet to ask people this question. 00:13:14 Speaker 1: So thank you denizens of the Internet for answering these questions. And if you are a denizen of the Internet and have not yet answered our questions, we want to hear your voice, especially if you have a super awesome, unusual, weird voice that people would like to listen to. But even if you don't and you like answering random questions, shoot us a note to questions at Danielandjorge dot Com. 00:13:35 Speaker 4: Here's what people had to say. 00:13:37 Speaker 7: I don't think nuclear fission can occur naturally because you always hear about how lighter elements, for like fuse to form heavier elements, and that's how all the heavier elements in the universe have been formed. But you never hear anything about the opposite reverse and like, there's no splitting, there's no creation of more sort of hydrogen and that you hear of. 00:14:01 Speaker 8: My initial response was, yes, nuclear fission occurs in nature naturally, and it was just a trick from nature that we've copied. But on the other hand, I don't see nuclear bombs spontaneously going off in nature underground all the time, so maybe not. But I can also imagine that in high. 00:14:22 Speaker 9: Energy occurrences like supernova or other I energy occurrences, stuff gets bombarded with neutrons and atom split. 00:14:34 Speaker 8: So I'd still have to go with yes, but I'm not totally certain. 00:14:39 Speaker 10: I would like to think so, but I think most nuclear fission that I know about is something man made, so. 00:14:48 Speaker 5: Maybe since we full split atoms in nuclear reactors, it sounds like it'd be a bit scary if it happened anywhere on Earth naturally. 00:14:56 Speaker 11: Yes, I believe it can. I think there's an example of it having happened to something billion years ago in continental Africa somewhere. I don't know of any other examples, but I believe it can happen naturally. 00:15:13 Speaker 1: You're quite sure about that. 00:15:16 Speaker 10: The strong forces which I'm pretty sure keeps those nuclei together, some electromenetic forces keeping it together.

That it would take a lot to oppose that. So I'm thinking maybe in some sort of extreme gravity situation. But still I still think those nuclear are too small and the strong force is too strong to have some sort of nuclear fission occur naturally. 00:15:40 Speaker 1: I think it can occurred naturally. I don't know how to explain it, and I don't know how. 00:15:45 Speaker 12: I do not know if nuclear fission occurs naturally, but I assume it does. Because of the vast quantities of different elements the universe has. So sure what's happened full in the universe. 00:16:03 Speaker 4: All right on the whole, it seems like most people thought that yes, the answer was yes, that you can have fission out there in nature happened naturally. 00:16:10 Speaker 1: Yeah, And I think this is motivated by the general feeling that like, wow, it's a big universe, and everything you imagine might happen is probably out there happening somewhere. 00:16:19 Speaker 4: They've heard our podcast so much that now they just assume that anything that sounds crazy is happening somewhere, at least in one spot in this infinite universe. 00:16:28 Speaker 1: And it's a good motivation. You know. Astrophysicists take advantage of that all the time. They can't like do experiments like what happens when two neutron stars collide. You can't build a neutron star collider. So you just look out in the universe and say, hey, let's watch and see if we spot it happening, and then we can do our experiment effectively. 00:16:45 Speaker 4: Yeah, so I guess why do you why do we even need to hire you, Daniel? 00:16:50 Speaker 1: Somebody's got to eat the plutonium man. 00:16:52 Speaker 4: Yeah, somebody's got to make the banana jokes. All right. So let's talk about this question of whether or not nuclear fission reactors can happen naturally out there in the universe. And so, first of all, I guess let's step through it in more detail. What is nuclear fission? 00:17:07 Speaker 1: So fission is when you break up heavy nuclei into smaller atoms, so everything above iron, everything that's heavier than iron, that has more protons in the nucleus than iron, if you crack it in half, then you release energy and you make two smaller nuclei. 00:17:26 Speaker 4: Right, Because I guess all matter, all the stuff we're made out of, is made out of atoms, and an atom is in nucleus with electrons flying around it, and so the only difference between like uranium and carbon is just how much stuff is in the nucleus, right, which is just protons and neutrons exactly. 00:17:41 Speaker 1: And the thing that defines an element is the number of protons in it. So if you add a proton, you change the charge because protons are charged, and then you need another electron and that changes the fundamental chemical reactions that it can be involved in, so that changes sort of the identity of it. You can add neutrons if you like. Neutrons are neutrals, so they don't change the charge and don't require another electron, but it does give you another isotope. And as you add protons and neutrons, things get heavy, and there are some arrangements that are stable they can hang out basically forever, but there are lots of these arrangements which are not stable, which will eventually just sort of break up on their own. We had a whole fun podcast about really heavy elements and which ones are stable and which ones are not stable, which you can check out if you're interested in the nuclear physics of it. 00:18:26 Speaker 4: So, I guess you're saying the identity of atoms has all everything to do with the protons in it. So like hydrogen just has one proton in the middle, but uranium has like two hundred and thirty five protons typically or hundreds of protons in the nucleus. 00:18:40 Speaker 1: Yeah, uranium has ninety two protons in it, but it occurs in nature in a couple of different isotopes uranium two thirty five, where two thirty five refers to the number of protons and neutrons together. So if you do some quick math, you can discover uranium two to thirty five has ninety two protons and one hundred and forty three neutrons stuffed into it. And it's also uranium two thirty eight, which comes with three more neutrons, And so most of the uranium out there is you two thirty eight, which is much more stable. You two thirty five is more rare and much more useful actually for fission. 00:19:18 Speaker 4: Right, right, But you know they're not as good as you two. 00:19:21 Speaker 1: I think they've been working on it for a lot longer though, still waiting to have that breakthrough album. 00:19:25 Speaker 4: They're a lot more heavy metal. 00:19:27 Speaker 1: Maybe there are no hit wonder now. 00:19:29 Speaker 4: I'm just kidding, I think. I think what you're saying is that, you know, uranium has ninety two protons and a whole bunch of neutrons, and it's sort of like legos, right, Like you can just add these building blocks and you get different atoms, which means that at some point you could potentially break them apart to get two of the lighter elements, right. 00:19:46 Speaker 1: Yeah, exactly, you break up that nucleus, and then you share those protons, those ninety two protons between the products, and so you get things made out of smaller numbers of protons. 00:19:57 Speaker 4: Yeah, And so that's a fission reaction. That's nuclear fission, that's right. 00:20:00 Speaker 1: And nuclear fission mostly we do it with uranium two thirty five and sometimes with plutonium two thirty nine, where again the number is the total number of protons and neutrons together, and so in most nuclear reactors that generate power. You have either uranium two thirty five or plutonium two thirty nine, all. 00:20:18 Speaker 4: Right, And so somehow breaking up the inside of an atom, the nucleus of an atom into smaller elements, somehow that could releases a whole bunch of energy, right, which is kind of weird to think about it. You you think about it, right, like, why

would breaking something release energy? 00:20:32 Speaker 1: Yeah, Well, because there's energy stored in there. You know, you can imagine if you like mechanical analogies, you can imagine like that they're stored in there with a bunch of springs that are really totly wound together, and when you break it, what happens is that the springs released and they shoot the parts out, and there's parts are now moving really really fast. So the energy that was stored in that spring has now been transformed into the motion of the particles that are flying out. And that's essentially what's happening here, except instead of having like literal springs, you have gluons, the carriers of the strong force that are tying these things together. There's a lot of energy in those bonds, and when you break it up, that energy is released and the particles come out moving really quickly. 00:21:13 Speaker 4: I guess maybe it might help if we maybe talked a little bit about what's actually going on, Like if I break a banana and two or if I break my cell phone or something like, I don't get a lot of energy getting released, right, Like, things are breaking and bonds are breaking, but there's not a lot of like where does that energy come from? Actually? 00:21:28 Speaker 1: Yeah, well, if you do break a banana and half or you break your cell phone and half, you are breaking bonds. Those are chemical bonds, right, Those are bonds between atoms, and the atoms are not changing. You might be taking a molecule and breaking it into its atoms, or you might be just sort of like cracking a crystal along you know, a part of its lattice. And so there are bonds between molecules that are being released, but you don't notice any energy being released there because the energy is really really small. But when you break a nucleus in half, then the energy released is huge. And the reason it's much bigger is because the strong force is involved. In the strong force as well, it's really strong, so it has a lot of energy stored inside these atoms. It's much stronger than the electromagnetic force, which is one that's holding your banana or your cell phone together. 00:22:13 Speaker 4: I guess it's kind of like you say that, like there's a spring holding these nuclei particles together, and so suddenly if you like detach those springs, they're gonna spring out, right, all that sort of stretched energy has to go somewhere. 00:22:24 Speaker 1: Yeah, it's sort of like a jack in the box, right, and you open the top and boom, everything pops out. Or it's like you know, one of those cans full of snakes, so you open it up and like bang, everything flies out. And that's exactly what happens here. You crack open the nucleus it was held together sort of delicately. You crack it open, and everything flies out with a bunch of energy. 00:22:42 Speaker 4: But it's sort of like a reverse jack in the box, right, because the springs are pulling stuff together, not sort of being compressed and wanting to explode. 00:22:50 Speaker 1: Yeah, exactly here in this case, the bonds are holding them together, so they're sort of trapped in a bound state where the bonds you know, have a potential well, where everything is like trapped inside. You can think of that sort of as like the box that's holding the jack in the box together, or the can that's holding the snakes inside. But inside there are things with a lot of energy that are desperate to get out. They're trapped into a stable configuration currently, but if you destroy the barriers that are holding them in, they will fly out. 00:23:18 Speaker 4: I wonder if it's like, you know, wrapping something open bungee cords and holding this time some something big together with bungee cords or rubber bands, and then when you cut a rubber band, you know, it snaps and they go flying out. 00:23:29 Speaker 1: Yeah, exactly, Take a huge ball of rubber bands and cut it in half with a circular saw. Then the rubber bands are going to go everywhere, and they're not just going to lie down nicely on the table. 00:23:38 Speaker 4: All right, Well, that's nuclear fission. That's what happens when fission happens in an atom. And so let's get into whether or not it happens naturally in nature and whether or not we've ever seen it happen. But first let's take a quick break. 00:23:56 Speaker 1: With big wireless providers. What you see is never what you get. 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It's just not counted in our podcast listenership, which I don't think is fair. 00:27:56 Speaker 4: I see right, right, we could have one more added to our. 00:27:59 Speaker 1: Data listening to the ads, in which case, hey, it's all cool, it's. 00:28:04 Speaker 4: All click through. But yeah, we talked about fission and what it is. It's when you break up a heavy atom into lighter atoms. When you redistribute the number of protons and the nucleus. And so the question we're asking today is can that happen naturally in nature? And more specifically, can can you like have a reactor of it that creates a bunch of energy happen in nature? 00:28:25 Speaker 1: Exactly because fission itself, like an atom breaking into smaller pieces and releasing energy, that happens all the time, like uranium just sitting around is unstable, and those atoms will crack and havel and they will fly apart, and lots of atoms are unstable, and every time that happens you call it radioactive decay. It really is fission. But what we do inside of reactor is not just have like one atom break in half or two atoms break in half. We have something special. We have a chain reaction, a self sustaining reaction sort of like fire. That's a very special arrangement which only in this century we were able to end engineer to make happen. 00:29:01 Speaker 4: So you're saying that like fission by itself does happen in nature, like things break apart in nature all the time, but it's getting it to be self sustaining and have it sort of be like a fire where it's constantly happening. That's harder, or like did you see the sun? For fusion, that's harder to do. 00:29:17 Speaker 1: Yeah, exactly. It's like the difference between having a spark and having a fire. You know, we've all been there at a campsite shooting sparks at something and trying to get a fire started. It's not always easy to get a fire started. Right. You can have sparks, which are evidence of energy being released, right, the same chemical process is at work. But to get a fire started, you need to get enough heat so that you're igniting more fuel, which can then release more heat, which can ignite more fuel. So it's a self sustaining part which is quite tricky to happen, even for a fire. Sometimes, I'm especially difficult for a fission chain reaction. 00:29:51 Speaker 4: So this happens in nature for fusion, like in the sun and the stars that it seems to happen more easily for fusion than for fission. 00:30:00 Speaker 1: Right, But again that's probably just because there is a lot of fuel for fusion around, right. Fusion requires light elements, and there are a lot of light elements in the universe. It's mostly hydrogen out there, and so that's fuel for fusion. 00:30:12 Speaker 4: All right. So you're saying that fission, making fission happen it constantly is hard, but we figured it out here on Earth right in our nuclear reactors and in our nuclear bombs. So how do we do it? 00:30:23 Speaker 1: So the key things you need to make a self sustaining fission reaction, you need two things. One is you need enough fuel sort of close to each other, because you need one fission reaction to trigger the next

one, which triggers the next one right, sort of like if you're trying to start a fire, you don't spread your logs out everywhere. Get them close together so the heat from one can ignite the next one. And then you also need something to get the neutrons that fly out to be at the right speed, because the neutrons that fly out don't always come out at just the right speed to trigger the next reaction. So you need one a critical mass, and two you need this thing called a neutron moderate which makes the neutrons go with just the right temperature. 00:31:03 Speaker 4: Yeah, those neutrons are not as neutral as they seem. Sometimes you get them pulling back sometimes. 00:31:07 Speaker 1: Well, they're just so excited to get out there in the world and do something like hey, neutron, look, let me give you some career advice. Okay, you don't want to burn out immediately. 00:31:15 Speaker 4: All right, So let's tackle each of these interns. So you say you need critical mass because in a chain reaction fission, in a fission chain reaction, you have like one atom splits open that releases a bunch of energy, and then that energy comes out as particles I guess or photons, and then those hit other heavy nuclei, which then causes them to break, and then those release more energy, which causes other things to break. So that's what you mean by chain reaction. 00:31:41 Speaker 1: Right, yeah, exactly. And what happens when you break up the uranium, for example, is you get the fragments, you get the lighter elements, and then mostly you get neutrons. Like you get some energy in terms of photons, but then also you get these neutrons, and that's critical because it's the neutrons that are going to trigger the neighboring atom to break apart. So, for example, you take a neutron and you shoot it into a uranium atom, and it will make it unstable. It will give it enough energy so that instead of being like a nicely built piece of lego, it's like it's a little wobbly and then it's going to break open. And so it's the neutron that triggers the reaction in the neighbor. 00:32:19 Speaker 4: Interesting, So I guess, first of all, when an atom breaks apart, why does it release a lot of neutrons and not like protons or something else. 00:32:27 Speaker 1: Yeah, it actually shoots out a bunch of particles, and so sometimes you get neutrons, sometimes you get gamma rays. You can also get protons. Mostly the protons like the cluster together into these other nucleis, so we call these nuclear fragments. They go off and form little daughter particles. But you can sometimes get protons out. And also the neutrons that you shoot out, they will eventually decay because neutrons are not stable, so you will eventually get protons coming out also. 00:32:51 Speaker 4: All Right, So you're saying that's pretty interesting, because that's one thing I didn't know is that I always thought that when fission reactions happen, it's like the energy from the shooting particles break the other ones apart. Bird, It's really more like you're shooting off hairs and they break the camels back of other nuca. 00:33:06 Speaker 1: Yeah, it's like little bullets, right. These neutrons are like little bullets, and they're shooting out and they have just the right interactions to mess up the neighbors. And so it's sort of like you know, divorces spreading throughout a friend group. You know, people get grumpy, they get divorced, they start complaining to their friends about their marriages, and their friends are like, oh, that sounds familiar, maybe we should get divorced. 00:33:27 Speaker 4: Yeah, it's like I was saying, it's like it's shooting hairs that break the camel's backs all around, and then when those camels break apart, it shoots off hairs that break other camel backs right exactly. 00:33:36 Speaker 1: And so what you need is a critical mass. When those neutrons fly out of the fissioning atom, they need something to hit. So you need to have enough fuel sort of packed densely together in order to make it so that you can have a self sustaining reaction. And critical mass is probably like a phrase you've heard before, and that's essentially the most important component in having a nuclear reaction. 00:33:56 Speaker 4: Right, because I guess if the camels are too far apart. You know, one of them will just break apart and send hairs flying up, but the hairs won't hit the other camels, So you need tom packed close together. 00:34:06 Speaker 1: I see that you prefer to talk about camels than divorces. 00:34:09 Speaker 4: I'll go, yeah, it's a bit of a bummer camels. It's just, you know, a more fun image. 00:34:15 Speaker 1: Are camel's monogamous? By the way, do they mate for life? 00:34:17 Speaker 4: Yeah, let's talk about camel divorce. 00:34:21 Speaker 1: I'm just trying to fuse it all together rather than fission our analogies into two different topics. 00:34:26 Speaker 4: Yeah, how many analogies for fission can we come up with? We've already broken bananas and Jack in the box inverse Jack in the boxes and camels and divorce. All right, so new critical mass we get a chain reaction of fission. And you also said you need to slow down the neutrons somehow. 00:34:43 Speaker 1: Yeah. The problem is that when the neutrons fly out, they have a lot of energy, so they're called fast neutrons. They're just moving really, really quickly, and even if you pack your uranium pretty tightly, the neutrons that come out are moving too quickly to ignite the neighboring uranium nuclei into breaks because the faster they're going, the more like the universe is compressed for them, and so they have a smaller chance of hitting those neighbors. So what you need is something to slow down those neutrons to just the right speed so they have a high enough chance of hitting a nucleus and triggering another reaction. 00:35:19 Speaker 4: Oh interesting, it's about like the probability of hitting another atom. Right, Like the hairs from the camel are flying

too fast, they'll just miss all the other camels. But if it's growing slow, then there's a bigger chance that you know, a camel will walk into the path of one of these hairs. 00:35:36 Speaker 1: Yeah, because you don't want your neutrons to fly all the way through your fuel and escape with their energy. You want them to deposit that energy in some other nuclei so it can trigger another reaction. So basically you have to make your fuel opaque to neutrons rather than transparent, and so to do that, you got to slow them down because fast neutrons will escape and slow neutrons will be captured by neighboring atoms and trigger more reactions. 00:35:59 Speaker 4: All right, you need critical mass and you need to slow down your neutrons, and if you do that, then you can get a fission chain reaction to heaven. And that's what gives you nuclear bombs and nuclear reactors. 00:36:10 Speaker 1: That's right, that's mostly the design for a nuclear reactor, non nuclear bomb. And so if you're a nice person out there and looking to build the next generation of nuclear reactors and provide clean, green energy to the future, then we support you. If you're out there trying to build a nuclear weapon, then you know, check out another podcast. 00:36:27 Speaker 4: Yeah, you're done here. You can basically turn this off down. 00:36:30 Speaker 1: But this was first done in nineteen forty two in Chicago by Enrico Fermi. And it's not an easy thing to accomplish this right balance of having the right mass of fuel and just the right sort of neutron moderator to get the neutrons at the right speed. It's really quite delicate. 00:36:46 Speaker 4: So that's how you make a nucleon fission reactor. And so now the question that we started with was does it occur naturally in nature? Are there stars out there? Are there things that are naturally reacting with fission constantly? So let's get into that question. But let's take another quick break. When you pop a piece of cheese into your mouth or enjoy a rich spoonful of Greek yogurt, you're probably not thinking about the environmental impact of each and every bite. But the people in the dairy industry are. US Dairy has set themselves some ambitious sustainability goals, including being greenhouse gas neutral by twenty to fifty That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. Take water, for example, most dairy farms reuse water up to four times the same water cools the milk, cleans equipment, washes the barn, and irrigates the crops. How is US dairy tackling greenhouse gases? Many farms use anaerobic digestors that turn the methane from maneuver into renewable energy that can power farms, towns, and electric cars. So the next time you grab a slice of pizza or lick an ice cream cone, know that dairy farmers and processors around the country are using the latest practices and innovations to provide the nutrient dense dairy products we love. With less of an impact. Visit usdairy dot com slash sustainability to learn more. 00:38:05 Speaker 5: Hi, I'm David Eagleman from the podcast Inner Cosmos, which recently hit the number one science podcast in America. I'm a neuroscientists at Stanford, and I've spent my career exploring the three pound universe in our heads. We're looking at a whole new series of episodes this season to understand why and how our lives look the way they do. Why does your memory drift so much? Why is it so hard to keep a secret, When should you not trust your intuition? Why do brains so easily fall for magic tricks? And why do they love conspiracy theories. I'm hitting these questions and hundreds more because the more we know about what's running under the hood, the better we can steer our lives. 00:38:50 Speaker 6: Join me weekly to explore the relationship. 00:38:52 Speaker 5: Between your brain and your life by digging into unexpected questions. Listen to Inner Cosmos with David Eagleman on the iHeartRadio app, Apple Podcasts, or wherever you get your podcasts. 00:39:06 Speaker 14: Parents, are you looking for a screen free, engaging way to teach your kids the Bible? One that's easy to understand and enjoyable for multiple ages. Kids Bible Stories Podcast is here to help. I created this for my own children and it's now a favorite among thousands of families. Kids love the vivid imagery, scriptures, and sound effects, while parents appreciate the apply section for meaningful conversations. We have hundreds and hundreds of beautiful episodes that bring the Bible to life when you simply press play. It's a sound and practical resource that walks alongside you as you teach your kids. We want kids to see how incredible God's word is in an engaging and memorable way with Kids' Bible Stories Podcast. Listen to Kids Bible Stories Podcast on the iHeartRadio app, Apple Podcasts, or wherever you get your podcasts. 00:39:57 Speaker 15: We think of Franklin as the dodling dude, fly a kite and no rain, but those experiments are the most important scientific discoveries of the time. 00:40:06 Speaker 1: I'm Evan Ratliffe. 00:40:07 Speaker 16: Last season, we tackled the ingenuity of Elon Musk with biographer Walter Isaacson. This time we're diving into the story of Benjamin Franklin, another genius who's desperate to be dusted off from history. 00:40:18 Speaker 15: His media empire makes him the most successful self made business person in America. I mean he was never early to bed, an early to rise type person. He's enormously famous. Women shut wearing their hair in what was called the coiffor a la Franklin. 00:40:36 Speaker 1: And who's more relevant now than ever. 00:40:38 Speaker 15: The only other person who could have possibly been the first president would have been Benjamin Franklin, but he's too old and wants Washington to do it. 00:40:48 Speaker 16: Listen to on Benjamin Franklin with Walter Isaacson on the iHeartRadio app, Apple Podcasts or

wherever you get your podcasts. 00:41:03 Speaker 4: All right? Can a fission reactor happen naturally on this universe? Daniel? I guess the question is, is there somehow, you know, like we see stars out there that are constant fusion reactors? Do we see I don't know, some weird concentration of uranium or plutonium that is constantly also reacting and giving off energy. 00:41:24 Speaker 1: Yeah, Well, what you would need are both of the elements, right, You need some critical mass of uranium or plutonium, and you'd need something to moderate the reaction so that it can self sustain rather than just like burning itself out by shooting these neutrons out and losing all of their energy. And so in our episode about fission stars, I think we concluded that there isn't enough uranium in the universe to make like dense blobs of uranium that could do that. But you know, there are deposits of uranium here in the crust of the Earth's surface, and so you could imagine, like, hmm, could they're just like happen to be really rich deposits of uranium in the Earth's surface and just the right arrangement to somehow like create natural fission reactors. 00:42:08 Speaker 4: Right, because I guess you could get a chain reaction going with any amount of uranium, but I guess if you only have like a tea spoon of it, it won't last very long. Right, So you're saying, like, maybe here on Earth we could have enough uranium together that we do get this sort of nuclear constant reaction going exactly. 00:42:24 Speaker 1: And this is something that in nineteen fifty six a business was thinking about. It was Paul Krota, and he predicted that it would be possible. He said, if you have a configuration in the Earth's crust where you have exactly the right amount of uranium in the right configuration, and like water leaks in and provides just the right kind of like neutron moderation, then you could get a nuclear reaction going just like by itself spontaneously underground. 00:42:51 Speaker 4: I guess I'm surprised that it doesn't happen more often. Is it the case that you know, we have a lot of uranium here on Earth and it's it's fissioning, it's breaking up apart, but it's not causing a chain reaction, so it's not sort of like burning up really quickly. 00:43:03 Speaker 1: That's exactly right. Uranium just sitting around is constantly fissioning and constantly breaking up, and sometimes it's even in critical mass, but there's not a neutron moderator, and so you need that second piece to make the self sustaining reaction happen. 00:43:18 Speaker 4: Well, and so that's happened here on Earth. So someone predicted it. But have we found an actual like natural fission reactor on Earth. 00:43:25 Speaker 1: Yes, Actually, somebody has figured out that billions of years ago deposits in the earth in Gabon in the African Continent did experience a nuclear self reaction. Basically, there was a reaction happening underground on Earth, and the way they discovered it is really quite a fun story what happened. Uranium is a very special and important material, right, and we don't want the wrong people to get their hands on it. So people do very careful accounting of like the amount of uranium. And remember that uranium comes in two flavors. There's the U two thirty five, which is important one you need for doing fission, and then there's U two thirty eight, which is much longer lasting and much less useful. So typically what you do is you mind uranium and then you try to get the U two thirty five out of it. You can do like centrifuging or any sort of like you know, processing to get it out, and most natural deposits have a pretty small amount of it, it's something like zero point seven percent. So there was this material that they mined in Gabon and they were processing it in France and they discovered a whole on a second, it's really really low in U two thirty five, and they were wondering, like did somebody steal all the U two thirty five? Like where did all the U two thirty five go? It's like this material has already been depleted of the fission material. 00:44:43 Speaker 4: Because I guess most of the uranium and Earth was sort of created at the same time, and so they all are have the same sort of ratio of the two kinds of uranium. 00:44:51 Speaker 1: That's right. And it's like a big clock. You know, billions of years ago there was more U two thirty five on Earth, and it's just depleting, like it's just cost instantly fissioning and breaking up and turning into other stuff. So the U two thirty five fraction in deposits is dropping all over the Earth constantly. And where was this made? When did this clock start? Well, we think that this stuff was made like in supernovas or in the collisions of neutron stars billions and billions of years ago, and so it's just been like slowly fissioning into other stuff very gradually over billions of years. And now just because of where we are in time, it happens to be about zero point seven percent of natural uranium. 00:45:33 Speaker 4: So I guess we assume that all of the uranium on Earth was made at the same time, like there was one event that created all this uranium. 00:45:40 Speaker 1: Yeah, mostly, or at least you know, to within a billion years or so. 00:45:43 Speaker 4: All right, So then we found this piece of uranium rock that had a different ratio of the two kinds of uraniums. It had less of the U two thirty. 00:45:50 Speaker 1: Five exactly, it had less of the useful stuff, the stuff that you could use to do fission. And so for first people were like, hold on a second, somebody must have like slurped it out or stole it or whatever. But then they discovered that all of the deposits from this one mine had this low fraction that you know, that most of the stuff was essentially already depleted of what you could use for fission. And so then they started thinking, whole on a second, maybe this is an example of a natural reactor. Maybe it's just sort of like

fissioned on its own and burnt out all of the useful uranium. 00:46:22 Speaker 4: Mmm, like it's ignited. Right, It's like you're looking for coal deposits, but you find some coal that already looks burned out. 00:46:29 Speaker 1: Yeah, exactly, And so that's exactly what happened. And what they figured out is that there are very rich deposits of uranium in this mine, so like excellent critical mass, just what you need, and that there were cracks in the rock where groundwater could seep in, and so the groundwater would seep in and then surround these deposits and essentially act like a neutron moderator. So like crack and get inside. And you know, this is something that like engineers spent a lot of time becoming proficient in how to design, but it just sort of like happened accidentally and randomly in this one spot, and it was just in the right way to moderate those neutrons so they have the right energy to trigger this self sustaining reaction. 00:47:12 Speaker 4: WHOA. So really all you need is like just add water to uranium in the right way and you can get a little nuclear reactor. 00:47:20 Speaker 1: Yeah, but you need water like internally. You can't just like put a chunk of uranium in a glass of water. You need to be internal so that you can like really capture those neutrons and slow them down and before they hit another piece of uranium. So you need like a cracked piece of uranium, you like it drill holes in the uranium first or something. 00:47:38 Speaker 4: Oh, I see, you need like a little water barrier between different parts of the uranium so that it slows down the neutrons. 00:47:44 Speaker 1: And then what happens, right, What happens is you produce a lot of heat, and so then the water gets hot and it turns into steam, and it boils away and it turns off the reaction. Then it cools down and more water drips in and it starts again. And so they were able to figure out that this thing was on a three hour cycle. Is like thirty minutes of intense fission reactions boiling this water into steam, and then like two and a half hours for it to cool down and for water to come back in and for things to kick off again. Wow. 00:48:13 Speaker 4: And so this happened for how long you think. 00:48:15 Speaker 1: This happened billions of years ago? For a few hundred thousand years. By counting like how much uranium has been depleted, they were able to figure out that this thing went on for quite a long time. 00:48:26 Speaker 4: Interesting, you said one hundred thousand years this was happening, So for one hundred thousand. 00:48:30 Speaker 1: Years, hundreds of thousands. 00:48:31 Speaker 4: Yeah, So for a few hundred thousand years, it's somewhere in Africa was unseasonably warm, or like the ground, somewhere in the ground or somewhere inside of a mountain. It was sort of like hot. 00:48:41 Speaker 1: Yeah, it was like a few hundred degrees celsius underground and over several hundred thousand years it consumed the fissile material in

like several tons of uranium. 00:48:54 Speaker 4: Wow. So it was like a naturally engineered nuclear reactor exactly. 00:49:00 Speaker 1: And it was producing crazy radiation, right, it was shooting off particles, and you know, if it had been really near the surface, it would like caused cancer in any animals or people living nearby. But of course it was billions of years ago. 00:49:12 Speaker 4: But it happened in Africa. So could that have somehow I no know, mutated some plant or animal and here we are. 00:49:19 Speaker 1: Yeah, this is like an alter version of two thousand and one, you know, like a uranium monolith that like mutates our ancestors and makes them intelligent or dumber. Maybe we would have been smarter if this thing happened. 00:49:29 Speaker 4: Happen. Interesting, I see, So maybe we are all really superheroes whose origin are and some you know, radioactive event. 00:49:38 Speaker 1: Yeah. The thing I find really interesting is that it's no longer possible because uranium is naturally depleting itself, Like this depleted itself really rapidly because of this critical mass and the neutron moderators, et cetera. But most uranium just sitting underground is naturally depleting itself, not through a self sustaining reaction, just as it sort of falls apart and so on. Average, the uranium around the Earth is doesn't have the critical mass anymore to do this. This happened billions of years ago because back then it was much richer in uranium two thirty five. It hadn't like fallen apart yet into the lighter elements. 00:50:12 Speaker 4: Oh, I see, so this couldn't happen again, really, I mean, if you like put the water in in just the right way, No. 00:50:18 Speaker 1: It couldn't happen again. You don't have the critical mass in naturally occurring uranium or anymore anymore. I'm not on Earth that we're aware of. Unless there's like a fresh batch of uranium that just landed from a neutron star collision in a neighborhood or somewhere else on another planet, it could certainly happen. But if there's uranium or that's sort of of the same date as the ones that we're typically discovering, then it's no longer rich enough for this to happen. 00:50:42 Speaker 4: Interesting, I see, it's like it's stale exactly. 00:50:46 Speaker 1: Those camels got stale to use your analogy. 00:50:49 Speaker 4: Yeah, they got wet or something. Well, And I see because the kind that we use for like nuclear reactors and nuclear bonds, we have to like refine it, right, we have to make it rich, sure, in this special kind of uranium. 00:51:01 Speaker 1: Hence the famous centrifuges used to make nuclear fuel. 00:51:05 Speaker 4: All right, so maybe it was once. It sounds like there was only a brief period of time maybe in the history of Earth, where a natural fission reactor could have occurred. But no, no longer, right. 00:51:15 Speaker 1: That's right. Now it's just up to us humans to engineer the precise conditions necessary to release this energy from the atoms. 00:51:22 Speaker 4: But I guess it could have happened in other parts of the Earth, not just in Africa, Like, there could have been other reactors that we don't know about yet, and there could be reactors happening in other planets perhaps or in other parts of the galaxy. 00:51:34 Speaker 1: Sure, this is the only one that we have found, but certainly possible that deeper in the Earth or just in undiscovered uranium deposits, there's evidence that it happened other times in the history of the Earth, and it certainly could be happening right now on a fresher planet out there, a less stale camel. 00:51:49 Speaker 4: All right, cool, well, I guess the answer to the question, can a fission reactor happen in nature? The answer is yes, with the right conditions and the right time, in the right place, you can't have like an actual nature vision reactor. 00:52:03 Speaker 1: How does that make you feel about the quality of human engineering versus just natural randomness? 00:52:07 Speaker 4: Well, humans were engineered by nature, so I think nature is the ultimate engineer. 00:52:14 Speaker 1: How about that Nature should be on all of our papers as well. 00:52:17 Speaker 4: It should be a Marvel superhero nature nature. 00:52:20 Speaker 1: And it should be totally naked. 00:52:21 Speaker 4: Right on natural, Man, your mind is going to some interesting places. Do they divorce nudity? Boy, Daniel, you know this is the family friendly podcast, right, We're not trying to fuse it with other ideas. 00:52:35 Speaker 1: I apologize clearly the nature character for Marvel should be a camel. 00:52:38 Speaker 4: You're right, all right? Well, we hope you enjoyed that and then got you to think about what an incredible place nature is. Right where suddenly, for some reason, fission reactors can happen. 00:52:49 Speaker 1: That's right. So everything that you can't imagine is probably happening out there somewhere in the universe. Events are conspiring to create even the most delicate and elaborates in it, in which the craziest particle interactions can occur. 00:53:03 Speaker 4: Well, thanks for joining us, See you next time. 00:53:14 Speaker 1: Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of iHeartRadio. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. When you pop a piece of cheese into your mouth, you're probably not thinking about the environmental impact. But the people in the dairy industry are. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. House US dairy tackling greenhouse gases. Many farms use anaerobic digestors to turn the methane from manure into renewal energy that can power farms, towns, and electric cars. Visit you asdairy dot COM's Last Sustainability to learn more. 00:54:08 Speaker 5: Hi, I'm David Eagleman from the podcast Inner Cosmos, which recently hit the number one science podcast in America. I mean neuroscientists at Stanford, and I've spent my career exploring the three pound universe in our heads. 00:54:21 Speaker 6: Join me weekly to explore the relationship. 00:54:23 Speaker 5: Between your brain and your life, because the more we know about what's running under the hood, that or we can steer our lives. Listen to Inner Cosmos with David Eagleman on the iHeartRadio app, Apple podcasts, or wherever you get your podcasts. 00:54:38 Speaker 2: I'm doctor Laurie Sandos, host of the Happiness Lab podcast. As the US elections approach, you can feel like we're angrier and more divided than ever. But in a new hopeful season of my podcast, I'll share with the science really shows that were surprisingly more united than most people think. 00:54:56 Speaker 16: We all know something is wrong in our culture and our pow politics. 00:55:00 Speaker 14: And that we need to do better and that we can do better. 00:55:03 Speaker 2: Listen on the iHeartRadio app, Apple podcasts, or wherever you listen to podcasts.