 Hi, I'm Zor. Welcome to Indizor Education. We continue talking about nuclear power, the power inside the atom's nucleus. Now, we were talking about the contents of the nucleus. There are protons and there are neutrons and there are strong forces, I mean, it's like a name of the force. It's not just strong as an adjective. So we have so-called strong forces which are keeping this nucleus together and we need these forces because the protons as electrically positively charged are repelling from each other. So we have to keep them together and that's what strong forces are about. So the nucleus is kept together by strong forces. Now, if we break the nucleus, what kind of energy is involved? Well, we do have to break strong forces and then the electric forces, the repelling forces, will start basically converting their potential energy into other kinds of energy. So that is the nuclear reaction. So today we will talk about a particular kind of nuclear reaction called fission. Now, this lecture is part of the course called Physics for Teens, presented on Unizor.com. The website is free, by the way, and it has textual material and exams. So it's much more convenient to use the website to study this particular course. All the lectures are logically presented and follow each other in special order. So back to nuclear reaction called fission. Now, we did talk about what happens if we combine certain protons and neutrons together to form a little bit bigger. Nucleus. And we did talk about something opposite, which means we can have a bigger nucleus and split it. So today we will talk about the fission, which is a reaction of splitting of larger, more, heavier nucleus into smaller parts. Okay. Now, we are interested in these nuclear reaction, basically, to get some energy, which means reaction should really be net positive as far as the energy is produced. Now, what energy is produced and what energy is released when we are breaking a nucleus? Well, again, nucleus contains protons and neutrons, and they're all together held by strong forces, which means if we would like to produce an energy first of all, by splitting. First of all, we have to split, which means we have to break strong forces. It requires a certain amount of energy. So this is the energy consumed by nuclear reaction. Okay. So if you have this nucleus and you would like to split it, first we have to spend a certain amount of energy and break away pieces of this nucleus against the strong forces, which are trying to keep it together. At the same time, if it's done, as soon as we have separated a little bit two pieces of this nucleus, and we know that the strong forces are acting only at very, very, very short distances. Electrostatic forces of repelling between protons, which are in this particular nucleus, are stronger on bigger distances, which means if we will be able to split it a little bit, strong forces will probably not play much of a role, and the forces of electrostatic repulsion will play much, much greater role, and the energy will be released just because these pieces will just go into different directions, repelling from each other. So let me make an analogy. Let's consider you have a spring, and you squeeze it together and you put some kind of thread here. So it's squeezed, which means it has certain potential energy. But it does not release because we have this thread which ties together both ends of this spring in a squeezed state. Now, if nothing happens, if we don't really cut this thread, the potential energy inside remains a potential energy. Nothing actually happens. So this particular thread keeps this potential energy unused, so to speak. So it plays the role of strong forces in the nucleus. These strong forces are keeping the nucleus together, not allowing the potential energy, which is in repulsion of the protons, the same thing as here. The thread is preventing the potential energy of a spring whenever it's just released to materialize. But if we will cut the strong forces here, immediately our spring will be activated, it will be released, and then the potential energy, which is inside the spring, will immediately convert into kinetic energy of the spring's ends. So same thing happens in this particular case. The question is, what is greater? The amount of energy we need to cut the strong forces to cut this thread, which keeps the spring in a squeezed position, or amount of kinetic or other types of energy released after we break this particular nucleus. And if the potential energy of the protons inside the nucleus is greater than the energy needed to split this particular nucleus, then the net result will be a positive release of energy. And in some cases, that's exactly what's happening. Now, let's think about it from another standpoint. The nucleus has protons and neutrons. Protons are repelling to each other, right? And strong forces are keeping it together. Now, neutrons also are inside the nucleus, and there are strong forces which are keeping them together with other neutrons and protons. Now, but the trick is neutrons do not have any electrostatic charge. They're neutral, which means they're not repelling from each other. They're not repelling from other protons. They're only bonding together with all of them, which means that the neutrons are actually the bonding material of the nucleus. Protons need really this special force, the strong force to keep them together. If not that force, they would just basically repel like a spring would be released, right? But neutrons are not like that. Neutrons and protons are not repelling each other. So the strong forces which exist between neutrons and protons are not really counteracted by repelling electrostatic forces, which means that the more neutrons are in the nucleus, the more stable this nucleus is, the more difficult it is to break it apart. That's very important consideration because many elements, I should say probably most of the elements, have not just one type of nucleus, but a few with the same number of protons. So the electrical charge is the same, which basically means it's the same number of electrons and that actually necessitates that their chemical reaction would be the same, etc. But different number of neutrons inside the nucleus. So the same number of protons, but different number of neutrons gives different nuclear qualities of the particular element. So all these different types of the same element, which have different number of neutrons, are called isotopes. Now, as an example, I would like to consider two isotopes of uranium. There is a uranium which always has 92 protons and 90 true electrons. Now, there is a uranium 238, and this is 92, now this is the number of protons and neutrons, atomic weight, atomic mass. So this is one isotope of uranium and there is another isotope, uranium 235. You see there are three neutrons less. So in this particular case, we have 146, right, difference neutrons. In this case, in this case, we have 143 neutrons less. And as we know, the less neutrons you have, the less stable, easier to break the nucleus is. And so it happens that this uranium really is easier to break than this one. Now, remember the spring and it's a squeezed position and you have a thread here. Just left by themselves, nothing happens. So we have to cut the spring, I mean, sorry, cut the thread to release the spring. So we need some action, some little push to this particular isotope of uranium to basically initiate the breaking. We have to hit it with something. Then it might actually break. Because again, you see, it's some kind of a equilibrium, if you wish, between electrostatic repulsion between the protons and strong forces which are keeping together. If they are very close to each other, it's easier to just hit it with something and then the nucleus will just fall apart. In case of this uranium-238, it's more difficult because there are more neutrons and it's more neutrons, we know, it's more bonding material, it's more difficult to break. So it doesn't really break so easily. But this one does. It's a different question where to get this one because this one is naturally occurring and this one is actually, well, significantly less. You need a special process to enrich this uranium, convert it into this uranium to really produce this isotope. Just by itself, you can't really find it very often. However, after it's done, after you have this, then there is a possibility to break this particular nucleus and release as a result, release some energy. Because the strong forces which we have to break are smaller here than there. But the number of protons is the same. So the repulsion is exactly the same between them. So what is necessary to break this particular nucleus and release the energy which is inside? To release the potential energy like this one, like in the spring, which is within 92 protons squeezed together by strong forces. All right. So we have to cut these strong forces with something. The question is what? With what? Well, the answer is all you need is a neutron. If you just hit this particular nucleus with a neutron, something will happen. This is a hit. And as soon as you hit it, it breaks certain equilibrium between the repulsion and bonding by the strong forces, repulsion of the protons and bonding and bonding with the strong forces. And this equilibrium is broken and then the nucleus falls apart. And here is what actually happens. Okay, if you have a neutron, the neutron has atomic mass of 1 and no protons. It's just one neutron, so no charge. Like in this case we have 92 positive charge. In this case, if it's a neutron, we have zero. Now, what happens if we bombard it with, if we will bombard this nucleus of uranium 235, which has 143 neutrons and 92 protons, and you bombard with one neutron. What happens? Well, not every time. But what might happen? Probably, you know, in certain cases it happens, in certain cases it doesn't happen, depending probably on different other conditions. But what might have happened is the following. The big and very heavy, see 235 is heavy. It's almost at the end of the Mandalayev's periodic table. Now uranium is, breaks the, it is break, breaks down between barium and kryptonite. Krypton. So what happens? All together protons and neutrons we have is 235. 92 protons and 143 neutrons. And we have one more neutron here. Neutron, neutron, neutron, sorry, neutron. Now this guy has 56 protons. Now the atomic mass is 141, so it leaves for neutrons, how many? 141 minus 56, it's 85 neutrons. Now the krypton has 36 protons plus 56 neutrons, right? So let's check the balance. 56 protons and 36 protons, together it's 92 protons, fine. 85 and 56, it's 131.41, right? 141, and here we have 143. And 1, so it's 144. So we need three more protons, neutrons, and that's what happens. Three free neutrons are just released as well. So this particular nucleus is breaking apart into two other nucleoses and also three new free neutrons are released. Okay, so that's what happens and apparently the potential energy of the protons, of 92 protons, which are separated into two big pieces, is greater than the amount of energy needed to break the nucleus apart into two other nucleoses. And as a result, we have release of energy. And not only we have released of energy, we also have released a couple of more neutrons. And this brings up a very important consequence. If you have a lot of uranium 235 together in one lump, whatever, and you have managed with one particular neutron to break one particular nucleus, it releases three new neutrons, which are going through this uranium 35 lump, and they can hit other nuclei of uranium 235 and break them. And then the other, and then the other, so every new breaking produce more neutrons than it consumes. And that's what actually happens in so-called chain reaction. This is the chain reaction. One particular breakage splitting of the nucleus can produce more and more and more, because every new one produces enough neutrons to have two three more. Now again, obviously not every nuclear gets reached basically by neutrons and gets broken down. So it's all very, very complicated reaction. But in theory, you understand how this chain reaction actually happens. So one nucleus is destroyed into these two smaller nuclei, and the new neutrons are responsible for hitting other nuclei of uranium and breaking them apart, et cetera, et cetera, et cetera. So if it happens very fast, that's what happens in atomic bomb. Now the question is, how can we control this reaction? We can control it only through this. We have to basically reduce the number of neutrons. What if we will be able to reduce it? Significantly down. So the chain reaction will not have enough neutrons to break the uranium, right? So basically that's what's happening in the nuclear power stations. They have special mechanisms to consume these neutrons so they don't really hit the new nuclei of uranium. And by doing that, we control the reaction. So it doesn't really go like an explosion. It releases a certain amount of energy, but under our control. And we are hitting something. For instance, we're hitting water. Water does whatever is necessary, produces the power. So the power release, the energy released by this particular reaction is in the power station, nuclear power station, is under control. And the reason is we have to control these neutrons by, I know, absorbing them into some substance, whatever it is. Well that's basically it. That's all I wanted to talk about fission. The fission is, again, it's a split of heavier nuclear like uranium or plutonium actually also has another reaction of splitting fission reaction into smaller nuclei and a certain amount of energy gets released. Next lecture will be the opposite process called fusion. That's where the light nuclei are fused together to get the bigger one. And again, the release of energy actually occurs because in that particular case the difference between bonding using the strong force energy and repelling of the protons is significantly, I mean, it just goes to another direction. The strong forces are stronger, so to speak. All right, that's it for today. Thank you very much and good luck.