Nuclear Reactions - Radioactive Decays

So let's talk about nuclear reactions. What are nuclear reactions? Well, they're reactions between nuclei. Alright, so what's conserved in a nuclear reaction? Well, the mass number and the charge are the two things that are always conserved in a nuclear reaction in every nuclear reaction. Every single radioactive decay, every single nuclear collision, every single nuclear reaction will conserve mass number and charge. Alright.

Now, the atomic number is not something that's conserved. So it actually often will change in a nuclear reaction and we get something called transmutation of the elements And this is something that cannot happen in a chemical reaction. It is impossible for a chemical reaction to change the atomic number. Nuclear reactions that's not the case. Almost always will have a change in the atomic number.

Nuclear reactions are associated with lots of energy. We're talking about reactions that happen inside of stars, Okay? In the core of a star. These are the reactions that are taking place. Also in a nuclear reactor, kind of why we call them nuclear reactors. Alright. So let's see how we can solve a problem involving a nuclear reaction.

Alright. So I'm going to imagine that inside of a star or inside of a nuclear reactor, I've got oxygen 16 running into lead 208. They have a big collision and after everything's said and done, we end up with carbon 12, two neutrons and something else. And the question is what is that something else? Alright.

To begin with, what I want to do is I want to write down all the atomic numbers because the atomic numbers tell me the charge of these guys and that's the other thing that's conserved. So, oxygen, oxygen's number 8 so I'll write it. Lead, lead's number 82 so I'll write it. Carbon, carbon is number 6. Neutrons have no protons. they're just neutrons. So that means that no charge one atomic mass unit. Alright. Now let's go through and just try to determine what this question mark has to be.

I'm going to write it as x and then we usually use a z down here and an a up here. Alright? Okay. So we'll say looking along the top, 16+208 has to equal 12+2+a, right? 12 and 2 is 14. So I'm going to take that away from this 16 and that will give me 2, 2+208 is 210. Alright? Let's do the charge. So we'll have 8+82 equals 6+, 2 times 0 is 0, plus z, alright? So I'll subtract this 6 from the 8 and that gives me 2. 2+82 is 84 and that means that our x guy here, is nothing more than, we've got 210 on the top, 84 on the bottom. The 84 tells us what to call it because that's the atomic number. 84 happens to be polonium, so this is polonium 210 that comes out of this nuclear reaction. Alright. Let's go ahead to the next one.

The next one tells us that a neutron is going to come in and hit a uranium 235 nucleus and then it's going to speed off a cesium 135 nucleus, three neutrons and something else. Alright. this reaction is actually a very important reaction. It's called the induced fission. So the neutron comes in, hits this uranium nucleus, splits it in two and spits off a couple of more neutrons. alright? So these guys are products of the nuclear fission reaction and they're going to come out as a result of nuclear reactors or as a result of a fission bond. Alright. So let's go ahead and solve this problem.

Alright. Once again a neutron one zero, uranium is number 92, cesium is number 55, we've got one zero and again we're going get rid of this guy we're going to call him azx because we don't know what else to call him yet. Alright. So we've got one plus two thirty that's 236 equals right, 135+3+a, alright? And if you go through this you'll find that a got to be 98. Alright, join the bottoms we have 92=55+z and again if you go through that you'll find that z has to be 37. Alright? So that means that this guy is going to be 98, 37. Who's number 37? Consult the periodic table, it's rubidium. Alright. So that's the other decay product. This guy's extremely unstable. He's going to decay very quickly. Alright.

Now let's look at the last reaction. This is actually a very important reaction that fuels the sun. It's called fus- fusion. We've got hydrogen 2 and hydrogen 3. they come together fuse and form helium 4 and something else. Now this one's really easy. Hydrogen is 1, hydrogen is 1, helium is 2. Right? So if we looked along the top we got 2 and 3 that's 5. We only got 4 there, so this guy has to have a one. 1 and 1 is 2 we already got that. So that means this one is a zero. And who's one zero? that's my neutron. And so this is a fusion reaction that spits off a neutron and this nice stable alpha particle helium 4.

That's nuclear reactions.