 Today, I want to talk about radioactivity. I'm sure you already have heard about radioactivity, but what is it actually? Radioactivity describes the process in which some isotopes which tend to be unstable become more stable by emitting some type of radiation. Why are these isotopes unstable to begin with? It seems that if the ratio between protons and neutrons in a nucleus exceeds certain values, that nucleus is not stable. Now that process of radioactivity can be described with a nuclear equation. In a nuclear equation, we have on the left side the initial nucleus and then as we have a chemical equation, we show the direction in which it goes. And then on the right side, we have the resulting nucleus and the radiation. So right from the start, you should be seeing something amazing or surprising. And when we talk about chemical equations, never ever did the elements change. Remember when you did stoichiometry, when you balanced your equations, no matter how much hydrogen you had on the left, that's the amount of hydrogen you got on the right. Now in this nuclear equation, the nucleus can change. So you don't have to have the same elements on the left as you have on the right. What stays the same is that the charge on both sides, the total charge should remain the same and the total mass number should remain the same, not the total mass. Why not the total mass? Some of the mass is going to be transformed according to probably the most famous physics formula that's out there. Some of the mass gets transformed into energy according to E equals mc squared. So the mass is not conserved, the elements are not conserved. However, the mass numbers are conserved as is the total charge on both sides of the equation. There are several types of radioactivity. Three of the more famous ones are alpha, eta and gamma radiation. Now what happens in alpha radiation? In alpha radiation, the radiation is made of a charged helium for isotope. So helium with a mass number of four and helium has a charge of two or two protons in there. So in alpha radiation, it's helium particles that are flying at you. So how did that happen? The unstable nucleus simply split and some helium is flying off. So if we give an example, for example, we could use polonium 11, polonium 211 and that should have 84 as the proton number. Now if we look at the fact that the total amount of mass number should be conserved, we can figure out what is the new nucleus that will appear once our polonium did undergo alpha decay. We call it this type of radiation decay, which is another word for it. So alpha decay from polonium, we have four on the left, we have 211 on the right. So 211 minus four must be the one that's going to end up here. So we have 207. And now for the number of protons, I had 84 protons here. I have two protons here. So I have a total charge of 84 on the left. To get 84 on the right, I need to be having 82 protons. And if I go look this up in the periodic table, lead will be my element with 82 protons. It doesn't have to be polonium, it doesn't have to be lead. It can be all kind of different things. The important thing is here the number goes down by minus four because we are forming helium four. And the number down here, the number of protons goes down by minus two. Now the next type of radiation is a beta radiation. Now if you thought alpha radiation is crazy, we're going to change the elements, look what happens in beta radiation. So in beta radiation, the thing that is flying at you is an electron right with a small e. The mass is neglectable. So its mass number is zero. And it doesn't have a proton. And actually it is negatively charged with negative charge of one. So we're going to write the minus one down here. And what also flies off is a neutrino. So the flash. For the moment, let's just ignore the neutrino. We can talk about that in more advanced situations. And let's say the neutrino has no charge and has no significant mass. So let's give an example. Hydrogen three undergoing beta decay. So we have a mass number of three and one proton under coserative beta decay. Now how did the electron come up here? So here's where it gets really fantastic if you think about it. So we had an unfavorable neutron to proton ratio in the initial isotope nucleus. So now what's happening is that one of the neutrons, think about that. One of the neutrons simply decides I'm going to become a proton. So the neutron transforms into the proton. So the neutron transforms into the proton. That means of the remaining new nucleus, I will have the same mass number three. But as a neutron transformed into a proton, we will have not two protons. As a neutron transformed into a proton, we have two protons. So we have one proton more than before. And of course if you look this up, this is helium itself. Now we say the total mass number is conserved. Yes, it is. And we say the total charge is deserved. So plus charge of one, then here we have plus charge of two. But then the electron is flying off. So what's actually happening is that neutron is not just becoming a proton. It becomes a proton and an electron and a neutrino. The last of the three types of charges kind of is almost boring. It's the gamma radiation that what it emits is something similar to light, which we could say is like a photon or depending on if you look at it as a wave an electromagnetic wave. The particle's name is a gamma. So a gamma particle. So similar to light, a photon or as an electromagnetic wave. And nothing else is actually really happening. So just your initial unstable nucleus emits some energy in form of a gamma particle to become more stable. So as an example, we have cobalt 60. Often we're going to mark an unstable nucleus with a little asterisk because you're going to see nothing really happens. The cobalt 60 remains cobalt 60. Just it is more stable. So the numbers here, if you go for gamma radiation, remain the same. Now after having looked at these three types of radiation or decay, let's look what they do to the human body. You're probably all aware of that radioactivity is bad for humans or any form of life. So why is that? So well, in the case of alpha radiation, which is out of the three, the one that causes actually the most damage to you, there are charged, there's a charge of two helium particles flying at you at a very, very high speed. So they will think of it like little bullets that hit you. They can really cause a lot of damage. The advantage, however, or the good part of alpha radiation, however, is as these particles are so big, should be enough to protect me from alpha radiation. If I'm not protected, alpha radiation will cause a lot of damage, mostly if it comes from the outside on the skin, because it cannot really penetrate that deep. But I can block it quite simply. Beta radiation causes much less damage. You see the particle is much smaller. It's basically an electron flying at you at very high speed. And it can be blocked, but you need more than a paper. You need a thick coat. You need some kind of thicker material. Very thick clothing can do the trick to protect you from beta radiation. Now gamma radiation, the last of those three, also doesn't cause so much damage. The particle is very small and goes basically through you without much interaction. So the damage is very small. But the problem is to block it, it's very complicated. You will need a very thick wall of concrete, or you need a very thick piece of lead to block your gamma radiation. So to sum it up, what is radioactivity? Radioactivity is when an unstable nucleus undergoes some form of decay and emits a radiation. Three common types of radiation is alpha radiation made of helium for particles, beta rations, radiation made of electrons, and gamma radiation made of an electromagnetic wave, which could also be looked at as photons. There are other types of radiations, but for the moment we just talk about those three. In alpha, you can find the new element that's forming by subtracting 4 to the mass number, subtracting 2 from the proton number, and then you go into periodic table and you look up, okay, which element has 82 protons for beta radiation, where a neutron transforms into a proton. You get the proton more, and an electron. So we get an electron appearing here, and a neutrino, and your mass number here on the top remains the same. So you just add one proton number, go into the periodic table, figure out which element has that proton number. And then for the last one, nothing happens to the mass number, nothing happens to the proton number, just the nucleus becomes more stable by emitting some radiation.