 Hi, I'm Zor. Welcome to Unisor Education. Today we will talk about certain nuclear transformations which are called alpha or beta or gamma decay. Now this lecture is part of the course called Physics for Teens presented on website Unisor.com. I do suggest you to watch this lecture and any other lectures of this course from the website. Because there are many reasons actually. First of all the website contains a prerequisite course, which is called Math for Teens. Secondly, every video lecture is supplemented on the website with a textual description which basically is like a textbook. I mean piece of the textbook, which is dedicated exactly to whatever I'm talking about during the lecture time. Then there are certain problems solved. There are exams if you want to take them and you can take as many as you want as many times as you want the same exam until you're perfect. Now the site is completely free. There are no advertisements. So it's just pure knowledge. I do suggest you to basically take a look at the website and take the whole course basically and obviously all the lectures are interrelated. I'm using something which I have presented before in subsequent lectures. So there is definitely certain sequence, logical sequence, all these lectures are put together. Okay, now back to business. We are talking about certain nuclear transformations. Now what transformations actually mean? It means that there was something in the nucleus like certain number of protons and neutrons and then there is something else for whatever reason. Now in the beginning of 20th century, it's like about 1900 approximately, physicists such as Rutherford and another guy, the French guy, Villard were experimenting with radioactive material like uranium or a radium or something and they have noticed that from this radioactive, what's the radioactivity actually mean from whatever they have observed? Well, it means that something is emitted. Now that something was actually experimented with and they have discovered that certain particles actually which were emitted are positively charged. Certain particles are negatively charged and then there are certain particles which are neutral to electricity. And they have decided to call them at the time alpha, beta and gamma rays. Now what decay was probably introduced later, I'm not sure, but basically it means again the transformation, something like something is going out from the nucleus and that's why the word decay was actually used. So alpha, beta or gamma particles, alpha, beta, gamma rays, alpha, beta, gamma decay as a process, all these are terms which later on were researched and through the experiments they have discovered that alpha, beta and gamma particles or rays, if you wish, they are something which they have discovered from other experiments as well. So let's start with alpha rays. So alpha rays experimentally discovered as to be a combination of two protons plus two neutrons as a particle, which is basically the same as a nucleus of helium. So there is a helium. It has four particles inside the nucleus. Two of them are protons and two of them are neutrons, exactly what it is. So sometimes alpha particles are cold helium nucleuses, nuclei. Okay, so now they are positive because there are two protons, protons are positive, neutrons are negative. Okay, so whenever something like a big chunk of nucleus goes away, well, it's what remains is a completely different nucleus. So let's just write down what happens in one particular case for example. Let's say you have a plutonium. That's a radioactive material. It has 94 protons and 239 is the total atomic mass. So total neutrons and protons is 239. Now we take out two protons and two neutrons. So we have remaining 92 protons and 235 is the total number of protons and neutrons minus 4, which is uranium. So it looks like plus alpha particle, which is helium 24. So that's what happens when plutonium, radioactive plutonium emits one alpha particle. Now when it emits, it transforms into uranium. Now uranium by itself is also radioactive and it might actually undergo its own transformations by emitting alpha or beta or gamma particles, but that's beside the point. I just wanted to exemplify what is in this particular case alpha decay of plutonium into uranium and and alpha particle. Now why it happens? Well, I can't really say why it happens, but it happens and certain elements have their own probability of happening. So every element like plutonium or uranium, etc., every atom actually of this element has certain probability of decaying during a certain period of time and obviously the greater period of time, the greater probability of decaying is asymptotically, obviously, going to the probability of one. So it can be investigated probabilistically and there are certain calculations, not very complicated, but based on theory of probability, basically, which gives, again, based on this probability, probability of decaying during certain amount of time as a function of time, probability is a function of time. So based on this function, you can calculate what is an average so-called half-life. So what is half-life? Half-life is the average time required for any quantity of the element to decay half of it. So half of it will convert from whatever original element is into another element imaging alpha particles. Basically, after half-life, from a chunk of, let's say, one gram of plutonium, they will remain on average only half a gram of plutonium and the rest will be something else. So this is called half-life. Now different elements have different half-life. Now, something which has a very long period of half-life probably emits slower and obviously during any period of time the amount of alpha particles emitted will be really low. But there are some other elements which are much faster decaying. So here in the unit of time they emit more alpha particles, so the more of this element is transformed into another element based on alpha decay. For example, there is an element called polonium and let me check. It was 84 protons and the total atomic mass is 210. So protons plus neutrons are 210. Now it emits alpha particles converting into H2, two protons less and four particles less, atomic masses of A. And this is plumbum, lead, plus alpha particle. Now this element has half-life of 138 days. So approximately in the 138 days from a gram of polonium will remain only half and the rest will be lead. Now what about the alpha particles? Now these are relatively heavy particles. I mean it's two protons and two neutrons. These are the heaviest particles. So it doesn't really travel fast or far in the air. Molecules of air would stop it. Also even a sheet of paper will be an obstacle for an alpha particle. It will not penetrate the sheet of paper. It will not penetrate the skin. So if you have a source of alpha particle, alpha particles near you, it will not penetrate your body. So it's safe. However, if it's inside your body, it will definitely bombard with alpha particles tissue around that place and it will destroy it slowly. But again, considering 138 days is half-life, if you have consumed something, it will relatively fast, like in two three weeks. It will be already felt as a damage down to your body. And that's what happened with poisoning of Russian spy Alexander Litvinenko. He actually was somehow given polonium. He was consumed with tea or something, I don't remember. So it was inside his body and as it is inside the body, it starts basically destroying the tissue around it and he died in whatever amount of relatively short amount of time. And nothing can be done about it because you cannot really extract it. It's already inside the whole body and the blood stream. So that's about alpha particles. Now let's talk about beta particles. So beta particles are cold those particles which are emitted and have negative electric charge. By the way, how did they find out that something has positive, something has negative electric charge? Well, they just put some electricity around some electric charge and they saw on some screen maybe how the flow of these particles is deviated from the original straight line. So if they saw something like this, they saw that there is an electric charge, obviously. So if you have some positive electric charge near the flow of beta particles and it turns on some screen, you can probably detect these particles or a photoscreen or whatever. So now it appears to be that beta particles are electrons, light electrons, much lighter than alpha particles because electron is tiny relative to proton and neutron. I think it's about one two thousands of protons. So if you have four particles, so it's one eight thousands of alpha. So it's a very small and that's why it travels a little further. But still it's not really very damaging because it's very light actually and it doesn't have a lot of penetration ability. Something like aluminum foil would stop it. Skin will not, but still I don't think it's very dangerous. It probably will be completely slowed down. In any case, it's a not very dangerous radiation. Again, it's light and it can be stopped by aluminum foil. Now, but how come the electrons are basically going from the nucleus? There are no electrons in the nucleus. There are protons and neutrons, but not electrons. So what is the beta decay in this case? How can it happen? Can electrons which are surrounding atoms just be flowing away? Well, sometimes it does happen, but you need some external force for this, not by itself. If you have a completely neutral atom actually of the element, electrons would not really from whatever electrons are surrounding. Electrons will not actually fly away because the protons inside the nucleus hold them. I mean, that's exactly how atom is made. So what actually is happening is the following. One of the neutrons inside the nucleus is transformed into positive proton and negative electron. So that's what happened. It does not change the total atomic mass because the total number of protons plus neutrons is exactly the same, but it releases one electron and it goes away basically. So, for example, here's what happens. For example, you have a carbon, but not a regular carbon, which has six protons and twelve is the total number of protons and neutrons. Let's say it has 14, which is unstable isotope of carbon. Now, in this particular case, when you have this beta decay, it's converted into something which has seven protons now. And the same 14 atomic mass. And that would be nitrogen and electron would be emitted. So that's what happens. Okay, so this is the beta decay. So beta decay is conversion of a neutron into a proton and electron. And electron can be emitted from the nucleus. Now, this is not really a complete reaction. There are some other components here. Now, in this particular case, the component is called antinutrina. It's a tiny particle which doesn't have a mass, doesn't have an electric charge. It's actually very hard to detect. But in any case, I don't want to go into the smaller details of this, because there are some energy released, etc. So we're not talking about these. These are probably much more specialized things. But the most important thing is this conversion. Neutron can spontaneously change into proton and electron. And electron gets released as beta decay. Now, the third one is gamma. Gamma decay, gamma rays. Now, these are rays which did not really have any electric charge. And as a result of experiments, what they have discovered, the gamma rays are just oscillations of electromagnetic field. This is electromagnetic oscillations of a very, very high frequency. So if you don't see them, it's beyond the visible spectrum. It's much more frequently oscillating. So the wavelengths correspondingly much smaller than the wavelengths of visible light. But because it's a very high frequency, now, you remember about duality between the particles and waves as far as electromagnetic oscillations are concerned. So whenever we are dealing with the higher frequency of oscillations of electromagnetic field, the more properties of the particles it has. So basically, it acts like a flow of lumps of energy, which is basically something which we called photons. So alpha rays are flows of photons. So during whatever the reaction nucleus of some atoms undergo, the result of this transformation is a meeting of gamma radiation. We have a lot of gamma radiation coming from space. And they are damaging, actually, because the higher frequency means that they are really having a very, their ability to penetrate is very, very high. Now, I was talking about penetration of alpha particles, and you can just stop it with a sheet of paper. You can stop beta particles, electrons, with aluminum foil, let's say. Now the gamma rays to be stopped, they need a good, thick layer of lead. And lead, you know, is a very heavy metal. It's very difficult to penetrate it with a particle or oscillations of electromagnetic field. So that's why in reactors, for example, the power plants, nuclear power plants, they have a lot of protection, including a lot of lead they're using in many different purposes for many different reasons. So that is about this gamma rays. Now, they are used, actually, for some useful purpose, not only for protection against something. They can be used for, for example, oil exploration because they have this penetration characteristic. They can penetrate the earth. And based on certain, I'm not really sure about what kind of devices, but something which can be sense about whatever the way how they go through the earth. And based on that, they make some decisions about whether there is oil or gas or not. Cancer treatment also might be radiation. Cancer treatment also involves gamma rays or diagnostics of something like cancer. So in medicine, it's used. But obviously, these are supposed to be relatively big. And well, obviously, whatever whoever is using should know really what he is doing. Based on experiments, etc., people come up with certain dosages which can be used for medical purposes or exploration purposes or something like this. But again, the gamma rays are dangerous and must be properly handled with. Alpha is not a deal, beta probably also, but gamma rays are very dangerous. And obviously, they can destroy the human body if the body is exposed. Many physicists of early 20th century who were dealing with radioactive materials, they did not really know about the gamma rays. And they did not really protect themselves properly. And some of them really died of radiation. I think Marie Curie, the famous physicist, she was working in France, but he was originally from Poland. I think she died of something like lymphoma or something like this. I'm not really sure, but definitely related to radiation because she was basically handling uranium with bare hands. That's definitely, she didn't know about how dangerous it might be. Anyway, my lecture today was about alpha, beta and gamma rays, decays and particles. And why I have decided to dedicate the whole lecture to this because it's very important for what I will be talking about next. And that will be something like splitting the atom, releasing energy, atomic bomb. So that will be next lecture. So thanks very much. I do suggest you to read notes for this lecture. It's on Unisor.com. Other than that, good luck.