atomic structure. But to be honest, it's really all about nuclei. So I like calling it nuclear physics. The idea of what atoms are like came about gradually. JJ Thompson discovered that atoms are made up of positive and negative charges. He came up with the plum pulling model of the atom. A positive charge with lots of little electrons dotted around it. It was Ernest Rutherford who found out that the positive part of the atom must be incredibly small. We now call this the nucleus. And the electrons must orbit relatively far away from it. Neils bore later discovered that electrons exist in shells or orbitals. Then James Chadwick discovered that the nucleus must also contain some neutral charges. He called them neutrons while the positive charges are called protons. Different types of atoms are represented by symbols which we also find in the periodic table. The bottom number is the atomic number. That's the number of protons in the nucleus. This is what determines what element you actually have. The top number is the mass number. This tells you how many protons and neutrons are in the nucleus. So that must mean that this carbon atom has six neutrons on top of its six protons to make 12. However, you can get a carbon atom with seven neutrons instead. So its mass is 13. These are isotopes, atoms of the same element, but different numbers of neutrons. The term radiation means any particle or wave that's emitted by something. The electromagnetic spectrum is all radiation, but they're all emitted by electrons. All apart from gamma radiation, that is. Gamma radiation is actually emitted by the nucleus of an atom. if it has excess energy it's getting rid of. Gamma rays are high energy EM waves. They can be dangerous as they can ionize atoms if absorbed by them, knocking electrons off. This can cause damage to the cells in your body and also cause cancer. But there are two other types of radiation nuclei can emit too. But these are actual particles and they're emitted when nuclei decay change. Isotopes with more neutrons are generally more unstable and likely to decay. Heavier nuclei like amarissium 241 decay by what we call alpha decay. To become more stable, the nucleus will emit a bundle of two protons and two neutrons. What we can just call an alpha particle. This is alpha radiation. This is what the nuclear decay equation would look like for this to show that the nucleus has decayed into two parts. The alpha particle which must have an atomic number of two and a mass of four and the daughter nucleus. That's just the nucleus left over, which of course is no longer going to be amorissium as it's lost protons to go from an atomic number of 95 to 93. Turns out that's Neptunium. But you'll never have to remember these. You just need to worry about the numbers. It's just maths. 95 goes to 93 + 2. And the mass is similar. 2 4 1 goes to 2 37 and 4. There is actually a nucleus that has the numbers 2 and 4. It's a helium nucleus. You do need to know that, but AQA also say that you should write H instead of an alpha symbol in a decay equation. I much prefer saying alpha, but you should get the mark either way. Lighter isotopes, lighter nuclei like carbon 14 decay by beta decay or beta decay instead. What happens is that a neutron in the nucleus turns into a proton and an electron. But the fastmoving electron that's ejected by the nucleus escapes and we now call this beta radiation. The mass of an electron is basically zero. So we put that on top. It has the opposite charge to a proton. So we say it has an atomic number of minus1. Now be careful here. Six goes to what? + minus one. No, it's not five. It's seven. 6 is equal to 7 + -1. Like we said, a neutron has turned into a proton. So the nucleus has gained a proton. It's gone from 6 to 7. The mass, however, is unchanged. So it's still 14. Once again, AQA like you to put E for an electron instead of a beta symbol, but they'll allow both. Alpha particles are massive and have a relatively large charge. So, as they travel, they knock loads of electrons off loads of atoms in their way. We say they have a high ionizing ability or high ionizing power. But as a result, they're stopped easily. They're absorbed by a few centimeters of air or just a piece of paper. If you have a Geiger Müller tube, a GM tube touching a source of alpha radiation like amarissium, it will detect the alpha radiation emitted. Move it a bit further away or stick a piece of paper between and the radiation counts per second will fall to zero or near zero. Anyway, I say near zero because there are background sources of radiation from the world around us. Radon gas comes out of concrete and rocks that's slightly radioactive. Cosmic rays from space are also background radiation. Man-made radiation like that from nuclear weapons contribute to it too. So, if you want an accurate radiation count over a minute from an alpha source, say, you should do a background count first, then take that number away from the count with the source. That will give you a corrected count. Alpha radiation can be useful, however. It's used in smoke detectors. Beta radiation is not as ionizing as alpha, but it has higher penetrating power. It's fairly good at both. It can pass through more air and a piece of paper easily, but it's absorbed by a few millm of aluminium. It can be used to detect thickness of thin materials like paper when made in a mill. Gamma radiation has low ionizing ability. So why is it so dangerous? Well, it's because it can actually get to you. Technically, there's nothing that can completely stop gamma radiation, but lead and concrete can reduce the intensity of it by absorbing some of it. Gamma has many uses actually. It can be used for radiotherapy or gamma knife surgery to kill cancer tumors in your brain for example. And it can be used to sterilize medical equipment as it kills any microbes on the scalpels etc. Radioactivity is the rate of decay of a source of alpha, beta or gamma. Now you know not really decay with gamma but the same idea. This rate can be measured with a GM tube like we said and we can calculate it by doing radiation count divided by time in seconds. This gives you the radioactivity sometimes just called activity in counts per second which is also called beckarel BQ for short. Over time, the number of unstable nuclei in a sample or source decreases as they're decaying into something else. So that means the activity decreases too. Halflife is what we call the time it takes for both of these to half. Actually, it also goes for mass too. The halflife of a radioactive isotope could be days, months, even millions of years long. If we draw a graph to show how activity changes over time, it might look something like this. How do we find the half-life? Well, we take the initial number, half it, then draw a line to the curve to see how long that took. What's interesting is that if we do the same again, it will take the same amount of time to half. It doesn't matter how much of the isotope you have or when you start timing, it will always take the same amount of time to half. You could be asked to calculate half-life. Let's say that we have a sample that started at 96 beckerel activity and it fell to 12 beckarel after 1 year, 12 months. The question you always have to ask is how many half- livives? You don't do 96 / 12, but instead count how many times you have to half it to get to the second number. One half life, 48 bearel. Two half lives, 24. Three half- livives, 12. It took three half- livives to decrease to 12 beckarel. So if 12 months is three half lives, that must mean that one half life is a third of that. 12 divided by 3, the half life is 4 months. Just some triple stuff to finish off. If you take a nucleus like uranium 235 and fire a neutron at it, that neutron will be absorbed and will make the nucleus more unstable. Instead of decaying by alpha or beta, it actually splits in half, producing two similar daughter nuclei. This is nuclear fision. What's weird though is that the total mass of the products of this fision is less than what we had to begin with. How's that possible? Well, it turns out that mass can turn into energy in these situations. Yes, we say that energy can't be created or destroyed, but at this level, we say that the reactants have mass energy to get around that. The energy produced is thermal or more accurately kinetic. As we talked about earlier, the clever thing is is that this fision also releases up to three more neutrons that can go off and cause more fision in other nuclei themselves and so on and more energy is released. We now have a chain reaction. Left unchecked, this can go out of control. That's what an atomic or nuclear bomb is. However, if you control this chain reaction in a nuclear reactor, you can produce a consistently safe and huge amount of energy that can be used to then produce electricity by heating steam to turn a turbine connected to a generator, etc. Fusion, however, is what happens in the sun to produce energy from mass. Two light nuclei like hydrogen fuse together into one heavier one, helium in this case, and energy is released, but only if they have a lot of kinetic energy to begin with. But hang on, how can both fision and fusion result in energy being released? Well, it's all to do with what nuclei you have to begin with. If you want to know more about this, do Alevel physics or watch my binding energy video. Scientists have been trying to make fusion reactors for decades, but they haven't managed to make one where they're able to harness enough energy from the radiation released from the process for it to be viable.