we saw in the last video that each element comes in a number of different forms called isotopes each of which has the same number of protons but a different number of neutrons importantly though only one or two of an element's isotopes are stable while the rest of them are unstable and so it can undergo radioactive decay which is where they emit something so that they can change slightly and become more stable so when we say that a material is radioactive all we mean is that it consists of unstable isotopes that can decay in this video we're going to take a closer look at the four types of nuclear radiation namely alpha particles beta particles gamma rays and neutrons and we'll cover how ionizing and how penetrating each of them are let's start with alpha radiation alpha particles are made up of two protons and two neutrons which is exactly the same as the nucleus of a helium atom so we normally represent alpha particles with helium's nuclear symbol h e importantly though alpha particles don't have any electrons so they have an overall charge of two plus from those two positive protons because they are relatively large alpha particles are easily stopped by collisions with other molecules which means that they can't penetrate very far into other materials in fact they can only travel a few centimeters in the air and are absorbed by a single sheet of paper however their large size and their strong charge does make them very strongly ionizing which just means they can easily knock electrons off any atoms they collide with next up we have pizza particles which are just electrons so they have a charge of -1 and virtually no mass now the weird thing is that electrons aren't emitted from one of the atoms shells instead one of the atoms neutrons decays into a proton and an electron the proton stays in the nucleus but the electron is emitted out at high speed because pizza particles are pretty tiny they are moderately ionizing and they penetrate moderately far into materials for example it would take several meters of air or about five millimeters of aluminium to stop them now gamma rays aren't particles at all they're actually waves of electromagnetic radiation like lighters and they're often emitted after alpha or vita radiation as a way of the nucleus getting rid of a bit of extra energy as they don't have any mass or charge they tend to pass straight through materials rather than colliding with any of the atoms which makes them only weakly ionizing this means they can penetrate really far into materials before being stopped so you can travel long distances through air and it takes thick sheets of lead or multiple meters of concrete to stop them the last type of radiation we need to look at is the emission of a neutron and there really isn't much to know if a nucleus contains too many neutrons which is making it unstable it can just throw out a neutron to increase the stability so to quickly recap alpha particles are made up of two protons and two neutrons and will be stopped by a single sheet of paper beta particles are just an electron and is stopped by a thin sheet of aluminium and gamma rays are electromagnetic waves which require a thick piece of lead to stop them that's everything for this video though so if you found it useful then you give us a like and subscribe and i'll see you next time