If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content

# Writing nuclear equations for alpha, beta, and gamma decay

## Video transcript

let's look at three types of radioactive decay and we'll start with alpha decay so in alpha decay an alpha particle is ejected from an unstable nucleus and so here's our unstable nucleus so uranium 238 an alpha particle has the same composition as a helium nucleus so we saw the helium nucleus in the previous video right there are two protons in the helium nucleus and two neutrons so I go ahead and draw on my two neutrons here since there are two protons the charge of an alpha particle is two plus so for representing an alpha particle in our nuclear equation since an alpha particle has the same composition as a helium nucleus we put an H II in here alright and it has two positive charges so we put a two down here and then a total of four nucleons so we put a 4 here trying to figure out the other product from our nuclear equation I know nucleons are conserved right so if I have 238 nucleons on the Left I need 238 nucleons in the right well I have 4 from my alpha particle so I need 234 more so 234 plus 4 gives me a total of 238 on the right and so therefore nucleons are conserved here in terms of charge I know charge is also conserved on the left I know I have 92 protons so 92 positive charges on the Left I need 92 positive charges on the right we already have 2 positive charges from our alpha particle and so we need 90 more so we need 90 positive charges and so we need an atomic number here of 90 so the identity of the other product just look at up here at table find atomic number of 90 and you'll see that's thorium here so thorium 234 is our other product all right so we think about what's happening visually all right we're starting off with a uranium nucleus right which is unstable it's going to eject an alpha particle so an alpha particle is ejected from this nucleus alright so we're losing this alpha particle and what's left behind is this thorium nucleus so this is just a visual red presentation of what's going on here in our nuclear equation all right let's do beta decay so in beta decay an electron is ejected from the nucleus and we saw in the previous video that you represent an electron since as a negative one charge and put a negative one down here right it's not a proton nor is it a neutron so we put a zero here so here's our electron and an electron ejected from the nucleus is called a beta particle and so we could put a beta here alright and it's an electron so negative one charge and then a zero here so if a beta particle is ejected from the nucleus of a thorium-234 so we're starting with thorium-234 this nucleus ejects a beta particle so we go ahead and put a beta particle in here so zero and negative one what else is produced here what else do we make well once again the number of nucleons is conserved so I have 234 nucleons on the left I need 234 on the right I have a zero here so I need 234 nucleons charge is also conserved so I have 90 positive charges on the left I have 90 protons on the right I have a negative charge here alright so I have a negative 1 charge and so I must need 91 positive charges because 91 positive charges and one negative charge gives me 90 positive charges on the right and so I need an atomic number of 91 and so if you if you look at the periodic table right and you find the atomic number of 91 you'll see that this is protactinium so we're going to make protactinium here so P a alright so what is happening in beta decay let's look at it a little bit more detail all right so we already talked about number of protons right so we have 90 protons on the left how many neutrons do we have well 234 minus 19 right 234 minus 90 gives us the number of neutrons that's 144 neutrons on the right we have we have 91 protons how many neutrons do we have will that be - 34 - 91 so 234 - 91 gives us a hundred and forty-three and neutrons so we went from a hundred and forty four neutrons on the left to 143 neutrons on the right and we went from 90 protons in the left to 91 protons on the right so we lost a neutron and we gained a proton so you could think about the neutron turning into a proton this is a kind of an oversimplified way of thinking about it but let's go ahead and let's go ahead and write that down here so a neutron turning into a proton so a neutron has no charge so we put a zero here so and and it's a neutron is nucleon so we put a one right here all right so a neutron is turning into a proton so let's go ahead and write our proton your proton has a plus one charge all right and it's a nucleon so we put a 1 here so when we think about what else is made right we know that nucleons are conserved so we have one nucleon the left one nucleon on the right and so therefore all right we would have a zero here in terms of charge if we have zero charge on the Left plus one on the right we need negative one right here and so this of course represents the electron so this is the electron that's ejected from the nucleus this is our beta particle and also actually and something else is produced you're also going to make an anti neutrino and that's this really not part of this video so we'll just ignore it for now so a neutron has turned into a proton alright and we're also getting a beta particle ejected from the nucleus so when this conversion this process is actually governed by the weak force the weak interaction so there's a lot of stuff going on in a nucleus which we just won't get into in this video all right so the important thing is to be able to look at a nuclear equation recognize it as beta decay and be able to write everything in your nuclear equation all right let's do one more type of decay this is gamma decay so gamma rays are given off and a gamma ray has no charge and mass is pretty much just energy to think about it so these are these are pretty easy decay problems all right let's start with technetium-99m and the em right here stands for meta stable which means a nucleus in its excited state so nucleus in its excited state so it has more energy all right so it's going to give off a gamma ray so let's go ahead and draw our gamma ray here alright so 0 & 0 so since we're dealing with zeros all right so these zeros aren't going to affect our numbers so if we start with nucleon sort we have 99 nucleons on the left alright we're going to have 99 nucleons on the right and in terms of charges right we have 43 positive charges on the left lead 43 positive charges on the right and since the atomic number isn't changing all right it's 43 on the left it's 43 on the right we're dealing with technetium here it's still technetium it's just in the ground stage all right so it's no longer in the excited States in the ground state so it's given off energy in the form of gamma rays and this in this example here and so technetium-99m is actually used in in several medical imaging and diagnostic procedures because we have ways of measuring the gamma radiation so this is very useful in medicine