Gamma decay | Physics | Khan Academy

if there's a tumor deep inside the brain how do you get rid of it without damaging the healthy tissues one way is using a procedure called gamma knife radio surgery what's funny about this is is neither uses a knife nor is it a surgery instead it uses radioactive gamma Decay but what exactly is a gamma Decay and how does it destroy the tumor without destroying the healthy tissues and why would we use gamma dkay and not alpha or beta dkay well let's find out let's start with something that we've already seen before if you have

unstable nuclei then they will undergo an alpha or a beta Decay and become more stable now we've talked a lot about these in our previous videos on Alpha and beta DK so if you want more info feel free to check that out but what's important over here is that the doter nuclei sometimes can be excited what does that mean well we've already heard of this before right when it comes to atoms and electrons we probably already know that if you take an atom any atom you want with electrons around it then the electrons can occupy

different energy levels usually electrons love to occupy the lowest energy level which we call the ground state but if you could somehow provide enough energy to it then you could make that electron jump to a higher energy level this is what we call excited state excited state basically means when the electron is in some higher energy level now electrons don't like to stay in that state for a long time and so they will quickly jump back to the ground state and when they do that the difference in the energy is released as a photon of

light and this is what happens in say LEDs which you find in a lot of flashlights these days when you pass current through an LED the electrons inside of it get excited to a high energy level and then when they de exite they release a photon of energy and that's how they glow and guess what something very similar is happening with over here turns out just like with the case of electrons just like with the electrons the protons and neutrons also have different energy levels inside the nucleus and when the daughter nucleus is formed after

an alpha or a beta Decay sometimes the protons and the neutrons can be in the higher energy levels that's what we mean that when we say the nucleus is excited so what's going to happen next well just like with the electrons the protons and neutrons will jump to the ground state and when they do that they will release a photon of light and this Photon of light is what we call gamma radiation and this DC is what we call a gamma DK so gamma radiation is just light electromagnetic waves wait a second this means radioactive

DK gives off light is this why radioactive stuff is usually glowing a lot in greenish color it makes all perfect sense right oh no these photos and the ones that you see in cartoons they are highly misleading radioactive stuff doesn't glow like this but why it's giving off light right well to understand that we need to understand we need to look at the electromagnetic spectrum electromagnetic waves because they are a wave can have different kinds of wavelengths if you have long wavelengths we usually call them radio waves or microwaves and short water wavelengths are where

we go towards ultraviolet light and x-rays and what you can immediately see over here is that our eyes are only sensitive to a certain range of wavelength so the question now would be what decides the wavelength now well the wavelength depends upon the energies of the photon you may recall that light has both the wave nature and the particle nature photons are the particles of light now it turns out that if you have low energy photons you will have longer wavelength there's an inverse relationship between them and if you have higher energy photons you will

have shorter wavelength higher the energy shorter the wavelength now if you consider the photons that you get from the electron transitions in the LEDs then their energies lies in this region that's why we can see it there will also be some photons that will lie in the infrared and the ultraviolet region which we can't see but a lot of them will lie in the visible region and so the question now would be what would be the energy of the gamma photons Well turns out gamma radiation these photons have energies much much higher than the energies

that we get over here and it kind of makes sense because the forces that we're dealing with over here are strong nuclear forces which are much much stronger than the electromagnetic forces that that we're dealing with so when a Proton or Neutron and you know in an excited nucleus jumps from a higher energy to a lower energy the photon that they release will have a much higher higher energy compared to the photons that are released over here so the energy of the gamma radiation is definitely higher than the visible light higher than even the x-rays

in fact it turns out to be the highest of all the electromagnetic waves gamma radiation has the highest energy photons so clearly it is invisible to our eyes so even though it releases gamma radiation which is electromagnetic waves which is technically light we can't see it and so clearly radioactive dks will not make the stuff glow there are materials that will glow due to different reasons but whenever they do you can just think that you know the glow whatever you can see is lying in the visible region and therefore the photons must have come from

the electron transitions not from the nucleus so just to get rid of that misconception we'll paint these photons some other color let's say pink okay how about we take an example example so if you take for example Cobalt 60 it's a radioactive isotope it turns into nickel 60 via a beta Decay now again don't worry too much about the details of the beta Decay we've covered that in the previous video but what's important over here is that this nickel the do of nucleus that you'll get will be in the excited state and the way we

show that is we just draw an asteris over here and so that nickel will undergo a gamma Decay and in doing so the nickel would have the nickel nucleus would have de exited and so immediately from this can you see some differences between gamma DK and Alpha and beta DK well first of all gamma DK will usually happen along with Alpha and beta DK it will rarely happen all by itself that kind of makes sense right because you know once you have had Alpha and beta DK then the the do nuclei would be in the

excited state and then when it de exites that's when you get the gamma Photon so it kind of makes sense you would expect gamma DK to happen along with Alpha and beta but not all by itself I mean it can happen but those are rare incidences the second big difference you can see is that in an alpha or a beta Decay the Isotopes change because the number of protons will change but in a gamma DK look that doesn't happen the mass number and the proton number stays put and again that kind of makes sense because

in a gamma DK there is nothing been spit out there are no protons and neutrons converting into each other like what happens over here basically protons and neutrons are just jumping from higher energy level to the lower energy level so since the number of protons and neutrons everything stays exactly the same the nucleus also stays exactly the same and that's why just to denote there are no changes in the proton or the neutron number we will put a zero here and a zero here as well and the last comparison we want to make is its

penetrating power again we've seen before that Alpha and beta radiations they have Alpha radiations for example they have the least penetrating power they can be stopped by just paper beta because they're slightly smaller they can pass through paper but you you need something like aluminium or some plastic to stop it what about gamma radiation well gamma radiation has the most penetrating power and again we can make sense of this if you go back to electromagnetic spectrum we know that the visible light for example cannot penetrate your skin but what about x-rays they have higher energies

and now they can penetrate your skin but they get bounced off by your bones that's why x-rays are used for Imaging your bones so higher the energy you can see its penetrating power increases gamma rays they have even more energy so they can penetrate even more so compared to all three gamma radiation has the highest penetration power so if you want to stop gamma radiation you better have few inches of few sheets of lead for example that's why you know if you're dealing with radioactive stuff you you want to contain it properly with a lot

of shielding usually we use lead thick lead walls to Shield it okay what about its ionizing power well all three radiations are ionizing radiation this means that they can knock off electrons from the atoms which means they can destroy tissues and cells and all of that but of the three gamma has the least ionizing power well again kind of makes sense because Alpha radiation has plus two charge so it's very easy for it to pull off electrons beta has just one positive or negative charge um so it has slightly lower and Gamma well they are

neutral they're photons they are neutral they don't carry any charge and so they will have the least ionizing ionizing power but they do ionize all three are ionizing ionizing radiation all three can cause damage to your tissue so all three can be dangerous all right now we ready to see how gamma knife radio surgery works we use Cobalt radio isotope to produce gamma radiations but what does that do well let's go back to it okay I'm going to use my Cobalt 60 to produce a narrow beam of gamma race again sorry for using the green

color uh remember it is supposed to be invisible okay but anyways um what's going to happen well because it has a high penetrating power it just goes straight through it is an ionizing radiation but if I keep the intensity low enough that means less number of photons over here then you know it's not going to cause a lot of damage to anything it's not going to cause any damage let's say which is good because we don't want the healthy tissues to be damaged but it's also bad news because it doesn't do anything to our tumor

but what if I use a second beam that intersects right at the tumor now the same thing is going to happen except we now have more photons on the tumor which means the chances of ionization increases this means more chances of damaging the tumor you see where we're going with this let's add more beams let's add 100 of them now that tumor is going to have a hard time it's going to get destroyed so you see how awesome this is individually the beams have low low enough intensity just that as it penetrates straight through it

doesn't ionize much but because there's so much concentration at that tumor at that specific location we have now a method to destroy stuff deep inside our brain without touching the healthy tissues this is how gamma knife radio surgery works and you can see why we're choosing gamma radiations and not alpha or beta because gamma has the most penetrating power if you had used alpha or beta they would probably get stuck somewhere in between they also have higher ionizing power that means more damage caused to the tissues so gamma radiation is the best choice I find

this absolutely incredible