MRI basics: part 1: Nuclear spin

And welcome to high school [physics] explained today I'd like to talk about Nuclear Spin and net Spin Now if you were to go [onto] [Youtube] or various websites and look up the concept of spin Then you will discover that there are lots of explanations that are quite good but if you don't have a basic understanding of quantum mechanics You'll probably struggle to understand it and so what I would like to do is talk about Spin from a high school perspective So I'm not going to go too much into quantum mechanics, but if you want to understand spin Especially if you're doing medical physics and want to understand spin in the context of Mris and hopefully this video will help you So let's start first of all you have two protons and a proton has a positive charge Now we're going to see that a proton has a number of properties and one of those properties is a concept called Spin now Spin is actually a historical term we know that it actually doesn't Literally spin, but if you consider that it is a positive charge Then if it's spinning it may Spin in that direction now if you're familiar with electromagnetism, then you know that a spinning charge will develop a Magnetic Field and that magnetic Field can be determined using a [right-hand] [grouper] also as a result of this spin it produces a magnetic [field] in such a way that it is actually Pointing upwards so in other words this end here will be the north pole this end over the south pole and as a result it produces a magnetic field that goes around like so What we have is this mediconnect field and the arrow represents the direction of the Magnetic field through the proton and so? We call this a magnetic moment Now what can also happen of course is I have a proton here You can also have a spin But in this case it could be spinning in the opposite direction and as a result similarly - [here] it will produce a magnetic moment that is in the opposite direction, so [here] I have a proton that has a magnetic moment that is pointing up, and we call it a spin up and over here we have a proton that has a magnetic moment that it's down and we call it a spin down and suffice to say in quantum mechanics we give this a value and so the spin up is given a value of 1/2 if it is spin up and Negative 1/2 if it's a spin down we don't worry about the numbers that goes into quantum mechanics And I want to spare you from that what about two neutrons now neutrons as you know have no charge but again And this shows you how spin actually isn't a correct term the fact is that that neutrons have Spin and so We can have a neutron that has a spin up and a neutron that has a spin down Now again as I said this cannot be explained by imagining this as a charge but nonetheless Protons and neutrons have what we call a property called spin And it can be two types of Spin Spin up or spin down Similarly the spin up has a value of 1/2 and the spin down as a value of a negative 1/2 and again I'm not going to go into detail as to why it is 1/2 or negative 1/2 and you can explore it yourself So what then will happen if we combine protons and neutrons together in atoms? So this is nuclear Spin, but what about if we combine those protons and neutrons? Now to help you understand this I want to briefly touch on the quantum mechanics only enough to help us understand what's going [on] here as you know that in terms of electrons, we know electrons exist in specific orbits or energy levels well the same thing is true in the Nucleus protons and neutrons exist in different energy levels to Represent this I've got this little staircase, so the base here is energy one energy level two three and four and five [now] Why is this important well if we start thinking about protons and neutrons. They are in the Nucleus they exist only in specific energy levels and only a certain number can fit in each energy level So let's take an example. Let's say we have one proton. So now we have hydrogen hydrogen has a nucleus of only one proton so it's nuclear spin actually ends up being its net Spin because net Spin is a Total sum total of its spin [now] what happens if I add another? Proton to it now if I add another proton to it. You'll notice that the arrow is pointing down and let me explain. Why the Pauli Exclusion principle says no to set of fermions Can have the same set [of] quantum numbers now let me borrow that down real into simple You can't have two fundamental particles having exactly [the] [same] properties Now I'm not going to get into the details Why that is so but needless to say I have two protons that have the same charge? [I] have two protons that have this sitting on the same energy level Therefore I cannot have them spinning in the same way so in order for them to coexist on to this energy level one has to have [a] spin up of 1/2 one has to have a spin down a value negative 1/2, so Although they have lots of similar properties and least in terms of spin They're in the opposite direction, but what happens here is is that their spins cancels out? although we have a nuclear spin here of 1/2 and a negative 1/2 over here that leads us into a net spin of 0 If I add another proton to it, so let's say again. I now have my proton here and another proton here, [I] Want to add another proton well this one can't exist in this level it has to go to the next level because it can't have The same numbers so in other words if now I have three protons in my nucleus That would be example lithium. We're ignoring the neutrons [you] can see what happens is these two cancel out? We now have another proton here It is not the same set of quantum numbers because it's now on energy level two and so it's net Spin in this case is [1/2] Because I have these two cancel out and have 1/2 left over, but let's consider neutrons now for a moment so let's look at an example of Deuterium now deuterium is Hydrogen with an extra neutron so here's my hydrogen one single proton, and I need a neutron over here And you'll notice that they [have] the same direction in terms of Spin, but that's allowed because [there] are different subatomic particles So they're allowed to coexist together as a result We have now a net spin of 1/2 for the proton and a half for the neutron and that leads us to a concept of net Spin of [1] So [deuteriums] nucleus has a net spin of 1 because the proton the neutron would come together So let's say I want to build up Helium so helium has two protons, so here we go I have a proton number 1 and I have to have a proton number 2 that spins in the opposite Direction I now can add a neutron and a neutron of course can be in the same energy level Because it is a different fundamental particle But now if I add a second and [neutron] it has to spin down because it's appearing up with the other [Neutron] and so now I have two protons two neutrons and in this case of [course] I Have helium and helium of course has the mass number of four and an atomic number of two But if you notice if you sum those spins up the net Spin ends up equaling Zero because these two cancel up to cancel out giving us a zero So you can see as we start to add? Protons and Neutrons together we will get different spin values Depending on what cancels out and what does not cancel out, so let's go a little bit more complex So let's have a look at another element and let's start with looking at Carbon 13 as an example so carbon 13 has 13 Nucleons and six of those are protons and as you can think of that that means there are seven neutrons to add So let's add our protons and neutrons to the ladder so let's start with the protons first So here's proton number one and here's proton number two you notice that they come in pairs spin up and spin down and we keep the process going now, we're going on to the next [energy] [level] and we keep going like so and Now I have my number of protons correct We now add the neutrons and again the same rules apply once we start adding neutrons to our nucleus but they always go up in pairs because they then jump up different energy levels, and I'm almost finished here and Finally we have a [situation] like this, so I have six protons and seven neutrons What is it spin? Well if you look carefully, you can clearly see that Every pair here cancels out so as a result the net Spin is Totally determined by this last remaining neutron and so the net spin Is equal to [1/2]? We've dealt with an example of a spin of 0 and we've dealt an example with a spin of a half and we've dealt example of a spin of a whole number so there are some basic rules to help you know very quickly what net Spin exists and The rules are like this if a is even and zed is odd then the spin is a whole number So think about it z is odd so therefore You're automatically going to have a half a spin left over a is even that means Automatically the number of neutrons is also. Odd which means you're going to have 1/2 left over those two halves or automatically mean you get a spin of One so here we go these two cancel out these add up We get a whole number [if] a is even and zed is even then Clearly we've got an even number of protons an even number of neutrons and as a result the net Spin is zero if a is odd Then basically you can get two combinations you either have an even number of protons and an oDd number of Neutrons or an even number of Neutrons and an odd number of protons What's left of course is that you get a spin of 1/2 in fact it is multiples of 1/2 again? That is quantum mechanics when I'm going to go into the reasons Why it can be 3 over 2 and 5 over 2 but needless to say? You always get multiples [over] [half] if the mass number is odd so that summarizes the concept of Nuclear Spin and Net Spin, and that should give you enough scope to help you with understanding the concept of Spin in the context of Mri [I] hope that's helped you and thanks for watching [bye] [for] now. I Hope you found that video useful and remember like share and subscribe Oh, and if you have a comment, or a [question] or you're like a concept for me to explain [to] you Please drop a comment down below I'm paul from High school physics explained. Bye for now

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Keywords: nuclear spin, nuclear spin simplified, proton spin, neutron spin, nucleon spin, atomic spin, mri basics, net spin, mri physics, magnetic resonance imaging, MRI, physics help, medical physics, help, physics course, magnetic moment, spin, physics simplified, high school, physics high school, how an mri work, medical science, medical scanning, mri high school physics explained, परमाणु स्पिन सरल, परमाणु स्पिन

Id: pcyfvwnHddA

Length: 12min 11sec (731 seconds)

Published: Sat Sep 17 2016