Hi. It's Paul Andersen and this is disciplinary core idea PS1C. It's on nuclear
processes. A lot of people are familiar with chemical reactions. Just like in the last
video we talked about the breaking of the bonds between atoms and the reforming of those
to create new molecules. But people are generally unfamiliar with nuclear processes. And that's
because the physics, in other words, the interactions at the subatomic level get real crazy. But
it's not any less important. The energy from the sun is produced through a nuclear process.
And so it's important that our students understand what's going on. First thing you should understand
is that there are four fundamental forces or interactions in the universe. And you're
probably only familiar with two. What's the first one? That's gravity. In other words
gravity is holding the earth in orbit. And it's holding me on the earth itself. What's
another force? That would be the electromagnetic force. In other words we found that electrons
and how they move in magnetism are tied together into this one electromagnetic force. How are
you familiar with that? Well if I were to push my hands together, they don't go through
each other because electromagnetic forces are opposing that. Or in other words why don't
I sink down through the earth? It's electromagnetic forces that are responsible for that. And
they're going to be much greater than gravity. How do we know that? Well gravity is pulling
you towards the center of the earth, but the electromagnetic forces are keeping you apart.
So what the next two? Those are the strong nuclear force and the weak nuclear force.
Let's start with the strong nuclear force. Where are we at? We're now looking at the
nucleus. And so all of the red balls right here are going to be protons. And the other
ones are going to be neutrons. And so these all have a positive charge. And then the blue
have no charge or a neutral charge. And so what you might think, if you know anything
about electromagnetism, is that if we have all of these positive charges right next to
each other, then all of the nuclei, except for hydrogen which just has one proton, should
be inherently unstable. In other words the protons should fly away from each other because
positive does not attract positive. In fact it repels it. And so what's holding that nucleus
together is the strong nuclear force. Why aren't we familiar with it? Because it only
operates on a really small distance. And so what is it doing? It's this attraction between
the neutrons and the protons that are holding the nucleus in place. And what you'll find
is we go down the periodic table. As we add more and more protons or in other words more
and more of these positive charges, we have to add more and more neutrons to just hold
that nucleus together. And so that's the strong nuclear force. What's the weak nuclear force?
It's even weirder than that. What's going on with the weak nuclear force? Well occasionally,
if we look at inside the protons and neutrons, they're made up of things called quarks. And
what can occur is that some of these, let's watch this one right here, can actually turn
from a proton into a neutron and it gives off something called an electron. And the
opposite can occur as we give off a positron. And this has to do with quarks and neutrinos
and you're head is probably spinning. It's not super important that you understand what's
going on, but that you know that it exists. And so what's going to occur with that is
we have radio active decay. And so the nuclei can breakdown or change form over time. And
so why is this important? Well let's start with the first reactions or these strong nuclear
forces. What can occur is that we can get fusion. Fusion occurs when we have smaller
nuclei fusing together to make larger nuclei So here we have two hydrogen nuclei that are
fusing together to make a helium nuclei. What does that create? It creates a huge amount
of energy. So now we're dealing with E=mc2. Where we can decrease the amount of mass but
we can release a huge amount of energy. And so where is the energy of the sun coming from?
It's coming from fusion of hydrogen into helium. And this continues on, helium can be fused
again. And we can move up the periodic table. What's fission then? Fission is going to be
when we have a big molecule. Here we're looking at uranium 235, that can be hit by another
particle and we can break it down into two different molecules. That's what fission is.
It's the breakdown of the nuclei. Now if we go back to fusion, this doesn't occur on our
planet. I mean it has just a few times in nuclear explosions, but fission occurs all
the time. Why doesn't fusion occur here? It's because you have to have a huge amount of
temperature and pressure to have it to go. Fission is going to be breakdown. And so an
atomic bomb is going to be usually a fission bomb. Where we seed it and then we just have
explosion. So we have fission, fission, fission. We have this change reaction. We also can
harness that in nuclear power as well. We can take the energy that's being released
and we can use that to run steam turbines and produce electricity. What's decay? Remember
decay is when we're changing from atom to another atom. So what's an example, a famous
one is carbon 14. Carbon 14 can undergo radioactive decay. It can lose an electron and it can
turn into nitrogen. Well, why is that important? On our planet most of the carbon is all carbon
12. It's got 6 protons and 6 neutrons. But a little bit of it is carbon 14. And it's
radio active. That means that it is going to break down. And as it does that we can
measure the rate at which it does that. And it's called radio metric dating. We can see
how old things are. And so we could look at the living materials. So like wood that was
found in these tombs. And we can date it using carbon 14 dating. What's nice about that is
that we can play that against the written record and we can look at written record of
the pharaohs. And we can figure out how accurate it actually is. Now as we get decay we get
different forms of radiation. We can have alpha, beta and gamma particles that are given
off. In this case we'd have beta decay. So let's talk about how you should cover this
in elementary grades. And the nice answer is that you shouldn't. If you look at the
breakdown, they say that you shouldn't talk about nuclear process in elementary. We shouldn't
really cover it until we get into middle school. And so you can breathe a sigh of relief if
you're an elementary teacher, but if you're a middle school teacher what should you talk
about? Well you should start by talking about fusion. Fusion is important because that produces
the energy in stars. What do we need to get fusion going? We need high temperature and
we also need high pressure. And so we don't have fusion going on on our planet. And that's
because we don't have enough mass to create enough pressure to create enough temperature.
But all the energy coming from stars is coming from nuclear fusion that's going on. A cool
quote from Carl Sagan said that we are all star stuff. What does he mean by that? Well
this occurs just for a little bit. So we can take hydrogen fuse it into helium. We can
then get up to iron, but as we get bigger and bigger and bigger, we really can't make
larger molecules. And so we're made up of pretty complex molecules. And so where did
we come from? The parts of us? Well anything on our planet that's not hydrogen and helium
had to come from stars and the formation of stars and the explosion of stars. And so we
literally are made of stardust. As you move into high school then you should talk about
these three processes. Fusion, which is the combination of the nuclei. Fission which is
the breakdown and then radioactive decay. What's causing that? That's the binding energies,
in other words the energy that are holding that nuclei together. And know this, that
just like in chemical reactions, the mass is conserved. In nuclear processes or reactions
the nucleons are going to be conserved. What does that mean? The protons and the neutrons
are going to stay the same. So even though we may have fusion, here, and we're creating
helium, we still have the same number of protons and neutrons. The total number. And even though
we may have decay where one is turning into another, the total number of nucleons is going
to be conserved. What's an important application? Especially for me like in biology? Radiometric
dating is an important thing that you should understand. A nuclear process. How does this
occur? Remember a small portion of carbon is carbon 14. But that's going to break down
into nitrogen. And so how often does that occur? Well it has a half life of 5730 years.
What does that mean? In 5730 years about half of the carbon is going to turn back into nitrogen
or turn into nitrogen. And we can measure that. So if we were to measure a sample of
living material after 5730 years, it will have about half of the carbon 14 that it should
have. And what do I mean should have? That it would normally have right now just in the
environment. So what's going to happen over the next 5000 years? Half of that that hasn't
decayed is going to decay. And then half of that is going to decay. And so after 17000
years we should have 12.5%. And so we could graph this right here. We could look at a
sample and then we could use that sample and the amount of carbon 14 in it to figure out
how old it is. Now my model here is really simplistic. There's going to be millions if
not billions and billions of these molecules in a sample. And so we can get highly accurate
results up to about 50,000 years. And then what do we do? We're going to have to switch
to a different isotope that we can measure. Last thing I would leave you with is this.
That in most stars we can get up to about the level of carbon through fusion. Or the
combining of the nuclei. In really big stars we could maybe get up into iron. But where
does the rest of the periodic table come from? It comes from a supernova. And so this is
going to be an explosion of super massive stars. They release a huge amount of energy,
where the light from one star outshines all of that in the sky. These are going to be
rare, but that's how we get everything on the periodic table, up from iron or large
in size than iron. And so those are nuclear processes. We don't deal with them on a day
to day life, but they're just as important as chemical reactions. And I hope that was
helpful.