Hi. It's Mr. Andersen and today I'm going to be talking about nuclear reactions.
Up to this point in physical science we've mostly been talking about chemistry and chemical
reactions. But there's a whole other group of reactions called nuclear reactions. And
people, they're no less important but the maybe are less understood. In other words
the nuclear reactions, the fusion reactions found in the sun are producing the energy
that create our food and the light that is coming in this window right here. And so in
this podcast I'm going to try to explain nuclear reactions and where they come from. Now to
understand nuclear reactions you first have to understand the four fundamental forces
in nature. The two major forces that most of you are familiar with are going to be gravity
and then electromagnetism. Or the electromagnetic force. Now what is gravity? Gravity holds
you where you are. And so you stick to the earth because there's a gravitational force
that's pulling you down towards it. This was first identified by Newton. The neat thing
about it is if we were to shoot you into space and you might be way out here in space, there's
still is a gravitational force that holding you towards the, towards the planet. Gravity
is cool in that it acts over a huge distance, but it's a relatively weak force. In other
words if we zoom down in here where your foot is. So if we look right down here where your
foot is. I'm going to try to draw your foot. Your foot look like this we'll say. The reason
you don't sink through the floor and actually move to the center of the earth is that there
is an electromagnetic force here. So there's all these electrons in your foot and all the
electrons in the floor. And they're repulsing each other. In other words my fingers don't
move through each other because there's an electromagnetic force pushing them apart.
Now, a scientist by the name of Maxwell was able to take the idea of electricity, which
was pretty mysterious, combine it with this idea of magnetism and so we now combine those
into one electromagnetic force. And so the two forces that you're familiar with, just
walking around forces are going to be the gravitational force and electromagnetic force.
But when we get down to the lower smaller level, at the level of the nucleus, we find
that there are two more forces. Those are called the strong and the weak nuclear forces.
So if we look down here in the nucleus, inside the nucleus, let's say these red ones are
the protons. The protons have a positive charge. And the neutrons have no charge. They have
a neutral charge. And so you would think with the electromagnetic force, all these positive
charges in here in the nucleus are actually going to make them push themselves apart.
Now why doesn't that occur? The reason that doesn't occur is that there are all these
strong nuclear forces that are holding all these atoms together or excuse me the nucleons.
The protons and the neutrons together. And so the strong nuclear force are all the forces
that hold together the nucleus. It wants to fly apart, but these nuclear forces are holding
it there. And that's the reason why as atoms get larger and larger and larger and they
have more protons in it, we actually have to have more neutrons in the center. There's
like a perfect number of neutrons compared to the number of protons you have just to
hold the nucleus apart. The problem with a strong nuclear force and the reason that you
don't deal with it is that it only acts over a very small distance. It's right here in
the middle. The last force is called the weak nuclear force. Weak nuclear force is crazier
yet. Sometimes, let me clear this off for a second, sometimes one of these neutrons
will actually turn into a proton. So how do you go from a neutron to a proton? Well, what
you give off is an electron. An electron which has no mass but has a negative one charge.
And so what is accountable for that? It's actually quarks inside this neutron and the
proton that are changing. But it's this weak nuclear force that causes that to occur. And
then sometimes even something weirder than that happens. Sometimes we'll have one of
these protons actually turn into a neutron. And what that does is it gives off a positron.
And so when it does that, we have another form of beta decay. But both of those are
caused by weak nuclear forces. And so this chart came from our book, but I think it's
a good way to kind of talk about the differences between the chemical reactions and then nuclear
reactions. And so in chemical reactions what are the players? The players in chemical reactions
are the valence electrons. In other words, in all the reactions we've talked about to
this point, it's the electrons out here, the electrons at the outside of the atom that
actually determines the chemical reaction. What reacts with what. And that's why the
periodic table looks the way it does. In a nuclear reaction however, in a nuclear reaction
it's going to be the nucleons that are at play. And so what are the nucleons? The nucleons
are the protons and the neutrons that are found in the nucleus in a chemical reaction.
Okay. What starts a chemical reaction? Well to start a chemical reaction you have to have
two reactants. And you have to somehow get their valence electrons close enough to each
other so that you can actually have a chemical reaction. What's one way we could do that?
Well we could add pressure to the system. If we squeeze these reactants towards each
other, they're more likely to react. We could increase the temperature. And that's going
to make them move around more quickly and more likely to bounce into each other. Or
another way we could do that is we could add a catalyst to that. A catalyst is something
that's going to lower the activation energy, change in energy due to activation. And what
that does is it lowers this barrier of energy that must be over come in order for a reaction
to occur. What about in a nuclear reaction? In a nuclear reaction there's two things that
could start a nuclear reaction. Number one, we could start with particles that are moving
fast enough. So if we bombard the nucleon with other particles, protons for example,
we can actually start a reaction. Or if we get huge temperature increases. If we increase
the temperature then we can have some nuclear reactions as well. And that's why we can have
the sun and the sun has enough mass to generate that kind of temperature. But we don't have
fusion reactions taking place on our planet. What about the end then? What do we create
at the end of a chemical reaction? We create bonds or there are new bonds that are formed.
Well, what's formed in a nuclear reaction? In a nuclear reaction we're going to form
new, not bonds, but since we're changing the amounts of protons we're going to end up with
new atoms. The last type is the amount of energy. The amount of energy in a chemical
reaction is going to be really small. Now you wouldn't say that dynamite is a small
amount of energy that's released. But it's relatively small compared to the amount of
energy you get from a nuclear reaction. Nuclear reaction we're going to get a huge amount
of energy. Why do we get a huge amount of energy? It actually requires talking a little
bit about this equation. So you're maybe familiar with this. E=mc^2. So this is Einstein's famous
equation. What does it mean? Well m stands for the mass. C stands for the speed of light.
And so what do you know about the speed of light? The speed of light is a huge number.
And then we're squaring it. So we're even making that number bigger yet. And so what
Einstein said is that you can't create mass. You can't destroy mass. But you can convert
mass into energy and energy back into mass. And so you can take a small amount of mass,
like the mass inside my finger and you can create a huge amount of energy from that.
And that's all that energy that's found inside the sun, we get in that kind of way. We could
take reactions and put them into two different types. We have first of all a fission reaction.
In a fission reaction what you have is a particle that's bombarding an atom. An atom that's
radioactive. In this case it's uranium 235. And what that does is it converts that into
another form of uranium. But it releases more of these neutrons. And those parts of atoms
are going to smash into other atoms which is going to cause this chain reaction. So
this is actually a fission weapon. This is the bomb that was dropped on, I think this
is on Nagasaki. And that's a fission reaction. And so inside the bomb you had to have something
that's able to create these flying particles, initially. And then once you start it, it's
like a chain reaction. YouTube has some great videos of a number of different mouse traps
set up with two ping pong balls on each mousetrap. And once it get's hit by one ping pong ball,
that's going to cause those two to fly. And that hits four. And that's a fission reaction
or a chain reaction. The other major type of a reaction that we have is fusion reactions.
And so this is actually the opposite taking place. In a fusion reaction what we have is
two different particles. In this case these are protons that are fusing together and they're
making hydrogen. This is actually deuterium because it has one neutron. Those neutrons
will fuse together to make this which is helium 3. So this is helium with 2 protons, 1 neutron.
These will then convert into something called beryllium 6 which is highly unstable and then
eventually converts to regular helium. And so helium has less mass than the 4 original
protons that were used to create it. And remember according to Einstein's theory, E=mc^2, the
tiny amount of mass that's lost when we convert those protons into helium or the hydrogen
into helium is given off in the form of energy. And that energy given off the sun comes from
fusion. Now what would we like to have? On our planet right now we only have fission
reactors. And so we can only make electricity using that process of nuclear fission. The
nice thing that we would like to be able to do is just take hydrogen that we have on our
planet and fuse that into helium. Because there's so much hydrogen here we could have
almost an infinite source of energy. The problem with that is you have this barrier of temperature.
We have to get enough temperature increase so we can actually have fusion taking place
on our planet. Most scientists think this is going to be decades away before we can
have that. But the nice thing is once we get a fusion reaction like that, we could do away
with the fossil fuels that we use today. And the chemical reactions that they have. And
so that's nuclear reactions. I'll talk a little bit more about radioactivity and carbon 14
dating in the next two podcasts. I hope that's helpful.