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Mr. Andersen contrasts nuclear reactions to chemical reactions. He explains the four main forces of nature; including gravity, electromagnetism, strong, and weak nuclear forces. He also explains how fusion differs from fission.
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Transcript Provided by YouTube:
00:05
Hi. It’s Mr. Andersen and today I’m going to be talking about nuclear reactions.
00:10
Up to this point in physical science we’ve mostly been talking about chemistry and chemical
00:14
reactions. But there’s a whole other group of reactions called nuclear reactions. And
00:19
people, they’re no less important but the maybe are less understood. In other words
00:23
the nuclear reactions, the fusion reactions found in the sun are producing the energy
00:28
that create our food and the light that is coming in this window right here. And so in
00:32
this podcast I’m going to try to explain nuclear reactions and where they come from. Now to
00:36
understand nuclear reactions you first have to understand the four fundamental forces
00:41
in nature. The two major forces that most of you are familiar with are going to be gravity
00:51
and then electromagnetism. Or the electromagnetic force. Now what is gravity? Gravity holds
00:57
you where you are. And so you stick to the earth because there’s a gravitational force
01:03
that’s pulling you down towards it. This was first identified by Newton. The neat thing
01:07
about it is if we were to shoot you into space and you might be way out here in space, there’s
01:12
still is a gravitational force that holding you towards the, towards the planet. Gravity
01:18
is cool in that it acts over a huge distance, but it’s a relatively weak force. In other
01:23
words if we zoom down in here where your foot is. So if we look right down here where your
01:27
foot is. I’m going to try to draw your foot. Your foot look like this we’ll say. The reason
01:34
you don’t sink through the floor and actually move to the center of the earth is that there
01:40
is an electromagnetic force here. So there’s all these electrons in your foot and all the
01:45
electrons in the floor. And they’re repulsing each other. In other words my fingers don’t
01:49
move through each other because there’s an electromagnetic force pushing them apart.
01:54
Now, a scientist by the name of Maxwell was able to take the idea of electricity, which
01:59
was pretty mysterious, combine it with this idea of magnetism and so we now combine those
02:04
into one electromagnetic force. And so the two forces that you’re familiar with, just
02:08
walking around forces are going to be the gravitational force and electromagnetic force.
02:13
But when we get down to the lower smaller level, at the level of the nucleus, we find
02:18
that there are two more forces. Those are called the strong and the weak nuclear forces.
02:23
So if we look down here in the nucleus, inside the nucleus, let’s say these red ones are
02:26
the protons. The protons have a positive charge. And the neutrons have no charge. They have
02:33
a neutral charge. And so you would think with the electromagnetic force, all these positive
02:38
charges in here in the nucleus are actually going to make them push themselves apart.
02:42
Now why doesn’t that occur? The reason that doesn’t occur is that there are all these
02:46
strong nuclear forces that are holding all these atoms together or excuse me the nucleons.
02:54
The protons and the neutrons together. And so the strong nuclear force are all the forces
02:59
that hold together the nucleus. It wants to fly apart, but these nuclear forces are holding
03:04
it there. And that’s the reason why as atoms get larger and larger and larger and they
03:08
have more protons in it, we actually have to have more neutrons in the center. There’s
03:12
like a perfect number of neutrons compared to the number of protons you have just to
03:17
hold the nucleus apart. The problem with a strong nuclear force and the reason that you
03:21
don’t deal with it is that it only acts over a very small distance. It’s right here in
03:26
the middle. The last force is called the weak nuclear force. Weak nuclear force is crazier
03:33
yet. Sometimes, let me clear this off for a second, sometimes one of these neutrons
03:41
will actually turn into a proton. So how do you go from a neutron to a proton? Well, what
03:48
you give off is an electron. An electron which has no mass but has a negative one charge.
03:55
And so what is accountable for that? It’s actually quarks inside this neutron and the
04:00
proton that are changing. But it’s this weak nuclear force that causes that to occur. And
04:05
then sometimes even something weirder than that happens. Sometimes we’ll have one of
04:09
these protons actually turn into a neutron. And what that does is it gives off a positron.
04:18
And so when it does that, we have another form of beta decay. But both of those are
04:23
caused by weak nuclear forces. And so this chart came from our book, but I think it’s
04:28
a good way to kind of talk about the differences between the chemical reactions and then nuclear
04:33
reactions. And so in chemical reactions what are the players? The players in chemical reactions
04:40
are the valence electrons. In other words, in all the reactions we’ve talked about to
04:45
this point, it’s the electrons out here, the electrons at the outside of the atom that
04:50
actually determines the chemical reaction. What reacts with what. And that’s why the
04:54
periodic table looks the way it does. In a nuclear reaction however, in a nuclear reaction
04:59
it’s going to be the nucleons that are at play. And so what are the nucleons? The nucleons
05:04
are the protons and the neutrons that are found in the nucleus in a chemical reaction.
05:10
Okay. What starts a chemical reaction? Well to start a chemical reaction you have to have
05:16
two reactants. And you have to somehow get their valence electrons close enough to each
05:22
other so that you can actually have a chemical reaction. What’s one way we could do that?
05:27
Well we could add pressure to the system. If we squeeze these reactants towards each
05:31
other, they’re more likely to react. We could increase the temperature. And that’s going
05:36
to make them move around more quickly and more likely to bounce into each other. Or
05:39
another way we could do that is we could add a catalyst to that. A catalyst is something
05:44
that’s going to lower the activation energy, change in energy due to activation. And what
05:52
that does is it lowers this barrier of energy that must be over come in order for a reaction
05:58
to occur. What about in a nuclear reaction? In a nuclear reaction there’s two things that
06:03
could start a nuclear reaction. Number one, we could start with particles that are moving
06:07
fast enough. So if we bombard the nucleon with other particles, protons for example,
06:14
we can actually start a reaction. Or if we get huge temperature increases. If we increase
06:19
the temperature then we can have some nuclear reactions as well. And that’s why we can have
06:24
the sun and the sun has enough mass to generate that kind of temperature. But we don’t have
06:28
fusion reactions taking place on our planet. What about the end then? What do we create
06:33
at the end of a chemical reaction? We create bonds or there are new bonds that are formed.
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Well, what’s formed in a nuclear reaction? In a nuclear reaction we’re going to form
06:46
new, not bonds, but since we’re changing the amounts of protons we’re going to end up with
06:51
new atoms. The last type is the amount of energy. The amount of energy in a chemical
06:58
reaction is going to be really small. Now you wouldn’t say that dynamite is a small
07:05
amount of energy that’s released. But it’s relatively small compared to the amount of
07:09
energy you get from a nuclear reaction. Nuclear reaction we’re going to get a huge amount
07:15
of energy. Why do we get a huge amount of energy? It actually requires talking a little
07:20
bit about this equation. So you’re maybe familiar with this. E=mc^2. So this is Einstein’s famous
07:28
equation. What does it mean? Well m stands for the mass. C stands for the speed of light.
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And so what do you know about the speed of light? The speed of light is a huge number.
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And then we’re squaring it. So we’re even making that number bigger yet. And so what
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Einstein said is that you can’t create mass. You can’t destroy mass. But you can convert
07:55
mass into energy and energy back into mass. And so you can take a small amount of mass,
08:00
like the mass inside my finger and you can create a huge amount of energy from that.
08:05
And that’s all that energy that’s found inside the sun, we get in that kind of way. We could
08:10
take reactions and put them into two different types. We have first of all a fission reaction.
08:16
In a fission reaction what you have is a particle that’s bombarding an atom. An atom that’s
08:22
radioactive. In this case it’s uranium 235. And what that does is it converts that into
08:28
another form of uranium. But it releases more of these neutrons. And those parts of atoms
08:37
are going to smash into other atoms which is going to cause this chain reaction. So
08:41
this is actually a fission weapon. This is the bomb that was dropped on, I think this
08:46
is on Nagasaki. And that’s a fission reaction. And so inside the bomb you had to have something
08:52
that’s able to create these flying particles, initially. And then once you start it, it’s
08:57
like a chain reaction. YouTube has some great videos of a number of different mouse traps
09:03
set up with two ping pong balls on each mousetrap. And once it get’s hit by one ping pong ball,
09:09
that’s going to cause those two to fly. And that hits four. And that’s a fission reaction
09:14
or a chain reaction. The other major type of a reaction that we have is fusion reactions.
09:20
And so this is actually the opposite taking place. In a fusion reaction what we have is
09:25
two different particles. In this case these are protons that are fusing together and they’re
09:30
making hydrogen. This is actually deuterium because it has one neutron. Those neutrons
09:36
will fuse together to make this which is helium 3. So this is helium with 2 protons, 1 neutron.
09:46
These will then convert into something called beryllium 6 which is highly unstable and then
09:52
eventually converts to regular helium. And so helium has less mass than the 4 original
10:00
protons that were used to create it. And remember according to Einstein’s theory, E=mc^2, the
10:08
tiny amount of mass that’s lost when we convert those protons into helium or the hydrogen
10:14
into helium is given off in the form of energy. And that energy given off the sun comes from
10:21
fusion. Now what would we like to have? On our planet right now we only have fission
10:26
reactors. And so we can only make electricity using that process of nuclear fission. The
10:32
nice thing that we would like to be able to do is just take hydrogen that we have on our
10:35
planet and fuse that into helium. Because there’s so much hydrogen here we could have
10:40
almost an infinite source of energy. The problem with that is you have this barrier of temperature.
10:47
We have to get enough temperature increase so we can actually have fusion taking place
10:51
on our planet. Most scientists think this is going to be decades away before we can
10:55
have that. But the nice thing is once we get a fusion reaction like that, we could do away
10:59
with the fossil fuels that we use today. And the chemical reactions that they have. And
11:04
so that’s nuclear reactions. I’ll talk a little bit more about radioactivity and carbon 14
11:08
dating in the next two podcasts. I hope that’s helpful.
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This post was previously published on YouTube.
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Photo credit: Screenshot from video
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