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In this segment, we delve into a world
of atomic and subatomic particles,
a world we can't see
but one that's part of every one of us.
This segment will help us understand nuclear energy
and why we can get so much energy
from such small particles.
Keep in mind, when we're talking about nuclear energy,
the nucleus of an atom is changing.
Atoms are the building blocks of life in our universe.
Our bodies, for example, are made up of trillions
and trillions of atoms.
There are 118 different types of atoms
that we know about and call elements.
Elements are the basic building blocks
of the universe.
Gold, for example, is an element.
Ninety-two elements are found in nature.
The others that you see on the periodic table
are created by humans.
There are 118 in all.
These elements are specific atoms.
Gold is one type of atom.
Carbon is another type.
To better understand,
let's take a look inside an atom,
where we'll find even smaller particles--
electrons, protons, and neutrons.
At the center of every atom is a nucleus.
That's where the protons and neutrons can be found.
The electrons orbit outside the nucleus
in an electron cloud.
They are what chemically atoms together into molecules,
everything from hydrogen gas to hemoglobin.
The nucleus is positively charged
and holds most of the mass of the atom.
The electrons are negatively charged
and have little mass.
Think about this...
If the nucleus of an atom was a golf ball
at the 50-yard line,
the electron cloud would be the size
of the entire football stadium.
Now, let's take a closer look at the formation
of those 118 elements.
We can use carbon as an example.
The number of protons defines what the element is.
That's the atomic number.
You could say it defines the element's identity.
A carbon atom always has six protons.
If it had seven protons,
it wouldn't be a carbon atom anymore.
It would be nitrogen.
The total number of protons and neutrons
is called the mass number.
Now, while all atoms of the element have the same number of protons,
they don't always have the same number of neutrons.
Atoms that differ in the number of neutrons
but not the number of protons
are isotopes of each other.
Isotopes of a given element have the same atomic number
but different mass numbers,
which, again, is a sum of protons and neutrons.
The way to write isotopes of a given element is to use
both a superscript and a subscript
in front of the element's symbol.
For example, this is uranium.
The "U" is the symbol for the element uranium.
Ninety-two is the atomic number,
which is the number of protons.
So, all atoms of uranium have 92 protons.
The 235 is the mass number,
the total number of protons
and neutrons combined.
If we know that there are 92 protons
and the total number of protons and neutrons is 235,
then there must be 143 neutrons.
Other ways to write it are uranium-235,
or U-235.
All of these ways show a difference
between U-235 and U-233.
Well, what's the difference?
U-233 only has 92 protons,
but it has 141 neutrons.
It's an isotope of U-235.
The mass of an element listed on a periodic table
is the average mass
of all the different isotopes of that element.
That's why we have a decimal value of mass.
So, on the periodic table,
uranium is listed as 238.0289,
which is the average of all the uranium isotopes.
Now, elements have both stable and unstable isotopes.
The stability of the element depends on the ratio
between protons and neutrons
and the ability of the strong nuclear force
to hold them together.
We'll talk about the strong nuclear force
a little later.
This chart shows the number of neutrons
in relation to the number of protons,
and from our experiences with isotopes,
we know which isotopes are more stable.
It turns out those more distant from the center yellow line
are less stable.
A challenge for scientists
has been to figure out
what holds the nucleus together.
How do positively charged protons
hang out together in the nucleus
without repelling each other?
Physicists discovered that these particles
are held together by the strong nuclear force,
one of the four fundamental forces.
It's what holds protons and neutrons
in the nucleus of the atom together.
The strong nuclear force is the strongest
of the four fundamental forces in the universe,
but it has a very short range,
about the diameter of a medium sized nucleus,
and it's only present in the nucleus.
The range is so short
that when an atom has a large nucleus
with lots of protons and neutrons,
the strong force is sometimes not strong enough
to keep electrical repulsion
between the protons from occurring.
That's when the nucleus becomes unstable.
It breaks down and emits radioactive particles or energy.
When a nucleus becomes too big and too unstable,
with too many particles in the nucleus
for the strong force to hold them together,
that's when the nucleus undergoes radioactive decay.
So, radioactivity is...
There are three types of radioactive decay.
Alpha decay occurs when a nucleus releases
an alpha particle.
What's an alpha particle?
Two protons and two neutrons bound together.
It's the equivalent of the nucleus of a helium-4 atom.
Alpha particles have a plus two charge.
They're the slowest and least penetrating form
of nuclear radiation.
A piece of paper can block their path.
Another type of decay is beta decay.
Beta decay occurs when a neutron in an atom's nucleus
decays into a proton,
or when a proton decays into a neutron.
When this happens, a beta particle is emitted.
That said, a beam of beta particles
can still be blocked by a thin layer of metal
like aluminum foil.
There's a fundamental force involved
when nucleus undergoes beta decay
called the weak nuclear force.
The weak force works inside protons
and holds the particles themselves together.
The weak force also keeps individual neutrons intact.
There are two types of beta decay.
Beta minus decay occurs
when a neutron decays into a proton,
an electron, and an antineutrino.
The proton stays in the nucleus
while the electron and the antineutrino
shoot out from the nucleus.
Antineutrinos and neutrinos are subatomic particles
with infinitesimally small masses and no charge.
The two are like mirror twins.
If the collide,
they will annihilate each other.
They're part of what's emitted during beta decay.
There's
during beta decay, a positron.
It has the same mass as an electron
but has a positive charge.
So, with beta minus decay,
a neutron decays into a proton,
an electron, and an antineutrino.
Beta plus decay occurs when a proton decays into a neutron,
a positron, and a neutrino.
The neutron remains in the nucleus,
and the positron and the neutrino
shoot out from the nucleus.
A third type of radiation can occur as a result
of alpha decay, beta decay,
or as a result of a violent collision
with another particle.
This type of decay is called gamma decay.
In these cases, the entire nucleus
is excited to a higher energy level.
As the decay occurs,
the nucleus falls back into its less excited state,
releasing gamma photons.
This gamma radiation is all energy
and no particles.
It's the most energetic wave on the electromagnetic spectrum.
Gamma rays travel at the speed of light
and have the smallest wavelength
and the highest frequency of light.
Gamma rays can penetrate matter more readily
than alpha or
Gamma radiation then is dangerous,
but it can be used to target and destroy cancer cells.
It has to be highly targeted
to avoid damaging healthy cells.
All of these radioactive decays are blurring the lines
between light, forces, and matter.
Particle physics and the field of cosmology
continue to raise questions
and produce understandings about our subatomic world
and the universe itself.
That's it for this segment of "Physics in Motion",
and we'll see you next time.
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