Hello and welcome to GeekTeach, Todays we
will be talking about stable and unstable
nuclei.
In the previous video we learned the basic
structure of an atom, neutrons and protons
in the nucleus and electrons surrounding it.
Now I just want you to think about what is
wrong with this. There is one fundamental
flaw in the explanation that doesn't allow
it to make sense.
Have you got it? protons and protons repel
so why doesn't the nucleus just blow apart?
Well the by the time we finish talking about
stable nuclei you will know the answer to
this question.
There are many forces acting on an nucleus.
The electrostatic force comes from the protons
electric charge. It is an infinitely repulsive
force that weakens with distance. And It is
this force that logically would cause the
nucleus to blow apart.
So why doesn't it. Well I guess we could talk
about gravity. Because the particles have
mass there will be a gravitational force.
But if you do the calculations, you wont need
to until A2, than you will see that the electrostatic
force is much much larger than the gravitational
force, honestly the gravitational force is
so small you can just ignore it when talking
about stable nuclei. This means that there
has to be another force acting on the nucleus
to hold it together.
And this force, my friends, is the Strong
Nuclear Force.
To hold the nucleus together it has to be
an attractive force that is stronger than
the electrostatic force. But this comes with
its own little problem. The nucleus under
the rule of this force would collapse into
a point because it cant overcome this attractive
force. This means that at very small distances,
around 0.5 femtometres, the strong nuclear
force must be repulsive.
Experiments have also shown that the range
of the strong nuclear force is about 1 femtometer,
or the size of a nucleus. If you go further
out than this the strength of the force rapidly
decreases. The final thing that is quite fantastic
about this force is that it works equally
on both charged and uncharged particles.
This graph shows the strong nuclear force
and the electrostatic force plotted against
distance. Here you can see the relationship
between the two forces. If you learn this
graph and you can explain it than you have
the answer to the similarity and difference
question about these forces.
Now we have finished with stable nuclei, lets
talk about the unstable stuff.
In GCSE we learn that unstable nuclei emit
radiation, this radiation is Alpha, Beta and
Gamma and the emission of radiation is a quest
for stability.
An alpha particle consists of 2 protons and
2 neutrons. It is essentially a Helium nucleus.
We know that the proton number defines the
element so when an unstable atom emits alpha
radiation it changes the element. Compared
to the other forms of radiation we will look
at this is the largest. Loosing 2 protons
is a big deal and very difficult to do so
alpha emission only happens in very big atoms,
generally with 82 protons or more. Elements
like Uranium and Radium emit alpha radiation.
We represent alpha emission with an equation.
X element to y element with the atomic number
minus 4 and the proton number minus 2 plus
the alpha particle.
While alpha radiation was the release of a
helium nucleus beta radiation is the release
of an electron or a positron, which we will
talk more about in the Particles and Antiparticles
video. In this video we will talk about beta
minus emission. This happens in Neutron rich
isotopes. When a nucleus emits a beta particle
one of its neutrons is changed into a proton.
This changes the element.
We can represent beta emission using Feynman
diagrams which we will learn about later but
we can also use equations.
X element changes into Y with the proton number
minus 1. Plus a beta minus particle and an
antineutrino. The antineutrino is a tiny particle
that was theorised because momentum and energy
could not be conserved without it. Neutrinos
and Antineutrinos are notoriously difficult
to detect, billions pass through us every
second. Amazingly 20 years after they where
theorised antineutrinos where finally detected
proving the hypothesis.
Gamma radiation is electromagnetic radiation
that has no mass or charge. Its emitted after
alpha or gamma radiation by atoms that have
too much energy.
Thanks for watching, don't forget to Check
out my Google docs page for some questions
and answers. And as always I look forward
to seeing you next time.
