Transcript GCSE Radiation - Bishopston Comprehensive School Moodle

Radiation
Menu
• The Atom
• History of the Atom
• Alpha Scattering
• Mass & Atomic Numbers
• Isotopes
• Fission
• Nuclear Equations
The ATOM
All things are made of atoms. They are
EVERYWHERE! Look around you.
EVERYTHING YOU SEE is made up of
atoms – the land, sea, walls, other people,
the sky……..
1cm3 of air at sea level (at 0oC) contains
about 50 billion billion atoms/molecules.
Now think of how many cm3 are in this
room…and outside….and in the Universe
There are a lot of atoms!
Atoms Are Extremely
Durable
Every atom in your body has been around
since the creation of the Universe. They
have passed through several stars and
been parts of millions of different
animals, plants and rocks before making
YOU!
Just think…..the atoms in your body were
once in the form of a Tyrannosaurus Rex!
What is an atom?
An atom is made up of
Positive Protons, Negative
electrons and NEUTral
NEUTrons.
Protons
Neutrons
Electrons
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What is the structure of the atom?
The NUCLEUS contains
protons & neutrons. It
makes up most of the
MASS of the atom – yet
it is tiny!
The ELECTRONS fly around the outside.
They’re negatively charged and really small.
They occupy a lot of space and this gives
the atom its overall size. (Even though it’s
mostly empty space)
What is the structure of
the atom?
Particle
Proton
Neutron
Electron
Relative
Mass
1
1
1/1840
Relative
Charge
+1
0
-1
MASS
NUMBER
(Number of
PROTONS &
NEUTRONS)
PROTON
NUMBER
(Number of
PROTONS)
What is Mass Number &
Proton Number?
4
2
He
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Isotopes
Isotopes are atoms with the SAME
NUMBER OF PROTONS but DIFFERENT
NUMBERS OF NEUTRONS
Hence they have the same atomic
number, but different mass number
Most elements have isotopes but
there is usually only one or two stable
ones
Isotopes
Carbon-12 and carbon 14 are
examples of isotopes.
12
6
C
Stable Isotope
C
14
6
Unstable
Radioactive
Isotope
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The History of the Atom
In 1804 John Dalton Said…..
Matter Was Made up
of Tiny Solid
Spheres Called
Atoms
An Atom!
Later they discovered electrons
could be removed from atoms.
Scientists then believed atoms had a
sphere of positive charge with tiny
negative electrons stuck in it.
Like plums in a
plum pudding!
Hence the name
‘PLUM PUDDING
MODEL’!
Then, Ernest Rutherford tried
firing positively charged alpha
particles at thin GOLD LEAF FOIL
GOLD was used as it could be beaten until it
became extremely thin. Ideally Rutherford
wanted just 1 layer of atoms for his
experiment!
Rutherford was very
surprised by the result.
1 in every 8,000 alpha
particles bounced back!
It was as if a cannon ball
was fired at a sheet of
tissue paper and the
cannon ball bounced back!
Gold Leaf
Alpha
Particles
Most alpha particles go straight through while
others bounce back! The conclusion is that an
atom is made up of mostly ‘space’ with a tiny
concentrated area of positive charge (the
nucleus) in the centre and orbiting electrons.
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Nuclear Equations
There are 3 equations for
EMISSION:
• Alpha Emission
• Beta Emission
• Gamma Emission
Make sure your Mass Numbers and
Atomic numbers Balance up on both sides!
Alpha Emission
An Alpha Particle is simply a Helium
Nucleus (Mass 4 and charge +2)
A Typical Alpha Emission:226
88
Ra
222
86
Rn + He
4
2
Beta Emission
A Beta Particle is simple an Electron
with NO Mass and a Charge of - 1
A Typical Beta Emission:14
6
C
14
7
N
0
-1
e
Gamma Emission
A gamma Ray is a photon with No
Mass & No Charge
After an Alpha or Beta Emission the
nucleus sometimes gives out an extra
bit of energy in the form of a Gamma
Ray. Gamma Emission Never changes
the Atomic or Mass Numbers.
Nuclear Fission
The Splitting up of Atoms Is
Called Nuclear Fission
Nuclear power stations and nuclear
submarines are both powered by nuclear
reactors
In a nuclear reactor, a controlled chain
reaction takes place in which uranium
atoms split up and release energy in the
form of heat. This turns water to steam
to drive a turbine & generate electricity
Nuclear Fission
neutron
neutron
1 neutron
Uranium
atom
neutron
Nuclear Fission
Each time a Uranium atom splits up it spits
out 2 or 3 neutrons, one of which hits
another uranium nucleus, causing it to split.
This keeps the chain reaction going.
The Chain Reaction
Uranium
atom
When the Uranium atom splits into two it
will form two lighter elements that are also
radioactive. This becomes radioactive waste
and is a big problem for nuclear power
stations as it can remain dangerous for
hundreds of years
You may
see
a
chain
reaction
Nuclear Fission
represented like this:
It is important to
control the numbers
of neutrons released
otherwise this
reaction will become
extremely
dangerous.We use
‘control rods’ to
absorb the unwanted
neutrons
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