2. Pre-nuclear model
JJ Thomson proposed the ‘plum pudding model’.
Image: mhhe.com
(This model is not correct)
In the model, the mass and charges in the atom
are spread uniformly throughout the atom.
3. Geiger and Marsden
In 1911, they fired alpha particles at gold foil.
Image: mhhe.com
Gold foil
Alpha emitter
Round screen
The theories of the time predicted that the particles would
easily pass through the thin foil since the gold was not
dense enough to stop them.
4. Unexpected result
Some alphas bounced right back!
Most alphas passed straight
through as predicted.
Some were slightly deflected.
But one in 8 000 was
bounced right back.
Rutherford said: “It was quite the most incredible
event that has ever happened to me in my life ... It was
then that I had the idea of an atom with a minute
massive centre, carrying a charge.” Image: PHET
5. Rutherford’s model
He discovered the nucleus
The nucleus of the atom is 20 000 times
smaller than the atom itself but contains
nearly all of its mass and the positive charge.
Empty Nucleus
space
The alpha particles are repelled by the nucleus (both
positive charges). A larger nucleus repels more strongly.
The faster the alpha particles, the less they are deflected.
6. Nuclearsplitting an unstable nucleus.
Huge amounts of energy from
fission
Can you balance the
1n neutron nuclear equation?
Solution over page
neutron fissions U-235 into 2 smaller daughter nuclei
gamma
The products are: 141Ba
★two nuclei eg krypton-92 and 92Kr
barium-141 both with a lot of KE
★three neutrons with KE
★gamma rays at the speed of light
3 1n
Image: PHET
7. Chainproduce energy from fission
How to continually
reaction
The fuel is enriched U-235, since U-238 does not fission.
The fission reaction produces fast neutrons. When these
are slowed down, they can cause new fission which
produces more fast neutrons ...
Scientists realised that if
at least one neutron
caused new fission, there
would be a chain reaction.
U
235
92
1 141 92 1
+ n 0 → Ba 56 + Kr 36 + 3n 0 plus loads and
loads of energy
Image: PHET
8. Nuclear fission reactor
The KE of the products makes the core extremely
hot. This heat energy is transferred to the exchanger;
steam turns the turbine and electricity is generated.
Image: Adrian Watt, Absorb Physics
9. Parts of a nuclear reactor
PART OF FUNCTION POSSIBLE
REACTOR OF THE PART MATERIALS
Fuel rods Chain reaction Enriched uranium oxide
in zirconium alloy
Slow down fast Graphite or
Moderator
neutrons heavy water
Absorb excess Boron or cadmium
Control rods
neutrons Water or
carbon dioxide
Coolant Transfer heat energy or liquid sodium
Thick lead, steel
Containment Radiation protection or concrete
10. Nuclear accident 2011?
What happened at Fukushima, Japan in March
When the earthquake struck, the A were Fill in the blanks
chain
pushed into the B to absorb neutrons and reaction
stop the C reaction in the D. But the control
earthquake had damaged the cooling rods
system, so super-hot E built up and reacted core
with the F round the fuel rods to produce fission
hydrogen which exploded. The hot core
fuel rods
broke through the G containment vessel
neutrons
and released H materials to the
radioactive
surroundings. To stop the reaction, acid
containing boron was added to absorb I and steam
stop the J. steel
zirconium
11. INTERESTING, BUT NOT FOR THE IGCSE
The interior of nuclear reactors glows blue
because of Cherenkov radiation which is caused
by electrons travelling in matter at speeds faster
than light can travel in that medium.
Image: wikipedia
12. a production
MUCH MORE AT
http://nothingnerdy.wikispaces.com
http://nothingnerdy.wikispaces.com/IGCSE+PARTICLES
