Transcript Slide 1

EDEXCEL IGCSE PHYSICS 7-4
Particles
Edexcel IGCSE Physics pages 226 to 231
December 4th 2010
THIS POWERPOINT IS NOT
All content COMPLETION
applies for Triple & Double ScienceUNTIL
DUE FOR
JULY 2012
Edexcel IGCSE Specification
Section 7: Radioactivity and particles
c) Particles
describe the results of Geiger and Marsden’s experiments with gold foil and
alpha particles
describe Rutherford’s nuclear model of the atom and how it accounts for the
results of Geiger and Marsden’s experiment and understand the factors
(charge and speed) which affect the deflection of alpha particles by a nucleus
understand that a nucleus of U-235 can be split (the process of fission) by
collision with a neutron, and that this process releases energy in the form of
kinetic energy of the fission products
recall that the fission of U-235 produces two daughter nuclei and a small
number of neutrons
understand that a chain reaction can be set up if the neutrons produced by
one fission strike other U-235 nuclei
understand the role played by the control rods and moderator when the fission
process is used as an energy source to generate electricity.
The Plum Pudding Atomic Model
Before about 1910
many scientists
believed that an atom
consisted of:
Positively charged
matter spread out like a
pudding embedded by
negatively charged
electrons (like plums in
a pudding).
The ‘Plum Pudding’ Model
Rutherford’s Atomic Model
In 1909 Ernest Rutherford suggested that an atom
consists of a a tiny positively charged nucleus
surrounded by negatively charged electrons.
Lord Rutherford
1871 - 1937
Geiger & Marsden’s alpha particle
scattering experiment
In 1909 Hans Geiger
and Ernest Marsden
performed an
experiment using alpha
particles to determine
which of the two
models was the better
in describing the
structure of an atom.
Geiger and Marsden
The apparatus
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4
3
1
What was observed
alpha
source
thin metal foil
1. Virtually all of the alpha particles went straight through the metal foil.
2. A few alpha particles were deflected through a small angle.
3. About 1 in 10 000 were deflected backwards.
How the results can be explained
atom
1. Deflections occur because there is
a force between the charged
nucleus and the positively charged
alpha particles.
2. Most of the alpha particles do not
go near enough to the nucleus to
be deflected.
3. Backwards deflections occur when
the alpha particles make near
head on collisions with the
positively charged nucleus.
nucleus (highly enlarged)
How their results supported
Rutherford’s atomic model
1. The relatively small number of
deflections indicates that most of
the atom is empty space with only
a very small nucleus.
2. The backward deflections can
only occur if the nucleus is
positively charged and contains
most of the atom’s mass.
3. The ‘plum pudding’ model would
not produce backward
deflections.
Choose appropriate words to fill in the gaps below:
Rutherford an atom consists of a tiny,
According to __________
positively
nucleus
___________
charged __________
surrounded by a cloud of
________
negative electrons. The nucleus also contains most of the
______
mass of an atom.
alpha particle scattering
This model was supported by the ______
experiment in 1909. In this experiment most alpha particles
straight through a thin metal foil with only about 1
passed ________
backwards
in 10000 being deflected _________.
WORD SELECTION:
Rutherford mass backwards negative
straight positively alpha nucleus
Nuclear fission
Nuclear fission is the splitting
of an atomic nucleus.
Nuclear fission can be used as
an energy source in a nuclear
reactor.
There are two fissionable
substances in common use in
nuclear reactors, uranium 235
and plutonium 239.
Chain reaction
The fission of a nucleus of
Uranium 235 can be initiated
by a neutron.
When this nucleus splits
further neutrons are
produced.
neutron
These neutrons in turn can
cause more nuclei to split.
An avalanche effect, called a
‘chain reaction’ can then
occur.
A chain reaction
Nuclear fission reactor
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3&4
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Nuclear reactor parts
1. Fuel rods
These contain U235 or Pu239. They
become very hot due to nuclear
fission.
4. Coolant
This transfers the heat energy of the
fuel rods to the heat exchanger.
Coolant be water, carbon dioxide gas
or liquid sodium.
2. Control rods
Made of boron, when placed inbetween the fuel rods these absorb
neutrons and so reduce the rate of
fission. Their depth is adjusted to
maintain a constant rate of fission.
5. Heat exchanger
Here water is converted into high
pressure steam using the heat energy
of the coolant.
3. Moderator
This surrounds the fuel rods and
slows neutrons down to make further
fission more likely. The moderator
can be water or graphite.
6. Reactor core
This is a thick steal vessel designed to
withstand the very high pressure and
temperature in the core.
7. Concrete shield
This absorbs the radiation coming
from the nuclear reactor.
Choose appropriate words to fill in the gaps below:
splitting up of the nucleus of an atom
Nuclear fission is the _________
energy and neutrons are also
into two smaller nuclei. ________
usually emitted.
reactors use Uranium _____
235 or Plutonium _____to
239
Nuclear ________
fission
produce energy by nuclear ________.
A controlled chain
control rods which
reaction is maintained by the use of _______
neutrons produced.
absorb some of the _________
atomic bomb is the consequence of an uncontrolled
An _______
chain reaction.
WORD SELECTION:
reactors energy 239 atomic splitting
neutrons 235 fission control
Particles
Notes questions from pages 226 to 231
1. Answer the questions on page 231.
2. Verify that you can do all of the items
listed in the end of chapter checklist on
page 231.
Online Simulations