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Slide 1

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In 1804 John Dalton
said that matter was
made up of tiny spheres
(atoms) that couldn't be
broken up, but he
thought that each
element was made up
of a different type of
The `Plum Pudding' Model
100 years later
Thomson discovered
that electrons could be
removed from atoms.
He said atoms were…read more

Slide 2

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The plum pudding theory
did not last that long, in
1909 Earnest Rutherford
and some of his students
tried firing alpha particles
at thin gold foil. Most of
them went straight
through, but the odd one
Lord Rutherford
came straight back at 1871 - 1937
them. Which was a bit of a
shocker.…read more

Slide 3

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Isotopes ­ the nuclei of some isotopes are unstable, they can split up or decay and release
radiation , such isotopes are called radio active isotopes. When a radioactive isotope decays ,
it forms a different atom with different numbers of protons.
When an atom emits alpha or beta radiation , its nucleus changes. It becomes the nucleus of a
different element. This is because the number of protons in the nucleus determines which
element the atom belongs to.
Alpha decay Beta decay Gamma decay
Change in the nucleus Nucleus loses two protons One neutron decays into a electromagnetic radiation
plus two neutrons. proton. from an unstable nucleus.
Properties They are emitted by some Electron is emitted as the Gamma radiation occurs
of the isotopes of the beta particle. after a nucleus has
heaviest elements. emitted an alpha or beta
Helium particles Are electrons particle.…read more

Slide 4

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Background radiation
is all around us.
Most background
radiation comes from
natural sources, while
most artificial radiation
comes from medical
Also a small amount
is due to nuclear
weapon testing and
nuclear power
stations.…read more

Slide 5

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Nuclear fission is the splitting of an atomic
Nuclear fusion is the joining of two atomic nuclei
to form a larger one.
Nuclear fission can be used as an energy source
in a nuclear reactor.
1. The fission of a nucleus of
Uranium 235 can be initiated
by a neutron.
2. When this nucleus splits
further neutrons are
3. These neutrons in turn can
cause more nuclei to split.
4. An avalanche effect, called a
`chain reaction' can then
occur.…read more

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