Nuclear Reactions

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Nuclear Reactions

• Rutherfords Alpha Scattering Experiment

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CS 4.1
Describe how Rutherford showed that
(a) The nucleus had a relatively small diameter
compared with that of the atom.
(b) Most of the mass of the atom is concentrated
in the nucleus.
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IN THE BEGINNING
In the early days of atomic theory, many
physicists tried to explain the model of an atom.
In 1902, Ernest Rutherford showed that alpha
particles emitted from the decay of unstable
radioactive materials were electrically charged
helium nuclei travelling at high speed.
In 1909, Rutherford used alpha particles to
investigate the composition of gold foil (i.e. to
explain the model of an atom).
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Aim
To investigate the composition of gold foil using
alpha particles (i.e. to explain the model of an
atom).
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Apparatus
Rutherfords alpha scattering apparatus
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Procedure
Rutherford fired alpha particles through a piece
of gold foil and used a zinc sulphide detector to
detect the scattered alpha particles and their
location.
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Results..
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Results
Rutherfords experiment found that

• Most of the alpha particles passed through the
  gold foil
• undeviated.

• A few alpha particles were deflected from their
  path
• but continued through the gold foil.

• A small number of alpha particles rebounded.

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Conclusion
From the results of his experiment, Rutherford
explained

• As most alpha particles passed through the gold
  foil
• atoms undeviated, Rutherford concluded that
  most of
• the atom was actually empty space.

• The deviation of some alpha particles from
  their
• original path were due to positive charges
  within the
• foil.

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Conclusion
From the results of his experiment, Rutherford
explained

• A small number of alpha particles had rebounded
  
• because they collided with something much
  larger and
• heavier and which contains a concentrated
  region of
• positive charge.

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Conclusion
As a result of his observations, Rutherford
suggested that the atom had a positively charged
centre which contained most of the mass.
He called the heavy positively charged centre the
nucleus.
He went on to suggest that the nucleus was
surrounded by orbiting electrons required for
electrical neutrality.
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Conclusion
As a result of his observations, Rutherford
suggested that the atom had a positively charged
centre which contained most of the mass.
He called the heavy positively charged centre the
nucleus.
He went on to suggest that the nucleus was
surrounded by orbiting electrons required for
electrical neutrality.
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Conclusion
As a result of his observations, Rutherford
suggested that the atom had a positively charged
centre which contained most of the mass.
He called the heavy positively charged centre the
nucleus.
He went on to suggest that the nucleus was
surrounded by orbiting electrons required for
electrical neutrality.
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Conclusion
As a result of his observations, Rutherford
suggested that the atom had a positively charged
centre which contained most of the mass.
He called the heavy positively charged centre the
nucleus.
He went on to suggest that the nucleus was
surrounded by orbiting electrons required for
electrical neutrality.
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Conclusion
As a result of his observations, Rutherford
suggested that the atom had a positively charged
centre which contained most of the mass.
He called the heavy positively charged centre the
nucleus.
He went on to suggest that the nucleus was
surrounded by orbiting electrons required for
electrical neutrality.
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Modern measurements show that the average nucleus
has a radius in the order of 10-15 m. This is
100, 000 times smaller than the radius of a
typical atom.
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