Chadwick Experiment

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Chadwick Experiment
Discovery of Neutron
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History

• 1930 Bothe Becker performed an expt.

Neutron is neutral and causes no ionization
and cannot be detected in a cloud chamber
Ref Further Physics
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• Curie and Joliot use n to bombard H, N C
  with mass number (A)

The nuclei A being positively charged could
be detected and their velocities could also be
measured.
The fact that these nuclei bounced forward
confirmed the existence of the neutral particle.
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However u is unknown!
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Chadwick realized that if the result for 2
different nuclei was considered, say M and M,
then u would cancel
Chadwick used H (3.3x107 m/s) and N (4.7x107 m/s)
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Solving
Mass of neutron m 1.1 mass of hydrogen nucleus
As a result
The experimental result is about 10 to 20
Modern measurement
Mass of neutron 1.675 x 10-27 kg
Mass of proton 1.673 x 10-27 kg
Free neutron will decay into a proton and an
electron within 15 minute with 50 chance
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Geiger Rutherford
He discovered radioactivity
END
Becquerel
Rutherford proposed the atomic model and Geiger -
his student invented the Geiger-Muller tube
J.J. Thomson
He discovered electron
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