Chadwick Experiment. History 1930 Bothe & Becker performed an expt. Neutron is neutral and causes no ionization and cannot be detected in a cloud chamber.

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Presentation transcript:

Chadwick Experiment

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

Curie and Joliot use n to bombard H, N & C with mass number (A) BeA  n 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.

BeA  n A n + A n + A Mass m M velocities u 0 v V However u is unknown!

Chadwick realized that if the result for 2 different nuclei was considered, say M and M’, then u would cancel Chadwick used H (3.3x10 7 m/s) and N (4.7x10 7 m/s)

The experimental result is about 10 to 20 % Mass of neutron m = 1.1 mass of hydrogen nucleus As a result Mass of neutron = x kg Mass of proton = x kg Solving Free neutron will decay into a proton and an electron within 15 minute with 50% chance Modern measurement

Geiger & Rutherford J.J. Thomson Becquerel He discovered radioactivity He discovered electron Rutherford proposed the atomic model and Geiger - his student invented the Geiger- Muller tube