3. Beryllium radiation

In 1930 the German physicists Bothe and Becker bombarded the light metal beryllium with alpha particles, and noticed that a very penetrating radiation was emitted. This radiation was non-ionising, and they assumed it was gamma rays.

In 1932 Irène and Frédéric Joliot-Curie investigated this radiation in France. They let the radiation hit a block of paraffin wax, and found it caused the wax to emit protons. They measured the speeds of these protons and found that the gamma rays would have to be incredibly energetic to knock them from the wax.

Chadwick reported the Joliot-Curie's experiment to Rutherford, who did not believe that gamma rays could account for the protons from the wax. He and Chadwick were convinced that the beryllium was emitting neutrons. Neutrons have nearly the same mass as protons, so should knock protons from a wax block fairly easily.

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