The magnetic field prevented b particles from reaching the detector (screen).

With no gas in the container, flashes of light (scintillations) were seen on the screen at a rate proportional to the intensity of the source of radiation.

When the container was filled with nitrogen gas, the scintillations became more frequent.

Rutherford suggested that an a particle knocks a proton out of a nitrogen nucleus. These fast moving protons then hit the screen causing the scintillations. His hypothesis is summarised in the following equation.

In this equation,   represents the proton.

This experiment was one of the first examples of the artificial transmutation of an element (the changing of one element into another).

The mass of the proton was measured by deflection in a magnetic field. This experiment is considered to be the discovery of the proton.

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