2. The elusive neutron

Rutherford described his 'neutral doublet', or neutron, in 1920. The particle would be uncharged but with a mass only slightly greater than the proton. Because it was uncharged there would be no electrical repulsion of the neutron as it passed through matter, so it would be much more penetrating than the proton. This would make the neutron difficult to detect.

The discovery of the neutron was made by James Chadwick, who spent more than a decade searching. Chadwick had accompanied Rutherford in his move from Manchester to Cambridge. He later became the Assistant Director of Research in the Cavendish, and was responsible for keeping Rutherford informed of any new developments in physics. Chadwick and Rutherford often discussed neutrons, and suggested 'silly' experiments to discover them, but the inspiration for Chadwick's discovery came from Europe, not Rutherford.

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