6. The decaying particle

Chadwick knew the neutron wasn't formed from an electron and a proton, and explained in his Nobel lecture that it seemed 'useless to discuss whether the neutron and proton are elementary particles or not'. He knew that a more powerful investigation of the neutron was necessary to decide if it was made up of anything else. We now believe that the neutron and the proton are made of even tinier particles called quarks.

To further confuse matters, free neutrons are not stable. If a neutron is outside the nucleus for several minutes it will transform into a proton, an electron, and an extremely light particle called a neutrino. The decay occurs because one of the quarks inside the neutron has transformed into a different quark, producing an additional positive charge in the particle.

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