The decaying particle
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.
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.