alpha-particles from the radioactive source hit
the beryllium nuclei and transformed them into carbon
nuclei, leaving one free neutron. When this neutron
hit the hydrogen nuclei in the wax it could knock a
proton free, in the same way that a white snooker ball
can transfer all its energy to a red snooker ball.
gave the best description of a neutron as a highly penetrating
neutral particle with a mass similar to the proton.
We now know it is not a combination of an electron
and a proton. Quantum mechanics restricts an electron
from getting that close to the proton, and measurements
of nuclear 'spin' provide experimental proof that the
nucleus does not contain electrons.