Sub-atomic just means smaller than an atom.
A proton is one of the particles that make up the nucleus at the centre of an atom.
A neutron is one of the particles that make up the nucleus at the centre of an atom.
It has the same mass as a proton, but no electrical charge.
Neutrons are used by some scientists to study the structure of materials. They are also very important in nuclear reactors, where they help sustain the nuclear reaction used to produce electrical power.
An electron is the third constituent of an atom and has a negative electrical charge. In an atom, electrons form a cloud around the nucleus.
A positron is the antiparticle of the electron.
A gamma ray is a form of light, but with much higher energy than visible light.
Sodium is one of the elements in table salt (sodium chloride). Normal sodium (sodium-23) has a mass of 23 atomic units, but sodium-22 is slightly lighter, with a mass of 22.
Sodium-22 is unstable and decays to give us neon-22, plus a positron.