Glossary
Sub-atomic
Sub-atomic just means smaller than an atom.
Protons, neutrons and electrons are all sub-atomic particles, and so are their anti-particles: anti-protons, anti-neutrons and positrons.
Proton
A proton is one of the particles that make up the nucleus at the centre of an atom.
The proton has a positive electrical charge that attracts electrons and keeps them attached to the atom. The mass of protons and neutrons in the nucleus makes up most of the mass of an atom.
Neutron
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.
Electron
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.
Electrons are also the particles that can carry charge around in metals, giving us electricity.
Positron
A positron is the antiparticle of the electron.
In other words, it has the same mass as an electron, but the opposite electrical charge (positive instead of negative). When a positron annihilates with an electron, they turn into gamma rays.
Gamma ray
A gamma ray is a form of light, but with much higher energy than visible light.
Gamma rays are produced in nuclear decay, and when matter and antimatter annihilate.
Sodium-22
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.
Half-life
Click here to read about an atom’s half-life.
Cloud chamber
Click here to read about cloud chambers.
Scientific notation: what does 1015 mean?
Click here to read about scientific notation.
