Ionization – the addition or removal of electrons from an atom thus giving the atom a positive or negative charge.

Electron – a charged particle (-1) with a small mass.   An electrons energy is related to its speed or kinetic energy

Photon – an electromagnetic wave with no mass and no charge.   Its energy is related to its frequency and wavelength (has a speed of 3 x 10 8 m/s in a vacuum)

Compton Interaction – is where a photon will deposit part of its energy to an outer or free orbital electron.   The electron is thus ejected and the photon looses energy

International Commision on Radiological Units and Measurments (ICRU) – in 1928 adopted the first quantitative unit to measure ionizing radiation which was the Roentgen (roentgen measures exposure, which is the amount of ionization produced in air)

Roentgen – measures exposure / the amount of ionization produced in dry air by photons (2.58 x 10 -4 Coulombs in Kg of dry air)

Standard Free Air Ionization Chamber – used to measure and collect all freed charged particles.   You need to know how much air is in the beam and how many electrons are freed to get a measurement.

Electronic equilibrium – the number of electrons gained is equal to the number of electrons lost