Ionisation and damage
Physics Narrative for 14-16
A unified view of ionising radiations
An atom or molecule is ionised by having at least one electron stripped from it:
atom → ion + electron
molecule → ion + electron.
In both cases, energy must be shifted to the atom to allow the change. One way to shift that energy is by ionising radiation striking the neutral particle. This can be either high-energy (and so high-frequency) photons or fast-moving massive particles (so with energy in their kinetic store to ionise the atoms).
Radiations that ionise and the units that are used to measure their effects
Detecting the ions produced in the absorber is a way of detecting the arrival of ionising radiation.
The rate at which the radiation is emitted is the activity, measured in bequerels.
The energy shifted to each kilogram of absorber is the dose, measured in grays.
The damage done by the dose is measured in sievert.
The dose to a particular target can be controlled by varying the thickness of absorber between the source and the target, the material from which the absorber is made and the energy of the radiations emitted from the source.