Deterministic effects (see graph above) have a threshold. If the dose is low deterministic effects can be ignored.

Stochastic effects have no threshold and increase linearly with dose. All doses therefore have a stochastic risk attached to them.

The risk of developing fatal cancer decreases with age at irradiation in part because the older person may have died of other causes before the cancer develops. Also because rapid cell division occurs in growing youngsters, those genetically inclined towards fatal cancer will have probably contracted it at an early age.

The type of cancer causing death at various ages also varies with age.

Exposure to ionising radiation is therefore strictly minimised by medical practicioners, especially for young children and the unborn.