Biological Effects of Radiation

Nuclear radiation, both particle and electromagnetic, is quantified in terms of activity and measured by radiation detectors. However, the biological effects of radiation exposure depend not only on the activity but also on the ionizing power, penetration ability, exposure time, and area exposed.

Each type of radiation penetrates matter to a different extent. Alpha particles have the least penetration ability, as they are relatively massive; most are stopped by the outer layer of skin. However, when ingested, they directly contact internal tissues and are highly damaging.

Charged particle radiation, such as alpha radiation, directly ionizes biomolecules within cells, whereas neutrons, gamma rays, and X-rays affect the cellular processes indirectly.

For example, gamma radiation ionizes water in living tissue to produce a hydroxyl radical, which further ionizes biomolecules, thereby damaging cells. The damage is greater if many ionizations are induced in a small area. 

The energy delivered by radiation to material is measured as the ‘absorbed dose’, the SI unit of which is the gray. The deposition of one joule of energy per kilogram of material corresponds to one gray. Longer exposur