When ionizing radiations pass through a biological environment, they cause ionization of the atoms and molecules near their trajectory. The effect of ionization on biological cells can be direct or indirect.
Direct Effect
If the radiation interacts with the atoms of the DNA molecules, or some other critical cellular components, it is referred to as a direct effect. If enough atoms are affected, the cells may die, mutate or stop replicating.
Indirect Effect
It is more likely that the radiation interacts with the water molecules in the body (which make up most of the cell volume) rather than the DNA molecules or some other critical cellular components directly. When radiation interacts with water, it may produce free radicals such as hydrogen (H) and hydroxyls (OH), which may then go on to attack the DNA molecules or some other critical cellular components.
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