When ionizing radiation, such as x-rays, deposit energy into matter, damage
can be done directly to sensitive targets, such as DNA, or damage can be done
indirectly through the creation of free radicals.
Free radicals are formed by breaking molecules into charged fragments. These
charged fragments are extremely reactive chemicals. Most of them re-combine in a
small fraction of a second after formation. Hence, most free radicals do not
Free radicals that do not recombine can interact with chemical compounds
within a cell and cause damage, possibly killing the cell. Multiple breaks of
DNA can also cause cell death after a few cell reproductive cycles.
Effects from Acute Radiation Doses
At very high doses, it is the killing of cells that creates tangible
biological effects. Skin that is exposed to 200,000 mrad may start to show
evidence of radiation burns in the form of reddening, very similar to a sun
burn. Higher doses of radiation will result in more severe effects.
Biological effects of this type only occur after a threshold level of
radiation dose has been exceeded. These threshold levels are very much higher
than doses received by radiation workers. The regulatory limits discussed
earlier have been set very much lower than the thresholds for all acute effects.