Biological Effects of Radiation

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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 cause injury.

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.


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