Free radical formation by radiation
Free radicals are neutral atoms or molecules with an unpaired electron
Free radicals can be made from complex molecules but it’s easier to look at a very simple example that doesn’t occur in cells.
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A single hydrogen atom consists of one proton and one electron. The proton is positive and the electron is negative so it has zero electrical charge. But this single electron is unpaired. Unpaired electrons make an atom or molecule extremely reactive.
Any neutral atom or molecule with an unpaired electron is called a ‘free radical’.
Two hydrogen free radicals can join to form a hydrogen molecule. There are now a pair of electrons so the hydrogen molecule is much more stable.
Gamma photons can split molecules into free radicals
A gamma photon can split a hydrogen molecule into two free radicals again. This is different from forming two hydrogen ions where the electrons are removed. The electrons are still there but unpaired.
Free radicals are normally only around for a tiny fraction of a second before they steal an electron from a nearby atom. This can start a chain reaction of electron theft. A chemical reaction is just the movement of electrons and these unwanted chemical reactions can damage DNA.