Ionizing radiation is radiation that has enough energy to knock electrons off atoms to create ions. This can cause all sorts of damage to DNA etc. Radiation wit

Ionizing radiation is radiation that has enough energy to knock electrons off atoms to create ions. This can cause all sorts of damage to DNA etc. Radiation with less energy is unable to affect the structure of matter in this way, and is therefore considered not as harmful/carcinogenic. If you look at chart of the electromagnetic spectrum, http://xkcd.com/273/ http://xkcd.com/273/ , everything from Ultraviolet upwards is generally considered 'ionizing'