Ionizing radiation refers to highly-energetic particles or waves that can detach (ionize) at least one electron from an atom or molecule. Ionizing ability is a function of the energy of individual particles or waves, and not a function of their number. A large flood of particles or waves will not, in the most-common situations, cause ionization if the individual particles or waves are insufficiently energetic.
Examples of ionizing radiation are energetic beta particles, neutrons, and alpha particles. The ability of light waves (photons) to ionize an atom or molecule varies across the electromagnetic spectrum. X-rays and gamma rays will ionize almost any molecule or atom; far ultraviolet light will ionize many atoms and molecules; near ultraviolet and visible light are ionizing to very few molecules; microwaves and radio waves are non-ionizing radiation. Visible light is so ubiquitous that molecules that are ionized by it will often react nearly spontaneously unless protected by materials that block the visible spectrum. Examples include photographic film and some molecules involved in photosynthesis.
If enough ionizations occur in a biological system, they can be destructive, such as by causing DNA damage in individual cells. Extensive doses of ionizing radiation have been shown to have a mutating effect on future generations arising from the individual receiving the dose.
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