What is ionizing radiation?
Electromagnetic radiation at frequencies above the UV band are classified as "ionizing radiation", because they have enough energy to effect changes in the atoms, by liberating electrons (ionizing) and thus altering their chemical bonds. X-rays and gamma rays are common forms of ionizing radiation.
Ionizing radiation occurs at frequencies above 2900 THz (2900×1012 Hz). This corresponds to a wavelength of about 103.4 nm, which lies near the lower wavelength-edge of the Ultraviolet (UV) spectrum.