From Scratchpad

Epsilon radiation is a form of electromagnetic radiation with an average wavelength about a billionth of that of gamma radiation. Exposure to it for any amount of time leads to disintegration of atoms into subatomic particles. This decay may also result in the conversion of small amounts of matter, such as electrons, into energy. Epsilon radiation has a very limited range of about 10 kilometers, but the only substances that can effectively shield against it are xyvors and aumas. The only elements that emit epsilon radiation are those in the ananium series.