Radio autography is a technique to find out, if a particular source consists of a particular type of isotope. Different radioactive isotopes emit different types of radiation. Chiefly there are 3 types. These are: a) Alpha rays, b) Beta Rays c) Gamma rays.

When we use a particular isotope we already know that is the type of emission. For instance, C14 emits β rays. When these rays are directed to a photo­graphic film they form characteristic markings and by these one can identify the type of radiation and thereby the isotope.