What's the difference between i.e. and e.g.?
radioactive isotope n.
An isotope having an unstable nucleus that decomposes spontaneously by emission of a nuclear electron or helium nucleus and radiation, thus achieving a stable nuclear composition.
any of several species of the same chemical element with different masses whose nuclei are unstable and dissipate excess energy by spontaneously emitting radiation in the form of alpha, beta, and gamma rays.