technoguy

Penetrating very short-wavelength electromagnetic radiation, similar to an X-ray but of higher energy, that is emitted spontaneously by some radioactive substances (see gamma decay; radioactivity). Gamma radiation also originates in the decay of certain subatomic particles and in particle-antiparticle annihilation (see also antimatter). Gamma rays can initiate nuclear fission, can be absorbed by ejection of an electron (see photoelectric effect), and can be scattered by free electrons.