gamma radiation 
noun [mass noun]
Gamma rays.The technical definition is the amount of X or gamma radiation that produces one electrostatic unit of ionic charge in one cubic centimeter of dry air at standard temperature and pressure....
- This process is called ionization, and this capability had led to gamma radiation being termed ionizing radiation.
- The property, possessed by certain nuclides, of spontaneously emitting particles of gamma radiation or of emitting radiation following orbital electron capture or spontaneous fission.