 The theory of early streamer emission proposes that if a lightning rod has a mechanism producing ionization near its tip, then its lightning capture area is greatly increased.At first, small quantities of radioactive isotopes (radium-226 or americium-241) were used as sources of ionization between 1930 and 1980, later replaced with various electrical and electronic devices.According to an early patent, since most lightning protectors' ground potentials are elevated, the path distance from the source to the elevated ground point will be shorter, creating a stronger field (measured in volts per unit distance) and that structure will be more prone to ionization and breakdown.