Certain kinds of particle accelerator experiments involve colliding positrons and electrons at relativistic speeds. Beta particles are high energy electrons or positrons. A very small fraction are stable particles of antimatter, such as positrons or antiprotons. Charged particles such as electrons, positrons, and protons may be separated from their common surrounding. Storage rings most commonly store electrons, positrons, or protons. Gravitationally, the universe will be dominated by dark matter, electrons, and positrons (not protons). The Stanford Linear Collider was a linear accelerator that collided electrons and positrons at SLAC. Hence, next to photons electrons and positrons usually dominate in air showers. It is suggested that the antimatter positrons are formed in terrestrial gamma-ray flashes (TGF). Annihilation of positrons produces only gamma rays. A similar process happened at about 1 second for electrons and positrons. Titanium becomes radioactive upon bombardment with deuterons, emitting mainly positrons and hard gamma rays. Fluorine-18 (F) is a fluorine radioisotope which is an important source of positrons. The PAMELA experiment (launched in 2006) detected excess positrons. Fairbank was never able to attempt the experiment with positrons.