# The Positron

| A positron is an elementary particle that behaves in all respects like an electron that has undergone certain symmetry operations that switched some signs - especially the sign of the elementary charge it carries.
|  | Elementary particles with these reversed symmetries are called anti-particles, and every particle has an anti-particle as a partner in symmetry.
|  | Even the photon has an anti-particle. However, since all photon properties for which the sign would be reversed upon the "anti"-operation are zero, the photon is its own anti-particle.
| Anti-particles can exist by themselves just as happily as "real" particles; they are, however, rare in our universe. There seems to be an excess of particles - all anti-particles have long since vanished. The prefix "anti", of course, just mirrors a human prejudice.
|  | If a particle and an anti-particle meet, they annihilate each other in a burst of radiation; in the case of electrons (e–) and positrons (e+), two g quanta with the combined energy of the two particles (according to E=mc2) are sent out (511 keV each if the particles were at rest).
| Do not confuse positrons with holes (h+).
|  | Holes are merely missing electrons in energy levels that are otherwise completely filled with electrons; they do not exist by themselves outside of a crystal as positrons do!

With frame

4.1.1 Experimental Techniques for Studying Point Defects

© H. Föll (Defects - Script)