Positrons

Low mass and adjustable kinetic energy makes the positron a probe perfectly suited to solid state research. As the anti-matter particle of the electron, positrons annihilate electrons with a characteristic lifetime. The emerging annihilation radiation provides detailed information of the local surroundings at the annihilation site. As an example, the positron life time is slightly larger in vacancy-like defects than in the unperturbed crystal lattice. In this way, vacancy concentrations as low as 1:10⁷ can be detected.

The high intensity beam of positrons is generated by pair production from absorbed high-energy gamma-rays. This source is positioned in the cusp of the beam tube SR11, where these gamma-rays are produced by the absorption of neutrons in a cadmium layer. The pair-conversion itself occurs in proximate platinum foils. The positrons are extracted by means of electric and magnetic fields and guided to several experimental stations attached to the positron beam facility of NEPOMUC.