Positron Spectroscopy in Atomic and Solid State Physics

Grzegorz P. Karwasz

Dipartimento di Fisica, Università di Trento, Italy
Instytut Fizyki, PAP - Pomeranian Pedagogical Academy, Słupsk, Poland

Positron, made possible thanks to Einstein's E=mc2 in 1905, calculated by Dirac in 1930 and observed in cosmic radiation by Andrerson in 1931 nowadays constitute a very useful tool both for fundamental Physics as well for practical applications, say in detecting defects in solids.

Two lines of positron experiments run at Trento University, Italy will be described. Positron annihilation techniques for solids (time of life, gamma Doppler broadening) allowed, among others, to explain why oxygen, contained always in huge amounts in Czochralski-grown silicon is electrically inactive.


Positrons in gases measure their diameters: total cross section for atoms and molecules is constant vs. energy, like for classical hard-sphere scattering. Furthermore, at least in He, positrons attach for a short time (10-15s) to the atom, forming a kind of molecule consisting of He+ and positronium atom.