The annihilation of positrons and positronium formation in gaseous Kr and Xe

Abstract

Positron annihilation and positronium formation have been studied in pure Kr and Xe gases and in mixtures of these gases with other inert and molecular species. Evidence is presented which, at least for Xe, suggests that positrons annihilate after self-trapping in clusters in the gas. Results are presented for the extra annihilation components visible in the low-density lifetime spectra and these are linked to the observed death of normal long-lived ortho-positronium.